JP2005266422A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a time required for determining a rotational speed difference between photoreceptor drums. <P>SOLUTION: Prior to performing color image formation using an electrographic process by rotationally driving a plurality of photoreceptor drums through phase adjustment for deviating phases, all the photoreceptor drums 102 are normally rotated at a speed higher than a rotational speed at image formation, the rotational speed difference between the photoreceptor drums 102 is detected and when performing the phase adjustment, the driving and rotational speeds of the photoreceptor drums 102 are changed to decrease the detected rotational speed difference. When detecting the rotational speed difference between the photoreceptor drums 102, all the photoreceptor drums 102 are normally rotated at the speed higher than the rotational speed at the image formation, thereby the time required for determining the rotational speed difference between the photoreceptor drums 102 is shortened. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus in which a plurality of photosensitive drums are rotationally driven with a phase shifted, and a color image is formed by an electrophotographic process.

  In a multicolor image forming apparatus having a plurality of photosensitive drums, a deviation in rotational speed of each photosensitive drum appears as a color shift of each color in a picture. The deviation of the rotational speed of each photosensitive drum is caused by, for example, an accuracy error of a driving unit that drives the photosensitive drum or an eccentricity of attachment. Such color misregistration of each color can be eliminated by making the rotation speed fluctuation periods of the respective photosensitive drums coincide. In other words, if the rotation speed fluctuation cycles of the respective photosensitive drums are made to coincide with each other, the amount of color misregistration of each color can be minimized and high image quality can be achieved.

  Techniques for matching the rotation speed fluctuation periods of the respective photosensitive drums are already known as can be seen in Patent Documents 1 to 3. According to the techniques described in these publications, a color misregistration correction pattern drawn on an image carrier is read by a pattern detection device, and a rotation speed fluctuation period and a period deviation amount of each photosensitive drum are calculated based on the read result. Based on the result, the rotational phase relationship between the photosensitive drums that minimizes the color misregistration amount is used as a basis. Then, the obtained information is stored as a profile in a volatile memory or the like, and at the time of actual image formation, the rotational phase of each photosensitive drum is made to follow the profile before image formation.

  In order to make the rotational phase of each photosensitive drum follow the profile, a reference position is set in advance on an object that rotates at the same speed as the photosensitive drum, for example, a driving gear of the photosensitive drum or a dedicated member. Set and mark. Each photosensitive drum is rotated at a constant speed at the time of image formation. At this time, the marking is detected by a sensor, and a pulse wave is extracted from the sensor output. Thereby, the rotational speed difference between the photosensitive drums can be obtained based on the difference in timing of the pulse wave corresponding to each photosensitive member. Therefore, the rotational phase of each photosensitive drum can be made to follow the profile by controlling the driving of each photosensitive drum, such as a motor, so as to reduce the difference in rotational speed between the photosensitive drums. .

JP 09-146329 A JP 2001-134039 A JP 2001-305820 A

  When the above-described method of copying the rotation phase of each photoconductor drum to the profile is employed, the time required to obtain the rotation speed difference between the photoconductor drums depends on the rotation speed of the photoconductor drum. For this reason, in an image forming apparatus with a small number of printable sheets per minute and a low printing speed, the rotational speed of the photosensitive drums is slow, and the time required to obtain the rotational speed difference between the photosensitive drums becomes long. There's a problem.

  An object of the present invention is to shorten the time required to obtain the rotational speed difference between the photosensitive drums.

  According to a first aspect of the present invention, in the image forming apparatus for performing color image formation by an electrophotographic process by adjusting the phase to shift the phase and rotationally driving the plurality of photosensitive drums, the photosensitive drums are individually independent. A drive unit that rotationally drives the detection unit, and a detection unit that constantly rotates all of the photosensitive drums at a speed faster than a rotation speed at the time of image formation, and detects a rotational speed difference between the individual photosensitive drums; And adjusting means for changing the driving rotational speed of each of the photosensitive drums by the driving unit so as to reduce the detected rotational speed difference when performing the phase adjustment.

