JP4701703B2 - Image forming apparatus and phase adjustment method in the apparatus - Google Patents

Description

  The present invention relates to a toner image formed on each of the plurality of image carriers while connecting the at least one image carrier to each of the plurality of drive motors and rotating the plurality of image carriers. In particular, the present invention relates to a technique for adjusting the rotational phase relationship among a plurality of image carriers.

  As an apparatus for forming a color image, a so-called tandem color image forming apparatus is known. In this image forming apparatus, a plurality of image forming stations that form toner images of different colors are arranged along the moving direction of a transfer medium such as an intermediate transfer belt. In each image forming station, an image carrier such as a photosensitive drum is rotated at a predetermined rotational speed, and a charging unit, an image writing unit, and a developing unit are disposed around the image carrier. Then, while rotating all the image carriers, the toner images formed on the respective image carriers are superimposed on the transfer medium to form a color image.

  In order to rotationally drive a plurality of image carriers in this way, it is roughly divided from the conventional ones. (1) A single drive motor is used and the rotational driving force of the drive motor is transmitted to each image carrier by a train wheel. And (2) a method using a plurality of drive motors. In particular, as the latter method, a number of methods in which a dedicated drive motor is provided for each color have been proposed. For example, in the apparatus described in Patent Document 1, four color image carriers are provided, and four drive motors are provided to rotationally drive the four color image carriers. And by controlling each drive motor, it is possible to rotate the image carrier of each color independently.

  By the way, in such a tandem apparatus using a plurality of drive motors, periodic color misregistration may occur due to factors such as shaft runout of each image carrier and eccentricity of a gear directly connected to each image carrier. . Therefore, in order to correct this periodic color shift, the four drive motors are individually controlled. That is, by controlling each drive motor individually, the rotational phases of the four color image carriers are individually controlled to adjust the rotational phase relationship between the respective color image carriers. As a result, periodic color misregistration is suppressed and image quality is improved.

Japanese Patent Laying-Open No. 2003-211943 (second page, FIG. 12)

  Incidentally, in the apparatus described in Patent Document 1, the rotational phase adjustment between the four image carriers is performed as follows. In this apparatus, when a motor activation command is given to the motor control unit that controls the drive motor, the drive of all the drive motors is started. Then, after waiting for the rotation speeds of all the drive motors to reach the steady rotation speed (corresponding to the “target rotation speed” of the present invention), the yellow image carrier (reference “ The detection of the rotational phase difference between the reference image carrier and the remaining image carriers is started. That is, when the reference position (home position) of the yellow image carrier is detected by the photosensor provided in correspondence with the reference image carrier, the counter value for time measurement is cleared, and then the count value is obtained at a constant cycle. Increment. Then, the increment of the count value is stopped when the reference position (home position) of the magenta image carrier is detected by the photosensor provided corresponding to the remaining image carrier, for example, the magenta image carrier. Since the count value thus obtained corresponds to position error information, this position error information is fed back to the position control loop of the drive motor, and the drive motor is controlled so as to eliminate the position error. As a result, the rotational phase of the image carrier is substantially the same between yellow and magenta, and the periodic color shift between the two colors is suppressed.

  Such detection of rotational phase difference and rotational phase adjustment are performed in response to a print command, and must be performed before a toner image is formed on each image carrier. Therefore, in order to shorten the time from the print command to the first print output, that is, the first print time, it is required to perform the rotational phase difference detection process and the rotational phase adjustment process as early as possible. . However, in the conventional apparatus, the rotational phase difference between the reference image carrier and the remaining image carriers can be detected only after the rotational speeds of all the drive motors reach the steady rotational speed. Further, the rotation phase cannot be adjusted between the image carriers based on the rotation phase difference. Therefore, in order to shorten the first print time, there is a demand for a technology that enables early detection processing and rotational phase adjustment processing of the rotational phase difference.

  The present invention has been made in view of the above problems, and at least one image carrier is connected to each of a plurality of drive motors that rotate at a predetermined target rotational speed to rotationally drive the plurality of image carriers. However, in an image forming apparatus that forms a color image by superimposing toner images formed on each of the plurality of image carriers, early detection of the rotational phase difference between the image carriers and early adjustment of the rotational phase are performed. The purpose is to make it possible.

In the image forming apparatus according to the present invention, at least one image carrier is connected to each of a plurality of drive motors that rotate at a predetermined target rotational speed, and the plurality of image carriers are rotationally driven. An image forming apparatus that forms a color image by superimposing toner images formed on each image carrier, and is provided corresponding to each of a plurality of drive motors in order to achieve the above object. A plurality of frequency generators for detecting a rotation frequency of the driving motor to output a pulse signal corresponding to the rotation frequency, and a reference among a plurality of image carriers based on the pulse signals output from the plurality of frequency generators The rotational phase difference of the remaining image carrier relative to the reference image carrier is determined, and a plurality of drive motors are controlled based on the rotational phase difference to adjust the rotational phase relationship between the plurality of image carriers. And phase control means for, provided corresponding to each of the plurality of image bearing members, and a plurality of detecting means, each of which outputs a detection signal by detecting the reference position of the corresponding image bearing member, a phase control means The image carrier corresponding to the detection signal output first from the start of rotation of the plurality of drive motors is used as a reference image carrier, and detection signals from detection means provided corresponding to the reference image carrier are obtained. Based on the number of pulses obtained by counting the pulse signal output between the output and the output of the detection signal from the detection means provided corresponding to the remaining image carrier, the rotational speed of the drive motor is the target It is characterized in that the rotational phase difference is obtained before the rotational speed is reached .

