JP2007047629A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve image quality in an image formed by an electrophotographic type image forming apparatus. <P>SOLUTION: Each image forming unit 10Y, 10M, 10C and 10K is provided with photoreceptor drums 11Y, 11M, 11C and 11K and rotating driving apparatuses 60Y, 60M, 60C and 60K. Each rotating driving apparatus 60Y, 60M, 60C and 60K is provided with driving motors 61Y, 61M, 61C, 61K and deceleration mechanisms 63Y, 63M, 63C and 63K. Each driving motor 61Y, 61M, 61C, 61K is controlled by a control part 40. The driving motors 61Y, 61M, 61C are stepping motors and the driving motor 61K is an outer rotor type DC brushless motor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, or a multifunction machine of these.

In an image forming apparatus such as a printer or a copying machine using an electrophotographic method, the surface of a rotating image carrier made of an organic photoconductor is charged by a charger and then exposed by a ROS (Raster Output Scanner). An electrostatic latent image is formed on the surface of the image carrier by an electrophotographic process. The electrostatic latent image formed on the surface of the image carrier is developed with a developing device to form a toner image. Next, the toner image is electrostatically transferred to a recording medium (such as paper) by a transfer device, and image formation is performed by fixing the toner image to the recording medium by a fixing device, for example.
Such an image forming apparatus includes a motor and a speed reducer that decelerates the rotation of the motor as a rotational drive device for rotating a photosensitive drum as an image carrier with relatively low speed and high accuracy. . The full-color image forming apparatus has such a rotation driving device for each of the photosensitive drums of yellow (Y), magenta (M), cyan (C), and black (K). That is, each photosensitive drum is driven to rotate independently from the other photosensitive drums.

Here, the motor constituting the rotation driving device is required to drive each photosensitive drum at a stable rotation speed. As a motor that satisfies such conditions, it is conventionally known to use an outer rotor type motor (see, for example, Patent Document 1).
In this patent document 1, since the outer rotor type motor is used, the inertia moment of the rotor is increased as the radius of the rotor is larger than that of the inner rotor type. This makes it difficult for rotational fluctuations caused by the motor to be transmitted to the photosensitive drum. As described above, when the outer rotor type motor is used as a rotation drive source for rotating the rotating drum, the rotation speed of the photosensitive drum is stabilized and the rotation unevenness is reduced, so that there is an effect of reducing banding. Therefore, Patent Document 1 proposes to employ an outer rotor type motor as a rotational drive source for all the photosensitive drums.

Japanese Patent Laid-Open No. 2002-171721 (5th page, FIG. 1)

However, using an outer rotor type motor has the advantage that it contributes to the stabilization of the rotational speed of the photosensitive drum, but the rotational angle at the time of starting and stopping the photosensitive drum tends to fluctuate depending on the load torque. There is.
That is, when trying to stop the rotating photosensitive drum, the outer rotor type motor is unlikely to stop due to the inertial force of the motor. For this reason, if the average load torque of the photosensitive drum is light, the stop position of the photosensitive drum varies greatly due to slight variations in the load torque.
If the stop positions in the circumferential direction of the respective photosensitive drums of yellow (Y), magenta (M), cyan (C), and black (K) vary, the phase relationship between the photosensitive drums changes each time. End up. If there is such a change in the phase relationship, there is a complicated sensitivity unevenness of the photosensitive drum as exemplified in JP-A-10-145596 (page 11, FIG. 13). As a countermeasure against such sensitivity unevenness, it is conceivable to perform density correction by forming a reference patch in a single color. However, when the colors are overlapped, it is difficult to correct the density unevenness with high accuracy, and the color is inevitably changed.
Due to such technical circumstances, in an electrostatic color image forming apparatus, when color stability of a color image similar to that of an offset printing machine is required, the phase relationship between the photosensitive drums must always be the same.

In this respect, since the rotation angle of the stepping motor is accurately controlled according to the number of input pulses, the rotation angle at the time of start and stop can be made constant regardless of the load torque. As described above, the stepping motor has advantages not found in the outer rotor type motor. However, using a stepping motor as a rotational drive source for all the photoconductive drums is concerned about another problem. That is, the stepping motor is an inner rotor type motor and has a demerit that the rotational speed tends to be unstable because the inertia is smaller than that of the outer rotor type motor.
As described above, it is desired that the rotational angle of the photosensitive drum is accurately controlled while stabilizing the rotational speed of the photosensitive drum, so that the phase relationship between the photosensitive drums is always constant.

  The present invention has been made to solve the technical problems as described above, and an object thereof is to further improve the image quality of an image formed by an electrophotographic image forming apparatus. .

