JP2016009134A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing wear of a color photoreceptor without deteriorating productivity in image formation in which a color image and a black-and-white image are mixed alternately by sheet.SOLUTION: An image forming apparatus (100) includes photoreceptors 124a to 124d provided for respective colors, development devices (33) that develop by toner latent images formed on the surfaces of photoreceptors, and an intermediate transfer body 130 that contacts with a photoreceptor and on which a developed toner image is transferred. The image forming apparatus (100) further includes a contact separation mechanism (40) that makes a photoreceptor and the intermediate transfer belt in contact with each other or separate from each other. The image forming apparatus determines whether an image to be formed is a color image consisting of a plurality of colors or a black-and-white image. When the image is determined to be a color image, the image forming apparatus brings the intermediate transfer body into contact with the photoreceptors of a plurality of colors and performs image formation by a first printing mode for operating the development devices of the plurality of colors. On the other hand, when the image is determined to be a black-and-white image, the image forming apparatus performs image formation by a second printing mode for stopping the operation of the development devices other than a black development device.

Description

  The present invention relates to an image forming apparatus that forms a color image by superimposing single-color images. In particular, the present invention relates to a technique for switching between a color image formation mode and a monochrome image formation mode.

  In an electrophotographic image forming apparatus that irradiates a photoconductor with a laser beam and forms an electrostatic latent image on the photoconductor, a configuration in which a color photoconductor is mounted in addition to a monochrome photoconductor is increasing. Yes. Some image forming apparatuses of this type perform control to switch between a monochrome mode in which only a monochrome photosensitive member is used and a color mode in which all the photosensitive members are used, depending on the image to be printed.

  In mixed data printing in which a monochrome image and a color image are switched for each sheet (for example, paper), the monochrome mode and the color mode are switched, thereby reducing the consumption of the color photoconductor. On the other hand, it takes time to switch between the monochrome mode and the color mode. For this reason, for example, when switching from sheet to sheet, there is a problem that productivity in image formation is reduced.

In order to cope with such a problem, there is an image forming apparatus disclosed in Patent Document 1 in the related art. In this image forming apparatus, the charging means for the color image photosensitive member is not immediately stopped during the formation of the black and white image, but only after a predetermined number or more of black and white images have been formed, the charging of the color image photosensitive member is not performed. Configured to stop. As described above, when the number of times of continuous black-and-white image formation is less than the predetermined number, control is performed so as not to switch modes. This eliminates the time for stopping and restarting the color photoconductor, thereby improving productivity.
On the other hand, when continuously forming a predetermined number of black and white images, charging of the color photoconductor is stopped. By controlling in this way, the life (lifetime) of the color photoconductor is ensured, that is, the consumption of the color photoconductor is reduced.

JP 2004-151462 A

However, as in the image forming apparatus described in Patent Document 1, the control of waiting until a predetermined number of black and white images continue is determined by “a predetermined number of black and white images depending on the interval (feed interval) between conveyed sheets”. The problem remains that it takes time until the condition “continuous” is established.
Generally, when image formation is continuously performed on a plurality of sheets, the interval between the preceding sheet and the succeeding sheet varies depending on various factors. For example, when a sheet having a size less than the width of the fixing device for thermally fixing the toner image is conveyed, the interval between the sheets may be increased by about 5 to 30 seconds in order to prevent the temperature rise at the end of the fixing device. is there. Even when the tray of the post-processing apparatus moves up and down for the binding process of binding the sheets after forming the image, the sheet interval may be increased by about 30 seconds.

  As described above, when the time taken until the condition that “a predetermined number of black and white images are continuous” becomes long, the color photoconductor is driven for a long time, and as a result, the color photoconductor is driven. This will affect the life of the photosensitive member.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an image forming apparatus capable of reducing the consumption of a color photoconductor without reducing productivity in image formation in which color images and black and white images are mixed for each sheet. This is the main purpose.

  The image forming apparatus of the present invention is an image forming apparatus that forms an image by superimposing a single-color image formed for each color on a sheet conveyed one by one, and a photoconductor provided for each color A developing unit that develops the latent image formed on the surface of the photosensitive member with toner, an intermediate transfer member that contacts the photosensitive member and onto which the developed toner image is transferred, and the photosensitive member and the intermediate member. A contact / separation mechanism for bringing the transfer body into contact with or separated from the transfer body; and a determination unit that determines whether the image to be formed is a color image composed of a plurality of colors or a black single-color image; When it is determined that the image is a color image, the plurality of color photosensitive members are brought into contact with the intermediate transfer member, and image formation is performed in a first printing mode in which the plurality of color developing units operate. If it is determined that the image is a black monochrome image Is characterized by having a control means for controlling to perform image formation in the second print mode for stopping the operation of the color of the developing means other than black.

  According to the present invention, the print mode is switched according to the length of the interval between the preceding sheet and the succeeding sheet. Accordingly, it is possible to suppress a decrease in productivity when forming an image in which a color image and a black and white image are mixed for each sheet, and to reduce the consumption of the color photoconductor.

1 is a schematic longitudinal sectional view for explaining a configuration of an image forming apparatus according to a first embodiment. FIG. 3 is a block diagram for explaining a control system of the image forming apparatus. FIG. 3 is a schematic longitudinal sectional view illustrating an example of a configuration of a cartridge included in the image forming apparatus. FIG. 3 is a diagram for explaining a contact / separation mechanism included in the image forming apparatus. 6 is a timing chart for explaining the timing of stopping the rotation operation and voltage application of the developing roller. 6 is a timing chart for explaining the separation operation of the intermediate transfer belt, the rotation operation of the color photoconductor and the timing at which the voltage application is stopped. 4 is a timing chart for explaining the contact operation of the intermediate transfer belt and the timing for starting the operation of the color photoconductor. FIG. 3 is a schematic longitudinal sectional view illustrating an example of a configuration of a fixing device included in the image forming apparatus. The figure for demonstrating that the edge part of the fixing device shown in FIG. 8 may be overheated. The table | surface for demonstrating the sheet | seat space | interval calculated in order to improve the printing productivity for every sheet | seat classification. (A), (b) is a figure for demonstrating the sequence of the print job which an image forming apparatus performs. 6 is a flowchart illustrating an example of a processing procedure of image formation by the image forming apparatus. FIG. 13 is a diagram for explaining the operation of the image forming apparatus based on the processing procedure described in FIG. 12. 9 is a flowchart illustrating an example of a processing procedure of image formation by the image forming apparatus according to the second embodiment. FIG. 15 is a diagram for explaining the operation of the image forming apparatus based on the processing procedure described in FIG. 14.

