JP2007101890A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing effect of variation in rotational speed of a transfer driving roller even when a diameter of a driving roller and a diameter of an image carrier are approximately the same and adjusting a difference in phase between image carriers at good precision. <P>SOLUTION: The image forming apparatus creates a reference pattern group for each color for a length which is the least common multiple of periphery length of the transfer driving roller 45 and periphery length of a photoreceptor 2, and measures detection time between the reference pattern images. Periodical variation in the transfer driving roller 45 can be effectively eliminated without forming the reference pattern to be needlessly long by an averaging process of measured data corresponding to a position of the photoreceptor 2 among the measured data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a FAX, and more particularly to an image forming apparatus such as a color copying machine and a color printer provided with a plurality of image carriers.

  Conventionally, a color image forming apparatus having a plurality of image carriers has advantages such as high speed, but there is a problem that the following color misregistration may occur. That is, when each toner image formed by different image carriers is transferred to a transfer member (intermediate transfer member) or a recording material (paper) moving on a transfer member, the positions of the toner images are accurately aligned. This is difficult, and there is a possibility that color shift may occur due to shift of the superimposed toner images.

  The color misregistration is caused by various factors, and one of them is due to the phase difference of the rotational speed fluctuation in one rotation cycle between the image carriers. Conventionally, the color shift due to the phase difference of the rotational speed fluctuation between the image carriers has been corrected as follows. That is, a plurality of reference pattern toner images are formed on each image carrier at a predetermined pitch, and these reference pattern toner images are transferred to a transfer member. The reference pattern toner image transferred to the transfer member is detected by a sensor (pattern image detecting means). Due to fluctuations in the rotational speed of the image carrier, the reference pattern toner image is not formed at a predetermined pitch, but is shifted from an ideal position. Based on the detection result of the sensor, the amount of deviation from the ideal position is calculated, the rotational speed fluctuation of each image carrier is calculated from the calculated deviation, and the phase difference of the rotational speed fluctuation between the image carriers is calculated. Correction is performed to correct color misregistration.

By the way, if the transfer driving roller that rotates the transfer member also has a rotational speed fluctuation of one rotation period, the rotational speed fluctuation component of the transfer driving roller is superimposed on the detection result of the sensor, and this is caused by the rotational speed fluctuation of the image carrier. The amount of misalignment could not be detected accurately.
Japanese Patent Application Laid-Open No. H10-228561 describes that a fluctuation component detected by a sensor is passed through a filter such as a bandpass filter to remove the fluctuation component of the transfer driving roller.

JP 2000-250285 A Japanese Patent No. 3648131

  When the diameter of the transfer driving roller is sufficiently smaller than the diameter of the image carrier, the frequency of the rotational speed fluctuation in one rotation cycle of the transfer driving roller is the frequency of the rotational speed fluctuation in one rotation cycle of the image carrier. Since it becomes a high frequency, if the high frequency component is removed by passing it through a filter as in Patent Document 1, the speed fluctuation of the transfer driving roller can be satisfactorily removed.

  However, if the diameter of the transfer driving roller and the diameter of the image carrier are substantially the same, the rotational speed fluctuation frequency of one rotation period of the transfer driving roller and the rotational speed fluctuation frequency of one rotation period of the image carrier are substantially the same. Thus, the filter cannot satisfactorily remove the rotational speed fluctuation in one rotation cycle of the transfer driving roller.

Patent Document 2 describes the following, that is, the length in the sub-scanning line direction of a reference pattern image group composed of a plurality of reference pattern images formed on a transfer belt is measured on the periphery of the image carrier. The length is set to n (integer) times, and each reference pattern image is detected to obtain measurement data. The measurement data obtained by detecting each reference pattern image includes n measurement data corresponding to each position of the image carrier. This is a description of averaging the n pieces of measurement data.
If the averaging process as shown in Patent Document 2 is performed, the fluctuation component of the transfer driving roller is leveled, and the fluctuation component of the transfer driving roller can be removed from the measurement data.

The reason will be described below.
FIG. 23 shows a waveform obtained from the measurement result of the deviation amount of each reference pattern from the ideal position. The thick line in FIG. 23 shows the waveform obtained by plotting the measured deviation amount, the solid line in the figure shows the rotational speed fluctuation of the image carrier, and the dotted line in the figure shows the rotation of the transfer driving roller. It shows the speed fluctuation. As shown in FIG. 23, it can be seen that the amount of deviation of each reference pattern from the ideal position is a superposition of the rotational speed fluctuation of the image carrier and the rotational speed fluctuation of the transfer drive roller.

  The time points A1 to A4 in FIG. 23 indicate times when the predetermined position of the image carrier rotates once. At the time points A1 to A4, the rotational speed fluctuation components of the image carrier have the same value, but the rotational speed fluctuation components of the transfer driving roller are different from each other. That is, as can be seen from the figure, the rotation speed fluctuation of the transfer drive roller varies positively at A2 and A3, but varies negatively at A4. Therefore, as described in Patent Document 2, when the measurement data corresponding to each position of the image carrier is averaged, the rotational speed fluctuation of the image carrier is not changed, but the rotational speed fluctuation of the transfer driving roller is not changed. Is averaged and approaches the average speed. That is, the rotational speed fluctuation approaches zero. Thereby, the averaged measurement data (sensor detection result) becomes measurement data in which the influence of the rotational speed fluctuation of the transfer drive roller is suppressed, and the phase difference between the image carriers can be calculated satisfactorily. Color shift can be suppressed. In the averaging process, if the number of rotations of the image carrier is increased and the number of data to be averaged is increased, the influence of fluctuations in the rotational speed of the transfer drive roller can be further suppressed, and the measurement data can be transferred to the image carrier. The rotation speed can be approximated. However, there is a problem that the measurement time becomes long and the processing time for color misregistration correction becomes long. Conversely, if the number of rotations of the image carrier is reduced, the measurement time is shortened and the processing time for color misregistration correction can be shortened, but the number of data to be averaged is reduced, and noise in fluctuations in the rotational speed of the transfer drive roller. Increases, and the phase difference between the image carriers cannot be adjusted with high accuracy.

  The present invention has been made in view of the above problems, and the object of the present invention is to influence the fluctuation of the rotational speed of the transfer driving roller even when the diameter of the driving roller and the diameter of the image carrier are substantially the same. An object of the present invention is to provide an image forming apparatus capable of suppressing the phase difference between the image bearing members with high accuracy.

In order to achieve the above object, the invention of claim 1 includes a transfer member, a transfer driving roller for rotationally driving the transfer member, a plurality of image carriers disposed along the transfer member, A pattern image detection unit that detects a plurality of reference pattern images formed in sequence in the sub-scanning line direction on the transfer body by a plurality of image carriers, and each image carrier based on the detection result of the pattern image detection unit In the image forming apparatus including a phase adjusting unit that adjusts the phase of the velocity fluctuation of the body, the length in the sub-scanning line direction of the group of reference pattern images sequentially formed on the transfer body in the sub-scanning line direction is The least common multiple of the circumference of the image carrier and the circumference of the transfer driving roller is used.
According to a second aspect of the present invention, there is provided a transfer member, a transfer driving roller that rotationally drives the transfer member, a plurality of image carriers disposed on the transfer member, and the plurality of image carriers. Pattern image detection means for detecting a plurality of reference pattern images formed in sequence in the sub-scanning line direction on the transfer body, and the phase of speed fluctuation of each image carrier based on the detection result of the pattern image detection means In the image forming apparatus including the phase adjusting unit for adjusting the image, the phase adjusting unit is arranged at a position separated from the circumference of the transfer driving roller after the pattern image detecting unit detects a predetermined reference pattern image. Based on the detection time until a certain reference pattern image is detected, the phase difference of the speed fluctuation between the image carriers is calculated, and the phase difference of the speed fluctuation between the image carriers is adjusted based on the calculated phase difference. It is characterized by doing.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the interval between the reference toner images formed on the image carrier is set to (1 / n) (n = integer) of the peripheral length of the transfer driving roller. It is characterized by that.
According to a fourth aspect of the present invention, a transfer member, a plurality of image carriers arranged along the transfer member, and the plurality of image carriers are sequentially arranged on the transfer member in the sub-scanning line direction. Image forming means comprising: a pattern image detecting means for detecting a plurality of reference pattern images formed in step 1; and a phase adjusting means for adjusting the phase of the speed fluctuation of each image carrier based on the detection result of the pattern image detecting means. The apparatus includes speed detecting means for detecting the speed of the transfer body, and the speed of the transfer body is controlled based on a detection result of the speed detecting means.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the interval between the reference toner images formed on the image carrier is set to (1 / m) (m = Integer).
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the plurality of image carriers include a black image carrier that carries a black toner image, and a yellow toner image. The image bearing member for yellow to be carried, the cyan image bearing member for carrying a cyan toner image, and the magenta image bearing member for carrying a magenta toner image are driven to rotate the black image bearing member. A black drive motor and a color drive motor that rotationally drives the yellow image carrier, the cyan image carrier, and the magenta image carrier are provided.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the plurality of image carriers include a black image carrier that carries a black toner image, and a yellow toner image. A black image carrier and a yellow image carrier comprising a yellow image carrier, a cyan image carrier carrying a cyan toner image, and a magenta image carrier carrying a magenta toner image. A first drive motor that rotationally drives any one of the carrier, the cyan image carrier, and the magenta image carrier, and a second drive motor that rotationally drives the other image carrier. It is what.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, there is provided an exchange detecting means for detecting that the image carrier or at least the process cartridge provided with the image carrier is exchanged. It is characterized by having.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the image carrier or at least the process cartridge including the image carrier is configured to be detachable from the apparatus main body. An attachment / detachment detecting means for detecting attachment / detachment of the body or the process cartridge is provided.
According to a tenth aspect of the present invention, in the image forming apparatus of the ninth aspect, the attachment / detachment detecting means detects opening / closing of a door of the apparatus main body that is opened when the image carrier or the process cartridge is attached / detached from the apparatus main body. The open / close detection means is a feature.
According to an eleventh aspect of the present invention, there is provided the image forming apparatus according to any one of the first to eighth aspects, or the ninth aspect, wherein the image carrier or at least a process cartridge including the image carrier is detachable from the apparatus main body. The image forming apparatus includes a rotation position detection unit that detects a rotation position of the image carrier, and the rotation position detection unit is provided on the apparatus main body side.
According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, the transfer member has a belt shape.
According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, the transfer member is formed in a drum shape.
According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, a DC motor is used as a drive motor for rotationally driving the image carrier.
According to a fifteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, a stepping motor is used as a drive motor for rotationally driving the image carrier.