As a result of intensive studies by the present inventors, an outer rotor having a rotor outside a stator as a drive source for rotating the photosensitive drum of each color in one image forming apparatus It has been found that this object can be achieved by adopting either an (outer rotor) type motor or an inner rotor type motor having a rotor inside the stator, depending on the color. In other words, for this purpose, the image forming apparatus to which the present invention is applied includes a plurality of types of motors having different characteristics as rotational drive sources of the photosensitive drums of the respective colors.
Specifically, an image forming apparatus to which the present invention is applied rotates by receiving a driving force, a first image carrier that carries a black toner image, and a driving force applied to the first image carrier. A first driving source to be supplied; a second image carrier that rotates by receiving a driving force and carries a toner image other than black; and a second driving that supplies the second image carrier with a driving force. And a transfer means for transferring a toner image carried on the first image carrier and the second image carrier onto a sheet, wherein the first drive source is an outer rotor type motor, The drive source is an inner rotor type motor.
The apparatus may further include a decelerating unit that is interposed between the second image carrier and the second drive source and decelerates the output from the second drive source. This speed reduction means is a roller speed reduction means for reducing the speed using a plurality of rollers, and a planetary roller speed reducer or a traction speed reducer can be used.
The first drive source is preferably an outer rotor type DC brushless motor. The second drive source is preferably a stepping motor.
The first image carrier is more preferably configured to have an outer diameter larger than that of the second image carrier.

From another point of view, an image forming apparatus to which the present invention is applied has an image forming unit including an image carrier that rotates by receiving a driving force and carries a toner image, and a drive source that drives the image carrier. , M, C, and K, an image forming apparatus that rotates by receiving a driving force and primarily transfers a toner image carried on each of the image forming means, and an intermediate transfer body And a secondary transfer body that transfers the toner image that has been primarily transferred to the sheet, and the drive source of the image forming means that forms the K toner image is an outer rotor type motor, and the Y, M, and C toner images The drive source of the image forming means for forming the is an inner rotor type motor.
The intermediate transfer member can be driven at a peripheral speed faster than the peripheral speed of the image carrier included in each of the plurality of image forming units.
Position control means for controlling the position of the drive source in synchronism with the same reference pulse so that the phase of the image carrier carrying the toner images of Y (yellow), M (magenta), and C (cyan) is not shifted. Furthermore, it can be characterized by including. It further includes a detector for detecting the phase of at least one of the image carriers that carry Y (yellow), M (magenta), and C (cyan) toner images. it can.

  According to the present invention, it is possible to further improve the image quality of an image formed by an electrophotographic image forming apparatus.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. The image forming apparatus shown in FIG. 1 is a so-called tandem type image forming apparatus, for example, a plurality of image forming units 10 (10Y, 10M, 10C, 10K) on which toner images of respective color components are formed by electrophotography. And an endless intermediate transfer belt (toner image carrier) 15 for sequentially transferring (primary transfer) and holding each color component toner image formed by each image forming unit 10, and transferring the toner image onto the intermediate transfer belt 15. A secondary transfer device 20 that collectively transfers (secondary transfer) the superimposed image to a sheet P as a transfer material, and a fixing device 30 that fixes the secondary transferred image on the sheet P are provided. Moreover, it has the control part 40 which controls operation | movement of each apparatus (each part).

In this embodiment, each image forming unit 10 (10Y, 10M, 10C, 10K) is provided with an electrophotographic device around the photosensitive drums 11Y, 11M, 11C, 11K rotating in the direction of arrow A. Yes. That is, the charger 12 that charges the photosensitive drums 11Y, 11M, 11C, and 11K, and the laser exposure unit 13 that writes an electrostatic latent image on the photosensitive drums 11Y, 11M, 11C, and 11K (FIG. 1). And a developing device 14 that accommodates each color component toner and visualizes the electrostatic latent images on the photosensitive drums 11Y, 11M, 11C, and 11K with the toner. Has been. Further, the primary transfer roll 16 that transfers the color component toner images formed on the photosensitive drums 11Y, 11M, 11C, and 11K to the intermediate transfer belt 15, and the residual toner on the photosensitive drums 11Y, 11M, 11C, and 11K A drum cleaner 17 to be removed is disposed.
These image forming units 10 are arranged in the order of yellow (Y color), magenta (M color), cyan (C color), and black (K color) from the upstream side of the intermediate transfer belt 15. In the present embodiment, as shown in FIG. 1, the outer diameter of the photosensitive drum 11K of the image forming unit 10K is equal to the outer diameter of the photosensitive drums 11Y, 11M, and 11C of the image forming units 10Y, 10M, and 10C. Bigger than. The outer diameters of the photosensitive drums 11Y, 11M, and 11C of the image forming units 10Y, 10M, and 10C are substantially the same.

