JP2016184054A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can suppress displacement of a sheet caused by characteristics unique to a fixing device, and suppress a reduction in image quality.SOLUTION: An image forming apparatus 1 comprises image forming parts 10Y, 10M, 10C, and 10K that form images and transfer the images to a sheet P; a fixing device 40 that fixes the images on the sheet P; and a control part 50. The control part 50 includes a function to acquire the sheet type of the sheet P (sheet type acquisition part), a function to acquire the ideal center of fixing according to the acquired sheet type (position acquisition part), and a function to perform position control to match the center of sheet conveyance with the ideal center of fixing (position control part).SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses are known as printers, copiers, and the like. In this image forming apparatus, when an image is formed on a sheet, a series of processes of transferring the image to the sheet and fixing the image on the sheet is executed.

  For example, Patent Document 1 discloses an image forming apparatus that forms an image on a sheet by a process of image transfer and image fixing. The image forming apparatus includes a conveyance direction correction device that corrects the bending in the conveyance direction of the sheet on which the image has been transferred so that the sheet is returned by the fixing device. According to this image forming apparatus, it is possible to prevent the occurrence of image distortion by returning the bending of the sheet with the fixing device.

  There is also known a method of making a device that periodically swings the fixing device and shifts the passage position of the sheet edge. For example, Patent Document 2 discloses a fixing member shift unit that moves a fixing member in a direction orthogonal to the sheet conveyance direction and a sheet fed to the toner image transfer unit in a direction orthogonal to the sheet conveyance direction. An image forming apparatus including a sheet shift unit that moves is disclosed. According to this image forming apparatus, it is possible to realize a reduction in scratches on the fixing member by effectively shifting the traveling position of the fixing member and the sheet, and to print a high-quality image on the sheet.

JP 2007-193087 A JP 2012-78679 A

  In general, in the image forming apparatus, various elements are designed so that the center position (sheet transport center) of the sheet transported along the transport path matches the center position (transport path center) in the transport path. This is also true for a fixing device that performs fixing processing. Therefore, the ideal sheet conveyance position (fixing ideal center) in the fixing device coincides with the sheet conveyance center.

  However, in an actual fixing device, the ideal fixing center may exist at a position shifted from the center of the conveyance path. In this case, in the process of passing through the fixing device, a paper shift occurs, that is, a phenomenon that the paper transport center moves toward the fixing ideal center. This is because the pressure distribution of the fixing nip is formed with reference to the ideal fixing center, so the pressure distribution is not evenly formed at the center position of the paper on the paper passing through the center of the conveyance path, This is because an unbalanced force acts.

  If a sheet shift occurs when the sheet remains in the transfer nip, the image on the sheet is bent. In addition, when a paper is bent between the fixing nip and the transfer nip to form a loop, the formation of the loop cannot be properly controlled, and the guide plate and the paper may be brought into contact with each other. There is. Since the image before fixing is carried on the paper, the contact may cause damage to the image.

  Further, since the deviation of the ideal fixing center is unique to the apparatus, it is difficult to adjust the deviation by uniform adjustment common to all image forming apparatuses.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image forming apparatus capable of suppressing a shift of a sheet due to a characteristic unique to a fixing device and suppressing a decrease in image quality. It is.

  In order to solve this problem, the present invention provides an image forming apparatus including an image forming unit that forms an image and transfers the image onto a sheet. The image forming apparatus includes a fixing device that fixes an image on a sheet, a paper type acquisition unit that acquires a paper type related to the paper, and an ideal image unique to the fixing device based on the paper type acquired by the paper type acquisition unit. A position acquisition unit that acquires an ideal fixing position, which is a paper conveyance position, and a position control unit that performs position control for making the conveyance position of the paper coincide with the ideal fixing position acquired by the position acquisition unit. doing.

  Here, in the present invention, the image forming apparatus further includes a storage unit that stores information defining a correspondence relationship between the paper type and the ideal fixing position, and the position acquisition unit is acquired by the paper type acquisition unit. It is preferable to obtain the ideal fixing position by searching the storage unit based on the paper type.

  In the present invention, it is preferable that the paper type includes at least one of paper size, paper thickness, and paper surface properties.