  According to the first, fifth to fifteenth aspects of the present invention, the length of the group of reference pattern images is set to the least common multiple of the circumferential length of the image carrier and the circumferential length of the transfer driving roller, as described below. If the detection results corresponding to each position of the image carrier are averaged, the phase of each image carrier can be adjusted with high accuracy. The fluctuation component in which the rotation speed fluctuation of the transfer driving roller and the rotation speed fluctuation of the image carrier are superimposed becomes a period fluctuation whose cycle length is the least common multiple of the circumference of the image carrier and the circumference of the transfer driving roller. . Even if the detection result corresponding to each position of the image carrier is averaged by forming a reference pattern image group having a length exceeding the least common multiple, the same detection result is obtained. Since this is repeated, there is no effect on the removal of the rotational speed fluctuation component of the transfer drive roller. On the other hand, when a reference pattern image group having a length less than the least common multiple is formed and the detection results corresponding to the respective positions of the image carrier are averaged, a reference pattern image group having the least common multiple length is formed to form an image. Since the number of data is smaller than that obtained by averaging the detection results corresponding to the respective positions of the carrier, fluctuations in the rotation speed of the transfer driving roller cannot be removed satisfactorily. Therefore, by setting the length of the reference pattern image group to the least common multiple, it is possible to remove the fluctuation in the rotational speed of the transfer driving roller from the detection result better than that of the least common multiple, and based on the detection result, The phase difference of the speed fluctuation of the image carrier can be adjusted with high accuracy. Further, the length of the reference pattern image group can be suppressed to the minimum necessary length that can accurately remove the rotational speed fluctuation of the transfer driving roller, and the processing time for color misregistration correction can be suppressed from increasing. .

  According to the invention of claim 2 or 3, the phase difference of the speed fluctuation between the image carriers is separated from the circumference of the transfer driving roller after the pattern image detecting means detects the predetermined reference pattern image. It is calculated from the detection time until the reference pattern image at the position is detected. Since the rotation speed fluctuation of the transfer driving roller is a period fluctuation with one rotation of the transfer driving roller as one cycle, half of one rotation is a minus fluctuation component and the other half is a plus fluctuation component. Since the negative fluctuation component and the positive fluctuation component are equal, they are offset during one rotation of the transfer drive roller, and the time for one rotation of the transfer drive roller may or may not vary due to eccentricity. And no difference. Therefore, the time from when the predetermined position of the transfer body passes through the pattern image detecting means until the position separated from the predetermined position of the transfer body by the circumference of the transfer driving roller passes through the pattern image detecting means is Since the plus fluctuation component and the minus fluctuation component of the rotation speed fluctuation with one rotation of the transfer driving roller as one cycle are canceled out, the time required when the transfer driving roller rotates at the average speed becomes equal. Therefore, if the reference pattern image is detected at the circumferential length interval of the transfer drive roller, the detection time will not be advanced or delayed due to the rotation speed fluctuation with one rotation of the transfer drive roller as one cycle. That is, the detection time does not fluctuate due to the influence of fluctuations in the rotational speed with one rotation of the transfer driving roller as one cycle. Therefore, by measuring the detection time from the detection of the predetermined reference pattern image by the pattern image detection means to the detection of the reference pattern image at the position where the circumference of the transfer driving roller is separated, the following effects can be obtained. Obtainable. That is, the detection time varies due to the influence of only the rotational speed fluctuation component of the image carrier, and the rotational speed fluctuation of the image carrier can be found based on this detection time. Thereby, the phase difference of the speed fluctuation between the image carriers can be obtained with high accuracy, and the phase of the speed fluctuation of each image carrier can be adjusted with high precision.

According to the fourth aspect of the invention, since the speed of the transfer body is controlled based on the detection result of the speed detecting means, the influence of the rotational speed fluctuation of the transfer driving roller during the formation of the reference pattern image on the transfer body. Appears to be suppressed. As a result, in the reference pattern image formed on the transfer body, only the influence of the rotational speed fluctuation of the image carrier appears, so the periodic fluctuation component calculated based on the detection result of detecting this reference pattern is It becomes the rotational speed fluctuation component of the image carrier, and from this, the phase difference of each image carrier can be obtained with high accuracy. As a result, the phase of the speed fluctuation of each image carrier can be adjusted with high accuracy.
It should be noted that the rotational speed detection means is attached to each image carrier, and the rotational speed of each image carrier is controlled to prevent the rotational speed variation of each image carrier. Color shift caused by fluctuations can be suppressed. However, it is necessary to provide a rotational speed detecting means for each image carrier, which increases the cost. On the other hand, in the invention of claim 5, if one speed detecting means is provided, it is possible to suppress the color shift caused by the fluctuation of the rotational speed of the image carrier and to reduce the cost.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described.
First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram showing the printer. In this figure, this printer includes process cartridges 1Y, C, M, K corresponding to respective colors of yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, K), and developing devices 20Y, C, M, K. The four process cartridges 1Y, 1C, 1M, and 4K and the four developing devices 20Y, 20C, 1M, and 1K use toners of different colors (Y, C, M, and K toners) as image forming substances. Other than the above, the configuration is the same, and each is replaced when the lifetime is reached. Taking a Y process cartridge 1Y using Y toner as an example, this has a drum-shaped photoconductor 2Y, a drum cleaning device 3Y, a charge eliminating lamp (not shown), a charging device 10Y, and the like. . For example, the developing device 20Y for Y using Y toner has a casing 21Y, a developing sleeve 22Y, a magnet roller 23Y, a first conveying screw 24Y, a second conveying screw 25Y, a toner concentration sensor 26Y, and the like. ing.

  In the casing 21 of the developing device 20Y, a cylindrical developing sleeve 22Y is rotatably disposed so as to expose a part of the peripheral surface from an opening provided in the casing 21Y. The magnet roller 23Y has a plurality of magnetic poles divided in the circumferential direction, and is fixed in the developing sleeve 22Y so as not to rotate with the developing sleeve 22Y. In the casing 21Y, an agitating / conveying portion 28Y is formed vertically below the developing portion 27Y in which the developing sleeve 22Y and the developing sleeve 23Y are disposed. Inside, a magnetic carrier, Y toner, and the like are formed. A Y developer (not shown) including In the agitating and conveying unit 28Y, a first conveying unit that accommodates the first conveying screw 24Y and a second conveying unit that accommodates the second conveying screw 25Y are partitioned by a partition wall 29Y. However, the partition wall 29Y has openings (not shown) at positions opposed to both end portions of the transport screw, and both transport portions communicate with each other through openings at both end portions.

  As the first conveying screw 24Y in the first conveying unit is driven to rotate by a driving means (not shown), the Y developer in the first conveying unit is moved from the near side to the far side in the direction perpendicular to the paper surface of the drawing. And carry with stirring. The Y developer transported to the vicinity of the back end in the drawing by the first transport screw 24Y passes through an opening (not shown) provided in the partition wall 29Y and near the back end in the drawing in the second transport section. enter in.