Further, the phase adjustment method according to the present invention is configured so that each of the plurality of image carriers is connected to each of the plurality of drive motors by rotating at least one image carrier and rotating the plurality of image carriers. A phase adjustment method for adjusting a rotational phase relationship between a plurality of image carriers in an image forming apparatus that forms a color image by superimposing toner images to be formed. A step of generating a pulse signal corresponding to the rotational frequency of the drive motor for each of the motors, a step of detecting a reference position of each of the plurality of image carriers and outputting a detection signal, and a plurality of image carriers based on the pulse signals A step of obtaining a rotational phase difference of the remaining image carrier relative to a reference image carrier as a reference, and a step of adjusting a rotational phase relationship by controlling a plurality of drive motors based on the rotational phase difference; Provided, first the reference image bearing member of the image bearing member corresponding to the detection signal output from the rotation start of driving of the plurality of drive motors, the output of the detection signal corresponding to the reference image bearing member, the rest of the image bearing member The rotational phase difference is obtained before the rotational speed of the drive motor reaches the target rotational speed based on the number of pulses obtained by counting the pulse signals output between the detection signals corresponding to .

In the invention thus configured (image forming apparatus and phase adjustment method in the apparatus), a frequency generator is provided for each of the plurality of drive motors, and each frequency generator is provided with a corresponding drive motor. Is detected and a pulse signal corresponding to the rotation frequency is output. This pulse signal reflects the rotational drive state of the drive motor that changes from moment to moment. For this reason, it is possible to refer to the pulse signal while the drive motor is in a steady state, and while it is in an unsteady state, for example, while the rotational speed is being accelerated. The rotational drive state of the drive motor can be accurately grasped. That is, the rotational phase difference between the image carriers can be accurately obtained without any restriction on the timing for obtaining the rotational phase difference of the image carriers. Therefore, the rotational phase difference between the image carriers can be detected at an early stage, and the rotational phase adjustment between the image carriers can be performed at an early stage. Further, the reference positions of a plurality of image carriers are detected, and based on the detection signals, the detection signals corresponding to the reference image carriers are output and the detection signals corresponding to the remaining image carriers are output. The rotational phase difference can be obtained more accurately by obtaining the number of pulses obtained by counting the number of pulse signals to be obtained as the rotational phase difference. Furthermore, the rotation phase difference can be obtained based on the detection signal output first by setting the image carrier corresponding to the detection signal output first from the start of rotation of each drive motor as the reference image carrier. it can. That is, when the detection signal is output, the rotational phase difference derivation process can be immediately executed, which is advantageous in shortening the first print time.

  Here, for example, in a device in which the ready signal is output to the phase control means when the rotational speed of the drive motor reaches the target rotational speed after the rotational drive of the drive motor is started, the phase control means before the ready signal is output. You may comprise so that a rotation phase difference may be calculated | required. In this way, the rotational phase difference can be detected without waiting for the output of the ready signal, thereby shortening the first print time.

  Further, since the rotational phase difference is obtained based on the pulse signal reflecting the rotational driving state of the drive motor, the rotational phase difference can be obtained even while the rotational speed of the drive motor is increased.

  When the rotational phase difference is detected before the ready signal is output as described above, the rotational phase relationship among the plurality of image carriers is further controlled by controlling the plurality of drive motors before the ready signal is output. You may comprise so that it may adjust. Thus, the first print time can be further shortened by performing not only the detection of the rotational phase difference but also the adjustment of the rotational phase before the output of the ready signal. Of course, after the ready signal is output for all of the drive motors, the phase control means may control the drive motor to adjust the rotational phase relationship among the plurality of image carriers. In this case, since the drive motor is controlled in a state where all the drive motors are stably rotated at the target rotation speed, the rotation phase adjustment is more stable than the device that controls before the ready signal is output. Excellent in terms.

  Moreover, you may start the rotational drive of a several drive motor substantially simultaneously. The phase control unit may derive the rotational phase difference and adjust the rotational phase relationship after at least one detection signal is output from the start of rotational driving of the plurality of drive motors. With this configuration, it is possible to reliably perform the rotational phase difference detection process that combines the detection signal and the pulse signal.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. The apparatus 1 includes a color printing process for forming a full color image by superposing four color toners (developers) of black (K), cyan (C), magenta (M), and yellow (Y), and black (K ) To selectively execute monochromatic printing processing for forming a monochrome image using only toner. In this image forming apparatus 1, when an image forming command (printing command) is given to a main controller (not shown) from an external device such as a host computer, an engine controller (not shown) is operated in accordance with the command from the main controller. Each part EG is controlled to execute a predetermined image forming operation, and an image corresponding to the image forming command is formed on a sheet (recording material) S such as a copy sheet, a transfer sheet, a sheet, and an OHP transparent sheet.

  1, an image forming apparatus 1 according to the present embodiment includes a housing body 2, a first opening / closing member 3 that is detachably mounted on the front surface of the housing body 2 (the right-hand side surface in FIG. 1), and the housing body 2. And a second opening / closing member 4 (also serving as a paper discharge tray) mounted on the upper surface so as to be freely opened and closed.