  Hereinafter, an embodiment of an image forming apparatus capable of forming a full color image (yellow: Y, magenta: M, cyan: C, black: K) to which the present invention is applied will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a schematic longitudinal sectional view for explaining the configuration of the image forming apparatus according to the present embodiment. FIG. 2 is a block diagram for explaining a control system of the image forming apparatus shown in FIG. The main functional configuration of the image forming apparatus according to the present embodiment will be described with reference to FIGS.

An image forming apparatus 100 shown in FIG. 1 includes a cartridge 120 (ad) that forms an image corresponding to each color, a laser scanner 122 (ad), a primary transfer unit 123 (ad), and an intermediate transfer member (intermediate). A transfer belt 130 and a secondary transfer unit 140. The image forming apparatus 100 also includes a paper feed cassette 150 (220), a paper feed pickup roller 151, a paper feed pickup sensor 152, a transport roller 155, a pre-registration transport sensor 160, and a pre-registration transport roller 161. The image forming apparatus 100 also includes a paper transport sensor 171, a transport flapper 172, a transport flapper 190, a paper discharge tray 196 (200), a fixing device 201, and a transport roller 232. In the image forming apparatus 100, conveyance paths such as paper conveyance paths 180, 181, 230, and 231 are formed.
The cartridge 120a forms yellow (Y), 120b forms magenta (M), 120c forms cyan (C), and 120d forms black (K). Each cartridge is configured to be attachable and detachable by the user. In the following description, the configuration related to Y, M, and C printing may be referred to as color, and the configuration related to K printing may be referred to as black and white. As described above, the image forming apparatus 100 forms an image by superimposing a single color image formed for each color on a sheet conveyed one by one.

As shown in FIG. 2, the image forming apparatus 100 includes a contact / separation mechanism 40, a control unit 300, an I / O (input / output) unit 310, a sensor unit 311, a load unit 312, an image forming unit 320, and an instruction / display. Unit (hereinafter referred to as UI unit) and a functional unit including an external device I / F 340.
The control unit 300 includes a CPU (Central Processing Unit) 301, a ROM (Read Only Memory) 302, and a RAM (Random Access Memory) 303. Each functional unit of the image forming apparatus 100 is controlled mainly by the CPU 301 of the control unit 300 reading, for example, a control program stored in the ROM 302 into the RAM 303 and executing it.

Further, the control unit 300 starts a sheet feeding operation from a sheet feeding cassette 150 or the like (for example, a recording medium such as a sheet) when receiving an instruction to start a printing operation via the UI unit 330 or the like. Specifically, driving of a pre-fixing conveyance motor (not shown) that is a driving source of the paper feed pickup roller 151 is started. Then, the paper feed pickup roller 151 is rotated and the paper in the paper feed cassette 150 is fed and conveyed one by one. At this time, it is monitored whether or not the paper feeding operation has been normally performed via the paper feed pickup sensor 152.
On the other hand, the control unit 300 starts an image forming operation so that the sheet conveyed on the conveyance path arrives at the timing when the sheet reaches the secondary transfer unit 140.

The UI unit 330 functions as an operation unit that receives an operation performed by a user and presents various information to the user. For example, an instruction to start a printing operation can be transmitted from the PC (personal computer) to the control unit 300 via the external device I / F 340.
The load unit 312 is a motor for rotationally driving a conveyance roller and the like. The control unit 300 drives and controls the load unit 312 via the I / O unit 310 in accordance with the received operation start instruction.
The sensor unit 311 is a sensor provided on the transport path, and detects whether the transported paper has passed. The control unit 300 receives the detection result of the sensor unit 311 via the I / O unit 310.
The contact / separation mechanism 40 is a mechanism for bringing the intermediate transfer belt 130 into contact with or separating from the photoreceptors 124a, 124b, 124c. The primary transfer units 123a, 123b, and 123c are also configured to move in accordance with the contact / separation of the intermediate transfer belt 130. Details will be described later.

The image forming unit 320 controls image formation in the image forming apparatus 100 based on an instruction from the control unit 300. Specifically, application of high voltage to the cartridge 120 (a to d), the intermediate transfer belt 130, the primary transfer unit 123 (a to d), the secondary transfer unit 140, control of driving, and the laser scanner 122 (a to d). Control of d) lighting start or end thereof. The control unit 300 controls the operation of the contact / separation mechanism 40 of the primary transfer units 123a to 123c corresponding to the color cartridges 120 (a to c).
Next, an image forming operation in the image forming apparatus 100 will be described with reference to FIGS. 1 and 2. The image forming operation described below is an example, and the present invention is not limited to this configuration.

FIG. 3 is a schematic longitudinal sectional view showing an example of the configuration of the Y cartridge 120a which is a yellow cartridge. The M cartridge 120b, the C cartridge 120c, and the K cartridge 120d have the same configuration. The cartridge 120a will be taken up as a representative and the description will proceed.
The cartridge 120a includes a photoconductor 124a, a charging roller 32a, a developing device 33a having a developing roller 43a, and a cleaning blade 34a. The photoconductor 124a and the charging roller 32a are configured to be the same drive. The developing roller 43a is configured to be driven separately from the photosensitive member 124a, and can be configured to stop only the developing roller 43a independently regardless of the driving state of the photosensitive member 124a.

  After the surface of the photoconductor 124a is charged by the charging roller 32a, a latent image is formed on the photoconductor 124a by the laser emitted from the laser scanner 122a. The formed latent image is developed on the photosensitive member 124a through the developing roller 43a by toner held in the developing device 33a. Thereafter, the toner image developed on the photoreceptor 124 a is transferred to the intermediate transfer belt 130 by applying a primary transfer voltage at the primary transfer portions 123 a to 123 d. The toner image transferred to the intermediate transfer belt 130 reaches the secondary transfer unit 140 by the rotation of the intermediate transfer belt 130.

