JP2011191629A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an image from being displaced due to an influence by paper conveying means located in front of and behind a transfer section. <P>SOLUTION: A sensor 6 detects a paper speed difference between a first condition in which paper is conveyed by being affected by a transfer means 4 and a resist means 3 and/or fixing means 5 and a second condition in which the paper is conveyed without being affected by at least the resist means 3 or fixing means 5 affecting paper in the first condition. The speed of the resist means 3 or fixing means 5 is controlled so as to reduce the paper speed difference. Accordingly, the paper speed difference between the first and second conditions is eliminated, thereby preventing displacement of an image. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic system.

  As a typical color image forming apparatus, a tandem type apparatus in which a plurality of image carriers are arranged side by side facing a belt transfer unit (transfer conveyance belt) is known. In the case of the direct transfer method, the sheet is fed toward the transfer conveyance belt by the timing with the toner image on the image carrier of the image forming unit by the registration means, and the sheet is conveyed while being held on the transfer conveyance belt. Then, each color image forming unit passes through a transfer position with the image carrier, and each color toner image is sequentially transferred onto the paper from each image carrier.

  The sheet on which the toner image has been transferred passes through the fixing device, whereby the unfixed toner image is fixed on the sheet. At present, a thermal fixing device is widely used as a fixing device, and a sheet is conveyed while being sandwiched between a fixing member and a pressure member, and an unfixed toner image is fixed on the sheet by heat and pressure.

  Here, the transfer conveyance belt has a function of conveying a sheet, and can be called a transfer section sheet conveyance unit. In general, a registration unit configured as a roller pair also has a function of conveying a sheet, and can be referred to as a pre-transfer sheet conveying unit located in front of the transfer unit (upstream in the sheet conveying direction). The fixing unit also has a function of conveying the sheet, and can be called a post-transfer sheet conveying unit located behind the transfer unit (downstream side in the sheet conveying direction).

  When there is a difference in paper conveyance speed between the transfer unit paper conveyance unit and the pre-transfer paper conveyance unit or the post-transfer paper conveyance unit, the paper is transferred to the transfer unit paper conveyance unit and the pre-transfer paper conveyance unit or after the transfer. A first state affected by the sheet conveying means, and a pre-transfer sheet conveying means or a post-transfer sheet conveying means (the pre-transfer sheet conveying means affecting the sheet in at least the first state or after the transfer). The paper conveyance speed may differ from the second state that is not affected by the paper conveyance means. In that case, a positional deviation occurs in the image transferred in each state. This may be caused by variations in the diameter of the fixing rotating body (fixing roller or the like) due to variations in component accuracy and differences in temperature conditions of the fixing means for each paper type.

  For example, Japanese Patent Application Laid-Open No. 2009-098267 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2007-199342 (Patent Document 2) describe the positional deviation of an image due to a change in the paper conveyance speed.

  In Patent Document 1, in a tandem image forming apparatus that forms a color image, an image forming unit that sequentially forms toner images of different colors is disposed along an endless transfer belt. The pattern formed by the first image forming unit is transferred to the transfer belt while the paper is not being conveyed, and the pattern formed by another second image forming unit is normally printed while the paper is being conveyed. Disclosed is a technology for transferring to a transfer belt at a predetermined transfer timing, detecting relative positional deviation information of both patterns, and correcting the paper conveyance speed based on the positional deviation information during actual printing on paper. Has been. This is because when the sheet is not being conveyed, the alignment pattern on the transfer belt is detected and alignment correction is performed. The object is to prevent image misalignment due to differences. In the invention described in this document, during normal printing, the paper is subjected to the brake load of the transport roller positioned in front of the transfer belt, and the speed of the transfer belt that is adsorbing the paper is also affected at the same time. It is an object to reduce the speed of the transfer belt that is transporting the paper while receiving the load of the transfer belt, compared to the speed of the transfer belt that is not transporting the paper.