  In the housing main body 2, an electrical component box 5 containing a power circuit board, a main controller, and an engine controller is provided. An image forming unit 6, a transfer belt unit 9, and a paper feed unit 10 are also disposed in the housing body 2. On the other hand, a fixing unit 12 is disposed on the first opening / closing member 3 side. In this embodiment, the consumables in the image forming unit 6 and the paper feeding unit 10 are configured to be detachable from the housing body 2. The consumables and the transfer belt unit 9 can be removed and repaired or exchanged.

  The transfer belt unit 9 is disposed below the housing body 2 and is driven to rotate by a black drive motor described later, and a driven roller 15 disposed obliquely above the drive roller 14. An intermediate transfer belt 16 that is stretched between the rollers 14 and 15 and driven to circulate in the direction of the arrow D16 in the figure, and a belt cleaner 17 that abuts against the surface of the intermediate transfer belt 16. The driven roller 15 is disposed obliquely above the drive roller 14 (upward on the left hand in FIG. 1). For this reason, the intermediate transfer belt 16 rotates and moves in the direction D16 while being inclined. Further, the belt surface 16a in which the belt conveyance direction D16 when the intermediate transfer belt 16 is driven is downward (right downward in FIG. 1) is positioned below. In the present embodiment, the belt surface 16a is a belt tension surface (surface pulled by the drive roller 14) when the belt is driven, and the peripheral speed is lower than the peripheral speed of the photosensitive drum (image carrier) 20 of each color. have. In this way, by setting the peripheral speed of the intermediate transfer belt 16 to be slower than the peripheral speed of each photosensitive drum 20, the photosensitive drum 20 is pulled by the intermediate transfer belt 16 in a direction that suppresses rotation. Driving.

The drive roller 14 also serves as a backup roller for the secondary transfer roller 19. A rubber layer having a thickness of about 3 mm and a volume resistivity of 10 ⁵ Ω · cm or less is formed on the peripheral surface of the drive roller 14, and the illustration is omitted by grounding through a metal shaft 2. A conductive path of the secondary transfer bias supplied from the secondary transfer bias generator through the secondary transfer roller 19 is used. Thus, by providing the driving roller 14 with a rubber layer having high friction and shock absorption, it is difficult for the impact when the sheet S enters the secondary transfer portion to be transmitted to the intermediate transfer belt 16, and deterioration of image quality is prevented. can do.

  In the present embodiment, the diameter of the driving roller 14 is smaller than the diameter of the driven roller 15. Thereby, the sheet S after the secondary transfer can be easily peeled by the elastic force of the sheet S itself. The driven roller 15 is also used as a backup roller for the belt cleaner 17. The belt cleaner 17 is provided on the side of the belt surface 16a facing downward in the transport direction, and includes a cleaning blade 17a that removes residual toner and a toner transport member that transports the removed toner, as shown in FIG. Yes. The cleaning blade 17a contacts the intermediate transfer belt 16 at a portion where the intermediate transfer belt 16 is wound around the driven roller 15, and cleans and removes toner remaining on the surface of the intermediate transfer belt 16 after the secondary transfer.

  The driving roller 14 and the driven roller 15 are rotatably supported by a support frame (not shown) of the transfer belt unit 9. Further, a primary transfer roller 21 is provided on the back surface of the belt surface 16a facing downward in the transport direction of the intermediate transfer belt 16 so as to face the photosensitive drum 20 of each image forming station Y, M, C, K described later. . These four primary transfer rollers 21 are rotatably supported with respect to the support frame, and are electrically connected to a primary transfer bias generator (not shown), and generate the primary transfer bias at an appropriate timing. A primary transfer bias is applied from the portion.

  The support frame is rotatable with respect to the housing main body 2 in the arrow direction D21 with the drive roller 14 as a rotation center. Then, by actuating an actuator (not shown), the support frame is rotated to face the photosensitive drums 20 of the yellow (Y), magenta (M), and cyan (C) image forming stations Y, M, and C. The primary transfer roller 21 arranged in this manner approaches the photosensitive drum 20 and moves away from the photosensitive drum 20. For this reason, when the primary transfer rollers 21 for yellow, magenta, and cyan are moved closer to the photosensitive drum 20, they are brought into contact with the photosensitive drum 20 with the intermediate transfer belt 16 interposed therebetween (solid line in FIG. 1). This contact position is the primary transfer position, and the toner image is transferred to the intermediate transfer belt 16 at the primary transfer position. Conversely, when the primary transfer rollers 21 for yellow, magenta, and cyan move away from the photosensitive drum 20, the photosensitive drum 20 and the intermediate transfer belt 16 of the image forming stations Y, M, and C are separated from each other (FIG. Dashed line in 1). On the other hand, the primary transfer roller 21 disposed facing the photosensitive drum 20 of the black (K) image forming station K rotates while being in contact with the photosensitive drum 20 with the intermediate transfer belt 16 interposed therebetween. Is configured to do. Therefore, as shown by the solid line in FIG. 1, the color printing process can be executed by positioning all the primary transfer rollers 21 on the photosensitive drum 20 side. On the other hand, as shown by a broken line in FIG. 5, the intermediate transfer belt is executed while only the monochrome printing process is performed by leaving the primary transfer roller 21 for black and separating the other primary transfer roller 21 from the photosensitive drum 20. 16 is separated from the image forming stations Y, M, and C, and yellow, magenta, and cyan colors can be set to a non-printing state. Note that the primary transfer roller 21 for black may also be configured to move away from the photosensitive drum 20 as necessary.

