JP2008203472A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which displacement or banding resulting from an error in processing or assembling a drive transmission system is reduced while coping with aging and an environmental change, and avoiding the need for a waiting time. <P>SOLUTION: In the image forming apparatus, an encoder (57) for detecting the rotating speed of an image carrier (8) or its rotating position is a two-phase output encoder (57) having two sensors. Having an output from one of the sensors as a reference signal, the encoder (57) directly provides a drive motor (50) with feedback. This encoder (57) includes: a computing means for computing the rotating speed or rotating position corresponding to the output of the other sensor; a reference position detecting means for detecting a reference position within one rotation of the image carrier (8); and a means for finely adjusting the input clock of the drive motor (50) on the basis of the result of the speed operation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus used for image formation by an electrostatic copying process, such as a copying machine, a facsimile machine, and a printer.

  In recent years, many image forming apparatuses such as copying machines and printers are capable of forming full-color images in accordance with market demands. In such an image forming apparatus capable of forming a color image, for example, a developing device for developing with different color toners is provided on each image carrier arranged on a straight line, and each image carrier is provided with a single color toner. An image is formed, and the single color toner image is transferred onto a rotating intermediate transfer belt so as to be sequentially overlapped by each primary transfer device disposed at a position facing the image carrier, and is a full color composite color. There is a so-called tandem type in which an image is formed and the image on the intermediate transfer belt is collectively transferred onto a recording medium by a secondary transfer device. In such a tandem type color image forming apparatus, a color image is formed by superimposing toner images of different colors formed on the photosensitive members on the intermediate transfer belt. If the color shift occurs, the color shift or subtle color tone will change on the image, resulting in a decrease in image quality. Therefore, the positional shift (color shift) of each color toner image becomes an important problem.

In particular, when there are asynchronous periodic position fluctuations and speed irregularities in a plurality of photoconductors, positional deviation and banding occur on the image, causing deterioration in image quality. In general, the speed fluctuation of the photosensitive member is caused by one rotation period or one tooth period of a gear depending on a gear processing error (particularly gear eccentricity or tooth shape accuracy) or an assembly error from a driving source. Appears as a speed fluctuation. Similarly, unevenness in speed also occurs due to cogging due to the number of phases or the number of poles of the drive motor winding. Further, in the drive system in which the photosensitive unit is detachable, it is also generated by a member for connecting the drive, for example, eccentricity of a cock ring, a joint, a gear or the like. Since these fluctuations depend on the processing accuracy of parts of the rotating body, the assembling accuracy, the configuration of the motor, and the like, the amount of deviation is initially the same within each rotation of the rotating body.
Therefore, in order to solve this problem, the rotational speed unevenness of the photosensitive member is detected and stored once, and the target rotational speed is corrected based on the stored information so that the speed unevenness is in an opposite phase. In addition, it has been proposed to perform feedforward control so that the actual rotation unevenness of the photosensitive member is set to a predetermined value or less.

For example, Patent Document 1 is not directly related to the present invention because the above concept is used in the transfer drive system, not the drive of the photoconductor, but the transfer body when the drive motor is rotated at a constant speed. Changes in the angular velocity of the drive shaft are stored, and based on the stored information, the target value of the drive motor is changed to make the angular velocity of the transfer body constant. Similarly, Patent Document 2 changes the target value of the drive motor so as to cancel the fluctuation based on the rotation information of the rotation detecting means provided on the photosensitive drum.
However, these methods have the disadvantage that they cannot cope with changes due to wear and deterioration of gears and couplings over time and unforeseen rotational fluctuations due to temperature and environmental fluctuations. There is also a drawback that the control oscillates with respect to the change of the transfer function. For this reason, Patent Document 1 proposes to obtain a rotation speed variation and a transfer function in a timely manner and change the feedback constant while confirming the gain margin and the phase margin. However, this method is also inefficient because a waiting time for the measurement, in which the speed fluctuation of the rotating body must be measured at least once, is generated. In addition, since the feed forward control is basically used, there is a disadvantage that the response is poor when a disturbance load is applied to the photosensitive member as a load.