  The pre-registration conveyance sensor 160 detects the position of the sheet conveyed by the conveyance roller 155. In consideration of the timing at which the leading edge of the sheet reaches the pre-registration conveyance sensor 160, the sheet is transported so that the leading edge of the sheet and the leading edge of the toner image on the intermediate transfer belt 130 coincide with each other at the secondary transfer unit 140. Is called. For example, when the sheet arrives early with respect to the toner image, the sheet is stopped for a predetermined time by the pre-registration conveyance roller 161, and then the conveyance is started again. In this way, the toner image is transferred to the paper by applying the secondary transfer voltage to the paper and the toner image that have reached the secondary transfer unit 140.

The transferred paper is conveyed toward the fixing device 201. The fixing device 201 functions as a fixing unit that heats and fixes the toner image on the paper to the paper. The sheet on which the toner image has been heat-fixed is further conveyed toward the downstream side on the conveyance path.
When the leading edge of the paper reaches the paper transport sensor 171, the transport flapper 172 is driven in accordance with the contents instructed in advance via the UI unit 330, and the subsequent paper transport destination is designated. Specifically, for example, when double-sided printing is instructed, the sheet is conveyed toward the sheet conveyance path 230. Further, when single-sided printing is instructed, or when printing on the back side in double-sided printing, the paper is conveyed to the paper conveyance path 231.
Hereinafter, a case where a sheet is conveyed toward the sheet conveyance path 231 will be described in detail as an example.

The paper transported to the paper transport path 231 is transported further downstream on the transport path by the transport roller 232. Further, the conveyance flapper 190 is driven in accordance with the contents instructed in advance via the UI unit 330, and the subsequent sheet conveyance destination is designated. Specifically, when the paper discharge designation destination designated by the user is the paper discharge tray 200, the paper is transported toward the paper transport path 180. If the paper discharge designation destination is the paper discharge tray 196, the paper is transported toward the paper transport path 181. In this way, image formation is performed in accordance with an instruction from the user.
Next, control of contact / separation between the cartridges 120a to 120d and the intermediate transfer belt 130 will be described with reference to FIG.

FIG. 4 is a diagram for explaining the contact / separation mechanism 40 included in the image forming apparatus 100.
The intermediate transfer belt 130, the primary transfer units 123 (ad) and the photosensitive members 124 (ad) of the image forming apparatus 100 are arranged at positions as shown in FIG. As shown in FIG. 4, the intermediate transfer belt 130 is stretched between the regulating roller 58 and the driving roller 52, and the photoconductors 124 a to 124 d are arranged along a straight line portion indicated by a broken line in the drawing. . The regulating roller 90 is disposed at an intermediate point between the photoconductor 124c and the photoconductor 124d, and supports the inner surface of the intermediate transfer belt 130.
The regulation roller 58 is configured to be movable up and down. The regulating roller 58 is raised, and the intermediate transfer belt 130 is brought into contact with the color photoconductors 124a, 124b, and 124c.
Further, the regulating roller 58 is lowered to separate the intermediate transfer belt 130 from the photoconductors 124a, 124b, and 124c. Note that the control unit 300 controls the raising and lowering of the regulating roller 58 that constitutes the contact / separation mechanism 40.

When forming a color image composed of a plurality of colors, the control unit 300, as shown by broken lines in FIG. 4, has black, cyan, magenta, and yellow in a state where the intermediate transfer belt 130 is in contact with each of the photosensitive members 124a to 124d. Control is performed to form a toner image of each color.
On the other hand, when forming a black single color image, that is, a black and white image, as shown by the solid line in FIG. 4, the black by the photoconductor 124d with the intermediate transfer belt 130 separated from the photoconductors 124a to 124c of colors other than black. Control is performed so that only the toner image is formed.

  Next, the life (lifetime) of the cartridges 120a to 120d will be described. There are mainly two causes that affect the life of the cartridges 120a to 120d. One is a change in toner held in the developing devices 33a to 33d, and the other is “scraping” of the surfaces of the photoconductors 124a to 124d.

First, the toner change and the avoidance method will be described. As described above, the electrostatic latent image on the photosensitive member is developed on the photosensitive member 124 a via the developing roller 43 by the toner held in the developing device 33. The toner is agitated by the operation of the developing roller 43 and rubs against the toner and the agitating member. Further, since a high voltage is applied to the developing roller 43 itself, the external additive contained in the toner is peeled off for the charge control and the fluidity control in a state where the toner is not used for a long time. Or embedded. Such a phenomenon changes charging performance, fluidity, and the like. As a result, problems such as insufficient transfer of toner or excessive transfer during development occur.
Such a phenomenon can be avoided by stopping the rotation operation of the developing roller 43 and the voltage application. Hereinafter, these points will be described in detail with reference to FIG.

FIG. 5 is a timing chart for explaining the rotation operation of the developing roller 43 and the timing for stopping the voltage application. With reference to FIG. 5, the rotation operation of the developing roller 43 and the timing for stopping the voltage application will be described.
The controller 300 sequentially turns on the laser scanners 122 (a to d) and starts forming images corresponding to the respective colors (400a to 400d: ON). In this manner, toner images are formed on the photoreceptors 124a to 124d. When the next image is black and white and only the photosensitive member 124d is used, the rotation operation and voltage application of the color developing roller 43 (ac) are stopped (OFF) in the order of the developed colors. As described above, the black-and-white developing roller 43d is not stopped, but is made to correspond to the development performed after the laser scanner 122d is turned on (401) for forming the next black-and-white image. The rotation operation of the developing roller 43 (ac) and the voltage application stop operation are completed in about 300 [msec] from the stop start (402a to 402c). When the next image is a color image, the color developing rollers 43a to 43c are started up again. The restarting of the developing roller is completed in about 300 [msec] from the restarting start (403a to 403c) as in the case of the stop operation.

Next, “scraping” of the surfaces of the photoconductors 124a to 124d will be described. The service life of the photoconductors 124a to 124d itself is affected by the degree of surface displacement due to sliding with the cleaning blades 34a to 34d, the intermediate transfer belt 130, and the like. In particular, the influence is great when the surface of the photosensitive member 124 is rubbed against the intermediate transfer belt 130 in a state where no toner image is formed. Due to such a phenomenon, for example, toner may not adhere to the photoconductor 124, and color loss or fading may occur in printing.
For example, when a toner image is not formed on the color photoconductors 124a to 124c, the intermediate transfer belt 130 is separated from these, and the rotation operation and voltage application of the photoconductors 124a to 124c are stopped. Thereby, the service life of the color photoconductors 124a to 124c can be extended. Hereinafter, these points will be described in detail with reference to FIGS.

