JP5113380B2 - Image forming apparatus - Google Patents

Description

The present invention mainly applies a plurality of images having different colors formed by a plurality of image forming means, such as a tandem type color copying machine or a color printer, onto a transfer belt, a sheet on the transfer belt, or an intermediate transfer member. In an image forming apparatus that transfers and forms a color image, it detects and corrects misregistration components of a plurality of different colors formed by each image forming unit, and in particular, a photoconductor such as each image forming unit those of the image forming equipment which can reduce the color shift or displacement caused by the rotational fluctuation of the drum.

  Recent image forming apparatuses have been colorized, and higher image quality has been demanded. Among them, the optimum condition for the speed difference between the photoconductor and the transfer belt is often in a very narrow area, and even if the speed difference slightly changes, the worm-eating image and banding level during transfer can be deteriorated. There is sex. Further, in a tandem type image forming apparatus having a plurality of photoconductors, if a single color photoconductor is misaligned, a color misalignment appears at the time of transfer.

  Conventionally, this type of image forming apparatus detects the rotational angular displacement or rotational angular velocity of the rotating shaft of a motor that drives a photosensitive drum, which is a latent image carrier, and feeds back the rotation of the motor based on the detection result. What is controlled is known. According to this image forming apparatus, by rotating the motor at a constant speed while suppressing fluctuations in the rotation speed of the motor, image position deviation, color deviation, and the like caused by fluctuations in the rotation speed of the photosensitive drum caused by fluctuations in the rotation speed of the motor. Image quality deterioration can be prevented.

  However, even if the motor is rotated at a constant speed, if there is an eccentricity or accumulated tooth pitch error in the drive gear as a drive transmission rotating member attached to the rotating shaft of the photosensitive drum, the photosensitive drum rotates once. Periodic rotational speed fluctuations will occur. Thus, an image forming apparatus is known in which a rotary encoder that detects a rotational angular velocity is attached to the rotating shaft of a photosensitive drum (see, for example, Patent Document 1). In this image forming apparatus, the rotation of the motor is feedback controlled so that the photosensitive drum rotates at a stable speed using the detection result of the rotary encoder attached to the rotating shaft of the photosensitive drum.

JP-A-12-231305

However, in order to obtain a sufficient suppression effect on the rotational speed fluctuation of the photosensitive drum due to the eccentricity of the drive gear using the rotary encoder, it is necessary to use a high-precision rotary encoder, which increases the cost. There was a problem that. This problem is not only the case where the controlled object rotating body is a photosensitive drum, but also an endless belt body such as an intermediate transfer body used in the image forming apparatus and a driving roller of the belt body are controlled object rotating bodies. This also occurs in some cases. In this case, in order to drive a plurality of photoconductors, it is necessary to mount a motor for each photoconductor.
The present invention has been made in view of the above problems, and without using a high-accuracy rotary encoder, which causes high costs, reduces the number of motors as much as possible, and controls due to eccentricity of the drive transmission rotor, etc. It is an object of the present invention to provide an image forming apparatus and a process cartridge that employ a rotating body drive control method capable of suppressing periodic rotational speed fluctuations of a target rotating body.

The image forming apparatus according to the first aspect of the present invention is as follows.
In an image forming apparatus having a plurality of image carriers to be rotated, and rotating at least two of these image carriers using one motor as a drive source.
Varies the rotational driving by the motor, the amplitude of fluctuation of the rotation cycle one image bearing member X1, the amplitude of fluctuation of the rotation period of the other image bearing member X2, in order to vary the rotational speed of the motor When the fluctuation amount of the amplitude of the rotational period of the motor corrected by the amplitude control of the phase opposite to the phase of the angular velocity fluctuation of the rotation of the image carrier applied to the motor is Z, (X1-Z), (X2-Z) ) To find the Z value that minimizes the larger absolute value of the two values, and use it as the correction amount by the amplitude control, and vary the rotation speed of the motor in a constant cycle according to the correction amount, A feature of the present invention is to prevent image misalignment due to angular velocity fluctuations of the two image carriers.