Japanese Patent No. 3107259 JP-A-7-129034

Therefore, the present invention has been made in view of the above-mentioned problems, and the problem is caused by processing and assembly errors of the drive transmission system without dealing with aging and environmental fluctuations and without waiting time. An object of the present invention is to provide an image forming apparatus that reduces misalignment and banding. Another object of the present invention is to provide an image forming apparatus capable of reducing positional deviation and banding by improving responsiveness even when a disturbance load is applied.
In addition, by switching the reference signal of the drive motor to the rotational speed of the motor itself, even if the encoder of the image carrier no longer generates a normal signal due to dirt or damage, the image forming apparatus as a whole can be rotated normally. An object of the present invention is to provide an image forming apparatus that prevents the image from going down.

The features of the present invention, which is a means for solving the above problems, are listed below.
The image forming apparatus of the present invention is a drive motor that rotationally drives the image carrier, and inputs an input clock signal for instructing the rotation speed and a clock signal corresponding to the rotation speed from the rotation body as a reference signal, An encoder for detecting the rotational speed or rotational position of an image carrier in an image forming apparatus having a drive motor for controlling a PLL (Phase Locked Loop) and the rotational speed of the image carrier, or an encoder for detecting the rotational position Is a two-phase output encoder that has two sensors. The output of either one is directly fed back to the drive motor as a reference signal and the rotation speed or rotational position of the other output is calculated, and the image carrier A reference position detecting means for detecting a reference position within one rotation of the body, and a fine input clock of the drive motor based on the speed calculation result. And a means for settling.
In the image forming apparatus of the present invention, the image carrier driving motor further has an encoder function for detecting the rotational speed or rotational position of the motor rotor itself, and is switched as a reference signal for the driving motor. It is characterized by having.
In the image forming apparatus of the present invention, the encoder for detecting the rotational speed or rotational position of the image carrier is a two-phase output encoder having two sensors, and serves as a reference signal for the drive motor. A calculation means for selecting the rotation speed or rotation position of the motor rotor itself, rotating the drive motor to calculate the rotation speed or rotation position of the two-phase output from the encoder of the image carrier, and 1 of the image carrier When a reference position detection means for detecting a reference position in the rotation is selected and one of the encoder two-phase signals from the image carrier is selected as a reference signal, the drive motor A means for finely adjusting the input clock signal is provided.
In the image forming apparatus of the present invention, the reference position detecting means for detecting the reference position within one rotation of the image carrier is rotated integrally with the image carrier or the image carrier. And a reference signal for means for finely adjusting the input clock of the drive motor.
In the image forming apparatus of the present invention, the image carrier further includes a holding member for holding the image carrier, a charging unit for charging the image carrier, and a latent image after exposure with a toner. It is configured integrally with any one or all of the developing means and the toner cleaning means for removing the residual toner after toner transfer, and is configured to be detachable from the main body of the image forming apparatus. In an image forming apparatus having a drive transmission means for driving and rotating the image bearing member formed in the holding member to rotate, the encoder for detecting the rotational speed or the rotational position of the image bearing member is: It is mounted in the integral holding member.

  As described above, in the image forming apparatus of the present invention, by using a two-phase output encoder, the influence of the rotational speed detection error due to the eccentricity of the encoder itself is reduced, and the positional deviation is reduced. It is possible to prevent the entire image forming apparatus from going down by rotating.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

  FIG. 1 is an overall view showing a configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus shown in FIG. 1 is a tandem type color copying machine. However, in the present invention, not only a copying machine but also a printer, a facsimile machine, or a printing machine can be targeted. In FIG. 1, the image forming apparatus can form an image using yellow (Y), magenta (M), cyan (C), and black (K), which are toners having a complementary color relationship to the color separation color. Image carriers (8) Y, M, C, and K are juxtaposed on the same line in the horizontal direction. Each image carrier is arranged in one image carrier unit (25), and this unit includes an apparatus for performing the image forming processing steps such as charging, cleaning, developing, and static elimination. It is. An intermediate transfer unit (1) containing a primary transfer device (20) using a belt having a developing surface parallel to the juxtaposition direction of the image carriers Y, M, C, and K is provided above the image carrier unit. ) Is arranged. A writing unit (9) in which a scanning device is disposed is disposed below the image carrier unit. A color image from each image carrier is sequentially transferred to an intermediate transfer belt (10) having a stretched surface facing each image carrier, and an image superimposed by primary transfer is fed to a paper feeder (20). A secondary transfer device (3) for batch transfer is disposed on the recording medium fed from the printer. A primary transfer device composed of a roller is installed at a position facing each image carrier, and a secondary transfer device composed of a roller is disposed at a position facing the intermediate transfer drive roller (5). Is arranged.

