Image forming apparatus, printing operation control method and computer-readable information recording medium

Abstract

An image forming apparatus includes a photosensitive member driving part that drives a photosensitive member, a counting part that carries out an adding operation when the photosensitive member driving part drives the photosensitive member, and carries out a subtracting operation when the photosensitive member driving part stops the photosensitive member; and a control part that interrupts, when a count value of the counting part becomes equal to or more than a first predetermined value, a printing operation of driving the photosensitive member, forming an electrostatic latent image on the photosensitive member, and fixing a toner adhering to the photosensitive member onto a recording sheet, and causes the counting part to start the subtracting operation.

Claims

1 . An image forming apparatus comprising: a photosensitive member driving part configured to drive a photosensitive member; the photosensitive member configured to be driven by the photosensitive member driving part and have an electrostatic latent image formed thereon; a fixing part configured to fix a toner that adheres to the electrostatic latent image onto a recording sheet; a counting part configured to carry out an adding operation when the photosensitive member driving part drives the photosensitive member, and carry out a subtracting operation when the photosensitive member driving part stops the photosensitive member; and a control part configured to interrupt, when a count value of the counting part becomes equal to or more than a first predetermined value, a printing operation of driving the photosensitive member, forming the electrostatic latent image on the photosensitive member, and fixing the toner adhering to the photosensitive member onto the recording sheet, and cause the counting part to start the subtracting operation. 2 . The image forming apparatus as claimed in claim 1 , wherein: the control part is configured to start the printing operation when the count value of the counting part becomes equal to or less than a second predetermined value that is smaller than the first predetermined value. 3 . The image forming apparatus as claimed in claim 1 , wherein: the counting part does not carry out the adding operation when the count value reaches a predetermined upper limit value. 4 . The image forming apparatus as claimed in claim 1 , further comprising: a fixing temperature detecting part configured to detect a temperature of the fixing part; and a non-volatile storing part configured to store the count value, wherein: when a power supply to the image forming apparatus is started or when the image forming apparatus returns from an energy saving mode, a value obtained from subtracting from the count value stored by the non-volatile storing part a value corresponding to a temperature detected by the fixing temperature detecting part is used as a new count value. 5 . The image forming apparatus as claimed in claim 1 , wherein: the control part is configured to change an adding amount which the counting part adds to the count value and a subtracting amount which the counting part subtracts from the count value. 6 . The image forming apparatus as claimed in claim 5 , wherein: the control part is configured to change the adding amount which the counting part adds to the count value according to whether the printing operation is a both-sides printing operation or a one-side printing operation. 7 . The image forming apparatus as claimed in claim 5 , further comprising: an external temperature measuring part configured to measure an external temperature of the image forming apparatus, wherein: the control part is configured to change the adding amount which the counting part adds to the count value and the subtracting amount which the counting part subtracts from the count value, based on the external temperature measured by the external temperature measuring part. 8 . The image forming apparatus as claimed in claim 7 , wherein: the adding amount and the subtracting amount are a first adding amount and a first subtracting amount when the external temperature is less than a predetermined temperature and are a second adding amount and a second subtracting amount different from the first adding amount and the first subtracting amount, respectively, when the external temperature is equal to or more than the predetermined temperature. 9 . The image forming apparatus as claimed in claim 5 , further comprising: a cooling fan that reduces an internal temperature of the image forming apparatus, wherein: the control part is configured to change the adding amount which the counting part adds to the count value and the subtracting amount which the counting part subtracts from the count value, according to an operating state of the cooling fan. 10 . The image forming apparatus as claimed in claim 9 , wherein: the cooling fan changes the operating state between a high speed rotating state and a low speed rotating state according to an operation of the image forming apparatus. 11 . The image forming apparatus as claimed in claim 10 , wherein: the control part is configured to use, in a case where the photosensitive member driving part stops driving the photosensitive member, the subtracting amount when the operating state of the cooling fan is the high speed rotating state, which subtracting amount is larger than the subtracting amount used when the operating state of the cooling fan is the low speed rotating state. 12 . The image forming apparatus as claimed in claim 10 , wherein: a high speed rotating time for which the operating state of the cooling fan is the high speed rotating state is a first time in a case where the count value is larger than a third predetermined value, and is a second time in a case where the count value is smaller than the third predetermined value, the second time being different from the first time. 13 . The image forming apparatus as claimed in claim 12 , wherein: the high speed rotating time is determined according to a relationship between the count value obtained at a time of a printing sheet ejecting operation after the printing operation or a time of an end of a warming up operation carried out and the third predetermined value. 14 . The image forming apparatus as claimed in claim 13 , wherein: the high speed rotating time is measured from the time of a printing sheet ejecting operation carried out after the printing operation or the time of an end of a warming up operation. 15 . The image forming apparatus as claimed in claim 4 , wherein: a timing at which the count value is stored in the non-volatile storing part is a first timing during the printing operation and is a second timing different from the first timing during an operation other than the printing operation. 16 . The image forming apparatus as claimed in claim 1 , wherein: the control part is configured to interrupt, in a case where the printing operation is a both-sides printing operation, the printing operation in such a manner as to prevent the recording sheet from passing through the image forming apparatus. 17 . The image forming apparatus as claimed in claim 7 , wherein: the control part is configured to interrupt the printing operation according to the external temperature measured by the external temperature measuring part. 18 . A printing operation control method carried out in an image forming apparatus in which a photosensitive member is driven, an electrostatic latent image is formed on the photosensitive member being driven, and a toner that adheres to the electrostatic latent image is fixed onto a recording sheet, the printing operation control method comprising: carrying out an adding operation on a count value when the photosensitive member is being driven, carrying out a subtracting operation on the count value when driving the photosensitive member is stopped, and storing the count value in a storing part; and interrupting, when the count value stored in the storing part becomes equal to or more than a first predetermined value, a printing operation of driving the photosensitive member, forming the electrostatic latent image on the photosensitive member, and fixing the toner adhering to the photosensitive member onto the recording sheet, and starting the subtracting operation. 19 . A computer-readable information recording medium storing a program which, when executed by a computer processor, performs a printing operation control method carried out in an image forming apparatus in which a photosensitive member is driven, an electrostatic latent image is formed on the photosensitive member being driven, and a toner that adheres to the electrostatic latent image is fixed onto a recording sheet, the printing operation control method comprising: carrying out an adding operation on a count value when the photosensitive member is being driven, carrying out a subtracting operation on the count value when driving the photosensitive member is stopped, and storing a count value in a storing part; and interrupting, when the count value stored in the storing part becomes equal to or more than a first predetermined value, a printing operation of driving the photosensitive member, forming the electrostatic latent image on the photosensitive member, and fixing the toner adhering to the photosensitive member onto the recording sheet, and starting the subtracting operation.
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus, a printing operation control method and a computer-readable information recording medium that stores a computer program for carrying out a printing operation of forming an electrostatic latent image on a photosensitive member and fixing toner that adheres to the electrostatic latent image onto a recording medium. [0003] 2. Description of the Related Art [0004] In a technical field of an image forming apparatus having a photosensitive member, it is known that, as a photosensitive member surface temperature increases, a state of the photosensitive member surface and/or image forming condition varies, which may result in degradation of an image formed in the image forming apparatus. An increase in the photosensitive member surface temperature may occur because of friction between the photosensitive member and a peripheral developing roller or transfer roller, friction heat caused by rotation of the roller, heat transmitted from a fixing device and so forth. [0005] In the image forming apparatus, as the photosensitive member surface temperature becomes a predetermined temperature or more, the photosensitive member surface may be damaged. In the image forming apparatus, if the photosensitive member surface is damaged, the damaged part cannot be used for development. Therefore, an image output from the image forming apparatus has a blank corresponding to the damaged part, and thus, the image is defective. [0006] In order to solve such a problem of an image defect caused by the photosensitive member surface temperature increase, the photosensitive member surface temperature is measured, and a printing operation in the image forming apparatus is continued or interrupted according to a thus-obtained temperature, for example. [0007] FIG. 1 shows a state in which the photosensitive member surface temperature increases during a both-sides printing operation. A broken line in FIG. 1 shows a threshold for a temperature zone such that there is a high likelihood of occurrence of an image defect if the photosensitive member surface temperature becomes the threshold or more. In an example of FIG. 1 , at a room temperature of 28° C. that is within an image compensation range, the photosensitive member surface temperature reaches the threshold (44° C.) when a printing operation is continued for approximately 55 minutes. In this case, such a control can be carried out that a printing operation is made to go on at a temperature of less than 44° C., and is interrupted at a temperature of 44° C. or more. [0008] For example, according to Japanese Laid-Open Patent Applications Nos. 05-241405, 01-172853 and 58-116544, a photosensitive member surface temperature of a fixing temperature is measured, and printing is allowed according to a result of the measurement. By this method, it is possible to reflect the photosensitive member surface temperature in a printing operation, and it is possible to easily solve a problem of an image defect. [0009] However, in order to realize the method, it is necessary to provide a sensor (temperature sensor) for measuring a temperature, which may result in a cost increase. Further, it is necessary to secure a space for disposing the temperature sensor. In conjunction with the space for disposing the temperature sensor, Japanese Laid-Open Patent Application No. 2003-043757 discusses the use of a measured temperature of another member that is in contact with the photosensitive member instead of directly measuring the photosensitive member surface temperature. Another method is to use a non-contact type temperature sensor (thermopile). SUMMARY OF THE INVENTION [0010] According to the present invention, an image forming apparatus includes a photosensitive