  The second transport screw 25Y in the second transport unit stirs and transports the Y developer in the second transport unit from the back side to the front side in the drawing as it is driven to rotate by a driving unit (not shown). In the process in which the Y developer is agitated and conveyed in the second conveying portion in this way, a part of the Y developer is rotated counterclockwise in the drawing by the magnetic force generated by the unillustrated pumping magnetic pole of the magnet roller 23Y. It is pumped up on the surface of 22Y. The Y developer that has not been pumped up by the developing sleeve 22Y is transported to the vicinity of the front end in the drawing in the second transporting portion as the second transporting screw 25Y is driven to rotate, and then provided to the partition wall 29Y. It enters into the 1st conveyance part through the opening which is not illustrated. In this manner, Y toner is triboelectrically charged while the Y developer is circulated and conveyed between the first conveyance unit and the second conveyance unit in the agitation conveyance unit 28Y.

  The Y developer pumped up by the developing sleeve 22Y is regulated in layer thickness on the sleeve by a doctor blade 30Y disposed so as to face the developing sleeve 22Y with a predetermined gap. As the developing sleeve 22Y rotates, the developing sleeve 22Y is conveyed to a developing area facing the Y photoconductor 2Y, where Y toner is attached to the electrostatic latent image on the photoconductor 2Y. By this adhesion, the electrostatic latent image on the photoreceptor 2Y is developed into a Y toner image. The Y developer that has passed through the developing region with the rotation of the developing sleeve 22Y returns to the developing portion 27Y in the casing 21Y, and then is affected by the repulsive magnetic field formed by the two magnetic poles of the magnet roller 23Y that repel each other. Receive and release from the sleeve surface. And it returns in the 2nd conveyance part of the stirring conveyance part 28Y.

  A toner concentration sensor 26Y made of a magnetic permeability sensor is fixed to the upper wall of the first conveyance unit of the agitation conveyance unit 28Y. The toner concentration sensor 26Y outputs a voltage having a value corresponding to the magnetic permeability of the Y developer passing thereunder. Since the magnetic permeability of the two-component developer containing toner and magnetic carrier shows a certain degree of correlation with the toner concentration, the toner concentration sensor 26Y outputs a voltage corresponding to the Y toner concentration. The value of the output voltage is sent to a toner supply control unit (not shown). The toner replenishment control unit includes a RAM (Random Access Memory) that stores Y Vtref that is a target value of the output voltage from the toner density sensor 26Y. The RAM also stores data for C Vtref, M Vtref, and K Vtref, which are target values of output voltages from a toner density sensor (not shown) mounted in another developing device. The Y Vtref is used for driving control of a Y toner conveying device (not shown). Specifically, the toner replenishment control unit drives and controls a Y toner conveyance device (not shown) so that the value of the output voltage from the Y toner density sensor 26Y approaches the V Vref for Y, and the agitation conveyance unit. Y toner is replenished into the 28Y first conveying section. By this replenishment, the Y toner concentration in the Y developer in the second transport unit is maintained within a predetermined range. For other developing devices, similar toner replenishment control using a C, M, K toner conveying device (not shown) is performed.

  In the Y process unit 1Y, the photosensitive member 2Y is driven to rotate clockwise in FIG. The surface of the photoreceptor 2 </ b> Y that is rotationally driven in this manner is uniformly charged by the charging device 10 </ b> Y and then scanned by the Y laser beam Ly to carry a Y electrostatic latent image. The Y electrostatic latent image is developed into a Y toner image by the Y developing device 20Y described above, and is then primarily transferred onto an intermediate transfer belt 41 described later.

  The drum cleaning device 3Y includes a cleaning blade 4Y that makes the front end abut against the photoreceptor 2Y, a recovery screw 5Y, a zinc stearate block 6Y, a spring 7Y, an application brush 8Y, and the like. The cleaning blade 4Y removes toner remaining on the surface of the photoreceptor 2Y after the primary transfer process. The removed toner falls on the collection screw 5Y. Then, along with the rotation of the collecting screw 5Y, it is conveyed to the end in the screw axis direction, and is discharged from the discharge port (not shown) to the outside of the drum cleaning device 3Y and then transferred into a waste toner bottle (not shown). On the downstream side in the drum rotation direction with respect to the contact position between the cleaning blade 4Y and the photosensitive member 2Y, the application brush 8Y having a plurality of raised brushes on the rotation shaft rotates with the brush tip contacting the photosensitive member 2Y. ing. A zinc stearate block 6Y is pressed against the application brush 8Y by a spring 7Y. As the application brush 8Y rotates, the zinc stearate is scraped off from the zinc stearate block 6Y and adhered to the tip of the brush, and then applied to the surface of the photoreceptor 2Y as a lubricant.

  The surface of the photoreceptor 2 </ b> Y coated with the lubricant in this way is discharged by a discharging lamp (not shown) and then uniformly charged by the charging device 10 </ b> Y. In the figure, the charging device 10Y is of a type that uniformly charges the photosensitive member 2Y by making the charging roller 11Y to which a charging bias is applied face the photosensitive member 2Y through a rubbing or a minute gap. showed that. Instead of the charging device 10Y having such a configuration, a charging charger using a corotron or a scorotron method may be used.

  In FIG. 1 described above, an optical scanning device 100 is disposed below the process cartridges 1Y, 1C, 1M, and 1K in the drawing. The optical scanning device 100 is controlled by an optical writing circuit (not shown). The optical writing circuit controls the driving of the optical scanning device 100 based on image information sent from a personal computer (not shown) or the like.

  The optical scanning device 100 optically scans the respective photosensitive members in the process cartridges 1Y, 1C, 1M, and 1K with a laser beam emitted based on a control signal of the optical writing circuit. By this optical scanning, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 2Y, 2C, 2M, and 2K. The optical scanning device 100 irradiates a photoconductor through a plurality of optical lenses and mirrors while deflecting a laser beam emitted from a laser oscillator by a polygon mirror rotated by a motor.

  Above the process cartridges 1Y, 1C, 1M, and 1K, a transfer unit 40 that moves the intermediate transfer belt 41 that is a transfer body endlessly while stretching is disposed. The transfer unit 40 serving as transfer means includes a cleaning device 42 in addition to the intermediate transfer belt 41. Also provided are four primary transfer bias rollers 43Y, 43C, 43M, 43K, a secondary transfer backup roller 44, a cleaning backup roller 45, a tension roller 46, a driven roller 47, and the like. The intermediate transfer belt 41 is endlessly moved in the counterclockwise direction in the figure by the rotational drive of at least one of the rollers while being stretched around these eight rollers. The primary transfer bias rollers 43Y, 43C, 43M, and 43K each have an intermediate transfer belt 41 that is moved endlessly in this manner between the photoreceptors 2Y, 2C, 2M, and 2K to form primary transfer nips. Yes. These primary transfer bias rollers are of a type in which a transfer bias having a polarity opposite to that of toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 41. All rollers except the primary transfer bias rollers 43Y, 43C, 43M, and 43K are electrically grounded. The intermediate transfer belt 41 sequentially passes through the primary transfer nips for Y, C, M, and K along with its endless movement, and Y, C, and M on the photoreceptors 2Y, C, M, and K are sequentially transferred. , K toner images are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 41.

  The eight rollers described above in the transfer unit 40 are all disposed inside the loop of the intermediate transfer belt 41. In addition to these eight rollers, the transfer unit 40 also has a secondary transfer roller 48 disposed outside the loop of the intermediate transfer belt 41. The secondary transfer roller 48 forms a secondary transfer nip with the intermediate transfer belt 44 sandwiched between the secondary transfer backup roller 44 described above. In the secondary transfer nip, a secondary transfer electric field is formed by a potential difference between the secondary transfer bias applied to the secondary transfer roller 48 and the secondary transfer backup roller 44 connected to the ground.

  In the lower part of the optical writing device 100 in the figure, paper storage means having a paper storage cassette 50, a paper feed roller 51 incorporated in these, and the like are disposed. The paper storage cassette 50 stores a plurality of transfer papers P as sheet members, and a paper feed roller 51 is brought into contact with the uppermost transfer paper P. When the paper feed roller 51 is rotated counterclockwise in the drawing by a driving means (not shown), the uppermost transfer paper P is sent out toward the paper feed path 52.

  A registration roller pair 53 is disposed near the end of the paper feed path 52. The registration roller pair 53 rotates both rollers so as to sandwich the transfer paper P as a recording sheet, but temporarily stops the rotation immediately after the sandwiching. Then, the transfer paper P is sent out toward the above-described secondary transfer nip at an appropriate timing. The four-color toner images formed on the intermediate transfer belt 41 are superimposed on the transfer paper P at the secondary transfer nip, and are collectively applied to the transfer paper P under the influence of the secondary transfer electric field and nip pressure. Secondary transferred. Then, combined with the white color of the transfer paper P, a full color toner image is obtained. The full-color toner image is sent to the fixing device 60 together with the transfer paper P and fixed on the surface of the transfer paper P.