  Therefore, when detecting the difference in rotational speed between the individual photosensitive drums, all the photosensitive drums are rotated at a speed higher than the rotational speed at the time of image formation. Thereby, the time for obtaining the rotational speed difference between the photosensitive drums is shortened.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus is rotatably supported so as to come into contact with the photosensitive drum, and is driven to rotate in the reverse direction at the same peripheral speed as the photosensitive drum. An image carrier is provided, and the detecting means is configured to rotate the image carrier at a rotational speed that is higher than the rotational speed at the time of image formation in accordance with the rotational speed of the photosensitive drum when detecting the rotational speed difference. Let

  Therefore, the photosensitive drum and the image carrier are driven to rotate with little difference in peripheral speed. This makes it difficult for both the image carrier and the photosensitive drum to be damaged.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, a brake motor is used as the drive unit, and the detection means sets the drive rotational speed of the photosensitive drum to be higher than the rotational speed at the time of image formation. When returning from the high speed to the rotational speed at the time of image formation, the brake of the brake motor is operated.

  Therefore, the rotation speed of the photosensitive drum rotating at a speed higher than the rotation speed at the time of image formation is returned to the rotation speed at the time of image formation in a shorter time.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the adjusting means changes the driving rotational speed of the photosensitive drum from a speed higher than a rotational speed at the time of image formation to a rotational speed at the time of image formation. When it is returned, the phase adjustment is performed.

  Therefore, the time required from the detection of the rotational speed difference between the individual photosensitive drums by the detecting means to the phase adjustment by the adjusting means is shortened.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the third and fourth aspects, the adjusting unit shifts a timing of operating a brake of the brake motor for each of the photosensitive drums, thereby Perform phase adjustment.

  Therefore, the time required from the detection of the rotational speed difference between the individual photosensitive drums by the detecting means to the phase adjustment by the adjusting means is shortened.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the adjusting means is configured such that the driving rotational speed of the photosensitive drum is higher than the rotational speed at the time of image formation for each of the photosensitive drums. The timing for returning to the rotational speed at the time of image formation is shifted from the speed, and thereby the phase adjustment is executed.

  Therefore, the time required from the detection of the rotational speed difference between the individual photosensitive drums by the detecting means to the phase adjustment by the adjusting means is shortened.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the fourth aspect, the adjusting means is configured such that the driving rotational speed of the photosensitive drum is higher than the rotational speed at the time of image formation for each of the photosensitive drums. The rotational speed when returning from the speed to the rotational speed at the time of image formation is shifted, and thereby the phase adjustment is executed.

  Therefore, the time required from the detection of the rotational speed difference between the individual photosensitive drums by the detecting means to the phase adjustment by the adjusting means is shortened.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the second and third to seventh aspects, the detection means has a driving rotational speed of the photosensitive drum higher than a rotational speed at the time of image formation. When the rotation speed is returned to the rotation speed at the time of image formation, the rotation speed of the image carrier is returned to the rotation speed at the time of image formation in accordance with the rotation speed of the photosensitive drum.

  Therefore, even when the drive rotation speed of the photosensitive drum is returned from the rotation speed higher than the rotation speed at the time of image formation to the rotation speed at the time of image formation, the circumferential speed of the photosensitive drum and the image carrier hardly occurs. Is driven to rotate. This makes it difficult for both the image carrier and the photosensitive drum to be damaged.