  A test pattern sensor 18 is installed on the support frame of the transfer belt unit 9 in the vicinity of the drive roller 14. This test pattern sensor 18 is a sensor for positioning each color toner image on the intermediate transfer belt 16, detecting the density of each color toner image, and correcting the color shift and image density of each color image.

  The image forming unit 6 includes image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality (four in this embodiment) of different color images. I have. Each of the image forming stations Y, M, C, and K is provided with a photosensitive drum 20 corresponding to the “image carrier” of the present invention. A charging unit 22, an image writing unit 23, a developing unit 24, and a photoconductor cleaner 25 are disposed around each photoconductor drum 20. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. In FIG. 1, since the image forming stations of the image forming unit 6 have the same configuration, for convenience of illustration, only some of the image forming stations are denoted by reference numerals, and the other image forming stations are omitted. . Further, the arrangement order of the image forming stations Y, M, C, and K is arbitrary.

  The photosensitive drums 20 of the image forming stations Y, M, C, and K are disposed so as to be in contact with the belt surface 16a facing downward in the transport direction of the intermediate transfer belt 16 at the primary transfer position TR1. As a result, the image forming stations Y, M, C, and K are also arranged in a direction inclined to the left in the drawing with respect to the driving roller 14. Each of these photosensitive drums 20 is connected to a dedicated drive motor and is driven to rotate at a predetermined peripheral speed in the conveyance direction of the intermediate transfer belt 16 as indicated by an arrow D20 in the figure. The drive mechanism and drive control of the photosensitive drum 20 will be described in detail later.

  The charging unit 22 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to be driven to rotate in contact with the surface of the photosensitive drum 20 at a charging position, and at a peripheral speed in the driven direction with respect to the photosensitive drum 20 as the photosensitive drum 20 rotates. Followed rotation. The charging roller is connected to a charging bias generator (not shown), and receives the charging bias from the charging bias generator to charge the surface of the photosensitive drum 20 at the charging position.

  The image writing unit 23 is an array writing in which elements such as a liquid crystal shutter including a light emitting diode and a backlight are arranged in a line in the axial direction of the photosensitive drum 20 (direction perpendicular to the paper surface of FIG. 1). The head is used and is spaced from the photosensitive drum 20. The array-like writing head has a shorter optical path length and is more compact than the laser scanning optical system. Therefore, it can be disposed close to the photosensitive drum 20 and has the advantage that the entire apparatus can be downsized.

  Next, details of the developing unit 24 will be described on behalf of the image forming station K. The developing unit 24 includes a toner storage container 26 for storing toner, two toner agitation supply members 28 and 29 disposed in the toner storage container 26, and a partition member disposed in proximity to the toner agitation supply member 29. 30, a toner supply roller 31 disposed above the partition member 30, a developing roller 33 that contacts the toner supply roller 31 and the photosensitive drum 20 and rotates in a direction indicated by an arrow at a predetermined peripheral speed, and a developing roller And a regulating blade 34 abutting on the bearing 33.

  In each developing unit 24, the toner stirred and carried by the toner stirring supply member 29 is supplied to the toner supply roller 31 along the upper surface of the partition member 30. The toner thus supplied is supplied to the surface of the developing roller 33 via the supply roller 31. The toner supplied to the developing roller 33 is regulated to a predetermined layer thickness by the regulating blade 34 and is conveyed to the photosensitive drum 20. The charged toner is developed at a developing position where the developing roller 33 and the photosensitive drum 20 come into contact with each other by a developing bias applied to the developing roller 33 from a developing bias generator (not shown) electrically connected to the developing roller 33. Moves from the developing roller 33 to the photosensitive drum 20, and the electrostatic latent image formed by the image writing unit 23 is visualized.

  In this embodiment, a photoreceptor cleaner 25 is provided in contact with the surface of the photoreceptor drum 20 on the downstream side of the primary transfer position TR1 in the rotation direction D20 of the photoreceptor drum 20. The photoconductor cleaner 25 is in contact with the surface of the photoconductor drum 20 to remove the toner remaining on the surface of the photoconductor drum 20 after the primary transfer.

  The sheet feeding unit 10 includes a sheet feeding unit including a sheet feeding cassette 35 in which sheets S are stacked and held, and a pickup roller 36 that feeds the sheets S from the sheet feeding cassette 35 one by one. In the first opening / closing member 3, a registration roller pair 37 that defines the timing of feeding the sheet S to the secondary transfer region TR 2, and a secondary transfer unit that is pressed against the drive roller 14 and the intermediate transfer belt 16. A secondary transfer roller 19, a fixing unit 12, a paper discharge roller pair 39, and a duplex printing conveyance path 40 are provided.

  The secondary transfer roller 19 is provided so as to be able to come into contact with and separate from the intermediate transfer belt 16 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 12 includes a heating roller 45 that includes a heating element such as a halogen heater and is rotatable, and a pressure roller 46 that presses and biases the heating roller 45. The image secondarily transferred to the sheet S is fixed to the sheet S at a predetermined temperature at a nip formed by the heating roller 45 and the pressure roller 46. In the present embodiment, the fixing unit 12 can be disposed in a space formed obliquely above the intermediate transfer belt 16, in other words, in a space opposite to the image forming unit 6 with respect to the intermediate transfer belt 16. Thus, heat transfer to the electrical component box 5, the image forming unit 6, and the intermediate transfer belt 16 can be reduced, and the frequency of performing the color misregistration correction operation for each color can be reduced.