  Transfer residual toner that has not been transferred to the transfer paper P adheres to the surface of the intermediate transfer belt 41 after passing through the secondary transfer nip. This is cleaned by the cleaning device 42 having the intermediate transfer belt 41 sandwiched between the cleaning backup roller 45 and then conveyed into the above-described waste toner bottle.

  The fixing device 60 includes a fixing roller 61 and a fixing belt unit 62 which are driven to rotate clockwise in the drawing by a driving unit (not shown) while including a heat source such as a halogen lamp inside. The fixing belt unit 62 moves the endless fixing belt 63 endlessly in the counterclockwise direction in the drawing while being stretched by the pressure roller 64 and the driven roller 65. The pressure roller 64 and the fixing roller 61 are in contact with each other with a predetermined pressure via the fixing belt 63. As a result, a fixing nip is formed in which the front surface of the fixing belt 63 and the fixing roller 61 are in contact with each other. The transfer paper P fed into the fixing device 60 is sandwiched between the fixing nips such that the unfixed toner image carrying surface is in close contact with the fixing roller 61. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full-color image is fixed on the surface of the transfer paper P.

  The transfer paper P on which the fixing process of the full-color image has been performed in the fixing device 60 is provided on the upper surface of the printer housing via the reverse conveyance path 70 and the paper discharge roller pair 71 after exiting the fixing device 60. Stacked on the stack unit 72.

  A bottle support portion is disposed between the intermediate transfer unit 40 and the stack portion 72 located above the intermediate transfer unit 40. The bottle support portion is equipped with toner bottles 73Y, 73C, 73M, and 73K that are toner containers for storing Y, C, M, and K toners. The Y, C, M, and K toners accommodated in the toner bottles 73Y, 73C, 73M, and 73K are respectively supplied to the developing devices 20Y and 20D as developing means by toner transport devices for Y, C, M, and K (not shown). Replenished in C, M, K. The toner bottles 73Y, C, M, and K can be attached to and detached from the printer main body independently of the process cartridges 1Y, 1C, 1M, and 1K.

  FIG. 3 is a diagram showing a drive mechanism 30 for the photoreceptor 2. The drive mechanism 30 includes four drive motors 31Y, 31C, 31M, and 31K of Y, C, M, and K. The driving force of the Y drive motor 31Y is transmitted to the Y photoconductor 2Y via the Y photoconductor gear 32Y. The driving force of the C driving motor 32C is transmitted to the C photoconductor 2C via the C photoconductor gear 32C, and the driving force of the M driving motor 31M is transferred to the M photoconductor gear 32M through the M photoconductor gear 32M. Is transmitted to the photosensitive member 2M. Similarly, the driving force of the K drive motor 31K is transmitted to the K photoconductor via the K photoconductor gear 32K. At the time of color mode printing, the four drive motors 31Y, 31C, 31M, and 31K are operated. On the other hand, during monochrome mode printing, only the K drive motor 31K is operated.

  As each drive motor, a stepping motor or a DC motor may be used.

  As shown in FIG. 4, the photoconductor 2 is attached to the photoconductor drive gear 32 via a coupling member 33 such as a coupling, and is removable from the drive mechanism 30. Further, the drive mechanism 30 is provided with position detection means 34 for detecting the rotational position of each photoconductor 2. As shown in FIG. 4, the rotational position detection means 34 includes a filler 34b attached to the side surface of each photoconductor gear 32, and a sensor 34a for detecting the filler 34b. As shown in FIG. 5, the filler 34 a has a length corresponding to a half circumference of the photoconductor gear 32. For example, when a reflective optical sensor is used as the sensor 34a for detecting the filler 34b, at least the sensor facing surface of the filler 34b is configured with a member that reflects light. When the sensor 34a faces the filler 34b, the filler 34b reflects the light from the reflective sensor, and an output signal is obtained from the sensor 34a. On the other hand, when the sensor 34a is not opposed to the filler 34b, the sensor 34a does not detect light, and thus an output signal cannot be obtained from the sensor 34a. As a result, the signal from the sensor 34a is switched from a state without an output signal to a state with an output signal, and from a state with an output signal to a state without an output signal, every half rotation cycle of the photosensitive member 2. In this way, by setting the filler 34 b to a length corresponding to a half circumference of the photoconductor gear 32, one of the two places where the output signal is switched can be set as the reference position of the photoconductor 2. Thus, when the sensor 34a faces the filler 34b, the point A in the figure where the output signal is switched to the state without the output signal can be set as the reference position of the photoconductor 2. Is not opposed to the filler 34b, the point B in the figure, where the output signal is switched to the non-output signal state, can be set as the reference position of the photoreceptor 2. That is, the reference position of the photoconductor 2 can be set only by rotating the photoconductor half at least. The length of the filler 34b is not limited to this. For example, as shown in FIG. 6, the length of the circumference of the photoconductor gear 32 is set to ¼, and the same filler 34b is provided on the opposite side. Anyway. In this way, the signal of the sensor 34a is switched in a quarter cycle, so that the reference position of the photoconductor 2 can be set by rotating at least the 1/4 photoconductor 2.

  In the present embodiment, the rotation detecting means is provided in the drive mechanism 30 provided in the apparatus main body. However, the rotation detection means is provided in the photosensitive member 2 detachably provided from the apparatus main body or a process cartridge including the photosensitive member 2. Also good. However, the rotation detecting means 34 has a longer life than the photoconductor and the process cartridge. Therefore, if the rotation detecting means 34 is provided on the apparatus main body side, the rotation detecting means 34 that has not reached the end of its life is replaced with the photoconductor and the process cartridge. Since there is nothing, the cost can be reduced.

  FIG. 7 is a perspective view of the intermediate transfer belt 41. In the figure, two reflection type photosensors 69 a and 69 b are disposed on the side of the intermediate transfer belt 41. These reflective photosensors 69a and 69b as optical sensors each have a light emitting element and a light receiving element (not shown).

  FIG. 8 is a block diagram showing a part of an electric circuit of the laser printer. In the figure, a control unit 150 includes electrically connected toner image forming units 1Y, 1M, 1C, and 1K, an optical writing unit 2, a paper feed cassette 3, 4, a registration roller pair 5, a transfer unit 6, and a reflection type. It is connected to photo sensors 69a and 69b. The control unit 150 includes a CPU 150a that performs arithmetic processing, a RAM 150b that stores data, and a DSP (Digital Signal Processor) 150c. The RAM 150b is provided with a phase adjustment program that adjusts the phase of the speed fluctuation of the photoconductor based on the detection result of the reflection type photosensor. This program is executed by the CPU 150a and the like, and the control unit 150 includes the phase difference adjusting means. Is functioning as

  The control unit 150 of the printer according to the present embodiment corrects a phase difference caused by a periodic rotation speed variation of each photoconductor, and performs color misregistration correction. In this color misregistration correction, a reference image, which is a reference visible image, is developed near both ends of the photoreceptors 2Y, 2C, 2M, and 2K, and sequentially transferred to the vicinity of the end of the intermediate transfer belt 41. As a result of this transfer, Y, C, M, and K reference pattern image groups SK, SM, SC, and SY for detecting misregistration as shown in FIG. 9 are formed at both ends of the intermediate transfer belt 41, respectively. Among the reference pattern images, the K reference pattern images (SK1 to SKn) and the C reference pattern images (SC1 to SCn) are reflected on the upper side in the drawing as pattern image detection means as the intermediate transfer belt 41 moves endlessly. Detected by the mold photo sensor 69b. On the other hand, the M-color reference pattern image (SM1 to SMn) and the Y-color reference pattern image (SY1 to SYn) are detected by the reflection type photosensor 69a on the lower side in the drawing as the intermediate transfer belt 41 moves endlessly. .

  When forming the reference pattern image group of each color, as shown in FIG. 10, the detection signals of the rotation position detecting means 34 are aligned, and the reference positions of the photoconductors 2 of the respective colors are matched. In FIG. 10, the reference position of each photoconductor 2 is set to the position B shown in FIG. 5, but the reference positions of some photoconductors may be set to the A position.

  Here, as shown in FIG. 11, the upper reference pattern image SU in the drawing of the intermediate transfer belt 41 is formed by the ideal photoconductor 2 having no periodic fluctuation, and the lower reference pattern image in the drawing. SD is assumed to be formed by a photoconductor having a rotational speed variation. Since the upper reference pattern image SU in the drawing is created by the photosensitive member 2 having no rotational speed fluctuation, the reference pattern images SU are formed at equal intervals P. As a result, the detection times ta1, ta2, ta3,... Of the reflective photosensor 69b are equally spaced. On the other hand, each reference pattern image (SD) on the lower side in the figure formed by the photosensitive member 2 having fluctuations in the rotational speed is displaced in the sub-scanning direction, and the intervals between the reference pattern images SD are not equal. As a result, as shown in FIG. 11, the lower reference pattern images (SD2, SD3, SD4) on the lower side of the intermediate transfer belt 41 from the formation position of the ideal reference pattern image (SU) formed on the upper side of the intermediate transfer belt 41. ) Are formed at positions separated by d1, d2, d3, and d4, respectively. As a result, the detection times tb1, tb2, tb3, tb4... Of the reflective photosensor 69a are also different.

