JP2023097764A - Image forming apparatus - Google Patents

Abstract

To prevent occurrence of an image defect associated with deterioration of toner, and prevent a delay in first printout time.SOLUTION: An image forming apparatus comprises: a plurality of process cartridges 9 that each has a photoconductor drum 1 and a developing roller 4 developing an electrostatic latent image on the photoconductor drum 1 by using toner; and an engine control unit 402 that controls contact and separation state of the photoconductor drum 1 and the developing roller 4 in each process cartridge 9. When the process cartridge 9 in which the color of toner counted by a toner deterioration degree calculation unit 411 is other than black is used for a duration of time less than a threshold, the engine control unit 402 performs image formation using the process cartridge 9 with toner in black color at first timing, and when the process cartridge is used for a duration of time equal to or more than the threshold, performs image formation using the process cartridge 9 with toner in black color at timing later than the first timing, the timing after the developing roller 4 in the process cartridge 9 with toner in the color other than black is separated from the photoconductor drum 1 and after the lapse of a predetermined passage time.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image forming apparatus using an electrophotographic process.

2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic process includes a process cartridge (also called a cartridge) in which a photosensitive drum and process means such as charging means, developing means, and cleaning means acting on the photosensitive drum are integrated. there is Then, process cartridges with toner colors of yellow (Y), magenta (M), cyan (C), and black (K) are arranged from the upstream in the movement direction of the intermediate transfer belt, and toner images are sequentially transferred onto the intermediate transfer belt. There is a color image forming apparatus that employs an in-line system. As a developing method for a process cartridge used in an in-line color image forming apparatus, a contact developing method is generally widely used in which development is performed while a developing roller is in contact with a photosensitive drum. .

For example, Japanese Patent Application Laid-Open No. 2002-100000 discloses a configuration in which a mechanism is provided that acts on a process cartridge to separate a photosensitive drum and a developing roller when image formation is not performed in a contact development type image forming apparatus. . In the development contact/separation mechanism disclosed in Patent Document 1, the contact/separation state between the developing roller and the photosensitive drum has the following three states. The three states are a full-color contact state in which the developing rollers of all color cartridges contact the photosensitive drum, a monochrome contact state in which only the developing rollers of the black cartridge contact the photosensitive drum, and a monochrome contact state in which the developing rollers of all the cartridges contact the photosensitive drum. This is the fully separated state in which the photosensitive drum is separated.

In the in-line color image forming apparatus described above, when forming a full-color image, image formation is started after the contact state between the developing roller of each color cartridge and the photosensitive drum is changed to the full-color contact state. On the other hand, when forming a monochrome image, image formation may be started after the contact state between the developing roller of each color cartridge and the photosensitive drum is changed to the monochrome contact state.

In the above-described in-line image forming apparatus, an image is sequentially formed from a station (here, a station using yellow toner) located upstream on the intermediate transfer belt based on a /TOP signal, which is a vertical synchronizing signal. formation takes place. For example, Japanese Patent Application Laid-Open No. 2002-200003 discloses a technique that enables selection of the first station to start image formation based on the /TOP signal in order to shorten the first printout time. In the conventional method, during monochrome printing, a /TOP signal for sending image data with a yellow toner color is used to output image data with toner colors of yellow, magenta, cyan, and black in this order. On the other hand, in Japanese Patent Application Laid-Open No. 2002-200013, when performing monochrome printing, an independently generated /TOP signal is used to output image data in which the toner color is black, and image formation is started from a station in which the toner color is black. Therefore, the method of Japanese Patent Laid-Open No. 2002-200020 can shorten the time from outputting image data with yellow toner to outputting image data with black toner, compared with the conventional method. Outtime is shortened. In the following description, the mode in which the image forming timing of the station whose toner color is yellow is determined based on the /TOP signal is referred to as the YTOP mode. On the other hand, a mode in which the /TOP signal is used as a reference to determine the image forming timing of a station whose toner color is black is called a KTOP mode.

When image formation is performed in the KTOP mode, if the /TOP signal is output after the transition to the full-color contact state is completed and image formation is started, an image defect may occur. That is, a plurality of stations with different toner colors are arranged upstream in the moving direction of the intermediate transfer belt from the station with black toner. In these stations, the contact streaks that occur when the developing roller and the photosensitive drum come into contact with each other and the separation streaks that occur when they separate are transferred to the image area on the intermediate transfer belt where the monochrome image is transferred. This may result in image defects. For example, in Patent Document 3, the above-described in-line color image forming apparatus has the image forming timing of the station of the reference color that forms the image first, so that the developing rollers of the stations other than the reference color contact and separate from the photosensitive drum. Decisions are made based on behavior. As a result, the color image forming apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2002-200010 can prevent image defects due to contact/separation operations between the developing roller and the photosensitive drum, and can provide normal printing operations.

JP 2007-213024 A JP-A-2001-121749 JP 2016-161715 A

In general, when the cartridge is used for a long period of time, toner deterioration progresses, and the amount of toner that does not have a predetermined amount of charge increases. Therefore, the above-described contact streaks and separation streaks, which do not occur at the beginning of use of the cartridge, may occur as the cartridge is used for a longer period of time. Applying the control disclosed in Japanese Patent Laid-Open No. 2002-200334 to a cartridge that has been used for a long time can prevent the occurrence of image defects due to the contact/separation operation between the developing roller and the photosensitive drum. However, if the control disclosed in Japanese Patent Application Laid-Open No. 2002-300034 is applied to a cartridge with a short usage period, the problem arises that the first printout time is delayed.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent the occurrence of image defects due to deterioration of toner and to prevent the delay of the first printout time.

In order to solve the above problems, the present invention has the following configuration.

(1) a plurality of image forming units each having a photoreceptor and developing means for developing an electrostatic latent image formed on the photoreceptor using toner as a toner image; an exposure unit that exposes a body to form the electrostatic latent image; an intermediate transfer member to which the toner images on the photoconductors of the plurality of image forming units are transferred; and the photoconductors of the plurality of image forming units. and control means for controlling whether the developing means is placed in a contact state in which the photoreceptor and the developing means are in contact or in a separated state in which the developing means is separated from the photoreceptor; counting means for counting the period of use of each of the image forming units, the plurality of image forming units having a first image forming unit and a second image forming unit; The photosensitive member of the forming section contacts the intermediate transfer member at a first contact position, and the control means controls the developing means of the first image forming section and the second image forming section and the After the photoreceptor is set in the contact state, the first image forming unit performs a first monochrome image formation on the intermediate transfer member at a first timing, and a first monochrome image formation at a first timing. a second monochrome image formation that is executed at a later timing than the second monochrome image formation, and the second monochrome image formation is performed when the developing means is separated from the photoreceptor of the second image forming unit. When toner adheres to the photoreceptor when the developing means of the second image forming unit separates from the photoreceptor, the toner passes through the first contact position. is the passage time, the second monochromatic image formation is performed after the passage time has elapsed after the developing means of the second image forming unit is separated from the photoreceptor, The control means performs the second monochrome image formation when the value related to the usage period of the second image forming section counted by the counting means is equal to or greater than a predetermined threshold value, and the value is equal to or exceeds the predetermined value. An image forming apparatus, wherein the first monochrome image formation is performed when the threshold value is not exceeded.

According to the present invention, it is possible to prevent the occurrence of image defects due to deterioration of toner and prevent the delay of the first printout time.

FIG. 2 is a sectional view showing the configuration of the image forming apparatus of Examples 1 and 2; A diagram for explaining the development contact/separation state in Examples 1 and 2. FIG. 2 is a block diagram showing the system configuration of the image forming apparatus according to the first embodiment; Timing Chart of Image Formation Control of Embodiment 1 A diagram for explaining the development contact/separation state of the first embodiment. Timing Chart of Image Formation Control of Embodiment 1 4 is a flow chart showing image formation control of the first embodiment; Schematic diagram showing the configuration of the optical sensor of Example 2 FIG. 11 is a block diagram showing the system configuration of the image forming apparatus according to the second embodiment; Timing chart of image formation control of the second embodiment Flowchart showing toner detection control of the second embodiment 5 is a flow chart showing image formation control of the second embodiment;

BEST MODE FOR CARRYING OUT THE INVENTION Below, embodiments of the present invention will be described in detail with reference to the drawings.

[Configuration of Image Forming Apparatus]
FIG. 1 is a schematic cross-sectional view showing the configuration of a color laser printer (hereinafter also simply referred to as an image forming apparatus), which is an example of an image forming apparatus. In FIG. 1, the stations, which are image forming units, are arranged in the order of the first station, the second station, the third station, and the fourth station from the left side of the drawing. The first station is a yellow (Y) toner image forming station (also referred to as a yellow station or Y station). The second station is a magenta (M) color toner image forming station (also referred to as a magenta station or M station). The third station is a station for forming a cyan (C) toner image (also referred to as a cyan station or C station). The fourth station is a station for forming a black (K) toner image (also referred to as a black station or K station). As shown in FIG. 1, each station has the same configuration. The subscripts a, b, c, and d attached to the end of the reference numerals indicating the members of each station indicate the members of the first station, second station, third station, and fourth station, respectively. In the following description, reference numeral suffixes are omitted unless they refer to specific station components.

