JP2007024920A - Image forming apparatus and phase adjustment method in this apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply and accurately adjust the phase relationship between image carriers, in an image forming apparatus in which at least one or more image carriers are connected to each of a plurality of drive motors and the plurality of drive motors are driven at a predetermined normal speed, so that toner images formed on each of a plurality of image carriers are superposed, while the plurality of image carriers are rotated, so as to form a color image. <P>SOLUTION: The phase difference between photoreceptor drums is obtained from an output time difference ▵ts, based on a detection signal outputted from a rotation phase detection sensor 56, while the drive motors are driven at a phase detection speed Vi slower than a normal speed Vdef, before the drive motors are driven at the normal speed Vdef. Only a control time ▵tm corresponding to the output time difference ▵ts is shifted to change the drive motors on a control side from the phase detection speed Vi to the normal speed Vdef. Thus, the phase difference between the photoreceptor drums is adjusted to a set phase difference. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention connects at least one or more image carriers to each of a plurality of drive motors, and drives a plurality of image carriers while rotating the plurality of image carriers by driving the plurality of drive motors at a predetermined normal speed. The present invention relates to an image forming apparatus that forms a color image by superimposing toner images formed on each of the carriers, and particularly relates to a technique for adjusting the 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, in the apparatus described in Patent Document 1, for example, three colors of yellow, magenta, and cyan are already phase-adjusted at the assembly stage and rotated by a common drive motor, while the black color is used. Is driven to rotate by a separate and independent drive motor.

  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, a plurality of drive motors are individually controlled. That is, by controlling each drive motor individually, the phase relationship between the image carriers of the respective colors is adjusted by controlling the phases of the image carriers of the four colors. As a result, periodic color misregistration is suppressed and image quality is improved.

JP 2003-66676 A ([0029] to [0036])

  In the apparatus described in Patent Document 1, a drive motor that drives a photosensitive drum whose phase is delayed based on the phase difference of pulses obtained by rotation of the color and black photosensitive drums (image carrier). Is increased to increase the rotational speed of the photosensitive drum, while the drive motor for driving the photosensitive drum whose phase is advanced is decelerated to decrease the rotational speed of the photosensitive drum. As a result, the phase difference between the two photosensitive drums is reduced. This is performed over a period of time until the phases are matched between the two photosensitive drums. In this way, the phase is adjusted while repeating the setting for changing the rotation speed. Moreover, even when the phase alignment is completed, the rotational speed at the end of the phase adjustment is different from the target rotational speed, that is, the rotational speed at the time of image formation, so the drive motor drive speed is set to the normal speed after phase adjustment. It is necessary to control so that all the photosensitive drums are driven at the same target rotational speed. Therefore, the phase adjustment process is complicated.

  The present invention has been made in view of the above-described problems, and connects a plurality of image carriers by connecting at least one image carrier to each of a plurality of drive motors and driving the plurality of drive motors at a predetermined normal speed. In an image forming apparatus that forms a color image by superimposing toner images formed on each of a plurality of image carriers while rotating the body, the phase relationship between the image carriers is easily and accurately adjusted. For the purpose.

  The present invention connects at least one or more image carriers to each of a plurality of drive motors, and drives a plurality of image carriers while rotating the plurality of image carriers by driving the plurality of drive motors at a predetermined normal speed. An image forming apparatus that forms a color image by superimposing toner images formed on each of the carriers, and is provided corresponding to each of the plurality of image carriers to achieve the above object. A plurality of phase detection means for detecting a reference position of the image carrier to be output and outputting a detection signal; and detection signals from the plurality of phase detection means while driving the plurality of drive motors at a phase detection speed slower than the normal speed. The output time difference is calculated, and the timing for changing each drive motor from the phase detection speed to the normal speed or the acceleration pattern for accelerating from the phase detection speed to the normal speed is controlled according to the calculation result. It is characterized in that a phase control means for adjusting the phase relationship between the image bearing member.

  Further, the present invention connects at least one or more image carriers to each of the plurality of drive motors, and drives the plurality of drive motors at a predetermined normal speed while rotating the plurality of image carriers. A phase adjustment method for adjusting a phase relationship between a plurality of image carriers in an image forming apparatus for forming a color image by superimposing toner images formed on each of the image carriers, and achieving the above object A step of detecting a reference position of the image carrier and outputting a detection signal for each of the plurality of image carriers while driving the plurality of drive motors at a phase detection speed slower than the normal speed; The step of obtaining the output time difference of the detection signal between the image carriers and the timing of changing each drive motor from the phase detection speed to the normal speed or acceleration from the phase detection speed to the normal speed according to the output time difference It is characterized by comprising the step of controlling the acceleration pattern that.