  Further, the sheet S thus subjected to the fixing process is conveyed to a second opening / closing member (discharge tray) 4 provided on the upper surface portion of the housing body 2 via the discharge roller pair 39. Further, when images are formed on both sides of the sheet S, when the rear end portion of the sheet S on which the image is formed on one side as described above is conveyed to the reverse position behind the pair of discharge rollers 39. The rotation direction of the discharge roller pair 39 is reversed, whereby the sheet S is conveyed along the duplex printing conveyance path 40. Then, it is put on the conveyance path again before the registration roller pair 37. At this time, the surface of the sheet S to which the image is transferred by contacting the intermediate transfer belt 16 in the secondary transfer region TR2 is transferred first. It is the opposite side of the surface that was made. In this way, images can be formed on both sides of the sheet S.

  FIG. 2 is a schematic diagram showing the positional relationship between the intermediate transfer belt and the photosensitive drums of the respective colors. FIG. 3 is a diagram showing a driving mechanism for rotating the photosensitive drum. FIG. It is a block diagram which shows the electrical structure which controls the rotation phase of a body drum. Hereinafter, a drive mechanism and drive control for driving the photosensitive drum 20 will be described in detail with reference to these drawings.

  In the image forming apparatus 1 according to this embodiment, four color photosensitive drums 20 are provided. In order to rotationally drive these photosensitive drums 20, four drive motors 50 (50Y, 50M, 50C,. 50K). By controlling each drive motor 50, it is possible to independently rotate the photosensitive drums (image carriers) 20 of the respective colors. Since the drive mechanisms for rotating the photosensitive drum 20 have the same configuration, only the yellow drive mechanism will be described here, and the other toner colors will be described with the same or corresponding reference numerals. Omitted.

  In this embodiment, a DC brushless motor is employed as the yellow drive motor 50Y. A motor pinion 51 is attached to the rotating shaft of the drive motor 50Y, and an idle gear 52 is meshed with the motor pinion 51. An idle gear 53 is attached coaxially to the idle gear 52. When the rotational driving force of the drive motor 50Y is transmitted to the idle gear 52 via the motor pinion 51, the idle gears 52, 53 are integrated with each other. Rotate. On the other hand, the idle gear 53 is meshed with the photoconductor gear 54 that is mounted coaxially with the rotation shaft of the photoconductor drum 20, and the idle gear 53 is driven to rotate as described above, whereby the photoconductor drum 20Y. Is driven to rotate. In this embodiment, in order to perform image formation while rotating the photosensitive drum 20 at 132 rpm, for example, the target rotational speed of the drive motor 50Y and the gear configurations of the motor pinion 51 and the gears 52 to 54 are set as follows. Can do.

(1) Target rotational speed of drive motor 50Y: 1905rpm
(2) About motor pinion 51 Number of teeth: 12
Pitch circle diameter: 6.4mm
(3) About idle gear 52 Number of teeth: 48
Pitch circle diameter: 25.5mm
(4) About idle gear 53 Number of teeth: 30
Pitch circle diameter: 16.0mm
(5) About the photoreceptor gear 54 Number of teeth: 108
Pitch circle diameter: 57.5mm
By using the driving force transmission mechanism including the gear group configured as described above, when the rotational speed of the drive motor 50Y reaches the target rotational speed (1905 rpm), the rotational speed is set to 476 rpm by the motor pinion 51 and the gear 52. It is decelerated and further decelerated to a desired rotational speed (132 rpm) by the gears 52 and 53.

  Further, in this embodiment, the photoconductor gear 54 directly connected to the rotating shaft of the photoconductor drum 20 has a larger diameter than the diameter (30 mm) of the photoconductor drum 20, and a recess 55 is formed at one place on the outer peripheral portion thereof. Is formed. A reflective optical sensor 56 is arranged as a rotational phase detection sensor on the rotation locus of the recess 55. For this reason, every time the reference position of the photosensitive drum 20 passes through the rotation phase detection sensor 56, a detection signal is output from the rotation phase detection sensor 56 to the pulse counter 58 of the phase control unit 57 provided in the engine controller. That is, in this embodiment, the rotational phase detection sensor 56 corresponds to the “detection means” of the present invention, and whether or not the photosensitive drum 20 has passed the reference position based on the output signal from the rotational phase detection sensor 56. Can be detected accurately, and the rotational phase of the photosensitive drum 20 can be detected.

  Further, the drive motor 50Y is provided with a frequency generator 59Y, which generates a frequency signal (hereinafter referred to as “FG signal”) corresponding to the rotation speed of the drive motor 50Y and controls the drive motor 50Y. To the unit 60Y and the pulse counter 58. The configuration of the frequency generator 59Y is not particularly limited, but in this embodiment, a pulse signal obtained by dividing one rotation of the drive motor 50Y by 60 is output as an FG signal. Therefore, the FG signal output from the frequency generator 59Y reflects the rotational driving state of the driving motor 50Y that changes from moment to moment, and while the driving motor 50Y reaches the target rotational speed and is in a steady state. Of course, while in the unsteady state, for example, even while the rotational speed is being accelerated, the rotational drive state of the drive motor 50Y can be accurately grasped by referring to the FG signal. .

