JP2006113200A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of efficiently adjusting the phase difference of a rotating cycle in a driving means for driving and rotating a plurality of image carriers in a short time and preventing color slurring and blotting from occurring on an output image with comparatively simple constitution. <P>SOLUTION: The image forming apparatus is equipped with the driving means for respectively driving and rotating a plurality of image carriers 1K and 1C by properly using a plurality of driving systems 60K and 60C, a plurality of detection means 80K and 80C for respectively detecting the rotation reference positions 63aK and 63aC of the image carriers 1K and 1C driven and rotated by the plurality of driving systems 60K and 60C, and a driving control means for driving and controlling the driving means 60K and 60C based on the result of detection by the plurality of detection means 80K and 80C so that the rotation reference positions 63aK and 63aC may be aligned with or approximate to each other. Then, the rotation reference positions 63aK and 63aC are set so as to correspond to the half round pitch of the image carriers 1K and 1C driven and rotated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof, and more particularly to a color image forming apparatus provided with a plurality of image carriers.

  2. Description of the Related Art Conventionally, in color image forming apparatuses such as color copying machines and color printers, driving means for driving a plurality of photosensitive drums (image carriers) separately in two driving systems have been used (for example, patent documents). 1).

  Specifically, in the image forming apparatus (tandem type color image forming apparatus), four photosensitive drums are arranged in parallel so as to face the intermediate transfer belt (or transfer belt). Black, cyan, magenta, and yellow images are formed on the four photosensitive drums, respectively. Then, the toner images of the respective colors formed on the four photosensitive drums are transferred on the intermediate transfer belt (or transfer material) in an overlapping manner.

  Here, the driving means for rotationally driving the four photosensitive drums includes a first driving system for rotationally driving one photosensitive drum related to black (black) image formation, and colors (cyan, magenta, yellow). It consists of two independent drive systems: a second drive system that rotationally drives three photosensitive drums related to image formation. In the image forming apparatus, only the first drive system is operated when black-only image formation (monochrome mode) is performed, and the first drive is performed when full-color image formation (full-color mode) is performed. The system and the second drive system are operated. In this way, an efficient driving means corresponding to the monochrome mode and the full color mode is achieved.

  On the other hand, Patent Document 2 and the like disclose a technology that is a tandem type color image forming apparatus and aims to form a color image without color misregistration. Specifically, the drive currents of the four motors that respectively drive the four photosensitive drums are detected, and the phase difference of the rotation cycle due to the eccentricity of the photosensitive drum is obtained. Then, the four motors are respectively controlled so as to eliminate the phase difference between the four photosensitive drums, thereby adjusting the number of rotations of the four photosensitive drums.

JP 2001-92194 A JP 2001-188395 A

  The above-described conventional technique cannot efficiently remove the phase difference of the rotation period in the driving means for rotating the plurality of image carriers in a short time. When such a phase difference of the rotation period occurs, color shift or blur occurs on the output image, which is a problem that cannot be ignored in a color image forming apparatus that requires high image quality.

Details are as follows.
The gear for rotationally driving the photosensitive drum (image carrier) is eccentric to some extent from the manufacturing limit. Therefore, when the photosensitive drum is driven to rotate, a phase of the rotation cycle is generated due to the eccentricity of the gear that rotates together with the photosensitive drum. When there is a phase difference because the phase of each photoconductive drum does not match the transfer timing to the intermediate transfer belt (or the transfer material), color misregistration or blurring corresponding to the phase difference occurs. It will occur.

  Here, when there is one drive system for driving the plurality of photosensitive drums, a gear is installed in the image forming apparatus main body in advance in the manufacturing stage so as not to cause a phase difference between the plurality of photosensitive drums. Can do. That is, by adjusting and assembling the eccentric positions of a plurality of gears, a drive system that does not cause a phase difference can be manufactured.

