JP2020098231A - Image forming apparatus - Google Patents

Abstract

To prevent wear of a photoconductor drum.SOLUTION: A body control unit 200, based on a stop phase in which it previously stopped photoconductor drums 13C, 13K and a rotational phase of the photoconductor drums 13C, 13K at a timing when it can stop the rotation of the photoconductor drums 13C, 13K (S120, S121), determines a rotational phase in which a rotational phase further rotating the rotation of the photoconductor drums 13C, 13K from the rotational phase in which it can stop the photoconductor drums is smaller than 180°, the rotational phase in which the difference from the stop phase in which it previously stopped the photoconductor drums is not a divisor of 360°, as a stop phase in which it stops the photoconductor drums this time (S122 to S129).SELECTED DRAWING: Figure 10

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer or a facsimile that forms an image by an electrophotographic method.

2. Description of the Related Art In recent years, in a color image forming apparatus, with the increase in image forming speed, a plurality of optical devices independently apply light beams to corresponding photoconductors to form electrostatic latent images. A toner image of each color is formed on the electrostatic latent image by the developing device. Then, the toner images of the respective colors are superposed and transferred on the intermediate transfer belt, and the superposed toner images are finally transferred to the paper or the superposed toner images are transferred to the transfer material on the transfer belt. Therefore, a method of forming an image is used.

In such a method of forming an image using a plurality of image forming units (hereinafter, referred to as an in-line method), since a plurality of photoconductors and a plurality of optical devices are used, color misregistration of four color toners easily occurs. There is a problem called. Regarding color misregistration, measures have been taken to reduce relative color misregistration by matching the relationship of the rotational phase of the photosensitive drum of each color to a desired state. In order to match the rotation phases of the photosensitive drums of the respective colors, a method of stopping the motors that drive the photosensitive drums by matching the rotation phases is used. For example, in Patent Documents 1 and 2, a phase detection sensor for detecting the rotational phase of each color photosensitive drum is provided, and when the photosensitive drum is stopped, the photosensitive drum is always stopped at a rotational phase different from that at startup, Control is performed to stop the motor that drives the photosensitive drum. This prevents local wear of the photosensitive drum.

JP, 2007-232894, A JP 2012-128367 A

However, the conventional image forming apparatus described above has the following problems. That is, the stop phase of the photosensitive drum is determined so as to be at a position shifted by a predetermined phase angle with respect to the stop phase at the start. Therefore, when the motor for driving the photosensitive drum is stopped, there is only one phase angle that can be stopped, and therefore, the photosensitive drum is stopped before the image formation is completed and the rotation stop of the photosensitive drum is permitted. The maximum rotation angle for idling is 355.9°. If the phase of the timing at which the rotation stop of the photosensitive drum is permitted has a random distribution, the rotation is 180° on average from the timing at which the rotation stop of the photosensitive drum is permitted until the motor driving the photosensitive drum is stopped. Need to let. Therefore, there is a problem that wear of the photosensitive drum is accelerated due to idle rotation of the motor.

The present invention has been made under such circumstances, and an object thereof is to suppress abrasion of the photosensitive drum.

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

(1) A plurality of photosensitive drums that carry images, a plurality of motors that drive the plurality of photosensitive drums, a rotational phase detection unit that detects the rotational phase of the photosensitive drums driven by each of the motors, and a plurality of Stop phase determining means for determining a stop phase for stopping the photosensitive drum, rotation phase of the photosensitive drum detected by the rotation phase detecting means, and stop of the photosensitive drum determined by the stop phase determining means Phase, and control means for controlling the rotation stop of the motor to stop the plurality of the photosensitive drums in the stop phase, the stop phase determining means for stopping the photosensitive drums. , A table storing a plurality of stop phases that are not divisors of 360°, and the stop phase determining means determines the stop phase when the plurality of photosensitive drums are stopped last time and the stop phase of each of the photosensitive drums. Based on the rotation phase of the photosensitive drum at the timing when the rotation can be stopped, the rotation phase is larger than the rotation phase of each of the photosensitive drums at the timing, and each of the photosensitive drums is further rotated from the rotation phase of the timing. An image forming apparatus, wherein a current stop phase whose phase to be made is smaller than 180° is selected from the plurality of stop phases in the table.

According to the present invention, abrasion of the photosensitive drum can be suppressed.

Sectional drawing which shows the structure of the image forming apparatus of Examples 1-3. FIG. 3 is a diagram showing an overall configuration of a drive unit that drives the photosensitive drums of Examples 1 to 3. The figure which shows the structure of the photosensitive drum gear of Examples 1-3. Block diagram showing a control unit of the image forming apparatus of Examples 1 to 3. FIG. 6 is a diagram illustrating the stop phase determination control according to the first embodiment. The graph which shows the distribution state of the stop phase in the fixed form job of Example 1. FIG. 3 is a diagram for explaining stop phase determination control of two motors according to the first embodiment. Timing chart for explaining the motor stop control of the first embodiment Flowchart showing a motor stop control sequence of the first embodiment 3 is a flowchart showing a control sequence for determining a motor stop phase according to the first embodiment. Timing chart for explaining the motor stop control of the second embodiment Flowchart showing the motor stop control sequence of the second embodiment Flowchart showing a control sequence for determining a motor stop phase according to the third embodiment A graph showing a distribution state of stop phases of a print job of the third embodiment

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Schematic configuration of image forming apparatus]
FIG. 1 is a cross-sectional view showing the configuration of an in-line type color image forming apparatus 100 (hereinafter referred to as image forming apparatus 100) according to the first embodiment. First, the configuration of the image forming apparatus 100 will be described with reference to FIG. In the in-line type image forming apparatus 100, four color toners image-formed by the process cartridges 12 (12Y, 12M, 12C, 12K) of yellow (Y), magenta (M), cyan (C), and black (K). Superimpose the images. Thereby, a full-color image can be output. In addition, Y, M, C, and K added to the end of the reference numerals represent yellow, magenta, cyan, and black, which are toner colors, respectively. The process cartridges 12 have the same configuration except that the toner colors are different, and in the following description, Y, M, C, and K at the end of the reference numerals are the same unless a member of a specific color is indicated. It shall be omitted.

The image forming apparatus 100 includes a laser scanner 11 that exposes a photosensitive drum 13 that is an image carrier to form an image of each color, and a process cartridge 12 (hereinafter, referred to as a cartridge 12) that forms a toner image on the photosensitive drum 13. ) Is provided. The cartridge 12 has a photosensitive drum 13, a charging roller 15, a developing roller 16, and a photosensitive drum cleaner 14. The photosensitive drum 13 rotates in the direction of the arrow (clockwise direction) in the figure, and the laser scanner 11 forms an electrostatic latent image. The charging roller 15 charges the photosensitive drum 13 to a predetermined potential. The developing roller 16 attaches toner to the electrostatic latent image formed on the photosensitive drum 13 and develops the electrostatic latent image to form a toner image. The photosensitive drum cleaner 14 wipes off the toner on the photosensitive drum 13.

Further, an intermediate transfer belt 17 is provided so as to be in contact with the photosensitive drum 13 of each cartridge 12, and a primary transfer roller 18 is provided at a position facing each photosensitive drum 13 with the intermediate transfer belt 17 interposed therebetween. Further, the intermediate transfer belt 17 is provided with a belt cleaner 19 for wiping off the toner on the intermediate transfer belt 17, and the wiped waste toner is stored in a waste toner container 20.

Further, a paper cassette 22 for storing the paper 21 is arranged below the image forming apparatus 100. The paper cassette 22 is provided with a size guide 23 that regulates the position of the paper 21 in the paper cassette 22, and a paper presence sensor 24 that detects the presence or absence of the paper 21 in the paper cassette 22. A paper feed roller 25 that feeds the paper 21, separation rollers 26a and 26b, and a registration roller 27 are provided on the conveyance path along which the paper 21 is conveyed. Further, a registration sensor 28 for detecting the conveyed sheet 21 is provided near the downstream side of the registration roller 27 in the sheet conveying direction. Further, in order to transfer the toner image on the intermediate transfer belt 17 onto the paper 21, a secondary transfer roller 29 is provided so as to be in contact with the intermediate transfer belt 17. Then, in order to fix the transferred toner image on the paper 21, a fixing device 30 is installed downstream of the secondary transfer roller 29 in the paper conveying direction.

