JP2009063970A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of coping with both cases where first print time is to be shortened and where a high-quality image is to be formed and coping with various user's needs. <P>SOLUTION: If amplitude of speed variation of a photoreceptor is equal to or less than a prescribed value or if a position sensor does not detect a reference mark until time t5 when a visible image can be formed on the photoreceptor, a control part 140 selects a condition that drive control to cancel the speed variation of the photoreceptor is not performed, to form the visible image on the photoreceptor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that detects the rotational position of an image carrier and controls driving so that the rotational speed of the image carrier becomes a target speed.

  A so-called tandem that obtains a color image by sequentially superimposing a plurality of image carriers corresponding to each color and each color toner image obtained by developing an electrostatic latent image formed on each image carrier on a transfer material. A type of image forming apparatus is known.

  In this tandem type image forming apparatus, each toner image on a plurality of image carriers is sequentially superimposed on a transfer material to form a color image. Therefore, if the toner images overlap, so-called color misregistration occurs. Occurs. This color misalignment is mainly caused by the mounting eccentricity of the drive gear provided on the image carrier, the gear molding accuracy, and the speed fluctuation caused by the joint portion connecting the drive gear and the image carrier. When the drive gear of the image carrier is mounted eccentrically, the surface movement speed of the photoconductor fluctuates periodically, and the toner image transferred onto the surface of the transfer material due to this fluctuation periodically expands and contracts. To do. Therefore, when the period of expansion / contraction of the toner image by each image carrier does not match on the surface of the transfer material, color deviation occurs.

Patent Documents 1 and 2 disclose image forming apparatuses that can suppress color misregistration caused by periodic fluctuations in the surface movement speed of an image carrier. The image forming apparatuses disclosed in these patent documents form a pattern image on a transfer material using a plurality of image carriers, read the pattern image, and detect periodic fluctuations in the surface movement speed of each image carrier. To do. Then, based on the detection result, drive control is performed so that the periodic fluctuations in the surface moving speed of each image carrier are offset, that is, the phase is opposite to the phase of the periodic fluctuations. Thereby, the periodic movement of the surface movement speed of each image carrier is eliminated, and the surface movement speed of each image carrier is constant.
In such drive control, as a premise, the rotational position of each image carrier must be accurately grasped. For this reason, in Patent Document 1, one target (reference mark) that moves on the circular orbit along with the rotation of the image carrier is provided on each image carrier, and this is provided with an optical or magnetic detection device (reference mark). Detection means) (see paragraph 0055 of the same document). Accordingly, the target is detected by the detection device once every time the image carrier rotates once. In this configuration, the rotational position of the image carrier when detected is uniquely determined. Therefore, the rotational position of each image carrier can be grasped by detecting this target.

JP-A-9-146329 JP 2001-305820 A

However, when the rotational position of the image carrier is grasped by such a method, the following problem occurs.
That is, when grasping the rotation position of the image carrier, after the rotation of the image carrier is started, the target detection operation by the detection device is started after the surface movement speed becomes a steady state. When a target is detected by the above-described optical or magnetic detection device, the detection device generally detects the target at a timing when the target enters the detection region of the detection device or leaves the detection region. Therefore, for example, in the case of a configuration in which the target is detected at the timing when the target enters the detection area, if the detection operation is started immediately after the tip of the target passes through the detection area, until the image carrier rotates once. The target cannot be detected by the detection device. Therefore, in this case, since the rotational position of the image carrier cannot be grasped until the image carrier rotates once, there arises a problem that the timing for starting the above-described drive control is delayed.
As a result of the above problems, the start timing of image formation performed after the drive control is delayed by a time during the maximum rotation of the image carrier, and the first operation is performed after waiting for the start of the drive control. Print time is delayed.
In the above description, the case where one target (reference mark) that moves on the circular orbit along with the rotation of the image carrier is provided on each image carrier is described. However, when a plurality of reference marks are provided. However, there is a problem that the timing for starting the drive control is delayed by the time until the target is detected.

  In recent years, the needs of the world have been diversified, and various needs have been reached, for example, when it is desired to make the first print time faster than the image quality, or when priority is given to the image quality even if the first print time is late. For this reason, in the case of an apparatus that always performs drive control to form an image, the first print time is always delayed, and it is not possible to cope with cases where it is desired to make the first print time faster than the image quality. In the case of an apparatus that forms an image without performing drive control, a high-quality image cannot be formed. As described above, in the conventional apparatus, it is not possible to cope with both cases where it is desired to increase the first print time and where a high-quality image is to be formed, and it is impossible to meet various needs of users.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of meeting various needs of users.

In order to achieve the above object, the invention of claim 1 comprises an image carrier for carrying a visible image, a visible image forming means for forming a visible image on the image carrier, and the image carrier. A drive source for rotation, a reference mark fixed to the image carrier and moving on a circular orbit as the image carrier rotates, and a reference mark detection for detecting the reference mark on a part of the circular orbit Means, a speed fluctuation detecting means for detecting a fluctuation in the surface movement speed of the front image carrier on the basis of the timing when the reference mark detecting means detects the reference mark, and the reference mark detecting means detects the reference mark. Drive control means for controlling the drive source so that the image carrier is rotated at a target speed by canceling the surface movement speed fluctuation of the image carrier detected by the speed fluctuation detection means based on the detected timing. Images In forming apparatus, it is characterized in that it comprises selection means for selecting whether or not to control the drive source according to the drive control means.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, a selection is made to select whether to control the drive source by the drive control unit based on the detection result of the speed fluctuation detection unit. It is characterized by comprising means.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, when the amplitude of the surface movement speed fluctuation is less than a predetermined value, the drive control means does not control the drive source. The selection means is configured to do so.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, a time measuring unit for measuring time is provided, and an elapsed time from the start of driving of the image carrier is set to a predetermined time. The selection means is configured to select not to perform control of the drive source by the drive control means when it reaches or exceeds a predetermined time.
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, a visible image can be formed on the image carrier after the drive of the image carrier is started for the predetermined time. It is characterized by the time until.
According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the visible image forming means is configured to include a plurality of the image carriers and to form visible images on the image carriers, respectively. Each visible image carried on the image carrier is superimposed and transferred to the intermediate transfer member and then transferred to the recording member at a time, or each visible image carried on the image carrier is superimposed on the recording member. A transfer means for transferring, and a selection to select whether to control the drive source by the drive control means based on whether the visible image transferred to the recording member is a color image or a single color image It is characterized by comprising means.
According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, when the visible image transferred to the recording member is the monochrome image, the drive control means controls the drive source. The selection means is configured.
According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, when the visible image transferred to the recording member is the monochromatic image, the drive control unit does not control the drive source. The selection means is configured as described above.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the drive control unit controls the drive source based on information input to an input unit to which information is input by a user. The selection means is configured to select whether to perform or not.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, the drive control is performed for the second and subsequent sheets in a continuous image forming process in which images are continuously formed on a plurality of recording members. A visible image is formed on the image carrier while the drive source is controlled by the means.
The invention of claim 11 is the image forming apparatus of claim 10, wherein when the drive control is not executed at the time of forming the first image, the first visible image formed on the image carrier is The control of the drive source by the drive control unit is started after the transfer to the intermediate transfer member or the recording member until the formation of the next visible image by the visible image forming unit is started. It is what.
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 speed fluctuation detecting unit detects a speed fluctuation of one rotation period of the image carrier. It is.
According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the first to twelfth aspects, the image carrier is a one-stage reduction mechanism using a drive transmission member having the same rotation center as the image carrier. It is characterized by being driven.
The invention according to claim 14 is the image forming apparatus according to any one of claims 1 to 13, wherein the visible image forming means includes a plurality of the image carriers and forms visible images on the image carriers. And a plurality of drive sources are provided, and each image carrier is individually driven.
According to a fifteenth aspect of the present invention, in the image forming apparatus according to any one of the first to fourteenth aspects, the image carrier and at least one of a charging device, a developing device, and a cleaning device are integrally formed from the apparatus main body. A process cartridge configured to be detachable is provided.