  In the present invention, the position control is preferably control for moving the fixing device in the paper width direction based on the ideal fixing position before the paper enters the fixing device.

  In addition, the present invention further includes a pair of registration rollers that convey the sheet to a transfer position by the image forming unit, and the position control is based on the ideal fixing position while the sheet is held between the pair of registration rollers. It is preferable to control the registration roller to move in the paper width direction.

  The present invention further includes a pair of side edge regulating plates for regulating the position of the paper side edge parallel to the paper conveyance direction for the paper fed to the conveyance path. Prior to this, it is preferable to control the pair of side end regulating plates in the paper width direction based on the ideal fixing position.

  In the present invention, it is preferable that the position control further includes control for correcting an image forming position by the image forming unit.

  The present invention further includes a swing control unit that performs swing control for swinging the fixing device in the paper width direction between sheets, and the swing control unit is a reference on a transport path for transporting the sheet. It is preferable to perform the swing control by moving the ideal fixing position starting from the position.

  Further, in the present invention, the swing control unit is configured such that the position where the preceding sheet enters and the position where the succeeding sheet enter differ between the passage of the preceding sheet and the subsequent sheet entering the fixing device. When the leading edge of the succeeding paper enters the fixing device, the position controller moves the fixing device relative to the reference position on the conveyance path until the trailing edge of the paper passes through the transfer nip. It is preferable to move the fixing device so that the ideal fixing positions coincide.

  In the present invention, the ideal fixing position is determined on the basis of the amount of deviation of the side edge position by detecting the position of the paper side edge parallel to the paper conveyance direction for the paper passing through the fixing device. preferable.

  Further, in the present invention, it is preferable that the ideal fixing position is determined on the basis of the amount of bending of the read image obtained by reading the image on the sheet that has passed through the fixing device.

  Here, the reading of the image is started from a position advanced by a predetermined distance from the leading edge of the sheet, and the predetermined distance is preferably a distance from the transfer position by the image forming unit to the fixing device.

  According to the present invention, by acquiring the fixing ideal position unique to the fixing device according to the paper type, it is possible to make this coincide with the paper transport position. As a result, the occurrence of paper misalignment can be suppressed. As a result, it is possible to suppress the occurrence of situations such as image bending and image damage due to contact with the guide plate, so that deterioration in image quality can be suppressed.

1 is a configuration diagram schematically showing an image forming apparatus according to a first embodiment. 1 is a block diagram illustrating a configuration of a control system of an image forming apparatus according to a first embodiment. Explanatory drawing which shows the detail of the position control performed by a control part 6 is a flowchart showing a control operation of the image forming apparatus according to the first embodiment. Explanatory diagram showing a table of ideal fixing centers Explanatory drawing showing an overview of position control FIG. 3 is a block diagram illustrating a configuration of a control system of an image forming apparatus according to a second embodiment. Explanatory drawing which shows the concept of rocking | fluctuation control in the image forming apparatus which concerns on 2nd Embodiment. Explanatory diagram showing the outline of swing control and fixing control

(First embodiment)
FIG. 1 is a configuration diagram schematically illustrating an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 is an electrophotographic image forming apparatus such as a copying machine, and is a so-called tandem type color image forming apparatus that forms a full-color image.

  The image forming apparatus 1 is mainly composed of a document reading device SC, image forming units 10Y, 10M, 10C, and 10K, a fixing device 40, and a control unit 50.

  The document reader SC illuminates the image of the document with the illumination device, reads the reflected light with the line image sensor, and obtains an image signal. The image signal is subjected to processing such as A / D conversion, shading correction, and compression, and then input to the control unit 50 as image data. Note that the image data input to the control unit 50 is not limited to the data read by the document reading device SC. For example, the image data received from a personal computer connected to the image forming device 1 or another image forming device 1 It may be stored in a portable recording medium such as a USB memory.

  The image forming units 10Y, 10M, 10C, and 10K are an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, and an image that forms a cyan (C) image. The image forming unit 10C corresponds to the image forming unit 10K that forms a black (K) image.

  The image forming unit 10Y includes a photosensitive drum 11Y, a charging unit disposed around the photosensitive drum 11Y, an optical writing unit 12Y, a developing device, and a drum cleaner.