  However, in an image forming apparatus provided with a plurality of drive systems, even if the phase difference is adjusted at the manufacturing stage, a phase difference will occur depending on the usage pattern thereafter. Specifically, in the case of an image forming apparatus provided with the first drive system related to the black image formation and the second drive system related to the color image formation described above, every time the monochrome mode is switched to the full color mode, A phase difference will occur between the first drive system and the second drive system.

  On the other hand, in the technique disclosed in Patent Document 2 and the like, after detecting the driving currents of the four motors that respectively drive the four photosensitive drums to obtain the phase difference of the photosensitive drums, Each motor is controlled. Therefore, it can be expected to some extent that the phase difference between the four photoconductive drums is reduced and problems such as color misregistration are suppressed.

  However, in order to detect the phase difference between the four photosensitive drums, the technique disclosed in Patent Document 2 must rotate each photosensitive drum by at least one turn and detect the displacement of the driving current. Further, in order to increase the detection accuracy of the phase difference, it is necessary to rotate the photosensitive drum a plurality of times and average the detection results. As described above, the technology disclosed in Patent Document 2 and the like has not been satisfactory in response until the phase difference between the plurality of photosensitive drums is adjusted. In addition, the detection of the phase difference is complicated, and the entire apparatus may be expensive. Further, in the case of the image forming apparatus provided with the first drive system related to the black image formation and the second drive system related to the color image formation described above, the number of the photosensitive drums that are rotationally driven by the respective drive systems. Therefore, there is a possibility that phase detection becomes more complicated and efficient control cannot be performed.

  The present invention has been made to solve the above-described problems, and with a relatively simple configuration, efficiently adjusts the phase difference of the rotation period in a driving unit that rotationally drives a plurality of image carriers in a short time. It is an object of the present invention to provide an image forming apparatus that can be used and that does not cause color misregistration or bleeding on an output image.

  According to a first aspect of the present invention, an image forming apparatus includes a plurality of image carriers, a driving unit that divides the plurality of image carriers into a plurality of driving systems, and rotationally drives the plurality of image carriers, and the plurality of driving systems. A plurality of detection means for respectively detecting rotation reference positions of the image carriers that are driven to rotate, and the rotation reference positions of the plurality of image carriers are matched or approximated based on the detection results of the plurality of detection means. Drive control means for driving and controlling the drive means, and the rotation reference position is set to correspond to a half-circumferential pitch of the image carrier to be rotationally driven.

  According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the rotation reference position is set based on an eccentric position of a gear that rotates together with the image carrier. is there.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, each of the plurality of drive systems includes a gear that rotates together with the image carrier. The gear includes a semicircular arc-like standing portion serving as the rotation reference position, and the detection means is a photosensor that detects the presence or absence of the standing portion.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, each of the plurality of drive systems includes a DC brushless motor. .

  An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to any one of the first to fourth aspects, wherein the plurality of drive systems rotate an image carrier associated with black image formation. A first driving system for driving and a second driving system for rotationally driving an image carrier for forming an image of a color other than black are used.

  The image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to any one of the first to fifth aspects, wherein each of the plurality of drive systems has a rotational speed of an image carrier that is rotationally driven. The drive control means controls the rotation speeds of the plurality of drive systems so as to match or approximate the rotation reference positions of the plurality of image carriers.

  The present invention sets the rotation reference position of an image carrier that is rotationally driven by a plurality of drive systems so as to correspond to the half-circumferential pitch of the image carrier, detects the rotation reference position, and drives the plurality of drive systems. I have control. As a result, with a relatively simple configuration, the phase difference of the rotation period in the driving means for rotationally driving a plurality of image carriers can be adjusted efficiently and in a short time, and color misregistration and blurring occur on the output image. Thus, an image forming apparatus can be provided.

Embodiment.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIGS.
FIG. 1 is a block diagram showing a laser printer as an image forming apparatus, and FIG. 2 is an enlarged view showing an image forming unit thereof.