  According to a first aspect of the present invention, in the image forming apparatus for performing color image formation by an electrophotographic process by adjusting the phase to shift the phase and rotationally driving the plurality of photosensitive drums, the photosensitive drums are individually independent. A drive unit that rotationally drives the detection unit, and a detection unit that constantly rotates all of the photosensitive drums at a speed faster than a rotation speed at the time of image formation, and detects a rotational speed difference between the individual photosensitive drums; And adjusting means for changing the driving rotational speed of each of the photosensitive drums by the driving unit so as to reduce the detected rotational speed difference when performing the phase adjustment. The time for obtaining the rotational speed difference can be shortened, and therefore the first print time can be shortened.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus is rotatably supported so as to come into contact with the photosensitive drum, and is driven to rotate in the reverse direction at the same peripheral speed as the photosensitive drum. An image carrier is provided, and the detecting means is configured to rotate the image carrier at a rotational speed that is higher than the rotational speed at the time of image formation in accordance with the rotational speed of the photosensitive drum when detecting the rotational speed difference. Therefore, the photosensitive drum and the image carrier can be rotationally driven in a state where there is almost no difference in peripheral speed. Therefore, it is possible to prevent the life of the image carrier and the photosensitive drum from being shortened. it can.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, a brake motor is used as the drive unit, and the detection means sets the drive rotational speed of the photosensitive drum to be higher than the rotational speed at the time of image formation. When returning from a high speed to the rotation speed at the time of image formation, the brake of the brake motor is operated, so that the rotation speed of the photosensitive drum rotating at a higher speed than the rotation speed at the time of image formation can be reduced in a shorter time. The rotational speed at the time of image formation can be restored, and therefore the first print time can be shortened.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the adjusting means changes the driving rotational speed of the photosensitive drum from a speed higher than a rotational speed at the time of image formation to a rotational speed at the time of image formation. Since the phase adjustment is performed at the time of returning, the time required from the detection of the rotational speed difference between the individual photosensitive drums by the detection means to the phase adjustment by the adjustment means can be shortened. Can be shortened.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the third and fourth aspects, the adjusting unit shifts a timing of operating a brake of the brake motor for each of the photosensitive drums, thereby Since the phase adjustment is executed, the rotation speed of the photosensitive drum rotating at a speed higher than the rotation speed at the time of image formation can be returned to the rotation speed at the time of image formation in a shorter time, and therefore, the first print time. Can be shortened.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the adjusting means is configured such that the driving rotational speed of the photosensitive drum is higher than the rotational speed at the time of image formation for each of the photosensitive drums. The timing for returning to the rotational speed at the time of image formation is shifted from the speed, thereby executing the phase adjustment, so that the rotational speed of the photosensitive drum rotating at a speed higher than the rotational speed at the time of image formation can be reduced in a shorter time. Thus, the rotational speed at the time of image formation can be restored, and therefore the first print time can be shortened.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the fourth aspect, the adjusting means is configured such that the driving rotational speed of the photosensitive drum is higher than the rotational speed at the time of image formation for each of the photosensitive drums. The rotational speed when returning from the speed to the rotational speed at the time of image formation is shifted, and thus the phase adjustment is executed. Therefore, the rotational speed of the photosensitive drum rotating at a speed higher than the rotational speed at the time of image formation is adjusted. The rotational speed at the time of image formation can be restored in a shorter time, and therefore the first print time can be shortened.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the second and third to seventh aspects, the detection means has a driving rotational speed of the photosensitive drum higher than a rotational speed at the time of image formation. When returning from the rotation speed at the time of image formation to the rotation speed of the image bearing member, the rotation speed of the image carrier is returned to the rotation speed at the time of image formation in accordance with the rotation speed of the photosensitive drum. Even when returning from a speed higher than the rotational speed to the rotational speed at the time of image formation, the photosensitive drum and the image carrier can be driven to rotate with almost no peripheral speed. It is possible to prevent the life of the photosensitive drum from being shortened.

  An embodiment of the present invention will be described with reference to FIGS. This embodiment is an example applied to a printer that executes a full-color image forming operation.

[Basic configuration]
FIG. 1 is a longitudinal side view showing an image processing process section of a printer. As shown in FIG. 1, the printer according to the present embodiment employs a tandem imaging system with four drums. An image processing process unit 101 shown in FIG. 1 includes four photosensitive drums 102 around which a charging device 103, an image writing device 104, a developing device 105, a transfer device 106, and A cleaning device 107 is provided. Among these units, the charging device 103, the developing device 105, and the cleaning device 107 are provided in a one-to-one relationship on each photosensitive drum 102.

  FIG. 2 is a vertical side view showing an example of a unitized consumable part. The charging device 103, the developing device 105, and the cleaning device 107 constituting the image processing unit 101 are unitized as a process unit 108 together with a single corresponding photosensitive drum 102. Accordingly, four process units 108 are provided corresponding to the respective photosensitive drums 102.

  On the other hand, the image writing device 104 is configured as a single unit so that laser light can be irradiated to each of the four photosensitive drums 102 independently using a single polygon mirror 109. The transfer device 106 transfers an image formed on the surface of the photosensitive drum 102 to an intermediate transfer belt 110 serving as an image carrier. The process unit 108 includes K (black), C (cyan), M (magenta), and Y (yellow) along the moving direction of the contact portion between the photosensitive drum 102 and the intermediate transfer belt 110 indicated by an arrow in FIG. ) Are arranged in this order.