member driving part configured to drive a photosensitive member; the photosensitive member configured to be driven by the photosensitive member driving part and have an electrostatic latent image formed thereon; a fixing part configured to fix a toner that adheres to the electrostatic latent image onto a recording sheet; a counting part configured to carry out an adding operation when the photosensitive member driving part drives the photosensitive member, and carry out a subtracting operation when the photosensitive member driving part stops the photosensitive member; and a control part configured to interrupt, when a count value of the counting part becomes equal to or more than a first predetermined value, a printing operation of driving the photosensitive member, forming the electrostatic latent image on the photosensitive member, and fixing the toner adhering to the photosensitive member onto the recording sheet, and cause the counting part to start the subtracting operation. [0011] Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIG. 1 shows a state of a photosensitive member surface temperature increase during a printing operation; [0013] FIG. 2 shows a photosensitive member surface temperature decrease curve during a standing-by operation; [0014] FIG. 3 illustrates a structure of an image forming apparatus 100 in the first embodiment of the present invention; [0015] FIG. 4 illustrates functions of an image forming apparatus 100 in a first embodiment of the present invention; [0016] FIG. 5 shows a photosensitive member surface temperature increase during a printing operation in the first embodiment of the present invention; [0017] FIGS. 6A , 6 B and 7 show a flowchart illustrating adding and subtracting operations of a count value (counter control process or control of interrupting a printing operation) in the first embodiment of the present invention; [0018] FIG. 8 shows a fixing temperature change after a power supply is turned off; [0019] FIG. 9 shows a flowchart illustrating a control carried out by a temperature reducing part 230 in the first embodiment of the present invention; [0020] FIG. 10 shows a flowchart illustrating an image adjusting process in the first embodiment of the present invention; [0021] FIG. 11 shows a flowchart illustrating a process of storing the count value C in a non-volatile memory 270 in the first embodiment of the present invention; [0022] FIG. 12 shows a flowchart illustrating a setting for an interruption of a printing operation in the first embodiment of the present invention; [0023] FIG. 13 shows a flowchart illustrating a process of reading the setting for an interruption of a printing operation in the first embodiment of the present invention; [0024] FIG. 14 shows a flowchart illustrating a process of determining a device type of an image forming apparatus 100 in a second embodiment of the present invention; [0025] FIGS. 15A and 15B show one example of an adding amount table 15 and a subtracting amount table 16 ; [0026] FIGS. 16A-16B and 17 show a flowchart illustrating adding and subtracting operations of a count value in the second embodiment of the present invention; [0027] FIG. 18 shows a flowchart illustrating an image adjusting process in the second embodiment of the present invention; [0028] FIG. 19 shows a change in an internal temperature of an image forming apparatus during a printing operation; [0029] FIG. 20 shows a change in the internal temperature of an image forming apparatus after a finish of a printing operation; [0030] FIG. 21 shows a structure of an image forming apparatus 100 A in a third embodiment of the present invention; [0031] FIGS. 22-23 show a flowchart illustrating a process of changing an adding/subtracting amount for a count value C in the third embodiment of the present invention; and [0032] FIG. 24 shows a flowchart illustrating a control of a rotational speed of a fixing cooling fan 161 and an internal cooling fan 162 in the third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0033] In any one of methods discussed in above-mentioned Japanese Laid-Open Patent Applications Nos. 05-241405, 01-172853, 58-116544 and 2003-043757, a temperature sensor is necessary, and thus, a cost increase results. [0034] Further, in a case of continuing and interrupting a printing operation according to a temperature detected by the temperature sensor, a downtime occurs from a time at which the temperature is a print preventing temperature through a time at which the temperature has decreased to a print allowing temperature. FIG. 2 shows that, in a case where the print preventing temperature is set as 44° C., and the print allowing temperature is set as the temperature lower than the print preventing temperature by 1° C., it is necessary to interrupt a printing operation for a time interval on the order of 10 minutes. A downtime of such a long time interval may cause remarkable degradation in productivity. FIG. 2 shows a photosensitive member surface temperature falling curve during a standing-by operation. [0035] Embodiments of the present invention described below have been devised in consideration of the situation for the purpose of solving the problem. According to the embodiments of the present invention, an image forming apparatus, a printing operation control method and a computer-readable information recording medium that stores a computer program are provided, in which no special temperature sensor is used for detecting a photosensitive member surface temperature, and degradation in productivity caused by a long-time interruption time (downtime) can be reduced. [0036] More specifically, according to the embodiments of the present invention, no special temperature sensor is used for detecting a photosensitive member surface temperature, a count value of a counter is used to determine a state of the photosensitive member, and it is determined whether printing can be made to continue. Thereby, it is possible to reduce an interruption time of a printing operation for each occurrence of an interruption, and an occurrence of an image defect is avoided. First Embodiment [0037] A first embodiment of the present invention will now be described with reference to figures. FIG. 3 illustrates an image forming apparatus 100 in the first embodiment of the present invention. [0038] As shown in FIG. 3 , the image forming apparatus 100 is of a so-called tandem-type, and includes AIO (All-In-One) cartridges ( 120 Bk, 120 M, 120 C and 120 Y) of respective colors arranged along a transfer belt 110 . [0039] The transfer belt 110 rotates counterclockwise in FIG. 3 , and the plural AIO cartridges (referred to as image forming parts, hereinafter) 120 Bk, 120 M, 120 C and 120 Y are arranged in the stated order from an upstream side of a rotating direction. The plural image forming part 120 Bk, 120 M, 120 C and 120 Y have a common structure and have respective colors of toner images different from one another. The image forming parts 120 Bk, 120 M, 120 C and 120 Y form a black image, a magenta image, cyan image, and a yellow image, respectively. [0040] Below, the image forming part 120 Bk will be described in detail. The other image forming parts 120 M, 120 C and 120 Y are the same as the image forming part 120 Bk. Therefore, for the image forming parts 120 M, 120 C and 120 Y, reference numerals are given as follows, and description thereof will be omitted. That is, Bk attached to reference numerals of respective components of the image forming part 120 Bk is replaced by M, C and Y, respectively, and thus, they are distinguished from one another. [0041] The transfer belt 110 is an endless belt wound on a secondary transfer driving roller 111 and a transfer belt tension roller 112 . The secondary transfer driving roller 111 is driven and rotated by a driving motor (not shown), and the driving motor, the secondary transfer driving roller 111 and the transfer roller 112 act as a driving part that drives the transfer belt 110 . [0042] The image forming part 120 Bk includes a photosensitive member 121 Bk, and a charger 122 Bk, an exposure unit 123 , a developer 124 Bk, a cleaner blade 125 Bk and so forth, which are arranged in the periphery of the photosensitive member 121 Bk. The exposure unit 123 is configured to irradiate laser light 126 Bk, 126 M, 126 C and 126 Y that is exposure light corresponding to the image colors of the respective image forming parts 120 Bk, 120 M, 120 C and 120 Y. [0043] In the first embodiment, in an image forming operation, an outer circumferential surface of the photosensitive member 121 Bk is charged uniformly by the charger 122 Bk in the dark, then, is exposed by laser light 126 Bk corresponding to a black image from the exposure unit 123 , and thus, has an electrostatic latent image formed thereon. The developer 124 Bk changes the electrostatic latent image thus formed on the outer circumferential surface of the photosensitive member 121 Bk into a visualized toner image by applying a black toner, and thus, forms a black toner image on the outer circumferential surface of the photosensitive member 121 Bk. [0044] The toner image thus formed on the outer circumferential surface of the photosensitive member 121 Bk is transferred onto the transfer belt 110 at a position (a primary transfer position) at which the photosensitive member 121 Bk comes into contact with the transfer belt 110 by a function of a primary transfer roller 127 Bk. By this transfer, the black toner image is transferred onto the transfer belt 110 . The photosensitive member 121 Bk from which the toner image has been thus transferred has a remaining unnecessary toner wiped off by the cleaner blade 125 Bk, and stands by for a subsequent image forming operation. [0045] The black toner image thus transferred onto the transfer belt 110 is conveyed to the next image forming part 120 M by the transfer belt 110 . The image forming part 120 M forms a magenta toner image on an outer circumferential surface of the photosensitive member 121 M by the same process as the above-described image forming process of the image forming part 120 Bk. The thus-formed magenta toner image is then transferred to the transfer belt 110 over the black toner image already formed on the transfer belt 110 . [0046] The black and magenta toner images thus transferred onto the transfer belt 110 in a one-over-the-other manner are then conveyed to the next image forming parts 120 C and 120 Y in sequence. Then, in the same operation, a cyan toner image formed on an outer circumferential surface of the photosensitive member 121 C and a yellow toner image formed on an outer circumferential surface of the photosensitive member 121 Y are transferred to the transfer belt 110 over the black and magenta toner images already formed on the transfer belt 110 in a one-over-the-other manner. Thus, on the transfer belt 110 , a full color toner image is formed as a result of the black, magenta, cyan and yellow toner images being transferred in a one-over-the-other manner. The full color toner image thus formed on the transfer belt 110 is then conveyed to a position of the secondary transfer roller 130 . [0047] It is noted that, in a case where printing is carried out only with the black toner, primary transfer rollers 127 M, 127 C and 127 Y are moved to positions away from the photosensitive members 121 M, 121 C and 121 Y, respectively. Thus, in this case, the above-mentioned image forming process is carried out only with the image forming part 120 Bk for forming a black toner image. [0048] Paper sheets 142 contained in a paper feeding tray 140 are fed in sequence from the top one as a result of a paper feeding roller 150 being rotated counterclockwise in a paper conveying operation of an image forming operation. The thus-fed paper sheet stands by at a position of a registration roller 151 . Driving of the registration roller 151 is started at such timing that a position of a toner image that has been conveyed by the transfer belt 110 agrees with a position of the paper sheet 142 on the secondary transfer roller 130 . At this time, the registration roller 151 feeds the paper sheet 142 as a result of being driven and rotated counterclockwise. [0049] The paper sheet 142 thus fed by the registration roller 151 has the toner image transferred thereto from the transfer belt 110 by the secondary transfer roller 130 . After that, the toner image thus transferred to the paper sheet 142 is fixed onto the paper sheet 142 by the fixing unit 160 with heat and pressure. Then, the paper sheet 142 is ejected to the outside of the image forming apparatus 100 by ejecting rollers 170 that are driven and rotated in such directions that the paper sheet 142 is ejected (referred to as ejecting directions, hereinafter). [0050] In a case where a both-sides printing is carried out, before the paper sheet 142 passes through the ejecting rollers 170 , the ejecting rollers 170 are driven and rotated in directions reverse to the ejecting directions, and thus the paper sheet 142 is conveyed to a both-sides conveyance path. The paper sheet 142 thus conveyed into the both-sides conveyance path then passes through a both-sides roller 180 , and then, is again conveyed to the registration