  As shown in FIG. 1, process cartridges 6Y, 6M, 6C, and 6K as image forming units corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged so as to face the intermediate transfer belt 8 of the intermediate transfer unit 15. It is installed side by side. The four process cartridges 6Y, 6M, 6C, and 6K installed in the apparatus main body 100 have substantially the same structure except that the toner colors used in the image forming process are different. The alphabet (Y, M, C, K) of the reference numerals for the photosensitive drum 1 and the primary transfer bias roller 9 is omitted.

  Referring to FIG. 2, in the process cartridge 6, a photosensitive drum 1 as an image carrier and a charging unit 4, a developing unit 5, and a cleaning unit 2 disposed around the photosensitive drum 1 are integrated. The apparatus body 100 is configured to be detachable. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process, charge eliminating process) is performed on the photosensitive drum 1 to form a desired toner image on the photosensitive drum 1. It will be.

  In the first embodiment, the photosensitive drum 1, the charging unit 4, the developing unit 5, and the cleaning unit 2 are integrated to form the process cartridge 6. It can also be installed detachably.

Referring to FIG. 2, the photosensitive drum 1 is rotationally driven in the clockwise direction in FIG. 2 by a drive system 60 (drive means). Then, the surface of the photosensitive drum 1 is uniformly charged at the position of the charging unit 4 (a charging process). Note that the drive system 60 that drives the photosensitive drum 1 is variably controlled by a control unit 70 that functions as a drive control unit. As a result, the rotational speed of the photosensitive drum 1 is varied.
Thereafter, the surface of the photosensitive drum 1 reaches the irradiation position of the laser beam L emitted from the exposure unit 7 (see FIG. 1), and an electrostatic latent image is formed by exposure scanning at this position. (It is an exposure process.)

Thereafter, the surface of the photosensitive drum 1 reaches a position facing the developing unit 5, and the electrostatic latent image is developed at this position to form a desired toner image (developing process).
Specifically, the developing unit 5 contains a developer G composed of toner and a carrier. The developer G in the developing unit 5 is adjusted so that the ratio (toner concentration) of the toner in the developer G detected by the toner concentration sensor 57 falls within a predetermined range. That is, according to the consumption of toner in the developing unit 5, toner is supplied from the toner transport pipe 43 into the developer containing unit 54 through the toner supply port 44.

  The toner transport pipe 43 communicates with the corresponding toner bottle among the toner bottles 32Y, 32M, 32C, and 32K installed in the bottle container 31 above the apparatus main body 100 with reference to FIG. As a result, the respective color toners are conveyed from the toner bottles 32Y, 32M, 32C, and 32K containing the respective color toners to the respective developing units 5 via the toner conveyance pipes 43.

  Thereafter, the toner replenished in the developer accommodating portion 54 circulates through the two developer accommodating portions 53 and 54 while being mixed and stirred together with the developer G by the second conveying screw 56 and the first conveying screw 55. (This is a movement in the direction perpendicular to the paper surface of FIG. 2). The toner in the developer G is attracted to the carrier by frictional charging with the carrier, and is carried on the developing roller 51 together with the carrier by the magnetic force formed on the developing roller 51.

  The developer G carried on the developing roller 51 is conveyed in the direction of the arrow in FIG. 2 and reaches the position of the doctor blade 52. Then, after the developer G on the developing roller 51 is regulated to an appropriate amount at this position, the developer G is conveyed to a position facing the photosensitive drum 1 (developing area). The toner is attracted to the latent image formed on the photosensitive drum 1 by the electric field formed in the development area.

  After the development process described above, the surface of the photosensitive drum 1 reaches a position facing the intermediate transfer belt 8 and the first transfer bias roller 9, and the toner image on the photosensitive drum 1 is transferred to the intermediate transfer belt 8 at this position. Transferred upward (this is a primary transfer step). At this time, a small amount of untransferred toner remains on the photosensitive drum 1.