  As an electrophotographic process in such an image processing process unit 101, the photosensitive drum 102 is uniformly charged by the charging device 103, and the image writing device 104 converts the uniformly charged photosensitive drum 102 into an image signal. A corresponding laser beam is irradiated. As a result, an electrostatic latent image is formed on the photosensitive drum 102. The electrostatic latent image formed on the photosensitive drum 102 is developed by the developing device 105 to become a toner image, and the toner image is transferred to the intermediate transfer belt 110 by the transfer device 106. The intermediate transfer belt 110 transfers the transferred toner image onto a transfer sheet P (see FIG. 3) arranged in the rotation locus. The transfer in this case is performed using a transfer device (not shown). The full-color toner image transferred to the transfer paper P is pressurized and heated by a fixing device (not shown) and firmly fixed to the transfer paper P. As a result, a full-color image is formed on the transfer paper P.

  The cleaning device 107 includes a cleaning brush 107a and a static elimination blade 107b. The cleaning brush 107 a removes toner remaining on the photosensitive drum 102 after the toner image is transferred to the transfer paper P. The neutralization blade 107b neutralizes the surface of the photosensitive drum 102 after the residual toner is removed, and prepares for the subsequent electrophotographic process.

  In the present embodiment, the process unit 108 is a consumable part having consumables such as the photosensitive drum 102, the charging device 103, the developing device 105, and the cleaning device 107. Such a process unit 108 is detachably mounted on a mounting portion (not shown) provided in the printer.

  The printer of the present embodiment has a control unit (not shown). As an example, this control unit has a microcomputer configuration including a CPU and a memory. The CPU executes various arithmetic processes according to a control program stored in the memory, and drives each unit connected to the I / O port, thereby forming a full color image. Each unit connected to the I / O port is, for example, a motor or a laser oscillator that constitutes a part of the above-described charging device 103, image writing device 104, developing device 105, transfer device 106, and cleaning device 107. .

[Phase adjustment between photosensitive drums 102]
In the quadruple-drum tandem imaging printer, each photosensitive drum 102 is arranged in the order of K (black), C (cyan), M (magenta), and Y (yellow), and toner images are intermediately transferred in that order. Transfer to belt 110. Therefore, the toner image transfer timing differs for each color. Therefore, when the photosensitive drum 102 is rotationally driven, it is necessary to perform phase adjustment for shifting the rotational phase of each photosensitive drum 102 individually. In addition, as described above, the rotational speed of each photosensitive drum 102 is deviated due to an accuracy error of a driving unit (driving motor 111 described later) for driving the photosensitive drum 102 or mounting eccentricity, which causes the color misregistration. It becomes. Therefore, when the photosensitive drums 102 are rotationally driven, it is necessary to adjust the phase so that the rotational speed fluctuation periods of the photosensitive drums 102 coincide with each other. Such phase adjustment is executed by a microcomputer provided in the control unit (not shown). Hereinafter, the phase adjustment process will be described in detail.

  FIG. 3 is a schematic diagram of the photosensitive drum 102 and the intermediate transfer belt 110 for explaining the phase adjustment. FIG. 4 is a perspective view of a detector that detects the phase of the photosensitive drum 102. The photosensitive drum 102 is driven to rotate by a driving motor 111 having a rotating shaft 101a as a driving unit. A drive gear 112 is coaxially fixed to the rotation shaft 101 a of the photosensitive drum 102. By driving the drive gear 112 by the drive motor 111, the rotational driving force of the drive motor 111 is transmitted to the photosensitive drum 102. The drive motor 111 is provided in a one-to-one relationship with the photosensitive drum 102. As such a drive motor 111, a brake motor is used. The brake motor applies a brake signal to apply, for example, a magnetic brake to a rotating shaft (not shown).

  The control unit detects the rotational speed of the photosensitive drum 102 using the detector 113 in order to adjust the phase of the photosensitive drum 102. As a structure for that purpose, as shown in FIG. 2, a detection body 114 as a marking is formed on a member constituting a part of the drive gear 112. The detector 113 is a transmissive optical sensor having a laser diode and a phototransistor (not shown), and changes the output signal when the detector 114 crosses the optical axis between the laser diode and the phototransistor. FIG. 5A shows an example of the output signal of the phototransistor when the detector 114 crosses the optical axis between the laser diode and the phototransistor. FIG. 5B shows another example of the output signal of the phototransistor when the detector 114 crosses the optical axis between the laser diode and the phototransistor. Thus, the detector 113 changes the output signal when the detector 114 crosses the optical axis between the laser diode and the phototransistor. Such an output signal of the detector 113 can be extracted as a pulse wave because the photosensitive drum 102 is rotating. Therefore, the control unit can determine the rotational speed difference between the photosensitive drums 102 by comparing the pulse wave based on the output signal of the detector 113 corresponding to each photosensitive drum 102 (detecting means). .