(Image forming section)
In each station, a photosensitive drum 1, which is a photosensitive member, is constructed by applying an organic photoconductor layer (OPC) to the outer peripheral surface of an aluminum cylinder. That is, the photosensitive drum 1 is formed by laminating a plurality of layers of functional organic materials, such as a carrier generation layer that generates charges by exposure to light and a charge transport layer that transports the generated charges, on a metal cylinder. The outer layer has low electrical conductivity and is generally insulating. The photosensitive drum 1 is rotatably supported by flanges at both ends thereof, and is driven by a drive motor (not shown) to rotate in the arrow direction (counterclockwise direction) in FIG.

The charging roller 2 , which is charging means, is a conductive roller that is in contact with the photosensitive drum 1 and is rotated by the photosensitive drum 1 . Charge the surface to a uniform potential. A DC voltage or a charging voltage obtained by superimposing an AC voltage is applied to the charging roller 2 from a charging voltage power supply 20 , and a small air gap upstream and downstream from the contact nip portion between the charging roller 2 and the surface of the photosensitive drum 1 is applied. The photosensitive drum 1 is charged by the discharge.

The cleaning unit 3 cleans the toner remaining on the photosensitive drum 1 (on the image bearing member) without being transferred onto the intermediate transfer belt 80 which will be described later. A developing unit 8 as developing means has a developing roller 4 in contact with the photosensitive drum 1 , a non-magnetic one-component developer 5 , and a developer coating blade 7 . The developing roller 4 is applied with a developing voltage from a developing voltage power supply 21, and adheres a developing material (toner) 5 to an electrostatic latent image formed on a photosensitive drum 1, which will be described later, to form a toner image. . A process cartridge (also referred to as a cartridge) 9 constituting each station includes a developing unit 8 as developing means having the above-described photosensitive drum 1, charging roller 2, cleaning unit 3, developing roller 4, and the like. The process cartridge 9 is detachably attached to the main body of the image forming apparatus.

An exposure section 11, which is exposure means, is provided corresponding to each station and is composed of a scanner unit or an LED array for scanning the photosensitive drum 1 with a laser beam. An electrostatic latent image is formed on the surface of the photosensitive drum 1 by irradiating the surface of the photosensitive drum 1 with the laser beam 12 emitted according to the image signal.

The intermediate transfer belt 80, which is an intermediate transfer member, is supported by three rollers, ie, a secondary transfer facing roller 86, a driving roller 14, and a tension roller 15, which are stretching members, so that an appropriate tension is maintained. ing. By driving the drive roller 14, the intermediate transfer belt 80 moves in the arrow direction (clockwise direction) in the drawing with respect to the photosensitive drum 1 of each station.

Inside the intermediate transfer belt 80 , a primary transfer roller 81 is provided so as to face the photosensitive drum 1 of each station and contact the intermediate transfer belt 80 . Each primary transfer roller 81 is connected to a primary transfer voltage power source 84 . When a transfer voltage is applied from the primary transfer voltage power supply 84 to the primary transfer roller 81 , a negative polarity voltage is applied to the intermediate transfer belt 80 (intermediate transfer body) in contact with the photosensitive drum 1 (on the photosensitive drum). The toner images are sequentially superimposed and transferred to form a multicolor image. The multicolor image formed on the intermediate transfer belt 80 is conveyed to a contact portion between the intermediate transfer belt 80 and a secondary transfer roller 82 which is a secondary transfer portion.

A neutralization member 23 is arranged downstream of the primary transfer roller 81 of each station in the rotation direction of the intermediate transfer belt 80 . Further, the drive roller 14, the tension roller 15, the neutralizing member 23, and the secondary transfer facing roller 86 are electrically grounded.

(Feeding section)
When the sheet P is fed from the main body cassette 16 , the main body cassette bottom plate 29 is raised by driving the cassette pickup roller 17 with a stepping motor (hereinafter referred to as a feeding motor), which is not shown, so that the sheet P is placed in the main body cassette 16 . The placed sheet P is pushed up. Among the pushed-up sheets P, the uppermost sheet P comes into contact with the cassette pickup roller 17, and the sheets P are separated and fed one by one by the rotation of the cassette pickup roller 17, and conveyed to the registration rollers 18. be. When the registration sensor 35, which is a paper sensor for detecting the sheet P, detects the leading edge of the conveyed sheet P in the conveying direction, it stops the driving of the feeding motor and stops the conveying of the sheet P temporarily.

(Sheet transport details)
The temporarily stopped sheet P is conveyed to the secondary transfer portion by the registration rollers 18 at the timing described below. That is, the registration rollers 18 move the leading edge of the multi-color image on the intermediate transfer belt 80 and the leading edge of the sheet P to the secondary transfer portion based on the timing at which the registration sensor 35 detects that the leading edge of the sheet P has arrived. The sheet P is conveyed so as to pass at the same timing. In addition, the engine control unit 402 (see FIG. 3) determines based on the elapsed time from the timing at which the sheet P is re-fed by the registration rollers 18 to the timing at which the registration sensor 35 detects the trailing edge of the sheet in the conveying direction. , the paper size of the sheet P is determined.

(Secondary transfer part)
The secondary transfer portion is a nip portion formed by contact between the secondary transfer roller 82 and the intermediate transfer belt 80 . The secondary transfer roller 82 is connected to a secondary transfer voltage power source 85 , and when the sheet P passes through the secondary transfer portion, a transfer voltage is applied to the secondary transfer roller 82 , so that the intermediate transfer belt 80 The upper multicolor image is transferred to the sheet P.

(fixing part)
The fixing unit 19 is a device that applies heat and pressure to the toner image, which is a multicolor image transferred onto the sheet P, to fix the toner image on the sheet P. and rollers (not shown). The elastic pressure roller sandwiches the fixing belt, and forms a fixing nip portion having a predetermined width with a belt guide member (not shown) and a predetermined pressure contact force.

With the fixing nip portion adjusted to a predetermined temperature, the sheet P onto which the unfixed toner image has been transferred from the secondary transfer portion is placed between the fixing belt and the elastic pressure roller in the fixing nip portion. A surface is introduced opposite the fuser belt surface. At the fixing nip portion, the image surface of the sheet P is in close contact with the outer surface of the fixing belt, and the sheet P is nipped and conveyed through the fixing nip portion together with the fixing belt. The unfixed toner image is heated by the fixing belt and fixed onto the sheet P while the sheet P is nipped and conveyed in the fixing nip portion together with the fixing belt. Then, the sheet P on which the toner image is fixed is discharged outside the image forming apparatus and stacked on the discharge tray 36 . Note that the optical sensor 40 will be described later.

[Contact and Separation Operation Between Developing Roller and Photosensitive Drum]
FIG. 2 is a diagram for explaining the contact/separation state between the photosensitive drum 1 and the developing roller 4 of each process cartridge 9 of this embodiment. In the drawing, Y, M, C, and K in parentheses at the end of the reference numerals of the process cartridges 9a, 9b, 9c, and 9d indicate yellow and magenta toner colors in the process cartridges 9a, 9b, 9c, and 9d, respectively. , cyan, and black.

First, the contact/separation between the photosensitive drum 1 and the developing roller 4 will be described with reference to the sectional view of the process cartridge 9a shown on the left side of FIG. 2(a). The driving force of a motor (not shown) rotates the photosensitive drum 1 in the direction of the arrow (counterclockwise direction) and the developing roller 4 in the direction of the arrow (clockwise) at a predetermined speed. The developing unit 8 is urged by a pressure spring 100 which is an elastic member, and the developing roller 4 is brought into contact with the photosensitive drum 1 with the rotation center of the photosensitive drum 1 as the rotation axis. A bearing member 101 is arranged at the end of the developing unit 8 in the axial direction (longitudinal direction) of the developing roller 4 . is separated. Note that the process cartridge (cartridge) is hereinafter also referred to as a station.

The image forming apparatus has a switching device for switching the contact state between the developing roller 4 and the photosensitive drum 1 . The contact state between the developing roller 4 of the process cartridge 9 and the photosensitive drum 1 is switched between the contact state where the developing roller 4 and the photosensitive drum 1 are in contact with each other and the separated state where the developing roller 4 is separated from the photosensitive drum 1 by the switching device. can be switched. In this embodiment, the contact state between the developing roller 4 and the photosensitive drum 1 can be changed to a fully separated state, a full-color contact state, a monochrome contact state, and a fully separated state, depending on the configuration of a mechanical mechanism such as a cam (not shown) and each actuator. It is a configuration of all state transition type that sequentially switches to .

FIG. 2(a) is a diagram showing the fully separated state. When image formation is not performed, force is applied to the bearing member 101 of each color station by a cam (not shown) or the like so that the photosensitive drum 1 and developing roller 4 of each color are completely separated.

FIG. 2(b) is a diagram showing a full-color contact state. By releasing the force applied to the bearing member 101 of each color station from the completely separated state of FIG. Become. Switching the state from FIG. 2(a) to FIG. 2(b) is a switching operation corresponding to a transition from the fully separated state to the full color contact state.

FIG. 2(c) is a diagram showing a monochrome contact state. From the full-color contact state shown in FIG. 2B, force is applied to the bearing members 101 of the yellow (Y), magenta (M), and cyan (C) stations by a cam (not shown) or the like. As a result, the photosensitive drums 1 and the developing rollers 4 of the yellow (Y), magenta (M), and cyan (C) stations are separated from each other to enter a monochromatic contact state. Switching the state from FIG. 2B to FIG. 2C is a switching operation corresponding to transition from the full-color contact state to the monochrome contact state. Also, the switching from the state of FIG. 2C to the state of FIG. In this manner, by successively transitioning the states of FIGS. 2A to 2C, the contact/separation switching operation of all state transition type is performed.