FIG. 6 is a timing chart for explaining the separation operation of the intermediate transfer belt 130, the rotation operation of the color photoconductors 124a to 124c, and the timing of stopping the voltage application.
As shown in FIG. 6, the control unit 300 sequentially turns on the laser scanners 122a to 122d to start forming images corresponding to the respective colors (405a to 405d). In this manner, toner images are formed on the photoreceptors 124a to 124d. When the next image is black and white and only the photoreceptor 124d is used, the rotation operation and voltage application of the color developing rollers 43a to 43c are stopped (406a to 406c) in the order of the developed colors. Further, the rotation operation and voltage application of the primary transfer units 123a to 123c, the photoconductors 124a to 124c, and the charging rollers 32a to 32c are also stopped.
Note that the developing roller 43d, the primary transfer unit 123d, the photosensitive member 124d, and the charging roller 32d of the cartridge 120d used for the black and white image are not stopped and are prepared for the development of the next black and white image.

The photoconductors 124a to 124c are controlled so that the rotation operation continues for about 2 [sec] after the primary transfer is completed (407a to 407c). This is to prevent the potential from remaining on the surface of the photosensitive member immediately when it is stopped and affecting the subsequent image formation. Therefore, the photosensitive members 124a to 124c are controlled to be discharged after being idled and stopped after the surface potential is removed. Then, after the photoreceptors 124a to 124c are sequentially stopped, the lowering of the regulating roller 58 is started (408). In this manner, the intermediate transfer belt 130 is separated from the photoconductors 124a to 124c. That is, the intermediate transfer belt 130 is separated from the cartridges 120a to 120c.
Note that it takes about 500 [msec] from the start of the separation operation to the completion of the separation. Accordingly, it takes about 2.5 [sec] to complete the separation operation after the primary transfer is completed. As shown in FIGS. 5 and 6, generally, the time required to stop the developing roller 43 (300 [msec]) is shorter than the time required to complete the separation operation (500 [msec]). .

FIG. 7 is a timing chart for explaining the contact operation of the intermediate transfer belt 130 and the timing for starting the operation of the color photoconductor.
As shown in FIG. 7, in the control unit 300, the black and white image laser scanner 122d draws a black and white image on the surface of the photosensitive member 124d, and the transfer from the photosensitive member 124d to the intermediate transfer belt 130 is completed (410). Then, for the next color image, an operation of bringing the primary transfer portions 123a to 123c and the intermediate transfer belt 130 into contact with the photosensitive members 124a to 124c is performed.

  The controller 300 starts (411) the restriction roller 58 ascending. In this way, the intermediate transfer belt 130 is brought into contact with the photoconductors 124a to 124c. Note that it takes about 500 [msec] from the start of the contact operation to the completion thereof. Upon completion of the contact operation (412), the controller 300 starts rotation driving and voltage application of the color image developing rollers 43 (ac) and the photoreceptors 124 (ac). At this time, an idling time of about 2 [sec] is required until the surface potential of the photoreceptor is stabilized.

  When the idling of the photoconductors 124a to 124c is completed and the surface potential of the photoconductor is stabilized, the controller 300 sequentially turns on the laser scanners 122a to 122d and starts forming images corresponding to the respective colors ( 413a-413d). In this manner, toner images are formed on the photoreceptors 124a to 124d. In addition, it takes about 2.5 [sec] time from the separated state to the contact state as in the case of the separating operation.

As described above, the time required for the stop operation of the developing roller 43 and the time required for the restart operation are 300 [msec], and the stop / restart is completed in about 600 [msec] in total. On the other hand, each of the contact operation and the separation operation takes a time of 2.5 [sec], and the state change of each of the contact state / separation state is completed in about 5 [sec].
Next, with reference to FIGS. 8 and 9, an excessive temperature rise at the end portion of the fixing device 201 and the influence of this on the productivity of image formation will be described.

FIG. 8 is a schematic longitudinal sectional view showing an example of the configuration of the fixing device 201 included in the image forming apparatus 100.
The fixing device 201 includes a fixing belt unit 202, a pressure roller 205, and temperature detection sensors 208 and 209. The fixing belt unit 202 includes a fixing belt 203, a fixing heater 204, and a heater holder 207.
The fixing heater 204 is formed, for example, by forming a resistance heating element on a ceramic substrate, and is fixed to the lower surface of the heater holder 207 along the length of the heater holder (perpendicular to the drawing). Note that a temperature detection sensor 208 is in contact with the fixing heater 204 so that the temperature of the fixing heater can be detected. Further, the control unit 300 controls the power supplied to the fixing heater 204 based on the detection result of the temperature detection sensor 208 so that the temperature of the fixing heater 204 becomes a desired temperature. The temperature detection sensor 209 is provided at an end portion in the longitudinal direction of the fixing belt unit 202 and detects an end portion temperature of the fixing belt unit 202.

  The fixing belt 203 has an elastic layer formed of a rubber layer having a high thermal conductivity on the surface thereof, and grease is applied to the inner surface side so as to ensure slidability with the heater holder 207. . The pressure roller 205 is disposed such that both ends of the core metal are rotatably supported between the side plates of the fixing device 201. The pressure roller 205 is driven to rotate at a predetermined peripheral speed in the counterclockwise direction indicated by an arrow by a drive mechanism (not shown).

  The fixing belt unit 202 is arranged in parallel with the pressure roller 205 with the side on which the fixing heater 204 is disposed contacting the pressure roller 205. As a result, a fixing nip portion 206 having a predetermined width is formed. The fixing nip portion 206 is configured so that, for example, both end portions of the heater holder 207 are biased toward the pressure roller 205 side, thereby generating a predetermined pressing force.

FIG. 9 is a diagram for explaining that the end of the fixing device 201 shown in FIG. 8 may be overheated. In FIG. 9, the fixing belt 203 and the fixing heater 204 are shown in a plan view, and further, the temperature change of the fixing belt 203 when paper is passed is shown.
First, the fixing output is turned on and the fixing device 201 is in a state of passing paper. The controller 300 controls the output so that the fixing heater 204 has a uniform heat distribution according to the maximum sheet passing width. For example, when the maximum sheet passing width is A4 size, the heat distribution is controlled so as to match the lateral width of 297 [mm]. In this case, for example, when a B5 size paper (width 257 [mm]) is passed through the fixing belt 203, an area where the paper passes (paper passing area) and an area where the paper does not pass (non-paper passing area). ), The heat distribution of the fixing belt 203 becomes non-uniform.
That is, the central portion 222 of the fixing belt 203 that is a sheet passing area is controlled so as to be optimal for the fixing temperature. However, at both end portions 221a and 221b, which are non-sheet passing regions, there is no heat absorption due to the sheet passing, resulting in overheating.