According to the first to fifteenth aspects of the present invention, the selection means can select whether or not to control the drive source by the drive control means, so that the selection means does not control the drive source by the drive control means. Is selected, the image forming operation can be performed at the stage when the surface moving speed reaches a steady state. Therefore, the first print time can be shortened. As a result, the drive source always rotates the image carrier at the target speed by always canceling the surface movement speed fluctuation of the rotating body detected by the speed fluctuation detecting means based on the timing at which the reference mark detecting means detects the reference mark. It is possible to shorten the first print time compared to a device that performs the above control.
Further, if the selection unit selects to control the drive source by the drive control unit, a high-quality image can be output.
In this way, by providing the selection means for selecting whether or not to control the drive source by the drive control means, it is possible to shorten the first print time and obtain a high-quality image. It is possible to meet various needs.

Hereinafter, an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described as an image forming apparatus to which the present invention is applied.
First, a basic configuration of the printer according to the embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a printer according to an embodiment. The printer shown in FIG. 1 includes four process units 1Y, 1C, 1M, and 1K for yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K) as process units as toner image forming means. ing. These use Y, C, M, and K toners of different colors as image forming substances for forming an image, but the other configurations are the same. Taking a process unit 1Y for generating a Y toner image as an example, this has a photoconductor unit 2Y and a developing unit 7Y as shown in FIG. As shown in FIG. 3, the photosensitive unit 2Y and the developing unit 7Y are integrally attached to and detached from the printer body as a process unit 1Y. However, in a state where it is detached from the printer main body, the developing unit 7Y can be attached to and detached from a photosensitive unit (not shown) as shown in FIG.

  In FIG. 2 described above, the photoconductor unit 2Y includes a drum-shaped photoconductor 3Y, a drum cleaning device 4Y, a static eliminator (not shown), a charging device 5Y, and the like.

  The charging device 5Y uniformly charges the surface of the photoreceptor 3Y that is driven to rotate in the clockwise direction in the drawing by a driving unit (not shown). In the figure, the charging roller 6Y that is driven to rotate counterclockwise in the drawing while a charging bias is applied by a power source (not shown) is brought close to the photosensitive member 3Y, thereby charging the photosensitive member 3Y uniformly. Device 5Y is shown. Instead of the charging roller 6Y, a roller that contacts a charging brush may be used. Further, a charger that uniformly charges the photoreceptor 3Y by a charger method, such as a scorotron charger, may be used. The surface of the photoreceptor 3Y uniformly charged by the charging device 5Y is exposed and scanned by a laser beam emitted from an optical writing unit to be described later, and carries a Y electrostatic latent image.

  The developing unit 7Y as developing means has a first agent accommodating portion 9Y in which a first conveying screw 8Y is disposed. Further, it also has a second agent storage portion 14Y in which a toner concentration sensor (hereinafter referred to as a toner concentration sensor) 10Y composed of a magnetic permeability sensor, a second conveying screw 11Y, a developing roll 12Y, a doctor blade 13Y, and the like are disposed. . In these two agent storage portions, a Y developer (not shown) composed of a magnetic carrier and a negatively chargeable Y toner is included. The first transport screw 8Y is driven to rotate by a driving unit (not shown), thereby transporting the Y developer in the first agent storage unit 9Y from the near side to the far side in the direction perpendicular to the drawing sheet. And it penetrates into the 2nd agent accommodating part 14Y through the communication port which is not shown in the partition wall between the 1st agent accommodating part 9Y and the 2nd agent accommodating part 14Y.

  The second transport screw 11Y in the second agent storage portion 14Y is driven to rotate by a driving means (not shown), thereby transporting the Y developer from the back side to the front side in the drawing. The toner concentration of the Y developer being conveyed is detected by the toner concentration sensor 10Y fixed to the bottom of the first agent storage portion 14Y. In this manner, the developing roll 11Y is arranged in a posture parallel to the second transport screw 11Y above the second transport screw 11Y that transports the Y developer. The developing roller 11Y includes a magnet roller 16Y in a developing sleeve 15Y made of a non-magnetic pipe that is driven to rotate counterclockwise in the drawing. A part of the Y developer conveyed by the second conveying screw 11Y is pumped up to the surface of the developing sleeve 15Y by the magnetic force generated by the magnet roller 16Y. Then, after the layer thickness is regulated by the doctor blade 13Y disposed so as to maintain a predetermined gap from the developing sleeve 15Y as a developing member, the layer thickness is regulated and conveyed to the developing area facing the photosensitive member 3Y. Y toner is adhered to the Y electrostatic latent image. This adhesion forms a Y toner image on the photoreceptor 3Y. The Y developer that has consumed the Y toner by the development is returned to the second conveying screw 11Y as the developing sleeve 15Y of the developing roll 12Y rotates. And if it conveys to the near end in a figure, it will return in the 1st agent accommodating part 9Y via the communication port which is not shown in figure.

  The result of detecting the magnetic permeability of the Y developer by the toner concentration sensor 10Y is sent as a voltage signal to a control unit (not shown). This control unit is composed of a CPU (Central Processing Unit) as a calculation means, a RAM (Random Access Memory) as a data storage means, a ROM (Read Only Memory), etc., and executes various calculation processes and control programs. be able to. Since the magnetic permeability of the Y developer shows a correlation with the Y toner density of the Y developer, the toner density sensor 10Y outputs a voltage having a value corresponding to the Y toner density. The control unit includes a RAM, in which a V Vref for Y which is a target value of the output voltage from the toner density sensor 10Y and a toner density sensor for C, M, and K mounted in another developing unit. The data of C Vtref, M Vtref, and K Vtref, which are target values of the output voltage, are stored. For the Y developing unit 7Y, the value of the output voltage from the toner density sensor 10Y is compared with the Y Vtref, and the Y toner supply device (not shown) is driven for a time corresponding to the comparison result. By this driving, an appropriate amount of Y toner is supplied to the Y developer whose Y toner density has been reduced by consumption of Y toner accompanying development in the first agent storage portion 9Y. For this reason, the Y toner concentration of the Y developer in the second agent container 14Y is maintained within a predetermined range. Similar toner supply control is performed for the developers in the process units (1C, M, K) for other colors.