[Separation streak]
When the developing roller 4 is separated from the photosensitive drum 1, the toner may adhere to the surface of the photosensitive drum 1 in streaks. Adhesion of toner caused by the separation of the developing roller 4 from the photosensitive drum 1 is called a separation streak. Some separation streaks tend to occur when the toner in the process cartridge 9 deteriorates. As the process cartridge 9 is used, the toner gradually deteriorates. Therefore, separation streaks do not occur when the process cartridge 9 is used for a short period of time, but may occur when the process cartridge 9 is used for a predetermined period of time.

[System Configuration of Image Forming Apparatus]
FIG. 3 is a functional block diagram for explaining the system configuration of the image forming apparatus. The controller section 401 is capable of mutual communication with the host computer 400 and the engine control section 402 . The controller unit 401 receives image information and a print command from the host computer 400, analyzes the received image information, and converts it into bit data as image data. Then, the controller unit 401 transmits the following commands and signals to the CPU 404 and the image processing GA 405 for each sheet P via the video interface unit 403 . That is, it transmits a print color mode designation command, a /TOP signal reference color designation command, a print reservation command, a print start command (also referred to as a print start command), and a video signal. More specifically, when controller unit 401 receives a print command from host computer 400 , controller unit 401 transmits a print color mode designation command, a /TOP signal reference color designation command, and a print reservation command to CPU 404 . Then, a print start command (print start command) is transmitted to the CPU 404 at the timing when the engine control unit 402 prepares for the image forming apparatus to become ready for printing.

The CPU 404 performs preparatory operations for executing printing according to the contents of the print color mode designation command, the /TOP signal reference color designation command, and the print reservation command from the controller unit 401 . Then, it waits for a print start command from the controller unit 401 to be transmitted. Upon receiving the print start command, the CPU 404 instructs each control unit (the image control unit 406, the fixing control unit 407, and the paper transport unit 408) to start the printing operation.

Upon receiving the print operation start instruction, the image control unit 406 determines the color mode from the content of the print color mode designation command received from the controller unit 401 as a preparatory operation. The image control unit 406 instructs a developing contact control unit (switching control unit) 409 for controlling the switching device to change the contact state between the developing roller 4 and the photosensitive drum 1 of each color station according to the designated color mode. Instruct to switch. Hereinafter, the contact state between the developing roller 4 and the photosensitive drum 1 is also referred to as a developing contact state.

A toner deterioration degree calculation unit 411, which is a calculation means (calculation unit), counts the rotational distance of the developing roller 4 of each station (process cartridge) in order to calculate the degree of toner deterioration according to the period of use of the process cartridge 9. do. In order to calculate the period of use of the process cartridges 9a to 9d, the toner deterioration degree calculator 411 counts the values of the rotation distances of the developing rollers 4a to 4d as the values of the period of use of the process cartridges 9a to 9d. The toner deterioration degree calculating section 411 can be called a counting section (counting means) for the period of use of the process cartridges 9a to 9d. The toner deterioration degree calculating section 411 has a function as an estimating section for estimating the usage period of the process cartridges 9a to 9d.

When the rotational distance of the developing roller 4 counted by the toner deterioration degree calculator 411 is less than the first threshold distance Dv, the image control unit 406 determines that separation streaks due to toner deterioration do not occur. On the other hand, when the rotational distance of the developing roller 4 counted by the toner deterioration degree calculation unit 411 is equal to or greater than the distance Dv, the image control unit 406 determines that separation streaks due to toner deterioration occur. Further, the image forming timing determining section 410 calculates and determines the image forming timing, which is the timing for starting image forming, based on the development contact state of each station.

The image control unit 406 determines whether or not the image formation timing determined by the image formation timing determination unit 410 has come. When the CPU 404 receives from the image control unit 406 that it is time to form an image, the CPU 404 transmits to the controller unit 401 a /TOP signal that is a request signal serving as a reference timing for outputting a video signal.

Upon receiving the /TOP signal from the CPU 404, the controller unit 401, which is image control means, outputs a video signal of the color specified by the /TOP signal reference color specification command based on the timing of receiving the /TOP signal. The image processing GA 405 , upon receiving a video signal from the controller unit 401 , transmits image formation data to the image control unit 406 . The image control unit 406 performs image formation based on the image formation data received from the image processing GA 405 . Upon receiving the instruction to start the printing operation, the paper conveying unit 408 starts feeding and conveying the sheet P. FIG. When the fixing control unit 407 receives the instruction to start the printing operation, the fixing control unit 407 starts preparation for fixing. The fixing control unit 407 starts adjusting the temperature of the fixing unit 19 based on the information of the print reservation command at the timing when the sheet P onto which the toner image has been transferred by the secondary transfer unit is conveyed. The toner image is fixed, and the sheet P on which the toner image is fixed is conveyed outside the machine.

[TOP mode]
Next, the image formation timing based on the /TOP signal will be described. 4A and 4B are timing charts when forming a monochrome image. FIG. 4A is a timing chart when the monochrome mode is designated by the print color mode designation command from the controller unit 401 and yellow (hereinafter referred to as YTOP mode) is designated by the /TOP signal reference color designation command. . On the other hand, FIG. 4B is a timing chart when the monochrome mode is designated by the print color mode designation command from the controller unit 401 and black (hereinafter referred to as KTOP mode) is designated by the /TOP signal reference color designation command. is. Note that the horizontal axes in FIGS. 4A and 4B indicate time.

First, the YTOP mode will be described with reference to FIG. 4(a). When the engine control unit 402 receives a print start command (501) from the controller unit 401, in order to form a monochrome image in the monochrome mode, the contact state (510) between the developing roller 4 and the photosensitive drum 1 is changed as follows. switch to That is, the contact state (510) between the developing roller 4 and the photosensitive drum 1 (referred to as the developing contact state in the figure) is changed from the fully separated state to the full-color contact state (511), and from the full-color contact state to the monochrome contact state. Switch to monochrome contact state (513) via state (512).

The engine control unit 402 transmits a /TOP signal (502) to the controller unit 401 after the development contact state has changed from the fully separated state to the full color contact state. A monochrome image is formed in a state where the developing roller 4d of the K station, which is a station whose toner color is black, is in contact with the photosensitive drum 1d. Therefore, in order to shorten the first printout time, in this embodiment, the engine control unit 402 transmits the /TOP signal (502) at the timing when the development contact state transitions from the fully separated state to the full color contact state. do.

When the controller unit 401 receives the /TOP signal (502) from the engine control unit 402, it starts image formation shown in the image formation state (520) in the figure, starting with the station (Y station) whose toner color is yellow. . Based on the start point of yellow image formation (521Y), a magenta image formation (522M), a cyan image formation (523C), Black image formation (524K) is started. Note that when monochrome image formation is performed, image data other than black is not transmitted (so-called blank space), so yellow, magenta, and cyan image formation is not performed. In FIG. 4A, in order to form a monochrome image, image formation is performed using a toner color other than black, that is, the second image forming units, the Y station using yellow toner, the M station using magenta toner, and the M station using magenta toner. No image formation is performed at the cyan C station.

Then, when the image formation (524K) at the K station, which is the first image forming unit, is completed, the engine control unit 402 changes the contact state of the developing roller 4 from the monochrome contact state to the fully separated state (514). to end the print operation. In this way, the monochrome image formation in the YTOP mode is a period in which image formation is not performed from when the /TOP signal is received until black image formation is started.

Next, the KTOP mode will be described with reference to FIG. 4(b). When the engine control unit 402 receives a print start command (501) from the controller unit 401, the contact state (530) between the developing roller 4 and the photosensitive drum 1 (in FIG. development contact state) is switched as follows. That is, the development contact state (530) is switched from the fully separated state to the full-color contact state (531), and from the full-color contact state to the monochrome contact state (532). A monochrome image can be formed if the developing roller 4d of the station (K station) whose toner color is black is in contact with the photosensitive drum 1d. Therefore, the engine control unit 402 transmits a /TOP signal (502) to the controller unit 401 after the contact state between the developing roller 4d and the photosensitive drum 1d transitions from the fully separated state to the full color contact state.

When the controller unit 401 receives the /TOP signal (502) from the engine control unit 402, the controller unit 401, based on the timing at which the /TOP signal (502) is received, changes the image forming status (540) to the K station. image formation (541) is started. Then, when the image formation at the K station (541K) is completed, the engine control unit 402 shifts the development contact state from the monochrome contact state to the fully separated state (534), and finishes the printing operation.

In this manner, the KTOP mode changes from a state in which the developing rollers 4a to 4d are separated from the photosensitive drums 1a to 1d (fully separated state) to a state in which the developing rollers 4a to 4d are in contact with the photosensitive drums 1a to 1d (fully separated state). contact state). An image forming operation performed using only the K (black) station can be called a monochrome image forming operation. On the other hand, an image forming operation performed using the Y, M, C, K stations can be called a multicolor image forming operation.

In the KTOP mode, compared to the full color mode and the YTOP mode, the time until the image forming section (541K) starts at the K station is shorter. That is, in the KTOP mode, the time from when the print start command (501) is transmitted from the controller unit 401 and received by the engine control unit 402 to when the image forming section (541K) is started at the K station is short. In the KTOP mode, compared with the full-color mode, the print start command (501) is transmitted from the controller unit 401 and received by the engine control unit 402 until the image forming section (541K) is started in the K station. time is short.

