JP2010230544A - Rotating body detector and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To specify the cause of abnormality, when the abnormality arises in a rotation detector which detects the rotational state of a rotating body, such as, a photosensitive drum. <P>SOLUTION: When the abnormality arises in the rotation detector, any one of an encoder wheel 111, a first encoder sensor 112 and a second encoder sensor 113 is specified to be abnormal, based on signals output from the first encoder sensor 112 and the second encoder sensor 113 in the state of rotating the photosensitive drum 11. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rotating body detection device that detects a rotating state of a rotating body, and an image forming apparatus that includes the rotating body detection device and forms an image on recording paper.

  In a conventional image forming apparatus, in order to rotate a rotating body such as a photosensitive drum at a constant speed, an encoder wheel having a slit pattern with a constant interval is provided on the shaft of the rotating body, and the pattern is detected by an encoder sensor and rotated. It was detecting the rotation speed of the body.

  In addition, since a detection error occurs due to the influence of the warp of the encoder wheel, the unevenness of the slit interval, the eccentricity due to the mounting error, etc., there is one in which two encoder sensors are provided to correct the error. Specifically, a first encoder sensor and a second encoder sensor are provided for the encoder wheel, and the average value of the outputs of the first and second encoder sensors is calculated to perform rotation control of the rotating body. It was.

  Furthermore, a method for detecting an abnormality in a rotation detection device having a first encoder sensor and a second encoder sensor has been proposed. Specifically, the abnormality of the encoder device was detected by comparing the signal output from the first encoder sensor and the second encoder sensor with the error reference value stored in the memory in advance. (For example, refer to Patent Document 1).

Japanese Patent Laid-Open No. 07-140856

  However, in the invention described in Patent Document 1, an abnormality of the rotation detection device can be detected, but it is specified whether the cause of the abnormality is the encoder wheel, the first encoder sensor, or the second encoder sensor. I couldn't. Therefore, when an abnormality occurs in the rotation detection device, there is a problem that work efficiency during maintenance by a service person or the like is poor.

  Therefore, an object of the present invention is to provide a rotating body detection device and an image forming apparatus that can identify the cause of an abnormality when an abnormality occurs in a rotation detection device that detects rotation of a rotating body.

  In order to achieve the above object, a rotation detection device according to the present invention is a rotation detection device that detects a rotation state of a rotating body, and is provided on an axis of rotation of the rotating body, and has an encoder wheel having a pattern with a constant interval. A first encoder sensor that detects a pattern of the encoder wheel; a second encoder sensor that is provided separately from the first encoder sensor and detects the pattern of the encoder wheel; and the first encoder sensor; Control means for controlling the rotation speed of the rotating body based on the output of the second encoder sensor, and the control means, when an abnormality occurs in the rotation detection device, the first encoder sensor And the encoder wheel, the first encoder sensor based on the signal output from the second encoder sensor. And abnormality in any of the second encoder sensors and identifies whether the occurred.

  An image forming apparatus according to the present invention includes the above rotation detection device, and forms an image on a recording sheet.

  ADVANTAGE OF THE INVENTION According to this invention, when abnormality arises in the rotation detection apparatus which performs rotation detection of a rotary body, the abnormality cause can be specified.

1 is a schematic cross-sectional view illustrating an overall configuration of an image forming apparatus. It is a figure explaining the drive structure of a photosensitive drum. 2 is a control block diagram of the image forming apparatus. FIG. It is a figure which shows the clock of CPU, and the output signal from an encoder apparatus. It is a flowchart which shows the abnormality detection process of an encoder sensor. It is a figure which shows the operation example at the time of normal, and the operation example at the time of abnormality.

  FIG. 1 is a schematic sectional view showing the overall configuration of an electrophotographic color copying machine according to an embodiment of an image forming apparatus of the present invention.

  The image forming apparatus 1 according to the present embodiment is a color image forming apparatus in which a plurality of image forming units are arranged in parallel and an intermediate transfer method is adopted. The image forming apparatus 1 includes an image reading unit 1R and an image output unit 1P. The image reading unit 1R optically reads a document image, converts it into an electrical signal, and transmits it to the image output unit 1P.