Therefore, the control unit 150 calculates a deviation amount (d1, d2, d3...) From the reference position of the reference pattern image based on the detection time between the reference pattern images and the moving speed of the intermediate transfer belt 41. Thus, the rotation speed fluctuation of the photosensitive member 2 is obtained. More specifically, the detection time between the reference pattern images of the K color reference pattern image group (SK) formed on the upper side of the intermediate transfer belt shown in FIG. 9 is stored in the storage unit in the control unit. In parallel with this, the detection time between the reference pattern images of the M color reference pattern image group (SM) formed on the lower side of the intermediate transfer belt is stored in the storage unit in the control unit. Based on the detection time of the K color reference pattern image and the moving speed of the intermediate transfer belt 41, the deviation amount (d1, d2, d3...) From the ideal position for the K color reference pattern image is calculated. It is. Thereby, the rotational speed fluctuation | variation of K photoconductor 2 can be calculated | required. Further, based on the detection time of the M color reference pattern image and the moving speed of the intermediate transfer belt 41, the registration deviation amount (d1, d2, d3...) From the ideal position for the M color reference pattern image is calculated. Then, the fluctuation in rotational speed of the M-color photoconductor 2 is obtained.
The C reference pattern image group SC formed on the downstream side in the moving direction of the intermediate transfer belt 41 of the K reference pattern image group SK is also subjected to the same processing as described above, so that Obtain the rotational speed fluctuation. Further, the Y-color reference image group SY formed on the downstream side in the moving direction of the intermediate transfer belt 41 of the M-color reference pattern image group SM also performs the same processing as described above, thereby performing the Y-color photoconductor 2Y. Obtain the rotation speed fluctuation.

  FIG. 12 is a graph showing the rotational speed fluctuation of the K-color photoconductor 2K and the rotational speed fluctuation of the M-color photoconductor 2M obtained by the above calculation. The horizontal axis in FIG. 12 represents the elapsed time since the first reference image of the reference image group was detected by the reflective photosensor 69, and the vertical axis represents the amount of deviation from the reference position at each elapsed time. As shown in FIG. 12, as a result of the phase difference B between the rotational speed fluctuation of the K-color photoconductor 2K and the rotational speed fluctuation of the M-color photoconductor 2M, the M color and the K color become large at a certain elapsed time. Color shift.

  Therefore, the control unit 150 calculates the phase difference B between the M color and the K color by calculation based on the periodic fluctuation of the K and M color photoreceptors 2 determined by the above calculation. Based on the obtained phase difference B, the M drive motor 31M is controlled to rotate the M color photoconductor 2M by a predetermined angle, so that the rotation reference position of the M color photoconductor 2M is set as shown in FIG. The phase difference B is shifted from the rotation reference position of the K color photoconductor. As a result, the phase difference between the periodic variation of the K color photoconductor and the periodic variation of the M color photoconductor is adjusted, and the color misregistration between the M color and the K color is reduced as shown in FIG.

  Also for the C color photoconductor 2C, a phase difference from the periodic fluctuation of the K color photoconductor is obtained by calculation, and the C color photoconductor is rotated by a predetermined angle based on the obtained phase difference to rotate the C color. The phase difference between the K color cycle variation and the C color cycle variation is adjusted by shifting the reference position from the phase difference and the rotation reference position of the K color photoreceptor. Similarly, for the Y color, the phase difference between the rotation reference position and the K color is adjusted. As a result, the phase difference between the Y, M, and C photoconductors is corrected based on the period variation of the K color photoconductor. Thereby, the color shift of each color can be reduced favorably.

If the interval P of the reference pattern image is not set to the circumferential length (1 / m) (m = integer) of the photosensitive member, the reference pattern image can be formed even if the photosensitive member is rotated once to form the reference pattern image group. The last reference pattern image in the group is formed before the photoconductor rotates once. Therefore, even if the periodic fluctuation of the photoconductor is calculated based on the reference pattern image, the cyclic fluctuation for one rotation of the photoconductor cannot be obtained. For this reason, in order to accurately obtain the waveform of the periodic fluctuation of the photoconductor, it is necessary to form a reference pattern image group that is equal to or longer than the circumference of the photoconductor. For this reason, the measurement time becomes longer, and the time for the positional deviation correction control becomes longer.
On the other hand, if the interval P of the reference pattern image is set to the circumferential length (1 / m) (m = integer) of the photoconductor, the period variation of the photoconductor can be achieved only by forming a reference pattern image group for the circumference of the photoconductor. Can be obtained with high accuracy, and the time for positional deviation correction control can be shortened. This is because, when the reference pattern image group is formed for the circumference of the photosensitive member by setting the interval P of the reference pattern image to the peripheral length (1 / m) (m = integer) of the photosensitive member, the last pattern of the reference pattern image group is formed. The reference pattern image is formed when the photoconductor rotates exactly once. Therefore, based on this reference pattern image, it is possible to obtain a periodic variation for one rotation of the photosensitive member. In addition, even when the interval between the reference pattern images is somewhat wide, measurement data during one rotation of the photosensitive member can be obtained, so that the phase can be detected with high accuracy.

  In the above description, the reflection type photosensors 69a and 69b are provided at both ends of the intermediate transfer belt. However, as shown in FIG. 15, the reflection type photosensors (69K, 69C, 69M, and. 69Y) may be provided. Thereby, each color reference image group can be detected at once, and the time required for the positional deviation correction control can be shortened.

  The rotational speed fluctuation with one rotation of the photosensitive member as one cycle occurs due to the eccentricity of the photosensitive member. Therefore, unless the photosensitive member is attached to or detached from the apparatus main body or replaced, the phase difference of the periodic fluctuation between the photosensitive members. Will not change. Therefore, color misregistration correction control may be performed when the photoconductor is detached from the apparatus main body or replaced. At this time, it is not necessary to perform the process on all the four color photoconductors, and the phase difference between the exchanged or detached photoconductor and the K color photoconductor which is a reference for adjusting the phase difference of the period variation is adjusted. do it. For this reason, it is not necessary to create four-color reference pattern images as described above, and it is only necessary to form a K-color reference pattern image group and a color reference pattern image corresponding to the exchanged or detached photoconductor. When the reference K-color photoconductor is replaced, the phase difference is calculated by adjusting the phase difference between the K-color photoconductor and any one of Y, C, and M photoconductors. On the other hand, for other photoconductors for which the phase difference was not calculated, the difference value between the phase difference calculated this time and the phase difference before replacement is taken, and the phase difference is adjusted by rotating the photoconductor by this difference value. To do.

In the above description, the drive motors 31 for driving the photoconductors are provided for the respective photoconductors. Therefore, if the drive motors 31K, 31M, 31C, and 31Y for the respective colors are controlled, the color photoconductors 2K, 2M, 2C, By adjusting the 2Y rotation reference position, the phase difference of the periodic fluctuation of the photosensitive member can be corrected. However, as shown in FIG. 16, the drive mechanism 30 drives a color drive motor 31A that drives three photoconductors M, C, and Y (color) and a black drive motor 31K that drives a K-color photoconductor. The three photoconductors 2M, 2C, and 2Y of M, C, and Y (color) cannot be driven independently of each other. Accordingly, even if there is a phase difference in one cycle of rotation of the photosensitive member between M color C color, C color Y color, and M color Y color, these phase differences cannot be corrected. For this reason, in the case of the drive mechanism having such a configuration, with respect to the M, C, and Y colors, the photoreceptors are arranged so that the phase of the periodic fluctuation with one revolution of the photoreceptor on the intermediate transfer belt is in phase. Assemble. In the figure, reference numeral 33 denotes an idler gear.
In the case of such a drive mechanism, the color misregistration of each color can be corrected by correcting the phase difference between the periodic variation of the K-color photoconductor 2K and the periodic variation of any of the M, C, and Y photoconductors. Therefore, it is possible to reduce the time for misalignment correction control and the calculation load for misalignment correction.

  Further, as shown in FIG. 17, a first drive motor 31B that drives the two photosensitive members 2K and 2M of K and M colors, and a second drive motor that drives the photosensitive members 2C and 2Y of C and Y colors. When the drive mechanism is composed of 31C, it is necessary to assemble the photoconductor so that no phase difference occurs between the M color and the K color. Further, the photoconductor is assembled so that no phase difference occurs between the C color and the Y color. In the case of such a drive mechanism, the color misregistration of each color can be corrected by correcting the phase difference between one of the K color and the C color and either the C color or the Y color.