  In the invention thus configured (image forming apparatus and phase adjustment method in the apparatus), the drive motor is driven at a phase detection speed slower than the normal speed before being driven to the normal speed. A plurality of image carriers are rotated by this motor drive, and phase detection means provided corresponding to each image carrier detects a reference position and outputs a detection signal. Therefore, the difference in detection signal output time between the image carriers corresponds to the phase difference between the image carriers. Therefore, when changing each drive motor from the phase detection speed to the normal speed, the change timing or acceleration pattern is controlled in accordance with the output time difference, and the phase relationship between the image carriers is adjusted. Thus, after obtaining the output time difference indicating the phase difference between the image carriers, the phase relationship between the image carriers can be adjusted by simply changing the drive speed of each drive motor to the normal speed. That is, the phase relationship between the image carriers can be easily and accurately adjusted.

  Here, one of the plurality of image carriers may be a reference image carrier. Then, the phase difference between the remaining image carriers with respect to the reference image carrier is obtained from the output time differences of the detection signals from the plurality of phase detection means, and a plurality of drive motors are controlled according to the output time differences to control the plurality of images. The phase relationship between the carriers can be easily and accurately adjusted.

  Further, in order to adjust the phase relationship between the image carriers, only the change timing from the phase detection speed to the normal speed may be controlled. That is, while accelerating the speed of the reference drive motor connected to the reference image carrier to the normal speed while fixing the acceleration pattern for accelerating from the phase detection speed to the normal speed, each of the remaining image carriers is The drive motor connected to the image carrier may be accelerated to a normal speed with a delay of a control time corresponding to the phase difference with respect to the image carrier. Thus, motor control can be further simplified by fixing the acceleration pattern for all the drive motors.

  Further, a control table in which the output time difference and the control time are associated with each other may be stored in the storage means, and the motor control may be performed using this control table. That is, an output time difference can be calculated based on detection signals from a plurality of phase detection means, and a control time corresponding to the calculation result can be read from the control table and determined. Of course, the control time may be determined from the output time difference by calculation. However, by using the control table in this way, calculation processing is not required, and the control can be further simplified.

  Also, the load on the drive motor may vary depending on the environment inside the apparatus. When this load fluctuation occurs, the control time suitable for adjusting the phase relationship may change before and after the fluctuation. Therefore, it is desirable to change and set the control time according to the environment inside the apparatus. For example, a plurality of control tables corresponding to the environment inside the apparatus are stored in advance in the storage means, the environment inside the apparatus is detected by the environment detection means, and the calculation result is determined from the control table corresponding to the detection result. You may comprise so that control time may be read and determined. As a result, the control time can be determined using a control table according to the environment inside the apparatus, and more accurate phase adjustment is possible.

  Furthermore, the reference image carrier can be set freely, but the image carrier corresponding to the phase detection means that first outputs the detection signal after a plurality of drive motors have started to be driven almost simultaneously is set as the reference image carrier. May be. In this case, the phase difference between the image carriers can be detected at an early stage, and the phase adjustment between the image carriers can be performed at an early stage, as compared with an apparatus in which the reference image carrier is fixed. .

  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 100 kΩ · cm or less is formed on the peripheral surface of the drive roller 14, and secondary transfer is omitted by grounding through a metal shaft. A conductive path of the secondary transfer bias supplied from the bias generation unit via 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, and FIG. 4 is a phase diagram of the photosensitive drum. It is a block diagram which shows the electric constitution which controls a relationship. 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 form an image while rotating the photosensitive drum 20 at a target rotation speed of 132 rpm (one round time Tdef = 454.5 ms), for example, the normal speed Vdef of the drive motor 50Y is set to 1584 rpm. The reduction ratio of the driving force transmission mechanism having the gear configuration of the motor pinion 51 and the gears 52 to 54 can be set to 1/12.