(Image forming process)
Next, an electrophotographic process in which the image forming apparatus forms an image on the sheet 21 will be described. When forming an image, first, in the cartridge 12, the surface of the photosensitive drum 13 is uniformly charged by the charging roller 15. Next, the laser scanner 11 irradiates the surface of the photosensitive drum 13 with laser light modulated according to the image data, and the charged electric charge of the portion irradiated with the laser light is removed, whereby the surface of the photosensitive drum 13 is electrostatically charged. A latent image is formed. The developing roller 16 adheres the charged toner to the electrostatic latent image on the photosensitive drum 13 to form a toner image on the photosensitive drum 13. Then, the toner images formed on the photosensitive drum 13 are sequentially transferred to the intermediate transfer belt 17 by the primary transfer roller 18 so as to be superposed. On the other hand, the paper 21 in the paper cassette 22 is fed by the paper feed roller 25, and when a plurality of papers 21 are fed, only one paper 21 is registered by the registration rollers 27 by the separation rollers 26a and 26b. Be transported to. Next, the toner image on the intermediate transfer belt 17 is transferred by the secondary transfer roller 29 onto the sheet 21 conveyed by the registration roller 27. The paper 21 on which the toner image is transferred is heated and pressed by the fixing device 30, so that the toner image on the paper 21 is fixed on the paper 21 and then discharged to the outside of the image forming apparatus 100.

[Structure of photosensitive drum drive mechanism]
Next, with reference to FIG. 2, the configuration of the drive mechanism that drives the photosensitive drum 13 of the first embodiment will be described. FIG. 2 is a diagram illustrating a drive mechanism that drives the photosensitive drum 13 of this embodiment.

In FIG. 2, the photosensitive drums 13Y, 13M, 13C and 13K and the photosensitive drum gears 31Y, 31M, 31C and 31K are always connected in the same phase by a coupling (not shown). The photosensitive drum gear 31Y of the yellow (Y) photosensitive drum 13Y and the photosensitive drum gear 31M of the magenta (M) photosensitive drum 13M are connected via an intermediate gear 33Y. Similarly, the photosensitive drum gear 31M of the magenta (M) photosensitive drum 13M and the photosensitive drum gear 31C of the cyan (C) photosensitive drum 13C are connected via an intermediate gear 33M. Further, in the present embodiment, as a motor for driving the photosensitive drum 13, a black motor 32K (first motor) and a cyan motor 32C (second motor) are provided. The black motor 32K is connected to the photosensitive drum gear 31K of the black (K) photosensitive drum 13K. On the other hand, the cyan motor 32C is connected to the photosensitive drum gear 31C of the cyan (C) photosensitive drum 13C. When the motors 32C and 32K rotate in the arrow direction (counterclockwise direction) in the figure, the photosensitive drum gears 31C and 31K rotate in the counterclockwise direction, respectively, and as a result, the photosensitive drums 13C and 13K move in the arrow direction in the figure. Rotate (clockwise).

Further, as the cyan (C) photosensitive drum gear 31C rotates, the photosensitive drum gear 31M of the magenta (M) photosensitive drum 13M rotates via the intermediate gear 33M, and as a result, the photosensitive drum 13M is indicated by an arrow in the figure. Rotate in the direction (walking clockwise). Further, by rotating the photosensitive drum gear 31M of the magenta (M) photosensitive drum 13M, the photosensitive drum gear 31Y of the yellow (Y) photosensitive drum 13Y rotates via the intermediate gear 33Y, and as a result, the photosensitive drum 13Y Rotate in the direction of the arrow (clockwise walking) in the figure. Further, the photosensitive drum gear 31C for cyan, the photosensitive drum gear 31M for magenta, and the photosensitive drum gear 31Y for yellow are mounted in a desired rotation phase that can reduce relative color misregistration. The phase sensors 36C and 36K will be described later.

By adjusting the phase relationship between the black photosensitive drum 13K and the cyan photosensitive drum 13C by the above-described photosensitive drum driving mechanism, it is possible to reduce the color misregistration between the photosensitive drums 13. Therefore, in the following description, when the phases of the photosensitive drums 13Y, 13M, 13C and 13K are adjusted, the phases of the photosensitive drums 13C and 13K are adjusted.

[Photosensitive drum phase detection method]
Next, with reference to FIG. 3, a method for detecting the phase of the photosensitive drum 13 of this embodiment will be described. FIG. 3 is a diagram of the black photosensitive drum gear 31K and the cyan photosensitive drum gear 31C viewed from three directions. The photosensitive drum gears 31K and 31C have the same configuration, and the trailing K and C indicating the toner color are omitted in FIG. 3A is a side view of the photosensitive drum gear 31 viewed from the side, FIG. 3B is a perspective view of the photosensitive drum gear 31 viewed from an oblique direction, and FIG. 3C is a front view of the photosensitive drum gear 31. It is the front view seen.

The photosensitive drum gear 31 is provided with a slit plate 34. The slit plate 34 is provided with a slit 35 that is a cutout portion. The phase sensor 36, which is a rotational phase detection unit that detects the rotational phase of the photosensitive drum 13, has a light emitting portion and a light receiving portion, and a slit plate that rotates between the light emitting portion and the light receiving portion integrally with the photosensitive drum gear 31. 34 passes through. Then, the light emitted from the light emitting portion of the phase sensor 36 passes through the slit 35 provided in the slit plate 34 and is received by the light receiving portion, whereby the phase of the photosensitive drum 13 can be detected. In the description below, the slit 35K of the photosensitive drum gear 31K and the photosensitive drum 13K, and the slit 35C of the photosensitive drum gear 31C and the photosensitive drum 13C have the same phase relationship.

[Control configuration of image forming apparatus]
Next, the control configuration of the image forming apparatus 100 according to the present exemplary embodiment will be described with reference to FIG. The main body control unit 200, which is a control unit, has a CPU, a ROM, and a RAM (not shown). The CPU controls the image forming apparatus 100 by executing a program stored in the ROM for controlling each device in the image forming apparatus 100 while using the RAM as a work area. Further, the CPU has a timer for measuring time. The main body control unit 200 includes a phase slit monitoring unit 300, a rotational phase calculation unit 301, a relative phase candidate table 302, a stop phase determination unit 303, a stop timing calculation unit 304, and a random number generation unit 305. The phase slit monitoring unit 300, the rotation phase calculation unit 301, the stop phase determination unit 303, the stop timing calculation unit 304, and the random number generation unit 305 represent the functions executed by the main body control unit 200.

The main body control unit 200 sends to the motor drive unit 50 an instruction to start and stop the motor 32K that drives the photosensitive drum 13K and the motor 32C that drives the photosensitive drum 13C, and control the rotation speed. In response to an instruction from the main body control unit 200, the motor drive unit 50 outputs a drive control signal to the motors 32K and 32C for controlling the start and stop of the motors 32K and 32C and the rotation speed. Further, the motor 32K and the motor 32C output an FG pulse signal indicating the rotation speed to the motor drive unit 50.

Further, the main body control unit 200 is connected to the phase sensor 36K and the phase sensor 36C described above. The main body control unit 200 uses the outputs (detection results) from the phase sensors 36K and 36C to detect the timing at which the slits 35K and 35C of the slit plate 34 pass through the phase sensor 36 while the motors 32K and 32C are rotating. Can be detected.

The phase slit monitoring unit 300 detects the timing when the slits 35K and 35C pass the phase sensor 36. The rotation phase calculation unit 301 calculates the current rotation phase of the photosensitive drum 13 based on the elapsed time from the timing when the phase slit monitoring unit 300 detects the slit 35. The relative phase candidate table 302 is a table stored in the ROM (ROM) of the main body control unit 200. The stop phase determination unit 303 determines a rotation phase at which the motor 32 is stopped at the end of the image forming operation. As will be described later, in the present embodiment, the motor 32C and the motor 32K are arranged so that the photosensitive drums 13 driven by the respective motors stop at the same rotation phase, that is, the photosensitive drums 13 have the same stop phase. The stop control is performed so that The stop timing calculation unit 304 calculates the time until the photosensitive drum 13 stops based on the relative phase of the photosensitive drum 13 and the rotation speed of the motor 32 that drives the corresponding photosensitive drum 13. The random number generation unit 305 generates a pseudo random number.