When an excessive temperature rise occurs in the fixing belt 203, there is a possibility that the fixing belt 203 is deteriorated and various devices provided adjacent to the fixing device 201 are deteriorated. Therefore, the temperature detection sensor 209 periodically detects the temperature of the end portion of the fixing belt 203 in the longitudinal direction. If it is determined from this detection result that an excessive temperature rise has occurred, control is performed so that the next sheet is not fed and the apparatus waits until the temperatures of the fixing belt 203 and the pressure roller 205 become uniform.
Note that the sheet interval time obtained by converting the distance from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet (hereinafter referred to as sheet interval) based on the conveyance speed generally exceeds 500 [msec]. There is nothing wrong. However, when an excessive temperature rise occurs, the feeding of subsequent sheets may be delayed by about 6 seconds at the maximum, and the sheet interval time becomes longer than usual.

FIG. 10 is a table for explaining sheet intervals calculated to increase printing productivity for each sheet type.
As shown in FIG. 10, the default sheet interval in the image forming apparatus 100 is set based on the sheet (paper) size and fixing performance for each type. The control unit 300 controls the sheet feeding and image formation timing (print timing) so as to satisfy this sheet interval. For example, for B5 size plain paper, the printing speed (productivity) is defined as 42 sheets / minute, and the sheet interval in this case is 1.4 seconds. However, when an excessive temperature rise occurs at the end of the fixing device 201, for example, the sheet interval increases to about 6 seconds, and the productivity decreases to 10 sheets / min. That is, when the sheet interval (predetermined interval) at the normal time when there is no temperature rise at the edge is set to 1.4 seconds, a sheet interval equal to or greater than the predetermined interval occurs when an excessive temperature increase occurs.

  FIG. 11 is a diagram for explaining a print job sequence executed by the image forming apparatus 100. FIG. 11A is an explanatory diagram of command exchange on the communication line between the image forming unit 320 or the external device I / F 340 and the control unit 300, and FIG. 11B shows information notified for each page. FIG. In FIG. 11A, the image data to be printed is received according to a predetermined procedure along a time series from the left to the right as viewed from the front of the figure.

  The image forming unit 320 or the external device I / F 340 (hereinafter referred to as an upper layer) first notifies the control unit 300 of a job start (570) before sending image data. When the control unit 300 receives the notification, it returns a response (571). Subsequently, the upper layer notifies the job start of the first page (572). Upon receiving the notification, the control unit 300 returns a response (573). The upper layer that has received the response sends the image data (574) to the control unit 300. The control unit 300 forms an image according to the image data. Further, when there is image data on the second page, the upper layer notifies the control unit 300 of the job start (575) on the second page. The control unit 300 that has received the notification returns a response (576). The upper layer that has received the response sends the image data (577) to the control unit 300. If there is no subsequent image data, the upper layer notifies the control unit 300 of the job end (578). The control unit 300 that has received the notification performs a termination process and then returns a response (579).

Here, the contents of the information 572 and 575 notified for each page are configured as shown in FIG. The information shown in FIG. 11B includes a command header 580 that indicates page information, a page ID 581 that is different for each page, and a paper feed unit ID 582 that indicates from which paper feed unit the paper is to be fed. The This information also includes a paper discharge ID 583 for specifying a paper discharge location, a paper type 584 for specifying a paper type such as thick paper and thin paper, and black and white indicating that the image data is a monochrome image or a color image. / Color 585 is included. Based on these pieces of information, the control unit 300 performs various settings such as parameters necessary for image formation.
Hereinafter, a processing procedure for suppressing the progress of the life of the color cartridge when printing mixed data in which the black and white image and the color image are switched for each sheet in the image forming apparatus 100 will be described.

FIG. 12 is a flowchart illustrating an example of an image forming process procedure performed by the image forming apparatus 100. 12 is mainly executed by the CPU 301 of the control unit 300. In the description, it is assumed that the following three modes are used as print modes when the image forming apparatus 100 according to the present embodiment forms an image.
The first printing mode is for color images, and is a mode in which all cartridges 120a to 120d operate.
The second printing mode is for black and white images, and the operation of the developing rollers 43a to 43c while the color photoconductors 124a to 124c are in contact with the intermediate transfer belt 130 while being operated (rotation driving and voltage application) ( In this mode, rotation driving and voltage application are stopped.
The third printing mode is for monochrome images, and is a mode in which the operations of the color photoconductors 124a to 124c are stopped and separated from the intermediate transfer belt 130, and the operations of the developing rollers 43a to 43c are stopped.

  The CPU 301 starts control from power activation and detects whether a job start is instructed (S501). When the CPU 301 detects a job start (S501: Yes), for example, it initializes a monochrome number counter (counting means for counting the number of times a black single color image is formed) stored in the RAM 303 (S502). The CPU 301 determines whether or not the voltage for the K cartridge 120d has been applied (S503). If not applied (S503: No), voltage application to the K cartridge 120d is started (S506).

  Next, the CPU 301 determines whether or not the image to be printed is a monochrome image according to the contents of the page data shown in FIG. 11B (S504). When it is determined that the image is a color image (S504: No), the CPU 301 determines whether or not the intermediate transfer belt 130 is in contact with the color cartridges 120a to 120c (S508). Note that the determination of whether they are in contact or separated is made based on the detection result of a position detection sensor (not shown) that detects the position of the regulating roller 58. In the following description, a state in which the intermediate transfer belt 130 is in contact with the cartridges 120a to 120c is referred to as a “contact state”, and a state in which the intermediate transfer belt 130 is separated is referred to as a “separation state”.

  When the CPU 301 determines that the contact state is not established (S508: No), the CPU 301 operates the restriction roller 58 so that the contact state is established. Further, rotation driving and voltage application of the color photoconductors 124a to 124c, the charging rollers 32a to 32c, and the developing rollers 43a to 43c are started (S509).

  If not (S508: Yes), that is, in the contact state, the CPU 301 determines whether or not the color developing rollers 43a to 43c are stopped (OFF state) (S524). If it has been stopped (S524: Yes), rotation driving and voltage application of the developing rollers 43a to 43c are started (S525). Note that the timings related to the start of each are as described in FIGS.