  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 as the “reference position” of the present invention. A reflective optical sensor 56 is arranged as a phase detection sensor on the rotation locus of the recess 55. For this reason, every time the reference position (concave portion 55) of the photosensitive drum 20 passes through the phase detection sensor 56, a detection signal is output from the phase detection sensor 56 to the phase control unit 57 provided in the engine controller. That is, in this embodiment, the phase detection sensor 56 corresponds to the “phase detection means” of the present invention, and it is determined whether the photosensitive drum 20 has passed the reference position based on the output signal from the phase detection sensor 56. While being able to detect correctly, the rotation 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”) according to the rotational speed of the drive motor 50Y, and supplies it to the drive motor 50 and the phase control unit 57. Output. 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 drive state of the drive motor 50Y that changes from moment to moment, and the drive motor 50Y reaches the drive speed set by the phase control unit 57 and is in a steady state. Of course, while it is in an unsteady state, for example, even while the rotational speed is being accelerated, the rotational drive state of the drive motor 50Y can be determined by referring to the FG signal. Accurately grasp.

  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, after the phase control unit 57 adjusts the phase relationship between the photosensitive drums 20 by executing the processing described below, each of the photosensitive drums 20 is kept steady at a desired rotation speed (132 rpm). Rotate. Note that reference numeral 58 in FIG. 4 denotes a memory, which stores arithmetic expressions, control tables, and the like for phase adjustment described below. Reference numeral 61 denotes a temperature sensor that detects the temperature inside the apparatus (in-machine temperature), and corresponds to the “environment detection means” of the present invention.

  FIG. 5 is a flowchart showing an operation for adjusting the rotational phase between the photosensitive drums. FIG. 6 is a timing chart showing the phase difference derivation and phase adjustment operations. Hereinafter, the phase difference detection operation and the rotation phase adjustment operation between the photosensitive drums 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, the drive speeds of the drive motors 50Y, 50M, 50C, and 50K are accelerated in two stages to a normal speed Vdef. Adjust to. As the first stage, the drive of all the drive motors 50Y, 50M, 50C, 50K is started simultaneously (step S1). In this embodiment, the drive speed of the drive motor 50 at this time is half the normal speed Vdef, that is, the phase detection speed Vi.
Vi = Vdef / 2 = 15884 rpm / 2 = 792 rpm
The phase control unit 57 gives control signals (pulse signals) to the motor rotation control units 60Y, 60M, 60C, and 60K so as to drive the drive motors 50 at the phase detection speed Vi. 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. Further, the phase control unit 57 waits for the ready (READY) signal to be output from the drive motor 50 for each color (step S2). This ready signal is a signal output from the drive motor 50 when the rotational speed of the drive motor 50 reaches the set speed range (set speed ± several%). In particular, in the first stage, the phase detection speed Vi is the set speed. Then, by detecting a ready signal from all the drive motors 50, the first stage speed adjustment is completed, and it is confirmed that the drive motor 50 and the photosensitive drum 20 are driven in a steady state. Can do. When the drive motor 50 is driven at the phase detection speed Vi, the rotational speed of the photosensitive drum 20 is 66 rpm, which is half the rotational speed (132 rpm) at the time of image formation, and the one-round time Ti of the photosensitive drum 20 is 909. Double to 1 ms.

  Then, the phase difference between the photosensitive drums 20 is detected while driving all the drive motors 50 at the phase detection speed Vi (steps S3 to S6). That is, 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 phase detection sensor 56, a detection signal is output from the phase detection sensor 56 to the phase control unit 57. This detection signal functions as a signal for detecting the rotational phase of the photosensitive drum 20, that is, a phase detection signal. By referring to the phase detection signal of each color, the position of the photosensitive drum 20 of the other color with respect to the reference color is detected. The phase difference can be obtained. Here, one of the four-color photosensitive drums 20 is set as a reference side and the remaining one is set as a control side, and phase difference detection and phase adjustment in both are described.

  The phase difference (phase angle) between the reference photoconductor drum 20 and the control photoconductor drum 20 corresponds to the output time difference Δts of the detection signal output from the phase detection sensor 56 provided corresponding to each photoconductor drum 20. To do. Therefore, by measuring the output time difference Δts of the detection signal, the phase difference between the two can be obtained, and how much the actually measured phase difference is deviated from the preset phase difference (set phase angle α) can be derived. Therefore, in this embodiment, when the reference position of the control side photosensitive drum 20 is detected (step S3), the phase control unit 57 that has received this detection signal starts counting the output time difference Δts (step S4). In this embodiment, the count clock CLK is set to 1 kHz, and data processing is performed using the output time difference Δts as the count value.