  The image output unit 1P includes four image forming units 10, a sheet feeding unit 20, an intermediate transfer unit 30, a fixing unit 40, a cleaning unit 50, a photo sensor 60, and a control unit 80 arranged in parallel. Have.

  In the four image forming units 10 arranged side by side, the photosensitive drums 11a to 11d as rotating bodies are rotatably supported and are driven to rotate in the direction of the arrow in the figure. Along the outer peripheral surfaces of the photosensitive drums 11a to 11d, primary chargers 12a to 12d, exposure devices 13a to 13d, mirrors 16a to 16d, developing devices 14a to 14d, and cleaning devices 15a to 15d are provided.

  The primary chargers 12a to 12d give a uniform charge amount to the surfaces of the photosensitive drums 11a to 11d. Next, the exposure devices 13a to 13d irradiate a laser beam modulated according to an image signal from the image reading unit 1R. The irradiated laser beams are guided onto the photosensitive drums 11a to 11d by the mirrors 16a to 16d, and electrostatic latent images are formed by exposing the surfaces of the photosensitive drums 11a to 11d.

  The developing devices 14a to 14d visualize the electrostatic latent images on the photosensitive drums 11a to 11d with developer of four colors such as yellow, cyan, magenta, and black (hereinafter referred to as “toner”). The visualized toner image is transferred to the intermediate transfer belt 31 constituting the intermediate transfer unit 30 in the primary transfer areas Ta to Td. The intermediate transfer belt 31 includes a driving roller 32 that transmits driving to the intermediate transfer belt 31, a tension roller 33 that applies an appropriate tension to the intermediate transfer belt 31 by biasing a spring (not shown), and a secondary transfer counter roller 34. It is wound around and stretched.

  Cleaning devices 15a to 15d are provided on the downstream side of the primary transfer regions Ta to Td. The cleaning devices 15 a to 15 d clean the surfaces of the photosensitive drums 11 a to 11 d by scraping off toner remaining on the photosensitive drums 11 a to 11 d without being transferred to the intermediate transfer belt 31. By the process described above, image formation with each toner is sequentially performed.

  Primary transfer chargers 35 a to 35 d are disposed on the inner surface side of the intermediate transfer belt 31 in the primary transfer regions Ta to Td where the photosensitive drums 11 a to 11 d and the intermediate transfer belt 31 face each other. A secondary transfer roller 36 is disposed to face the secondary transfer counter roller 34, and a secondary transfer region Te is formed by a nip with the intermediate transfer belt 31. The secondary transfer roller 36 is pressed against the intermediate transfer belt 31 with an appropriate pressure.

  On the other hand, the paper feed unit 20 includes a cassette 21, a pickup roller 22, a paper feed roller pair 23, a conveyance path 24, and a registration roller 25. The recording paper P stored in the cassette 21 is sent out one by one by the pickup roller 22 and is transported on the transport path 24 by the pair of paper feed rollers 23. The recording paper P transported on the transport path 24 is sent out to the secondary transfer region Te by the registration roller 25 in accordance with the image forming timing of each image forming unit.

  A cleaning unit 50 for cleaning the image forming surface of the intermediate transfer belt 31 is disposed downstream of the secondary transfer region Te of the intermediate transfer belt 31. The cleaning unit 50 includes a cleaning blade 51 for removing toner on the intermediate transfer belt 31 and a collected toner box 52 for storing collected toner.

  The fixing unit 40 includes a fixing roller 41a provided with a heat source such as a halogen heater therein, and a pressure roller 41b (which may also include a heat source). Further, the fixing unit 40 is provided with a guide 43 for guiding the recording paper P to the nip portion between the fixing roller pair 41a and the pressure roller 41b, and a fixing heat insulating cover 46 for confining the heat of the fixing unit. Yes.

  The inner paper discharge roller 44 is a roller for transporting the recording paper P that has been transported from the roller pair including the fixing roller pair 41a and the pressure roller 41b. The recording paper P conveyed by the inner paper discharge roller 44 is further conveyed by the vertical path rollers 45 a and 45 b and discharged onto the paper discharge tray 47 by the outer paper discharge roller 48.