In the YTOP mode, there is a waiting time corresponding to Y, M, and C image formation from the reception of the /TOP signal to the start of black image formation. On the other hand, in the KTOP mode, black image formation can be started immediately after receiving the /TOP signal. In order to shorten the first printout time of the image forming apparatus, introducing the KTOP mode to form a monochrome image is very effective.

[Description of Image Defects Due to Development Separation Operation]
FIG. 5 is a cross-sectional view showing changes in the state of each station during image formation in the KTOP mode of FIG. 4(b). FIG. 5A shows a state in which the developing rollers 4 and the photosensitive drums 1 of all stations are separated from each other (fully separated state). In FIG. 5A, the distance K_Y (unit: mm) represents the distance between the station of the /TOP signal reference color (here, the most downstream black station) and the primary transfer portion of the yellow station. Similarly, the distance K_M (unit: mm) represents the distance between the primary transfer portions of the black station and the magenta station, and the distance K_C (unit: mm) represents the distance between the primary transfer portions of the black station and the cyan station. ing. Further, the distance B (unit: mm) shown in FIG. 5C is the distance from the contact position (development contact position) between the developing roller 4 and the photosensitive drum 1 at each station (cyan station in this case) to the primary transfer portion. represents distance.

Each primary transfer portion can be called a contact position where the photosensitive drum 1 and the intermediate transfer belt 80 contact each other. The abutment position of the black station can be called a first abutment position. Also, the contact positions of the yellow station, the magenta station, and the cyan station can be called second contact positions.

Further, here, it is assumed that the rotational distance of the developing roller 4c of the cyan station is equal to or greater than the threshold distance Dv, and the rotational distance of the developing rollers 4 of the yellow station and the magenta station is less than the distance Dv.

When the engine control unit 402 does not form an image, the developing roller 4 is separated from the photosensitive drum 1 at all stations (FIG. 5A), as shown in FIG. 5A. ing. When the engine control unit 402 receives a print start command from the controller unit 401, the engine control unit 402 shifts from the fully separated state shown in FIG. The state is changed to the contact state (FIG. 5(b)). The engine control unit 402 transmits a /TOP signal to the controller unit 401 at the timing of transition to the full-color contact state. The engine control unit 402 exposes the photosensitive drum 1d with a laser beam (601) emitted from the exposure unit 11 according to the video signal received from the controller unit 401, and performs image formation on the black station.

At the same time when the /TOP signal is transmitted, the engine control unit 402 changes the contact state between the developing roller 4 and the photosensitive drum 1 from the full-color contact state (FIG. 5(b)) to the monochrome contact state (FIG. 5(c)). transition to As shown in FIG. 5C, in the photosensitive drum 1d of the black station, an electrostatic latent image 602 is formed on the photosensitive drum 1d by laser light (601) emitted from the exposure unit 11. As shown in FIG. Further, by transitioning to the monochromatic contact state, the developing roller 4 and the photosensitive drum 1 move from the contact state to the separated state at the yellow station, the magenta station, and the cyan station. As described above, since the rotational distances of the developing rollers 4a and 4b in the yellow station and magenta station are less than the threshold distance Dv, separation streaks do not occur even if the developing rollers 4a and 4b are separated. On the other hand, since the rotational distance of the developing roller 4c of the cyan station is equal to or greater than the threshold distance Dv, when the developing roller 4c is separated from the photosensitive drum 1c, separation streaks (600c) may occur at the time of separation.

FIG. 5(d) is a cross-sectional view showing the progress of image formation in the black station in the monochromatic contact state shown in FIG. 5(c). At the black station shown in FIG. 5D, the electrostatic latent image formed on the photosensitive drum 1d is attached with toner by the developing roller 4d to form a toner image (602), which passes through the primary transfer section and is sequentially transferred to the toner image (602). , are transferred onto the intermediate transfer belt 80 . However, the separation streak (600c) formed on the photosensitive drum 1c of the cyan station installed upstream in the moving direction of the intermediate transfer belt 80 is also transferred onto the intermediate transfer belt 80. FIG. As a result, the toner image (602) formed on the photosensitive drum 1d of the black station is transferred to the area on the intermediate transfer belt 80 where the separation streak (600c) has been transferred, resulting in an image defect.

[Control of image formation timing in this embodiment]
In this embodiment, when the period of use of the station upstream of the black station, which is the reference color, is equal to or greater than a predetermined threshold value, when an image is formed in the monochrome contact state, an image defect due to separation streaks does not occur. Adjust the image formation timing. Specifically, when the rotational distance of the developing roller 4 in the station upstream of the black station, which is the reference color, is equal to or greater than the threshold distance Dv, and image formation is performed in the monochrome contact state, an image defect due to separation streaks occurs. Adjust the image formation timing so that it does not occur. A method of adjusting the timing of image formation for normal image formation without causing image defects will be described below.

FIG. 6 is a timing chart when the monochrome mode is designated by the print color mode designation command from the controller unit 401, and the black-and-white KTOP mode is designated by the /TOP signal reference color designation command to form a monochrome image. Note that the horizontal axis of FIG. 6 indicates time. Also, in FIG. 6, as in FIG. 5, it is assumed that the rotation distance of the developing roller 4c of the cyan station is equal to or greater than the threshold distance Dv.

When the engine control unit 402 receives a print start command (701) from the controller unit 401, the contact state (710) between the developing roller 4 and the photosensitive drum 1 (developing contact state) is switched as follows. That is, the engine control unit 402 shifts the development contact state from the fully separated state to the full-color contact state (711), transitions from the full-color contact state to the monochrome contact state (712), and shifts the state from the full-color contact state to the monochrome contact state (712). Transition to state (713). Reference numeral 712 denotes a moving section of the developing rollers 4a to 4c. Movement of the developing rollers 4a to 4c starts at the start point of 712, the developing rollers 4a to 4c are separated from the photosensitive drums 1a to 1c in the middle of 712, and the movement of the developing rollers 4a to 4c is completed at the end point of 712.

Here, in the Y, M, and C stations where the rotational distance of the developing roller 4 is equal to or greater than the threshold distance Dv, separation streaks (toner) adhere to the photosensitive drum 1 when the developing roller 4 separates from the photosensitive drum 1. Sometimes. Assuming that a separation streak occurs, it takes a certain amount of time for the separation streak to be transferred from the photosensitive drum 1 to the intermediate transfer belt 80 and pass through the primary transfer portion of the black station. This time is called a separated streak passing time (passing time) T_pass. When the rotational distance of the developing roller 4 is equal to or greater than the threshold distance Dv, the engine control unit 402 controls the black color after the separation streak passing time (passing time) T_pass elapses after the developing roller 4 is separated from the photosensitive drum 1 . A station forms an image on the intermediate transfer belt 80 . This prevents the image formed on the intermediate transfer belt 80 by the black station from being superimposed on the separation streak.

The engine control unit 402 calculates a separation streak passage time T_pass (721) from the timing when the development contact state transitions to the full-color contact state. Here, the separation streak passing time T_pass relates to the cyan station in which the rotational distance of the developing roller is equal to or greater than the threshold distance Dv. That is, it is the time during which the toner adhered to the position where the developing roller 4c of the cyan station is separated from the photosensitive drum 1c passes through the primary transfer portion of the black station of the /TOP signal reference color station.

The engine control unit 402 determines that the image at the position where the developing roller 4c of the cyan station where the rotation distance of the developing roller 4 is equal to or greater than the threshold value Dv is separated from the photosensitive drum 1c (separation streak) is the primary transfer unit of the black station, which is the reference color. Calculate the time to pass through The calculated time corresponds to the separated streak passing time T_pass (721) shown in FIG. The engine control unit 402 sends a /TOP signal to the controller unit 401 after the separation streak passage time T_pass (721) has elapsed since the development contact state (710) transitioned from the fully separated state to the full-color contact state. (703) is sent. The timing of transition from the fully separated state to the full color contact state is the /TOP signal output timing (502) described in FIG. 4B.

When the controller unit 401 receives the /TOP signal (703) from the engine control unit 402, the controller unit 401, based on the timing at which the /TOP signal (703) is received, changes the image forming status (720) to the black station. image formation (722K) is started. Then, when image formation (722K) at the black station is completed, the engine control unit 402 changes the contact state of the developing roller 4 from the monochrome contact state (713) to the fully separated state (714). End the print operation.

The timing at which the development contact state transitions to the full-color contact state is the same as the /TOP signal (502) (see FIG. 4), and is indicated as /TOP signal (702) in FIG. The /TOP signal (703) shown in FIG. 6 is transmitted/received at a timing delayed by the separated streak passage time T_Pass from the timing at which the /TOP signal (702) is transmitted/received.

In the KTOP mode shown in FIG. 6, the start of image formation (722K) at the black station after the print start command 701 is transmitted/received is delayed by the separation streak passing time T_Pass from the KTOP mode shown in FIG. The KTOP mode (see FIG. 4) in which the period of use of the station upstream of the black station, which is the reference color, does not exceed a predetermined threshold can be called the first KTOP mode. The KTOP mode (see FIG. 6) in which the period of use of at least some of the stations upstream of the black station, which is the reference color, exceeds a predetermined threshold can be called a second KTOP mode.

Performing a monochrome image forming operation in the first KTOP mode on the intermediate transfer belt 80 by the black station is called first monochrome image formation. Performing monochrome imaging operations in the second KTOP mode by the black station is referred to as second monochrome imaging.