Next, the counting of the output time difference Δts is continued until the reference position of the reference side photosensitive drum 20 is detected (steps S5 and S6). Thereby, an output time difference Δts indicating a phase difference between the reference side and the control side photosensitive drum 20 is obtained. Further, the phase control unit 57 has the following equation: Δtm = ((Vi / (Vdef−Vi)) * Δts) + ((Tdef * Ti) / (Ti−Tdef) * (α / 360))
Based on the above, the control time Δtm corresponding to the output time difference (phase difference) Δts is calculated (step S7). This control time Δtm corresponds to a timing difference in which the drive speed of the drive motor 50 is changed to the normal speed Vdef between the reference side and the control side as will be described below. Can be made to substantially coincide with the set phase angle α. For example, when the set phase angle α is “0”,
Δtm = ((Vi / (Vdef−Vi)) * Δts)
The phase angle between the reference side and the control side can be adjusted to zero by setting the control time Δtm determined by.

  When the reference side reference position (concave portion 55) is detected, the phase control unit 57 gives a control signal to the reference side motor rotation control unit 60 so as to drive the reference side drive motor 50 at the normal speed Vdef. Thus, the reference side drive motor 50 is driven at the normal speed Vdef while maintaining the drive speed of the control side drive motor 50 at the phase detection speed Vi (step S8). Thus, by providing a speed difference (= Vdef−Vi) between the drive motors, the phase angle of the reference-side and control-side photosensitive drum 20 can be changed over time. Therefore, in this embodiment, the phase angle is adjusted while maintaining the speed difference for the control time Δtm calculated as described above (steps S9 to S11). That is, counting is started simultaneously with the speed change of the reference side drive motor 50 (step S9). When the count value reaches the count value corresponding to the control time Δtm and the passage of the control time Δtm is confirmed (YES in step S10), the drive speed of the control side drive motor 50 is also phased. The detected speed Vi is changed to the normal speed Vdef (step S11). That is, the phase control unit 57 gives a control signal to the control-side motor rotation control unit 60 so as to drive the control-side drive motor 50 at the normal speed Vdef. Thus, by providing the speed difference for the control time Δtm, the phase difference between the reference side and the control side photosensitive drum 20 becomes the set phase angle α, and the phase relationship adjustment is completed, and the image can be formed as it is. it can.

  As described above, according to this embodiment, before driving the drive motor 50 at the normal speed Vdef, the detection output from the phase detection sensor 56 while driving at the phase detection speed Vi slower than the normal speed Vdef. Based on the signal, the phase difference between the photosensitive drums 20 is obtained as an output time difference Δts. The phase difference between the photosensitive drums 20 is adjusted to the set phase angle α by controlling the timing at which each drive motor 50 is changed from the phase detection speed Vi to the normal speed Vdef. In this way, the phase difference between the photosensitive drums 20 is obtained in the middle of changing the drive speed of each drive motor 50 to the normal speed Vdef, and the drive speed of the drive motor 50 is changed to the normal speed Vdef according to the phase difference. By controlling the timing, the phase relationship between the photosensitive drums 20 is adjusted. Therefore, the phase relationship can be accurately adjusted, and the phase adjustment can be easily performed by detecting the phase difference once.

  Further, as a method of adjusting the drive speed of the drive motor 50 to the normal speed Vdef by changing it in two steps, for example, the phase detection speed Vi is set faster than the normal speed Vdef, and the speed is reduced after the phase difference is detected (output time difference Δts). Then, it can be considered to change to the normal speed Vdef. However, in the above embodiment, since a DC motor is used as the drive motor 50, it is difficult to accurately perform such deceleration control, and the deceleration pattern may vary depending on the load state on each drive motor 50. Therefore, setting the phase detection speed Vi slower than the normal speed Vdef is effective in preventing the occurrence of the above problem, and is particularly beneficial in an apparatus using a DC motor as the drive motor 50. It can be said.

  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 control time Δtm corresponding to the output time difference Δts is calculated based on an arithmetic expression. However, for example, a control table as shown in FIG. 7 may be used. This control table associates the output time difference (count value) Δts with the control time Δtm, and can be stored in the memory 58 in advance. Then, the control time Δtm corresponding to the actually measured output time difference Δts may be read from the control table and determined. By using the control table in this way, the above-described arithmetic processing becomes unnecessary and phase adjustment control can be further simplified. In this embodiment, the memory 58 functions as the “storage unit” of the present invention.