  The intermediate transfer belt 15 as an intermediate transfer member is a film-like endless belt in which an appropriate amount of a conductive agent such as carbon black is contained in a resin such as polyimide or polyamide. The intermediate transfer belt 15 can be circulated and rotated (rotated) at a predetermined speed in the direction of arrow B shown in FIG. 1 by various rolls. As these various rolls, there are provided a drive roll 31 that is driven by a motor (not shown) to rotate the intermediate transfer belt 15 and a function of giving a constant tension to the intermediate transfer belt 15 and preventing meandering of the intermediate transfer belt 15. Tension roll 32. As other various rolls, there are a driven roll 35 that supports the intermediate transfer belt 15 and applies a constant tension, and a backup roll (support roll) 28 provided in a secondary transfer portion.

  In the IBT module 18 provided to face each of the photosensitive drums 11Y, 11M, 11C, and 11K, each primary transfer roll 16 provided inside the intermediate transfer belt 15 that extends substantially linearly has a toner charging polarity and A reverse polarity voltage is applied. Thus, the toner images on the respective photosensitive drums 11Y, 11M, 11C, and 11K are sequentially electrostatically attracted to the intermediate transfer belt 15, and a superimposed toner image is formed on the intermediate transfer belt 15. .

  The secondary transfer device 20 includes a secondary transfer roll 22 disposed on the toner image carrying surface side of the intermediate transfer belt 15 and a backup roll 28 as an opposite roll. That is, the secondary transfer roll 22 is disposed in pressure contact with the backup roll 28 with the intermediate transfer belt 15 interposed therebetween. By the secondary transfer device 20 configured as described above, the visible image that has been multiplex-transferred onto the intermediate transfer belt 15 is transferred to a sheet P conveyed from a sheet tray 50 described later.

A belt cleaner 37 that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15 is provided on the downstream side of the backup roll 28 so as to be able to contact and separate. .
On the other hand, on the upstream side of the secondary transfer position in the secondary transfer device 20, a reference sensor (home position sensor) 39 that generates a reference signal serving as a reference for taking the image forming timing in each image forming unit 10 is arranged. ing. The reference sensor 39 recognizes a predetermined mark provided on the back side of the intermediate transfer belt 15 to generate a reference signal, and each image forming unit 10 receives the instruction from the control unit 40 based on the recognition of the reference signal. It is configured to start image formation.
Further, an image density sensor 38 for adjusting image quality is disposed on the downstream side of the black image forming unit 10K.
In the present embodiment, a paper tray 50 for storing the paper P is provided. The paper P accumulated in the paper tray 50 is taken out at a predetermined timing and conveyed to a secondary transfer position by the secondary transfer device 20. When the secondary transfer is performed at the secondary transfer position, the paper P is conveyed to the fixing device 30.

  Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. Image data output from an image reading device (IIT) (not shown), a personal computer (PC) (not shown), or the like is input to the image forming apparatus shown in FIG. In the image forming apparatus, after predetermined image processing is performed by an image processing apparatus (IPS) (not shown), an image forming operation is performed by the image forming unit 10 or the like. In the image processing apparatus (IPS), the input reflectance data is subjected to image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, and movement editing. . The image data subjected to the image processing is converted into color material gradation data of four colors of yellow (Y), magenta (M), cyan (C), and black (K), and is output to the laser exposure unit 13. .

In the laser exposure device 13, for example, an exposure beam Bm emitted from a semiconductor laser is applied to the photosensitive drums 11Y, 11M, 11C of the image forming units 10Y, 10M, 10C, 10K according to the input color material gradation data. , 11K. In the photosensitive drums 11Y, 11M, 11C, and 11K of the image forming units 10Y, 10M, 10C, and 10K, the surface is charged by the charger 12, and then the surface is scanned and exposed by the laser exposure unit 13, thereby electrostatic latent images. Is formed. The formed electrostatic latent image is developed as a toner image of each color of yellow, magenta, cyan, and black in each of the image forming units 10Y, 10M, 10C, and 10K.
The toner images formed on the photosensitive drums 11Y, 11M, 11C, and 11K of the image forming units 10Y, 10M, 10C, and 10K are in contact with the photosensitive drums 11Y, 11M, 11C, and 11K and the intermediate transfer belt 15. The image is transferred onto the intermediate transfer belt 15 at the primary transfer portion. More specifically, in the primary transfer portion, the primary transfer roll 16 applies a voltage having a polarity opposite to the charged polarity of the toner to the base material of the intermediate transfer belt 15, and the unfixed toner image is transferred to the surface of the intermediate transfer belt 15. Are sequentially superposed on each other to perform primary transfer. The unfixed toner image primarily transferred in this way is conveyed to the secondary transfer device 20 as the intermediate transfer belt 15 rotates.