  Patent Document 2 includes a speed detection unit that detects a conveyance speed of a recording medium immediately after entering a fixing unit, and a speed change unit that changes a conveyance speed of a sheet passing through the fixing unit. A technique is described in which, based on the detected speed of the sheet immediately after entering the fixing means, the speed changing means changes the transport speed of the paper passing through the fixing means to match the target speed. The purpose of this is to prevent image misalignment due to fluctuations in the sheet conveyance speed in the fixing means depending on the type of sheet.

  However, in the one described in Patent Document 1, since the pattern is formed by separate image forming units, other than misalignment due to the speed difference of the transfer belt in a state where the sheet is not conveyed by the transfer belt. There is a possibility that the misalignment due to other factors is corrected together. Therefore, when the user uses the device, the misalignment due to another factor is not exactly the same as the correction, and when the user uses the device, the misalignment of the factor is amplified. there is a possibility. Another factor is a variation in the thickness of the belt within one circumference of the transfer belt. The speed of the transfer belt is determined by the radius of rotation when the belt is wound around the transfer drive roller. Therefore, if the belt thickness varies, the radius of rotation varies and the belt speed fluctuates. In this way, the difference in the belt speed when the pattern is formed by the first image forming unit and the belt speed when the pattern is formed by the second image forming unit caused by the variation in the thickness of the belt is corrected in the invention of Patent Document 1. If included, the belt speed at the time of pattern formation by the first image forming unit and the belt speed at the time of pattern formation by the second image forming unit according to the position of the belt at the time of correction are determined while the user is using the device. The position deviation due to the belt thickness variation may be on the opposite side of the correction, and the position deviation amount for the belt thickness variation out of the position deviation correction amount set at the time of correction may vary. There is a possibility that an amplified misalignment is generated in the misalignment caused by the thickness of the belt. In addition, when the correction is executed in a state where the positional deviation due to the speed difference of the transfer belt of the different toner images and the positional deviation due to the variation in the thickness of the transfer belt are shifted to the opposite side, both cancel each other, thereby causing the positional deviation. In this case as well, if the conditions when the pattern is detected and the user uses the device are different, the paper may be affected by the transport roller. An image misalignment occurs due to a difference in the speed of the transfer belt when it is not.

  Furthermore, due to variations in rotational speed between image carriers and periodic rotational fluctuations of the transfer drive roller, a pattern is formed when a pattern is formed by the first image forming unit and when a pattern is formed by the second image forming unit. Variation occurs in the timing of transferring the toner onto the belt. Therefore, the pattern width formed on the belt varies, and the positional deviation is affected in the same manner as the belt thickness variation.

  And in the thing of the said patent document 2, it is conveyed in unstable state, such as dispersion | variation in the length of a sheet | seat, and the conveyance state of a sheet | seat (when it is conveyed diagonally or a paper rear end part moves up and down). Therefore, there is a possibility that the detected paper passing timing and other paper passing timing vary and the image positional deviation is not improved.

  The present invention solves the above-described problem of image misregistration in a conventional image forming apparatus, and provides an image forming apparatus capable of obtaining a high-quality output image by preventing image misregistration. Is an issue.

  According to the present invention, there is provided an image forming apparatus for transferring an image formed on an image carrier onto a sheet by a transfer unit, wherein the transfer unit conveys the sheet by the transfer unit, and the transfer unit In an image forming apparatus comprising: a pre-transfer sheet transport unit that transports a sheet immediately upstream of a sheet transport direction of a section; and a post-transfer sheet transport unit that transports a sheet immediately downstream of the transfer section in a sheet transport direction. A first state in which the transfer unit is conveyed under the influence of the sheet conveyance unit, the pre-transfer sheet conveyance unit or the post-transfer sheet conveyance unit; and the sheet affects the sheet at least in the first state. A speed detecting means for detecting a difference in paper speed in the second state being conveyed without being influenced by the pre-transfer paper transport means or the post-transfer paper transport means, and detecting the paper speed detected by the speed detection means; Low difference As to the transfer portion paper transport unit, the pre-transfer paper transport unit, it is solved by controlling the speed of one of the said post-transfer sheet conveyance means.