  Next, a case where images are formed on both sides of the recording paper P will be described. After the toner image on the first surface of the recording paper P fed from the cassette 21 is fixed, the recording paper P is conveyed by the inner paper discharge roller 44 and the vertical pass roller 45a. In response to the trailing edge of the recording paper P passing the branch position 70 of the conveyance path and advancing a predetermined distance, the vertical pass roller 45a stops rotating and then reversely rotates to start conveying the recording paper P in the reverse direction. . A mechanism such as a flapper for switching the transport direction of the recording paper P is provided at the branch position 70 of the transport path as necessary.

  The recording sheet P on which the first image has been formed is conveyed on the duplex conveying path 71 and is conveyed again to the conveying path 24 at a timing at which it does not collide with the subsequent recording sheet P conveyed from the cassette 21. Is done. Then, the recording sheet P on which the toner image on the second surface is fixed by the fixing unit 40 is conveyed by the inner discharge roller 44 and the vertical pass rollers 45a and 45b, and discharged onto the discharge tray 47 by the outer discharge roller 48. Is done.

  FIG. 2 is a diagram illustrating a driving configuration of the photosensitive drum.

  The rotation detection device according to the present embodiment is a device that detects the rotation state of the photosensitive drum 11 and includes an encoder device 110 and the like. Driving of the photosensitive drum 11 is transmitted from a drum driving shaft 103 as a rotating shaft through a coupling 102. A drum drive gear 101 and an encoder wheel 111 are fixed to the drum drive shaft 103, and the drum drive shaft 103, the drum drive gear 101, and the encoder wheel 111 rotate at the same angular velocity.

  The encoder device 110 includes an encoder wheel 111, a first encoder sensor 112, and a second encoder sensor 113. A slit is printed / engraved on the encoder wheel 111 at regular intervals. The first encoder sensor 112 and the second encoder sensor 113 for detecting the slit pattern of the encoder wheel 111 supply a signal having a period corresponding to the angular velocity of the drum drive shaft 103 to the drive control unit 200 (FIG. 3). To do.

  FIG. 3 is a control block diagram of the image forming apparatus having the rotation detection device.

  The drive control unit 200 includes a CPU 114, a ROM 115, and a RAM 116. The CPU 114 is a control circuit that controls the entire image forming apparatus 1. The ROM 115 stores a control program for controlling various processes executed by the image forming apparatus 1. The RAM 116 is a system work memory for the CPU 114 to operate, and also functions as an image memory for temporarily storing image data. The operation unit 118 is provided with an input key for receiving an operation input from the user and a display unit, and is connected to the drive control unit 200 so as to be communicable.

  The CPU 114 sends a drive signal to a motor driver 117 for driving the drum motor 100 based on signals from the first encoder sensor 112 and the second encoder sensor 113. The motor driver 117 drives the drum motor 100 based on the drive signal from the drive control unit 200 and rotates the drum drive gear 101 to rotate the photosensitive drum 11.

  Next, the drive control of the drum motor 100 will be described in more detail with reference to FIG.

  The CPU 114 detects the pulse width (cycle) of the encoder signal 401 from the encoder device 110. The encoder signal 401 changes between an H (High) level and an L (Low) level. Specifically, the CPU 114 detects the pulse width of the encoder signal 401 by counting with the clock 402 that drives the CPU 114.

  Here, as the encoder signal 401, a signal obtained by averaging the edge timings of the signals from the first encoder sensor 112 and the second encoder sensor 113 is used. By using the average value, the detection error can be reduced due to the influence of the warp of the encoder wheel, the unevenness of the slit interval, the eccentricity due to the mounting error, and the like.

  Note that the clock 402 is generated by a crystal resonator (not shown) or the like and is not necessarily a clock that drives the CPU 114. In addition, it is desirable to select a frequency of the clock 402 that is more suitable for the cycle of the encoder signal 401. In this embodiment, the frequency from the rising edge of the encoder signal 401 to the next rising edge is repeatedly counted at 40 MHz (N1, N2,. ...). Further, when disturbance such as chattering may affect the encoder signal 401, an algorithm for removing the disturbance may be added as necessary.