  The Y toner image formed on the photoreceptor 3Y which is an image carrier and a latent image carrier is intermediately transferred to an intermediate transfer belt described later. The drum cleaning device 4Y of the photoreceptor unit 2Y removes the toner remaining on the surface of the photoreceptor 3Y after the intermediate transfer process. As a result, the surface of the photoreceptor 3Y that has been subjected to the cleaning process is neutralized by a neutralizing device (not shown). By this charge removal, the surface of the photoreceptor 3Y is initialized and prepared for the next image formation. In FIG. 1 described above, in the process units 1C, M, and K for other colors, C, M, and K toner images are formed on the photoreceptors 3C, M, and K in the same manner as an endless moving body. Intermediate transfer is performed on the intermediate transfer belt.

  An optical writing unit 20 is arranged below the process units 1Y, 1C, 1M, and 1K in the drawing. The optical writing unit 20 serving as a latent image forming unit irradiates the photoreceptors 3Y, C, M, and K of the process units 1Y, C, M, and K with the laser light L emitted based on the image information. Thereby, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 3Y, 3C, 3M, and 3K. The optical writing unit 20 deflects the laser light L emitted from the light source by the polygon mirror 21 that is rotationally driven by a motor, and passes through the photosensitive members 3Y, 3C, 3M, and 3K via a plurality of optical lenses and mirrors. Is irradiated. In place of such a configuration, an optical scanning device using an LDE array may be employed.

  A first paper feed cassette 31 and a second paper feed cassette 32 are disposed below the optical writing unit 20 so as to overlap in the vertical direction. In each of these paper feed cassettes, a plurality of recording papers P as recording members are accommodated in a stack of recording papers. The uppermost recording paper P includes a first paper feed roller 31a, The second paper feed rollers 32a are in contact with each other. When the first paper feed roller 31a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost recording paper P in the first paper feed cassette 31 is vertically oriented on the right side of the cassette in the figure. The paper is discharged toward the paper feed path 33 arranged so as to extend. Further, when the second paper feed roller 32 a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost recording paper P in the second paper feed cassette 32 is directed toward the paper feed path 33. Discharged. A plurality of transport roller pairs 34 are arranged in the paper feed path 33, and the recording paper P fed into the paper feed path 33 is sandwiched between the rollers of the transport roller pair 34 while being fed between the paper feed paths 33. 33 is conveyed from the lower side to the upper side in the figure.

  A registration roller pair 35 is disposed at the end of the paper feed path 33. The registration roller pair 35 temporarily stops the rotation of both rollers as soon as the recording paper P fed from the conveyance roller pair 34 is sandwiched between the rollers. Then, the recording paper P is sent out toward a later-described secondary transfer nip at an appropriate timing.

  Above each of the process units 1Y, 1C, 1M, and 1K, a transfer unit 40 that is endlessly moved counterclockwise in the drawing while an intermediate transfer belt 41 that is an endless moving body is stretched is disposed. The transfer unit 40 serving as transfer means includes an intermediate transfer belt 41, a belt cleaning unit 42, a first bracket 43, a second bracket 44, and the like. Further, four primary transfer rollers 45Y, 45C, 45M, 45K, a secondary transfer backup roller 46, a drive roller 47, an auxiliary roller 48, a tension roller 49, and the like are also provided. The intermediate transfer belt 41 is endlessly moved counterclockwise in the figure by the rotational driving of the driving roller 47 while being stretched by these eight rollers. The four primary transfer rollers 45Y, 45C, 45M, 45K each sandwich the intermediate transfer belt 41 moved endlessly in this manner from the photoreceptors 3Y, 3C, 3M, and 3K to form primary transfer nips. ing. Then, a transfer bias having a polarity opposite to that of the toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 41. The intermediate transfer belt 41 sequentially passes through the primary transfer nips for Y, C, M, and K along with its endless movement, and on the photoreceptor 3Y, C, M, and K on the front surface. The Y, C, M, and 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 secondary transfer backup roller 46 sandwiches the intermediate transfer belt 41 with the secondary transfer roller 50 disposed outside the loop of the intermediate transfer belt 41 to form a secondary transfer nip. The registration roller pair 35 described above feeds the recording paper P sandwiched between the rollers toward the secondary transfer nip at a timing at which the recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 41. The four-color toner image on the intermediate transfer belt 41 is affected by the secondary transfer electric field formed between the secondary transfer roller 50 to which the secondary transfer bias is applied and the secondary transfer backup roller 46, and the influence of the nip pressure. The secondary transfer is batch-transferred onto the recording paper P in the secondary transfer nip. Then, combined with the white color of the recording paper P, a full color toner image is obtained.

  Untransferred toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 41 after passing through the secondary transfer nip. This is cleaned by the belt cleaning unit 42. In the belt cleaning unit 42, the cleaning blade 42a is brought into contact with the front surface of the intermediate transfer belt 41, whereby the transfer residual toner on the belt is scraped off and removed.

  The first bracket 43 of the transfer unit 40 swings at a predetermined rotation angle about the rotation axis of the auxiliary roller 48 as the solenoid (not shown) is turned on / off. When forming a monochrome image as a single color image, the printer of the present image forming system rotates the first bracket 43 slightly in the counterclockwise direction in the figure by driving the solenoid described above. This rotation causes the Y, C, M primary transfer rollers 45Y, C, M to revolve counterclockwise in the drawing around the rotation axis of the auxiliary roller 48, thereby causing the intermediate transfer belt 41 to move in the Y, C direction. , M is separated from the photoconductors 3Y, 3C, 3M. Of the four process units 1Y, 1C, 1M, and 1K, only the K process unit 1K is driven to form a monochrome image. As a result, it is possible to avoid exhaustion of the process units due to wastefully driving the process units for Y, C, and M during monochrome image formation.

  A fixing unit 60 is disposed above the secondary transfer nip in the drawing. The fixing unit 60 includes a pressure heating roller 61 that includes a heat source such as a halogen lamp, and a fixing belt unit 62. The fixing belt unit 62 includes a fixing belt 64 as a fixing member, a heating roller 63 containing a heat source such as a halogen lamp, a tension roller 65, a driving roller 66, a temperature sensor (not shown), and the like. Then, the endless fixing belt 64 is endlessly moved in the counterclockwise direction in the drawing while being stretched by the heating roller 63, the tension roller 65, and the driving roller 66. In the process of endless movement, the fixing belt 64 is heated from the back side by the heating roller 63. A pressure heating roller 61 that is rotationally driven in the clockwise direction in the drawing is in contact with the surface of the fixing belt 64 that is heated in this manner from the front side. Thereby, a fixing nip where the pressure heating roller 61 and the fixing belt 64 abut is formed.

  Outside the loop of the fixing belt 64, a temperature sensor (not shown) is disposed so as to face the front surface of the fixing belt 64 with a predetermined gap, and the fixing belt 64 just before entering the fixing nip. Detect surface temperature. This detection result is sent to a fixing power supply circuit (not shown). The fixing power supply circuit performs on / off control of power supply to the heat generation source included in the heating roller 63 and the heat generation source included in the pressure heating roller 61 based on the detection result of the temperature sensor. As a result, the surface temperature of the fixing belt 64 is maintained at about 140 [°].

  In FIG. 1 described above, the recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 41 and then sent into the fixing unit 60. Then, in the process of being conveyed from the lower side to the upper side in the figure while being sandwiched between the fixing nips in the fixing unit 60, the full-color toner image is fixed by being heated or pressed by the fixing belt 64.