  Further, the positional deviation correction according to the present embodiment only needs to know the phase difference between the two colors. That is, if the reference pattern image when the amount of registration deviation from the reference position is maximum in the detection time of the reference pattern image is known for each color, the phase difference between the colors can be known, and the color deviation can be corrected. More specifically, for example, when the reference pattern image having the maximum detection time is SK3 in the K photoconductor and the reference pattern having the maximum detection time is SM5 in the M photoconductor, the K color is used. It can be seen that there is a phase difference of two reference patterns between the periodic variation of the photoconductor and the periodic variation of the M color photoconductor. Since the pitch between the reference patterns is set in advance, the rotation angle of the photoconductor for adjusting the phase difference is calculated from the distance between the pitches and the diameter of the photoconductor. Then, the M drive motor is rotated by the calculated angle to shift the M rotation reference position from the K rotation reference position by a phase difference.

  Next, features of the present embodiment will be described. As described above, the detection time obtained by forming the reference pattern image on the intermediate transfer belt and detecting the reference pattern image by the reflection type photosensor 69 includes the periodic fluctuation of the transfer driving roller 45 as noise. It will be. As a result, the periodic variation obtained from the detection time of the photo sensor 69 and the speed of the intermediate transfer belt 41 is actually the periodic variation of the photoconductor 2 and the periodic variation of the transfer driving roller 45 superimposed. It is. Therefore, the phase difference between the two colors cannot be accurately detected due to the periodic fluctuation of the transfer driving roller 45, and the color misregistration cannot be accurately corrected. Therefore, in order to suppress the positional deviation of the photosensitive member 2 with high accuracy, it is necessary to accurately remove the periodic fluctuation of the transfer driving roller 45 that is noise. The printer according to the present embodiment has a function of accurately removing periodic fluctuations of the transfer driving roller 45. Embodiments 1 to 3 will be described below as means for accurately removing the periodic fluctuation of the transfer driving roller 45 that is noise.

[Example 1]
In the first embodiment, the length of the reference pattern image group of each color formed on the intermediate transfer belt is set to the least common multiple of the circumferential length of the photosensitive member and the circumferential length of the transfer driving roller. If the peripheral length of the driving roller 45 is sufficiently small relative to the peripheral length of the photosensitive member, the frequency of periodic fluctuation with one rotation of the photosensitive member 2 as one cycle and the frequency with one rotation of the driving roller 45 as one cycle are large. Different. For this reason, if a frequency analysis is performed and a high frequency component is removed, the period fluctuation | variation of the drive roller 45 can be removed accurately. Therefore, if a reference pattern image group corresponding to at least the circumference of the photoconductor 2 is created, the periodic variation component of the photoconductor can be accurately detected.

  However, if the circumference of the photoconductor 2 and the circumference of the drive roller 45 are close, the frequency with one rotation of the photoconductor 2 as one cycle and the frequency with one rotation of the drive roller 45 as one cycle are close to each other. It becomes difficult to remove the period fluctuation of the driving roller 45 by the frequency analysis. Thus, when the circumference of the photoconductor 2 and the circumference of the driving roller 45 are close, the length of the reference pattern image group is set to a plurality of cycles of the photoconductor 2 to detect the reference pattern image detection time and the intermediate transfer. It is conceivable to remove the periodic fluctuation of the transfer driving roller 45 by averaging the waveform calculated from the speed of the belt 41 with the period of the rotational speed fluctuation of the photosensitive member 2. In order to remove the periodic fluctuation of the transfer driving roller 45 with high accuracy, the length of the reference pattern image group should be made sufficiently long to increase the number of times of averaging processing. However, if the length of the reference pattern image group is too long, the time required for misregistration correction control becomes longer. In addition, if the length of the reference pattern image group is short, it is not possible to sufficiently remove the period variation of the transfer driving roller 45, and it becomes impossible to perform accurate positional deviation correction.

  In the first exemplary embodiment, the length of the reference pattern image group of each color formed on the intermediate transfer belt is set to the least common multiple of the peripheral length of the photosensitive member 2 and the peripheral length of the transfer driving roller 45, thereby allowing the reference image pattern group. Can be minimized, and the period fluctuation component of the drive roller can be satisfactorily removed.

  Specific description will be given below. FIG. 18 is a diagram illustrating a periodic variation of the transfer driving roller 45 and a periodic variation of the photosensitive member 2 when the diameter of the photosensitive member 2 is 80 [mm] and the diameter of the transfer driving roller 45 is 70 [mm]. . A dotted line in FIG. 18 indicates a periodic variation of the transfer driving roller 45, and a solid line in the drawing indicates a periodic variation of the photosensitive member 2. The thick line in the figure is a waveform when the deviation amount from the ideal position of the reference pattern image is plotted. As shown in the figure, it can be seen that the deviation amount from the ideal position is obtained by superimposing the periodic variation of the photosensitive member and the periodic variation of the transfer driving roller.

  As shown in FIG. 18, when the photosensitive member rotates 7 times (7 cycles) and the driving roller rotates 8 times (eight cycles), the phase of the periodic variation of the photosensitive member 2 and the phase of the periodic variation of the transfer driving roller 45 are different. Be the same. That is, the speed variation in which the periodic variation of the transfer driving roller 45 and the periodic variation of the photosensitive member 2 are superimposed is the periodic variation having the periodic length of the least common multiple of the circumferential length of the photosensitive member and the circumferential length of the transfer driving roller 45 It becomes. Therefore, when the speed fluctuation in which the period fluctuation of the transfer driving roller 45 and the period fluctuation of the photoconductor 2 are superimposed is divided by the rotation period of the photoconductor, the seventh part (W7) from the first part (W1). Up to this point, the period fluctuation of the transfer driving roller and the phase difference between the photosensitive member are different. On the other hand, the phase difference between the periodic variation of the transfer driving roller in the eighth (W8) portion and the periodic variation of the photosensitive member is the same as that in the first portion (W1), and the ninth (W9) portion. The period fluctuation of the transfer driving roller, the period fluctuation of the photosensitive member, and the phase difference are the same as the second part (W2). Therefore, if the speed variation corresponding to the least common multiple of the circumferential length (cycle) of the transfer driving roller 45 and the circumferential length (cycle) of the photosensitive member is known, the subsequent speed variation can be predicted. For this reason, if the reference pattern image group is created by the least common multiple of the circumference of the transfer drive roller 45 and the circumference of the photosensitive member, the detection interval between the reference pattern images is measured, and if the speed fluctuation by the least common multiple is known, The speed fluctuation after that can also be grasped.

Further, the phase of the cycle variation of the transfer driving roller is different from W1 to W7. Therefore, when the measurement data corresponding to each position of the photoconductor is averaged, the periodic variation component of the photoconductor is the same at each position of the photoconductor, so that the value does not change even if the averaging process is performed. However, if the periodic fluctuation component of the transfer driving roller 45 is averaged, the average speed of the transfer driving roller is equalized, and the periodic fluctuation of the transfer driving roller can be brought close to zero. However, when averaging up to W8, the phase of the transfer driving roller at W8 is the same as W1, so the period fluctuation component of the transfer driving roller at W1 is emphasized, and when averaged In addition, the fluctuation noise of the transfer driving roller may be worse than when averaged by W1 to W7. That is, even if the averaging process is performed with the measurement data (W7) or more when the circumference of the transfer driving roller 45 is equal to the least common multiple of the circumference of the photosensitive member, it is not very effective in removing the cycle fluctuation of the transfer driving roller. There is no.
Therefore, the reference pattern image group is created by the least common multiple of the circumference of the transfer driving roller 45 and the circumference of the photosensitive member, the detection time between the reference pattern images is measured, and the position of the photosensitive member in the measured data is measured. By averaging the corresponding measurement data, it is possible to effectively remove the period fluctuation of the transfer driving roller without unnecessarily forming a long reference pattern.

[Example 2]
Next, Example 2 will be described. In the second embodiment, the interval between the photoconductors is determined based on the detection time from when the first reference image of the reference pattern image group is detected until the reflection type sensor 69 detects the reference image separated by the circumference of the transfer driving roller 45. The phase difference is adjusted. Since the period fluctuation of the transfer driving roller 45 is one period of one rotation of the transfer driving roller, the rotation speed fluctuation is canceled by one rotation of the transfer driving roller. Therefore, if the reference pattern images are detected at intervals of the circumferential length of the transfer driving roller 45, the detection time will not be advanced or delayed due to fluctuations in the rotational speed with one rotation of the transfer driving roller as one cycle. That is, the detection time does not fluctuate due to the fluctuation of the rotation speed with one rotation of the transfer driving roller as one cycle. Therefore, the detection time fluctuates due to the influence of only the rotational speed fluctuation component of the photoconductor, and the phase difference of the speed fluctuation between the photoconductors can be accurately obtained based on this detection time.