  The surface of the photosensitive drum 11Y is uniformly charged by the charging unit, and a latent image is formed on the photosensitive drum 11Y by scanning exposure by the optical writing unit 12Y. Further, the developing device develops the latent image on the photosensitive drum 11Y by developing with toner. As a result, a predetermined color image (toner image) corresponding to yellow is formed on the photosensitive drum 11Y. The image formed on the photosensitive drum 11Y is sequentially transferred to a predetermined position on the intermediate transfer belt 15 by the primary transfer roller.

  The image forming units 10M, 10C, and 10K are composed of the photosensitive drums 11M, 11C, and 11K, and charging units, optical writing units 12M, 12C, and 12K disposed around the photosensitive drums 11M, 11C, and 11K, a developing device, and a drum cleaner. Details of these elements are the same as those of the image forming unit 10Y.

  The intermediate transfer belt 15 is an endless belt and is stretched around a plurality of rollers including a secondary transfer counter roller and a belt driven roller. The image composed of each color transferred onto the intermediate transfer belt 15 is transferred by the secondary transfer roller 16 to the paper P transported at a predetermined timing by the paper transport unit 20. The secondary transfer roller 16 is a roller-like rotating member, and is in pressure contact with the secondary transfer counter roller via the intermediate transfer belt 15 (transfer nip).

  The paper transport unit 20 transports the paper P fed from the paper feed units 22 and 24 along the transport path.

  The paper P is stored in the paper tray 21, and the paper P stored in the paper tray 21 is taken in by the paper supply unit 22 and sent out to the transport path. The paper tray 21 is provided with a pair of side edge regulating plates 21a for regulating the position of the paper side edge parallel to the paper conveyance direction for the paper P fed to the conveyance path. With the pair of side end regulating plates 21a, it is possible to set the position of the paper P that is transported along the transport path, that is, the transport position of the paper P. Normally, the transport position of the paper P is set to coincide with the reference position on the transport path for transporting the paper, and the positions of the pair of side end regulating plates 21a are also matched with the transport position of the paper P. Is set.

  In this specification, the transport position of the paper P is defined with reference to the center position in the paper width direction of the paper P transported through the transport path, and is hereinafter referred to as “paper transport center”. The reference position on the transport path is defined by the center position in the paper width direction on the transport path, and is hereinafter referred to as “transport path center”.

  In addition, a paper feed tray 23 for introducing paper P such as manual feed paper or long paper into the apparatus is disposed at a side end of the main body housing of the image forming apparatus 1. The paper P placed on the paper feed tray 23 is taken in by the paper feed unit 24 and sent out to the transport path. The paper feed tray 23 is provided with a pair of side edge regulating plates 23a for regulating the position of the paper side edge parallel to the paper conveyance direction for the paper P fed to the conveyance path. The positions of the pair of side end regulating plates 23a are set together with the sheet conveyance center.

  The fed paper P is transported in the apparatus by a plurality of transport roller pairs such as a pair of loop rollers 27 and a pair of registration rollers 26, whereby a transfer nip, that is, an image transfer position by the secondary transfer roller 16. Supplied to. Specifically, when the fed paper P is transported by the pair of loop rollers 27 and the transport roller pair on the upstream side, the leading end of the paper P strikes the pair of registration rollers 26 in the rotation stopped state. . In this state, the pair of loop rollers 27 continues to rotate, whereby a loop is formed on the paper P. By this operation, the bending of the paper P is corrected. Thereafter, the pair of registration rollers 26 starts rotating at a predetermined timing, and feeds the paper P to the transfer position.

  The fixing device 40 is a device that performs a fixing process for fixing the image on the paper P to which the image has been transferred. The fixing device 40 includes a pair of fixing rollers 41 that form a nip (fixing nip) by being placed in pressure contact with each other, and a heating unit that heats the fixing roller 41. As the heating means, a heater such as a halogen lamp can be used. The fixing device 40 conveys the paper P and fixes the image on the paper P by performing pressure fixing with a pair of fixing rollers 41 and heat fixing with a heater.