  FIG. 6 is a timing chart showing the relationship between the rotation speed (vertical axis) and time (horizontal axis) of each photoconductive drum 102 in order to explain the phase difference of each photoconductive drum 102. Now, it is assumed that the phase relationship between the photosensitive drums 102 is in the state shown in FIG. At this time, in order to achieve an ideal state (profile) in which the color misregistration is minimized, it is necessary to shift the phase relationship of the photosensitive drums 102 in accordance with the arrangement state of the photosensitive drums 102. In the present embodiment, as described above, the process unit 108 moves along the moving direction of the contact portion between the photosensitive drum 102 and the intermediate transfer belt 110 indicated by an arrow in FIG. Cyan), M (magenta), and Y (yellow) are arranged in this order. Therefore, with reference to the K (black) photosensitive drum 102, the C (cyan) photosensitive drum 102 is θ1, the M (magenta) photosensitive drum 102 is θ2, and the Y (yellow) photosensitive drum 102. Must be shifted in phase by θ3. Such a rotational phase difference of each photosensitive drum 102 is stored and saved in, for example, a nonvolatile memory included in the control unit as a profile that defines an ideal state in which the color shift is minimized. Therefore, prior to the image forming operation, the control unit drives and controls the drive motor 111 of each photoconductive drum 102 so that the phase difference of each photoconductive drum 102 follows the profile (adjustment unit). This is phase adjustment.

  Here, as described above, a deviation occurs in the rotational speed of each photoconductive drum 102 due to an accuracy error of the drive motor 111 that drives the photoconductive drum 102, mounting eccentricity, and the like, and this causes a color shift. When adjusting the phase, the control unit refers to the detected rotational speed difference between the photosensitive drums 102 and reduces the rotational speed difference so that the rotational speed fluctuation periods of the photosensitive drums 102 are matched. To adjust the phase.

  FIG. 7 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum 102 during conventional phase adjustment. Conventionally, in phase control, all the photosensitive drums 102 are rotationally driven at the rotation speed at the time of image formation, and after detecting the phase difference of each photosensitive drum 102, the phase relationship of each photosensitive drum 102 is illustrated in FIG. The rotational speed of each photoconductor drum 102 is controlled so as to follow the profile. Thereby, an image with little color misregistration is obtained.

  However, when such a method is adopted, as shown in FIG. 7, the phase difference of the photosensitive drum 102 is detected in a printer in which the speed (V1) of the photosensitive drum 102 during image formation is low, in other words, in a printer with a low printing speed. The time (T1 to T2) until it is detected becomes longer. For this reason, there is an inconvenience that the first print time (T4) is delayed as compared with a printer having a high printing speed.

  FIG. 8 is a timing chart showing the relationship between the rotation speed (vertical axis) and time (horizontal axis) of each photoconductive drum 102 during phase adjustment, in order to explain a first example of phase adjustment. In contrast to such a conventional printer, in the printer of the present embodiment, when the photosensitive drums 102 for phase adjustment are started, all the photosensitive drums 102 are faster than the speed (v1) at the time of image formation. The phase of each photosensitive drum 102 is detected by steady rotation in (v2) (first example of phase adjustment). Thereby, the phase difference of the photosensitive drum 102 can be detected within a short time, so that printing can be started earlier.

  Further, in the present embodiment, the control unit executes control to make the peripheral speed of the intermediate transfer belt 110 in contact with the photosensitive drum 102 coincide with the peripheral speed of the photosensitive drum 102 when the phase of the photosensitive drum 102 is adjusted. . The reason why the peripheral speed of the intermediate transfer belt 110 coincides with the peripheral speed of the photosensitive drum 102 is that when the rotational speed of the photosensitive drum 102 is made faster than the rotational speed at the time of image formation, This is both the situation when returning to the rotational speed at the time of formation. As a result, sliding between the photosensitive drum 102 and the intermediate transfer belt 110 is prevented as much as possible when the phase of the photosensitive drum 102 is adjusted, and damage to both the photosensitive drum 102 and the intermediate transfer belt 110 is reduced. It is possible to prevent the life of the body drum 102 and the intermediate transfer belt 110 from being shortened.