  In this case, if the pitch of the reference pattern image is set to be (1 / N (integer)) times the circumferential length of the transfer driving roller 45, the cycle fluctuation of the transfer driving roller 45 can be more easily removed. . For example, if the circumferential length of the transfer drive roller 45 is 82.47 [mm] and the pitch between the reference images is 2.5 [mm], the pitch of the reference image is (1/34) of the circumference of the transfer drive roller 45. It becomes. In this case, as shown in FIG. 19, the detection time tc1 from the first reference pattern image (S1) to the 34th reference pattern image (S34) is examined. Similarly, the detection time tc2 from the second reference pattern image (S2) to the 35th reference pattern image (S35), the detection times tc3, tc4,. I will investigate. The detection time is obtained as follows. When the first reference pattern image S1 is detected by the reflective photosensor 69, time measurement is started. Each time the reflective sensor 69 detects the reference pattern image, the time at that time is numbered and stored. After the detection of the reference image pattern group, the difference between the 34th measurement time stored in the storage unit and the first measurement time is calculated to detect the first reference pattern image, and then the 34th measurement time. The detection time tc1 until the reference pattern image is detected can be obtained. Similarly, detection times tc2 for the second reference pattern image (S2) and 35th reference pattern image (S35), and detection times tc3 for the third and thirty-sixth faces are obtained. And the position used as the maximum detection time is memorize | stored from the calculated | required detection time tc. For example, for the K color, tc3 is the maximum detection time, and for the M color, if tc5 is the maximum detection time, the M color may have a phase difference of two reference images with respect to the K color. Recognize. When the diameter of the photosensitive member is 30 [mm], the rotation angle with respect to the pitch of 2.5 [mm] is 9.5 °, so that the circumferential length of the 5.0 [mm] photosensitive member is shifted. The phase difference with respect to the K color can be eliminated by rotating the color photoconductor by 19 °. By performing the same processing on the photoconductors of other colors, the phase difference between the Y and C colors with respect to the K color can be eliminated.

  In the above description, the pitch of the reference pattern image is set to be (1 / N (integer)) times the circumference of the transfer driving roller 45, but the pitch of the reference pattern image is (1 / M (integer)) times, the phase difference can be corrected more easily. For example, as described above, if it is found that the M color has a phase difference of two reference images with respect to the K color, the phase difference is eliminated by rotating the M color (360 ° / 2 m). Can do. Therefore, the phase difference can be easily corrected as compared with the case where the pitch of the reference image is only (1 / N (integer)) times the circumferential length of the transfer driving roller 45.

[Example 3]
Next, Example 3 will be described. In the third embodiment, the encoder detects the speed fluctuation of the intermediate transfer belt 41 caused by the period fluctuation of the transfer drive roller 45, and feedback-controls the detection result to the drive motor that drives the transfer drive roller 41, thereby enabling the intermediate transfer belt. 41 is rotated at a constant speed. FIG. 20 is a diagram in which an encoder sensor 110 is provided on the drive roller 45 of the transfer unit 40. When the transfer driving roller 45 is rotated by the motor M, a pulse signal is output from the encoder sensor 110 to the encoder rotation detection unit. The signal output to the encoder rotation detection unit is sent to the motor control unit. The motor control unit controls the motor M based on a signal from the encoder rotation detection unit. As a result, the reference pattern image formed on the intermediate transfer belt is not affected by the periodic fluctuation of the transfer driving roller 45. As a result, the detection interval detected by the reflection type photosensor 69 is not affected by the periodic fluctuation of the transfer driving roller 45, the phase difference between the colors of the photoconductor can be detected well, and the color misregistration is accurately corrected. can do.

In the present embodiment, the misregistration correction control is executed when the photoconductor is replaced. The attachment / detachment of the photoconductor is provided with a detecting means for detecting whether the door of the apparatus main body is opened or closed. When the door of the apparatus main body is opened / closed, it is determined that the photoconductor is attached / detached from the apparatus main body, and the positional deviation is corrected. FIG. 21 is an example of an execution flow of misalignment correction control.
First, the control unit 150 checks whether or not the door of the apparatus main body is closed (S1). If the door is open (NO in S1), check whether the open flag is set (S2), and if it is set (S2 YES), return to the flow of S1 as it is and if it is not set (NO in S2), sets the open flag (S3), and returns to the flow in S1. If the door is closed (YES in S1), it is checked whether an open flag is set (S4). If the open flag is set (S4 YES), the photoconductor is likely to be replaced, so that misregistration correction control is executed (S5). When the positional deviation correction control is performed, the door open flag is cleared (S6).

Accordingly, it is possible to reliably execute the positional deviation correction control when the photoconductor is replaced. However, in the case of the control shown in FIG. 21, the positional deviation correction control is executed even if the door is opened and closed without replacing the photosensitive member 2. Therefore, a detection means for detecting the replacement of the photosensitive member may be provided, and when the replacement is detected, the positional deviation correction control may be executed.
As the detection means for detecting the exchange, it is determined whether or not the exchange is performed based on the unique information stored in the IC tag and the storage means such as an IC tag for storing unique information such as an identification number in the photosensitive member or the process cartridge. And determination means. This determination unit functions by the control unit 150.
FIG. 22 is an execution flowchart of misregistration correction control when an IC tag is provided in a photoconductor or a unit including the photoconductor. As shown in FIG. 22, when the door is closed and there is an open flag (YES in S4), communication with the IC tag is performed (S5), and the identification number stored in the IC tag is changed from the IC tag. get. Next, it is checked whether or not the acquired identification number is the same as the identification number stored in the apparatus main body (S6). If they are the same (S6 YES), the exchange is not performed, so the open flag is deleted (S8), and the process returns to S1. When the identification numbers are different (NO in S6), misalignment correction control is performed (S7), and the open flag is erased (S8). Next, the identification number stored in the apparatus main body is rewritten to the acquired identification number (S9).
In this way, by providing the IC tag on the photosensitive member or the unit including the photosensitive member, even if the door of the apparatus main body is opened and closed, if the photosensitive member is not exchanged, the positional deviation correction is not performed. can do.

  In addition, a detection unit that detects the presence or absence of the process cartridge or the photoconductor may be provided, and in this case, when the process cartridge or the photoconductor is removed from the apparatus main body, misalignment correction control may be performed.

  In this embodiment, an example in which the transfer body is an intermediate transfer belt has been described. However, the present invention is not limited thereto, and the transfer body may be an intermediate transfer drum.