In a color copying machine, an electrostatic latent image corresponding to a writing scan is formed after charging each image carrier, and when the electrostatic latent image is subjected to a visible image processing by a developing device, the image is transferred from each image carrier to the transfer device. The color images are sequentially transferred through the primary transfer device to form a superimposed image, and the superimposed image is collectively transferred to the image medium by the secondary transfer device. The recording medium onto which the superimposed images are collectively transferred by the secondary transfer device is fixed by the fixing device (6) provided in the conveyance path to the paper discharge tray (24) and is discharged.
FIG. 2 is a diagram illustrating a configuration around the secondary transfer device. A secondary transfer roller (4) is installed at a fixed position in the secondary transfer unit (3). The secondary transfer roller (4) is located opposite to the intermediate transfer drive roller (5) and is disposed with an angle θ with respect to the horizontal line (B). A secondary transfer unit pressurizing spring (13) is installed approximately on the line extension of θ, whereby the entire secondary transfer unit (3) can be pressurized, and the secondary transfer unit rotation fulcrum (17 ) Around the intermediate transfer driving roller (5).

FIG. 3 is a configuration diagram showing an outline of the first embodiment of the present invention.
The image carrier (8) is fixed via an image carrier drive shaft (54) and an image carrier flange (58), and is rotatably held via a bearing of an image carrier holding member (25). Although not shown, the image carrier holding member (25) holds a developing device, a cleaning unit, and the like together. The encoder plate is integrally held on the flange (58) of the image carrier, and rotates integrally with the image carrier. The encoder plate (56) is subjected to screen printing or photomask processing on a transparent sheet-like film, and a generally radial light-dark pattern is created. By creating a pattern in a generally radial pattern, it is configured to suppress the deterioration of the angular velocity detection accuracy due to the eccentricity of the plate as much as possible. In order to read the brightness of the pattern portion of the plate, an encoder sensor (57) is detachably provided on the image carrier holding member side. The encoder sensor (57) outputs a clock having a frequency proportional to the rotation speed of the image carrier. A coupling 1 (51) for connecting the main body side coupling 2 (52) and transmitting drive is attached to the tip of the image carrier unit side driving shaft. When the image carrier holding member (25) is attached to the main body along a guide member on the main body side (not shown), the couplings are connected to each other, and the driving force is transmitted to rotate the image carrier.

A speed command signal (input clock signal) for giving a predetermined rotation speed command is input to the image carrier driving motor (50), and further, the encoder signal is input as an illumination clock signal. Inside the motor, the current is controlled by the PLL function so that the phases of the input clock signal and the reference clock signal match, and the motor rotates. That is, even if there is a drive gear or coupling eccentricity, the rotation speed of the image carrier is automatically controlled so as to be the same as the input clock signal. If the input clock signal of the speed command is constant (usually constant), the rotation on the motor side fluctuates in a phase opposite to the rotation fluctuation due to an error in the drive transmission system, and the image carrier rotates at a constant speed. As a result, the rotation detection signal of the image carrier is directly used as the reference signal for the drive motor of the phase carrier having PLL control, thereby improving the response to disturbance load and reducing positional deviation and banding. it can. Furthermore, periodic rotational fluctuations due to processing errors in the transmission system can also be reduced at low cost without using a storage device or arithmetic device. In addition, the waiting time for measuring the speed fluctuation of the image carrier can be reduced.
In this configuration, when replacing the image carrier, the image carrier needs to be detached while the central axis of the image carrier remains in the machine body. For this reason, when the image carrier is detached, it interferes with the developing device, cleaning device, and transfer device arranged in the vicinity, and is scratched or soiled. In particular, the gap with the developing device is set very narrow, and is easily scratched. Further, when the image carrier is detached, a mechanism for escaping the developing device is necessary and the cost is high. Therefore, in recent years, in order to improve maintainability, a system in which a developing device, a cleaning device, and the like around the image carrier are unitized to be attached and detached as a whole has become common. By doing so, the unit having a narrow gap is detached and attached, so that the image carrier is not damaged. In this case, since the drive shaft of the image carrier is also mounted on the unitized side, the drive shaft must be separated from the drive shaft on the main body side. Therefore, a coupling mechanism for connecting the drive is required. If the coupling mechanism is interposed, eccentricity and shaft angle errors due to position errors when the coupling is mounted occur, and even if the encoder mounted on the main body is corrected so that it rotates constantly, the gear to the encoder Although the speed unevenness due to the eccentricity can be corrected, there is a problem that the speed unevenness due to the coupling remains in the rotational speed unevenness of the image carrier after being coupled by the coupling. This unevenness of speed changes because the meshing is not fixed every time the photosensitive unit is detached. The object of the present invention is to maintain a constant rotational speed of the image carrier even when the image carrier is detached as a unit and the drive is coupled by coupling, thereby preventing positional displacement and obtaining a high-quality image. .