Further, it is preferable that the paper speed difference is reduced by controlling the pre-transfer paper transport unit or the post-transfer paper transport unit.
Further, the transfer unit paper transporting means is configured to be able to transfer an image from the image carrier, and a first pattern and a second pattern are formed of images formed on the image carrier at at least two locations at the same interval. The first pattern transferred to the transfer unit paper transport unit in the second state, and the second pattern transferred to the transfer unit paper transport unit in the first state, It is preferable to detect the paper speed difference by detecting the speed by the speed detecting means.

  In addition, it is preferable that the second pattern is formed without being affected by the other of the pre-transfer paper transport unit or the post-transfer paper transport unit that affects paper transport in the first state. .

Further, it is preferable that a plurality of sets of the first pattern and the second pattern are created and detected by the speed detecting means, and the difference in speed detected in each set is averaged to obtain the difference in the sheet speed.
In addition, it is preferable that the first pattern and the second pattern are transferred to the same phase area of the transfer unit paper transport unit.

In addition, it is preferable that the first pattern and the second pattern are formed in a region that is an integral multiple of the circumference of the image carrier.
In addition, it is preferable that the first pattern and the second pattern are transferred to an area that is an integral multiple of the circumferential length of a driving roller that drives the transfer unit paper transporting unit.

  The timing at which the speed detection unit detects the first pattern and the second pattern is preferably in a state where the sheet is not affected by the pre-transfer sheet conveyance unit and the post-transfer sheet conveyance unit. It is.

In addition, it is preferable to perform control to reduce the difference in the paper speed detected by the speed detection means when the paper type setting is provided and the paper type setting is changed.
And an input unit that can input that the post-transfer sheet transporting unit has been replaced with a new one, and when the input unit inputs that the post-transfer sheet transporting unit has been replaced with a new unit, It is preferable to carry out control to reduce the difference in the paper speed detected by the detecting means.

  According to the image forming apparatus of the present invention, the position of the image is reduced by reducing the difference in the sheet speed between the first state that is affected by the sheet conveyance in the transfer unit and the second state that is not affected. A high quality output image can be obtained by preventing the shift.

  According to the configuration of the second aspect, the speed of the transfer section paper transporting means is not changed, so that the speed relationship between the image carrier and the transfer section is maintained, and the pre-transfer paper transporting means or the post-transfer so as to prevent image displacement. Even when the paper conveying means is controlled, there is no occurrence of image quality deterioration other than misalignment.

  With the configuration according to the third aspect, it is possible to detect a difference in sheet speed between the first state and the second state by using a low-cost sensor without complicating the configuration of the image forming apparatus.

  According to the configuration of the fourth aspect, at the time of pattern formation, the image forming apparatus is not affected by the conveying unit that is not the conveying unit affecting in the first state, and the effect of reducing the image misalignment is not reduced.

  According to the configuration of the fifth aspect, a plurality of sets of patterns are created, and the speed difference detected in each set is averaged and used for control (correction), thereby reducing the influence of variations in the sheet conveying means and high accuracy. Detection is possible.

According to the configuration of the sixth aspect, it is possible to eliminate the influence due to the traveling property of the transfer unit paper transporting unit and to prevent the reduction in the effect of reducing the image position deviation.
According to the configuration of the seventh aspect, even if the image carrier has a periodic rotational fluctuation, it is possible to eliminate the influence and prevent the reduction in the effect of reducing the image position deviation.

  According to the configuration of the eighth aspect, even if the driving roller for driving the transfer unit paper transporting unit has a periodic rotational fluctuation, it is possible to eliminate the influence and prevent a reduction in the effect of reducing the image misalignment.

According to the ninth aspect of the present invention, the pattern can be detected without being affected by the pre-transfer paper transport unit and the post-transfer paper transport unit, and the paper speed difference can be accurately detected.
According to the configuration of the tenth aspect, it is possible to prevent image misalignment that occurs when the paper type is changed.

  According to the configuration of the eleventh aspect, even when the post-transfer paper conveying means that affects the paper speed is replaced, it is possible to prevent the image from being displaced.