  The paper P subjected to the fixing process by the fixing device 40 is discharged by a paper discharge roller 28 to a paper discharge tray (not shown) attached to the side surface of the housing. When image formation is also performed on the back surface of the paper P, the paper P on which image formation on the front surface of the paper has been completed is conveyed by the switching gate 29 to the reverse roller below. The reversing roller pinches the trailing end of the conveyed paper P, reverses the paper P by reverse feeding, and sends it out to the refeed conveyance path. The paper P sent out to the re-feed transport path is transported by a plurality of transport roller pairs and returns to the transfer position.

  The operation panel 45 is a touch panel type input unit capable of inputting information in accordance with information displayed on the display. The user can set information on the paper P (paper type and the like), image density, magnification, and the like through an operation on the operation panel 45, and the information is acquired by the control unit 50. The operation panel 45 also functions as a display unit that displays various information to the user via the operation panel 45 by being controlled by the control unit 50.

  The control unit 50 has a function of controlling the image forming apparatus 1 in an integrated manner. As the control unit 50, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an I / O interface can be used. The control unit 50 controls the image forming units 10Y, 10M, 10C, 10K, and the like to form an image and transfer the image onto the paper P, or controls the fixing device 40 to transfer the image onto the paper P. The paper P is fed and transported by fixing or controlling the paper transport unit 20 and the like.

  FIG. 2 is a block diagram illustrating a configuration of a control system of the image forming apparatus 1 according to the present embodiment. FIG. 3 is an explanatory diagram showing details of the position control executed by the control unit 50. Here, “Cst” shown in FIG. 3 indicates the center of the conveyance path. In relation to the present embodiment, the control unit 50 has the following functions.

  First, the control unit 50 acquires the paper type related to the paper P in the image formation (paper type acquisition unit 50a). For example, the control unit 50 can acquire the paper type from the job information set by the user through the operation panel 45 or the like. Here, the paper type includes information on the size of the paper P, the thickness of the paper P, and the surface property of the paper P.

  Since the thickness of the paper P has a correlation with the basis weight of the paper P, in this specification, the thickness is handled using the basis weight. Further, the surface property of the paper P indicates the degree of the surface roughness. In the present embodiment, for convenience, two surface properties of coated paper and non-coated paper will be described as an example.

  Secondly, the control unit 50 acquires the ideal fixing position based on the paper type (position acquisition unit 50b). In the present embodiment, the control unit 50 acquires the ideal fixing position from the storage unit 51 that stores information in which the ideal fixing position unique to the fixing device 40 is associated with each paper type.

  Here, the ideal fixing position indicates an ideal transport position of the paper P in the fixing device 40, and is determined as unique to the device. In this specification, the ideal fixing position is defined with reference to the center position of the paper P passing through the ideal fixing position, and is hereinafter referred to as “the ideal fixing center”.

  In general, in the image forming apparatus 1, various elements are designed so that the sheet conveyance center coincides with the conveyance path center Cst. This is also true for the fixing device 40. Accordingly, the ideal fixing center and the sheet conveyance center are essentially the same. However, in the actual fixing device 40, there is a case where the ideal fixing center exists at a position shifted from the transport path center Cst. In this case, in the process of passing through the fixing device 40, a phenomenon occurs in which the paper P moves from the conveyance path center Cst toward the fixing ideal center.

  Such misalignment of the ideal fixing center includes a manufacturing error of a crown shape (or reverse crown shape) applied to each fixing roller 41, a pressure contact balance between both fixing rollers 41, and a distortion (roller when each fixing roller 41 is assembled). This is due to factors such as alignment. That is, this deviation is due to a practical error that does not occur in the design stage. Then, the deviation of the fixing ideal center appears in a state unique to each fixing device. Further, the deviation of the ideal fixing center is determined based on the paper type such as the paper size in the paper width direction (direction intersecting the paper conveyance direction), the thickness of the paper P, and the surface property of the paper P, while being determined on the basis of each device. Is also different.

  A storage unit 51 is connected to the control unit 50. The storage unit 51 stores a table that defines the correspondence between the paper type and the fixing ideal center. This table is created at the time of product manufacture or by executing the adjustment mode of the image forming apparatus 1 and specifying the ideal fixing center for each paper type.