Here, the peripheral speed of the intermediate transfer belt 15 is higher than the peripheral speed of the photosensitive drums 11Y, 11M, 11C, and 11K at the primary transfer portion where the photosensitive drums 11Y, 11M, 11C, and 11K contact the intermediate transfer belt 15. Also, the rotational speeds of the drive roll 31 and the photosensitive drums 11Y, 11M, 11C, and 11K are controlled so as to be slightly faster. When the speed is controlled in this way, the photosensitive drum 11 acts as a brake on the intermediate transfer belt 15 by the electrostatic attraction force. By such an action, if the rotation speed of the photosensitive drum 11K of the image forming unit 10K is stable, the rotation of the intermediate transfer belt 15 is also stabilized, and furthermore, the photosensitive members of the image forming units 10Y, 10M, and 10C. The rotation of the drums 11Y, 11M, and 11C is also stabilized.
By ensuring stable rotation of the photosensitive drum 11K in this manner, the rotational speeds of the other photosensitive drums 11Y, 11M, and 11C and the intermediate transfer belt 15 can be stabilized.
In the rotational direction of the intermediate transfer belt 15, the photosensitive drum 11Y is positioned on the upstream side, and the photosensitive drum 11K is positioned on the downstream side. Further, the photosensitive drum 11K is disposed at a position farthest from the driving roll 31 for driving the intermediate transfer belt 15 than the other photosensitive drums 11Y, 11M, and 11C. That is, the photosensitive drum 11K is positioned on the side where the intermediate transfer belt 15 is pulled by the drive roll 31.

In the secondary transfer device 20, the secondary transfer roll 22 is pressed against the backup roll 28 in a state where the intermediate transfer belt 15 is sandwiched therebetween in accordance with the timing of the secondary transfer onto the paper P. At this time, the sheet P conveyed at the same timing is sandwiched between the intermediate transfer belt 15 and the secondary transfer roll 22. Then, an unfixed toner carried on the intermediate transfer belt 15 at a secondary transfer position where a transfer electric field is formed as a counter electrode on the secondary transfer roll 22 and is pressed by the secondary transfer roll 22 and the backup roll 28. The image is electrostatically transferred onto the paper P.
Thereafter, the sheet P on which the toner image has been electrostatically transferred is conveyed as it is while being peeled off from the intermediate transfer belt 15 by the secondary transfer roll 22. Then, the speed is changed in accordance with the optimum transport speed in the fixing device 30, and the paper P is transported to the fixing device 30. The unfixed toner image on the paper P is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 30. The paper P on which the fixed image is formed is discharged to the outside of the apparatus by a discharge roll (not shown).
On the other hand, after the transfer to the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit as the intermediate transfer belt 15 rotates, and is removed from the intermediate transfer belt 15 by the belt cleaner 37. Removed.

Next, the photosensitive drum 11 (11Y, 11M, 11C, 11K) and the rotation driving device 60 (60Y, 60M, 60C, 60K) for driving the photosensitive drum 11 will be described with reference to FIG.
FIG. 2 is a block diagram showing the relationship among the photosensitive drum 11, the rotation driving device 60, and the control unit 40.
As shown in FIG. 2, each of the image forming units 10Y, 10M, 10C, and 10K includes photosensitive drums 11Y, 11M, 11C, and 11K, and rotation driving devices 60Y, 60M, 60C, and 60K. Each of the rotational drive devices 60Y, 60M, 60C, and 60K includes drive motors 61Y, 61M, 61C, and 61K and speed reduction mechanisms 63Y, 63M, 63C, and 63K. Each of the drive motors 61Y, 61M, 61C, 61K is controlled by the control unit 40.
With such a configuration, the drive motors 61Y, 61M, 61C, and 61K transmit the driving force to the speed reduction mechanisms 63Y, 63M, 63C, and 63K according to the control from the control unit 40. In the speed reduction mechanisms 63Y, 63M, 63C, and 63K, the speed is reduced to a predetermined rotational speed and transmitted to the photosensitive drums 11Y, 11M, 11C, and 11K.
Here, the drive motors 61Y, 61M, and 61C are inner rotor type stepping motors, and the drive motor 61K is an outer rotor type DC brushless motor. That is, two types of motors are provided. The photosensitive drums 11Y, 11M, and 11C on which yellow, magenta, and cyan toner images are formed are driven by a stepping motor, and the photosensitive drum 11K on which a black toner image is formed are driven by an outer rotor type DC brushless motor. Is done.