1 is a cross-sectional configuration diagram illustrating an outline of a color printer which is an example of an image forming apparatus according to the present invention. 6 is a graph showing the sheet speed when the fixing device is affected and when it is not. It is a graph which shows a mode that the speed difference of the 1st state and the 2nd state was eliminated by applying this invention. It is a schematic diagram for demonstrating the pattern used for the detection of a speed difference. It is a schematic diagram showing that the pattern formation position is affected when different color patterns are formed on different image carriers. FIG. 10 is a schematic diagram for explaining an increase in image position shift due to a thickness variation of the transfer conveyance belt.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional configuration diagram showing an outline of a color printer which is an example of an image forming apparatus according to the present invention. The color printer shown in this figure is a direct transfer type color printer that can form a full-color image by adopting a tandem method, and four sets of image forming units 1 (a, b, c, d) are provided at almost the center of the apparatus main body. ). Each image forming unit 1 is arranged in parallel to face the transfer means 4. Each image forming unit 1 has the same configuration except for the color of the toner to be handled, and includes a photosensitive drum 2 as an image carrier. Around the photosensitive drum 2, a charging unit, a developing device, a cleaning unit and the like (not shown) are arranged. Further, an optical writing device (not shown) is provided.

  The transfer unit 4 includes a conveyance belt 4a wound around a plurality of support rollers including a driving roller, a transfer roller 4b disposed so as to face each photosensitive drum 2 in a loop of the conveyance belt 4a, and the like. ing. The conveyor belt 4a is driven to run counterclockwise in the drawing by rotating the drive roller with a drive source (not shown). A transfer bias is applied to the transfer roller 4b from a power supply unit (not shown). The transfer means 4 having a paper transport function is a transfer section paper transport means in the present invention.

  A paper feed tray 8 on which the paper P is stacked is disposed at the lower part of the apparatus main body. On the right side of the paper feed tray 8 is a paper feed roller 9 that feeds the papers stacked on the paper feed tray, and feeds the papers one by one. A transport roller 10 is disposed obliquely above the paper feed roller 9 (downstream side in the paper transport direction). Further, a registration roller pair 3 is provided downstream of the conveying roller 10. The registration roller pair 3 having a paper transport function is a pre-transfer paper transport unit positioned in front of the transfer unit 4 (upstream in the paper transport direction).

  A fixing device 5 is provided on the side opposite to the registration roller pair 3 with the transfer unit 4 interposed therebetween. The fixing device 5 having a paper transport function is a post-transfer paper transport unit located behind the transfer unit 4 (downstream in the paper transport direction). The fixing device 5 of this example includes a fixing roller and a pressure roller. The paper is sandwiched and conveyed by both rollers, and an unfixed toner image transferred onto the paper is fixed to the paper by heat and pressure. A belt fixing device may be used.

An image forming operation in the color printer configured as described above will be briefly described.
The photosensitive drum 2 of the image forming unit 1 is driven to rotate clockwise in the figure, and the surface of the photosensitive drum 2 is uniformly charged to a predetermined polarity by the charging means. The charged photoreceptor surface is irradiated with scanning light from an optical writing device, whereby an electrostatic latent image is formed on the photoreceptor drum 2 surface. At this time, the image information exposed on each photosensitive drum 2 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. Each color toner is applied from the developing device to the electrostatic latent image formed in this way, and visualized as a toner image.

  On the other hand, the paper is fed from the paper feed tray 8 and sent to the transfer means 4 by the registration roller pair 3 in a timing with the toner image formed on the photosensitive drum 2. The transfer means 4 sucks and holds the paper on the belt surface and conveys the toner image of each color from the photosensitive drum 2 of each color image forming unit on the paper in order to form a full-color image on the paper. The A single color image can be formed using any one of the image forming units 1, and a two-color or three-color image can be formed using a plurality of image forming units. When the sheet on which the toner image has been transferred passes through the fixing device 5, the toner image is fused and fixed to the sheet by heat and pressure. The sheet on which the toner image has been fixed is conveyed by a conveying roller 11 and discharged by a discharge roller 12 to a discharge tray 13 formed on the upper surface of the apparatus main body and stacked.