  The recording paper P subjected to the fixing process in this manner is discharged outside the apparatus after passing between the rollers of the paper discharge roller pair 67. A stack unit 68 is formed on the upper surface of the housing of the printer main body, and the recording paper P discharged to the outside by the discharge roller pair 67 is sequentially stacked on the stack unit 68.

  Above the transfer unit 40, four toner cartridges 100 Y, C, M, and K that store Y, C, M, and K toners are disposed. The Y, C, M, and K toners in the toner cartridges 100Y, 100C, M, and K are appropriately supplied to the developing units 7Y, C, M, and K of the process units 1Y, C, M, and K. These toner cartridges 100Y, 100C, 100M, and 100K are detachable from the printer main body independently of the process units 1Y, 1C, 1M, and 1K.

  In this printer having the above basic configuration, each color process unit 1Y, M, C, K or optical writing unit 20 is visible to each color photoconductor 3Y, C, M, K as an image carrier. It functions as a visible image forming means for forming Y, M, C, and K toner images.

  FIG. 5 is a perspective view showing a main body side drive transmission unit which is a drive transmission system fixed in the printer housing. FIG. 6 is a plan view showing the main body side drive transmission portion from above. A support plate is erected in the printer housing, and four process drive motors 120Y, 120C, 120M, 120K, and 120K are fixed thereto. Driving gears 121Y, C, M, and K are connected to the rotation shafts of process drive motors 120Y, 120C, 120M, and 120K serving as drive sources so as to rotate on the same axis as the rotation shaft.

  Below the rotation shafts of the process drive motors 120Y, 120C, 120M, 120K, development gears 122Y, 122C, 122M, 122K, which are slidably rotatable while engaging with a fixed shaft (not shown) projecting from the support plate. Is arranged. The developing gears 122Y, 122C, 122C, 122M, 122C, 122C, 122C, 122C, 122C, 122C, 122C, and 122-C have first gear portions 123Y, 123M, 123K that rotate on the same rotational axis. The second gear portions 124Y, C, M, K are located closer to the front end side of the rotation shafts of the process drive motors 120Y, C, M, K than the first gear portions 123Y, 123C, 123M, 123K. The developing gears 122Y, 122M, 122C, 122K, and 122K are engaged with the first gear portions 123Y, 123M, 123C, and 123K in mesh with the driving gears 121Y, 121C, 121M, and 121K of the process drive motors 120Y, 120C, 120M, 120K. By the rotation of the drive motors 120Y, 120C, 120M, and 120K, sliding rotation is performed on the fixed shaft.

  The process drive motors 120Y, 120C, 120M, 120K, which are drive sources, include a DC servo motor, which is a kind of DC brushless motor, a stepping motor, and the like. The reduction ratio between the driving gears 121Y, 121C, 121M, and 121K and the photoconductor gears 133Y, 133C, 133M, and 133K is, for example, 1:20. The reason why the number of speed reduction stages from the driving gear to the photoconductor gear is set to one is to reduce the number of parts and reduce the cost, and to reduce the cause of meshing error and transmission error due to eccentricity by using two gears. It is from the aim to do. By reducing the speed by one step, the photosensitive member gear has a larger diameter than the photosensitive member at a relatively large reduction ratio of 1:20. By using such a large-diameter photoconductor gear, it is possible to reduce the pitch error on the photoconductor surface corresponding to one gear meshing and to reduce the influence of print density unevenness (banding) in the sub-scanning direction. There is also an aim. The reduction ratio is determined based on the speed region where high efficiency and high rotation accuracy can be obtained from the relationship between the target speed of the photoreceptor and the motor characteristics.

  On the left side of the developing gears 122Y, 122C, 122M, and 122K, first relay gears 125Y, 125C, 125M, and 125K that slide and rotate while engaging with a fixed shaft (not shown) are disposed. These mesh with the second gear portions 124Y, C, M, and K of the developing gears 122Y, 122C, 122K, and receive rotational driving force from the developing gears 122Y, 122C, 122M, and 122K, on the fixed shaft. Slide and rotate. The first relay gears 125Y, C, M, and K are engaged with the second gear portions 124Y, C, M, and K on the upstream side in the drive transmission direction, and the clutch input gears 126Y, C on the downstream side in the drive transmission direction. , M, K are engaged. These clutch input gears 126Y, C, M, and K are supported by the developing clutches 127Y, 127C, 127M, and 127K. The development clutches 127Y, 127C, 127M, 127K, and the like are connected to the clutch shaft with the rotational driving force of the clutch input gears 126Y, 126C, 126M, 126K, as the power supply is turned on / off by a control unit (not shown). The input gear 126Y, C, M, K is idled. Clutch output gears 128Y, 128C, 128M, and 128K are fixed to the front ends of the clutch shafts of the developing clutches 127Y, 127C, 127M, and 127K. When power is supplied to the developing clutches 127Y, 127C, 127C, 127M, 127K, the rotational driving force of the clutch input gears 126Y, 126C, 126M is connected to the clutch shaft, and the clutch output gears 128Y, 128C, 128M, 128K Rotate. On the other hand, when the power supply to the development clutches 127Y, 127C, 127M, 127K is cut off, the clutch input gears 126Y, 126C, 126M, 126K, 126Y, 126C, 126M, 126K, 126Y, 126C, 126M Rotates idly on the clutch shaft, the rotation of the clutch output gears 128Y, 128C, 128M, 128K stops.

  On the left side of the clutch output gears 128Y, C, M, and K, second relay gears 129Y, 129Y, C, M, and K that are slidably rotated while being engaged with a fixed shaft (not shown) are disposed. It rotates while meshing with the clutch output gear 128Y, C, M, K.

  FIG. 7 is a partial perspective view showing one end of the Y process unit 1Y. The developing sleeve 15Y in the casing of the developing unit 7Y has a shaft member penetrating the side surface of the casing and protruding outside. The sleeve upstream gear 131Y is fixed to the protruding shaft member portion. A fixed shaft 132Y projects from the side of the casing, and the third relay gear 130Y engages with the sleeve upstream gear 131Y while being slidably rotated.

  In a state where the Y process unit 1Y is set in the printer main body, the second relay gear 129Y previously shown in FIGS. 5 and 6 is engaged with the third relay gear 130Y in addition to the sleeve upstream gear 131Y. Then, the rotational driving force of the second relay gear 129Y is sequentially transmitted to the third relay gear 130Y and the sleeve upstream gear 131Y, and the developing sleeve 13Y is rotationally driven.

  Although only the process unit 1Y for Y has been described with reference to the drawings, the rotational driving force is similarly transmitted to the developing sleeve also in the process units for other colors.