FIG. 4 is a configuration diagram showing an outline of the second embodiment of the present invention. Differences from the first embodiment will be described.
An encoder sensor A (57-1) and an encoder sensor B (57-2) are detachably attached to the image carrier holding member (25). These are arranged at approximately 180 degrees in the pattern generation section of the encoder plate. The arrangement angle may not be 180 degrees. A reference position detection sensor (60) for detecting the reference position of the image carrier is also mounted. In the embodiment, it is arranged so as to detect the mark on the photosensitive member. However, the member rotates integrally with the image carrier, for example, a driving gear (54), a main body side driving shaft (55), or the like. It may be detected.
First, as in the first embodiment, the signal of the encoder sensor A (57-1) is used as a reference signal for the drive motor, and the image carrier is rotated with the input clock kept constant. Thus, by using a two-phase output encoder, it is possible to reduce the influence of the rotational speed detection error due to the eccentricity of the encoder itself, and to reduce the positional deviation.

  Each signal at that time is shown in FIG. FIG. 5 is a diagram illustrating each signal when the A-phase output is used as a reference signal. Since the A-phase signal is used as the reference signal, the A-phase rotational speed signal is controlled to be substantially constant. At this time, the rotation speed of the encoder sensor B is uneven due to the slight eccentricity of the encoder plate (56) as shown by the solid line in FIG. This is substantially the same in phase with the reference signal every time the image carrier auxiliary member is not removed. The speed unevenness in FIG. 5 is exaggerated. If there is uneven speed due to the eccentricity of the encoder, when the output of the sensor A is used as a reference signal, the eccentricity of the encoder is also corrected. Therefore, the actual rotational speed of the image carrier is deviated as shown by the dotted line. It will be controlled with the core part included. This is about half of the amplitude detected in the B phase.

  These signals are measured and stored by the rotation speed calculation means. FIG. 6 is a diagram illustrating each signal when the output of the A phase is used as a reference signal and the input clock is corrected by the speed calculation result of the B phase output. Next, the stored speed unevenness is sent to the clock generator, and a signal whose phase is shifted by 180 degrees at about half the amplitude of the phase B speed unevenness is generated as shown in FIG. Sent to the clock. The phase difference to be shifted is determined by the arrangement of the two sensors, and when arranged at 90 degrees, a signal having a phase difference of 90 degrees is generated. As a result, the rotational speed of the image carrier is as follows. As shown by the dotted line in FIG. The non-uniformity in the rotation speed of the A phase becomes the same by performing PLL control on the input signal. The B phase has the same amplitude with a 180 degree deviation. As described above, the uneven rotation speed of the image carrier caused by the eccentricity of the encoder is corrected. As a result, the encoder of the motor rotor itself is used as a reference signal to rotate the motor at a constant speed, and the rotational speed of the two-phase encoder of the image carrier at that time is detected, so that the drive transmission system and the image carrier When the velocity unevenness due to the encoder eccentricity error is detected and stored, and the feedback is changed to the feedback by the encoder of the image carrier, the velocity target value is reversely corrected, so that highly accurate positional deviation correction can be performed.