  FIG. 9 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photoconductor drum at the time of phase adjustment in order to explain a second example of phase adjustment. As shown in FIG. 9, when the control unit returns the rotation speed of the plurality of photosensitive drums 102 from the speed (v2) faster than the rotation speed at the time of image formation to the rotation speed (v1) at the time of image formation, A brake signal is input to the drive motor 111 that drives the photosensitive drum 102 (second example of phase adjustment). As a result, the drive motor 111 brakes the rotating shaft (not shown). Then, the control is performed so that the rotational speed of the photosensitive drum 102 becomes the rotational speed at the time of image formation when the brake is released. Thereby, the photosensitive drum 102 can be returned to the rotation speed at the time of image formation in a short time compared with the case where the drive motor 111 is controlled only by the rotation control signal. Therefore, printing can be started earlier.

  FIG. 10 is a timing chart showing, as a reference example, the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum at the time of phase adjustment in order to explain a third example of phase adjustment. . FIG. 11 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum during phase adjustment as a reference example different from FIG. In the example of phase difference adjustment shown in FIG. 10, the control unit executes the detection unit and the adjustment unit separately. That is, the control unit detects the phase difference of each color photosensitive drum 102 between t1 and t2 by making the rotation speed of the color photosensitive drum 102 higher than the rotation speed at the time of image formation (detection means), and forms an image. Return to the hourly speed v1. Thereafter, in order to adjust the phase, the control unit performs phase adjustment by rotating the photosensitive drum 102 at a phase difference control speed v3 for a predetermined time (t6 to t7), and thereafter the rotational speed of the photosensitive drum 102 is adjusted. To the speed v1 during image formation. As a result, the phase of each photosensitive drum 102 is adjusted. In such phase adjustment, the value of v3 or the time from t5 to t8 is adjusted and controlled for each photoconductor drum 102, so that the phase difference becomes in accordance with the profile at time t8.

  The example of phase adjustment shown in FIG. 9 is different from the example of phase adjustment shown in FIG. 8 only in that the phase difference detection speed (detection means) immediately shifts to the phase difference control speed (adjustment means).

  FIG. 12 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photoconductor drum at the time of phase adjustment in order to explain a third example of phase adjustment. Compared to the phase adjustment examples shown in FIGS. 8 and 9, in the third example of phase adjustment of the present embodiment, the control unit determines that the drive rotation speed of the photosensitive drum 102 is higher than the rotation speed at the time of image formation. However, it is different in that the phase adjustment is executed when the rotational speed is returned to the rotational speed at the time of image formation. When the photosensitive drum 102 is rotated at a phase control speed for a predetermined time and then returned to the original rotation speed, a transition time is required for the drive motor 111 to rise and fall. On the other hand, if phase adjustment is performed when returning from the rotational speed for phase difference detection, which is faster than the rotational speed at the time of image formation, to the rotational speed at the time of image formation, the transient state of the drive motor 111 is only a fall. Become. As a result, the individual photosensitive drums 102 can be brought into the same phase relationship as the profile in a short time, and printing can be started earlier.

  FIG. 13 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum at the time of phase adjustment in order to explain a fourth example of phase adjustment. FIG. 12 shows an example of phase adjustment in which the phase adjustment is performed when the drive rotation speed of the photosensitive drum 102 is returned from the speed higher than the rotation speed at the time of image formation to the rotation speed at the time of image formation. The fourth example of phase adjustment provides a method of phase adjustment at that time. That is, in the fourth example, the control unit changes and adjusts the timing at which the control unit transmits a brake signal to the drive motor 111 for each photoconductor drum 102, thereby causing the phase difference of each photoconductor drum 102 to follow the profile. I am doing so.

  FIG. 14 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum at the time of phase adjustment in order to explain a fifth example of phase adjustment. FIG. 12 shows an example of phase adjustment in which the phase adjustment is performed when the drive rotation speed of the photosensitive drum 102 is returned from the speed higher than the rotation speed at the time of image formation to the rotation speed at the time of image formation. The fifth example of phase adjustment also provides a method for phase adjustment at this time. That is, in the fifth example, the control unit controls the drive motor 111 corresponding to each photoconductor drum 102 and returns the rotation speed of each photoconductor drum 102 to the rotation speed at the time of image formation. Thus, the phase difference of each photosensitive drum 102 is made to follow the profile.