Next, the rotational drive devices 60Y, 60M, and 60C will be described with reference to FIGS. As described above, the rotational drive devices 60Y, 60M, and 60C have substantially the same basic configuration. Therefore, the rotational drive devices 60Y, 60M, and 60C will be collectively described as the rotational drive device 60. The rotary drive device 60K can take a structure as shown in Patent Document 1 described above, and a description thereof is omitted here. The drive motors 61Y, 61M, 61C and the drive motor 61K are of different types, but these may be collectively referred to as the drive motor 61.
FIGS. 3 and 4 are configuration diagrams for explaining components constituting the rotary drive device 60, and FIG. 4 omits the illustration of the housing 620. FIG. 5 is a longitudinal sectional view of the input coupling 62 that constitutes a part of the rotary drive device 60.
Although not shown in detail, the photosensitive drums 11Y, 11M, 11C, and 11K have a drive shaft 110 (see FIG. 6) that penetrates the drum body in the width direction. Both ends of the drive shaft 110 (see FIG. 6) are rotatably held by a frame F (see FIG. 6) of the image forming apparatus via bearings.

3 and 4 is arranged outside the frame F (see FIG. 6) of the image forming apparatus. The rotary drive device 60 includes a drive motor 61 as a drive source for the photosensitive drums 11Y, 11M, and 11C, an input coupling 62 attached to the drive motor 61, and a deceleration connected via the input coupling 62. And a mechanism 63.
The drive motor 61 includes a motor housing 610, a joint flange 611 provided at one end of the motor housing 610, an output shaft 612 (see FIG. 4) disposed so as to protrude from the joint flange 611 side, a motor A lead wire joint portion 613 provided in the housing 610.

The speed reduction mechanism 63 includes a housing 630 (see FIG. 3), a solar roll 631 to which rotation of the drive motor 61 is input, a plurality (for example, three) of planetary rolls 632 disposed around the solar roll 631, And a carrier 633 that supports a plurality of planetary rolls 632. Further, the speed reduction mechanism 63 has an output drive shaft 634 that is provided coaxially with the sun roll 631 and outputs rotation reduced by the planetary roll 632. The solar roll 631, the planetary roll 632, the carrier 633, and the output drive shaft 634 are stored inside the housing 630 (see FIG. 3). As described above, the planetary roller speed reduction mechanism or the traction speed reduction mechanism is employed as the speed reduction mechanism 63.
As shown in FIG. 3, the housing 630 of the speed reduction mechanism 63 has a hollow cylindrical protrusion 635 into which the input coupling 62 can be inserted and received from one end side thereof. The housing 630 is fastened with a fastener (for example, a screw or the like) (not shown) between the two in a state where the tip of the cylindrical protruding portion 635 is in contact with the joining flange 611 of the motor housing 610.

As shown in FIGS. 4 and 5, the input coupling 62 is disposed so as to protrude outward toward the reduction mechanism 63 on the outer peripheral surface of the thick-walled cylindrical coupling body 621 and the coupling body 621. And a disc-shaped flywheel 622.
As shown in FIG. 4, the input coupling 62 is incorporated in advance on the speed reduction mechanism 63 side. Further, the input coupling 62 can be formed of, for example, S45C (carbon steel for mechanical structure).

As shown in FIG. 5, the coupling body 621 has a connection hole 621 a having a hole diameter d ₁ into which the output shaft 612 of the drive motor 61 is fitted and a hole diameter d ₂ in which the sun roll 631 of the speed reduction mechanism 63 is fitted. A connecting hole 621b is formed. The coupling main body 621 is provided with a female screw 621c that penetrates from the outer peripheral portion to the coupling hole 621a. And in the coupling main body 621, the solar roll 631 is press-fitted in the connection hole 621b.
Further, the output shaft 612 is fitted into the coupling hole 621a of the coupling body 621, and the coupling body 621 and the output shaft 612 are fixed by a set screw (not shown) via a female screw 621c. In this way, the input coupling 62 and the output shaft 612 of the drive motor 61 are connected. In addition, in order to make the operation | work which performs this connection easy, the working hole 636 is provided in the cylindrical protrusion part 635 among the housings 630 (refer FIG. 3) of the deceleration mechanism 63. FIG.