  The ideal fixing center is determined by the following method, for example.

  The first method is a method using a detecting means for detecting the position of the paper side edge such as a CCD line sensor. Specifically, the paper P is transported along the center of the transport path, and the position of the paper side edge is detected by the detecting means for the paper P that is passing through the fixing device 40. Then, the shift amount of the side edge position is monitored after the leading edge of the paper reaches the fixing device 40 and before the trailing edge of the paper passes through the fixing device 40. Based on this deviation amount, the ideal fixing center is determined.

  The second technique is a technique using an image reading device mounted on the image forming apparatus 1 or mounted on a device disposed on the downstream side of the image forming apparatus 1. Specifically, the paper P is conveyed along the center of the conveyance path, a predetermined test image is transferred to the paper P by the image forming units 10Y, 10M, 10C, and 10K, and the image is fixed on the paper P by the fixing device 40. For the paper P that has passed through the fixing device 40, an image on the paper is read by the image reading device. Then, based on the amount of bending of the read image, the ideal fixing center is determined.

  Note that the transfer image is bent after the leading edge of the sheet P enters the fixing device 40. Therefore, it is preferable that reading of an image by the image reading apparatus starts from a position that has advanced a predetermined distance from the leading edge of the paper P. Here, the predetermined distance corresponds to the distance from the transfer position to the fixing nip.

  Thirdly, the control unit 50 performs position control for making the sheet conveyance center coincide with the ideal fixing center (position control unit 50c). The position control is executed by at least one method among control for moving the pair of side end regulating plates 21a and 23a, control for moving the pair of registration rollers 26, and control for moving the fixing device 40.

  First, a control method for moving the fixing device 40 will be described. The fixing device 40 includes, for example, a fixing driving unit 57 configured by a power transmission mechanism such as an electric motor or a gear, and the fixing driving unit 57 is controlled by the control unit 50. The controller 50 can move the fixing device 40 along the paper width direction by driving the fixing driving unit 57. Therefore, by moving the fixing device 40 before the paper P reaches the fixing device 40, it is possible to make the paper transport center coincide with the ideal fixing center.

  Next, a control method for moving the pair of registration rollers 26 will be described. The pair of registration rollers 26 includes, for example, a registration driving unit 56 configured by a power transmission mechanism such as an electric motor or a gear, and the registration driving unit 56 is controlled by the control unit 50. The control unit 50 can move the pair of registration rollers 26 along the paper width direction by driving the registration driving unit 56. Therefore, by moving the pair of registration rollers 26 while the paper P is sandwiched between the pair of registration rollers 26, it is possible to make the paper conveyance center coincide with the ideal fixing center.

  Finally, a control method for moving the pair of side end regulating plates 23a will be described. The pair of side end regulating plates 23a includes, for example, a side end regulating plate driving unit 55 configured by a power transmission mechanism such as an electric motor or a gear, and the side end regulating plate driving unit 55 is configured by the control unit 50. Controlled by The controller 50 can move the pair of side end regulating plates 23 a along the paper width direction by driving the side end regulating plate driving unit 55. Therefore, by moving the pair of side end regulating plates 23a prior to feeding the paper P, it is possible to make the paper transport center coincide with the ideal fixing center. Note that this method can be similarly applied to the pair of side end regulating plates 21a on the paper tray 21 side.

  When the pair of side end regulating plates 21a and 23a or the pair of registration rollers 26 are moved, the control unit 50 performs image formation by the image forming units 10Y, 10M, 10C, and 10K according to the movement direction and the movement amount. Further, a control for correcting the writing position of the optical writing units 12Y, 12M, 12C, and 12K is further performed. Even if the position of the paper P entering the secondary transfer roller 16 moves in the paper width direction by this correction control, the image position formed on the paper P and the paper P should be formed on the paper P. Matching with the image position can be achieved.

  FIG. 4 is a flowchart showing the control operation of the image forming apparatus 1 according to this embodiment. The processing shown in this flowchart is executed by the control unit 50 with the execution of a job as a trigger.