  Further, in FIG. 7, only one end portion of the Y process unit 1Y is shown, but the shaft member on the other end side of the developing sleep 15Y penetrates the side surface on the other end side of the casing and protrudes to the outside. A sleeve downstream gear (not shown) is fixed to the protruding portion. Further, the first conveying screw 7Y and the second conveying screw 10Y previously shown in FIG. 2 also have their shaft members penetrating through the side surface on the other end side of the casing, and the protruding portion includes a first screw gear (not shown), The second screw gear is fixed. When the developing sleeve 15Y is rotated by drive transmission by the sleeve upstream gear 131Y, the sleeve downstream gear is rotated on the other end side. Then, the second conveying screw 11Y receiving the driving force by the second screw gear meshing with the sleeve downstream gear rotates, and the first conveying screw 8Y receiving the driving force by the first screw gear meshing with the second screw gear. Rotates. The process units for other colors have the same configuration.

  FIG. 8 is a perspective view showing the Y photoconductor gear 133Y and its peripheral configuration. In the figure, the driving gear 121Y fixed to the motor shaft of the process drive motor 120Y meshes with the first gear portion 123Y of the developing gear 122Y and the photosensitive gear 133Y as a driven gear. The photoconductor gear 133Y is rotatably supported by the main body side drive transmission unit. The diameter of the photoconductor gear 133Y is larger than the diameter of the photoconductor. When the process drive motor 120Y rotates, the rotational driving force is transmitted from the driving gear to the photosensitive member gear 121Y at a one-step reduction, and the photosensitive member is driven to rotate. The process units for other colors have the same configuration.

  The rotating shaft of the photoconductor of the process unit and the photoconductor gear supported on the printer main body side are coupled by a coupling.

  In the printer configured as described above, when the photoconductor gear 133Y is rotationally driven by the process driving motor 120Y, the Y photoconductor causes a speed fluctuation due to the eccentricity of the photoconductor gear 133Y. As described above, this speed fluctuation has a fluctuation characteristic that draws a sine curve for one cycle per rotation of the photosensitive member.

  In FIG. 1 described above, when speed fluctuations occur in the photoreceptors 3Y, 3C, 3M, and 3K, latent images formed on the photoreceptors 3Y, 3C, 3M, and 3K at the light irradiation position by the optical writing unit 20 are displayed. The time required to move to the primary transfer nip immediately after formation changes. This causes subtle misalignment of each color dot in the primary transfer nip.

Next, a characteristic configuration of the printer will be described.
FIG. 9 is a perspective view showing the Y photoconductor gear 133Y and its peripheral configuration from the process drive motor side. In the figure, a marking reference mark 134Y is projected from a predetermined position in the rotation direction of the gear portion of the photoconductor gear 133Y. Further, a position sensor 135Y serving as a reference mark detection unit is disposed on the side of the photoconductor gear 133Y. When the photoconductor gear 133Y assumes a predetermined rotational attitude, the reference mark 134Y is positioned at a portion facing the position sensor 135Y and is detected by the position sensor 135Y. Thereby, the timing at which the photosensitive gear 133Y reaches a predetermined rotation angle is detected by the position sensor 135Y every time it rotates one time.

  FIG. 10 is a schematic diagram of the printer when the photoreceptors 3Y, 3C, 3M, and 3K are viewed from the axial direction. The reference marks 134Y, C, M, and K provided on the photoconductor gears 133Y, 133C, M, and K that rotate on the same axis as the photoconductors 3Y, C, M, and K are the photoconductor gears 133Y, 133C, M, and K, respectively. Each time K rotates once, it is detected by position sensors 135Y, 135C, 135M, and 135K including photo sensors.

  The transfer unit 40 includes an optical sensor unit 136 composed of two reflection type photosensors (not shown) arranged at a predetermined interval in the width direction of the intermediate transfer belt 41 via a stretched surface of the intermediate transfer belt 41 and a predetermined gap. It arrange | positions so that it may oppose.

  The rotation speed of each process drive motor 120Y, C, M, K is controlled by a control unit 140 as drive control means. The control unit 140 performs process control of the entire printer, and includes a CPU, a ROM, a RAM, and the like. The control unit 140 receives detection signals output from the position sensors 135Y, 135C, M, and K provided to detect the rotational positions of the photoreceptors 3Y, 3C, 3M, and 3K. Based on this detection signal, the control unit 140 starts control of each process drive motor 120Y, C, M, K, and starts speed control of each photoconductor 3Y, C, M, K.

  Further, the control unit 140 as a speed fluctuation detecting unit detects a speed fluctuation pattern per one rotation caused by the eccentricity of the photoconductor gears 133Y, 133C, M, and K for each of the photoconductors 3Y, 3C, 3M, and 3K. Speed detection control for this is performed at a predetermined timing. Examples of the predetermined timing include when an operation for changing a speed fluctuation pattern such as when a process unit is replaced, or when a print command is issued in a state where the high-quality print mode is selected.

  In the speed detection control, the formation of a latent image of the speed variation detection image of each color is started based on the timing at which the reference mark 134 of each color photoconductor gear 133Y, C, M, K is detected by the position sensor 135. Then, the image for speed variation detection is transferred onto each of the photoreceptors 3Y, 3C, 3M, and 3K without being superimposed on the intermediate transfer belt 41. As shown in FIG. 11, the speed fluctuation detection image is an example of a speed fluctuation detection image for K. A plurality of K toner images tk01, tk02, tk03, tk04, tk05, tk06... The image is transferred onto the belt so as to be arranged at a predetermined pitch along the moving direction (sub-scanning direction). However, although theoretically arranged at a predetermined pitch, the actual arrangement pitch of these K toner images has an error corresponding to the speed fluctuation due to the speed fluctuation of the K photoconductor (3K). come.

  In FIG. 11 described above, each toner image in the speed variation detection image formed on the intermediate transfer belt 41 is conveyed to a position facing the optical sensor unit 136 along with the endless movement of the belt. Then, the optical sensor unit 136 detects it when it passes directly under the optical sensor unit 136 as the belt moves. Thereby, the detection time pitch error of each toner image in the speed fluctuation detection image of each color is detected. This detection time pitch error corresponds to the speed fluctuation caused by the eccentricity of the photoconductor gear of each color.

  The control unit 140 of the printer determines one of the photoconductor gears 133Y, 133C, M, and K based on the detection time pitch error and one rotation period of the photoconductor gears 133Y, 133C, 133M, and 133K for each color. Analyze the speed fluctuation pattern in rotation. As one of the analysis methods, there is a method in which the average value of all data is set to zero and the amplitude and phase of the fluctuation component are analyzed from the zero cross of the fluctuation value or the peak value. However, since the detection data is greatly affected by noise, the error becomes large and is not practical. Therefore, this printer employs a method of analyzing the speed fluctuation pattern by orthogonal detection processing. By performing the orthogonal detection process, it is possible to analyze the speed fluctuation pattern with a small amount of fluctuation data, which is difficult to calculate by the zero cross of fluctuation and the peak detection.

  In this printer, the speed variation pattern of the photoconductor gear and the speed variation pattern of the photoconductor have a slight difference in amplitude, but the waveform phases are completely synchronized. Therefore, detecting the speed fluctuation pattern of the photoconductor gears 133Y, 133C, 133M, and K is the same as detecting the speed fluctuation pattern of the photoconductor.