According to claim 2,
There are four image carriers to be rotated, and the first to third image carriers among these image carriers are rotationally driven using one motor as a drive source, and the fourth image carrier is In an image forming apparatus having a separate motor as a drive source for rotational driving,
Of the first to third image carriers, the amplitude X1 of the fluctuation of the rotation cycle of one image carrier, the amplitude X2 of the fluctuation of the rotation cycle of the other image carrier , which fluctuates due to the rotational drive by the motor . Moreover the amplitude of fluctuation of the rotation period of the other image carrier X3, the angular speed variation of rotation of the image bearing member to apply these three image bearing member to said motor to vary the rotational speed of the motor for rotating The absolute value of the three values (X1-Z), (X2-Z), and (X3-Z), where Z is the fluctuation amount of the amplitude of the rotation period of the motor corrected by the amplitude control of the phase and the opposite phase. The value of Z that minimizes the amplitude of the image carrier having the maximum value is found and used as the correction amount by the amplitude control, and the number of rotations of the motor is fluctuated at a constant period according to the correction amount, and the three images Prevents image displacement due to angular velocity fluctuations of the carrier To.

Those according to claim 3, in the image forming apparatus according to claim 2, wherein the first from the third image bearing member is an image bearing member for forming a toner image of a color, the fourth image bearing member Is an image carrier that forms a black toner image .

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the image carrier is included in a process cartridge configured to be detachable from a main body housing of the image forming apparatus, said image bearing member in the process cartridge and said Rukoto such as a more rotatably driven to the motor outside the process cartridge.

  In the present invention, it is possible to control the rotational speed of the motor and prevent the positional deviation of the image on the image carrier.

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

  FIG. 1 is a conceptual cross-sectional view of a main part of a printer that is an embodiment of the present invention. The printer of this embodiment is a tandem type image forming apparatus having four photoconductors 1a to 1d, which are, from the right, a black photoconductor 1a, a magenta photoconductor 1b, a cyan photoconductor 1c, and a yellow photoconductor 1d. . A latent image is formed on each of the photoreceptors 1a to 1d by exposure beams 5a to 5d of each color irradiated from a writing unit (not shown), and each of the photoreceptors 1a to 1d is developed on each of the developing rollers 2a to 2d. A toner image is formed. Thereafter, a toner image is sequentially transferred onto the intermediate transfer belt 3 at the transfer positions 6a to 6d of the respective colors in the order of the yellow photoreceptor 1d, the cyan photoreceptor 1c, the magenta photoreceptor 1b, and the black photoreceptor 1a, and the secondary transfer roller. In step 4, the image is transferred to transfer paper.

  In the image forming apparatus as described above, at least two of the four photoconductors 1a to 1d, for example, the drive source of the magenta photoconductor 1b and the cyan photoconductor 1c are provided as one drive source as shown in FIGS. The motor 13 is configured to prevent the positional deviation of the images on the two photoconductors 1 by changing the number of rotations at a constant period. Note that the pitch between stations, that is, the distance between the photoconductors 1a to 1d, which are image carriers, is the same as their one rotation period.

  In other words, the fluctuation period is one rotation period of the photosensitive member, and in order to prevent the positional deviation of the angular velocity fluctuation of one rotation period on the photosensitive member 1, the motor 13 is subjected to the amplitude control of the opposite phase (amplitude control). Details will be described later). In this embodiment, one rotation component of the photoconductor 1 is corrected. However, if the dependence of the multiple-order periodicity is high, the rotation can be performed even if the rotation is not one rotation.

  When the motor 13 is applied with the opposite phase of one rotation of the photoconductor, when driving a plurality of photoconductors, the effect is obtained unless the phase of the angular velocity fluctuation of each photoconductor 1 is matched on each photoconductor 1. There may not be. Therefore, at least the large-diameter gears 12b and 12c are assembled so as to match the phase of the angular velocity fluctuation of one rotation at the time of assembly.