Thereafter, the surface of the photoreceptor 1 reaches a position facing the cleaning unit 2, and untransferred toner remaining on the photoreceptor drum 1 at this position is collected by the cleaning blade 2a (cleaning process).
Finally, the surface of the photosensitive drum 1 reaches a position facing a neutralization unit (not shown), and the residual potential on the photosensitive drum 1 is removed at this position.
Thus, a series of image forming processes performed on the photosensitive drum 1 is completed.

  The image forming process described above is performed by each of the four process cartridges 6Y, 6M, 6C, and 6K. That is, referring to FIG. 1, laser light L based on image information is directed onto the photosensitive drums of the process cartridges 6Y, 6M, 6C, and 6K from the exposure unit 7 disposed below the process cartridge. Is irradiated. Specifically, the exposure unit 7 emits laser light L from a light source, and irradiates the photosensitive drum through a plurality of optical elements while scanning the laser light L with a polygon mirror that is rotationally driven. Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 8 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 8.

  Here, referring to FIG. 1, the intermediate transfer unit 15 includes an intermediate transfer belt 8 as an image carrier, four primary transfer bias rollers 9Y, 9M, 9C, and 9K, a secondary transfer backup roller 12, and a counter roller. 13, a tension roller 14, a cleaning unit 10, and the like. The intermediate transfer belt 8 is stretched and supported by the three roller members 12 to 14 and is endlessly moved in the direction of the arrow in FIG.

The four primary transfer bias rollers 9Y, 9M, 9C, and 9K respectively sandwich the intermediate transfer belt 8 with the photosensitive drums 1Y, 1M, 1C, and 1K to form a primary transfer nip. A transfer bias having a polarity opposite to the polarity of the toner is applied to the primary transfer bias rollers 9Y, 9M, 9C, and 9K.
The intermediate transfer belt 8 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 9Y, 9M, 9C, and 9K. In this way, the toner images of the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1K are primarily transferred while being superimposed on the intermediate transfer belt 8.

  Thereafter, the intermediate transfer belt 8 on which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 19. At this position, the secondary transfer backup roller 12 sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip. The color toner image formed on the intermediate transfer belt 8 is transferred onto a transfer material P such as transfer paper conveyed to the position of the secondary transfer nip. At this time, the untransferred toner that has not been transferred to the transfer material P remains on the intermediate transfer belt 8.

Thereafter, the intermediate transfer belt 8 reaches the position of the cleaning unit 10 for the intermediate transfer belt 8. At this position, the untransferred toner on the intermediate transfer belt 8 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed.

Here, the transfer material P transported to the position of the secondary transfer nip is transported from a paper feed unit 26 disposed below the apparatus main body 100 via a paper feed roller 27, a registration roller pair 28, and the like. It has been done.
Specifically, a plurality of transfer materials P such as transfer paper are stored in the paper supply unit 26 in a stacked manner. When the paper feed roller 27 is rotated in the counterclockwise direction in FIG. 1, the uppermost transfer material P is fed between the rollers of the registration roller pair 28.

  The transfer material P conveyed to the registration roller pair 28 is temporarily stopped at the position of the roller nip of the registration roller pair 28 that has stopped rotating. Then, the registration roller pair 28 is rotationally driven in synchronization with the color image on the intermediate transfer belt 8, and the transfer material P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the transfer material P.

Thereafter, the transfer material P on which the color image has been transferred at the position of the secondary transfer nip is conveyed to the position of the fixing unit 20. At this position, the color image transferred to the surface is fixed on the transfer material P by heat and pressure generated by the fixing roller and the pressure roller.
Thereafter, the transfer material P is discharged out of the apparatus through the rollers of the discharge roller pair 29. The transferred P discharged from the apparatus main body 100 by the discharge roller pair 29 is sequentially stacked on the stack unit 30 as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

Next, driving means for driving the photosensitive drum 1 as an image carrier will be described with reference to FIGS.
FIG. 3 is a cross-sectional view showing the state in which the photosensitive drum 1 of the process cartridge 6 is mounted on the drive system 60 of the apparatus main body 100 from above. In FIG. 3, the constituent members of the process cartridge 6 other than the photosensitive drum 1 are not shown.