  Further, in this printer, for the purpose of shortening the execution time of the speed detection control, as shown in FIG. 12, the speed change detection image PVk for K and the speed change detection image PVm for M are obtained. The intermediate transfer belt 41 is formed side by side in the belt width direction. Then, the speed change detection image PVk for K formed at one end in the belt width direction is detected by the first optical sensor 137 of the optical sensor unit 136, and for M formed at the other end in the belt width direction. Are detected by the second optical sensor 138 of the optical sensor unit 136. Thus, the detection time pitch error of each K toner image in the K speed fluctuation detection image PVk and the detection time pitch error of each M toner image in the M speed fluctuation detection image PVm are detected simultaneously, The execution time of the fluctuation pattern detection control can be shortened. Similarly, for Y and C, the respective detection time pitch errors are simultaneously detected.

When the control unit 140 of the printer detects a speed fluctuation pattern per rotation of each photoconductor by speed detection control, such a change that draws a sine curve for one cycle per rotation of the photoconductor as shown in FIG. Characteristics are obtained.
The control unit 140 detects the reference marks 134 of the photoconductor gears 133Y, 133C, 133M, and 133K for each color at the timing detected by the position sensor 135 so that the driving speed pattern has an opposite phase relationship with the fluctuation characteristics. By varying the clock applied to the process drive motors 120Y, 120C, 120M, 120M, 120K, the fluctuations in the speed of the photosensitive member due to the eccentricity are driven by the process drive motors 133Y, 133C, 133M, K as shown in FIG. By canceling out the change in speed, the speed change of the photosensitive member can be almost eliminated.

  The control unit 140 starts the waveform of the fluctuation characteristics (at the time when a latent image corresponding to the tip of the speed fluctuation detection image starts to be formed), that is, the reference marks of the photoconductor gears 133Y, 133C, 133M, and 133K are positioned. Drive control of the process drive motor 120 for canceling the fluctuation characteristics is performed at the timing detected by the sensor. For this reason, after the driving of the process drive motor 120 is started by the print start command, the photosensitive member speed fluctuation is detected at the timing when the position sensor 135 detects the reference mark 134 with the rotational speed of the process drive motor 120 reaching the target speed. The control to cancel is started. When a reference mark as shown in FIG. 9 is used, in addition to the timing at which the gear reference mark 134 is detected by the position sensor 135, the photosensitive member speed fluctuation is also detected at a timing at which the reference mark 134 is not detected by the position sensor 135. Although the control to cancel can be started, in this case, the control to cancel the fluctuation of the photosensitive member speed cannot be started until the photosensitive member 3 is rotated halfway at the maximum. As a result, the latent image start timing is delayed and the first print time becomes long.

  In conventional printers, image formation is performed by always performing drive control, so the first print time is delayed, and even if the image quality is lowered, it is not possible to meet the needs of users who want to shorten the first printer. Further, conventionally, even when the amplitude of the speed fluctuation of the photosensitive member is equal to or less than a predetermined value and the drive control is not performed and a high-quality image with suppressed color misregistration is obtained, the drive control is always performed. As a result, the first print time is delayed.

  Therefore, in the printer of this embodiment, process driving for canceling the fluctuation characteristics at the timing when the reference marks of the photoreceptor gears 133Y, 133C, M, and K are detected by the position sensor based on the detected speed fluctuation pattern and the like. Whether or not to control the drive of the motor 120 is selected by the control unit 140 as selection means. Below, it demonstrates concretely based on Examples 1-3.

[Example 1]
First, Example 1 will be described.
FIG. 15 is a control flow chart during image formation in the first embodiment.
FIG. 16 is a sequence diagram during image formation in the first embodiment.
As shown in FIG. 15, when receiving the image information sent from a personal computer or the like, the control unit 140 checks whether the amplitude of the speed fluctuation per one rotation of the photoconductor detected by the speed detection control is equal to or less than a predetermined value ( S1). As an example, the control unit 140 reads the speed fluctuation amplitude stored in a memory such as a RAM and checks whether the speed fluctuation amplitude is equal to or less than a predetermined value. When the amplitude of the speed fluctuation is equal to or smaller than the predetermined value (YES in S1), the color misregistration is sufficiently suppressed without performing the drive control, and thus image formation is performed without performing the drive control (S2, S8). . In the present embodiment, if the color misregistration is 10 [μm] or less, the color misregistration can be suppressed to a level that is not easily noticeable to the human eye, so the predetermined value of the amplitude is set to 5 [μm] or less. Thereby, the color shift does not exceed 10 [μm].
As described above, when the amplitude value of the speed fluctuation is equal to or smaller than the predetermined value, the image formation is performed without performing the drive control, so that the image quality can be maintained and the first print time can be shortened.

  On the other hand, when the amplitude of the speed fluctuation is equal to or larger than the predetermined value (NO in S1), the photosensitive member is started to be driven (S3). Then, as shown in FIG. 16, when the time t1 from the start of driving of the photosensitive member until the speed of the photosensitive member reaches a steady state has elapsed, the time measuring function of the time measuring circuit as the time measuring means provided in the control unit 140 is used. Then, timing is started (S4). When the position sensor 135 detects the reference mark (S5) before the time t5 has elapsed (time t4 in FIG. 16), the control unit 140 performs drive control to cancel the photoreceptor speed fluctuation (S6). Then, image formation is performed (S8). Thereby, a high-quality image can be formed without impairing the first print time.

  On the other hand, if the position sensor 135 does not detect the reference mark even after time t5 has elapsed (NO in S5, YES in S7), image formation is performed without performing drive control for canceling the photoreceptor speed fluctuation (S8). ). In the present embodiment, the time t5 is set to a time when the polygon motor of the writing unit 20 rotates at a predetermined rotational speed and the fixing temperature is raised to the predetermined temperature and preparation for image formation is completed. In this way, the first print time is not delayed by setting the time t5 to the time when preparation for image formation is completed. In addition, the time t5 becomes shorter with respect to the photoconductor disposed upstream in the moving direction of the intermediate transfer belt.

  Alternatively, the time t5 may be set to a time when the photoconductor rotates half a circle. By setting in this way, image formation can be performed even if the position sensor 135 is in a state where the reference mark cannot be detected due to a failure or the like.

[Example 2]
Next, Example 2 will be described.
FIG. 17 is a control flow during image formation in the second embodiment.
As shown in FIG. 17, in the second embodiment, first, when the control unit 140 receives image information sent from a personal computer or the like, based on the image information, whether the image to be formed is a color image or a monochrome image. Is checked (S11). In the case of a monochrome image (NO in S11), image formation is performed without executing drive control (S12, S18). Thereby, the first print at the time of a monochrome image can be shortened. In this embodiment, the drive control is not executed for a monochrome image. Conversely, for a monochrome image, the drive control is executed and the image forming operation is started. You may make it do. In this case, a good monochrome image without density unevenness can be obtained.

  On the other hand, when the image to be formed is a color image (YES in S11), the control unit 140 selects whether or not to execute drive control according to the amplitude value of the photoreceptor speed fluctuation (S13) as in the first embodiment. ). When the amplitude value of the photosensitive member is equal to or smaller than the predetermined value (YES in S13), image formation is performed without executing drive control (S12, S18). On the other hand, if the amplitude is equal to or larger than the predetermined value (NO in S13), if the reference mark is detected before the image formation preparation is completed (YES in S15), drive control is started (S16) and the image forming operation is performed. (S18). On the other hand, when the image formation preparation is completed before the reference mark is detected, the image forming operation is performed without executing the drive control (S15, S17, S18).