  When there is a difference in sheet conveyance speed between the transfer section sheet conveyance unit (transfer unit 4) and the pre-transfer sheet conveyance unit (registration roller pair 3) or the post-transfer sheet conveyance unit (fixing device 5), the sheet is transferred. The first state in which the paper is transported under the influence of both the sheet paper transporting means and the pre-transfer paper transporting means or the post-transfer paper transporting means; The sheet speed is different from the second state in which the sheet is conveyed without being affected (at least without being affected by the pre-transfer sheet conveying unit or the post-transfer sheet conveying unit affecting the sheet in the first state). Sometimes.

  Therefore, in the present invention, the transfer unit paper transport unit and the pre-transfer paper transport unit are configured so as to detect the speed difference (paper speed difference) between the first state and the second state and to reduce the image positional deviation. Any one of the post-transfer sheet conveying means is controlled. In the configuration example of FIG. 1, the speed difference between the first state and the second state is detected by a sensor 6 (speed detection unit) provided below the transport unit 4. In the case of this example, the speed difference is detected by detecting the belt speed of the transfer means 4 with this sensor 6 (for example, using a reflection type optical sensor).

  Here, the characteristics of the present invention will be described by taking as an example a case where a sheet is affected by the fixing device 5 which is a sheet transfer means after transfer. Further, the reduction of the speed difference will be described in the case where it is performed by controlling the fixing device 5.

  FIG. 2 is a graph showing the sheet speed when the fixing device is affected or not. The vertical axis of the graph is the paper speed, the horizontal axis is the paper position, and the thick line indicates the paper speed at each paper position. As shown in this graph, the paper speed before entering the fixing device is V0, but the influence of the fixing device starts to appear from the time when the paper enters the fixing device, and the paper speed becomes V1 at a certain time.

  In the illustrated example, the sheet conveyance speed by the fixing device is larger than the sheet conveyance speed by the transfer unit. That is, when the sheet conveyance speed of the fixing device 5 in the first state is higher than the sheet conveyance speed of the transfer unit 4, the sheet P is pulled by the influence of the fixing device 5 after entering the fixing device 5, and the second state. In this state (here, before entering the fixing), the sheet is conveyed at a speed higher than the sheet speed. As a result, the position where the image is transferred to the paper P is shifted from the target image position.

  Therefore, in this example, the sensor 6 detects the speed difference of the transfer means 4 in the first state and the second state, and feedback-controls the speed of the fixing device 5 in the first state (in this case, the fixing device). 5), the speed difference between the first state and the second state is eliminated. Thereby, it is possible to prevent the influence of the fixing device 5 on the image positional deviation. The graph of FIG. 3 shows how the present invention is applied to eliminate the speed difference between the first state and the second state. In the graph of FIG. 3, it can be seen that the sheet speed is the same (V0) before and after the fixing device enters.

  In this embodiment, since the sheet P is electrostatically attracted to the transfer unit 4 (conveying belt 4a), the speed of the transfer unit 4 is also affected at the same time when the sheet P is affected by the fixing device 5. By utilizing this, the sensor 6 detects the speed difference of the transfer means 4 in the first state and the second state. The speed of the transfer means 4 is determined by transferring a predetermined pattern (described later) onto the transfer means 4 (on the belt) and detecting the pattern with the sensor 6.

  As a pattern used for detecting the speed difference, a set of patterns (pattern 7a, pattern 7b) as in the example shown in FIG. 4 is used. The pattern 7a is in the second state, the pattern 7b is in the first state, and at least one (same) photosensitive drum 2 selected from the photosensitive drums (2a to 2d) as the image carrier is used. The pattern is formed in two places at the same interval (in the example shown, a pattern composed of at least two line images having the same interval is formed). When the pattern is transferred to the transfer unit 4, the fixing is performed in the first state. Since the sheet P is pulled by the apparatus 5 and the speed of the sheet P and the transfer unit 4 is higher than that in the second state, the line interval of the pattern 7b transferred in the first state is transferred in the second state. It becomes wider than the line interval of the pattern 7a. The patterns 7a and 7b are detected by the sensor 6, and based on the timing (line image detection timing), the speed difference of the transfer means 4 in the first and second states is detected, and the fixing in the first state is performed. Feedback on the speed of the device 5. In this example, by reducing the speed of the fixing device 5 in the first state, it is possible to eliminate the speed difference between the second state and the first state, thereby preventing the positional deviation of the formed image.