  As apparent from the control table of FIG. 7, when the set phase angle α is relatively large, the control time Δtm is longer than the one-round time Ti of the photosensitive drum 20. Therefore, for example, as shown in FIG. 8, a time obtained by subtracting one round time Ti may be set as the control time Δtm. Thereby, an extra low speed rotation operation can be omitted and the time required for the phase adjustment can be shortened. This is the same in the embodiment in which the control time Δtm is obtained by an arithmetic expression.

  Further, the load state applied to the drive motor 50 may vary depending on the temperature inside the apparatus, so-called in-machine temperature. In order to cope with this, a plurality of types, for example, a high temperature control table, a normal temperature control table, and a low temperature control table can be stored in the memory 58 in advance. The phase control unit 57 can be configured to perform phase adjustment using a control table corresponding to the in-machine temperature detected by the temperature sensor 61. In this case, even if the in-machine temperature fluctuates, the phase adjustment corresponding to the fluctuation can be performed, and the phase relationship between the photosensitive drums 20 can be adjusted more accurately. This is the same in the embodiment in which the control time Δtm is obtained by an arithmetic expression.

  In the above embodiment, the reference side (reference color) setting method is not particularly mentioned. However, when the method of taking the reference is fixed, the detection time of the output time difference Δts may become long. Therefore, in order to shorten the detection time, it is desirable to set the reference according to the detection state of the reference position, for example, as shown in FIG. Hereinafter, the difference from the above embodiment will be mainly described with reference to FIG.

  In this embodiment, 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, the phase control unit 57 is driven by each drive motor 50 at the phase detection speed Vi as in the above embodiment. A control signal is given to each motor rotation control unit 60Y, 60M, 60C, 60K so as to drive the motor. 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 (step S1). Then, by detecting a READY signal from all the drive motors 50, it is confirmed that the first stage speed adjustment is completed and the drive motor 50 and the photosensitive drum 20 are driven in a steady state ( Step S2).

Subsequently, steps S21 to S28 are executed, and the toner color for which the phase detection signal is first output among the four colors is used as the reference color. That is, as shown in FIG. 9, when the reference position (concave portion 55) is first detected and a phase detection signal is output (step S21), the initial detection signal is output from the phase detection sensor 56 of any toner color. A reference color is determined by determining whether the color has been output (steps S22 to S28). That means
Output from phase detection sensor 56K: reference color is black,
Output from phase detection sensor 56Y: reference color is yellow,
Output from the phase detection sensor 56M: the reference color is magenta,
Output from phase detection sensor 56C: reference color is cyan,
It is judged.

  When the toner color to be used as the reference side is determined in this way, the process proceeds to step S3 to detect the phase difference and adjust the phase relationship in the same manner as in the above embodiment.

  As described above, the toner color corresponding to the phase detection signal output first after the start of rotation of all the drive motors 50 is used as the reference color, that is, the photosensitive drum 20 of the toner color is used as the “reference image carrier” of the present invention. And the phase adjustment is performed by obtaining the phase difference between the reference-side photosensitive drum 20 and the remaining control-side photosensitive drum 20. For this reason, it is possible to detect the phase difference between the photosensitive drums 20 earlier than when the reference color is set in advance. That is, as soon as the phase detection signal is output, the phase difference derivation process can be executed. Accordingly, early detection of the phase difference between the photosensitive drums (image carriers) 20 and early adjustment of the rotational phase can be performed, and a high-quality color image can be formed in an excellent first print time.

  In the above embodiment, the acceleration pattern from the phase detection speed Vi to the normal speed Vdef is fixed, while the timing at which the drive speed of the drive motor 50 is changed from the phase detection speed Vi to the normal speed Vdef is controlled. The phase relationship between the drums 20 is adjusted. The phase adjustment method is not limited to this, and the phase relationship may be adjusted by controlling the acceleration pattern when accelerating from the phase detection speed Vi to the normal speed Vdef. Of course, the phase relationship between the photosensitive drums 20 may be adjusted by controlling the change timing and the acceleration pattern.

  Further, in the above embodiment, as shown in FIG. 6, the speed from the phase detection speed Vi to the normal speed Vdef is accelerated at a constant acceleration, so that more accurate phase adjustment can be performed. However, when such speed control is performed, it is necessary to continuously change the control signal. Therefore, in order to simplify the control, it is desirable that the phase detection speed Vi be switched to the normal speed Vdef at a stroke.