  A target pulse width is stored in advance in the RAM 116, and the CPU 114 calculates a difference between the detected pulse width of the encoder signal 401 and the target pulse width stored in the RAM 116. Then, the CPU 114 calculates a control value necessary for the drum drive shaft 103 to rotate at a constant angular velocity based on the calculated difference.

  In this embodiment, the control value is calculated by PID control. The control value MV is obtained by the following mathematical formula based on the difference e between the detected pulse width of the encoder signal 401 and the target pulse width stored in the RAM 116.

Here, the gain values K _P , T _I , and T _D are determined by the CPU 114 according to the speed of the drum drive shaft 103. Then, the CPU 114 outputs a control signal (in this embodiment, PWM DUTY) according to the calculated control value to the motor driver 117 to control the rotation speed of the photosensitive drum 11.

  Next, encoder sensor abnormality detection processing will be described with reference to the flowchart of FIG. A program for executing this flowchart is stored in the ROM 115 and is executed by being read by the CPU 114.

  First, the CPU 114 starts the rotation of the photosensitive drum 11 by outputting a signal for driving the drum motor 100 to the motor driver 117 (S501). Then, the CPU 114 continues to rotate the photosensitive drum 11 and determines whether there is no output signal from the first encoder sensor 112 for a predetermined time (S502). The “predetermined time” here is set to be equal to or longer than the time for which the encoder wheel 111 makes one rotation. When there is no output signal from the first encoder sensor 112 for a predetermined time, the CPU 114 displays an abnormality of the first encoder sensor 112 on the display unit provided in the operation unit 118 (S503).

  Next, the CPU 114 determines whether there is no output signal from the second encoder sensor 113 for a predetermined time while the photosensitive drum 11 continues to rotate (S504). When there is no output signal from the second encoder sensor 113 for a predetermined time, the CPU 114 displays an abnormality of the second encoder sensor 113 on the display unit provided in the operation unit 118 (S505).

  When there is no abnormality in either the first encoder sensor 112 or the second encoder sensor 113, the CPU 114 sets the first count value C1 and the second count value C2 for determining the abnormality of the encoder wheel 111 to 0. (S506). Then, the CPU 114 determines whether or not the rising edge at which the signal from the first encoder sensor 112 has changed from the L level to the H level is detected while driving the drum motor 100 and continuing to rotate the photosensitive drum (S507). ). When the rising edge is detected, the CPU 114 adds 1 to the first count value C1 and clears the second count value C2 to zero (S508).

  Next, the CPU 114 determines whether or not the rising edge of the signal from the second encoder sensor 113 has been detected (S509). When the rising edge is detected, the CPU 114 clears the first count value C1 to zero and adds 1 to the second count value C2 (S510).

  Thereafter, the CPU 114 determines whether the first count value C1 has reached a predetermined value (set to 2 in the present embodiment) or whether the second count value C2 has reached the predetermined value. (S511). When it is determined that the first count value C1 has reached the predetermined value or the second count value C2 has reached the predetermined value, the CPU 114 has an abnormality in the encoder wheel 111 on the display unit on the operation unit 118. A message to the effect is displayed (S512). On the other hand, if it is determined that neither the first count value C1 nor the second count value C2 has reached the predetermined value, the process returns to step S507 described above.

  When the encoder wheel 111 is normal, rising edges of signals from the first encoder sensor 112 and the second encoder sensor 113 are detected alternately. However, when the encoder wheel 111 has an abnormality such as dirt, the rising edge is continuously detected from one encoder sensor, and the rising edge cannot be detected from the other encoder sensor. From this, it is possible to determine whether or not an abnormality has occurred in the encoder wheel 111 based on the continuous count value of the rising edge.

  In steps S504 and S506, the rising edge is detected. However, the falling edge that has changed from the H level to the L level may be detected.