  Note that the pattern 7a has a timing at which the sheet P has entered the fixing device 5 and has passed through the photosensitive drum (it is on the transfer means 4) before the sheet P reaches the transfer means 4. These are examples formed by the photosensitive drum 2, respectively.

  The pattern 7a is detected by the sensor 6 before the paper P enters the fixing device 5, and the pattern 7b is detected by the sensor 6 after the paper P has passed through the fixing device 5, whereby the patterns 7a and 7b are detected. The detection can be performed in the same state where the transfer unit 4 is not affected by the fixing device 5.

  Further, by forming the speed detection patterns 7a and 7b with one image carrier, the rotational speed between the image carriers generated when the patterns of toner images of different colors are formed on at least two image carriers. Deviation in pattern formation timing due to variations in the speed of the transfer means 4 caused by variations in the belt thickness of the transfer means 4 caused by variations and the distance between the image carriers, and the speed of the transfer means when the pattern is detected by the sensor 6 It is possible to reduce detection timing shifts due to fluctuations.

  FIG. 5 is a graph showing a difference in pattern formation timing due to variations in rotational speed between image carriers and speed fluctuations of the transfer means 4 when a pattern of toner images of different colors is formed on at least two image carriers. 6 shows that the detection timing shift due to the speed fluctuation of the transfer means 4 at the time of detection at 6 is combined with the speed of the transfer means 4 in the first state or the second state, and the pattern forming position is affected. It is a schematic diagram which shows.

  In FIG. 5, the sheet B is formed in a state where the sheet P enters the fixing unit 5, and the interval B between the black and cyan patterns formed before the sheet reaches the transfer unit 4 (the cyan pattern is indicated by a one-dot chain line). Since there is a difference in the interval C between the black pattern and the cyan pattern formed with the paper passing through the fixing unit, the speed difference is detected by the detection timing, but the fixing unit is more than the transfer unit 4 at the time of pattern formation. When the speed of 5 is fast and the pattern is only affected by this, the black pattern forming the interval C is shifted backward from the target position. However, after forming the black pattern shifted backward, when the cyan pattern is formed, for example, when the transfer unit rotates faster than the target speed due to variations in the belt thickness of the transfer unit 4, the cyan pattern The position is formed behind the target position (the distance D). As a result, the interval D between the black pattern and the cyan pattern becomes wider than the target interval C, and further, for example, when the interval D is the same as the interval B, it is detected that no positional deviation has occurred. . However, when the user actually uses the apparatus to output an image, the conditions are not always the same as those at the time of pattern formation. Therefore, misalignment occurs due to the influence of the fixing means that has not been corrected.

  Further, as in the example shown in FIG. 6, the speed of the transfer unit 4 at the time of black pattern formation and the speed of the transfer unit 4 at the time of cyan pattern formation according to the position of the belt at the time of correction Position deviation due to variations in belt thickness may be on the opposite side of the correction, and out of the misalignment correction amount set during correction, There is also a possibility that an amplified misalignment is generated in the misalignment caused by the thickness of the belt (becomes the interval F).

  On the other hand, when the sheet P is affected by the fixing unit 5 in the first state, the pattern 7b is not affected by the registration unit 3 and does not include a speed fluctuation corresponding to the load. By detecting the speed of the transfer means 4, it is possible to prevent a decrease in alignment accuracy.

  Also, when forming the transfer speed detection pattern, the speed variation of the transfer means 4 and the image due to the running performance of the belt (because the belt speed fluctuates within one circumference due to the belt thickness fluctuation within one belt circumference). Since the variation in the rotation of the carrier is included, the speed of only a part of the variation is detected with only two toner images, and the accuracy of the detected speed difference may be low. That is, when the difference in the sheet speed is obtained by only one set of patterns 7a and 7b, there is a possibility that the conveyance speed of the sheet conveying unit varies.