Here, from the viewpoint of obtaining a desired inertial force, the flywheel 622 is appropriately formed as a ring-shaped member having a predetermined outer diameter D and thickness m from a material, and press-fitted into the outer peripheral surface of the coupling body 621. It is fixed by other methods. In particular, the outer diameter D of the flywheel 622 may be selected as appropriate, but it may be at least three times the outer diameter d ₁ of the output shaft 612 of the drive motor 61 (corresponding to the diameter of the connecting hole 621a). preferable.
In addition, although the flywheel 622 is provided in the structure mentioned above, the structure which abbreviate | omits the flywheel 622 is also considered.

  Since the rotary drive device 60 is configured as described above, it has the following operation. The drive motor 61 and the speed reduction mechanism 63 of the rotation drive device 60 are coaxially connected via an input coupling 62. Since the input coupling 62 includes the flywheel 622 on a part of the outer peripheral surface of the coupling body 621, the vibration from the output shaft 612 of the drive motor 61 is effectively attenuated by the inertial force of the flywheel 622. . Therefore, when the drive motor 61 is a stepping motor, a vibration damping member such as an external flywheel 622 is added to the opposite side of the output shaft 612 of the drive motor 61, or one end side of the photosensitive drums 11Y, 11M, and 11C. Even if a vibration attenuating member such as the external flywheel 622 is not added to the motor, it is possible to effectively attenuate the vibration that is likely to occur in the output shaft 612 of the drive motor 61 due to the resonance of the drive motor 61.

Next, the rotary encoder 70 will be described with reference to FIGS. The rotary encoder 70 is for controlling the rotational speed or rotational position of the photosensitive drums 11Y, 11M, and 11C. For the photoconductor drum 11K, a rotary encoder different from those shown in FIGS. 6 to 7 may be used. It is also conceivable that the rotary encoder is not attached if the rotation unevenness can be reduced.
FIG. 6 is an explanatory diagram illustrating a configuration of a drive control mechanism including the rotary encoder 70, and FIG. 7 is an explanatory diagram illustrating a rotatable disc 71 used in the rotary encoder 70.
As shown in FIG. 6 or FIG. 7, the rotary encoder 70 that constitutes a part of the position control means is a disk that is fixed so as to rotate integrally with the drive shafts 110 of the photosensitive drums 11Y, 11M, and 11C. 71, a detected portion 71a in which a large number of slits are arranged in a ring shape at predetermined intervals along the edge of the disc 71, and a reference position in which only one slit is arranged at a position near the center of the detected portion 71a. And a detector 71b. The rotary encoder 70 includes a speed detector 72 disposed at a position corresponding to the detected portion 71a of the disk 71 and a reference position detector disposed at a position corresponding to the slit of the reference position detecting portion 71b. 73.

  Here, the control unit 40 uses a signal from the rotary encoder 70 to feedback control the drive shaft 110, so that a CPU (Central Processing Unit) 41, a reference clock 42, and a frequency division ratio storage RAM (Random Access Memory) 43, a print control unit 44, and a motor drive circuit 45. Information acquired by the reference position detector 73 as a reference position signal is input to the print control unit 44, and the reading position of the exposure amount correction table of the photosensitive drums 11Y, 11M, and 11C is reset based on the information.

With such a configuration, the drive control mechanism operates as follows. First, when a print signal is started from the printer controller, a frequency division ratio that gradually increases the rotation speed of the motor is sequentially read from the frequency division ratio storage RAM 43. Then, a step-up signal is generated by dividing the reference clock by the division ratio, and a drive pulse is output to the motor drive circuit 45.
Then, after a predetermined time has elapsed, the drive motor 61 (see FIG. 3) is switched to the constant speed operation mode. In this constant speed operation mode, the detection signal of the speed detector 72 provided in the rotary encoder 70 of the drive shaft is input to the CPU 41 while the photosensitive drums 11Y, 11M, and 11C are rotating. In the CPU 41, the pulse interval of the rotary encoder 70 is measured by a pulse interval measuring circuit, and a deviation (position error) from the position that should be originally at the time is calculated based on the information. Position error time series information (position error information up to several times before) is multiplied by a predetermined weight to add FIR filtering of the position error, which is used as a feedback amount. This feedback amount is added to the frequency division ratio at the constant speed to calculate a new frequency division ratio that can cancel the speed and position fluctuations. Then, the drive speed or position of the drive motor 61 is controlled by dividing the reference clock by the division ratio. By repeating such an operation, position errors of the photosensitive drums 11Y, 11M, and 11C do not accumulate during the constant speed operation mode, so that the phase relationship between the photosensitive drums is kept constant.