  The image forming apparatus according to the first embodiment includes a first drive system 60K that rotates only the photosensitive drum 1K related to black image formation, three photosensitive drums 1Y related to color image formation, And a second drive system 60C that rotationally drives 1M and 1C.

Specifically, as shown in FIG. 3, each drive system 60 is mainly composed of a DC brushless motor 61, a drive gear 62, a gear 63, a drive shaft 64, a joint 65, and the like.
The DC brushless motor 61 is fixed to the side plate 90 of the apparatus main body 100 via a bracket. A drive gear 62 is provided on the rotating shaft of the DC brushless motor 61. The drive gear 62 meshes with a gear 63 that rotates integrally with the drive shaft 64. A joint 65 that engages with an engaging portion of the flange 11 provided on the end surface of the photosensitive drum 1 is inserted into the drive shaft 64.

The photosensitive drum 1 (process cartridge 6) is attached to and detached from the drive system 60 configured as described above by movement in the width direction (the vertical direction in FIG. 3).
Specifically, when the photosensitive drum 1 is mounted, the photosensitive drum 1 is inserted toward the drive system 60 into the apparatus main body 100 with the face plate 95 removed. At this time, the drive shaft 64 of the drive system 60 is inserted into the bearing of the photosensitive drum 1. Further, the claw member of the joint 65 in the drive system 60 is engaged with the engaging portion of the photosensitive drum 1 by the biasing force of the spring. Then, after the insertion of the photosensitive drum 1 is completed, the position of the photosensitive drum 1 with respect to the apparatus main body 100 is determined by fixing the face plate 95 to the side plate 90.

Thus, the drive system 60 to which the photosensitive drum 1 is mounted rotates the photosensitive drum 1 in a predetermined direction. Specifically, the controller 70 controls the power supply unit (not shown) to supply a predetermined drive current to the DC brushless motor 61. When the DC brushless motor 61 is operated, a driving force is transmitted from the driving gear 62 to the gear 63. Further, the driving force is transmitted from the joint 65 of the driving shaft 64 to the engaging portion 11 so that the photosensitive drum 1 is rotationally driven.
A second drive system 60C that rotationally drives the three photosensitive drums 1Y, 1M, and 1C is driven from a drive gear 62 installed in one DC brushless motor 61 via a gear train (not shown). Thus, the driving force is transmitted to the gears 63 respectively installed on the shafts of the three photosensitive drums 1Y, 1M, and 1C.

  Here, with reference to FIG. 4, in the first drive system 60K, the gear 63K that rotates together with the black photosensitive drum 1K is provided with a semi-arc-shaped upright portion 63aK (filler). Similarly, in the second drive system 60C, a gear 63C that rotates together with the color photoconductor drums 1Y, 1M, and 1C (in the present embodiment, it is provided on the axis of the cyan photoconductor drum 1C). ) Is also provided with a semicircular upright portion 63aC (filler). FIG. 4 is a schematic front view of the first drive system 60K and the second drive system 60C as viewed from the gear 63 side (a plane parallel to the paper surface of FIGS. 1 and 2).

3 and 4, upright portions 63aK and 63aC provided on gears 63K and 63C stand up toward the outside of drive systems 60K and 60C. In the apparatus main body 100, photosensors 80K and 80C as detection means are fixed at positions facing the upright portions 63aK and 63aC. The photosensors 80K and 80C include a light emitting element such as a light emitting diode and a light receiving element such as a photodiode, and detects the presence or absence of the upright portions 63aK and 63aC between the light emitting element and the light receiving element. Specifically, when the light emitted from the light emitting element reaches the light receiving element, it is determined that there are no standing parts 63aK and 63aC, and when the light emitted from the light emitting element does not reach the light receiving element, the standing part is raised. It is determined that the parts 63aK and 63aC are present.
In this embodiment, transmissive photosensors are used as the photosensors 80K and 80C, but reflective photosensors can be used instead.