The engine control unit 402 can selectively execute the first monochrome image formation and the second multicolor image formation. As described above, when the timing at which the first monochrome image formation is performed is the first timing, the second monochrome image formation is performed at the second timing later than the first timing.

As shown in FIGS. 4 and 6, the engine control unit 402 sets the Y, M, C, and K stations to the contact state before the first monochromatic image formation and the second monochromatic image formation. and a second multicolor image formation. Before forming the first monochrome image or during the formation of the first monochrome image, the developing rollers 4a-4c of the Y, M, and C stations are separated from the photosensitive drums 1a-1c. On the other hand, the second monochromatic image formation is performed with the developing rollers 4a-4c of the Y, M, and C stations separated from the photosensitive drums 1a-1c.

In the first KTOP mode, the K station performs an image forming operation based on the /TOP signal (502). Image forming operation is performed. That is, the time from transmission/reception of the print start command 501 (701) to execution of the second KTOP mode is longer than the time from transmission/reception of the print start command 501 (701) to the first KTOP mode. As described above, in the Y, M, and C stations where the rotational distance of the developing roller 4 is equal to or greater than the threshold distance Dv, when the developing roller 4 separates from the photosensitive drum 1 , separation streaks (toner) are formed on the photosensitive drum 1 . It may adhere. Therefore, when the rotation distance of the developing roller 4 is equal to or greater than the threshold distance Dv in at least some of the Y, M, and C stations, the engine control unit 402 performs the second monochrome image formation. In other words, the engine control unit 402 uses the black station after the separation streak passing time T_Pass has passed after the developing roller 4 of the station where the rotation distance of the developing roller 4 is equal to or greater than the threshold distance Dv is separated from the photosensitive drum 1 . An image is formed on the transfer belt 80 . This prevents the image formed on the intermediate transfer belt 80 by the black station from being superimposed on the separation streak.

On the other hand, when the rotation distance of the developing roller 4 does not exceed the threshold distance Dv in the Y, M, and C stations, the engine control unit 402 performs the first monochrome image formation, thereby increasing the speed of the image forming apparatus. First printout time can be shortened. The first monochrome image formation is performed after the developing rollers 4 of the Y, M, and C stations are separated from the photosensitive drum 1 and before the separation streak passing time T_Pass elapses.

[Control Sequence of Image Formation Timing in this Embodiment]
FIG. 7 is a flowchart showing a control sequence from when the engine control unit 402 receives a print start command from the controller unit 401 to when it transmits the /TOP signal for the first image in this embodiment. The processing shown in FIG. 7 is activated and executed by the engine control unit 402 when the engine control unit 402 receives a print start command from the controller unit 401 . In FIG. 3, the engine control unit 402 has respective control units (the image control unit 406, the fixing control unit 407, and the sheet conveying unit 408), but here, the engine control unit 402 will be described. Further, the distance between the primary transfer portions of each station is a distance determined by the configuration of the image forming apparatus, and in this embodiment, it is presumed to be held in the storage portion that stores the information of the engine control portion 402 in advance. do. Further, the distance B from the position where the developing roller 4 of each color station abuts (separates) from the photosensitive drum 1 to the primary transfer portion is a distance determined by the configuration of the image forming apparatus. It is assumed that the information is held in the storage unit of engine control unit 402 . Further, when the separation streak formed on the photosensitive drum 1 has a certain width, the rear end position of the separation streak in the rotation direction of the photosensitive drum is set as the separation position.

In step (hereinafter referred to as S) 800, the engine control unit 402 determines whether or not a print start command in the KTOP mode has been received from the controller unit 401 (denoted as "KTOP?" in the figure). When the engine control unit 402 determines that the print start command has been received in the KTOP mode, the engine control unit 402 confirms the rotation distance of the developing roller 4 at each station upstream in the moving direction of the intermediate transfer belt 80 from the black station. The process proceeds to S801. On the other hand, when the engine control unit 402 determines that the print start command has not been received in the KTOP mode, the process advances to S810.

In S801, the engine control unit 402 acquires the rotation distance of the developing roller 4a of the yellow (Y) station from the toner deterioration degree calculation unit 411, and determines whether or not the acquired rotation distance is equal to or greater than the threshold distance Dv. If the engine control unit 402 determines that the rotational distance of the developing roller 4a is greater than or equal to the distance Dv, the process advances to S802. Proceed to S803. In S802, the engine control unit 402 acquires the distance K_Y (unit: mm) between the primary transfer units of the black (K) station and the yellow (Y) station, which are the stations of the /TOP signal reference color, from the storage unit, and performs processing. to S807.

In S803, the engine control unit 402 acquires the rotation distance of the developing roller 4b of the magenta (M) station from the toner deterioration degree calculation unit 411, and determines whether the acquired rotation distance is equal to or greater than the threshold distance Dv. If the engine control unit 402 determines that the rotational distance of the developing roller 4b is greater than or equal to the distance Dv, the process advances to S804. Proceed to S805. In S804, the engine control unit 402 acquires the distance K_M (unit: mm) between the primary transfer units of the black (K) station and the magenta (M) station, which are the stations of the /TOP signal reference color, from the storage unit, and processes the distance. to S807.

In S805, the engine control unit 402 acquires the rotation distance of the developing roller 4c of the cyan (C) station from the toner deterioration degree calculation unit 411, and determines whether the acquired rotation distance is equal to or greater than the threshold distance Dv. If the engine control unit 402 determines that the rotational distance of the developing roller 4c is greater than or equal to the distance Dv, the process advances to S806. Proceed to S810. In S806, the engine control unit 402 acquires the distance K_C (unit: mm) between the primary transfer units of the black (K) station and the cyan (C) station, which are the stations of the /TOP signal reference color, from the storage unit. to S807.

In this embodiment, the distance between the primary transfer portions of each station is preliminarily held in the storage unit that stores the information of the engine control unit 402. Alternatively, the distance between the parts may be calculated. Let S be the distance between the primary transfer portions of each station, and let n be the number of stations between the station in which the developing roller 4 rotates by a distance Dv or more and the station of the /TOP signal reference color. /TOP signal reference color station (black (K) station) and yellow (Y), magenta (M), and cyan (C) stations whose rotational distance of developing roller 4 is equal to or greater than distance Dv, distance K_Y between primary transfer portions; K_M and K_C can be calculated by (n+1)×S.

In S807, the engine control unit 402 stores the distance B (unit: mm) between the contact position (separation position) of the developing roller 4 on the photosensitive drum 1 separated from the photosensitive drum 1 and the primary transfer portion in the station. Get more. In S808, the engine control unit 402 calculates the separation streak passing time T_pass, which is the time required for the separation streak of the station where the rotation distance of the developing roller is Dv or more to pass the primary transfer portion of the black (K) station. The separation streak passing time T_pass is the sum of the distances K_Y, K_M, and K_C (unit: mm) between the primary transfer portions obtained in S802, S804, and S806, and the distance B (unit: mm) obtained in S807. It is a value divided by 80 conveying speed PS (mm/sec). In this embodiment, it is assumed that the value of the conveying speed PS is stored in advance in the storage section of the engine control section 402 . If there are a plurality of stations whose developing roller rotation distance is Dv or more, the separated streak passing time T_pass is the separated streak passing time T_pass of the station arranged on the upstream side in the moving direction of the intermediate transfer belt 80 .

In S809, the engine control unit 402 sets the separation streak passage time T_pass calculated in S808 to the /TOP output extension time, which is the time for delaying the timing of transmitting the /TOP signal, and advances the process to S811. In S810, engine control unit 402 sets the /TOP output extension time to 0 because it is not necessary to delay the timing of transmitting the /TOP signal to controller unit 401, and advances the process to S811.

In S811, the engine control unit 402 transitions from the completely separated state in which the developing rollers 4 of all stations and the photosensitive drums 1 are separated to the full-color contact state in which the developing rollers 4 of all stations and the photosensitive drums 1 are in contact with each other. Let In S812, the engine control unit 402 determines whether or not the transition to the full-color contact state has been completed (denoted as "Full-color contact state transition completed?" in the drawing). If the engine control unit 402 determines that the transition to the full-color contact state has been completed, the process proceeds to S813, and if it determines that the transition to the full-color contact state has not been completed, the process proceeds to S812. return.

In S813, the engine control unit 402 resets and starts a timer of the engine control unit 402 in order to measure the /TOP output extension time. In S814, engine control unit 402 refers to the timer to determine whether or not the /TOP output extension time has elapsed (denoted as "/TOP output extension time elapsed?" in the figure). If the engine control unit 402 determines that the /TOP output extension time has elapsed, the process proceeds to S815, and if it determines that the /TOP output extension time has not elapsed, the process returns to S814. In S815, the engine control unit 402 transmits the /TOP signal to the controller unit 401, and terminates the process.

As described above, in this embodiment, in the following cases, engine control is performed so that separation streaks generated in the upstream station of the intermediate transfer belt 80 are not transferred into the image forming area of the downstream station. A section 402 controls the transmission timing of the /TOP signal. That is, in the control of this embodiment, a station whose rotational distance of the developing roller 4 is equal to or greater than the threshold distance Dv exists upstream of the station of the /TOP signal reference color, and stations other than the most upstream station are /TOP signals. Executed if it is a reference color station. In this way, when the deterioration of the toner progresses more than a predetermined amount, the image forming timing of the station of the reference color is determined based on the contact/separation operation of the developing roller 4 and the photosensitive drum 1 of the stations other than the reference color. On the other hand, if the toner has not deteriorated, the delay in the first printout time can be prevented by synchronizing with the image forming timing of the reference color station. As a result, the engine control unit 402 can minimize the delay in the first printout time, prevent the occurrence of image defects, and perform normal image formation.