As shown in FIG. 10, the CPU 301 waits for the start of printing until the printing timing corresponding to the calculated sheet interval is reached in order to increase the printing productivity for each sheet (S505). Note that waiting for temperature equalization at the end of the fixing belt 203 described with reference to FIGS. 8 and 9 is a part of this control. The print timing is determined by detecting the elapse of the standby time using, for example, a timer (not shown) and adjusting the timing of starting the feeding of the next sheet.
In response to the print timing (S505: Yes), the CPU 301 sequentially turns on the laser scanners 122a to 122d to perform printing (S510). Thereafter, when the printing is completed, the CPU 301 determines whether the job is completed based on the sequence shown in FIG. 11 (S511). When it is determined that the job is finished (S511: No), the series of processing is finished. If not (S511: Yes), the next image data is received (S513). Thereafter, the CPU 301 determines whether or not the received next image is a black and white image (S514).

When the CPU 301 determines that the received next image is a color image (S514: No), the CPU 301 initializes the monochrome number counter on the RAM 303 (S518). Thereafter, the process returns to step S503. As described above, when the next image is a color image, the first print mode in which all the cartridges 120a to 120d operate is executed.
If not (S514: Yes), that is, if it is determined that the next image is a monochrome image, the CPU 301 determines whether or not the intermediate transfer belt 130 is in contact with the color cartridges 120a to 120c. It discriminate | determines (S515). If it is determined that the contact state is not established (S515: No), the process proceeds to step S518. If not (S515: Yes), that is, in the contact state, the CPU 301 compares the sheet interval time with the time required to bring the intermediate transfer belt 130 into the separated state (S516).
The sheet interval is calculated based on, for example, the sheet conveyance speed in the image forming apparatus 100, the size and type of the sheet, and the temperature rise of the fixing device. Further, for example, the ROM 302 stores information representing the time taken for the intermediate transfer belt 130 in contact to be in a separated state in advance.

  Here, the separation operation for changing from the contact state to the separation state and the contact operation for changing from the separation state to the contact state each require 2.5 seconds as a predetermined interval. Explained. That is, if the sheet interval time is 2.5 seconds or more, the intermediate transfer belt 130 can be separated from the color cartridges 120a to 120c until the succeeding sheet arrives. Even when the next image is a color image, the intermediate transfer belt 130 can be brought into contact with the color cartridges 120a to 120c until the subsequent sheet arrives.

Returning to the description of FIG. 12, when the CPU 301 determines that the sheet interval is longer than the separation time (a predetermined interval or more) (S516: Yes), the CPU 301 separates the intermediate transfer belt 130 from the color cartridges 120a to 120c (see FIG. 12). S517).
That is, the third printing mode is executed in which the rotation driving and voltage application of the color photoconductors 124a to 124c are stopped and separated from the intermediate transfer belt 130, and the rotation driving and voltage application of the developing rollers 43a to 43c are stopped. To do.

If not (S516: No), that is, if it is determined that the sheet interval is shorter than the separation time (less than the predetermined interval), the CPU 301 increments the monochrome sheet number counter (S519). In this case, the separation of the cartridges 120a to 120c is not completed until the subsequent sheet arrives. For this reason, the CPU 301 shifts to determination based on the monochrome number counter.
Thereafter, the CPU 301 determines whether or not the monochrome sheet number counter has exceeded a predetermined value (for example, two sheets) (S520). When it is determined that the predetermined value has been exceeded (S520: Yes), the CPU 301 determines that there is a high possibility that the monochrome image will continue to be printed in the future, and starts the separation operation of the color cartridges 120a to 120c (S517).
That is, the third printing mode is executed in which the rotation driving and voltage application of the color photoconductors 124a to 124c are stopped and separated from the intermediate transfer belt 130, and the rotation driving and voltage application of the developing rollers 43a to 43c are stopped. To do.

If not (S520: No), that is, if it is less than the predetermined value, the CPU 301 determines whether or not the color developing rollers 43a to 43c are operating (ON state) (S521). If it is determined that the operation has stopped (S521: No), the process returns to step S503.
Otherwise (S521: Yes), if the next is black-and-white image data, the operation of the color developing rollers 43a to 43c becomes unnecessary, so the operation of the color developing rollers 43a to 43c is unnecessary. Is stopped (S522).
That is, in the second printing mode, the color photoconductors 124a to 124c are rotated and applied with voltage, and the rotation of the developing rollers 43a to 43c and the application of voltage are stopped while maintaining the state in contact with the intermediate transfer belt 130. Execute.

  FIG. 13 is a diagram for explaining the operation of the image forming apparatus 100 based on the processing procedure described in FIG. FIG. 13 illustrates an example in which the image forming apparatus 100 executes a job in which color images and black and white images are mixed from the first sheet to the seventh sheet.

  As shown in FIG. 13, first, the first image is a color image. Therefore, printing is started with the intermediate transfer belt 130 in contact and the developing rollers 43a to 43c in operation. That is, the print mode is the first print mode. Next, the second image is a black and white image. Therefore, the CPU 301 stops (550) rotation driving and voltage application of the color developing rollers 43a to 43c. That is, the print mode is set to the second print mode.

  The third and fourth images and the black and white image continue, but at the time of the fourth image, the monochrome number counter becomes 3, which exceeds the predetermined value 2. Therefore, the CPU 301 starts separating the intermediate transfer belt 130 before starting the printing of the fourth sheet (551). That is, the print mode is set to the third print mode. When printing of the fourth monochrome image is completed, the next fifth image is a color image. Therefore, the CPU 301 returns the intermediate transfer belt 130 to the contact state, and starts rotation driving and voltage application of the color developing rollers 43a to 43c (552). That is, the print mode is set to the first print mode.

When the CPU 301 detects an excessive temperature rise in the fixing device 201 during printing of the fifth color image (555), the CPU 301 performs adjustment to widen the sheet interval in order to lower the fixing temperature. The sixth image after the fifth color image is a black and white image. When the CPU 301 determines that the cartridges 120a to 120c can be separated within the adjusted sheet interval time, the CPU 301 starts the separation of the intermediate transfer belt 130 (553). Further, the rotation driving and voltage application of the color developing rollers 43a to 43c are stopped (553). That is, the print mode is set to the third print mode.
Subsequently, after completing the printing of the sixth black and white image, the CPU 301 returns the intermediate transfer belt 130 to the contact state again in order to print the seventh color image, and the color developing rollers 43 a to 43. Rotation driving and voltage application are started (554). That is, the print mode is set to the first print mode.