[Motor stop control]
Next, the phase adjustment stop control of the photosensitive drum 13 of the present embodiment will be described with reference to FIG. FIG. 5 is a diagram showing a phase relationship between the phase sensor 36 and the slit plate 34. Since the photosensitive drum gear 31 provided with the slit plate 34 is fixed to the photosensitive drum 13 as described above, the rotational phase of the slit plate 34 is also the rotational phase of the photosensitive drum 13. In FIG. 5, the rotational phase θz when the slit 35 is detected by the phase sensor 36 is 0°. In FIG. 5, the rotational phase based on the phase θz (=0°) is represented as the absolute phase by the symbol θ, and the relative phase between the absolute phase and the absolute phase is represented by the symbol φ.

In FIG. 5, the absolute phase θx indicates the phase of the slit plate 34 when the motor 32 was stopped during the previous image formation. The phase slit monitoring unit 300 acquires the timing when the phase sensor 36 detects the slit 35 during image formation. The rotation phase calculator 301 calculates the absolute phase θ of the slit plate 34 based on the timing when the phase slit monitor 300 detects the slit 35 and the elapsed time Te from the timing when the slit 35 is detected. Assuming that the rotation time required for the photosensitive drum 13 to make one rotation is Td, the absolute phase θ (unit:°) of the slit plate 34 can be obtained by the following (Equation 1).
θ=(Te÷Td×360) mod 360 (Equation 1)

In the image forming operation this time, the absolute phase of the photosensitive drum 13 at the timing when the image formation is finished and the rotation of the photosensitive drum 13 can be stopped, that is, the stop control for stopping the rotation of the motor 32 can be started. Let θy. The relative phase between the absolute phase θy and the absolute phase θx, which is the stop phase of the photosensitive drum 13 when the motor 32 is stopped during the previous image formation, is represented by the relative phase φyx (=θy−θx).

The relative phase candidate table 302 is a table that stores a candidate list of relative phases at which the photosensitive drum 13 can be stopped as a relative phase based on the absolute phase θx of the photosensitive drum 13 when the motor 32 was stopped last time. is there. Table 1 shows an example of the relative phase candidate table 302. In Table 1, nine candidate positions are listed as the candidates for the relative phase at which the photosensitive drum 13 can be stopped, and the relative positions (relative phases) of the respective candidates are all numerical values that are not divisors of 360°. They are provided 9° apart. The relative position of each candidate is indicated by absolute phases θ1 to θ9 in FIG. The element of the relative phase (°) in Table 1 is set to 41.9°. The photosensitive drum 13 contacts the developing roller 16 during the image forming operation to form a nip portion. When the angle of the photosensitive drum 13 for one rotation is 360° and the angle of the nip portion between the photosensitive drum 13 and the developing roller 16 is A, the relationship of 41.9°>A is established. For example, when the rotation of the photosensitive drum 13 is stopped and the angular difference B from the previous stop position of the photosensitive drum 13 is B<A, the same portion of the photosensitive drum 13 is in contact with the developing roller 16, that is, A nip portion will be formed. On the other hand, when the respective stop phases are separated by 41.9°, the minimum value of the angular difference B becomes 41.9°, and the angular difference B>angle A, so that the same portion of the photosensitive drum 13 and the developing roller 16 are nipped. You can avoid becoming a part. Therefore, the angle at which the relative positions are separated from each other, 41.9°, is larger than the angle at the nip portion between the photosensitive drum 13 and the developing roller 16.

The stop phase determining unit 303 selects the smallest phase that is equal to or larger than the value of the relative phase φyx from the candidate list of the relative phases in which the photosensitive drum 13 can be stopped and is stored in the relative phase candidate table 302. Select as the phase φzx. The absolute phase θz for stopping can be obtained by θz=θx+φzx. Then, the difference between the relative phase φzx and the relative phase φyx becomes the relative phase φz (=φzx−φyx) for additionally driving the motor 32 and rotating the photosensitive drum 13. The main body control unit 200 calculates the time corresponding to the relative phase φz by the stop timing calculation unit 304, and after waiting for the calculated time, stops the motor 32. Here, a method of calculating a specific relative phase φzx for stop will be described with θx=55.0°, θy=210.0°, and φyx=155.0°. In the table of Table 1, when the value of the relative phase φyx (=210.0°-55.0°=155.0°) or more and the smallest phase is selected, the relative phase φzx for stop is 167. It will be 6°. As a result, the relative phase φz for additionally rotating the motor 32 becomes 12.6° (=167.6°−155.0°).

In the actual operation of the product, in the case of a user who executes only a fixed job (for example, a print job that prints the same number of sheets with the same paper size), the above-described relative phase φyx has a substantially the same value each time, that is, a fixed value. FIG. 6 is a diagram in which the rotation phase when the motor 32 is stopped in the present embodiment is plotted when a fixed-size job having two patterns of relative phases φyx=0° and φyx=320° is repeated 50 times. .. In FIG. 6, the vertical axis represents the rotational phase (absolute phase) (unit: °) when the motor 32 is stopped, and the horizontal axis represents the number of trials (unit: times) of the fixed job. Further, in the plots in FIG. 6, black circles are plots of the rotation phase of a fixed job with a relative phase φyx of 0°, and triangles are plots of a rotation phase of a fixed job with a relative phase φyx of 320°. Is. All the candidates for the relative positions listed in Table 1 are numerical values that are not divisors of 360°. Therefore, it can be seen from FIG. 6 that even if the same candidate value is used, it is possible to reduce the frequency of returning to the same rotation phase when the motor 32 is repeatedly started and stopped. .. In this embodiment, the candidate list of the relative phases that can be stopped shown in Table 1 is stored in the ROM, but one phase value that is not a divisor of 360° is determined, and a multiple of that value can be stopped. Alternatively, the method may be used as a candidate list of various relative phases.

[Phase alignment method when the photosensitive drum is stopped]
As for the stop control of the motor 32 described above, the control of one motor 32 has been described. In the image forming apparatus 100, when forming an image in the full color mode, both the motor 32C and the motor 32K are rotated to form an image using the four process cartridges 12. Since all the photosensitive drums 13 driven by the motor 32C and the motor 32K are stopped at the same stop phase at the time of stop, the rotation phase of the motor 32C and the rotation phase of the motor 32K are substantially matched during image formation. It's spinning. However, due to the uneven rotation of the motor 32C and the motor 32K during image formation and the variation in the braking distance when the motor 32C and the motor 32K are stopped, the rotational phase of the photosensitive drum 13C and the rotational phase of the photosensitive drum 13K during the image formation are different. Some deviation may occur.

Next, a method of determining the timing to stop both the motor 32C and the motor 32K will be described. FIG. 7A is a diagram illustrating an example in which the candidates for the absolute phase for stopping the photosensitive drum 13C driven by the motor 32C and the photosensitive drum 13K driven by the motor 32K are the same. FIG. 7A is a diagram using FIG. 5 described above, and the absolute phase θx indicates the phases of the photosensitive drums 13C and 13K when the motors 32C and 32K were stopped during the previous image formation. Further, the absolute phase θy_K indicates the absolute phase of the photosensitive drum 13K at the timing when the stop process of the motor 32K is started in the current image forming operation. The relative phase φy_K represents the relative phase (=θy_K−θx) between the absolute phase θy_K and the absolute phase θx. Similarly, the absolute phase θy_C indicates the absolute phase of the photosensitive drum 13C at the timing when the stopping process of the motor 32C is started in the image forming operation this time. The relative phase φy_C represents the relative phase (=θy_C−θx) between the absolute phase θy_C and the absolute phase θx.

The rotation phase calculation unit 301 determines the absolute values of the photosensitive drums 13C and 13K at the timing of starting the stop processing of the motors 32C and 32K based on the timing of detecting the slits 35 and the elapsed time from the detection of the slits 35. The phases θy_C and θy_K are calculated. The stop phase determining unit 303 determines the phases (stop phases) of the photosensitive drums 13C and 13K for stopping the motors 32C and 32K from Table 1 corresponding to the relative phase candidate table 302, respectively. In the case of FIG. 7A, the absolute phase θ4 is selected as the phase for stopping the photosensitive drums 13C and 13K. The stop timing calculation unit 304 calculates the relative phase φz_C (=θ4−θy_C) until the photosensitive drum 13C rotates from the absolute phase θy_C to the absolute phase θ4. Further, the stop timing calculation unit 304 calculates the relative phase φz_K (=θ4−θy_K) until the photosensitive drum 13K rotates from the absolute phase θy_K to the absolute phase θ4. Then, the main body control unit 200 starts deceleration of the motor 32C at the timing when the time corresponding to the relative phase φz_C has passed from the timing (timing of the absolute phase θy_C) at which the stopping process of the motor 32C can be started. Similarly, the main body control unit 200 starts deceleration of the motor 32K at a timing when a time corresponding to the relative phase φz_K has passed from the timing (timing of the absolute phase θy_K) at which the stopping process of the motor 32K can be started.