  Each drive motor 50 and the drive mechanism are configured as described above. While the apparatus 1 is waiting for an image formation command (print command) from an external device such as a host computer, all the drive motors 50 stop rotating. ing. When a print command is given, the main controller converts the job data into a format suitable for the operation instruction of the engine unit EG and sends it to the engine controller. In response to this, the engine controller gives a drive command to the phase control unit 57 to rotate the photosensitive drum 20 at a desired target rotational speed (132 rpm). More specifically, the phase control unit 57 includes a pulse counter 58, a comparison unit 61, and a rotation speed setting unit 62 as shown in FIG. After the rotation phase is adjusted, the respective photosensitive drums 20 are rotated at a desired rotation speed (132 rpm).

  FIG. 5 is a flowchart showing an operation for adjusting the rotational phase between the photosensitive drums. FIG. 6 is a flowchart showing the reference color determining operation. FIG. 7 is a flowchart showing the derivation of the rotational phase difference and the phase adjustment operation. Further, FIG. 8 is a diagram showing the derivation of the rotational phase difference and the phase adjustment operation. Hereinafter, the rotational phase difference detection operation and the rotational phase adjustment operation will be described in detail with reference to these drawings.

  In this apparatus, when a drive command is given from the engine controller to the phase control unit 57 in response to a print command from an external device, driving of the photosensitive drum 20 is started for all colors (step S1). At this time, no pulse output of the FG signal is given to the pulse counter 58, and the rotation speed setting unit 62 drives each drive motor 50 at a preset acceleration based on the signal given from the comparison unit 61. A control signal is given to each motor rotation control part 60Y, 60M, 60C, 60K. As a result, the motor rotation control units 60Y, 60M, 60C, and 60K operate the drive motors 50Y, 50M, 50C, and 50K, respectively, to start driving the photosensitive drum 20.

  When the drive motors 50 (50Y, 50M, 50C, 50K) are operated to rotate the photosensitive drums 20 as described above, the rotational speed of the drive motor 50 gradually increases from the start of driving as shown in FIG. It will be accelerated. In this embodiment, the rotational speed of the drive motor 50 is set to reach the target rotational speed in about 0.5 seconds from the start of the rotational driving. Further, an FG signal is output as the drive motor 50 rotates. This FG signal reflects the rotational state of the drive motor 50, and the pulse interval of the FG signal becomes shorter as the rotational speed increases. That is, by monitoring the FG signal, it is possible to accurately grasp the rotational drive state of the drive motor 50Y regardless of whether it is in a steady state or an unsteady state. On the other hand, when the photosensitive drum 20 is rotationally driven by the drive motor 50 and the reference position of the photosensitive drum 20 passes through the rotational phase detection sensor 56, a detection signal from the rotational phase detection sensor 56 is sent to the pulse counter 58 of the phase control unit 57. Is output. This detection signal functions as a signal for detecting the rotation phase of the photosensitive drum 20, that is, a rotation phase detection signal. By referring to the rotation phase detection signal of each color, another color (hereinafter referred to as “adjustment color”) with respect to the reference color is referred to. The rotation phase difference of the photosensitive drum 20 can be obtained. In this embodiment, the toner color from which the rotational phase detection signal is output first among the four colors is used as the reference color (step S2).

In step S2, as shown in FIG. 6, when the first rotation phase detection signal is detected (step S21), the first detection signal is output from the rotation phase detection sensor 56 of any toner color. A reference color is determined by determining whether it is present (steps S22 to S28). That means
Output from rotational phase detection sensor 56K: reference color is black,
Output from the rotational phase detection sensor 56Y: the reference color is yellow,
Output from rotational phase detection sensor 56M: reference color is magenta
Output from rotational phase detection sensor 56C: reference color is cyan,
It is judged. When the reference color is determined in this way, the number of FG pulses FGC (0) stored in the pulse counter 58 of the phase control unit 57 is cleared (step S29). This FG pulse number FGC (0) is a value obtained by counting the number of pulses of the FG signal. As will be described later, in this embodiment, the FG pulse number FGC (0) is used as an index value indicating the rotational phase difference. Is done.

  After the reference color is determined as described above and the FG pulse number FGC (0) of the reference color is cleared, the FG output from the frequency generator 59 provided corresponding to the drive motor 50 for the reference color. Based on the signal, the pulse counter 58 starts counting FG pulses (step S3). Then, phase adjustment is performed for each of the remaining toner colors (first adjustment color to third adjustment color) (step S4).

  In this phase adjustment process, the phase control unit 57 operates as follows to determine the rotation phase difference with respect to the reference color for the nth adjustment color (n = 1, 2, 3), and based on the rotation phase difference, the drive motor 50 is accelerated / decelerated to adjust the rotation phase. That is, the FG pulse number FGC (n) is cleared (step S41). When the rotational phase detection signal is detected in step S42, the current reference color FG pulse number FGC (0) is stored as the rotational phase shift amount (phase difference) RD (step S43). Thus, the rotational phase shift amount RD (n) of the nth adjustment color with respect to the reference color can be obtained.