  Next, at least the large-diameter gear 12a for driving the magenta photosensitive member 1b and the large-diameter gear 12c for driving the cyan photosensitive member 1c are molded products of plastic, and have a large-diameter shape as shown in FIGS. A mark 21 is dug into the molded product so that the phase in the rotational direction of the gear 12 can be visually recognized. The phase of the angular velocity fluctuation caused by the eccentricity of the large-diameter gear 12 or the accumulated pitch error shows a substantially equivalent profile if molded with the same mold, and is a mark for the large-diameter gear 12b driving the magenta photoreceptor 1b. If the phase of 21a and the mark 21b for driving the cyan photosensitive member 1c are matched and assembled, the phase of angular velocity fluctuations of the photosensitive members 1b and 1c at the time of driving is almost matched.

  However, in the case where a plurality of dies for the large-diameter gear 12 are taken, the phases of angular velocity fluctuations do not necessarily coincide when different cavities are assembled in the same drive train. Further, when the large-diameter gear 12 is finished with very high accuracy, the phases may not always coincide. In these situations, phase alignment by another method is required instead of a mark by digging into the mold.

  In such a case, it is preferable to use a profile measuring jig 25 for the large-diameter gear 12 as shown in FIG. The large-diameter gear 12 to be measured is driven by the jig motor 27. A load brake 26 is mounted on the same axis of the large-diameter gear 12 and a load equivalent to driving the photosensitive member 1 is applied. Further, an encoder 29 is arranged on the same axis as the gear 28 to which the driving force is transmitted from the large-diameter gear 12, and the angular velocity fluctuation is measured here.

  As shown in FIG. 7, the measurement result shows a waveform in a form in which a component other than the AC component of one rotation component of the large-diameter gear 12 is canceled. Accordingly, if markings 22a to 22b are provided at the peak phase positions in FIG. 7 as shown in FIG. 3 and the markings are assembled so that the phases of the markings are matched, the phase of the angular velocity fluctuations during driving is further matched. Become. Further, when the image forming apparatus main body needs to recognize the phase in the rotation direction of the photoconductor 1 in real time, as shown in FIG. 6, a filler having protrusions by 180 ° on the large-diameter gear 12. 15 and a phase sensor 16 for detecting the presence / absence of the protrusion of the filler 15 and assembling the filler by combining the peak of the waveform and the edge of the phase sensor for detecting the presence / absence of the protrusion of the filler 15 as shown in FIG. For example, when the photosensitive member 1 is driven, the image forming apparatus main body can recognize the phase state of the photosensitive member in real time. The phase sensor 16 and the filler 15 need only be provided in one system driven by the same motor 13, and in this embodiment, the phase sensor 16 and the filler 15 are attached to the magenta large-diameter gear 12b as shown in FIG. 4, and the cyan large-diameter gear 12c. The phase is recognized by arranging the marking 22b and assembling the filler edge portion and the marking portion together.

  Next, regarding the amount of fluctuation given to the motor, if the data measured by the profile measuring jig 25 of the large-diameter gear 12 is the magenta amplitude Xm and the cyan amplitude Xc, and the amount to be corrected by applying the opposite phase is Z, A value of Z that minimizes the absolute value of the two values (Xm-Z) and (Xc-Z) is calculated and determined as a correction amount.

  Next, when the data obtained by the large-diameter gear profile measuring jig 25 has a large variation, specifically, when magenta has a single-side amplitude Xm [μm] and cyan has Xc [μm], the difference between Xm and Xc ( When Xm−Xc) is large, as shown in FIG. 10, even if the motor is subjected to amplitude control of the opposite phase of one rotation of the photosensitive member, the effect of reducing the positional deviation is small. On the other hand, when the difference between Xm and Xc (Xm-Xc) of the data obtained by the jig 25 is small, as shown in FIG. The reduction effect is great. Therefore, if the large-diameter gears 12b and 12c to be assembled are classified according to the amplitude level based on the data obtained by the jig 25, and the same-amplitude gears are assembled as a set, the effect of reducing the displacement is increased. In the present embodiment, as in the table 1 shown in FIG. 1, the large-diameter gear 12 is classified into three based on the data obtained by the jig 25, and the large-diameter gears 12 a to 12 d are similarly classified. It is assembled as a set.