roller 151 . The paper sheet 142 thus conveyed to the registration roller 151 is again fed from the registration roller 151 , and has a toner image transferred to a reverse side of the paper sheet 142 by the secondary transfer roller 130 . The transferred toner image is fixed by the fixing unit 160 with heat and pressure, and is ejected to the outside of the image forming apparatus 100 by the ejecting rollers 170 that are driven and rotated in the ejecting directions. [0051] Next, with reference to FIG. 4 , a functional configuration of the image forming apparatus 100 in the first embodiment of the present invention will be described. FIG. 4 illustrates the functional configuration of the image forming apparatus 100 in the first embodiment. [0052] The image forming apparatus 100 includes a control mechanism (engine board) 200 , a controller 210 , a photosensitive member driving motor 220 , a temperature reducing part 230 , a fixing temperature detecting part 240 and an external temperature measuring part 250 . [0053] The control mechanism 200 controls an operation of the image forming apparatus 100 , and includes a processing part 260 , a ROM (Read Only Memory) 261 , a RAM (Random Access Memory) 262 , an A/D (Analog to Digital) converter 263 , a non-volatile memory 270 , and a drive 271 . [0054] The processing part 262 is a CPU (Central Processing Unit) for causing the image forming apparatus 100 to function properly. The ROM 261 is a fixed storage device that stores a computer program, and so forth. The RAM 262 is a main storage of the processing part 260 , and includes a counting part 264 . [0055] The processing part 262 in the first embodiment carries out a process described below with reference to flowcharts by executing a printing operation control program (computer program) stored in the ROM 261 . It is noted that the printing operation control program may be stored in a recording medium 272 . In this case, the printing operation control program may be driven by the driver 271 from the recording medium 272 , stored in the RAM 262 , and executed by the processing part 260 . [0056] It is noted that the recording medium 272 may be a computer-readable information recording medium such as a CD-ROM (Compact Disk Read Only Memory) or such. In a case where the image forming apparatus 100 includes a communication unit that carries out network communication with the outside, the printing operation control program may be downloaded via a communication network by the communication unit, and installed in the RAM 264 . Further, in a case where the image forming apparatus 100 has an interface such as a USE (Universal Serial Bus) that connects with an external storage device, the printing operation control program may be read from the external storage device via a USE connection. [0057] The A/D converter 263 is included in the processing part 260 in a built-in manner, and converts data indicating a temperature measured by the fixing temperature measuring part 240 and the external temperature measuring part 250 into digital data. [0058] The counting part 264 is a part of the RAM 262 , and stores a count value C to be incremented or decremented by the processing part 260 according to a driving state of the photosensitive member driving part 220 . Specifically, the processing part 260 increments the count value C when the photosensitive member driving motor rotates, and decrements the count value C when the photosensitive member driving motor 220 stops. [0059] Further, in the first embodiment, the processing part 264 carries out incrementing (adding) or decrementing (subtracting) the count value C according to a state of the image forming apparatus 100 . For example, the processing part 260 increments the count value C by 2 in a case where a both-sides printing operation is carried out, and by 1 in a case where a one-side printing operation or a warming up operation is carried out. The warming up operation is a preparing operation for making it possible to carry out a printing operation in the image forming apparatus 100 after a power supply is started in the image forming apparatus 100 or after the image forming apparatus 100 returns from an energy saving mode such as a sleep mode. [0060] Further, the processing part 260 carries out decrementing the count value C, for example, according to an internal temperature (a temperature in the inside) of the image forming apparatus 100 , in a case where the photosensitive member driving motor 220 stops. [0061] The RAM 262 includes a count value calculating buffer Cbuff, and a fixing temperature storing buffer Tfus as will be described later. The count value calculating buffer Cbuff stores a value that acts as an initial value used when the counting value is calculated. The fixing temperature storing buffer Tfus stores a temperature of the fixing unit 160 detected by the fixing temperature detecting part 240 when a power supply in the image forming apparatus 100 is started and when the image forming apparatus 100 returns from the energy saving mode such as the sleep mode. [0062] The counting part 264 previously stores thresholds used by the processing part 260 to determine whether to interrupt a printing operation. The processing part 260 determines whether to interrupt a printing operation by comparing the thresholds previously stored in the counting part 264 and the count value C also stored in the counting part 264 , as will be described later. [0063] It is noted that, “to interrupt a printing operation” in the first embodiment means to interrupt a printing operation in timing after the completion of printing of a current page before starting of printing of a subsequent page. Therefore, when a printing operation is interrupted, a paper sheet 142 has passed through the inside of the image forming apparatus 100 , and has been ejected to the outside of the image forming apparatus 100 . A state in which any paper sheet(s) 142 is(are) on passing through the inside of the image forming apparatus 100 will be referred as a paper passing state, hereinafter. [0064] The non-volatile memory 270 acts as a non-volatile storing part. [0065] Next, the above-mentioned count value C stored in the counting part 264 in the first embodiment will be described. [0066] The count value C stored in the counting part 264 in the first embodiment corresponds to the photosensitive member surface temperature (a surface temperature of the photosensitive member 121 (including the photosensitive members 121 Bk, 121 M, 121 C and 121 Y)). The values previously stored in the counting part 264 include a count upper limit Cmax, a print preventing threshold C 1 , and a print allowing threshold C 2 . It is noted that the RAM 262 includes a volatile area and a non-volatile area such as a NVRAM, the count value C is stored in the volatile area and the thresholds Cmax, C 1 and C 2 are stored in the non-volatile area. [0067] The count upper limit Cmax indicates the count value C of the counting part 264 in a state in which the photosensitive member surface temperature reaches an upper limit, and thus, the photosensitive member surface temperature is saturated. Therefore, in a case where the count value C of the counting part 264 is the count upper limit Cmax, it can be seen that the photosensitive member surface temperature reaches the upper limit. [0068] The print preventing threshold C 1 is a value for controlling an increase of the photosensitive member surface temperature. In a case where the count value C of the counting part 264 in the first embodiment is the print preventing threshold C 1 or more, it can be seen that the photosensitive member surface temperature increases at a permissible rate or more. [0069] The print allowing threshold C 2 is a threshold used to determine whether to re-start a printing operation. [0070] Thus, the processing part 260 in the first embodiment determines that the photosensitive member surface temperature is saturated in a case where the count value C of the counting part 264 is the count upper limit Cmax. Further, the processing part 260 determines that a current state is such a state that an image defect may occur, in a case where the count value C of the counting part 264 is the print preventing threshold C 1 or more. Further, the processing part 260 determines that a current state is such a state that an image defect does not occur, in a case where the count value C of the counting part 264 is less than the print allowing threshold C 2 . [0071] The count upper limit Cmax, the print preventing threshold C 1 and the print allowing threshold C 2 may be set based on, for example, a relationship between the photosensitive member surface temperature and a time shown as a curve 51 in FIG. 5 , and stored in the non-volatile memory 270 . FIG. 5 shows a temperature increase of the photosensitive member surface temperature during printing in the first embodiment. The origin of curves 51 and 52 in FIG. 5 corresponds to a state where the photosensitive member surface temperature is 28° C. The curve 51 shows a state of a temperature increase in a case where no particular countermeasure is provided against a temperature increase of the photosensitive member surface temperature. The curve 52 shows a state of a temperature increase in a case where a countermeasure is provided against a temperature increase of the photosensitive member surface temperature by a control by using the count value C described later. It is noted that the curves 51 and 52 in FIG. 5 are experimental values resulting from an experiment carried out in which the photosensitive member driving motor 220 is turned on from a state where the photosensitive member surface temperature is 28° C. [0072] According to FIG. 5 , it is possible to expect a time required for increasing the photosensitive member surface temperature or such. Therefore, in the first embodiment, according to the curves of an increase of the photosensitive member surface temperature, the count upper limit Cmax, the print preventing threshold C 1 and the print allowing threshold C 2 can be set. In the first embodiment, the count upper limit Cmax=2500, the print preventing threshold C 1 =2400 and the count allowing threshold C 2 is 2040. [0073] Below, the backgrounds of the count upper limit Cmax, the print preventing threshold C 1 and the print allowing threshold C 2 will be described. [0074] According to the curve 51 of FIG. 5 , when 40 minutes have elapsed since the photosensitive member driving motor 220 is turned on from a state where the photosensitive member surface temperature is 28° C., the photosensitive member surface temperature increases by approximately 15° C., and thus becomes 43° C. (15[° C.]+28[° C.]=43[° C.]). Therefore, for example, in a case where the count value C of the counting part 264 is incremented by 1 every second by the processing part 260 , the photosensitive member surface temperature reaches 43° C. from 28° C. (an increase of 15° C.) while the count value C of the counting part 264 is incremented 2400 times (60[sec]×40[min]=2400[sec]). In the first embodiment, an image defect may occur when the photosensitive member surface temperature reaches 44° C., for example. Therefore, a maximum temperature of the photosensitive member surface temperature is determined as 43° C., for example, for ensuring carrying out printing without causing an image defect, and it is determined that printing is prevented when the photosensitive member surface temperature reaches 43° C. The above-mentioned print preventing threshold C 1 =2400 corresponds to a time required for the photosensitive member surface temperature reaching 43° C. from 28° C. (an increase of 15° C.) in a case where, for example, the count value C of the counting part 264 is incremented by 1 every second (60[sec]×40[min]=2400[sec]) by the processing part 260 . [0075] The count upper limit Cmax=2500 corresponds to a case where the count value C of the counting part 264 is incremented by 2 or more every second by the processing part 260 , for example, and indicates that the photosensitive member surface temperature is 43° C. or more. The background of the print allowing threshold C 2 =2040 will be described later. [0076] Returning to FIG. 4 , the controller 210 gives a printing instruction for the processing part 260 , or carries out image processing. The controller 210 transmits a printing request signal 211 that directs carrying out printing to the processing part 260 . The printing request signal 211 is turned on and off once for one sheet of printing. [0077] Further, the controller 210 transmits and receives a communication signal 212 with the processing part 260 , which signal is for carrying out communications between the controller 210 and the processing part 260 . It is noted that, the controller 210 in the first embodiment informs the processing part 260 of whether to carry out one-side printing or both-sides printing before turning on the printing request signal 211 . [0078] Further, the controller 210 receives from the processing part 260 a print allowing signal 213 indicating whether the image forming apparatus 100 is in a printing allowed state. The processing part 260 transmits the print allowing signal having a high