  FIG. 15 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photoconductor drum at the time of phase adjustment in order to explain a sixth example of phase adjustment. FIG. 12 shows an example of phase adjustment in which the phase adjustment is performed when the drive rotation speed of the photosensitive drum 102 is returned from the speed higher than the rotation speed at the time of image formation to the rotation speed at the time of image formation. The sixth example of phase adjustment also provides a method of phase adjustment at this time. That is, in the sixth example, the control unit controls the drive motor 111 corresponding to each photoconductor drum 102 and returns the rotation speed of each photoconductor drum 102 to the rotation speed at the time of image formation. Thus, the phase difference of each photosensitive drum 102 is made to follow the profile.

FIG. 2 is a longitudinal side view illustrating an image processing process unit of a printer as an embodiment of the present invention. It is a vertical side view which shows an example of the consumable part unitized. FIG. 3 is a schematic diagram of a photosensitive drum and an intermediate transfer belt for explaining phase adjustment. It is a perspective view of the detector which detects the phase of a photoconductive drum. 6 is a timing chart illustrating signals generated at the output of the detector when the phase of the photosensitive drum is detected. 4 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum in order to explain the phase difference of each photosensitive drum. 10 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum during conventional phase adjustment. FIG. 6 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum during phase adjustment in order to explain a first example of phase adjustment. FIG. 6 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum during phase adjustment in order to explain a second example of phase adjustment. FIG. 9 is a timing chart showing a relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum at the time of phase adjustment as a reference example in order to explain a third example of phase adjustment; FIG. 11 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum during phase adjustment as a reference example different from FIG. 10. FIG. 10 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum during phase adjustment in order to explain a third example of phase adjustment. FIG. 9 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum during phase adjustment in order to explain a fourth example of phase adjustment. FIG. 10 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum during phase adjustment in order to explain a fifth example of phase adjustment; FIG. 10 is a timing chart showing the relationship between the rotational speed (vertical axis) and time (horizontal axis) of each photosensitive drum during phase adjustment in order to explain a sixth example of phase adjustment;

Explanation of symbols

102 Photosensitive drum 110 Image carrier (intermediate transfer belt)
111 Drive unit (drive motor, brake motor)

Claims (8)

In an image forming apparatus that performs phase adjustment to shift the phase and rotationally drives a plurality of photosensitive drums to perform color image formation by an electrophotographic process,
A driving unit for rotating the photosensitive drums independently;
Detection means for detecting a rotational speed difference between the individual photosensitive drums by rotating all of the photosensitive drums at a speed higher than a rotational speed at the time of image formation;
Adjusting means for changing the driving rotational speed of each of the photosensitive drums by the driving unit so as to reduce the detected rotational speed difference when performing the phase adjustment;
An image forming apparatus comprising: An image carrier that is rotatably supported so as to be in contact with the photosensitive drum and is driven to rotate in the reverse direction at the same peripheral speed as the photosensitive drum;
The detecting means, when detecting the rotation speed difference, rotates the rotation speed of the image carrier in a steady manner at a speed faster than the rotation speed at the time of image formation in accordance with the rotation speed of the photosensitive drum. The image forming apparatus according to claim 1. A brake motor is used as the drive unit,
The detecting means activates a brake of the brake motor when returning the driving rotational speed of the photosensitive drum from a speed higher than a rotational speed at the time of image formation to a rotational speed at the time of image formation.
The image forming apparatus according to claim 1.   The adjustment unit performs the phase adjustment when the drive rotation speed of the photosensitive drum is returned from a speed higher than a rotation speed at the time of image formation to a rotation speed at the time of image formation. The image forming apparatus according to 1.   5. The image forming according to claim 3, wherein the adjusting unit shifts a timing at which a brake included in the brake motor is operated for each of the photosensitive drums, and thereby executes the phase adjustment. 6. apparatus.   The adjusting unit shifts the timing at which the driving rotational speed of the photosensitive drum is returned from the speed higher than the rotational speed at the time of image formation to the rotational speed at the time of image formation for each of the photosensitive drums. The image forming apparatus according to claim 4, wherein phase adjustment is executed.   The adjusting means shifts the rotational speed when the rotational speed of the photosensitive drum is returned from the speed higher than the rotational speed at the time of image formation to the rotational speed at the time of image formation for each of the photosensitive drums, The image forming apparatus according to claim 4, wherein the phase adjustment is performed in this way. The detection means returns the driving rotation speed of the photoconductor drum from the speed higher than the rotation speed at the time of image formation to the rotation speed at the time of image formation to match the rotation speed of the photoconductor drum. The image forming apparatus according to claim 2, wherein the rotation speed is returned to the rotation speed at the time of image formation.

Images