In addition to the detection of the rotational phase detection signal, the pulse counter 58 starts counting FG pulses based on the FG signal output from the frequency generator 59 provided corresponding to the drive motor 50 of the adjustment color (step S44). ). Then, until the rotational speed of the drive motor 50 reaches the target rotational speed and the READY signal is output, the following relational expression:
FGC (n) = FGC (0) + RD (n)
The acceleration / deceleration control of the drive motor 50 of the adjustment color is performed (step S45). As a result, the phase of the photosensitive drum 20 of the adjustment color that has been delayed from the reference color catches up with the photosensitive drum 20 of the reference color, and the rotational phase difference is eliminated. The rotational phases are matched, and the photosensitive drums 20 for both colors are rotated at a predetermined rotational speed.

  As described above, according to this embodiment, the rotational frequency of the drive motor 50 is detected by the frequency generator 59 provided corresponding to each of the drive motors 50 to obtain the FG signal corresponding to the rotational frequency. Yes. This FG signal reflects the rotational drive state of the drive motor 50 that changes from moment to moment. For this reason, the rotational drive state of the drive motor 50 can be accurately grasped by referring to the FG signal, and the rotational phase difference of the photosensitive drum 20 can be accurately obtained. In particular, in this embodiment, the rotational phase shift amount RD (n) is derived from the start of rotation of the drive motor 50 until the ready signal is output, and the photosensitive drum 20 is based on the rotational phase shift amount RD (n). The rotation phase is adjusted between the two. Thus, early detection of the rotational phase difference and early adjustment of the rotational phase between the photosensitive drums (image carriers) 20 are performed, and a high-quality color image can be formed in an excellent first print time. it can.

  Further, since the rotational phase difference is obtained by combining the rotational phase detection signal output from the rotational phase detection sensor 56 and the FG signal, a highly accurate rotational phase difference can be obtained. Since the drive control of the drive motor 50 is performed based on the rotation phase difference, the rotation phase can be adjusted with high accuracy.

  In addition, the drive start timing of the drive motors 50 for each color is not particularly limited. However, as in the present embodiment, the phase control unit starts almost simultaneously and outputs the first rotational phase detection signal. By configuring the rotational phase difference to be derived and the rotational phase relationship to be adjusted by 57, the rotational phase difference detection process can be performed earlier and more reliably.

  Further, the toner color corresponding to the rotational phase detection signal output first from the start of the rotational drive of all the drive motors 50 is used as the reference color, that is, the photosensitive drum 20 of the toner color is the “reference image carrier” of the present invention. And the phase adjustment is performed by obtaining the rotational phase difference between the reference image carrier and the photosensitive drum 20 of the adjustment color. For this reason, the following effects can be obtained as compared with the case where the reference color is set in advance. That is, in an apparatus in which the reference color is fixed, it is necessary to detect the reference position of the reference image carrier and wait for the rotation phase detection signal to be output from the rotation phase detection sensor 56 to obtain the rotation phase difference. On the other hand, in this embodiment, the rotational phase difference can be obtained based on the rotational phase detection signal output first. That is, when the rotational phase detection signal is output, the rotational phase difference can be derived immediately, which is very advantageous for shortening the first print time.

  FIG. 9 is a flowchart showing another embodiment of the image forming apparatus according to the present invention. FIG. 10 is a diagram showing the derivation of the rotational phase difference and the phase adjustment operation in the embodiment of FIG. In this embodiment, as in the previous embodiment, the adjustment color of the photosensitive drum 20 with respect to the reference color photosensitive drum 20 is determined based on the rotation phase detection signal and the FG signal before the ready signal is output. The rotational phase difference is obtained. However, after the ready signal is output in step S46, that is, after the rotational speed of the drive motor 50 has reached a steady state, the drive phase of the adjustment color is controlled to adjust the rotation phase. Thus, in this embodiment, since the drive motor 50 is controlled in a state where the drive motor 50 is stably rotated at the target rotation speed, the rotation phase adjustment can be performed more stably. .

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the rotational speed is linearly increased after the drive of the drive motor 50 is started. However, the rotational speed may be increased stepwise.

  In the above-described embodiment, the reference position of the photosensitive drum 20 is detected by detecting the recess 55 provided in the photosensitive gear 54 that is directly connected to the rotation shaft of the photosensitive drum 20, and is rotated from the rotational phase detection sensor 56. Although the phase detection signal is output, the rotational phase detection method is not limited to this, and any method can be used as long as the reference position of the photosensitive drum 20 can be detected. For example, a characteristic portion that rotates with the rotation of the drum may be provided in a part of the photosensitive drum 20, and a sensor may be disposed on the rotation locus of the characteristic portion.

  In the above-described embodiment, the photosensitive drums 20Y, 20M, 20C, and 20K are connected to the drive motors 50Y, 50M, 50C, and 50K, respectively, and the respective photosensitive drums 20 are rotationally driven. At least one or more photosensitive drums may be connected to each other to rotate the four color photosensitive drums. For example, the black photosensitive drum 20K may be driven by a black driving motor, while the yellow, magenta, and cyan photosensitive drums may be driven by a color driving motor. In such an apparatus, as in the above embodiment, the rotational phase difference is derived based on the FG signal from the start of rotation of the drive motor until the ready signal is output, and the rotational position is output before or after the ready signal is output. By adjusting the rotational phase between the photosensitive drums based on the phase difference, early detection of the rotational phase difference between the photosensitive drums and early adjustment of the rotational phase are possible, and high-quality color can be achieved with excellent first print time. An image can be formed.