level (referred to as an H level, hereinafter) when the image forming apparatus 100 is in the printing allowed state. Further, the processing part 260 in the first embodiment transmits the print allowing signal 213 having a low level (referred to as an L level, hereinafter) when the image forming apparatus 100 is in a printing not allowed state. That is, in the first embodiment, in a case where the print allowing signal 213 is turned on, a printing operation is allowed, and in a case where the print allowing signal 213 is turned off, a printing operation is not allowed. Therefore, in the first embodiment, when the image forming apparatus 100 receives a printing request and the printing request signal 211 is turned on, and also, the print allowing signal is turned on, the processing part 260 starts a printing operation. Then, in a case where the print allowing signal 213 is turned off during the printing operation, the processing part 260 interrupts the printing operation. Then, in a case where the print allowing signal 212 is turned on during the interruption of the printing operation, the processing part 260 re-starts the printing operation. [0079] The photosensitive member driving motor 220 rotates (is turned on) when receiving a turning-on instruction from the processing part 260 . When the photosensitive member driving motor 220 thus rotates, a driving force of the photosensitive member driving motor 220 is transmitted to the photosensitive member 121 and the developing unit 124 (including the developing units 124 Bk, 124 M, 124 C and 124 Y) by means of a driving force transmitting mechanism (not shown). The photosensitive member driving motor 220 stops (is turned off) when receiving a turning-off instruction from the processing part 260 . When the photosensitive member driving motor 220 thus stops, the photosensitive member 121 and the developing unit 124 stop accordingly. In the first embodiment, during the photosensitive member driving motor 220 rotating, friction heat is generated in the photosensitive member 121 and the developing unit 124 , and the photosensitive member surface temperature increases accordingly. [0080] The temperature reducing part 230 is, for example, a fan motor for removing heat generated in the inside of the image forming apparatus 100 . The temperature reducing part 230 is turned on and turned off under the control of the processing part 260 by receiving an operation instruction from the processing part 260 . The temperature reducing part 230 starts operation (rotation) in response to receiving a turning-on instruction from the processing part 260 , circulates heat accumulated in the image forming apparatus 100 or transfers the heat to the outside of the image forming apparatus 100 to reduce a temperature in the inside of the image forming apparatus 100 . [0081] The fixing temperature detecting part 240 is, for example, a thermistor that detects a temperature (temperature of a surface of a fixing roller (not shown)) of the fixing unit 160 . The fixing temperature detecting part 240 always carries out the temperature detecting operation while the processing part 260 is operating. The external temperature measuring part 250 is a temperature sensor that is mounted on a housing of the image forming apparatus 100 , and measures a temperature of the outside of the image forming apparatus 100 . [0082] Next, with reference to FIGS. 6A-6B , incrementing and decrementing (adding and subtracting) of the count value C of the counting part 264 (counter control process or control of interrupting a printing operation) will be described. FIGS. 6A-6B shows a first flowchart for illustrating incrementing and decrementing the count value of the counting part 264 in the first embodiment. An operation shown in FIGS. 6A-6B is a loop operation repeatedly carried out every second after the image forming apparatus 100 is turned on. [0083] In the image forming apparatus 100 in the first embodiment, the processing part 260 of the control mechanism 200 determines whether the photosensitive member driving motor 220 is turned on (step S 601 ). In a case where the photosensitive member driving motor 220 is turned on, step S 602 is carried out. In a case where the photosensitive member driving motor 220 is turned off (No) in step S 601 , step S 615 is carried out. [0084] In a case where the photosensitive member driving motor 220 is turned on, the processing part 260 determines whether the count value C of the counting part 264 is equal to or more than the count upper limit Cmax (step S 602 ). In a case where the count value C of the counting part 264 is less than the count upper limit Cmax, the processing part 260 determines whether the image forming apparatus 100 is on a printing operation (step S 603 ). [0085] On the other hand, in a case where the count value C of the counting part 264 is equal to or more than the count upper limit Cmax in step S 602 , the processing part 260 rewrites the count value C of the counting part 264 with the count upper limit Cmax (step S 604 ), and then, carries out step S 609 . [0086] In a case where the image forming apparatus 100 is on a printing operation in step S 603 , the processing part 260 determines whether the printing operation is a both-sides printing operation (step S 605 ). In a case where the image forming apparatus 100 is not on a printing operation in step S 603 , the processing part 260 obtains a new count value C from adding 1 to the current count value C of the counting part 264 (step S 606 ), and proceeds to step S 609 . [0087] In a case where the printing operation is a both-sides printing operation in step S 605 , the new count value C obtained from adding 2 to the current count value C of the counting part 264 is stored in the counting part 264 in step S 607 . In a case where the printing operation is not a both-sides printing operation in step S 605 , this means that the printing operation is a one-side printing operation, and the processing part 260 stores the new count value C obtained from adding 1 to the current count value C (step S 608 ), and carries out step S 609 . [0088] It is noted that factors of increasing the photosensitive member surface temperature include various factors. For example, a degree of an increase of the photosensitive member surface temperature is different between a case where no paper passing state occurs in the image forming apparatus 100 such as a case of a warming up operation, and a case where a paper passing state occurs in the image forming apparatus 100 such as a case of a printing operation. Further, in a case where a printing operation is carried out, a degree of an increase of the photosensitive member surface temperature is different between a case of one-side printing operation and a case of a both-sides printing operation, because a state of an air flow in the image forming apparatus 100 is different between the cases because of a structure of bristles (brush) or such provided in the image forming apparatus 100 . Therefore, a timing at which an image defect occurs may vary in a nonuniform fashion. [0089] An increase of the photosensitive member surface temperature is faster in an order of both-sides printing>one-side printing>warming up operation, and a decrease of the same is faster in the reverse order. This is because a paper sheet passing through the image forming apparatus 100 blocks an internal air exit hole, and thereby heat is accumulated in the image forming apparatus 100 . In particular, in a both-sides printing operation, there is a case where two paper sheets simultaneously pass through the image forming apparatus 100 for the purpose that a printing speed is increased. Thus, heat is easily accumulated in the image forming apparatus 100 , and as a result, the photosensitive member surface temperature rapidly increases. It is noted that in the flowchart of FIGS. 6A-6B , because an increment of the count value C is an integer, the increment in a case of one-side printing is 1 (“+1” in step S 608 ), and also, the increment in a case of a warming up operation is 1 (“+1” in step S 606 ). [0090] Thus, the increment of the count value C of the counting part 264 varies according to an operation state of the image forming apparatus 100 (steps S 606 , S 607 and S 608 ). Thus, it is possible to increment the count value C more appropriately. [0091] The processing part 260 determines whether the count value C stored in the counting part 264 is equal to or more than the print preventing threshold C 1 (step S 609 ). [0092] In a case where the count value C is less than the print preventing threshold C 1 in step S 609 , the processing part 260 finishes the current counter control process (or control of interrupting a printing operation) without turning off the print allowing signal 213 . [0093] In a case where the count value C is equal to or more than the print preventing threshold C 1 in step S 609 , the processing part 260 measures a temperature of the outside of the image forming apparatus 100 by means of the external temperature measuring part 250 , and determines whether the external temperature is equal to or more than 27° C. (step S 610 ). [0094] In a case where the external temperature is equal to or more than 27° C. in step S 610 , the processing part 260 again determines whether the image forming apparatus 100 is on a printing operation (step S 611 ). In a case where the external temperature is less than 27° C. in step S 610 , the processing part 260 does not carry out the control of interrupting a printing operation. In the first embodiment, as shown in FIG. 5 , the image forming apparatus 100 enters a state in which an image defect may occur when a predetermined time has elapsed from a state where the photosensitive member surface temperature is 28° C. Therefore, in a case where the photosensitive member surface temperature is less than 27° C., a likelihood of an image defect occurring is low. Normally, the photosensitive member surface temperature is higher than the external temperature because respective devices in the image forming apparatus 100 generate heat. [0095] In consideration of the above, the control of interrupting a printing operation is not carried out in a case where the external temperature is less than 27° C. as mentioned above because a likelihood of the photosensitive member surface temperature reaching the above-mentioned 43° C. is low in this case, in the first embodiment. [0096] In a case where the image forming apparatus 100 is on a printing operation in step S 611 , the processing part 260 determines whether the printing operation is a both-sides printing operation or a one-side printing operation (step S 612 ). In a case where the image forming apparatus 100 is not on a printing operation in step S 611 , the processing part 260 turns off the print allowing signal 213 and prevents a printing operation (step S 613 ). [0097] In a case where the processing part 260 determines that the printing operation is a both-sides printing operation in step S 612 , the processing part 260 determines whether a paper passing state occurs in the image forming apparatus 100 (step S 614 ). In a case where the printing operation is not a both-sides printing operation in step S 612 , this means that the printing operation is a one-side printing operation, and step S 613 is carried out. In step S 613 , the print allowing signal 213 is turned off, and the printing operation is interrupted. [0098] In a case where no paper passing state occurs in the image forming apparatus 100 in step S 614 , the processing part 260 turns off the print allowing signal 213 and interrupts a printing operation in step S 613 . In a case where a paper passing state occurs in the image forming apparatus 100 in step S 614 , the processing part 260 finishes the current counter control process (or control of interrupting a printing operation) without turning off the print allowing signal so that the currently processed image forming operation is allowed to continue. [0099] In a case where the photosensitive member driving motor 220 is turned off in step S 601 , the processing part 260 determines whether the count value C of the counting part 624 is equal to or more than the print allowing threshold C 2 (step S 615 ). In a case where the count value C is equal to or more than the print allowing threshold C 2 in step S 615 , this means that a difference between the photosensitive member surface temperature and an external temperature is large, and therefore, the photosensitive member surface temperature decreasing speed is high. Therefore, the processing part 260 subtracts “6” (relatively large amount) from the count value C (step S 616 ), and finishes the current counter control process (or control of interrupting a printing operation) without turning off the print allowing signal. [0100] It is noted that, in the first embodiment, the reason for the above-mentioned print allowing threshold C 2 =2040 is as follows: A situation is assumed in which 1 minute (60 seconds) has elapsed from a state where the photosensitive member surface temperature is at the printing preventing threshold C 1 =2400, in a condition in which the photosensitive member surface temperature