FIG. 7B is a diagram illustrating an example in which the candidates for the absolute phase for stopping the photosensitive drum 13C driven by the motor 32C and the photosensitive drum 13K driven by the motor 32K are different. 7B, like FIG. 7A, the absolute phase θx shows the phases of the photosensitive drums 13C and 13K when the motors 32C and 32K were stopped during the previous image formation. Further, the absolute phase θy_K indicates the absolute phase of the photosensitive drum 13K at the timing when the stopping process of the motor 32K can be started in the image forming operation this time. The relative phase φy_K represents the relative phase (=θy_K−θx) between the absolute phase θy_K and the absolute phase θx. Similarly, the absolute phase θy_C indicates the absolute phase of the photosensitive drum 13C at the timing when the stopping process of the motor 32C can be started in the current image forming operation. The relative phase φy_C represents the relative phase (=θy_C−θx) between the absolute phase θy_C and the absolute phase θx. 7B is different from FIG. 7A in that the absolute phase θy_C and the absolute phase θy_K are on the opposite sides of the absolute phase θ4 which is a phase candidate for stop. ..

The rotation phase calculation unit 301 determines the absolute values of the photosensitive drums 13C and 13K at the timing of starting the stop processing of the motors 32C and 32K based on the timing of detecting the slits 35 and the elapsed time from the detection of the slits 35. The phases θy_C and θy_K are calculated. The stop phase determining unit 303 determines the stop phases of the photosensitive drums 13C and 13K from Table 1 corresponding to the relative phase candidate table 302, respectively. At this time, the stop phase determination unit 303 determines that the photosensitive drum 13C stops at the absolute phase θ4, and determines that the photosensitive drum 13K stops at the absolute phase θ5. However, since the absolute phases for stopping the photosensitive drum 13C and the photosensitive drum 13K do not match, the stop phase determining unit 303 performs the following calculation. The additional phase (angle) for stopping the photosensitive drum 13C at the absolute phase θ5 by the motor 32C and the additional phase (angle) for stopping the photosensitive drum 13K at the absolute phase θ4 by the motor 32K are obtained. Judge whether (angle) is small. In order to stop the photosensitive drum 13K at the absolute phase θ4, it is necessary to rotate the photosensitive drum 13K by about 360° by the motor 32K. Therefore, the additional phase angle becomes smaller when the photosensitive drum 13C is stopped at the absolute phase θ5 by the motor 32C. As a result, the stop phase determining unit 303 determines the absolute phase for stopping the photosensitive drums 13C and 13K as the absolute phase θ5. The stop timing calculation unit 304 calculates the relative phase φz_C (=θ5-θy_C) until the photosensitive drum 13C rotates from the absolute phase θy_C to the absolute phase θ5. Further, the stop timing calculation unit 304 calculates the relative phase φz_K (=θ5-θy_K) until the photosensitive drum 13K rotates from the absolute phase θy_K to the absolute phase θ5. Then, the main body control unit 200 starts deceleration of the motor 32C at a timing when a time corresponding to the relative phase φz_C has elapsed from the timing (timing of the absolute phase θy_C) at which the stopping process of the motor 32C can be started. Similarly, the main body control unit 200 starts deceleration of the motor 32K at a timing when a time corresponding to the relative phase φz_K has elapsed from the timing (timing of the absolute phase θy_K) at which the stopping process of the motor 32K can be started.

As a method different from the method described above, for example, for the photosensitive drum 13 corresponding to one motor 32 (motor 32C or motor 32K), the absolute phase for stop is selected from the candidate list of the phases for stop shown in Table 1. select. Then, a method of determining a stop timing according to the selected absolute phase and stopping the motors 32C and 32K at the same time may be used. In this case, since the motor 32C and the motor 32K do not match the absolute phase at the time of stop, the motor 32C and the motor 32K stop with a phase difference. Therefore, as is publicly known, at the start of the next image forming operation, a method of eliminating the phase shift by shifting the start timing of the motor 32C and the motor 32K may be used.

[Timing chart of motor stop control]
FIG. 8 is a timing chart for explaining stop control of the motor 32C and the motor 32K. FIG. 8 is a graph showing the operating state of the motor 32C, the phase of the photosensitive drum 13C driven by the motor 32C, and the output of the phase sensor 36C that detects the slit 35 of the photosensitive drum gear 31C driven by the motor 32C in order from the top. ing. Further, FIG. 8 shows a graph showing the operating state of the motor 32K, the phase of the photosensitive drum 13K driven by the motor 32K, and the output of the phase sensor 36K that detects the slit 35 of the photosensitive drum gear 31K driven by the motor 32K. There is. The horizontal axis represents time (timing). In FIG. 8, t1c, t2c, t1k, and t2k represent time (timing).

In FIG. 8, the operating states of the motors 32C and 32K are the period of steady rotation during image forming operation, the period of waiting for stop for stopping the motor 32, the period of deceleration for decelerating the rotation of the motor 32, and the motor 32. It consists of a period of suspension. The phases of the photosensitive drums 13C and 13K are represented by sine waves. In the graph showing the outputs of the phase sensors 36C and 36K, the timing at which the output changes from the high level to the low level is the timing at which the phase sensors 36C and 36K detect the slits 35, respectively.

In FIG. 8, timing t1c indicates the stop permission timing of the motor 32C in the image forming sequence (that is, the timing at which the process of stopping the rotation of the motor 32C can be started). The stop permission of the motor 32C is determined at the timing satisfying the condition for stopping the rotation of the photosensitive drum 13C in the image forming sequence such as the completion of the primary transfer from the photosensitive drum 13C to the intermediate transfer belt 17. Timing t1k indicates the stop permission timing of the photosensitive drum 13K in the image forming sequence (that is, the timing at which the process of stopping the rotation of the motor 32K can be started). In this embodiment, the motor 32K that drives the photosensitive drum 13K also drives the intermediate transfer belt 17. Therefore, the stop permission timing of the motor 32K is determined in consideration of conditions such as the sheet 21 having passed the secondary transfer roller 29. As a result, the timing at which the stop permission is determined for the motor 32C and the motor 32K in the image forming sequence is the stop permission timing t1k of the motor 32K, which is the timing at which both the rotation stop of the motor 32C and the motor 32K are permitted. Become. The main body control unit 200 starts the stop processing of the motors 32C and 32K at timing t1k, and determines the absolute phase at which the photosensitive drums 13C and 13K are stopped by the method described above. Then, the main body control unit 200 starts deceleration of the motor 32C at the timing t2c when the time Tc corresponding to the movement of the photosensitive drum 13C by the relative phase φz_C (see FIG. 7) by the motor 32C has started from the timing t1k. Let Similarly, the main body control unit 200 decelerates the motor 32K at a timing t2k when a time Tk corresponding to the movement of the photosensitive drum 13K by the motor 32K by the relative phase φz_K (see FIG. 7) has elapsed from the timing t1k as a starting point. Let it start.

[Motor stop control sequence]
FIG. 9 is a flowchart showing a control sequence when stopping the motors 32C and 32K of this embodiment. The process shown in FIG. 9 is started when the image forming operation is started, each process is executed by the main body control unit 200, and the process is ended when the image forming operation is ended. It should be noted that FIG. 9 is a flow chart showing the control of the motors 32C and 32K, and the processing regarding the image forming operation is not shown. Further, in the above description, each functional block of the main body control unit 200 shown in FIG. 4 is described as performing the corresponding process, but each process shown in FIGS. 9 and 10 is performed by the main body control unit 200. It will be described as a thing.