  FIG. 6A illustrates an operation example at the normal time, and FIG. 6B illustrates an operation example at the abnormal time.

  In the region from A to B in FIG. 6A, even when the speed of the photosensitive drum 11 changes suddenly due to the influence of disturbance or the like, the rising edges of the signals from the respective encoder sensors are alternately generated. This abnormality detection operation is not affected.

  Further, in FIG. 6B, the second count value C2 reaches 2 when the signal from the first encoder sensor 112 lacks one pulse due to the occurrence of an abnormality due to contamination of the encoder wheel 111 or the like. Thereby, the CPU 114 can detect an abnormality in the encoder wheel 111.

  Note that when the signal from the first encoder sensor 112 and the signal from the second encoder sensor 113 are shifted in substantially the same phase, the encoder sensor is normal due to an error or the like. May be detected as abnormal. That is, due to factors such as phase errors of the encoder sensors 112 and 113, the first and second count values C1 and C2 may be counted up to 2 even though these encoder sensors are normal. In this case, the number of times that an abnormality is determined may be set to 3, or a signal from the first encoder sensor 112 may be detected as a rising edge, and a signal from the second encoder sensor 113 may be detected as a falling edge.

  Although the photosensitive drum has been described as an example of the rotating body, the present invention may be applied to various rollers provided in the image forming apparatus, such as a conveyance roller for conveying recording paper and a driving roller for driving an intermediate transfer belt. I do not care.

  As described above, according to this embodiment, when an abnormality occurs in the rotation detection device, it is determined whether the cause of the abnormality is the encoder wheel, the first encoder sensor, or the second encoder sensor. can do. In addition, since the location where the abnormality has occurred is displayed on the display unit provided in the operation unit 118, work efficiency during maintenance by a service person or the like can be improved.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Photosensitive drum 110 Encoder apparatus 111 Encoder wheel 112 1st encoder sensor 113 2nd encoder sensor 114 CPU
118 Operation unit 200 Drive control unit

Claims (8)

A rotation detection device that detects a rotation state of a rotating body,
An encoder wheel provided on a rotating shaft of the rotating body and having a pattern of a constant interval;
A first encoder sensor for detecting a pattern of the encoder wheel;
A second encoder sensor provided separately from the first encoder sensor for detecting a pattern of the encoder wheel;
Control means for controlling the rotational speed of the rotating body based on the outputs of the first encoder sensor and the second encoder sensor;
The control means generates an abnormality in any of the encoder wheel, the first encoder sensor, and the second encoder sensor based on signals output from the first encoder sensor and the second encoder sensor. Rotation detection device characterized by identifying whether or not   2. The rotation detection device according to claim 1, wherein when there is no output signal from the first encoder sensor for a predetermined time, the control means specifies that an abnormality has occurred in the first encoder sensor. .   The rotation detection device according to claim 2, wherein the control means specifies that an abnormality has occurred in the second encoder sensor when there is no output signal from the second encoder sensor for a predetermined time. .   The control means counts the number of patterns of the encoder wheel detected by the first encoder sensor and the second encoder sensor, and counts the pattern of the encoder wheel detected by the first encoder sensor. The rotation detection device according to claim 3, wherein an abnormality of the encoder wheel is specified based on a value and a count value of the pattern of the encoder wheel detected by the second encoder sensor.   In the control means, after the encoder wheel pattern is detected by one of the first encoder sensor and the second encoder sensor, the encoder wheel pattern is detected by the other encoder sensor. 5. The abnormality of the encoder wheel is specified when a continuous count value of the pattern due to the encoder wheel pattern being detected again by the one encoder sensor reaches a predetermined value. The rotation detection device described.   An image forming apparatus comprising the rotation detection device according to claim 1, wherein an image is formed on a recording sheet using a rotating body of the rotation detection device.   The image forming apparatus according to claim 6, wherein the rotating body includes at least one of a photosensitive drum on which a toner image is formed and a driving roller that drives an intermediate transfer belt on which the toner image is transferred.   The rotation detection apparatus according to claim 6, further comprising display means for displaying an abnormality occurrence location specified by the control means.