decreasing speed is high as mentioned above (corresponding to the above-mentioned subtraction of “6” from the count value C). In this situation, a decrease in the photosensitive member surface temperature corresponds to 6×60[sec]=360. Therefore, the resulting photosensitive member surface temperature corresponds to 2400−360=2040. In a case where the photosensitive member surface temperature decreases from the print preventing threshold C 1 =2400 to become the above-mentioned print allowing threshold C 1 =2040, it is expected that the photosensitive member surface temperature becomes equal to or less than the above-mentioned 43° C. even in a case where the photosensitive member surface temperature decreasing speed is a normal one, and thus, a printing operation can be allowed to be carried out. Thus, the print allowing threshold C 1 =2040 is determined. [0101] In a case where the count value C of the counting part 264 is less than the print allowing threshold C 2 in step S 615 , the processing part 260 determines whether the print allowing signal is turned off (step S 617 ). [0102] In a case where the print allowing signal 213 is turned off in step S 617 , the processing part 260 turns on the print allowing signal 213 (step S 618 ). In a case where the print allowing signal 213 is turned on in step S 617 , the processing part 260 proceeds to step S 619 . [0103] When the print allowing signal is turned on, the processing part 260 subtracts 1 from the count value C of the counting part 264 (step S 619 ). Next, the processing part 260 determines whether the count value C is less than 0 (step S 620 ). In a case where the count value C is less than 0, the processing part 260 changes the count value C to 0 (step S 621 ), and finishes the current counter control process (or control of interrupting a printing operation). In a case where the count value C is equal to or more than 0, the processing part 260 finishes the current counter control process (or control of interrupting a printing operation). [0104] In the first embodiment, as described above, it is possible to make the rate of the photosensitive member surface temperature increase be relatively small, as indicated by a curve 52 of FIG. 5 , by controlling the count value C of the counting part 264 . Further, as shown in FIG. 5 , the photosensitive member surface temperature enters a balanced state at a temperature of 43° C. (=28+15), and thus, does not reach 44° C. at which an image defect may occur as mentioned above, even when a continuous printing operation is carried out. [0105] This is because an amount (increment) added to the count value C in steps S 606 through S 608 is set such that a slope steeper than an actual slope of the photosensitive member surface temperature increase is set. The amount (increment) of adding to the count value C in the first embodiment is set as a value that is larger than a value corresponding to the photosensitive member surface temperature increase every second, for example. Therefore, by thus controlling an interruption of a printing operation according to the count value C as in the first embodiment, it is possible to achieve a control based on the photosensitive member surface temperature increase that has a slope steeper than an actual slope of the photosensitive member surface temperature increase. [0106] Further, in the first embodiment, the photosensitive member surface temperature is made to decrease by turning off the print allowing signal 213 to interrupt a printing operation since a printing operation is interrupted until the count value C becomes the print allowing threshold C 2 =2040. Thus, the photosensitive member surface temperature falls during the count value C being thus decreased. Therefore, in the first embodiment, it is possible to always keep the photosensitive member surface temperature at a temperature at which no image defect occurs. [0107] It is noted that, in the image forming apparatus 100 in the first embodiment, even in a case where, in step S 613 of FIGS. 6A-6B , the print allowing signal 213 is turned off, and a printing operation is interrupted, an original reading operation may be continued as a result of the controller 210 transmitting an original reading instruction to an original reading device (not shown). In the first embodiment, in this case, the original reading device is configured to be controllable solely and separately from the image forming apparatus, and carries out an original reading operation in response to the original reading instruction given by the controller 210 . Therefore, only an operation of reading an original (paper sheet) can be carried out in advance regardless of an operation of the image forming apparatus 100 . [0108] Next, with reference to FIG. 7 , another operation of adding to and subtracting from (incrementing and decrementing) the count value C in the image forming apparatus 100 in the first embodiment. FIG. 7 shows a second flowchart illustrating adding to and subtracting from the count value C in the first embodiment. A process of FIG. 7 is carried out once when a power supply is started in the image forming apparatus 100 and when the image forming apparatus 100 returns from the energy saving mode such as the sleep mode. In the first embodiment, when the process of FIG. 7 is finished, a loop operation (once per second) of the above-described process of FIGS. 6A-6B is started. [0109] In the process of FIG. 7 , a time elapsed since a power supply in the image forming apparatus 100 is turned off or when the energy saving mode is started is expected due to a temperature change of the fixing unit 160 , and a thus-expected time is reflected in the count value C. [0110] The processing part 260 stores in a counter initial value storing buffer Cini the count value C that has been stored in the non-volatile memory 270 (step S 701 ). The count value C stored in the non-volatile memory 270 is the count value C obtained when a power supply is turned off in the image forming apparatus 100 or the energy saving mode is started. Next, the processing part 260 stores in the fixing temperature storing buffer Tfus provided in the RAM 262 a fixing temperature detected by the fixing temperature detecting part 240 (step S 702 ). [0111] The processing part 260 stores in a count value calculating buffer Cbuff a count value corresponding to the temperature stored in the fixing temperature storing buffer Tfus in steps S 703 through S 710 . For example, the processing part 260 determines whether the temperature in the fixing temperature storing buffer Tfus is higher than 50° C. (step S 703 ). In a case where the temperature in the fixing temperature storing buffer Tfus is higher than 50° C., the processing part 260 proceeds to step S 704 . In a case where the temperature in the fixing temperature storing buffer Tfus is equal to or less than 50° C., the processing part 260 stores 2400 in the count value calculating buffer Cbuff provided in the RAM 262 , and proceeds to step S 712 . [0112] The processing part 260 carries out the same process also in steps S 704 through S 710 . [0113] In a case where the temperature in the fixing temperature storing buffer Tfus is higher than 120° C., the processing part 260 , it is determined that a time having elapsed since the power supply was turned off or the energy saving mode was started is very small, and thus, this time is not considered. Therefore, in this case, the processing part 260 reflects the value of the counter initial value storing buffer Cini in the count value C (step S 711 ). [0114] The processing part 260 determines a relationship between the respective values in the counter initial value storing buffer Cini and the counter calculating buffer Cbuff (step S 712 ). [0115] In a case where the value in the counter initial value storing buffer Cini is equal to or less than the value in the count value calculating buffer Cbuff in step S 712 , the processing part 260 sets 0 in the count value C (step S 713 ), and proceeds to step S 715 . In a case where the value in the counter initial value storing buffer Cini is larger, the processing part 260 sets in the counter value C a difference between the value in the counter initial value storing buffer Cini and the value in the count value calculating buffer Cbuff (step S 714 ), and proceeds to step S 715 . [0116] The processing part 260 determines whether the count value C is equal to or more than the print allowing threshold C 2 (step S 715 ). In a case where the count value C is equal to or more than the print allowing threshold C 2 , the processing part 260 turns off the print allowing signal 213 , and interrupts a printing operation by the controller 210 (step S 716 ). In a case where the count value C is less than the print allowing threshold C 2 , the processing part 260 turns on the print allowing signal 213 , and allows a printing operation by the controller 210 (step S 717 ). After completing step S 716 or S 717 , the processing part 260 carries out the process of FIGS. 6A-6B from step S 601 . [0117] FIG. 8 shows a fixing temperature change after a power supply in the image forming apparatus 100 is turned off. For example, it is assumed that a fixing temperature of the fixing unit 160 in the first embodiment is 200° C. In this case, as shown in FIG. 8 , it is seen that, when the fixing temperature at a time of a power supply being turned on in the image forming apparatus 100 is 120° C., 5 minutes have elapsed since a power supply was turned off in the image forming apparatus 100 . Similarly, it is seen that, when the fixing temperature at a time of a power supply being turned on in the image forming apparatus 100 is 90° C., 10 minutes have elapsed since a power supply was turned off in the image forming apparatus 100 . In the first embodiment, a subtracting amount corresponding to a time having elapsed since a power supply was turned off or the energy saving mode was started is reflected in the count value C stored before a power supply was turned off or the energy saving mode was started. [0118] That is, from FIG. 8 , it is seen that, in a case where the fixing temperature is 50° C. (step S 703 ), a time having elapsed since a power supply was turned off or the energy saving mode was started is 40 minutes. Therefore, the count value C is set to be a value obtained from subtracting 40×60[sec]=2400 (Cbuff) from the count value C (Cini) obtained when a power supply was turned off or the energy saving mode was started (steps S 705 S 712 and S 714 ). The same method is applied for the other fixing temperatures 70° C., 90° C. and 120 (steps S 704 , S 706 and S 708 ). [0119] The photosensitive member surface temperature depends on heat generated at a time of fixing a toner image onto a paper sheet. Therefore, in the first embodiment, a state of the fixing temperature is reflected in the count value. Thus, it is possible to determine a state of the photosensitive member surface temperature appropriately even when a power supply is turned off and on in the image forming apparatus 100 , or the power saving mode is started and the image forming apparatus 100 returns from the power saving mode. [0120] Next, with reference to FIG. 9 , a control carried out by the temperature reducing part 230 will be described. FIG. 9 shows a flowchart illustrating a control carried out by the temperature reducing part 230 . [0121] The temperature reducing part in the first embodiment is a fan motor or such that removes heat from the inside of the image forming apparatus 100 . The control of FIG. 9 is carried out every 5 milliseconds. [0122] In the image forming apparatus 100 in the first embodiment, the processing part 260 determines whether the photosensitive member driving motor 220 is turned on (step S 901 ). In a case where the photosensitive member driving motor 220 is turned on in step S 901 , the processing part 260 turns on the temperature reducing part 230 (referred to as a fan motor 230 , hereinafter) (step S 902 ). [0123] In a case where the photosensitive member driving motor 220 is turned off in step S 901 , the processing part 260 determines whether the print allowing signal 213 is turned off (step S 903 ). In a case where the print allowing signal 213 is turned off in step S 903 , the processing part 260 proceeds to step S 902 , and turns on the fan motor 230 . It is noted that, in a case where both the photosensitive member driving motor 220 is turned off and the print allowing signal 213 is turned off, there is a possibility that the internal temperature of the image forming apparatus 100 increases. Therefore, in the first embodiment, the fan motor 230 is turned on in a case where both the photosensitive member driving motor 220 is turned off and the print allowing signal 213 is turned off, so that the temperature in the inside of the image forming apparatus 100 is reduced. [0124] In a case where the print allowing signal 213 is turned on in step S 903 , the processing part 260 turns off the fan motor 230 (step S 904 ). [0125] Thus, in the first embodiment, based on whether the print allowing signal 213 is turned on or off, a control of turning on and off of the fan motor 230 is carried out. Thereby, it is possible to control the fan