  Here, the standing portions 63aK and 63aC provided in the gears 63K and 63C are formed so as to correspond to the half-circumferential pitch of the photosensitive drums 1K and 1C (or gears 63K and 63C) that are rotationally driven. That is, since the gears 63K and 63C rotate together with the photosensitive drums 1K and 1C, the upright portions 63aK and 63aC are formed in an arc shape in a range of 180 ° from the center of the gears 63K and 63C.

Furthermore, the upright portions 63aK and 63aC are installed with reference to the eccentric positions of the gears 63K and 63C. For example, the standing parts 63aK and 63aC are formed so that the centers of the arcs of the standing parts 63aK and 63aC coincide with the eccentric directions of the gears 63K and 63C. The standing portions 63aK and 63aC serve as rotation reference positions of the photosensitive drums 1K and 1C that are rotationally driven.
The upright portions 63aK and 63aC are preferably configured to be detachable from the gears 63K and 63C. Thereby, the upright portions 63aK and 63aC can be installed based on the result of the eccentricity inspection after the gears 63K and 63C are molded, and the rotation reference position can be set optimally.

  On the other hand, the two photosensors 80K and 80C are arranged corresponding to the transfer timing to the intermediate transfer belt 8 in both the photosensitive drums 1K and 1C. Specifically, the photosensor 80K of the first drive system 60K is both photoconductors with respect to the installation position of the photosensor 80C of the second drive system 60C (the position indicated by the broken line in FIG. 4). The drums 1 </ b> K and 1 </ b> C are arranged at positions in the reverse rotation direction (counterclockwise direction) by the distance X between the axes. As a result, when the standing parts 63aK and 63aC serving as the rotation reference positions simultaneously pass through the positions of the photosensors 80K and 80C, the phases caused by the eccentricity of the gears 63K and 63C are matched.

Next, drive control for the drive means described above will be described with reference to FIGS.
FIG. 5 is a chart showing an example of signals detected by the photosensors 80K and 80C of the two drive systems 60K and 60C. When there is a phase difference due to gear eccentricity between the first drive system 60K and the second drive system 60C (for example, when switching from the monochrome mode to the full color mode), as shown in FIG. A similar phase difference occurs between the output S1 (black photoconductor sensor signal) of the first photosensor 80K and the output S2 (color photoconductor sensor signal) of the second photosensor 80C. In FIG. 5, the horizontal axis indicates the rotation angle of the gear 63 (or the photosensitive drum 1).

  Referring to FIG. 5, when drive control is started (position Q), from when one of the two photosensors 80K and 80C is switched to when the other signal is switched. Time (corresponding to the angular difference A−α) is detected. Here, the switching of the signals of the photosensors 80K and 80C corresponds to the detection of the standing parts 63aK and 63aC as the rotation reference positions described above.

Then, the number of rotations of each of the photosensitive drums 1K and 1C is increased or decreased according to the time when the detected signal is switched. For example, referring to FIG. 6, when the detection time is detected as 80 msec (angle difference is 45 °), the rotation speed of the black photosensitive drum 1K is reduced by 10%, and the color photosensitive drum The rotational speed of 1C (the other photosensitive drums 1M and 1Y also follow) is accelerated by 10%. FIG. 6 shows the relationship between the detection time (angle difference A−α) and the rotational speed fluctuation rate of each of the photosensitive drums 1K and 1C.
Then, based on FIG. 6, the two drive systems 60K and 60C are driven and controlled so that the detection time is within a range of ± 40 msec (angle difference is ± 22.5 °). That is, the two drive systems 60K and 60C are driven and controlled so that the rotation reference positions (stands 63aK and 63aC) of both the gears 63K and 63C match or approximate.