Next, an embodiment in the case where the profile on the image is actually read to determine the amplitude and phase of the fluctuation amount given to the motor will be described.
FIG. 8 shows pattern detection means 7a to 7b for detecting pattern images 41a to 41b for detecting fluctuation components on the intermediate transfer belt 3 formed by the image forming unit. One set of the pattern detection means 7 is arranged at each end in the width direction in the image area of the intermediate transfer belt 3. As the variation component detection pattern 41, for example, as shown in FIG. 15, toner images of one color of black, magenta, cyan, and yellow are arranged in parallel at a predetermined pitch perpendicular to the conveyance direction of the intermediate transfer belt 3. A pattern group is formed, and a detection time from an arbitrary reference timing is read in accordance with the movement of the intermediate transfer belt 3. Here, the detection times from any reference timing are recognized as tk01, tk02, and tk03 in the order of the formed patterns. In this way, by forming a single color pattern densely, it is possible to detect the displacement component with higher accuracy.

  In this embodiment, black and other patterns of one color different from each other are formed on the intermediate transfer belt 3 at two left and right ends, respectively, so that the fluctuation components of the two photoconductors 1 are detected simultaneously. . If the same operation is repeated once again for cyan and yellow, all colors can be detected. Further, one set of the pattern detecting means 7 is arranged at both ends in the width direction in the image area of the intermediate transfer belt 3, but there is no problem even if only one pattern detecting means 7 is provided. In this case, if the same operation is repeated four times, profiles for four colors can be detected.

  A waveform as shown in FIG. 16 can be formed by reading the pattern and extracting only one rotation component of the positional deviation AC component of each of the photoconductors 1a to 1d. If the outputs of the drum phase sensors 16a and 16b are also sampled at the same time, it is possible to associate the drum phase sensor 16a with the phase of the black photoreceptor 1a, and the drum phase sensor 16b and the other three colors of photoreceptors 1b to 1d. Association with the phase becomes possible. Specifically, if the rising portion of the drum phase sensor 16 is used as a reference and the fluctuation peak is used as a reference, information on the angular relationship between the drum phase sensor and the fluctuation waveform can be obtained. As described above, after associating the drum phase sensor 16 with the waveform profile of the positional deviation on the image, the motor clock is varied so as to correct the black amplitude Xk, and a substantially straight line as shown in FIG. 17 is obtained. The positional deviation is cancelled.

  On the other hand, when the color is magenta amplitude Xm, cyan amplitude Xc, and yellow amplitude Xy, assuming that the amount to be corrected by applying an opposite phase is Z, (Xm-Z), (Xc-Z), ( A value of Z that minimizes the absolute value of the three values of (Xy−Z) is calculated and determined as a correction amount. In this case, after correction, a waveform as shown in FIG. 17 is obtained. FIGS. 18 and 19 show color misregistrations of other colors with respect to black before and after correcting the rotational speeds of the black motor 11 and the color motor 13. When correction is applied, color misregistration with respect to black is reduced.

  In the above operation, a pattern 41 is formed on the transfer belt 3, and the amount of variation given to at least the motor 13 that drives the magenta photosensitive member 1b and the cyan photosensitive member 1c is determined by the pattern detection sensor 7 reading the pattern 41. The amplitude and phase are determined.

  Further, a similar effect can be expected by forming a pattern as shown in FIG. 15 on the photosensitive member 1 and detecting the amplitude and phase of each color by the drum pattern reading sensors 51a to 51d shown at the positions in FIG. it can.