As described above, the image forming apparatus 100 switches the print mode depending on whether the image to be printed is a color image or a monochrome image. Further, when printing a monochrome image, the print mode is further switched according to the length of the sheet interval (sheet interval time) of continuously fed sheets. Further, when an excessive temperature rise of the fixing device 201 is detected and the sheet interval is widened to lower the fixing temperature, it is determined whether or not the print mode can be switched within the sheet interval time in the widened sheet interval. Then, the printing mode corresponding to the determination result is executed.
Accordingly, it is possible to suppress a decrease in productivity when forming an image in which a color image and a black and white image are mixed for each sheet, and to reduce the consumption of the color photoconductor.
Further, even when printing a black and white image and switching the print mode within the sheet interval time, that is, when the color cartridge cannot be separated, by stopping the color developing roller, It is possible to reduce the consumption of the color photoconductor.

[Second Embodiment]
A description will be given of an image forming apparatus capable of performing control for suppressing the life progression of a color cartridge, which is different from the first embodiment, when printing mixed data in which a black and white image and a color image are switched for each sheet. Specifically, the image forming apparatus performs control to separate the intermediate transfer belt 130 from the color cartridges 120a to 120c without stopping the rotation driving and voltage application of the color developing rollers 43a to 43c.
In addition, the same thing as the functional structure already demonstrated in 1st Embodiment attaches | subjects the same code | symbol, and abbreviate | omits the description.

FIG. 14 is a flowchart illustrating an example of a processing procedure of image formation by the image forming apparatus according to the present embodiment. Note that the first printing mode already described in the first embodiment and the fourth printing mode described below are used as the printing modes performed by the image forming apparatus according to the present embodiment.
The fourth printing mode is for monochrome images, and is a mode in which the rotation driving and voltage application of the color photoconductors 124a to 124c are stopped and the intermediate transfer belt 130 is separated from the color photoconductors 124a to 124c. . Note that the fourth printing mode is a mode in which rotation driving and voltage application of the developing rollers 43a to 43c are not controlled.

The CPU 301 starts control from power activation and detects whether a job start is instructed (S601). When the CPU 301 detects a job start (S601: Yes), for example, the CPU 301 initializes a monochrome sheet number counter stored in the RAM 303 (S602).
The CPU 301 determines whether or not the voltage for the K cartridge 120d has been applied (S603). If not applied (S603: No), voltage application to the K cartridge 120d is started (S606).

  Next, the CPU 301 determines whether or not the image to be printed is a monochrome image according to the contents of the page data shown in FIG. 11B (S604). When it is determined that the image is a color image (S604: No), the CPU 301 determines whether or not the intermediate transfer belt 130 is in contact with the color cartridges 120a to 120c (S608). Note that the contact state or the separated state is determined based on a detection result of a sensor (not shown) that detects the position of the restriction roller 58.

  When the CPU 301 determines that the contact state is not established (S608: No), the CPU 301 operates the restriction roller 58 so that the contact state is established. Further, rotation driving and voltage application of the color photoconductors 124a to 124c, the charging rollers 32a to 32c, and the developing rollers 43a to 43c are started (S609). Thereafter, the process proceeds to step S605.

As shown in FIG. 10, the CPU 301 waits for the start of printing until the printing timing corresponding to the calculated sheet interval is reached in order to increase the printing productivity for each sheet (S605). Note that waiting for temperature equalization at the end of the fixing belt 203 described with reference to FIGS. 8 and 9 is a part of this control. Further, the printing timing is detected by using a timer (not shown), for example, to detect the elapse of the waiting time, and the timing for starting the feeding of the next sheet is adjusted.
When the print timing is reached (S605: Yes), the CPU 301 sequentially turns on the laser scanners 122a to 122d to perform printing (S610). After that, when the printing is completed, the CPU 301 determines whether or not the job is completed based on the sequence shown in FIG. 11 (S611). When it is determined that the job is finished (S611: No), a series of processing is finished. If not (S611: Yes), the next image data is received (S613). Thereafter, the CPU 301 determines whether or not the received next image is a black and white image (S614).

When the CPU 301 determines that the received image is a color image (S614: No), the CPU 301 initializes a monochrome number counter on the RAM 303 (S618). Thereafter, the process returns to step S603. As described above, when the next image is a color image, the first print mode in which all the cartridges 120a to 120d operate is executed.
If not (S614: Yes), that is, if it is determined that the next image is a black and white image, the CPU 301 determines whether or not the intermediate transfer belt 130 is in contact with the color cartridges 120a to 120c. A determination is made (S615). If it is determined that the contact state is not established (S615: No), the process proceeds to step S618. If not (S615: Yes), that is, if it is determined that the sheet is in the contact state, the CPU 301 compares the sheet interval time with the time required to place the intermediate transfer belt 130 in the separated state (S616). ).

  When the CPU 301 determines that the sheet interval time is longer than the separation time (S616: Yes), the CPU 301 separates the intermediate transfer belt 130 from the color cartridges 120a to 120c (S617). That is, the fourth printing mode in which the rotational driving and voltage application of the color photoconductors 124a to 124c are stopped and the intermediate transfer belt 130 is separated is executed.

If not (S616: No), that is, if it is determined that the sheet interval time is shorter than the time required for separation, the CPU 301 increments the monochrome sheet number counter (S619).
Thereafter, the CPU 301 determines whether or not the monochrome sheet number counter has exceeded a predetermined value (for example, 2 sheets) (S620). If it is determined that the predetermined value has been exceeded (S620: Yes), the CPU 301 determines that there is a high possibility that printing of monochrome images will continue in the future, and starts the separation operation of the color cartridges 120a to 120c (S617). A fourth printing mode is executed in which the rotation driving and voltage application of the color photoconductors 124a to 124c are stopped and the intermediate transfer belt 130 is separated. Otherwise (S620: No), the process returns to step S603.

  FIG. 15 is a diagram for explaining the operation of the image forming apparatus based on the processing procedure described in FIG. FIG. 15 illustrates an example in which the image forming apparatus according to the present embodiment executes a job in which color images and black and white images are mixed from the first to seventh sheets.