In this embodiment, the contact/separation mechanism between the developing roller 4 and the photosensitive drum 1 has been described using an all-state transition type configuration that transitions to a specific contact state while passing through each contact state. . This embodiment can apply the control described above even in an independent transition type configuration in which each color station can be independently controlled.

In this embodiment, the transmission timing of the /TOP signal is determined based on the separation position of the developing roller 4 from the photosensitive drum 1 in the station where the rotational distance of the developing roller 4 is equal to or greater than the threshold distance Dv. For example, when a contact streak occurs when the developing roller 4 contacts the photosensitive drum 1, the /TOP signal transmission timing is set based on the contact position of the developing roller 4 on the photosensitive drum 1 at each station. may decide.

Further, in this embodiment, control is performed such that image formation is performed after the separated streak of the developing roller 4 of the station upstream in the moving direction of the intermediate transfer belt 80 from the station of the reference color passes through the primary transfer portion of the station of the reference color. explained. For example, the image forming timing is set so that the leading edge of the toner image of the reference color station passes through the primary transfer portion after the separated streak of the developing roller 4 of the upstream station passes through the primary transfer portion of the reference color station. It is also possible to decide

In this embodiment, the threshold value Dv for the rotation distance of the developing roller 4 is a common value for each station, but a different threshold value may be set for each station. Further, in this embodiment, the toner deterioration degree calculation unit 411 uses the rotation distance of the developing roller 4 to calculate the toner deterioration degree. For example, instead of the rotation distance of the development roller, the rotation time of the development roller 4, the rotation distance and rotation time of the photosensitive drum 1, the remaining amount of toner, the cumulative number of prints, and the like may be used. The degree of deterioration of the toner may be calculated by combining them.

As described above, according to the present embodiment, it is possible to prevent the occurrence of image defects due to deterioration of toner and prevent the delay of the first printout time.

In the first embodiment, when the rotation distance of the developing roller in the station upstream of the black station of the reference color is equal to or greater than the threshold value and image formation is performed in the monochrome contact state, the separation streak is not transferred into the black image area. I explained how to adjust the timing. In the second embodiment, an embodiment will be described in which the image forming timing is adjusted when the rotation distance of the developing roller in the station upstream of the black station, which is the reference color, is equal to or greater than the threshold value and in the following conditions. . That is, when the rotational distance of the developing roller of the upstream station is equal to or greater than a threshold value, and the optical sensor detects a separation streak due to the separation operation of the developing roller on the intermediate transfer belt, the image forming timing is adjusted. As for the configuration of the image forming apparatus of the present embodiment, only the portions different from the configuration described in the first embodiment will be described, and the same reference numerals will be used for the same configurations, and description thereof will be omitted here.

In this embodiment, the image forming apparatus is provided with detection means for detecting toner on the intermediate transfer belt 80 . The controller unit 401 determines whether or not to execute the second monochrome image forming operation based on the detection result of the detection unit when the rotation distance of the developing roller of the station upstream of the black station of the reference color is equal to or greater than the threshold value. to decide.

[Explanation of optical sensor]
FIG. 8 is a schematic diagram for explaining the configuration of the optical sensor 40, which is the detection means, shown in FIG. The optical sensor 40 includes a light-emitting element 900 such as an LED, light-receiving elements 901a and 901b such as photodiodes, an IC (not shown) for processing received light data, the light-emitting element 900, the light-receiving elements 901a and 901b, and the IC. It consists of a holder (not shown) that A light-emitting element 900 that is a light-emitting portion irradiates the intermediate transfer belt 80 with light. On the other hand, light-receiving elements 901a and 901b, which are light-receiving portions, detect the amount of reflected light by receiving light emitted from the light-emitting element 900 and reflected from the intermediate transfer belt 80 or the toner 903 on the intermediate transfer belt 80. ,Measure. Further, the light receiving element 901 a detects the amount of diffusely reflected light emitted from the light emitting element 900 , and the light receiving element 901 b detects the amount of specularly reflected light emitted from the light emitting element 900 . In this manner, the optical sensor 40 detects and measures both the amount of specularly reflected light and the amount of diffused reflected light, and based on the measurement results, detects the reflected light from the surface of the intermediate transfer belt 80 and high- to low-density toner patches. can do.

[Image forming apparatus system configuration]
FIG. 9 is a functional block diagram for explaining the system configuration of the image forming apparatus of this embodiment. In FIG. 9, the separation streak detection unit 1000 emits light from the light emitting element 900 of the optical sensor 40, and detects the toner on the intermediate transfer belt 80 based on the regular reflection light amount and the diffuse reflection light amount detected by the light receiving elements 901a and 901b. Detects the presence or absence of (separation streaks).

If there is a station where the rotation distance of the developing roller 4 counted by the toner deterioration degree calculation unit 411 is equal to or greater than the second threshold distance Dx, the image control unit 406 counts the number of images formed (number of times) Pn. do. As will be described later, in this embodiment, the number of times the /TOP signal is transmitted is the number of images formed. The image control unit 406 determines whether the number of formed images Pn is equal to or greater than the threshold value Px (equal to or greater than a predetermined value) in post-processing after image formation is completed. When the number Pn of formed images is equal to or greater than the threshold value Px, the image control unit 406 changes the contact state of the developing roller 4, which has been shifted from the monochrome contact state to the fully separated state in the post-processing, from the fully separated state. Transition to full-color contact state. The engine control unit 402 shifts the contact state of the developing roller 4 from the full-color contact state to the monochrome contact state. Detects separation streaks. When the separation streak detection unit 1000 detects a separation streak on the intermediate transfer belt 80, the engine control unit 402 separates the developing roller 4 based on the elapsed time from the execution of the separation operation to the detection of the separation streak. Identify the station where the streak occurred. Then, the image formation timing determination unit 410 calculates the image formation timing for starting image formation based on the state of contact between the developing roller 4 and the photosensitive drum 1 of the identified station in subsequent image formation, decide. The image control unit 406 sets the number of formed images Pn to 0 when the separation streak detection unit 1000 detects a separation streak. Therefore, when there is a station where the rotation distance of the developing roller 4 is Dx or more, separation streak detection by the separation streak detection unit 1000 is performed every time Px sheets of the sheet P are printed. The control operations of other control units and controller units shown in FIG. 9 are the same as those in FIG. 3 of the first embodiment, and description thereof will be omitted here.

[Control of image formation timing in this embodiment]
FIG. 10 is a timing chart when the monochrome mode is designated by the print color mode designation command from the controller unit 401 and the black KTOP mode is designated by the /TOP signal reference color designation command to form a monochrome image. be. Note that the horizontal axis of FIG. 10 indicates time. FIG. 10A is a timing chart in the case where separation streak detection is not performed by the separation streak detection unit 1000 described above in post-processing after performing image formation of a monochrome image. On the other hand, FIG. 10(b) is a timing chart in the case where separation streak detection is performed by the separation streak detection unit 1000 described above in post-processing after monochrome image formation.

First, the timing chart shown in FIG. 10(a) will be described. The engine control unit 402 shifts the developing contact state (1110) between the developing roller 4 and the photosensitive drum 1 to the monochrome contact state (1111), and transmits a /TOP signal (1101) to the controller unit 401 to produce a monochrome image. image formation (1121K) is performed. The engine control unit 402 then transmits a /TOP signal (1102) to the controller unit 401 to form a monochrome image (1122K). Every time the /TOP signal is transmitted, the image control unit 406 adds 1 to the number of images Pn for which image formation is started if there is a station where the rotation distance of the developing roller 4 is equal to or greater than the threshold distance Dx.

When the monochrome image formation (1121K, 1122K) is completed, the image control unit 406 starts post-processing (1103). At this time, when there is no station where the rotational distance of the developing roller 4 is the distance Dx or more, or there is a station where the rotational distance of the developing roller 4 is the distance Dx or more, but the number Pn of images formed is less than the threshold value Px. , separation streak detection is not performed. Therefore, the image control unit 406 shifts the developing contact state between the developing roller 4 and the photosensitive drum 1 from the monochrome contact state (1111) to the fully separated state (1112), and finishes the post-processing (1103).

Next, the timing chart shown in FIG. 10(b) will be described. The engine control unit 402 shifts the developing contact state (1130) between the developing roller 4 and the photosensitive drum 1 to the monochrome contact state (1131), and transmits a /TOP signal (1101) to the controller unit 401. A monochrome image is formed (1141K). The engine control unit 402 then transmits a /TOP signal (1102) to the controller unit 401 to form a monochrome image (1142K). Every time the /TOP signal is transmitted, the image control unit 406 adds 1 to the number of images Pn for which image formation is started if there is a station where the rotation distance of the developing roller 4 is equal to or greater than the threshold distance Dx.