  Furthermore, the fluctuation range and phase applied to the motor 13 are determined so that the amplitude of the image carrier that maximizes the amplitude of the angular velocity fluctuation among the plurality of photoconductors driven after the fluctuation is given is minimized. Specifically, if the magenta amplitude Xm, the cyan amplitude Xc, and the yellow amplitude Xy are Z, and the amount to be corrected by applying the opposite phase is Z, (Xm-Z), (Xc-Z), (Xy The value of Z is calculated such that the absolute value of the three values of -Z) is minimized, and is determined as the correction amount.

Next, the drive system of the photoreceptors 1a to 1d will be described with reference to FIG. 12 (a perspective view of the drive system of the photoreceptor 1) and FIG. 13 (a view seen from the rear of the photoreceptor 1 drive system). The black photosensitive member 1a is driven and transmitted by a large-diameter gear 12a meshed with the driving shaft (driving gear) of the motor 11 as a driving source, and drives the photosensitive member 1a. On the other hand, the color photosensitive member branches in two directions from the output shaft of the color drum motor 13. The first is engaged with the large-diameter gear 12b to drive the coaxial magenta photoreceptor 1b. The other is engaged with the large-diameter gear 12c and drives the cyan photoreceptor 1c on the same axis. The idler gear 14 meshes with the large-diameter gear 12c, and the idler gear 14 meshes with the large-diameter gear 12d to drive the yellow photoreceptor 1d coaxial with the large-diameter 12d. The previous large diameter gear 12, there is disposed a joint 31a~31d shown in FIG. 14, to engage the drive transmission engaged with the photosensitive body side joint. In the above configuration , the four photoconductors 1 a to 1 d are driven by the two motors 11 and 13.

  In addition, as a modification, yellow is generally less susceptible to human eyes than other colors, such as banding, bug eaters, and color misregistration. Therefore, priority is given to colors other than yellow. The value of Z that minimizes the absolute value of the two values (Xm-Z) and (Xc-Z), where Z is the amount corrected by multiplying the magenta amplitude Xm, the cyan amplitude Xc, and the opposite phase. Even if it is calculated and determined as the correction amount, a sufficient effect can be obtained.

  Further, as described above, if an optimum fluctuation of one rotation cycle of the photosensitive member 1 is given to both the motor 11 and the motor 13, a waveform as shown in FIG. 17 is obtained after correction. When correction is applied, color misregistration with respect to black is reduced.

  Next, the photoconductors 1a to 1d in the present embodiment are included in the process cartridge 32 (FIG. 14), and are driven and transmitted from a joint 31 coaxial with the large-diameter gear 12 and can be attached to and detached from the main body casing. It is configured. Further, the process cartridge 32 is equipped with a new article detection (not shown). When the process cartridge 32 is replaced, a mode for re-determining the phase and amplitude of the fluctuation of one rotation period of the photoconductor 1 of the motors 11 and 13 is executed. Yes.

Two methods for determining the correction amplitude Z will be described.
FIG. 20 is a table showing a method for determining the correction amplitude Z when two photoconductors (magenta and cyan) are driven by one drive motor.
In this method, when the amplitude of magenta is Xm and the amplitude of cyan is Xc, the amplitude Z of the antiphase applied to the drive motor to correct these amplitudes is the absolute value of (Xm-Z) and (Xc-Z). It is determined so that the amplitude of the photoconductor having the larger value is minimized. For example, assuming that Xm = 20 μm and Xc = 13 μm as shown in the table below, Z having the smallest absolute value of (Xm−Z) and (Xc−Z) is Z = 16.5 μm. It turns out that.

FIG. 21 is a table showing a method for determining the correction amplitude Z when three photoconductors (magenta, cyan, and aero) are driven by one drive motor.
When the amplitude of magenta is Xm, the amplitude of cyan is Xc, and the amplitude of yellow is Xy, the anti-phase amplitude Z applied to the drive motor to correct these amplitudes is (Xm-Z), (Xc-Z) , (Xy−Z) is determined so that the amplitude of the photosensitive member that maximizes the absolute value is minimized. For example, when Xm = 20 μm, Xc = 16 μm, and Xy = 9 μm as shown in the table below, the amplitude of the photoconductor having the maximum absolute value of (Xm−Z), (Xc−Z), and (Xy−Z). Z that minimizes is Z = 14.5 μm.