[Example 3]
Next, Example 3 will be described.
FIG. 18 is a control flow during image formation in the third embodiment.
In the third embodiment, a program that displays a screen on which the user can select the image quality priority mode and the speed priority mode on the personal computer is displayed on the application software installed in the personal computer as an input means for inputting information by the user. have. When the user prints an image, the user selects the image quality priority mode or the speed priority mode by operating the personal computer so that the selected mode information is transmitted to the control unit 140 together with the image information. It has become. Alternatively, the image quality priority mode or the speed priority mode can be selected by a user's key input operation on an operation display unit (not shown) configured by a liquid crystal display provided in the printer, various key buttons, and the like. ing.

  In the third embodiment, first, when the control unit 140 receives image information sent from a personal computer or the like, the control unit 140 checks whether the setting mode is an image quality priority mode or a speed priority mode (S21). In the speed priority mode (NO in S21), the drive control of the process drive motor 120 for canceling the fluctuation characteristics is performed at the timing when the reference marks of the photoconductor gears 133Y, 133C, 133K are detected by the position sensor. Instead, image formation is performed (S24). Thereby, the first print time can be shortened. On the other hand, in the case of the image quality priority mode (YES in S21), the driving of the process drive motor 120 for canceling the fluctuation characteristics at the timing when the reference marks of the photoconductor gears 133Y, 133C, 133K are detected by the position sensor. Control is performed to form an image (S22 to S24). Thereby, it is possible to obtain a high-quality image in which color misregistration is suppressed.

  In the third embodiment, since the user can set the speed priority mode and the image priority mode, it is possible to meet the needs of users who want to prioritize image quality and users who want to speed up the first print time.

  As shown in the first to third embodiments, before the image forming operation, the fluctuation characteristics are canceled at the timing when the control unit 140 detects the reference marks of the photoreceptor gears 133Y, 133C, 133M, and 133K by the position sensor. The first print time can be shortened by selecting whether or not to perform the drive control of the process drive motor 120.

  Further, in the continuous image formation, at least the photosensitive member during the period from when the first image is transferred to the intermediate transfer belt 41 until the latent image on the second sheet is written on the photosensitive member (so-called paper interval), Rotate more than half a circle. Therefore, if drive control is not performed when the first image is formed, the image quality of the second and subsequent sheets can be improved by detecting the reference mark between the sheets and starting the drive control. it can.

FIG. 19 is a control flow diagram of the image forming operation when the second and subsequent images are formed.
As shown in FIG. 19, when the control of Examples 1 to 3 is performed and the image on one photoconductor is transferred to the intermediate transfer belt 41, it is checked whether or not there is a second image. If there is a second image (YES in S32), it is checked whether or not drive control is performed. If drive control is not performed (NO in S33), a reference mark is detected. Then, drive control is executed (S34, S35). Then, the second and subsequent images are formed with the drive control being executed (S36).

  As described above, since the second and subsequent images can be formed with the drive control being performed, high-quality images can be output for the second and subsequent images. .

  Further, as shown in FIG. 20, the present invention is also applied to a color image forming apparatus using a drum-shaped intermediate transfer body 141 instead of the intermediate transfer belt 41 in the electrophotographic color image forming apparatus of the intermediate transfer tandem method. be able to. Further, as shown in FIG. 21, the present invention can also be applied to a direct transfer tandem type color image forming apparatus.

As described above, according to the image forming apparatus of the present embodiment, the image forming apparatus includes the photoconductor as the image carrier that carries the toner image that is a visible image, the process unit, and the optical writing unit, and forms a visible image on the photoconductor. And a visible image forming means. Also, a process drive motor that is a drive source for rotating the photosensitive member, a reference mark that is fixed to the photosensitive member and moves on the circular orbit along with the rotation, and a reference mark detection unit that detects the reference mark on a part of the circular orbit It has a position sensor. Further, the control unit which is a speed fluctuation detecting means is configured to detect a speed fluctuation pattern which is a fluctuation in the surface movement speed of the photosensitive member based on the timing at which the position sensor detects the reference mark. Further, the control unit as drive control means is configured to control the process drive motor so that the photosensitive member rotates at a target speed that cancels the speed fluctuation pattern detected based on the timing at which the position sensor detects the reference mark. Yes. The control unit, which is a selection unit, selects whether to control the process drive motor so that the photosensitive member rotates at a target speed that cancels the speed fluctuation pattern detected based on the timing at which the position sensor detects the reference mark. It is configured to
With this configuration, if the control unit selects not to control the process drive motor, an image forming operation can be performed when the surface movement speed reaches a steady state. Can be shortened. Therefore, the first print time is shorter than the apparatus that controls the process drive motor so that the photosensitive member rotates at a target speed that always cancels the speed fluctuation pattern detected based on the timing at which the position sensor detects the reference mark. It becomes possible to shorten.
If the control unit selects to control the process drive motor, a high-quality image without color misregistration can be output.
Therefore, in this embodiment, the first print time can be shortened and a high-quality image can be obtained, and it is possible to meet various needs of the user.

  Further, the control unit is configured to select whether or not to control the process drive motor based on the detected speed fluctuation pattern. Image quality such as color misregistration varies depending on the speed variation pattern. By selecting whether to control the process drive motor based on this speed pattern, the image quality is maintained and the first print time is shortened. It becomes possible to do.

  In particular, when the amplitude of the speed variation pattern falls below a predetermined value, the control unit is configured to perform drive control, so that the image quality can be maintained and the first print time can be shortened.

  Further, as shown in the first embodiment, a clock circuit serving as a clocking means for clocking is provided in the control unit, and the elapsed time from the start of driving of the photosensitive member reaches a predetermined time or exceeds a predetermined time. In this case, the control unit is configured to perform drive control and make a selection. Thereby, even if the position sensor is out of order, image formation can be performed.

  In particular, the first print time can be shortened by setting the predetermined time as a time from when the driving of the photosensitive member is started until a visible image can be formed on the photosensitive member.

  Further, as shown in the second embodiment, whether to control the process drive motor is selected based on whether the toner image transferred to the recording paper as the recording member is a color image or a monochrome image as a monochrome image. Constitute. Thereby, it is possible to select whether to shorten the first printer time or give priority to the image quality independently for each of the color image and the monochrome image.

  In particular, when the control unit is configured to select to perform drive control when the image is a monochrome image, the monochrome image can output a good image without density unevenness.

  On the other hand, if the control unit is configured to select not to perform drive control for a monochrome image, the first print time at the time of monochrome image formation can be shortened.

  Further, as shown in the third embodiment, control is performed so as to select whether or not to control the process drive motor based on information input to a personal computer or an operation display unit that is an input means for inputting information by the user. Parts. This makes it possible to select whether to shorten the first print time or to output a high-quality image according to the user's preference.

  Further, in the continuous image forming process in which images are continuously formed on a plurality of recording sheets, the second and subsequent sheets are controlled so as to form a toner image on a photoconductor in a state where drive control is performed. From the eyes on, high-quality images without color misregistration can be output.