(1)
According to the image forming apparatus of the first embodiment, the length of the group of reference pattern images is the least common multiple of the circumference of the image carrier and the circumference of the transfer driving roller, so that the rotation of the photoconductor as the image carrier is performed. If the averaging process is performed at a period, the phase of each photoconductor can be adjusted with high accuracy.
(2)
Further, according to the image forming apparatus of the second embodiment, the detection from the detection of the predetermined reference pattern image by the pattern image detecting unit to the detection of the reference pattern image at the position where the circumference of the transfer driving roller is separated. In time, the influence of fluctuations in the rotational speed of the transfer drive roller does not appear. Therefore, if the detection is performed at such an interval, the rotational speed fluctuation of the photoconductor can be calculated, and the phase difference of each photoconductor can be adjusted with high accuracy.
(3)
Further, the interval between the reference toner images formed on the transfer belt is set to (1 / n) (n = integer) of the circumference of the transfer driving roller, so that the turn image detecting means detects a predetermined reference pattern image. Then, it is possible to detect the reference pattern image at the position where the circumference of the transfer driving roller is separated.
(4)
Further, a reference pattern image group corresponding to the circumference of the photosensitive member is formed by setting the interval between the reference toner images formed on the transfer belt to be (1 / m) (m = integer) of the circumference of the image carrier. By simply doing this, it is possible to determine the periodic fluctuation of the photoconductor with high accuracy and to shorten the time for the positional deviation correction control.
(5)
Further, according to the third embodiment, since the speed of the transfer body is controlled based on the detection result of the encoder sensor that is the speed detecting means, the rotational speed fluctuation of the transfer driving roller is changed during the formation of the reference pattern image on the transfer belt. The influence is suppressed from appearing. As a result, the reference pattern image formed on the transfer belt is only influenced by fluctuations in the rotational speed of the photosensitive member. Therefore, based on the detection result of detecting this reference pattern, the calculated periodic fluctuation component is It becomes a rotational speed fluctuation component of the body, and the phase difference of each photoconductor can be obtained with high accuracy. As a result, the phase of the speed fluctuation of each photoconductor can be adjusted with high accuracy.
(6)
Further, the four drive motors are constituted by the K drive motor for rotating the K photoconductor and the color drive motor for rotating the Y photoconductor, the C photoconductor and the M photoconductor. The number of drive motors can be reduced compared to the provided one, and the cost can be reduced. Further, since the Y photoconductor, the C photoconductor and the M photoconductor rotate together, the phases do not differ if the phase differences are accurately matched. Therefore, if the phase difference between the photoconductor for K, the photoconductor for Y, the photoconductor for C, and the photoconductor for M is adjusted, the color shift can be suppressed, and the color shift correction can be performed in a short time. Can be done.
(7)
Even if the first drive motor for driving the K photoconductor and the M photoconductor and the second drive motor for driving the C photoconductor and the Y photoconductor to rotate, the above (6) Similar effects can be obtained.
(8)
In addition, when the photoconductor is replaced, the phase difference of the photoconductor is different from that when the photoconductor is corrected. If corrected, even if the photoconductor is replaced, no color misregistration occurs.
(9)
In addition, even if the photoconductor is attached to or detached from the apparatus main body, the phase difference of the photoconductor is different. Therefore, when the photoconductor is attached or detached and the attachment or detachment is detected, the phase difference of each photoconductor is corrected. For example, even if the photoconductor is attached or detached, color misregistration does not occur.
(10)
In addition, if the door to be opened or closed when the photoconductor is attached or detached is opened, the photoconductor may be attached or detached.Therefore, an open / close detecting means for detecting the opening and closing of the door of the apparatus main body is provided to open and close the door. If detected, if the phase difference of each photoconductor is corrected, no color shift will occur even if the photoconductor is attached or detached.
(11)
Further, a rotation position detecting means for detecting the rotation position of the photosensitive member is provided on the apparatus main body side. Since the photosensitive member and the process cartridge are frequently replaced as compared with the apparatus main body, if the photosensitive member and the process cartridge are provided on the photosensitive member and the process cartridge, they are replaced even if the rotational position detecting means has not reached the end of its service life. As a result, the cost of the photoconductor and the process cartridge may be increased. However, by providing the rotation position detection means on the apparatus main body side, the rotation position detection means is not replaced with a photoconductor or a process cartridge, and the cost can be suppressed.
(12)
In this embodiment, even if the transfer driving roller for driving the transfer belt has a rotational speed, the phase of each photoconductor can be accurately adjusted from the reference pattern image formed on the transfer belt.
(13)
Even if the transfer body is in the form of a drum, the phase of each photoconductor can be accurately adjusted from the reference pattern image formed on the transfer belt.
(14)
Furthermore, even if the drive motor for rotating the photoconductor is a DC motor, the phase of each photoconductor can be adjusted with high accuracy.
(15)
Even if the drive motor that rotates the photosensitive member is a stepping motor, the phase of each photosensitive member can be adjusted with high accuracy.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating a Y process unit and a developing device in the printer. The figure which shows the drive mechanism of a photoreceptor. The figure which shows a photoconductor and a drive mechanism. The figure which shows a rotational position detection means. The figure which shows the other example of a rotation position detection means. FIG. 3 is a perspective view of an intermediate transfer belt. FIG. 2 is a block diagram showing a part of an electric circuit of the printer. FIG. 4 is a diagram illustrating a state in which a reference pattern image is formed on an intermediate transfer belt. The figure which shows the signal of a rotation position detection means. The figure which shows a mode that the reference | standard pattern is formed in the position shifted | deviated from the ideal position. The figure which shows the color shift amount before phase difference adjustment. The figure which shows the signal of the rotation position detection means after phase difference adjustment. The figure which shows the color shift amount after phase difference adjustment. The perspective view of the other example of an intermediate transfer unit. The other structural example of a drive mechanism is shown. Still another configuration example of the drive mechanism will be described. The figure which shows the period variation of the least common multiple of a photoconductor and a transfer drive roller. FIG. 10 is a diagram for explaining misalignment correction control according to the second embodiment. FIG. 6 is a diagram illustrating a configuration of a third embodiment. The figure which shows the execution flow of position shift correction control. FIG. 6 is a flowchart of execution of misalignment correction control when an IC tag is provided in a photoconductor or a unit including the photoconductor. The waveform obtained by measuring the deviation | shift amount from the ideal position of each reference pattern is shown.

Explanation of symbols

2Y, C, M, K: Photoconductor 20Y, C, M, K: Developing device 30: Drive mechanism 34: Rotation position detection means 40: Transfer unit 41: Intermediate transfer belt 45: Transfer drive roller 69: Reflective photo sensor

Claims (15)

A transfer member, a transfer driving roller for rotating the transfer member, a plurality of image carriers disposed on the transfer member, and a plurality of image carriers on the transfer member in the sub-scanning line direction Pattern image detecting means for detecting a plurality of reference pattern images formed side by side, and phase adjusting means for adjusting the phase of the speed fluctuation of each image carrier based on the detection result of the pattern image detecting means. In the image forming apparatus,
The length in the sub-scanning line direction of a group of reference pattern images formed sequentially on the transfer body in the sub-scanning line direction is the least common multiple of the circumference of the image carrier and the circumference of the transfer driving roller. An image forming apparatus. A transfer member, a transfer driving roller for rotating the transfer member, a plurality of image carriers disposed on the transfer member, and a plurality of image carriers on the transfer member in the sub-scanning line direction Pattern image detecting means for detecting a plurality of reference pattern images formed side by side, and phase adjusting means for adjusting the phase of the speed fluctuation of each image carrier based on the detection result of the pattern image detecting means. In the image forming apparatus,
The phase adjusting means is based on a detection time from when the pattern image detecting means detects a predetermined reference pattern image until it detects a reference pattern image at a position where the circumference of the transfer driving roller is separated, An image forming apparatus characterized by calculating a phase difference of speed fluctuation between image carriers, and adjusting a phase difference of speed fluctuation between image carriers based on the calculated phase difference. The image forming apparatus according to claim 2.
An image forming apparatus, wherein the interval between reference toner images formed on the image carrier is (1 / n) (n = integer) of the circumference of the transfer driving roller. A transfer body, a plurality of image carriers arranged along the transfer body, and a plurality of reference pattern images formed in sequence in the sub-scanning line direction on the transfer body by the plurality of image carriers. In an image forming apparatus, comprising: a pattern image detecting means for detecting; and a phase adjusting means for adjusting the phase of the speed fluctuation of each image carrier based on the detection result of the pattern image detecting means.
An image forming apparatus comprising: a speed detection unit that detects the speed of the transfer body; and the speed of the transfer body is controlled based on a detection result of the speed detection unit. The image forming apparatus according to claim 1,
An image forming apparatus characterized in that the interval between reference toner images formed on the image carrier is set to (1 / m) (m = integer) of the circumference of the image carrier. The image forming apparatus according to claim 1,
The plurality of image carriers include a black image carrier that carries a black toner image, a yellow image carrier that carries a yellow toner image, and a cyan image carrier that carries a cyan toner image. And a magenta image carrier that carries a magenta toner image, a black drive motor that rotates the black image carrier, a yellow image carrier, a cyan image carrier, and a magenta image carrier. An image forming apparatus comprising: a color drive motor that rotationally drives the body. The image forming apparatus according to claim 1,
The plurality of image carriers include a black image carrier that carries a black toner image, a yellow image carrier that carries a yellow toner image, and a cyan image carrier that carries a cyan toner image. And a magenta image carrier that carries a magenta toner image, and the black image carrier, the yellow image carrier, the cyan image carrier, and the magenta image carrier are rotated. An image forming apparatus comprising: a first drive motor for driving; and a second drive motor for rotating and driving another image carrier. The image forming apparatus according to claim 1,
An image forming apparatus, comprising: an exchange detection unit configured to detect that the image carrier or at least a process cartridge including the image carrier is exchanged. The image forming apparatus according to claim 1,
An image characterized in that the image carrier or at least a process cartridge including the image carrier is configured to be detachable from an apparatus main body, and includes an attachment / detachment detecting means for detecting attachment / detachment of the image carrier or the process cartridge. Forming equipment. The image forming apparatus according to claim 9.
An image forming apparatus characterized in that the attachment / detachment detection means is an opening / closing detection means for detecting opening / closing of a door of an apparatus main body that is opened when the image carrier or the process cartridge is attached / detached from the apparatus main body. The image forming apparatus according to any one of claims 1 to 8, or the image forming apparatus according to claim 9, wherein the image bearing member or at least a process cartridge including the image bearing member is configured to be detachable from the apparatus main body.
An image forming apparatus comprising: a rotation position detection unit that detects a rotation position of the image carrier; and the rotation position detection unit is provided on the apparatus main body side. 12. The image forming apparatus according to claim 1, wherein
An image forming apparatus, wherein the transfer body is formed in a belt shape. 12. The image forming apparatus according to claim 1, wherein
An image forming apparatus, wherein the transfer body is formed in a drum shape. The image forming apparatus according to claim 1,
An image forming apparatus, wherein a DC motor is used as a drive motor for rotationally driving the image carrier. The image forming apparatus according to claim 1,
An image forming apparatus using a stepping motor as a drive motor for rotationally driving the image carrier.

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