The image forming apparatus of the present invention has a rotation drive member for each image carrier coaxially with at least two or more of the image carriers driven by a motor, and the rotation drive member has an angular velocity of one rotation. It is also possible to configure by incorporating the phase of the fluctuation.
In the image forming apparatus, the rotation driving member of the image carrier may have a mark that can recognize the positional relationship in the rotation direction. This mark can be provided based on the result of measuring the phase of the angular velocity fluctuation of one rotation of the rotary drive member in advance.
Further, the fluctuation range and phase of the rotation period of the image carrier 1 given to the motor can be determined in advance based on the result of measuring the phase and amplitude of the angular velocity fluctuation of the driving member.
Further, the rotary drive member can be classified and incorporated according to the result of measuring the amplitude of the angular velocity fluctuation in advance.
Further, an image is formed by transferring directly on the transfer material carried on the endless carrier that is rotationally driven in contact with a plurality of image carriers, or on the endless carrier. A pattern forming means for forming a rotation fluctuation detection pattern of the image carrier formed on the image carrier, a pattern detection means for detecting the rotation fluctuation detection pattern formed on the endless carrier, and the pattern detection means. Calculating means for obtaining the amplitude and phase of the rotation component of the image carrier 1 of the fluctuation component of the pattern interval with respect to the periodic rotation fluctuation of the image carrier, based on the calculation result of the calculation means. A variation amount and a phase to be given to the motor which is a driving source of the two image carriers can be determined.
In this image forming apparatus, pattern forming means for forming a rotation fluctuation detection pattern of an image carrier formed on the image carrier, pattern detection means for detecting a pattern formed on the image carrier, and pattern detection means Calculation means for obtaining the amplitude and phase of the rotation component of the image carrier 1 of the fluctuation component of the pattern interval related to the periodic rotation fluctuation of the image carrier based on the detection data from A variation amount and a phase to be given to a motor that is a driving source of the carrier can be determined.
In this image forming apparatus, each image carrier is included in the process cartridge, and after the process cartridge is replaced, the phase and amplitude of the fluctuation amount of one rotation period of the image carrier of the first motor or the second motor are determined again. It is also possible to have an executable mode.