In addition, while the photosensitive drum 11 (11Y, 11M, 11C, 11K) is rotating at a constant speed, the reference position detector 73 performs an operation of detecting the reference position on the way to the print control unit 44. Output the signal.
After the reference position is detected, the print control unit 44 resets the reading position of the exposure amount correction table stored in advance. Thereafter, the exposure amount can be corrected over one rotation of the photosensitive drum 11 by sequentially shifting the reading position of the exposure amount correction table in accordance with the rotation angle of the photosensitive drum 11. Further, the reference position detector 73 may be attached to each of the drive shafts 110 of the photosensitive drums 11Y, 11M, and 11C. However, since the phase relationship is always maintained, the reference position detector 73 may be attached to any one of the drive shafts 110. It is enough.

  Then, when the print signal is stopped from the printer controller, the frequency dividing ratio is exited from the constant speed operation mode and the frequency dividing ratio that gradually decreases the rotational speed of the drive motor 61 is sequentially read from the frequency dividing ratio storing RAM 43, and the reference clock A step-down signal is generated by dividing 42 by the division ratio, and a drive pulse is output to the motor drive circuit 45. When the rotational speed becomes sufficiently small, the output of the drive pulse is stopped and the drive motor 61 is stopped.

  Here, in the control operation described above, the reference clock 42, the division ratio at the constant speed, the division ratio at the step-up and step-down, and the timing at the time of entering and exiting the constant speed operation mode are mutually set. By making them the same, the phase relationship between the photosensitive drums 11 can always be kept constant. In the above-described configuration, the division ratio storage RAM 43 may be replaced with a ROM, and the functions of the CPU and RAM may be combined and replaced with an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). It is.

As described above, in the present embodiment, the outer rotor type DC braless motor is employed as the drive motor 61 that drives the photosensitive drum 11K of the black image forming unit 10K, thereby rotating the rotational speed of the photosensitive drum 11K. Can be stabilized.
On the other hand, since the stepping motor is employed as the drive motor 61 for driving the photosensitive drums 11Y, 11M, and 11C of the other image forming units 10Y, 10M, and 10C, the rotation of the photosensitive drums 11Y, 11M, and 11C is performed. The speed tends to become unstable. However, if the peripheral speed of the intermediate transfer belt 15 is made slightly faster than the photosensitive drums 11Y, 11M, 11C, and 11K, the photosensitive drum 11K is stably rotated, so that the other photosensitive drums 11Y, 11M, 11C, and The rotational speed of the intermediate transfer belt 15 can be stabilized.

By adopting a stepping motor as the drive motor 61 that drives the photosensitive drums 11Y, 11M, and 11C, the rotation angle can be accurately controlled including when the photosensitive drums 11Y, 11M, and 11C are started and stopped. Can do. That is, the photosensitive drums 11Y, 11M, and 11C can always be controlled to a predetermined amount regardless of the load torque fluctuation, and the phase relationship between the photosensitive drums 11Y, 11M, and 11C can be always constant. In this way, by controlling so that the phases of the photoconductor drums 11Y, 11M, and 11C are always the same, the potential measurement on the surface of the photoconductor is stabilized, which is caused by uneven sensitivity of the photoconductor drums 11Y, 11M, and 11C. Color variation can be suppressed. Therefore, it is possible to reduce the color difference variation as compared with the case where the outer rotor type motors are employed for all the four drive motors 61 of the photosensitive drums 11Y, 11M, 11C, and 11K.
With this configuration, it is possible to overcome the disadvantage of unstable rotation caused by the stepping motor in the photosensitive drums 11Y, 11M, and 11C, and to fully utilize the advantages of the stepping motor. The photosensitive drum 11K has a problem that it is difficult to always make the phase with the other photosensitive drums 11Y, 11M, and 11C the same. However, this defect only changes the brightness of the entire image transferred to the paper. That is, if the color differences of only Y, M, and C match, the high image quality requirement of the user can be satisfied, and even if there is a deviation from Y, M, and C, K is not easily noticeable by humans, and there is a problem. I can hardly say. For this reason, the configuration of the present embodiment can provide an image forming apparatus with little color variation as a whole.

Further, since the outer diameter of the photosensitive drum 11K is larger than that of the other photosensitive drums 11Y, 11M, and 11C, the inertia is increased, and the rotation speed of the photosensitive drum 11K can be further stabilized. Here, even if the drum surface speed is the same as that of the photosensitive drums 11Y, 11M, and 11C, the inertia effect is proportional to the square with respect to the speed and proportional to the fourth power with respect to the outer diameter. For this reason, as a result, the rotational speed of the photosensitive drum 11K is further stabilized. For example, if the outer diameter of the photosensitive drum 11K is 60 mm and the outer diameter of the photosensitive drums 11Y, 11M, and 11C is 40 mm, the rotational angular velocity is 2/3 of the photosensitive drums 11Y, 11M, and 11C. Become. That is, the inertia speed effect is (2/3) ² = 0.444 times, but the diameter effect is (60/40) ⁴ = 5.06 times. Therefore, the total inertia effect is 0.444 × 5.06 = 2.25 times.
In addition, since the outer diameter of the photoconductor drum 11K is large, the life of the photoconductor drum 11K can be extended, and the replacement frequency of the photoconductor drum 11K can be reduced, so that maintainability can be improved.