When the image forming operation is started, in step (hereinafter referred to as S) 101, the main body control unit 200 controls the motor driving unit 50 to simultaneously activate the motors 32C and 32K to start rotation. In S102, the main body control unit 200 determines whether or not the timing t1k (first timing) at which the image formation is completed and the rotation stop of the black motor 32K is permitted is reached. When determining that the timing t1k has been reached, the main body control unit 200 advances the process to S103, and when determining that the timing t1k has not been reached, returns the process to S102. In S103, the main body control unit 200 activates the stop phase determination process in order to determine the stop phase of the photosensitive drums 13C and 13K, and when the stop phase determination process ends, the process proceeds to S110 and S112. The stop phase determination process will be described later with reference to FIG.

The processes of S110 to S112 and S113 to S115 are processes for the motor 32C and the motor 32K, respectively, and the main body control unit 200 performs the processes for the motor 32C and the motor 32K at the same time in parallel. The parallel notation is used as follows.

In S110, the main body control unit 200 calculates the additional rotation phase θz_C of the photosensitive drum 13C based on the stop phase θz acquired in the process of S103. Then, the main body control unit 200 calculates the time Tc until the photosensitive drum 13C moves by the motor 32C to the phase corresponding to the calculated additional rotation phase θz_C, resets the timer, and starts the timer. In S111, the body control unit 200 refers to the timer and determines whether the time Tc has elapsed. When determining that the time Tc has elapsed, the body control unit 200 advances the process to S112, and when determining that the time Tc has not elapsed, returns the process to S111. In S112, the main body control unit 200 controls the motor drive unit 50 to start decelerating the rotation of the motor 32C.

In S113, the main body control unit 200 calculates the additional rotation phase θz_K of the photosensitive drum 13K based on the stop phase θz acquired in the process of S103. Then, the main body control unit 200 calculates the time Tk until the photosensitive drum 13K is moved by the motor 32K to the phase corresponding to the calculated additional rotation phase θz_K, resets the timer, and starts the timer. In S114, the body control unit 200 refers to the timer and determines whether the time Tk has elapsed. When determining that the time Tk has elapsed, the main body control section 200 advances the process to S115, and when determining that the time Tc has not elapsed, returns the process to S114. In S115, the main body control unit 200 controls the motor driving unit 50 to start decelerating the rotation of the motor 32K. When the rotations of the motor 32C and the motor 32K are stopped, the main body control unit 200 ends the image forming process.

FIG. 10 is a flowchart showing a control sequence of a subroutine for performing a process of determining the stop phase of the motor 32C and the motor 32K which is started from the process of S103 of FIG. In S120, the main body controller 200 calculates the absolute phase θy_C of the photosensitive drum 13C based on the elapsed time from the timing when the phase sensor 36C detects the slit 35 to the timing t1k. In S121, the main body controller 200 calculates the absolute phase θy_K of the photosensitive drum 13K based on the elapsed time from the timing when the phase sensor 36K detects the slit 35 to the timing t1k. In S122, the main body control unit 200 uses the above-described method based on the absolute phase θx when the photosensitive drum 13 was stopped last time, the absolute phase θy_C calculated in S120, and the absolute phase candidate list for stopping the photosensitive drum 13, A stop phase θz_C for stopping the photosensitive drum 13C is determined. In S123, the main body control unit 200 uses the above-described method based on the absolute phase θx when the photosensitive drum 13 was stopped last time, the absolute phase θy_K calculated in S121, and the candidate list of the absolute phase for stopping the photosensitive drum 13, The stop phase θz_K for stopping the photosensitive drum 13K is determined.

In S124, the main body control unit 200 determines whether or not the stop phase θz_C for stopping the photosensitive drum 13C determined in S122 and the stop phase θz_K for stopping the photosensitive drum 13K determined in S123 are the same. When determining that the stop phase θz_C and the stop phase θz_K are the same, the main body control unit 200 advances the process to S125, and when determining that the stop phase θz_C and the stop phase θz_K are not the same (different). , The process proceeds to S126. In S125, the body control unit 200 substitutes the stop phase θz_C for the stop phase θz and ends the process.

In S126, the main body control unit 200 determines that the additional rotation phase φz_C2 (first phase difference) for stopping the photosensitive drum 13C at the stop phase θz_K and the additional rotation phase φz_K2 for stopping the photosensitive drum 13K at the stop phase θz_C. (Second phase difference) is calculated. In S127, the body control unit 200 determines whether the additional rotation phase φz_C2 is smaller than the additional rotation phase φz_K2 (φz_C2<φz_K2). When the main body control unit 200 determines that the additional rotation phase φz_C2 is smaller than the additional rotation phase φz_K2, the process proceeds to S128. On the other hand, when the main body control unit 200 determines that the additional rotation phase φz_C2 is not smaller than the additional rotation phase φz_K2 (φz_C2≧<φz_K2) (the first phase difference is greater than or equal to the second phase difference), the process is S129. Proceed to. In S128, the body control unit 200 should stop the photosensitive drum 13C at the absolute phase θz_K, so the absolute phase θz_K is substituted for the stop phase θz, and the process ends. In S129, the main body control unit 200 should stop the photosensitive drum 13K at the absolute phase θz_C, so the absolute phase θz_C is substituted for the stop phase θz, and the process ends.

As described above, by applying the present embodiment, it is possible to reduce the idle running time when the photosensitive drum 13 is stopped by adjusting the phase when the photosensitive drum 13 is stopped. As a result, the idle running time of the photosensitive drum 13 is reduced. Can also be reduced and wear of the photosensitive drum 13 can be suppressed. Further, the rotation phase of the photosensitive drum 13 when stopped is not concentrated on the same phase, and local abrasion of the photosensitive drum 13 can be prevented. Further, as a method of preventing the rotation phases from gathering in the same phase, a method of storing and referencing a history of past stop phases may be considered, but in the present embodiment, a history of stop phases of the motor 32 is stored. As a result, it is possible to reduce the memory usage.

As described above, according to this embodiment, it is possible to suppress the abrasion of the photosensitive drum.

In the first embodiment, the stop process of the motor 32 is started after the timing at which both the motors 32C and 32K can be stopped (hereinafter, also referred to as stop permission timing). In the image forming sequence, the motor 32C that drives the photosensitive drum 13 on the upstream side in the moving direction of the intermediate transfer belt 17 may be in a state where it can be stopped earlier. Therefore, when the time difference between the stop permission timings of the motor 32C and the motor 32K is large, the idling time of the motor 32C becomes long in the method of the first embodiment. Therefore, in the present embodiment, the motor stop control when the time difference between the stop permission timings of the motor 32C and the motor 32K is large will be described. The configuration of the image forming apparatus 100, the configuration of the control unit, and the method of determining the stop phase of the motor 32 are the same as those in the first embodiment, and the description thereof is omitted here.

[Timing chart of motor stop control]
In FIG. 11, two types of timing charts are shown according to the photosensitive drum 13 that is a priority target for reducing wear. FIG. 11A is a timing chart when the wear reduction of the photosensitive drum 13K driven by the motor 32K is prioritized, that is, the idle running time of the motor 32K is shorter than the idle running time of the motor 32C. On the other hand, FIG. 11B is a timing chart when the reduction of wear of the photosensitive drums 13Y, 13M, and 13C driven by the motor 32C is prioritized, that is, the idle running time of the motor 32C is shorter than the idle running time of the motor 32K. ..

FIG. 11A is a timing chart illustrating stop control of the motor 32C and the motor 32K when the idle running time of the motor 32K is shorter than the idle running time of the motor 32C. FIG. 11A shows the operating state of the motor 32C, the phase of the photosensitive drum 13C driven by the motor 32C, and the output of the phase sensor 36C that detects the slit 35 of the photosensitive drum gear 31C driven by the motor 32C, in order from the top. The graph is shown. Further, FIG. 11A is a graph showing the operating state of the motor 32K, the phase of the photosensitive drum 13K driven by the motor 32K, and the output of the phase sensor 36K that detects the slit 35 of the photosensitive drum gear 31K driven by the motor 32K. Is shown. The horizontal axis represents time (timing). In FIG. 11A, t1c, t2c, t3c, t1k, and t2k represent time (timing).