  In particular, when drive control has not been executed when the first image is formed, the first toner image formed on the photoconductor is transferred to an intermediate transfer belt or recording paper as an intermediate transfer member, and then a visible image is displayed. Control is performed so that drive control is started before the formation of the next visible image by the forming unit is started. As a result, the second and subsequent images can be made high-quality images without color misregistration without affecting the first image.

  Further, the control unit can suppress the speed fluctuation in one rotation cycle of the photoconductor by detecting the speed fluctuation in one rotation cycle of the photoconductor.

  Further, since the one-stage reduction mechanism using the photoconductor gear as the drive transmission member having the same rotation center as that of the photoconductor, the number of parts can be reduced and the cost can be reduced. Further, by using two gears, the cause of meshing errors and transmission errors due to eccentricity can be reduced, and the speed fluctuation cycle of the photoconductor can be almost limited to one rotation cycle of the photoconductor.

  In addition, since a plurality of process drive motors are provided and the respective photoconductors are individually driven, speed fluctuations of the respective photoconductors are cancelled, and an image in which the toner image does not expand or contract is formed on all the photoconductors. As a result, when the drive unit is selected to perform drive control, a good image without color misregistration can be obtained.

  In addition, the process unit can be easily replaced by making the process unit detachable from the apparatus main body.

1 is a schematic configuration diagram illustrating a printer according to a first embodiment. FIG. 3 is an enlarged configuration diagram illustrating a process unit for Y of the printer. The perspective view which shows the process unit. The perspective view which shows the image development unit of the process unit. The perspective view which shows the main body side drive transmission part which is a drive transmission system fixed in the housing of the printer. The top view which shows the same main body side drive transmission part from upper direction. The fragmentary perspective view which shows the one end part of the process unit for Y. FIG. 2 is a perspective view showing a Y photoconductor gear and its peripheral configuration in the printer. FIG. 3 is a perspective view showing the photoconductor gear and its peripheral configuration from the process drive motor side. FIG. 2 is a schematic diagram of a printer when each photoconductor is viewed from the axial direction. FIG. 3 is a schematic plan view showing a speed variation detection image for K formed by the printer. The perspective view which shows a transfer unit and an optical sensor unit. The figure which shows the speed fluctuation pattern of the photoconductor of K color. The figure which shows the speed fluctuation pattern of the photoreceptor of K color after drive control. FIG. 4 is a control flow diagram during image formation in Embodiment 1. 2 is a sequence diagram during image formation in Embodiment 1. FIG. FIG. 6 is a control flow diagram during image formation in Embodiment 2. FIG. 10 is a control flow diagram during image formation in Embodiment 3. FIG. 6 is a control flow diagram of an image forming operation when forming an image for the second and subsequent sheets. 1 is a diagram illustrating an intermediate transfer type tandem color image forming apparatus using an intermediate transfer drum. FIG. The figure which shows the tandem type color image forming apparatus of a direct transfer system.

Explanation of symbols

1Y, C, M, K: Process unit (part of visible image forming means)
3Y, C, M, K: photoconductor (image carrier)
40: Transfer unit (transfer means)
41: Intermediate transfer belt (endless moving body)
20: Optical writing unit (part of visible image forming means)
120Y, C, M, K: Process drive motor (drive source)
133Y, C, M, K: photoconductor gear (driven gear)
133aY: Gear part 133bY: Engagement part 135Y, C, M, K: Position sensor (rotation angle detection means)
136: Optical sensor unit (image detection means)
P: Recording paper (recording medium)
PVk, PVm: Image for speed fluctuation detection

Claims (15)

An image carrier for carrying a visible image;
A visible image forming means for forming a visible image on the image carrier and a drive source for rotating the image carrier;
A reference mark fixed to the image carrier and moving on a circular orbit along with the rotation of the image carrier;
A reference mark detection means for detecting the reference mark in a part of the orbit,
Speed fluctuation detecting means for detecting a surface movement speed fluctuation of the front image carrier on the basis of the timing at which the reference mark detecting means detects the reference mark;
Based on the timing at which the reference mark detection unit detects the reference mark, the surface movement speed variation of the image carrier detected by the speed variation detection unit is canceled, and the drive is performed so that the image carrier rotates at a target speed. In an image forming apparatus comprising a drive control means for controlling a source,
An image forming apparatus comprising: a selection unit that selects whether or not the drive source is controlled by the drive control unit. The image forming apparatus according to claim 1.
An image forming apparatus comprising: a selection unit configured to select whether to control the drive source by the drive control unit based on a detection result of the speed variation detection unit. The image forming apparatus according to claim 2.
An image forming apparatus comprising: a selection unit configured to select that the drive control unit does not control the drive source when the amplitude of the surface movement speed fluctuation is less than a predetermined value. The image forming apparatus according to claim 1,
Provided with time measuring means for measuring time, and when the elapsed time from the start of driving of the image carrier reaches a predetermined time or exceeds a predetermined time, the drive control means controls the drive source. An image forming apparatus comprising a selection unit configured to select no. The image forming apparatus according to claim 4.
2. The image forming apparatus according to claim 1, wherein the predetermined time is a time from when the driving of the image carrier starts until a visible image can be formed on the image carrier. The image forming apparatus according to claim 4.
A plurality of the image carrier,
The visible image forming means is configured to form a visible image on each of the image carriers, and the visible images carried on the image carriers are superposed and transferred to the intermediate transfer member, and then onto the recording member. A transfer means for transferring or transferring a visible image carried on each of the image carriers by superimposing them on a recording member;
The selection unit is configured to select whether to control the drive source by the drive control unit based on whether the visible image transferred to the recording member is a color image or a single color image. Image forming apparatus. The image forming apparatus according to claim 6.
An image forming apparatus comprising: a selection unit configured to control the drive source by the drive control unit when the visible image transferred to the recording member is the monochrome image. The image forming apparatus according to claim 7.
An image forming apparatus comprising: a selection unit configured not to control the drive source by the drive control unit when the visible image transferred to the recording member is the monochrome image. The image forming apparatus according to claim 1,
An image forming apparatus comprising: a selection unit configured to select whether to control the drive source by the drive control unit based on information input to an input unit to which information is input by a user . The image forming apparatus according to claim 1,
In the second and subsequent sheets in the continuous image forming process in which images are continuously formed on a plurality of recording members, a visible image is formed on the image carrier while the drive source is controlled by the drive control means. An image forming apparatus. The image forming apparatus according to claim 10.
When the drive control is not executed when the first image is formed, the first visible image formed on the image carrier is transferred to the intermediate transfer member or the recording member, and then the visible image forming unit The control of the drive source by the drive control means is started before the formation of the next visible image by is started. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the speed fluctuation detecting unit detects a speed fluctuation of one rotation period of the image carrier. The image forming apparatus according to any one of claims 1 to 12,
An image forming apparatus, wherein the image carrier is driven by a one-stage reduction mechanism using a drive transmission member having the same rotation center as that of the image carrier. The image forming apparatus according to claim 1.
A plurality of the image carriers are provided, the visible image forming means is configured to form a visible image on each of the image carriers, and a plurality of drive sources are provided to drive each of the image carriers individually. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 14,
An image forming apparatus comprising a process cartridge in which the image carrier and at least one of a charging device, a developing device, and a cleaning device are integrally detachable from the apparatus main body.

Images