  Therefore, the sensor 6 detects the first pattern (7a) and the second pattern (7b), which form toner images at a plurality of positions so as to have at least two intervals, for each interval of the toner images. The detection accuracy can be improved by detecting the difference in speed obtained by averaging the speeds of the toner image intervals. That is, by creating a plurality of sets of patterns 7a and 7b and averaging the speed difference detected in each set and using it for control (correction), the influence of the above-described variation can be reduced and detection with high accuracy becomes possible. .

Furthermore, by forming (transferring) the pattern in the same phase region of the endless belt transfer means 4, it is possible to prevent the influence of the belt speed variation on the alignment accuracy.
Forming the pattern in the same phase region means forming the first pattern and the second pattern at the same position in the belt conveyance direction.
Further, the rotation variation of the image carrier or the transfer driving roller is formed by forming a pattern in an area that is an integral multiple of the circumference of the transfer driving roller that rotates by transmitting the drive to the image carrier 2 or the endless belt transfer means 4. This can prevent the influence on the alignment accuracy.
That is, by setting the interval between the first pattern and the second pattern to an integral multiple of the circumference of the image carrier 2 or the transfer drive roller, the outer diameter of the image carrier 2 or the transfer drive roller varies ( The effects of rotational fluctuations can be eliminated.

  Further, in the image forming apparatus to which the present invention is applied, correction processing is performed in advance for each paper type set in the specification of the apparatus in the manufacturing process, and a paper transport unit (registration unit) positioned before and after the transfer unit. If the speed of the fixing device, etc. is adjusted, correction processing will not be performed when the device is used in the market (correction processing will be performed when the fixing means is replaced), so it is possible to reduce the waiting time of the user. is there. However, in mass production, it is necessary to reduce the adjustment process as much as possible in order to shorten the manufacturing process time.If the paper transport means before and after the transfer means are not adjusted within the manufacturing process, the It is effective to execute the correction process every time the setting is changed.

  In the above description, the sheet conveying means that affects the sheet speed is the fixing device 5 positioned after the transfer means 4, but the sheet conveying means (registration means 3 in the embodiment) positioned before the transfer means 4 is used. Even when an influence is exerted, the speed difference (paper speed difference) between the first state and the second state may be detected and controlled (corrected) so as to reduce the positional deviation of the image in the same manner as described above. .

  In addition, when the fixing device 5 is replaced with a new one, the influence on the sheet speed is different from that of the fixing device before replacement due to variations in component accuracy, and there is a possibility that image misalignment occurs. . Therefore, when the fixing device 5 is replaced with a new one by inputting that the fixing device 5 has been replaced with a new one from an operation panel (not shown) or the like of the image forming apparatus, the first state described above. It is preferable to execute a control (correction) for detecting a speed difference (paper speed difference) between the second state and the second state, and reducing an image positional deviation.

  In the above description, the difference in the paper speed is reduced by the control of the fixing device 5 (post-transfer paper transport unit). However, the transfer unit paper transport unit and the pre-transfer paper transport unit (resisting unit are affected by the influence). In this case, control (correction) can be performed by any of the post-transfer sheet conveying means. However, when controlled (corrected) by the transfer section paper transport means, the speed relationship between the image carrier and the transfer section paper transport means fluctuates, so that the image misalignment is improved, but the image quality other than misalignment is affected. There is a possibility to give. Therefore, the correction is more preferably performed by the pre-transfer paper transport unit or the post-transfer paper transport unit.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. For example, the fixing device may be configured to use a fixing belt or a pressure belt. As the heating method, any method such as induction heating can be adopted. The extending form of the endless belt constituting the transfer means is also arbitrary. It is also possible to use a transfer charger instead of the transfer roller. An appropriate configuration can be adopted for detecting the sheet speed, and a sensor having an appropriate configuration and method can be used as a sensor. The pattern used for detection is not limited to two images, and may be three or more images. If there is another sheet conveying unit between the transfer unit and the fixing device, and the sheet conveying unit affects the sheet conveyance with the transfer unit, the sheet conveying unit is the post-transfer sheet conveying unit. .