motor 230 according to a state of the image forming apparatus 100 for when the photosensitive member driving motor 220 is turned off. That is, according to the first embodiment, in a case where both the photosensitive member driving motor 220 is turned off and the print allowing signal 213 is turned off, it is seen that the photosensitive member driving motor 220 is thus turned off probably because of an increase in a temperature of the inside of the image forming apparatus 100 . Therefore, the processing part 260 turns on the fan motor 230 (steps S 901 , S 903 and S 902 ). [0126] Further, in a case where both the photosensitive member driving motor 220 is turned off and the print allowing signal 213 is turned on, it is seen that the photosensitive member driving motor 220 is turned off because a printing request is not given. Therefore, the processing part 260 turns off the fan motor 230 (steps S 901 , S 903 and S 904 ). It is noted that, in the image forming apparatus 100 in the first embodiment, the print allowing signal 213 is turned on in a standing by state in a normal condition. [0127] By the above-mentioned control, it is possible to reduce the photosensitive member surface temperature by driving the fan motor 230 and removing heat from the inside of the image forming apparatus 100 , only in a case where the print allowing is turned off (steps S 901 , S 903 and S 902 ). [0128] Next, with reference to FIG. 10 , a control of an image adjustment process in the first embodiment will be described. FIG. 10 shows a flowchart illustrating a control of an image adjustment process in the first embodiment. [0129] The image adjustment process in the first embodiment described below is a process of detecting a change in image forming process conditions caused by a change in a temperature and/or humidity, optimizing the process conditions, and providing stable images. The image adjustment process is, for example, such that, when a change in a temperature and/or humidity in the image forming apparatus 100 is detected, the controller 210 outputs an image adjustment process carrying-out request to the control mechanism 200 . [0130] Normally, when the image adjustment process is carried out in a case where the photosensitive member surface temperature is high, an image may be distorted. Therefore, in the image forming apparatus 100 in the first embodiment, the image adjustment process is prevented in a case where the photosensitive member surface temperature is high. The process of FIG. 10 is started up and carried out every 5 milliseconds. [0131] In the image forming apparatus 100 in the first embodiment, the processing part 260 determines whether an image adjustment process carrying-out request is given (step S 1001 ). In a case where no image adjustment process carrying-out request is given in step S 1001 , the processing part 260 finishes the current process of FIG. 10 . [0132] In a case where an image adjustment process carrying-out request is given in step S 1001 , the processing part 260 determines whether the print allowing signal 213 is turned on (step S 1002 ). In a case where the print allowing signal 213 is turned on in step S 1002 , the processing part 260 carries out an image adjustment process (step S 1003 ). In a case where the print allowing signal 213 is turned off in step S 1002 , the processing part 260 finishes the current process of FIG. 10 . [0133] In the first embodiment, the print allowing signal is turned off so that the photosensitive member surface temperature does not become higher than the threshold (step S 613 of FIG. 6B ). Therefore, in the first embodiment, in a case where an image adjustment process carrying-out request is given, the image adjustment process is carried out only when the print allowing signal is turned on (steps S 1001 , S 1002 and S 1003 ). Thereby, it is possible to prevent the image adjustment process from being carried out in a case where the photosensitive member surface temperature is high. [0134] Next, with reference to FIG. 11 , a process of storing in the non-volatile memory 270 the count value C of the counting part 264 in the first embodiment will be described. FIG. 11 shows a flowchart illustrating a process of storing in the non-volatile memory 270 the count value C of the counting part 264 . The process of FIG. 11 described below is started up and carried out every second. [0135] In the image forming apparatus 100 in the first embodiment, the processing part 260 determines whether the printing request signal 211 from the controller 210 is turned on (step S 1101 ). In a case where the printing request signal 211 is turned on in step S 1101 , the processing part 260 stores the count value C in the non-volatile memory 270 (step S 1102 ). In a case where the printing request signal 211 is turned off in step S 1101 , the processing part 260 determines whether the photosensitive member driving motor 220 is turned on (step S 1103 ). [0136] In a case where the photosensitive member driving motor 220 is turned on in step S 1103 , the processing part 260 sets (1) a photosensitive member driving motor on flag Fmot (step S 1104 ). In a case where the photosensitive member driving motor 220 is turned off in step S 1103 , the processing part 260 determines whether the photosensitive member driving motor on flag Fmot is set (step S 1105 ). [0137] In a case where the photosensitive member driving motor on flag Fmot is set in step S 1105 , the processing part 260 resets (0) the photosensitive member driving motor on flag Fmot (step S 1106 ). Then, the processing part 260 stores the count value C in the non-volatile memory 270 (step S 1107 ). [0138] In a case where the photosensitive member driving motor on flag Fmot is not set in step S 1105 , the processing part 260 determines whether the image forming apparatus 100 currently carries out a printing operation or another operation (step S 1108 ). It is noted that, another operation is, for example, a warming up operation, an error processing operation, an operation in the standing by mode or such. [0139] In a case where the image forming apparatus 100 carries out another operation in step S 1108 , the processing part 260 determines whether the count value C is 300 (step S 1109 ). In a case where the count value C is 300 in step S 1109 , the processing part 260 stores the count value in the non-volatile memory 270 (step S 1110 ). In a case where the image forming apparatus 100 carries out a printing operation in step S 1108 , the processing part 260 finishes the process of storing the count value C. [0140] In a case where the count value C is not 300 in step S 1109 , the processing part 260 determines whether the count value C is 600 (step S 1111 ). In a case where the count value C is 600 in step S 1111 , the processing part 260 proceeds to step S 1110 . [0141] In a case where the count value C is not 600 in step S 1111 , the processing part 260 determines whether the count value C is 1200 (step S 1112 ). In a case where the count value C is 1200 in step S 1112 , the processing part 260 proceeds to step S 1110 . [0142] In a case where the count value C is not 1200 in step S 1112 , the processing part 260 determines whether the count value C is 2400 (step S 1113 ). In a case where the count value C is 2400 in step S 1113 , the processing part 260 proceeds to step S 1110 . In a case where the count value C is not 2400 in step S 1113 , the processing part 260 finishes the process of storing the count value C. [0143] In the first embodiment, through the above-described process of FIG. 11 , the count value C of the counting part 264 can be stored in the non-volatile memory 270 . [0144] Further, in the image forming apparatus 100 in the first embodiment, it is possible not to make valid an operation of interrupting a printing operation using the count value C of the counting part 264 . In the image forming apparatus 100 in the first embodiment, it is set whether an operation of interrupting a printing operation is valid, by using a communication signal 212 received from the controller 210 . Below, with reference to FIG. 12 , a process of setting whether an operation of interrupting a printing operation is valid will be described. FIG. 12 shows a flowchart illustrating a process of setting whether an operation of interrupting a printing operation is valid. The process described with reference to FIG. 12 is started up and carried out when the processing part 260 receives from the controller 120 a notification of whether an operation of interrupting a printing operation is valid, through the communication signal 212 . The setting of whether an operation of interrupting a printing operation is valid is carried out, for example, by a user. [0145] In the image forming apparatus 100 in the first embodiment, the processing part 260 determines whether setting contents reported through the communication signal 212 from the controller 210 indicate a setting that makes valid an operation of interrupting a printing operation (step S 1201 ). In a case where the setting contents indicate a setting that makes valid an operation of interrupting a printing operation in a step S 1201 , the processing part 260 substitutes 1 for PRN_STOP that is a storage area secured in the RAM 262 (step S 1202 ). In a case where the setting contents indicate a setting that does make valid an operation of interrupting a printing operation in a step S 1201 , the processing part 260 substitutes 0 for PRN_STOP that is a storage area secured in the RAM 262 (step S 1203 ). The processing part 260 stores the value of PRN_STOP stored in the RAM 262 in the non-volatile memory 270 (step S 1204 ). [0146] Next, with reference to FIG. 13 , a process of reading a setting of whether to make valid an operation of interrupting a printing operation will be described. FIG. 13 shows a flowchart illustrating a process of reading a setting of whether to make valid an operation of interrupting a printing operation in the embodiment. A process described with reference to FIG. 13 is carried out only once immediately after a power supply is started in the image forming apparatus 100 and when the image forming apparatus 100 returns from the energy saving mode such as the sleep mode. [0147] In the image forming apparatus 100 , the processing part 260 reads from the non-volatile memory 270 the contents of a setting of whether to make valid an operation of interrupting a printing operation (step S 1301 ). It is noted that the contents of a setting of whether to make valid an operation of interrupting a printing operation are the value of PRN_STOP stored in the non-volatile memory 270 in step S 1204 of FIG. 12 . The processing part 260 determines whether the read setting of whether to make valid an operation of interrupting a printing operation indicates to make valid (1) an operation of interrupting a printing operation (step S 1302 ). [0148] In a case where the setting indicates to make valid (1) in step S 1302 , the processing part 260 substitutes 1 for PRN_STOP secured in the RAM 262 (step S 1303 ). In a case where the setting indicates not to make valid (1) in step 1302 , the processing part 260 substitutes 0 for PRN_STOP secured in the RAM 262 (step S 1304 ). [0149] As described above, in the image forming apparatus 100 in the first embodiment, a control is carried out by the processing part 260 such that, based on the count value C of the counting part 264 , it is determined whether to interrupt a printing operation. Therefore, in the image forming apparatus 100 in the first embodiment, it is possible to interrupt a printing operation according to the photosensitive member surface temperature without providing a temperature sensor. Thus, it is possible to avoid an image defect otherwise occurring because of an increase in the photosensitive member surface temperature, at low cost. Further, in the first embodiment, it is possible to shorten an interruption time (downtime), for every interruption occurring, of a printing operation being interrupted by the above-mentioned operation of interrupting a printing operation. Thus, it is possible to avoid degradation in productivity otherwise occurring because of a long interruption operation. This advantage is particularly effective for such a low-end user that the number of printing sheets every time is small. Second Embodiment [0150] With reference to the figures, a second embodiment of the present invention will now be described. The second embodiment of the present invention is different from the above-described first embodiment in that a device type of the image forming apparatus 100 is considered. Therefore, in a description of the second embodiment below, only points different from the first embodiment will be described. For parts/components having the same functional configurations as those in the first embodiment, the same reference numerals as those in the first embodiment are given, and duplicate description thereof will be omitted. [0151] In the second embodiment, a device type of the image forming apparatus 100 is determined. In the image forming apparatus 100 in the second embodiment, device type information indicating a device type of the image forming apparatus 100 is