In the present embodiment, the upright portions 63aK and 63aC are formed in a semicircular arc shape, and the rotation reference position is made to correspond to the half-circumferential pitch of the photosensitive drums 1K and 1C. In the meantime, the rotation reference position can be detected in a short time.
Broken lines S1 'and S2' shown in FIG. 5 indicate photosensor outputs when the standing parts 63aK and 63aC are formed not in a 180 ° arc shape but in an arc shape with a minimum angle. In such a case, as indicated by broken lines S1 ′ and S2 ′, the time (angle A ′) from the start of control to the first detection of signal switching is longer than the time for half rotation of the photosensitive drum. Sometimes. Therefore, it becomes difficult to align the rotation reference position in a short time.

  As described above, in the present embodiment, the rotation reference positions of the photosensitive drums 1K and 1C that are rotationally driven by the plurality of drive systems 60K and 60C correspond to the half-circumferential pitch of the photosensitive drums 1K and 1C. The plurality of drive systems 60K and 60C are driven and controlled by setting the rotation reference position. Accordingly, the phase difference of the rotation period in the driving unit that rotationally drives the plurality of photosensitive drums 1K and 1C can be efficiently adjusted in a short time with a relatively simple and inexpensive configuration. That is, it is possible to provide an image forming apparatus that does not cause color shift or blur on the output image.

In the present embodiment, since the DC brushless motor 61 is used as a drive source of the drive systems 60K and 60C for drive control, it is possible to perform variable rotation speed control with high accuracy in a short time with low noise.
Further, in the present embodiment, the two drive systems 60K and 60C are configured so as to be capable of variable speed control independently of each other, and therefore, compared to the case where variable speed control is performed for only one drive system. The time for variable control is shortened. In addition, a problem that the rate of change in the rotational speed of only one drive system increases and damage to the photosensitive drum 1 and the intermediate transfer belt 8 increases can be prevented.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating the vicinity of an image forming unit in the image forming apparatus. 2 is a cross-sectional view showing the vicinity of a drive system in the image forming apparatus. FIG. It is the schematic which shows two drive systems. It is a chart which shows the signal detected with the photo sensor of two drive systems. It is a table | surface which shows the rotational speed fluctuation rate of two drive systems based on the detection result of a photosensor.

Explanation of symbols

1, 1Y, 1M, 1C, 1K photosensitive drum (image carrier),
6, 6Y, 6M, 6C, 6K process cartridge (imaging part),
60 drive system, 60K first drive system, 60C second drive system,
61 DC brushless motor, 62 drive gear,
63, 63K, 63C gear,
63a, 63aK, 63aC Standing part, 70 Control part,
80, 80K, 80C photosensor (detection means),
90 side plate, 95 face plate,
100 Image forming apparatus main body (apparatus main body).

Claims (6)

A plurality of image carriers;
Drive means for rotating the plurality of image carriers in a plurality of drive systems, respectively;
A plurality of detection means for detecting rotation reference positions of the image carrier that is rotationally driven by the plurality of drive systems;
Drive control means for driving and controlling the drive means so that rotation reference positions of the plurality of image carriers coincide or approximate based on detection results of the plurality of detection means,
The image forming apparatus, wherein the rotation reference position is set so as to correspond to a half-circumferential pitch of the image carrier to be rotationally driven. The image forming apparatus according to claim 1, wherein the rotation reference position is set based on an eccentric position of a gear that rotates together with the image carrier. Each of the plurality of drive systems includes a gear that rotates together with the image carrier,
The gear includes a semicircular arc-like standing portion serving as the rotation reference position,
The image forming apparatus according to claim 1, wherein the detection unit is a photosensor that detects the presence / absence of the upright portion. The image forming apparatus according to claim 1, wherein each of the plurality of drive systems includes a DC brushless motor. The plurality of drive systems include a first drive system that rotationally drives an image carrier associated with black image formation, a second drive system that rotationally drives an image carrier associated with image formation of a color other than black, The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Each of the plurality of drive systems is configured to be able to vary the number of rotations of the image carrier to be rotationally driven,
6. The drive control unit according to claim 1, wherein the number of rotations by the plurality of drive systems is varied to control the rotation reference positions of the plurality of image carriers so as to match or approximate. The image forming apparatus according to any one of the above.

Images