  The configuration of the image forming unit of the image forming apparatus is also arbitrary, and the order of the colors of the color image forming units in the tandem system is arbitrary. Further, the present invention can be applied to a full-color machine using three color toners and a multi-color machine using two color toners. Of course, the image forming apparatus is not limited to a printer, and may be a copier, a facsimile machine, or a multifunction machine having a plurality of functions.

1 Image forming unit 2 Photosensitive drum (image carrier)
3 Registration roller (paper transfer means before transfer)
4 Transfer means (transfer section paper transport means)
5 Fixing device (paper transfer means after transfer)
6 Sensor (speed detection means)
8 Paper tray 13 Paper output tray

JP 2009-098267 A JP 2007-199342 A

Claims (11)

An image forming apparatus for transferring an image formed on an image carrier onto a sheet by a transfer unit, wherein the transfer unit conveys the sheet by the transfer unit, and immediately upstream of the transfer unit in the sheet conveying direction. In an image forming apparatus comprising: a pre-transfer paper transport unit that transports a paper; and a post-transfer paper transport unit that transports the paper immediately downstream of the transfer unit in the paper transport direction;
A first state in which the sheet is conveyed under the influence of the transfer unit sheet conveying unit, the pre-transfer sheet conveying unit or the post-transfer sheet conveying unit; and the sheet affects the sheet in at least the first state. A speed detecting means for detecting a difference in paper speed in the second state in which the paper is transported without being affected by the pre-transfer paper transport means or the post-transfer paper transport means,
The speed of any of the transfer section paper transporting means, the pre-transfer paper transporting means, and the post-transfer paper transporting means is controlled so as to reduce the difference in paper speed detected by the speed detecting means. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the reduction in the paper speed difference is performed by controlling the pre-transfer paper transport unit or the post-transfer paper transport unit. The transfer section paper conveying means is configured to be able to transfer an image from the image carrier,
Forming a first pattern and a second pattern composed of images formed at the same intervals in at least two locations on the image carrier,
The speed detection unit detects the first pattern transferred to the transfer unit paper conveyance unit in the second state and the second pattern transferred to the transfer unit paper conveyance unit in the first state. The image forming apparatus according to claim 1, wherein the sheet speed difference is detected.   In the first state, the second pattern is formed without being influenced by the other of the pre-transfer paper transport unit or the post-transfer paper transport unit that affects paper transport. The image forming apparatus according to claim 5.   The plurality of sets of the first pattern and the second pattern are generated and detected by the speed detection unit, and the difference in speed detected in each set is averaged to obtain the difference in the sheet speed. 5. The image forming apparatus according to 3 or 4.   6. The image forming apparatus according to claim 3, wherein the first pattern and the second pattern are transferred to the same phase area of the transfer unit paper transport unit. 6.   The image forming apparatus according to claim 3, wherein the first pattern and the second pattern are formed in an area that is an integral multiple of the circumference of the image carrier.   8. The method according to claim 3, wherein the first pattern and the second pattern are transferred to an area that is an integral multiple of a peripheral length of a driving roller that drives the transfer unit paper transport unit. The image forming apparatus described in the item.   The timing at which the first pattern and the second pattern are detected by the speed detection unit is a state in which the sheet is not affected by the pre-transfer sheet conveyance unit and the post-transfer sheet conveyance unit. The image forming apparatus according to any one of claims 3 to 8.   10. A control for reducing the difference in paper speed detected by the speed detecting means when the paper type setting is provided and the paper type setting is changed. The image forming apparatus according to any one of the above. The speed detecting means has an input means capable of inputting that the post-transfer paper transport means has been replaced with a new one, and that the input means inputs that the post-transfer paper transport means has been replaced with a new one. The image forming apparatus according to claim 1, wherein control for reducing the difference between the sheet speeds detected in step 1 is performed.

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