In FIG. 11A, the main body control unit 200 calculates the remaining time Tr until the stop permission timing t1k of the motor 32K at the timing t1c which is the stop permission timing of the motor 32C. Here, the main body control unit 200 is premised on that the post-rotation processing of the image forming operation is executed based on the stop timing of the motor 32 based on a predetermined time. Therefore, when the stop permission timing of the motor 32C is determined, the stop permission timing of the motor 32K is uniquely determined. The main body control unit 200 obtains a remaining time T13c obtained by dividing the remaining time Tr until the stop permission timing t1k of the motor 32K by the circulation time Td of the photosensitive drum 13 by the following (Equation 2). The time T13c is the first timing after the timing t1c, which is the same as the rotation phase of the photosensitive drum gear 31C at the timing t1k.
T13c=Tr mod Td (Equation 2)

The main body control unit 200 calculates the timing t3c which is the timing when the time T13c has elapsed from the timing t1c which is the stop permission timing of the motor 32C. Then, the main body control unit 200 determines the absolute phase θz for stopping the photosensitive drums 13C and 13K based on the rotation phases of the photosensitive drums 13C and 13K at the timing t3c according to the method described in the first embodiment. Next, the main body control unit 200 obtains an elapsed time Tc from the timing t3c until the motor 32C starts decelerating, and an elapsed time Tk from the timing t1k that is the stop permission timing of the motor 32K to the deceleration of the motor 32K. .. The main body control unit 200 causes the motor 32C to start decelerating the motor 32C via the motor drive unit 50 when the time Tc has elapsed from the timing t3c. The timing t1k at which the motor 32K is permitted to stop is the timing after the lap time Td of the photosensitive drum 13 has passed from the timing t3c. The rotational phase of the photosensitive drum 13K at the timing t1k and the rotational phase of the photosensitive drum 13K at the timing t3c are the same. Therefore, the main body control unit 200 starts deceleration of the motor 32K via the motor drive unit 50 at the timing t2k when the already calculated time Tk has elapsed from the timing t1k that is the stop permission timing of the motor 32K. Let By controlling in this manner, the motor 32C and the motor 32K can be stopped at a desired absolute phase.

FIG. 11B is a timing chart illustrating stop control of the motor 32C and the motor 32K when the idle running time of the motor 32C is shorter than the idle running time of the motor 32K. The configuration of the timing chart shown in FIG. 11B is the same as that of FIG. 11A described above, and the description thereof is omitted here. In FIG. 11B, t1c, t2c, t1k, t2k, and t3k indicate time (timing).

The main body control unit 200 determines the absolute phase θz for stopping the photosensitive drums 13C and 13K based on the rotation phase of the photosensitive drums 13C and 13K at the timing t1c which is the stop permission timing of the motor 32C. Next, the main body control unit 200 determines a time Tc from the stop permission timing t1c of the motor 32C to the start of deceleration of the motor 32C and a time Tk from the timing t3k to the stop of the motor 32K. It should be noted that the timing t3k is the timing at which the two revolution times Td of the photosensitive drum 13 have elapsed from the stop permission timing t1c of the motor 32C. The main body control unit 200 starts deceleration of the motor 32C via the motor driving unit 50 at a time point t2c when a time Tc has elapsed from the timing t1c.

Further, the body control unit 200 calculates the remaining time Tr until the stop permission timing t1k of the motor 32K at the timing t1c which is the stop permission timing of the motor 32C. After reaching the timing t1k after the remaining time Tr from the timing t1c to the stop permission timing t1k of the motor 32K elapses, the main body control unit 200 stands by for the timing t1c to be the starting point and to match the stop phase with the photosensitive drum 13C. .. The waiting time T13k in that case is calculated by the following (formula 3). The waiting time T13k is the first timing after the timing t1k, which is the same timing as the rotation phase of the photosensitive drum gear 31K at the timing t1c.
T13k=Td-Tr mod Td (Equation 3)

The main body control unit 200 starts deceleration of the motor 32K via the motor drive unit 50 at the timing t2k when the already calculated time Tk has elapsed, starting from the timing t3k when the time T13k has elapsed from the timing t1k. The timing t3k, which is the timing of waiting for the time T13k from the timing t1k, is a multiple of the circulation time Td of the photosensitive drum 13 with respect to the timing t1c. Therefore, the photosensitive drum 13C and the photosensitive drum 13K can be stopped at a desired absolute phase.

As described above, the main body control unit 200 gives priority to which one of the photosensitive drums 13Y, 13M and 13C driven by the motor 32C and the photosensitive drum 13K driven by the motor 32K, that is, wear reduction of the photosensitive drum 13. decide. Then, the main body control unit 200 determines the control based on either the timing chart of FIG. 11A or FIG. 11B described above according to the determined priority. In this embodiment, the minimum value of the remaining life of the photosensitive drums 13Y, 13M, and 13C is compared with the remaining life of the photosensitive drum 13K, and the control that suppresses the abrasion of the photosensitive drum 13 having the smaller remaining life is selected. To do. The remaining life of the photosensitive drum 13 is determined based on the traveling distance of the photosensitive drum 13, and the traveling distance of the photosensitive drum 13 is stored in a memory (not shown) provided in each cartridge. Shall be updated each time is rotated.

[Motor stop control sequence]
FIG. 12 is a flowchart showing a control sequence when stopping the motors 32C and 32K of this embodiment. The process illustrated in FIG. 12 is started when the image forming operation is started, each process is executed by the main body control unit 200, and the process is ended when the image forming operation is ended. It should be noted that FIG. 12 is a flowchart showing the control of the motors 32C and 32K, and the processing relating to the image forming operation is not shown. Further, in the above description, each functional block of the main body control unit 200 illustrated in FIG. 4 is described as performing the corresponding process, but each process illustrated in FIG. 12 is described as being performed by the main body control unit 200. To do.

When the image forming operation is started, in S201, the main body control unit 200 controls the motor drive unit 50 to simultaneously activate the motors 32C and 32K to start rotation. In S202, the main body control unit 200 determines whether or not the image formation is completed and the timing t1c at which the rotation stop of the cyan motor 32C is permitted is reached. When determining that the timing t1c (second timing) has been reached, the main body control unit 200 advances the process to S203, and when determining that the timing t1c has not been reached, the process returns to S202. In S203, the main body control unit 200 determines whether to prioritize wear reduction of the photosensitive drum 13K. When the main body control unit 200 determines to prioritize reduction of wear of the photosensitive drum 13K, the process proceeds to S204. On the other hand, when the main body control unit 200 does not determine to give priority to wear reduction of the photosensitive drum 13K (determines to give priority to wear reduction of the photosensitive drums 13Y, 13M, 13C), the process proceeds to S250. ..

In S204, the main body control unit 200 determines whether or not the timing t3c (see FIG. 11A) N cycles before the photosensitive drum 13 is reached with respect to the timing t1k that is the stop permission timing of the motor 32K. When the main body control unit 200 determines that the timing t3c before N laps of the photosensitive drum 13 has been reached, the process proceeds to S205, and when it is determined that the timing t3c before N laps of the photosensitive drum 13 has not come. Returns the process to S204. In S205, the main body control unit 200 activates the subroutine (see FIG. 10) for performing the stop phase determination process described in the first embodiment, and based on the rotational phases of the photosensitive drums 13C and 13K at that time, the photosensitive drum 13C, The stop phase θz for stopping 13K is determined.

In S206, the main body control unit 200 obtains the additional rotation phase φz_C for additionally rotating the photosensitive drum 13C by the motor 32C from the stop phase θz acquired in the processing of S205. Then, the main body control unit 200 calculates the time Tc until the photosensitive drum 13C moves to the phase (position) corresponding to the additional rotation phase φz_C, resets the timer, and starts the timer. The main body control unit 200 refers to the timer and determines whether the time Tc corresponding to the additional rotation phase φz_C has elapsed. When determining that the time Tc has elapsed, the main body control unit 200 advances the process to S207, and when determining that the time Tc has not elapsed, returns the process to S206. In S207, the main body control unit 200 controls the motor drive unit 50 to start decelerating the rotation of the motor 32C.

In S208, the body control unit 200 determines whether or not the timing t1k (third timing) at which the rotation stop of the black motor 32K is permitted is reached. When determining that the timing t1k has been reached, the main body control unit 200 advances the process to S209, and when determining that the timing t1k has not been reached, returns the process to S208. In S209, the main body control unit 200 obtains the additional rotation phase φz_K for additionally rotating the photosensitive drum 13K by the motor 32K from the stop phase θz acquired in the process of S205. Then, the main body control unit 200 calculates the time Tk until the photosensitive drum 13K moves to the phase (position) corresponding to the additional rotation phase φz_K, resets the timer, and starts it. The main body control unit 200 refers to the timer and determines whether the time Tk corresponding to the additional rotation phase φz_K has elapsed. When determining that the time Tk has elapsed, the main body control section 200 advances the process to S210, and when determining that the time Tk has not elapsed, returns the process to S209. In S210, the main body control unit 200 controls the motor drive unit 50 to start deceleration of the rotation of the motor 32K, and ends the process.