When the image formation (1141K, 1142K) of the monochrome image is completed, the image control unit 406 starts the post-processing (1103). At this time, if there is a station where the rotational distance of the developing roller 4 is equal to or greater than the threshold distance Dx, and the number of images Pn formed by image formation is equal to or greater than the threshold value Px, the image control unit 406 determines whether the separation streak is formed in post-processing. The separation streak detection is performed by the detection unit 1000 . In order to detect a separation streak by the separation streak detection unit 1000, the image control unit 406 changes the development contact state from the monochrome contact state to the full separation state (1132), and from the full separation state to the full color contact state (1133). and transition. Further, the image control unit 406 transitions the development contact state from the full-color contact state to the monochrome contact state (1134), and from the monochrome contact state to the full separation state (1135). The separation streak detection unit 1000 detects the elapsed time until the optical sensor 40 detects the toner (separation streak) on the intermediate transfer belt 80 based on the timing of transition from the full-color contact state to the monochrome contact state (1134). Based on this, the station where the separation streak has occurred is specified. When the station where the separation streak occurs is specified, the image control unit 406 calculates the time T_pass for the separation streak to pass through the primary transfer unit of the black station. After that, image formation is performed.

[Control Sequence of Image Formation Timing in this Embodiment]
11 and 12, an image forming timing control sequence in this embodiment will be described. FIG. 11 is a flow chart showing a control sequence for detecting separation streaks caused by the separating operation of separating the developing roller 4 from the photosensitive drum 1 in the post-processing of the image forming process in this embodiment. FIG. 12 is a flow chart showing the control sequence from when the engine control unit 402 receives a print start command from the controller unit 401 to when it transmits the /TOP signal for the first image in this embodiment.

First, FIG. 11 will be described. The processing shown in FIG. 11 is started and executed by the engine control unit 402 when image formation is completed. In FIG. 11, the engine control unit 402 has each control unit (the image control unit 406, the fixing control unit 407, and the sheet conveying unit 408), but here, the engine control unit 402 will be described. It is assumed that thresholds D_Y and D_M for specifying a station in which a separation streak has occurred, which will be described later, are held in advance in a storage unit that stores information of the engine control unit 402 .

In S1200, the engine control unit 402 transitions to the fully separated state in which the developing rollers 4 and the photosensitive drums 1 of all stations are separated. In S1201, the engine control unit 402 determines whether or not the transition to the fully separated state has been completed (denoted as "Completed transition to the fully separated state?"). The engine control unit 402 advances the process to S1202 when determining that the transition to the fully separated state has been completed, and returns the process to S1201 when determining that the transition to the fully separated state has not been completed.

In S1202, the engine control unit 402 acquires the rotation distance of the developing roller 4 of each station from the toner deterioration degree calculation unit 411, and determines whether or not there is a station with the acquired rotation distance equal to or greater than the threshold distance Dx. If the engine control unit 402 determines that there is a station where the rotation distance of the developing roller 4 is greater than or equal to the distance Dx, the process proceeds to S1203, and determines that the rotation distance of the developing roller 4 of all stations is less than the distance Dx. If so, the process advances to S1221. In S1203, the engine control unit 402 acquires the number Pn of images formed and determines whether the number Pn of images formed is greater than or equal to the threshold value Px. If the engine control unit 402 determines that the number of formed images Pn is equal to or greater than the threshold value Px, the process advances to step S1204. The process proceeds to S1221.

In S1204, the engine control unit 402 transitions from the completely separated state in which the developing rollers 4 of all stations and the photosensitive drums 1 are separated to the full-color contact state in which the developing rollers 4 of all stations and the photosensitive drums 1 are in contact with each other. Let In S1205, the engine control unit 402 determines whether or not the transition to the full-color contact state has been completed (denoted as "Full-color contact state transition completed?" in the figure). If the engine control unit 402 determines that the transition to the full-color contact state has been completed, the process proceeds to S1206, and if it determines that the transition to the full-color contact state has not been completed, the process proceeds to S1205. return.

In S1206, the engine control unit 402 shifts from the full-color contact state in which the developing rollers 4 of all stations and the photosensitive drums 1 are in contact with each other to the monochrome contact state in which only the developing rollers 4d and the photosensitive drums 1d of the black station are in contact. transition to In S1207, the engine control unit 402 sets a timer of the engine control unit 402 to measure the time from the timing when the full-color contact state is changed to the monochrome contact state until the separation streak detection unit 1000 detects the separation streak. reset and start. In S1208, separation streak detection by the separation streak detection unit 1000 using the optical sensor 40 is started (denoted as "toner detection by optical sensor 40 is started" in the figure). In S1209, the engine control unit 402 determines whether or not the transition to the monochrome contact state has been completed (denoted as "monochrome contact state transition completed?" in the drawing). If the engine control unit 402 determines that the transition to the monochrome contact state has been completed, the process proceeds to S1210, and if it determines that the transition to the monochrome contact state has not been completed, the process proceeds to S1209. return.

In S1210, the engine control unit 402 shifts from the monochrome contact state in which only the developing roller 4d of the black station and the photosensitive drum 1d are in contact with each other to the fully separated state in which the developing roller 4d of all stations and the photosensitive drum 1d are separated from each other. transition. In S1211, the engine control unit 402 determines whether or not the transition to the fully separated state has been completed (denoted as "Completed transition to the fully separated state?" in the drawing). The engine control unit 402 advances the process to S1212 when determining that the transition to the fully separated state has been completed, and returns the process to S1211 when determining that the transition to the fully separated state has not been completed.

In S<b>1212 , the engine control unit 402 determines whether or not the separation streak is detected by the separation streak detection unit 1000 using the optical sensor 40 . If the engine control unit 402 determines that a separation streak has been detected by the separation streak detection unit 1000, the engine control unit 402 advances the process to S1213. proceed to

In S1213, the engine control unit 402 calculates the distance D_P (unit: mm) at which the separation streak was detected from the time T_P (unit: seconds) at which the separation streak was detected. Note that the distance D_P (unit: mm) at which the separation streak is detected is a value obtained by multiplying the time T_P at which the separation streak is detected by the conveying speed PS (mm/sec) of the intermediate transfer belt 80 . In this embodiment, it is assumed that the value of the conveying speed PS is stored in advance in the storage section of the engine control section 402 .

In S1214, engine control unit 402 determines whether or not distance D_P at which separation streaks are detected is greater than or equal to threshold value D_Y. If the engine control unit 402 determines that the distance D_P at which the separation streak is detected is equal to or greater than the threshold value D_Y, the process proceeds to S1215; The process proceeds to S1216. In S1215, engine control unit 402 determines that the station in which the separation streak occurs is the yellow (Y) station, and advances the process to S1220.

In S1216, engine control unit 402 determines whether or not distance D_P at which separation streaks are detected is greater than or equal to threshold value D_M. If the engine control unit 402 determines that the distance D_P at which the separation streak is detected is equal to or greater than the threshold D_M, the process advances to S1217; The process proceeds to S1218. In S1217, engine control unit 402 determines that the station where the separation streak occurs is the magenta (M) station, and advances the process to S1220. In S1218, engine control unit 402 determines that the station where the separation streak occurs is the cyan (C) station, and advances the process to S1220.

Here, the distance from the primary transfer portion of the black station to the optical sensor 40 is assumed to be distance SK (unit: mm). The distance K_Y (unit: mm) is the distance between the primary transfer portions of the black station and the yellow station, and the distance K_M (unit: mm) is the distance between the primary transfer portions of the black station and the magenta station. Further, the distance K_C (unit: mm) is the distance between the primary transfer portions of the black station and the cyan station, and the distance B (unit: mm) is the distance from the separation position of the developing roller 4 from the photosensitive drum 1 in each station to the primary transfer portion. This is the distance to the transfer section. The threshold values D_Y and D_M for identifying the station where the separation streak described above are set to values that satisfy the following relationship.
(Distance B + Distance K_Y + Distance SK) > Threshold D_Y > (Distance B + Distance K_M + Distance SK)
>threshold D_M>(distance B+distance K_C+distance SK)

In S1219, engine control unit 402 determines that there is no station in which separation streaks occur, and advances the process to S1220. In S1220, the engine control unit 402 sets the number of formed images Pn to 0, and ends the process. At S1221, the engine control unit 402 determines that there is no station in which separation streaks occur, and terminates the process.

Next, FIG. 12 will be described. FIG. 12 is a flow chart showing the control sequence from when the engine control unit 402 receives a print start command from the controller unit 401 to when it transmits the /TOP signal for the first image in this embodiment. The processing shown in FIG. 12 is activated and executed by the engine control unit 402 when the engine control unit 402 receives a print start command from the controller unit 401 . In FIG. 12, the engine control unit 402 has respective control units (the image control unit 406, the fixing control unit 407, and the sheet conveying unit 408). Further, the distance between the primary transfer portions of each station is a distance determined by the configuration of the image forming apparatus, and in this embodiment, it is presumed to be held in the storage portion that stores the information of the engine control portion 402 in advance. do. Further, the distance B from the position where the developing roller 4 of each color station abuts (separates) from the photosensitive drum 1 to the primary transfer portion is a distance determined by the configuration of the image forming apparatus. It is assumed that the information is held in the storage unit of engine control unit 402 . Further, when the separation streak formed on the photosensitive drum 1 has a certain width, the rear end position of the separation streak in the rotation direction of the photosensitive drum is set as the separation position.

In S1300, the engine control unit 402 determines whether or not a print start command in the KTOP mode has been received from the controller unit 401 (denoted as "KTOP?" in the figure). When the engine control unit 402 determines that the print start command has been received in the KTOP mode, the engine control unit 402 advances the processing to S1301 to confirm whether or not the separation streak of the developing roller 4 of each station upstream of the black station occurs. proceed to On the other hand, when the engine control unit 402 determines that the print start command has not been received in the KTOP mode, the process advances to S1310.