  FIG. 7 shows a schematic diagram of Embodiment 3 of the present invention. The image carrier drive motor (50) has an encoder function for detecting the rotational speed of the rotor itself (usually called an FG signal), and generates a drive motor encoder signal (60). This is input to the signal switching means (61) together with the encoder sensor (57) on the image carrier side, and can be freely switched as a motor reference signal. For example, when the encoder sensor A (57) becomes dirty and becomes abnormal, it is possible to perform the image forming operation without temporarily bringing down the machine by switching the reference signal. It is possible to notify the user that cleaning is necessary by displaying a service man call or the like. As a result, by switching the reference signal of the drive motor to the rotational speed of the motor itself, even if the encoder of the image carrier no longer generates a normal signal due to dirt or damage, the image forming apparatus can be rotated normally. The whole can be prevented from going down.

1 is an overall view illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration around a secondary transfer device. It is a block diagram which shows the outline of Example 1 of this invention. It is a block diagram which shows the outline of Example 2 of this invention. It is a figure showing each signal when the output of A phase is used as a reference signal. It is a figure showing each signal at the time of correcting an input clock with the speed calculation result of B phase output by making the output of A phase into a reference signal. It is a block diagram which shows the outline of Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Intermediate transfer unit 2 Intermediate transfer belt cleaning unit 3 Secondary transfer device 4 Secondary transfer roller 5 Intermediate transfer drive roller 6 Fixing unit 7 Toner replenishment unit 8 Image carrier 9 Writing unit 10 Intermediate transfer belt 11 Reading unit 20 Primary transfer Device 21 Paper feeder 24 Paper discharge tray

Claims (5)

A drive motor for rotating the image carrier, and an input clock signal for instructing the rotation speed and a clock signal corresponding to the rotation speed from the rotation body are input as a reference signal, and PLL (Phase Locked Loop) control is performed. In the image forming apparatus having a drive motor and an encoder for detecting the rotational speed of the image carrier, or the rotational position,
The encoder for detecting the rotational speed or rotational position of the image carrier is a two-phase output encoder having two sensors. One of the outputs is directly fed back to the drive motor as a reference signal, and the other output is output. Calculation means for calculating the rotation speed or rotation position, reference position detection means for detecting a reference position within one rotation of the image carrier, and means for finely adjusting the input clock of the drive motor based on the speed calculation result An image forming apparatus comprising: The image forming apparatus according to claim 1.
An image forming apparatus comprising: an image carrier driving motor having an encoder function for detecting a rotational speed or a rotational position of a motor rotor itself, and having a reference signal switching means for switching as a reference signal of the driving motor. The image forming apparatus according to claim 2.
The encoder that detects the rotation speed or rotation position of the image carrier is a two-phase output encoder that has two sensors, and selects the rotation speed or rotation position of the motor rotor itself as a reference signal for the drive motor. Then, by rotating the drive motor, the calculation means for calculating the rotational speed or rotational position of the two-phase output from the encoder of the image carrier and the reference position within one rotation of the image carrier are detected. And means for finely adjusting the input clock signal of the drive motor according to the calculation result of the above calculation when one of the encoder two-phase signals from the image carrier is selected as the reference signal. An image forming apparatus. The image forming apparatus according to claim 2 or 3,
The reference position detecting means for detecting the reference position within one rotation of the image carrier is provided on the image carrier or a connecting member that is rotated mechanically and integrally with the image carrier, and is input clock of the drive motor. A reference signal for means for finely adjusting the image forming apparatus. The image forming apparatus according to any one of claims 1 to 4,
The image carrier is configured to remove a holding member for holding the image carrier, a charging unit for charging the image carrier, a developing unit for developing a latent image after exposure with toner, and a residual toner after toner transfer. The image forming apparatus main body is configured integrally with any one or all of the toner cleaning means for the image forming apparatus, and the driving force from the main body side driving source is configured in the holding member. In an image forming apparatus having a drive transmission unit that transmits and rotates to an image carrier, an encoder that detects the rotational speed or rotation position of the image carrier is mounted in the integral holding member. An image forming apparatus.