written in the non-volatile memory 270 when the image forming apparatus 100 is shipped from a factory. The device type information in the second embodiment is information indicating whether the image forming apparatus 100 is a multi-function peripheral (MFP) that has functions including a printing function and also those other than a printing function, or a printer that has a printing function only. [0152] FIG. 14 shows a flowchart illustrating a process of determining a device type of the image forming apparatus 100 in the second embodiment. The process of FIG. 14 is carried out only once immediately after a power supply is started in the image forming apparatus 100 and when the image forming apparatus 100 returns from the energy saving mode such as the sleep mode. [0153] The processing part 260 in the second embodiment reads the device type information from the non-volatile memory 270 (step S 1401 ). The processing part 260 determines whether the image forming apparatus is a printer based on the read device type information (step S 1402 ). [0154] In a case where the image forming apparatus 100 is a printer in step S 1402 , the processing part 260 substitutes 0 for KISYU that is a storage area secured in the RAM 262 (step S 1403 ). In the second embodiment, a value thus substituted for KISYU is regarded as device type information. In a case where the image forming apparatus 100 is not a printer in step S 1402 , this means that the image forming apparatus is a multi-function peripheral, and the processing part 260 substitutes 1 for KISYU that is the storage area secured in the RAM 262 (step S 1404 ). [0155] Next, an operation of interrupting a printing operation in the second embodiment will be described. In the second embodiment, when the count value C is incremented or decremented (added to or subtracted from) in a control of interrupting a printing operation, an amount (increment or decrement) according to the device type of the image forming apparatus 100 is used. [0156] In the image forming apparatus 100 in the second embodiment, an adding amount table 15 and a subtracting amount table 16 are stored in the non-volatile memory 270 . The adding amount table 15 is such that the device type information and adding amounts (increments) added to the count value C are associated with each other. The subtracting amount table 16 is such that the device type information and subtracting amounts (decrements) subtracted from the count value C are associated with each other. The adding amount table 15 and the subtracting amount table 16 will now be described. [0157] FIGS. 15A-15B show one example of the adding amount table 15 and the subtracting amount table 16 . In the adding amount table 15 , the device type information is associated with each of an adding amount (increment) to be added at a time of both-sides printing, an adding amount to be added at a time of one-side printing and an adding amount to be added at a time of an operation other than a printing operation. In the subtracting table 16 , the device type information is associated with each of a subtracting amount (decrement) to be subtracted in a case where the count value C is equal to or more than the print allowing threshold C 2 , and a subtracting amount to be subtracted when the count value C is less than the print allowing threshold C 2 . [0158] In the second embodiment, the adding amount table 15 and the subtracting amount table 16 are referred to, and an operation of interrupting a printing operation is controlled. [0159] Below, with reference to FIGS. 16A-16B , a control of interrupting a printing operation in the second embodiment will now be described. FIGS. 16A-16B show a flowchart illustrating a process of adding to and subtracting from (incrementing and decrementing) the count value C in the second embodiment. [0160] Processes of steps S 1601 through S 1604 in FIGS. 16A-16B are the same as steps S 601 through S 604 in FIGS. 6A-6B , and thus, duplicate description thereof is omitted. [0161] In a case where the image forming apparatus 100 is not on a printing operation in step S 1603 , the processing part 260 refers to the adding amount table 15 , and adds to the count value C a value corresponding to NOT_PRN[KISYU] (step S 1606 ). For example, in a case where a device type of the image forming apparatus 100 is a MFP, a value “1” is substituted for KISYU. Therefore, the processing part 260 adds 2 corresponding to NOT_PRN[KISYU] for KISYU=1 in FIG. 15A to the count value C. For the other cases, the same method is applied. [0162] In a case where the image forming apparatus 100 is not on a both-sides printing operation in step S 1605 , the processing part 260 refers to the adding amount table 15 , and adds to the count value C a value corresponding to DUP[KISYU] (step S 1607 ). In a case where the image forming apparatus 100 is not on a both-sides printing operation but on a one-side print operation in step S 1605 , the processing part 260 refers to the adding amount table 15 , and adds to the count value C a value corresponding to SIMP[KISYU] (step S 1608 ). [0163] Processes of steps S 1609 through S 1614 in FIGS. 16A-16B are the same as steps S 609 through S 614 in FIGS. 6A-6B , except for a case where a determination result of any one of steps S 1609 , S 1610 and S 1614 is NO. Thus, duplicate description thereof will be omitted, and the case where a determination result of any one of steps S 1609 , S 1610 and S 1614 is NO will be described later. [0164] In a case where no paper passing state occurs in the image forming apparatus 100 in step S 1614 , the processing part 260 determines whether the contents of PRN_STOP are 1 (setting for interrupting a printing operation is valid) (step S 1615 ). In a case where the setting for interrupting a printing operation is valid in step S 1615 , the processing part 260 proceeds to step S 1613 . [0165] The above-mentioned case where a determination result of any one of steps S 1609 , S 1610 and S 1614 is NO will now be described, together with a case where a determination result of step S 1615 is NO. The processing part 260 finishes the current process of FIGS. 16A-16B with the print allowing signal turned on (step S 1616 ), in any one of a case where the count value C is less than the printing preventing threshold C 1 in step S 1609 , a case where the external temperature is less than 27° C. in step S 1610 , a case where a paper passing state occurs in the image forming apparatus 100 in step S 1614 and a case where a setting for interrupting a printing operation is not valid in step S 1615 . [0166] In a case where the photosensitive member driving motor 220 is turned off in step S 1601 , the processing part 260 determines whether the count value C is equal to or more than the print allowing threshold C 2 (step S 1617 ). [0167] In a case where the count value C is equal to or more than the print allowing threshold C 2 in step S 1617 , the processing part 260 refers to the subtracting amount table 16 , and subtracts from the count value C a value corresponding to C 2 _OVER[KISYU] (step S 1618 ). Then, the processing part 260 finishes the current process of FIGS. 16A-16B . [0168] In a case where the count value C is less than the print allowing threshold C 2 in step S 1617 , the processing part 260 determines whether the print allowing signal 213 is turned off (step S 1619 ). In a case where the print allowing signal 213 is turned off in step S 1619 , the processing part 260 turns on the print allowing signal 213 (step S 1620 ). In a case where the print allowing signal 213 is turned on in step S 1619 , the processing part 260 proceeds to step S 1621 . [0169] In a case where the print allowing signal 213 is turned on in step S 1620 , the processing part 260 refers to the subtracting amount table 16 , and subtracts from the count value C a value corresponding to C 2 _UNDER[KISYU] (step S 1621 ). Processes of steps S 1622 and 1623 are the same as those of steps S 620 and S 621 of FIG. 6A , and duplicate description thereof will be omitted. [0170] Next, with reference to FIG. 17 , another operation of adding to and subtracting from (incrementing and decrementing) the count value C in the image forming apparatus 100 in the second embodiment will be described. FIG. 17 shows a second flowchart illustrating adding to and subtracting from the count value C in the second embodiment. A process described with reference to FIG. 17 is carried out once when a power supply is started in the image forming apparatus 100 and when the image forming apparatus 100 returns from the energy saving mode such as the sleep mode. [0171] Processes of steps S 1701 through S 1714 are the same as those of steps S 701 through S 714 of FIG. 7 , and duplicate description thereof will be omitted. When finishing a process of step S 1711 , S 1713 or S 1714 , the processing part 260 returns to step S 1601 of FIG. 16A , and carries out the process of FIGS. 16A-16B . [0172] Next, with reference to FIG. 18 , an image adjustment process in the second embodiment will be described. FIG. 18 shows a flowchart illustrating the image adjustment process in the second embodiment. The process described with reference to FIG. 18 is carried out when a power supply is started in the image forming apparatus 100 and when the image forming apparatus 100 returns from the energy saving mode such as the sleep mode. The process described with reference to FIG. 18 is started up and carried out every 5 milliseconds. [0173] In the second embodiment, in a case where the photosensitive member surface temperature is high, the image adjustment process is carried out after the photosensitive member surface temperature falls. [0174] The processing part 260 determines whether the count value C is less than the print allowing threshold C 2 (=2040) (step S 1801 ). In a case where the count value C is equal to or more than the print allowing threshold C 2 in step S 1801 , the processing part 260 repeats the process of step S 1801 , and waits for the count value C to become less than the print allowing threshold C 2 . In the second embodiment, at this time, devices such as the photosensitive member driving motor 220 and so forth stop. [0175] In a case where the count value C is less than the print allowing threshed C 2 in step S 1801 , the processing part 260 carries out the image adjustment process (step S 1802 ). [0176] Thus, in the second embodiment, the processing part 260 waits for the count value C to become less than the print allowing threshold C 2 . Therefore, it is possible to prevent the image adjustment process from being carried out while the photosensitive member surface temperature is high. [0177] As described above, in the second embodiment, it is possible to interrupt a printing operation according to the photosensitive member surface temperature without requiring a temperature sensor, whether the image forming apparatus 100 is a printer that carries out only a printing operation or is a multi-function peripheral that carries out plural functions including a facsimile function, a scanning function and so forth in addition to a printing function. Thus, it is possible to avoid an image defect otherwise occurring because of an increase in the photosensitive member surface temperature, at low cost. Further, in the second embodiment, it is possible to shorten an interruption time (downtime), for every interruption occurring, of a printing operation being interrupted by the above-mentioned operation of interrupting a printing operation. Thus, it is possible to avoid degradation in productivity otherwise occurring because of a long interruption operation. This advantage is particularly effective for such a low-end user that the number of printing sheets every time is small. Third Embodiment [0178] Below, a third embodiment of the present invention will be described with reference to figures. The third embodiment of the present invention is different from the above-described first embodiment in that two fans are provided in the image forming apparatus. Therefore, in a description of the third embodiment below, only points different from the first embodiment will be described. For parts/components having the same functional configurations as those in the first embodiment, the same reference numerals as those in the first embodiment are given, and duplicate description thereof will be omitted. [0179] The image forming apparatus 100 A in the third embodiment carries out a control of interrupting a printing operation in consideration of a temperature in the outside of the image forming apparatus 100 A. [0180] A temperature in the inside of the image forming apparatus 100 A (internal temperature) is affected by a temperature in the outside of the image forming apparatus 100 A (external temperature). FIG. 19 shows a change in the internal temperature during a printing operation, and FIG. 20 shows a change of the internal temperature after a printing operation is finished. [0181] It is seen from FIGS. 19 and 20 that the internal temperature of the image forming apparatus 100 A is affected by the external temperature of the image forming apparatus 100 A both during a printing operation and after a printing operation is finished. As