In S250, the main body control unit 200 activates the subroutine (see FIG. 10) for performing the stop phase determination process described in the first embodiment. Then, the main body control unit 200 determines the stop phase θz for stopping the photosensitive drums 13C and 13K based on the processing result of the stop phase determination processing and based on the rotation phase of the photosensitive drums 13C and 13K at the timing t1c. In S251, the main body control unit 200 obtains the additional rotation phase φz_C for additionally rotating the photosensitive drum 13C by the motor 32C from the stop phase θz acquired in the process of S250. Then, the main body control unit 200 calculates the time Tc until the photosensitive drum 13C moves to the phase corresponding to the additional rotation phase φz_C, resets the timer, and starts the timer. The main body control unit 200 refers to the timer and determines whether the time Tc corresponding to the additional rotation phase φz_C has elapsed. When determining that the time Tc has elapsed, the body control unit 200 advances the process to S252, and when determining that the time Tc has not elapsed, returns the process to S251. In S252, the body control unit 200 controls the motor drive unit 50 to start decelerating the rotation of the motor 32C.

In S253, the body control unit 200 determines whether or not the timing t1k at which the rotation stop of the black motor 32K is permitted is reached. When determining that the timing t1k has been reached, the main body control unit 200 advances the process to S254, and when determining that the timing t1k has not been reached, the main body control unit 200 returns the process to S253. In S254, the main body control unit 200 determines whether or not the elapsed time from the stop permission timing t1c of the motor 32C is the timing after N rotations of the photosensitive drum 13. When determining that the elapsed time is the timing after N laps of the photosensitive drum 13, the main body control unit 200 advances the process to S255, and determines that the elapsed time is not the timing after N laps of the photosensitive drum 13. If so, the process returns to S254. In S255, the main body control unit 200 obtains the additional rotation phase φz_K for additionally rotating the photosensitive drum 13K by the motor 32K from the stop phase θz acquired in the process of S205. Then, the main body control unit 200 calculates the time Tk until the photosensitive drum 13K moves to the phase corresponding to the additional rotation phase φz_K, resets the timer, and starts the timer. The main body control unit 200 refers to the timer and determines whether the time Tk corresponding to the additional rotation phase φz_K has elapsed. When determining that the time Tk has elapsed, the body control unit 200 advances the process to S256, and when determining that the time Tk has not elapsed, returns the process to S255. In S256, the main body control unit 200 controls the motor drive unit 50 to start deceleration of the rotation of the motor 32K, and ends the process.

Although the number of the motors 32 for driving the photosensitive drums 13 is two in the present embodiment, the present embodiment is applicable to a configuration in which each of the photosensitive drums 13 has a motor 32 for driving the photosensitive drums 13. And is not limited by the number of motors 32.

As described above, in this embodiment, the deceleration start timing for stopping the rotations of the motors 32C and 32K is set to the timing separated by the revolution time Td of the photosensitive drum 13. As a result, even if there is a time difference in the timing at which the rotation stop of each motor 32 that drives the photosensitive drum 13 is permitted (the timing at which the rotation stop process can be started) after the image formation is completed, the rotation stop is started. The idle running time of the motor 32 can be shortened. As a result, the idling time of the photosensitive drum 13 can be shortened, and the abrasion of the photosensitive drum can be reduced.

As described above, according to this embodiment, it is possible to suppress the abrasion of the photosensitive drum.

In the first embodiment, the method of selecting the relative phase from the previous stop position of the photosensitive drum 13 from a plurality of candidates that are not divisors of 360° has been described. Since the relative phase is selected from a plurality of candidates, the phase at which the photosensitive drum 13 stops may be concentrated on the angle (phase) of a partial area depending on the print job of the user. A specific description will be given using the parameters used in the first embodiment. When a job is repeated in which the relative phase φyx from the previous stop phase θx has the value described in Table 2 below, the stop phase θx is between 164.6° and 240.7°. The phase (angle) will be used repeatedly. As a result, the stop phase of the photosensitive drum 13 is concentrated in a partial area where the phase is limited.

Here, Table 2 includes the previous stop phase θx of the photosensitive drum 13, the relative phase φyx from the previous stop phase θx, and the stop relative phase φz. The stop relative phase φz indicates the relative phase closest to the relative phase φyx from the previous stop phase θx selected from Table 1 of the first embodiment. In Table 2, when the previous stop phase θx is 180° and the relative phase φyx from the previous stop phase θx is 0°, 41.9° is selected from Table 1 as the relative phase φz for stop. It The stop phase θx to be stopped this time is 221.9° (=180°+41.9°). Then, when the stop phase θx stopped last time is 221.9° and the relative phase φyx from the previous stop phase θx is 300°, from Table 1, the relative phase φz for stop is 335.2°. Selected. Then, the current stop phase θx becomes 197.1° (=(221.9°+335.2°)−360°). As a result of the determination of the stop phase θx in this manner, the stop phase θx shown in Table 2 is repeatedly selected such that the minimum stop phase is 164.6° and the maximum stop phase is 240.7°. Has been done.

Therefore, in this embodiment, a plurality of relative phase candidate lists for stopping the photosensitive drum 13 are provided so that the stop phase of the photosensitive drum 13 is not concentrated in a part of the area, and the relative phase to be used is selected from the plurality of candidate lists. A method of randomly selecting the phase candidate list will be described. The configuration of the image forming apparatus 100, the configuration of the control unit, and the method of determining the stop phase of the photosensitive drum 13 driven by the motor 32 are the same as those in the first embodiment, and the description thereof is omitted here.

[Motor stop control sequence]
FIG. 13 is a flowchart showing a control sequence for determining the stop phase of the photosensitive drum 13C and the photosensitive drum 13K. The stop phase determination process shown in FIG. 10 of the first embodiment is partially performed according to the third embodiment. It is the changed flowchart. Note that the processing of FIG. 13 is executed by the main body control unit 200, as in the case of FIG. 10 of the first embodiment.

In S300, the main body controller 200 calculates the absolute phase θy_C of the photosensitive drum 13C based on the elapsed time from the timing when the phase sensor 36C detects the slit 35 to the timing t1k. In S301, the main body controller 200 calculates the absolute phase θy_K of the photosensitive drum 13K based on the elapsed time from the timing when the phase sensor 36K detects the slit 35 to the timing t1k. In S302, the main body control unit 200 generates an integer random number R of 1 to 5 by the random number generation unit 305 described above. The random number R is generated by using a known linear congruential method with the time data that the main body control unit 200 internally has at the timing of executing the process of S302 as a seed. The main body controller 200 has five relative phase candidate lists (groups of candidates) including a plurality of relative phase candidates for stopping the photosensitive drum 13 as the relative phase candidate table 302 of this embodiment. Table 3 shows an example of each relative phase candidate list.

In Table 3, five types of relative phase candidate lists from List 1 to List 5 are shown. In List 1, 12 relative phase candidates whose relative phase is an integer multiple of 31.1° are listed, and in List 2, 11 relative phase candidates whose relative phase is an integer multiple of 35.3° are listed. Therefore, in List 3, nine relative phase candidates whose relative phase is an integral multiple of 41.9° are listed. Similarly, in List 4, eight relative phase candidates whose relative phase is an integer multiple of 44.9° are listed, and in List 5, eight relative phase candidates whose relative phase is an integer multiple of 48.7° are listed. Listed.

In S303, the main body control unit 200 determines the relative phase candidate list to be used based on the random number R generated in S302. In S304, the main body control unit 200 determines the photosensitive drum 13C based on the absolute phase θx at the previous stop, the absolute phase θy_C calculated in S300, and the Rth relative phase candidate list determined in S303. The stop phase θz_C for stopping 13C is determined. In step S305, the main body control unit 200 selects the photosensitive drum 13K based on the absolute phase θx of the photosensitive drum 13K when stopped last time, the absolute phase θy_K calculated in step S301, and the Rth relative phase candidate list determined in step S303. The stop phase θz_K to be stopped is determined. The processing of S306 to S311 is the same as the processing of S124 to S129 of FIG. 10 of the first embodiment, and the description thereof is omitted here.