FIG. 2B is a conceptual cross-sectional view of a main part of the printer according to the embodiment of the present invention, and FIG. Rear view showing an example in which the drive source of two photosensitive members is a single motor Rear view showing an example in which the drive source of two photosensitive members is a single motor Rear view showing an example in which the drive source of two photosensitive members is a single motor Side view showing profile measuring jig for large-diameter gear The perspective view which shows the example which provided the phase sensor which detects the filler 15 which has a protrusion for 180 degrees on a large diameter gear, and the presence or absence of the protrusion of a filler An encoder 29 is arranged on the same axis as the gear 28 to which the driving force is transmitted from the large-diameter gear 12, and the angular velocity fluctuation is measured here. The perspective view which shows the pattern detection means which detects the pattern image for the fluctuation | variation component detection on the intermediate transfer belt formed of the image forming unit. Conceptual cross-sectional view of a main part of another printer according to an embodiment of the present invention. The figure which shows an example with little position shift reduction effect, even if it applies the amplitude control of the antiphase of 1 rotation of a photoconductor to a motor. FIG. 5 is a diagram showing an example of a large positional shift reduction effect when the motor is subjected to amplitude control of the reverse phase of one rotation of the photosensitive member. Perspective view of the drive system of the photoreceptor Rear view of photoconductor drive system A perspective view showing the arrangement of joints A pattern group is formed in which toner images of one color of black, magenta, cyan, and yellow are arranged in parallel at a predetermined pitch that is perpendicular to the conveyance direction of the intermediate transfer belt, and from any reference timing according to the movement of the intermediate transfer belt Diagram showing an example of reading the detection time The figure which shows the waveform which can be formed by extracting only one rotation component of position shift AC component of each photoconductor. The figure which shows the waveform after giving and giving the optimal fluctuation | variation of the 1 rotation period of a photoreceptor to both two motors. The figure which shows the example which calculated the color shift of the other color with respect to black before and after applying correction to the rotation speed of a black motor and a color motor The figure which shows the other example which calculated the color shift of the other color with respect to black before and after applying correction to the rotation speed of a black motor and a color motor. The figure which shows the table which shows the determination method of the correction | amendment amplitude Z in the case of driving two photoconductors (magenta, cyan) with one drive motor. The figure which shows the table which shows the determination method of the correction | amendment amplitude Z in the case of driving three photoconductors (magenta, cyan, and aero) with one drive motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a-1d Photoconductor 2a-2d Developing roller 3 Intermediate transfer belt 4 Secondary transfer roller 5a-5d Exposure beam 6a-6d Transfer position 7a-7b Pattern detection means 11 Black motor 12a, 12b, 12c Large diameter gear 13 Motor (color motor)
14 idler gear 15 filler 16a, 16b drum phase sensor 21a, 21b mark 22a-22b marking 25 profile measuring jig 26 load brake 27 motor for jig 28 gear 29 encoder 31a-31d joint 32 process cartridge 41a-41b pattern image 51a-51d drum pattern Reading sensor

Claims (4)

In an image forming apparatus having a plurality of image carriers to be rotated, and rotating at least two of these image carriers using one motor as a drive source.
Varies the rotational driving by the motor, the amplitude of fluctuation of the rotation cycle one image bearing member X1, the amplitude of fluctuation of the rotation period of the other image bearing member X2, in order to vary the rotational speed of the motor When the fluctuation amount of the amplitude of the rotational period of the motor corrected by the amplitude control of the phase opposite to the phase of the angular velocity fluctuation of the rotation of the image carrier applied to the motor is Z, (X1-Z), (X2-Z) ) To find the Z value that minimizes the larger absolute value of the two values, and use it as the correction amount by the amplitude control, and vary the rotation speed of the motor in a constant cycle according to the correction amount, An image forming apparatus that reduces image misalignment due to angular velocity fluctuations of two image carriers. There are four image carriers to be rotated, and the first to third image carriers among these image carriers are rotationally driven using one motor as a drive source, and the fourth image carrier is In an image forming apparatus having a separate motor as a drive source for rotational driving,
Of the first to third image carriers, the amplitude X1 of the fluctuation of the rotation cycle of one image carrier, the amplitude X2 of the fluctuation of the rotation cycle of the other image carrier , which fluctuates due to the rotational drive by the motor . Moreover the amplitude of fluctuation of the rotation period of the other image carrier X3, the angular speed variation of rotation of the image bearing member to apply these three image bearing member to said motor to vary the rotational speed of the motor for rotating The absolute value of the three values (X1-Z), (X2-Z), and (X3-Z), where Z is the fluctuation amount of the amplitude of the rotation period of the motor corrected by the amplitude control of the phase and the opposite phase. The value of Z that minimizes the amplitude of the image carrier having the maximum value is found and used as the correction amount by the amplitude control, and the number of rotations of the motor is fluctuated at a constant period according to the correction amount, and the three images characterized in that to reduce the displacement of the image due to the variation in the angular velocity of the carrier An image forming apparatus.   3. The image forming apparatus according to claim 2, wherein the first to third image carriers are image carriers that form color toner images, and the fourth image carrier forms a black toner image. An image forming apparatus which is an image carrier.   4. The image forming apparatus according to claim 1, wherein the image carrier is included in a process cartridge configured to be detachable from a main body housing of the image forming apparatus, and the image carrier in the process cartridge is included. The image forming apparatus can be driven to rotate by the motor outside the process cartridge.