the external temperature is higher, an increasing speed of the internal temperature is higher, and as the external temperature is lower, a decreasing speed of the internal temperature is higher. [0182] In the third embodiment, an influence of the external temperature of the image forming apparatus 100 A is reduced. FIG. 21 illustrates the image forming apparatus 100 A in the third embodiment. The image forming apparatus 100 A in the third embodiment has a fixing cooling fan 161 and an internal cooling fan 162 . The fixing cooling fan 161 is provided near the fixing unit 160 , and cools the fixing unit 160 . The internal cooling fan 162 is provided near the plural image forming parts 120 Bk, 120 M, 120 C and 120 Y, and cools the inside of the image forming apparatus 100 A. [0183] In the image forming apparatus 100 A in the third embodiment, the fixing cooling fan 161 and the internal cooling fan 162 rotate at high speeds while the photosensitive member 121 rotates. When the photosensitive member 121 stops rotation, a time for which the high speed rotation of the fixing cooling fan 161 and the internal cooling fan 162 is continued is determined with reference to the count value C. Then, the fixing cooling fan 161 and the internal cooling fan 162 rotate at high speeds for the thus-determined time, and after that, rotate at low speeds. [0184] In the third embodiment, for rotational speeds of the fixing cooling fan 161 and the internal cooling fan 162 , levels are provided previously. That is, as the levels for the rotational speeds, a high-speed rotation level and a low-speed rotation level in which rotational speeds are lower than those in the high-speed rotation level are set. The fixing cooling fan 161 and the internal cooling fan 162 in the third embodiment rotate at high speeds or low speeds according to an instruction given by the processing part 260 , for example. [0185] In the image forming apparatus 100 A in the third embodiment, the adding and subtracting amounts (increment and decrement) for the count value C are changed according to states of the fixing cooling fan 161 and the internal cooling fan 162 . In the third embodiment, thereby, it is possible to prevent a decreasing speed of the internal temperature of the image forming apparatus 100 A from being affected by the external temperature of the image forming apparatus 100 A. [0186] FIG. 22 shows a first flowchart illustrating a process of changing the adding and subtracting amounts (increment and decrement) for the count value C in the third embodiment. A process described with reference to FIG. 22 is started up and carried out every second. [0187] In the image forming apparatus 100 A in the third embodiment, the processing part 260 determines whether the photosensitive member driving motor 220 is turned on (step S 2201 ). In a case where the photosensitive member driving motor 220 is turned on in step S 2201 , the processing part 260 determines rotational speeds of the fixing cooling fan 161 and the internal cooling fan 162 to be of the high-speed rotation level (step S 2202 ). [0188] Processes in steps S 2203 through S 2209 are the same as those in steps S 1602 through S 1608 of FIG. 16A , and duplicate description thereof will be omitted. [0189] In a case where the photosensitive member driving motor 220 is turned off in step S 2201 , the processing part 260 determines whether the rotational speeds of the fixing cooling fan 161 and the internal cooling fan 162 are of the high-speed rotation level (step S 2210 ). [0190] In a case where the rotational speeds of the fixing cooing fan 161 and the internal cooling fan 162 are of the high-speed rotation level in step S 2210 , the processing part 260 refers to the subtracting amount table 16 , and subtracts from the count value C a value corresponding to C 2 _OVER[KISYU] (step S 2211 ). In a case where the rotational speeds of the fixing cooling fan 161 and the internal cooling fan 162 are not of the high-speed rotation level in step S 2210 (i.e., of the low-speed rotation level), the processing part 260 refers to the subtracting amount table 16 , and subtracts from the count value C a value corresponding to C 2 _UNDER[KISYU] (step S 2212 ). [0191] Processes in steps S 2213 through S 2214 are the same as those in steps S 1622 through S 1623 of FIG. 16A , and duplicate description thereof will be omitted. [0192] In the third embodiment, in a case where the fixing cooling fan 161 and the internal cooling fan 162 rotate at high speeds, a decreasing speed of the photosensitive member surface temperature is high. Therefore, in the case of the high-speed rotation, the value larger than the value that is subtracted from the count value C in the case of low-speed rotation is selected (see FIG. 15B ) as a subtracting amount to subtract from the count value C. Thus, in the case of high-speed rotation, the count C reduces within a short time. Thus, in the third embodiment, the count value C can be changed according to the rotational speeds of the fixing cooling fan 161 and the internal cooling fan 162 . [0193] Next, with reference to FIG. 23 , a process of changing the adding and subtracting amounts (increment and decrement) for the count value C according to the external temperature at a time when a power supply is started in the image forming apparatus 100 A and when the image forming apparatus 100 A returns from the energy saving mode such as the sleep mode. [0194] FIG. 23 shows a second flowchart illustrating a process of changing adding and subtracting amounts (increment and decrement) for the count value C in the third embodiment. The process described with reference to FIG. 23 is started up and carried out only once when a power supply is started in the image forming apparatus 100 A and when the image forming apparatus 100 A returns from the energy saving mode such as the sleep mode. [0195] In the image forming apparatus 100 A, the processing part 260 determines whether the external temperature measured by the external temperature measuring part 250 is less than a TB 1 (=15° C.) (step S 2301 ). [0196] In a case where the external temperature is less than TB 1 in step S 2301 , the processing part 260 subtracts 0.2 from a value of SIMP[KISYU], 0.3 from a value of DUP[KISYU] and 0.2 from a value of NOT_PRN[KISYU] of the adding amount table 15 (step S 2302 ). Further, the processing part 260 adds 0.2 to a value of C 2 _OVER[KISYU] and 0.1 to a value of C 2 _UNDER[KISM] of the subtracting amount table 16 (step S 2302 ). [0197] In a case where the external temperature is equal to or more than TB 1 in step S 2301 , the processing part 260 determines whether the external temperature is equal to or more than TB 1 and less than TB 2 (=25° C.) (step S 2303 ). In a case where the external temperature is equal to or more than TB 1 and less than TB 2 in step S 2303 , the processing part 260 finishes the current process of FIG. 23 . In a case where the external temperature is not equal to or more than TB 1 and less than TB 2 in step S 2303 , the processing part 260 adds 0.2 to a value of SIMP[KISYU], 0.3 to a value of DUP[KISYU] and 0.2 to a value of NOT_PRN[KISYU] of the adding amount table (step S 2304 ). Further, the processing part 260 subtracts 0.2 from a value of C 2 _OVER[KISYU] and 0.1 from a value of C 2 _UNDER[KISYU] of the subtracting amount table 16 (step S 2304 ). [0198] That is, in the third embodiment, based on the external temperature, the adding amount table 15 and the subtracting amount table 16 are updated. In the third embodiment, thereby, it is possible to control the count value C to make the count value C be a value that is one in consideration of the external temperature, and it is possible to reduce an influence of the external temperature. [0199] Next, with reference to FIG. 24 , a control of rotational speeds of the fixing cooling fan 161 and the internal cooling fan 162 in the third embodiment will be described. FIG. 24 shows a flowchart illustrating a control of rotational speeds of the fixing cooling fan 161 and the internal cooling fan 162 in the third embodiment. [0200] In the image forming apparatus 100 A in the third embodiment, the processing part 260 determines whether the photosensitive member driving motor 220 is turned on (step S 2401 ). In a case where the photosensitive member driving motor 220 is turned on in step S 2401 , the processing part 260 causes the fixing cooling fan 161 and the internal cooling fan 162 to rotate at high speeds (step S 2402 ). [0201] In a case where the photosensitive member driving motor 220 is turned off in step S 2401 , the processing part determines whether a warming up operation of the image forming apparatus 100 A has not been finished yet, or whether final paper sheet ejection has not been finished yet (step S 2403 ). The final paper sheet ejection means a final paper sheet being ejected in a series of a printing operation. For example, in a case where a printing operation for printing on three paper sheets is carried out, the final paper sheet ejection means the third paper sheet being ejected. [0202] In a case where a warming up operation of the image forming apparatus 100 A has not been finished yet, or final paper sheet ejection has not been finished yet in step S 2403 , the processing part 260 proceeds to step S 2402 . [0203] In a case where a warming up operation of the image forming apparatus 100 A has been finished, or final paper sheet ejection has been finished in step S 2403 , the processing part 260 determines whether the count value C is less than TA 1 (=100) (step S 2404 ). In a case where the count value C is less than TA 1 in step S 2404 , the processing part 260 determines a high-speed rotation time HT for which the fixing cooling fan 161 and the internal cooling fan 162 are rotated at high speeds to be 10 seconds (step S 2405 ). In a case where the count value C is equal to or more than TA 1 in step S 2404 , the processing part 260 determines the high-speed rotation time HT for which the fixing cooling fan 161 and the internal cooling fan 162 are rotated at high speeds to be 60 seconds (step S 2406 ). [0204] The processing part 260 causes the fixing cooling fan 161 and the internal cooling fan 162 to rotate at high speeds for the high-speed rotation time HT determined in step S 2405 or S 2406 (step S 2407 ). After finishing the high-speed rotation of the fixing cooling fan 161 and the internal cooling fan 162 for the high-speed rotation time HT, the processing part 260 then causes the fixing cooling fan 161 and the internal cooling fan 162 to rotate at low speeds (step S 2408 ). [0205] It is noted that the specific values of TA 1 and the high-speed rotation time HT are obtained from experimental values or such. In the image forming apparatus 100 A in the third embodiment, in a case where the count value C becomes equal to or more than 100, the high-speed rotation time HT is determined to be 60 seconds, thus the fixing cooling fan 161 and the internal cooling fan 162 are rotated at high speeds for the 60 seconds, and thereby, the internal temperature falls sufficiently. Further, in the image forming apparatus 100 A in the third embodiment, in a case where the count value C is less than 100, the high-speed rotation time HT is determined to be 10 seconds, thus the fixing cooling fan 161 and the internal cooling fan 162 are rotated at high speeds for 10 seconds, and thereby, the internal temperature falls sufficiently also in this case. [0206] The high-speed rotation time HT is determined in consideration of both reducing a time of rotating the fixing cooling fan 161 and the internal cooling fan 162 at high speeds to reduce noise, and sufficiently reducing the internal temperature of the image forming apparatus 100 A to such a degree to avoid an image defect. [0207] Thus, in the third embodiment, in a case where the count value C is smaller in comparison to the predetermined value TA 1 , it is determined that the internal temperature of the image forming apparatus 100 A is not high, and the high-speed rotation time HT of the fixing cooling fan 161 and the internal cooling fan 162 is set shorter. Further, in a case where the count value C is larger in comparison to the predetermined value TA 1 , it is determined that the internal temperature of the image forming apparatus 100 A is high, and the high-speed rotation time HT of the fixing cooling fan 161 and the internal cooling fan 162 is set longer. [0208] Thus, in the third embodiment, it is possible to adjust the internal temperature of the image forming apparatus 100 A while avoiding an influence of the external temperature without requiring a temperature sensor or such. Thereby, in the third embodiment, it is possible to perform a printing operation according to the photosensitive member surface temperature while avoiding an influence of the external temperature. [0209] The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention. [0210] The present application is based on Japanese priority applications Nos. 2009-064573 and 2010-052379, filed Mar. 17, 2009 and Mar. 9, 2010, respectively, the entire contents of which are hereby incorporated herein by reference.

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