In S1301, the engine control unit 402 determines, based on the detection result of the separation streak detection unit 1000, whether separation streaks will occur at the yellow (Y) station. If the engine control unit 402 determines that separation streaks will occur at the yellow (Y) station, the process proceeds to S1302; if it determines that separation streaks will not occur at the yellow (Y) station, the process proceeds to S1303. . In S1302, the engine control unit 402 acquires the distance K_Y (unit: mm) between the primary transfer units of the black (K) station and the yellow (Y) station, which are the stations of the /TOP signal reference color, from the storage unit, and processes the distance. to S1307.

In S1303, the engine control unit 402 determines, based on the detection result of the separation streak detection unit 1000, whether a separation streak occurs at the magenta (M) station. If the engine control unit 402 determines that separation streaks will occur at the magenta (M) station, the process proceeds to S1304, and if it determines that separation streaks will not occur at the magenta (M) station, the process proceeds to S1305. . In S1304, the engine control unit 402 acquires the distance K_M (unit: mm) between the primary transfer units of the black (K) station and the magenta (M) station, which are the stations of the /TOP signal reference color, from the storage unit. to S1307.

In S1305, the engine control unit 402 determines, based on the detection result of the separation streak detection unit 1000, whether a separation streak occurs in the cyan (C) station. If the engine control unit 402 determines that separation streaks will occur at the cyan (C) station, the process proceeds to S1306, and if it determines that separation streaks will not occur at the cyan (C) station, the process proceeds to S1310. . In S1306, the engine control unit 402 acquires the distance K_C (unit: mm) between the primary transfer units of the black (K) station and the cyan (C) station, which are the stations of the /TOP signal reference color, from the storage unit, and performs processing. to S1307.

In this embodiment, the distance between the primary transfer portions of each station is preliminarily held in the storage unit that stores the information of the engine control unit 402. Alternatively, the distance between the parts may be calculated. Let S be the distance between the primary transfer portions of each station, and n be the number of stations between the station where it is determined that a separation streak will occur and the station of the /TOP signal reference color. /TOP signal reference color station (black (K) station) and yellow (Y), magenta (M), and cyan (C) stations where separated streaks are determined to occur K_Y, K_M, distance between primary transfer portions K_C can be calculated by (n+1)*S.

The processing of S1307 to S1315 is the same as the processing of S807 to S815 shown in FIG. 7 of the first embodiment, and the description thereof is omitted here. In S<b>1316 , the engine control unit 402 acquires the rotation distance of the developing roller 4 of each station from the toner deterioration degree calculation unit 411 . Then, the engine control unit 402 determines whether or not there is a station where the obtained rotation distance of the developing roller 4 is equal to or greater than the threshold distance Dx. If the engine control unit 402 determines that there is a station whose rotational distance of the developing roller 4 is equal to or greater than the threshold distance Dx, the process advances to S1317, and the engine control unit 402 advances the process to S1317, and determines that the rotational distance of the developing roller 4 is equal to or greater than the threshold distance Dx. If it is determined that there is no such, the process is terminated. In S1317, the engine control unit 402 adds 1 to the number of formed images Pn, and ends the process.

As described above, in this embodiment, when image formation is performed in a monochrome contact state in a state in which the rotation distance of the developing roller 4 in the station upstream of the black station, which is the reference color, is equal to or greater than the threshold value Dx, The engine control unit 402 performs the following control. That is, when the number Pn of formed images is equal to or greater than the threshold value Px, the engine control unit 402 uses the optical sensor 40 to determine whether or not the separation streak is generated due to the separation operation of the developing roller 4 . When the optical sensor 40 detects the separation streak, the engine control unit 402 transfers the separation streak to the image area on the intermediate transfer belt 80 where the toner image formed in the black station is transferred in the subsequent image formation. The image forming timing is determined so as not to On the other hand, if the rotational distance of the developing roller 4 is less than the threshold Dx, or if the number Pn of images formed is less than the threshold Px even if the rotational distance of the developing roller 4 is equal to or greater than the threshold Dx, the image of the reference color station Match the formation timing. This prevents a delay in the first printout time. As described above, in this embodiment, the engine control unit 402 can minimize the delay of the first printout time, prevent the occurrence of image defects, and perform normal image formation.

In this embodiment, the contact/separation mechanism between the developing roller 4 and the photosensitive drum 1 has been described using an all-state transition type configuration that transitions to a specific contact state while passing through each contact state. . This embodiment can apply the control described above even in an independent transition type configuration in which each color station can be independently controlled.

Also, in the present embodiment, a method for detecting whether or not separation streaks occur in the post-processing of image formation has been described. For example, it is detected whether a contact streak occurs when the developing roller 4 contacts the photosensitive drum 1. If there is a station where a contact streak occurs, the contact position of the developing roller 4 at each station is used as a reference. Alternatively, it may be configured to determine the transmission timing of the /TOP signal.

In this embodiment, the control for forming an image after the separated streak of the developing roller 4 of the station upstream in the moving direction of the intermediate transfer belt 80 from the station of the reference color passes through the primary transfer portion of the station of the reference color will be described. bottom. For example, the image forming timing is set so that the leading edge of the toner image of the reference color station passes through the primary transfer portion after the separated streak of the developing roller 4 of the upstream station passes through the primary transfer portion of the reference color station. It is also possible to decide

In this embodiment, the threshold value Dx for the rotation distance of the developing roller 4 is a common value for each station, but a different threshold value may be set for each station, for example. Further, in this embodiment, the toner deterioration degree calculation unit 411 uses the rotation distance of the developing roller 4 to calculate the toner deterioration degree. For example, instead of the rotation distance of the development roller, the rotation time of the development roller 4, the rotation distance and rotation time of the photosensitive drum 1, the remaining amount of toner, the cumulative number of prints, and the like may be used. The degree of deterioration of the toner may be calculated by combining them. In this embodiment, the configuration for detecting the toner on the intermediate transfer belt 80 with the optical sensor 40 has been described. configuration may be used.

As described above, according to the present embodiment, it is possible to prevent the occurrence of image defects due to deterioration of toner and prevent the delay of the first printout time.

1 photosensitive drum 4 developing roller 9 process cartridge 402 engine control section 411 toner deterioration degree calculating section

Claims (9)

a plurality of image forming units each having a photoreceptor and developing means for developing an electrostatic latent image formed on the photoreceptor using toner as a toner image;
exposing means for exposing the photoreceptors of the plurality of image forming units to form the electrostatic latent images;
an intermediate transfer member to which the toner images on the photoreceptors of the plurality of image forming units are transferred;
The photoreceptors and the developing means of the plurality of image forming units are in a contact state in which the photoreceptors and the developing means are in contact with each other, or in a separated state in which the developing means is separated from the photoreceptors. a control means for controlling whether to
counting means for counting the usage period of each of the image forming units;
with
The plurality of image forming units has a first image forming unit and a second image forming unit, and the photoreceptor of the first image forming unit is positioned at a first contact position with the intermediate transfer member. abut the
After setting the developing means and the photosensitive member of the first image forming unit and the second image forming unit to the contact state, the control unit causes the first image forming unit to control the intermediate image forming unit. A first monochromatic image formation executed at a first timing and a second monochromatic image formation executed at a timing later than the first timing can be selectively executed on the transfer member. ,
The second monochromatic image formation is performed in a state in which the developing means is separated from the photosensitive member of the second image forming section,
When toner adheres to the photoreceptor when the developing means of the second image forming unit separates from the photoreceptor, the time required for the toner to pass through the first contact position passes. When time is set, the second monochrome image formation is performed after the passage time elapses after the developing means of the second image forming unit is separated from the photoreceptor,
The control means performs the second monochrome image formation when the value related to the usage period of the second image forming section counted by the counting means is equal to or greater than a predetermined threshold value, and the value is equal to or exceeds the predetermined value. An image forming apparatus, wherein the first monochrome image formation is performed when the threshold value is not exceeded. 2. A method according to claim 1, wherein said developing means is separated from said photosensitive member of said second image forming section before forming said first monochromatic image or during said forming of said first monochromatic image. image forming device. When there are a plurality of second image forming units whose value is equal to or greater than the predetermined threshold value, the passing time is the above-mentioned value for the second image forming unit arranged upstream in the moving direction of the intermediate transfer member. 3. The image forming apparatus according to claim 1, wherein the time is transit time. 4. The first monochromatic image formation is performed after the developing means of the second image forming section is separated from the photoreceptor and before the passing time elapses. The image forming apparatus according to any one of . comprising image control means for generating image data;
3. The control means transmits to the image control means a request signal for requesting generation of the image data for the exposure means to expose the photoreceptor of the first image forming section. 5. The image forming apparatus according to any one of 1 to 4. a detecting means for detecting toner on the intermediate transfer member;
2. When said value is equal to or greater than said predetermined threshold, said control means determines whether or not to execute the second monochrome image formation based on the detection result of said detection means. 6. The image forming apparatus according to any one of 1 to 5. The detection means has a light-emitting portion that emits light and a light-receiving portion that receives light, and detects toner on the intermediate transfer member based on a measurement result of the amount of light received by the light-receiving portion. 7. The image forming apparatus according to claim 6, wherein: the developing means of the first image forming unit has black toner;
8. The image forming apparatus according to claim 1, wherein the developing means of the second image forming section contains toner other than black. The developing means has a developing roller for attaching toner to the electrostatic latent image on the photoreceptor,
9. The image forming apparatus according to claim 1, wherein said counting means counts a value relating to a rotational distance of said developing roller as said value.

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