  As shown in FIG. 15, first, the first image is color. Therefore, printing is started with the color cartridges 120a to 120c being in contact and the developing rollers 43a to 43c being in operation. That is, the print mode is the first print mode. Next, the second image is black and white. However, the continuous number of black and white images does not exceed a predetermined value (for example, two). Therefore, the CPU 301 does not execute the separation operation of the color cartridges 120a to 120c at this timing.

  The third and fourth images and the black and white image continue, but at the time of the fourth image, the monochrome number counter becomes 3, which exceeds the predetermined value 2. Therefore, the CPU 301 starts the separation of the intermediate transfer belt 130 before starting the printing of the fourth sheet (651). That is, the print mode is set to the fourth print mode. When printing of the fourth monochrome image is completed, the next fifth image is a color image. Therefore, the CPU 301 returns the intermediate transfer belt 130 to the contact state, and starts rotation driving and voltage application of the color developing rollers 43a to 43c (652). That is, the print mode is set to the first print mode.

When the CPU 301 detects an excessive temperature rise in the fixing device 201 during printing of the fifth color image (655), the CPU 301 widens the sheet interval in order to lower the fixing temperature. The sixth image after the fifth color image is a black and white image. When the CPU 301 determines that the intermediate transfer belt 130 can be separated within the sheet interval time, the CPU 301 starts the separation of the intermediate transfer belt 130 (653). That is, the print mode is set to the fourth print mode.
Subsequently, after completing the printing of the sixth monochrome image, the CPU 301 returns the intermediate transfer belt 130 to the contact state and rotates the color developing rollers 43a to 43c in order to print the seventh color image. Driving and voltage application are started (654). That is, the print mode is set to the first print mode.

As described above, in the image forming apparatus according to the present embodiment, the contact and separation between the color cartridges 120a to 120c and the intermediate transfer belt 130 are controlled without stopping the operation of the color developing rollers 43a to 43c. can do.
As a result, while reducing the number of objects to be controlled in the apparatus, it is possible to suppress a decrease in productivity when forming an image in which a color image and a black and white image are mixed for each sheet, and to reduce the consumption of a color photoconductor. be able to.

  The embodiment described above is for explaining the present invention more specifically, and the scope of the present invention is not limited to these examples. For example, in the above-described embodiments, the configuration in which the intermediate transfer belt 130 is moved and separated from the color cartridges 120a to 120c has been described. However, the color transfer cartridges 120a to 120c are moved and moved to the intermediate transfer belt 130. It may be configured to be separated from.

  32 (ad) ... charging roller, 33 (ad) ... developing device (developing means), 34 (ad) ... cleaning blade, 40 ... contact / separation mechanism, 43 (Ad) Development roller 52 ... Driving roller 58, 90 ... Restriction roller (contact / separation means) 120 (ad) ... Cartridge 122 (ad) ... Laser scanner, 123 (ad) ... Primary transfer portion, 124 (ad) ... Photoconductor, 130 ... Intermediate transfer belt, 140 ... Secondary transfer portion, 150 ( 220) ... feed cassette, 151 ... feed pickup roller, 152 ... feed pickup sensor, 155 ... conveying roller, 160 ... pre-registration conveyance sensor, 161 ... pre-registration conveyance Roller, 171... Paper transport sensor, 172. , 190... Paper transport flapper, 196 (200)... Paper discharge tray, 201... Fixing device, 232... Transport roller, 180, 181, 230, 231. 300: Control unit (control means), 320: Image forming unit.

Claims (7)

An image forming apparatus for forming an image by superimposing a single color image formed for each color on a sheet conveyed one by one,
A photoreceptor arranged for each color;
Developing means for developing the latent image formed on the surface of the photoreceptor with toner;
An intermediate transfer member to which the developed toner image is transferred in contact with the photosensitive member;
A contact / separation mechanism for bringing the photoconductor and the intermediate transfer body into contact with or separated from each other;
A discriminating means for discriminating whether the image to be formed is a color image composed of a plurality of colors or a black monochromatic image;
When it is determined that the image is a color image, the plurality of color photosensitive members are brought into contact with the intermediate transfer member, and image formation is performed in a first printing mode in which the plurality of color developing units operate. Control means for controlling to perform image formation in a second printing mode for stopping the operation of the developing means for a color other than black when it is determined that the image is a single black color image. Characterized by the
Image forming apparatus. The control means is such that the image formed on the succeeding sheet is the black monochrome image, and the sheet interval between the sheet conveyed in advance and the sheet conveyed subsequently is less than a predetermined interval. In some cases, control is performed so that image formation is performed in the second printing mode. When the sheet interval is equal to or greater than a predetermined interval, the photoconductors of colors other than black are removed from the intermediate transfer member. Control is performed so as to form an image in a third printing mode in which the operation of the developing unit other than the black color is stopped and the operation of the developing unit is stopped.
The image forming apparatus according to claim 1. And further has a counting means for counting the number of times that a black monochrome image is continuously formed,
When the image formed on the subsequent sheet is the black monochrome image and the number of times counted by the counting unit is less than a predetermined value, the control unit performs the image in the second printing mode. Control to perform the formation, and if the predetermined value is exceeded, control to perform the image formation in the third print mode,
The image forming apparatus according to claim 2. The control means performs the operation of the developing means when the image formed on the succeeding sheet is the black monochrome image and the number counted by the counting means exceeds the predetermined value. The image forming device is controlled to perform image formation in a fourth printing mode in which the photoconductors of colors other than black are separated from the intermediate transfer member while maintaining
The image forming apparatus according to claim 3. Temperature detecting means for detecting an excessive temperature rise in a fixing unit for fixing the toner image transferred to the sheet;
And an adjustment unit that adjusts the sheet interval by delaying the start of feeding of the next sheet when the excessive temperature rise is detected compared to when the excessive temperature rise is not detected. And
The image forming apparatus according to claim 2, 3 or 4. When the image formed on the succeeding sheet is the black monochrome image and the sheet interval after adjustment by the adjustment unit is equal to or greater than a predetermined interval, the control unit performs the third printing mode. Control to perform image formation with
The image forming apparatus according to claim 5. The control unit performs control so that an operation of separating the photosensitive member of the color other than black from the intermediate transfer member is started after the operation of the developing unit of all colors other than black is stopped. Features
The image forming apparatus according to claim 1.