  In the above embodiment, the reference color is changed based on the output timing of the rotation phase detection signal. However, the reference color may be fixed in advance. Also in this case, the same effects as those in the above-described embodiment can be obtained by obtaining the rotational phase difference of each photosensitive drum based on the FG signal and performing the rotational phase adjustment based on the rotational phase difference.

  Further, in each of the above embodiments, the present invention is applied to an apparatus that forms a color image using toners of four colors of yellow, magenta, cyan, and black. The types and number of toner colors are described above. Without being limited thereto, the plurality of image carriers are connected to each of a plurality of drive motors, and at least one image carrier such as a photosensitive drum is connected to rotate the plurality of image carriers. The present invention can be applied to all image forming apparatuses that form a color image by superimposing toner images formed on each of the above.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a schematic diagram illustrating an arrangement relationship between an intermediate transfer belt and photosensitive drums of respective colors. FIG. 3 is a diagram illustrating a driving mechanism that rotationally drives a photosensitive drum. FIG. 3 is a block diagram showing an electrical configuration for controlling the rotational phase of the photosensitive drum. 6 is a flowchart illustrating an operation for adjusting a rotation phase between photosensitive drums. 5 is a flowchart showing a reference color determining operation. The flowchart which shows derivation | leading-out of rotation phase difference, and phase adjustment operation | movement. The figure which shows derivation | leading-out of rotation phase difference, and phase adjustment operation | movement. 9 is a flowchart showing another embodiment of the image forming apparatus according to the present invention. The figure which shows derivation | leading-out of rotation phase difference and phase adjustment operation | movement in embodiment of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 20, 20Y, 20M, 20C, 20K ... Photosensitive drum (image carrier), 50, 50Y, 50M, 50C, 50K ... Drive motor, 56, 56Y, 56M, 56C, 56K ... Rotation phase Detection sensor (detection means) 57: Phase control unit 58: Pulse counter 59, 59Y, 59M, 59C, 59K ... Frequency generator RD: Rotation phase shift amount (rotation phase difference)

Claims (7)

At least one image carrier is connected to each of a plurality of drive motors that rotate at a predetermined target rotation speed, and the plurality of image carriers are rotationally driven to form each of the plurality of image carriers. In an image forming apparatus that forms a color image by superimposing toner images to be
A plurality of frequency generators provided corresponding to each of the plurality of drive motors, each detecting a rotation frequency of the corresponding drive motor and outputting a pulse signal corresponding to the rotation frequency;
Based on the pulse signals output from the plurality of frequency generators, the rotational phase difference of the remaining image carriers relative to the reference image carrier serving as a reference among the plurality of image carriers is obtained, and based on the rotational phase difference, Phase control means for controlling a plurality of image bearing members by controlling a plurality of drive motors ;
A plurality of detection means provided corresponding to each of the plurality of image carriers, each detecting a reference position of the corresponding image carrier and outputting a detection signal;
With
The phase control means is provided corresponding to the reference image carrier, with the image carrier corresponding to the detection signal output first from the start of rotational driving of the plurality of drive motors as the reference image carrier. Based on the number of pulses obtained by counting the pulse signals output between the detection signal output from the detection means and the detection signal output from the detection means provided corresponding to the remaining image carriers. The image forming apparatus characterized in that the rotational phase difference is obtained before the rotational speed of the drive motor reaches the target rotational speed . The image forming apparatus according to claim 1, wherein a ready signal is output to the phase control unit when the rotational speed of the drive motor reaches the target rotational speed after the rotational drive of each drive motor is started.
The image forming apparatus in which the phase control means obtains the rotational phase difference before outputting the ready signal.   The image forming apparatus according to claim 2, wherein the phase control unit obtains the rotational phase difference while increasing the rotational speed of each drive motor.   The image forming apparatus according to claim 2, wherein the phase control unit controls the plurality of drive motors before the ready signal is output to adjust a rotational phase relationship between the plurality of image carriers.   The phase control means controls the plurality of drive motors to adjust the rotational phase relationship among the plurality of image carriers after the ready signal is output for all of the plurality of drive motors. 3. The image forming apparatus according to 3. The image forming apparatus according to any one of claims 1 to 5 the rotational driving of the plurality of drive motors are substantially simultaneously started. At least one image carrier is connected to each of the plurality of drive motors, and the plurality of image carriers are rotationally driven, and the toner images formed on each of the plurality of image carriers are superimposed. In an image forming apparatus for forming a color image, a phase adjustment method for adjusting a rotational phase relationship between the plurality of image carriers,
Creating a pulse signal corresponding to the rotational frequency of the drive motor for each of the plurality of drive motors;
Detecting a reference position of each of the plurality of image carriers and outputting a detection signal;
Obtaining a rotational phase difference of the remaining image carriers relative to a reference image carrier serving as a reference among the plurality of image carriers based on the pulse signals;
Adjusting the rotational phase relationship by controlling the plurality of drive motors based on the rotational phase difference, and
The image carrier corresponding to the detection signal output first from the start of rotation of the plurality of drive motors is used as the reference image carrier, the detection signal output corresponding to the reference image carrier, and the remaining image carriers. The rotational phase difference is obtained before the rotational speed of the drive motor reaches the target rotational speed based on the number of pulses obtained by counting the pulse signals output between the detection signals corresponding to the body. <br/> A phase adjustment method characterized by the above.

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