  Further, since the planetary roll speed reduction mechanism is employed as the speed reduction mechanism 63 of the rotation drive devices 60Y, 60M, 60C, and 60K, rotation unevenness does not occur as compared with a gear speed reduction mechanism that causes rotation unevenness due to a meshing error. Better rotational stability can be obtained. In other words, if the meshing error is large, even if the configuration as in this embodiment is adopted, the occurrence of banding may not be sufficiently reduced, but since the planetary roller speed reduction mechanism is adopted, the occurrence of banding is prevented. It can be sufficiently reduced.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied. It is a block diagram which shows the relationship between a photoconductor drum, a rotation drive device, and a control part. It is a block diagram for demonstrating the components which comprise a rotational drive apparatus. It is a block diagram for demonstrating the components which comprise a rotational drive apparatus. It is a longitudinal cross-sectional view of the input coupling which comprises some rotational drive apparatuses. It is explanatory drawing which shows the structure of the drive control mechanism containing a rotary encoder. It is explanatory drawing explaining the rotatable disc used for a rotary encoder.

Explanation of symbols

11 (11Y, 11M, 11C, 11K) ... photosensitive drum, 15 ... intermediate transfer belt, 40 ... control unit, 41 ... CPU, 42 ... reference clock, 43 ... frequency division ratio storage RAM, 44 ... print control unit, 45 ... Motor drive circuit, 60 (60Y, 60M, 60C, 60K) ... Rotary drive device, 61 (61Y, 61M, 61C, 61K) ... Drive motor, 62 ... Input coupling, 63 (63Y, 63M, 63C, 63K) ) ... Deceleration mechanism, 70 ... Rotary encoder

Claims (12)

A first image carrier that rotates by receiving a driving force and carries a black toner image;
A first driving source for supplying a driving force to the first image carrier;
A second image carrier that rotates upon receiving a driving force and carries a toner image other than black;
A second driving source for supplying a driving force to the second image carrier;
Transfer means for transferring a toner image carried on the first image carrier and the second image carrier to paper;
The image forming apparatus is characterized in that the first drive source is an outer rotor type motor and the second drive source is an inner rotor type motor.   2. The decelerating unit according to claim 1, further comprising a decelerating unit interposed between the second image carrier and the second drive source and decelerating an output from the second drive source. Image forming apparatus.   The image forming apparatus according to claim 2, wherein the deceleration unit is a roller deceleration unit that decelerates using a plurality of rollers.   The image forming apparatus according to claim 2, wherein the speed reducing unit is a planetary roller speed reducer.   The image forming apparatus according to claim 2, wherein the speed reducing unit is a traction speed reducer.   The image forming apparatus according to claim 1, wherein the first drive source is an outer rotor type DC brushless motor.   The image forming apparatus according to claim 1, wherein the second drive source is a stepping motor.   The image forming apparatus according to claim 1, wherein the first image carrier has an outer diameter larger than that of the second image carrier. Image forming means including an image carrier that rotates by receiving a driving force and carries a toner image and a drive source that drives the image carrier is represented by Y (yellow), M (magenta), C (cyan), and K (black). ) Image forming apparatus provided for each color,
An intermediate transfer member that rotates by receiving a driving force and primarily transfers a toner image carried on each of the image forming units;
A secondary transfer body for transferring the toner image primarily transferred by the intermediate transfer body onto a sheet;
And the image forming means that forms a K (black) toner image is driven by an outer rotor type motor, and forms Y (yellow), M (magenta), and C (cyan) toner images. An image forming apparatus characterized in that a driving source of the forming means is an inner rotor type motor.   The image forming apparatus according to claim 9, wherein the intermediate transfer member is driven at a peripheral speed faster than a peripheral speed of the image carrier included in each of the plurality of image forming units.   Position control means for controlling the position of the drive source in synchronism with the same reference pulse so that the phase of the image carrier that carries toner images of Y (yellow), M (magenta), and C (cyan) is not shifted. The image forming apparatus according to claim 9, further comprising:   12. A detector for detecting a phase of at least one of the image carriers carrying toner images of Y (yellow), M (magenta), and C (cyan). The image forming apparatus described in 1.

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