FIG. 14 shows the motor 32 in the case where there is one relative phase candidate list shown in the first embodiment (one table) and in the case where the relative phase candidate list is randomly selected from a plurality of relative phase candidate lists of the present embodiment (table random selection). It is the graph which plotted the stop phase. FIG. 14 is a plot of the rotation phase of the photosensitive drum 13 at the time of stop when the print job is repeated 50 times. The vertical axis of FIG. 14 shows the rotation phase at stop (unit: °), and the horizontal axis. Indicates the number of trials (unit: times). The triangular plots show the stop phase of the photosensitive drum 13 in the case of one table, and the circle plots show the stop phase of the photosensitive drum 13 in the case of table random selection. The plurality of relative phase candidate lists in this embodiment are based on the relative phase candidate list shown in Table 3. As can be seen from FIG. 14, by randomly selecting a candidate list from a plurality of candidate lists of stop phases, it is possible to vary the stop phases and reduce the possibility of locally abrading the photosensitive drum 13. You can

Further, in this embodiment, a method of randomly selecting the relative phase candidate list from a plurality of stop phase candidates is adopted. For example, the same effect can be obtained by a method of generating a random value of the candidate list of the stop phase when the photosensitive drum 13 is stopped without storing the candidate list of the stop phase in the memory such as the ROM in advance. Further, by adding an additional phase generated by using a random number to the stop phase θz, the same effect can be obtained by the method of varying the stop phase as in the present embodiment.

As described above, it is possible to prevent the stop phase from being concentrated on a part of the phases depending on the job pattern of the user.

As described above, according to this embodiment, it is possible to suppress the abrasion of the photosensitive drum.

13C photosensitive drum 13K photosensitive drum 200 main body control unit

Claims (9)

A plurality of photosensitive drums carrying images,
A plurality of motors for driving a plurality of the photosensitive drums,
Rotation phase detection means for detecting the rotation phase of the photosensitive drum driven by each of the motors,
Stop phase determining means for determining a stop phase for stopping the plurality of photosensitive drums,
Stop the plurality of photosensitive drums in the stop phase based on the rotation phase of the photosensitive drum detected by the rotation phase detection means and the stop phase of the photosensitive drum determined by the stop phase determination means. Control means for controlling the rotation stop of the motor in order to
Equipped with
The stop phase determination means can stop the photosensitive drums based on a stop phase at which the photosensitive drums were stopped last time and a rotational phase of the photosensitive drums at a timing when the rotation of the photosensitive drums can be stopped. The rotation phase at which the plurality of photosensitive drums are further rotated from the timing rotation phase is smaller than 180°, and the difference from the previously stopped stop phase is not a divisor of 360° this time. An image forming apparatus characterized by determining a stop phase to be stopped. A first motor for driving one of the plurality of photosensitive drums;
A second motor for driving the photosensitive drums other than the one photosensitive drum among the plurality of photosensitive drums;
Equipped with
The stop phase determining means excludes the one photosensitive drum and the one photosensitive drum except the one photosensitive drum at a first timing at which rotation of the photosensitive drum except the one photosensitive drum can be stopped. The stop phase to be stopped this time is determined based on a rotation phase of the photosensitive drum and a stop phase in which the photosensitive drum excluding the one photosensitive drum and the one photosensitive drum is stopped last time. The image forming apparatus according to claim 1. The control means stops the rotation of the first motor when the time for the one photosensitive drum to rotate from the rotation phase at the first timing to the stop phase to be stopped this time has elapsed, and stops the rotation of the first motor. The rotation of the second motor is stopped when a time period during which the photosensitive drums other than the photosensitive drums rotate from the rotation phase at the first timing to the stop phase at which the photosensitive drum is stopped this time is elapsed. Item 2. The image forming apparatus according to item 2. A first motor for driving one of the plurality of photosensitive drums;
A second motor for driving the photosensitive drums other than the one photosensitive drum among the plurality of photosensitive drums;
Equipped with
The second timing at which the rotation of the photosensitive drum except the one photosensitive drum can be stopped is earlier than the third timing at which the rotation of the one photosensitive drum can be stopped,
The stop phase determining means determines the rotation phase of the one photosensitive drum and the photosensitive drum excluding the one photosensitive drum at the third timing, and the one photosensitive drum and the one excluding the one photosensitive drum. The image forming apparatus according to claim 1, wherein the stop phase at which the photosensitive drum is stopped this time is determined based on the stop phase at which the photosensitive drum was stopped last time. The control unit causes the photosensitive drums other than the one photosensitive drum to rotate to the same rotational phase as the rotational phase at the first third timing after the second timing, and then stops this time. When the time to rotate to the stop phase has elapsed, the second motor is stopped, and when the time to rotate from the rotation phase at the third timing to the stop phase to be stopped this time has elapsed, The image forming apparatus according to claim 4, wherein the first motor is stopped. A first motor for driving one of the plurality of photosensitive drums;
A second motor for driving the photosensitive drums other than the one photosensitive drum among the plurality of photosensitive drums;
Equipped with
The second timing at which the rotation of the photosensitive drum except the one photosensitive drum can be stopped is earlier than the third timing at which the rotation of the one photosensitive drum can be stopped,
The stop phase determining means determines the rotation phase of the photosensitive drum excluding the one photosensitive drum and the one photosensitive drum at the second timing, and the rotational phase of the photosensitive drum excluding the one photosensitive drum and the one photosensitive drum. The image forming apparatus according to claim 1, wherein the stop phase at which the photosensitive drum is stopped this time is determined based on the stop phase at which the photosensitive drum was stopped last time. The control unit stops the second motor when a time period during which the photosensitive drums other than the one photosensitive drum rotate from the rotation phase of the second timing to the stop phase to be stopped this time has elapsed. , When the one photosensitive drum rotates to the same rotational phase as the rotational phase at the first second timing after the third timing and then rotates to the stop phase to be stopped this time, The image forming apparatus according to claim 6, wherein the first motor is stopped. The stop phase determining means has a storage means for storing a candidate group including a plurality of stop phase candidates for stopping the photosensitive drum,
The rotation phase of the one photosensitive drum at a timing at which the rotation of the one photosensitive drum can be stopped, and the rotation phase of the photosensitive drum excluding the one photosensitive drum are calculated, and the one photosensitive drum is calculated as described above. Stop phase having the smallest phase difference when further rotated from the rotation phase, and the smallest stop phase having the smallest phase difference when further rotating the photosensitive drum excluding the one photosensitive drum from the calculated rotation phase, Each is selected from the plurality of stop phases stored in the storage means,
When the stop phase of the selected one photosensitive drum is the same as the stop phase of the photosensitive drum excluding the selected one photosensitive drum, the selected one photosensitive drum is excluded. The stop phase of the photosensitive drum is determined as the stop phase to be stopped this time,
When the stop phase of the selected one photosensitive drum and the stop phase of the photosensitive drum other than the selected one photosensitive drum are different,
Position when the photosensitive drum excluding the one photosensitive drum is further rotated from the calculated rotational phase of the photosensitive drum excluding the one photosensitive drum to the stop phase of the selected one photosensitive drum. When the phase difference is smaller than the phase difference when rotating the one photosensitive drum to the stop phase of the photosensitive drum except the one photosensitive drum from the calculated rotational phase of the one photosensitive drum, The stop phase of the selected one of the photosensitive drums is determined to be the stop phase at which to stop this time,
Position when the photosensitive drum excluding the one photosensitive drum is further rotated from the calculated rotational phase of the photosensitive drum excluding the one photosensitive drum to the stop phase of the selected one photosensitive drum. In the case where the phase difference is equal to or more than the phase difference in the case where the one photosensitive drum is rotated to the stop phase of the photosensitive drum except the one photosensitive drum from the calculated rotational phase of the one photosensitive drum, The image according to any one of claims 2 to 7, wherein the stop phase of the photosensitive drums other than the selected one of the photosensitive drums is determined as a stop phase at which the photosensitive drum is stopped this time. Forming equipment. The storage means stores a plurality of the candidate groups,
The stop phase determining means selects one candidate group of the plurality of candidate groups based on the generated random number, and selects the one photosensitive drum and the one of the photosensitive drums excluding the one photosensitive drum. The image forming apparatus according to claim 8, wherein the stop phase to be stopped this time is selected from the plurality of stop phases included in the one candidate group.

Images