  In the above embodiment, the phase detection speed Vi is set to half of the normal speed Vdef. However, the phase detection speed Vi is not limited to this, and can be set slower than the normal speed Vdef.

  In the above-described embodiment, the reference position of the photosensitive drum 20 is detected by detecting the concave portion 55 provided in the photosensitive gear 54 that is directly connected to the rotation shaft of the photosensitive drum 20, and the phase detection sensor 56 detects the phase. Although the signal is output, the phase detection method is not limited to this, and any phase detection method can be used as long as it can detect the reference position of the photosensitive drum 20. 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.

  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, each of the plurality of image carriers is connected to each of the plurality of drive motors while 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 the surface.

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 adjusting the phase relationship between the photosensitive drums. 6 is a flowchart illustrating an operation for adjusting the phase relationship between the photosensitive drums. The timing chart which shows derivation | leading-out of a phase difference, and phase adjustment operation | movement. FIG. 6 is a diagram showing another embodiment of the image forming apparatus according to the present invention. FIG. 5 is a diagram showing another embodiment of the image forming apparatus according to the present invention. FIG. 6 is a view showing still another embodiment of the image forming apparatus according to the present invention.

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 ... Phase detection Sensor (phase detection means), 57 ... Phase control unit, 58 ... Memory (storage means), 61 ... Temperature sensor (environment detection means)

Claims (7)

At least one image carrier is connected to each of the plurality of drive motors, and the plurality of image carriers are rotated while driving the plurality of drive motors at a predetermined normal speed. In an image forming apparatus that forms a color image by superimposing toner images formed on each body,
A plurality of phase 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;
While driving the plurality of drive motors at a phase detection speed slower than the normal speed, an output time difference of detection signals from the plurality of phase detection means is calculated, and the phase detection of each drive motor is performed according to the calculation result. Phase control means for adjusting a phase relationship between the plurality of image carriers by controlling a timing for changing from a speed to the normal speed or an acceleration pattern for accelerating from the phase detection speed to the normal speed. An image forming apparatus.   The phase control means uses one of the plurality of image carriers as a reference image carrier, and determines the phase difference of the remaining image carriers relative to the reference image carrier as a detection signal from the plurality of phase detection means. The image forming apparatus according to claim 1, wherein the image forming apparatus calculates the phase relationship between the plurality of image carriers by obtaining the output time difference and controlling the plurality of drive motors according to the output time difference. The phase control means includes
While fixing the acceleration pattern that accelerates from the phase detection speed to the normal speed,
After accelerating the speed of the reference drive motor connected to the reference image carrier to the normal speed, each of the remaining image carriers is delayed by a control time corresponding to the phase difference with respect to the reference image carrier. 3. The image forming apparatus according to claim 2, wherein the speed of a drive motor connected to the image carrier is accelerated to the normal speed. Storage means for storing a control table associating the output time difference with the control time;
The image forming apparatus according to claim 3, wherein the phase control unit calculates an output time difference based on detection signals from the plurality of phase detection units, and reads and determines a control time corresponding to the calculation result from the control table. It further comprises environment detection means for detecting the environment inside the device,
The storage means stores a plurality of control tables set in advance according to the environment inside the apparatus,
The image forming apparatus according to claim 4, wherein the phase control unit reads and determines a control time corresponding to the calculation result from a control table corresponding to a detection result by the environment detection unit.   6. The phase control means sets the image carrier corresponding to the phase detection means that first outputs a detection signal after the plurality of drive motors are started substantially simultaneously as the reference image carrier. The image forming apparatus according to any one of the above. At least one image carrier is connected to each of the plurality of drive motors, and the plurality of image carriers are rotated while driving the plurality of drive motors at a predetermined normal speed. In an image forming apparatus for forming a color image by superimposing toner images formed on each of the bodies, a phase adjustment method for adjusting a phase relationship between the plurality of image carriers,
A step of detecting a reference position of the image carrier and outputting a detection signal for each of the plurality of image carriers while driving the plurality of drive motors at a phase detection speed slower than the normal speed;
Obtaining an output time difference of detection signals between the plurality of image carriers;
And a step of controlling a timing for changing each drive motor from the phase detection speed to the normal speed or an acceleration pattern for accelerating from the phase detection speed to the normal speed according to the output time difference. A phase adjustment method in an image forming apparatus.

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