  First, in step 1 (S1), the control unit 50 acquires the paper type of the paper P used for image formation by executing the job. The control unit 50 can acquire the paper type from the job information set by the user via the operation panel 45 or the like. By this step 1, the control unit 50 acquires information on the size of the paper P (paper width) in the paper width direction, the basis weight of the paper P, and whether or not the paper is coated paper.

  In step 2 (S2), the control unit 50 determines whether or not the paper P is uncoated paper. If an affirmative determination is made in step 2, that is, if the paper P is uncoated paper, the process proceeds to step 3 (S3). On the other hand, if a negative determination is made in step 2, that is, if the paper P is a coated paper, the process proceeds to step 4 (S4).

  In step 3, the control unit 50 calculates the shift amount of the paper P based on the table prepared for the uncoated paper. Here, FIG. 5A is an explanatory diagram showing a table of ideal fixing centers corresponding to uncoated paper. This table defines the ideal fixing center for uncoated paper as a deviation amount from the original paper conveyance center (conveyance path center Cst), and the deviation amount is associated with each paper width and basis weight. . When the amount of deviation is indicated by a minus value, the ideal fixing center is shifted to the back side of the apparatus, that is, to the right side when the conveyance path of the paper P is viewed from upstream to downstream. On the other hand, when the amount of deviation is indicated by plus, the ideal fixing center is displaced toward the front side of the apparatus. The table is stored in the storage unit 51, and the control unit 50 searches the table based on the sheet width and basis weight, and calculates the ideal fixing center (deviation amount from the original sheet conveyance center).

  In step 4, the control unit 50 calculates the shift amount of the paper P based on the table prepared for the coated paper. Here, FIG. 5B is an explanatory diagram showing a table of ideal fixing centers corresponding to coated paper. This table defines the ideal fixing center for coated paper as a deviation amount from the original paper conveyance center (conveyance path center Cst), and the deviation amount is associated with each paper width and basis weight. When the amount of deviation is negative, the ideal fixing center is deviated toward the back of the apparatus. On the other hand, when the amount of deviation is indicated by plus, the ideal fixing center is displaced toward the front side of the apparatus. The table is stored in the storage unit 51, and the control unit 50 searches the table based on the sheet width and basis weight, and calculates the ideal fixing center (deviation amount from the original sheet conveyance center).

  In Step 5 (S5), the control unit 50 performs position control based on the ideal fixing center acquired in Step 3 or Step 4. Here, FIG. 6 is an explanatory diagram showing an outline of position control.

  As shown in FIG. 5A, the position control can be performed by moving the fixing device 40, for example. The controller 50 moves the fixing device 40 based on the acquired ideal fixing center Cf. For example, when the ideal fixing center Cf is shifted to the back side of the apparatus (upper side in the drawing) with respect to the transport path center Cst, the control unit 50 is closer to the front side of the apparatus (by the amount of deviation of the ideal fixing center Cf). The fixing device 40 is moved to the lower side in the drawing. Thus, the feeding of the paper P is started, and when the paper P enters the fixing device 40, the paper transport center and the fixing ideal center Cf coincide with each other.

  Further, as shown in FIG. 5B, the position control can be performed by moving a pair of side end regulating plates 23a, for example. The controller 50 moves the pair of side end regulating plates 23a based on the acquired ideal fixing center Cf. For example, when the ideal fixing center Cf is shifted to the back side of the apparatus (upper side in the drawing) with respect to the transport path center Cst, the control unit 50 increases the back side of the apparatus (the amount of shift of the ideal fixing center Cf). The pair of side end regulating plates 23a is moved to the upper side in the drawing. By the movement of the pair of side end regulating plates 23a, the paper feed position of the paper P is shifted in the paper width direction, so that the paper P starts to be fed and the paper P enters the fixing device 40. The sheet conveyance center and the fixing ideal center Cf coincide with each other. Note that this method can be similarly applied to the pair of side end regulating plates 21a on the paper tray 21 side.

  Further, when the pair of side end regulating plates 21a and 23a is moved, the control unit 50 controls the image forming units 10Y, 10M, 10C, and 10C according to the deviation amount and the deviation direction of the paper P by the pair of side end regulating plates 23a. Control for correcting the image forming position by 10K, that is, the image writing position by the optical writing units 12Y, 12M, 12C, and 12K is further performed. In the above example, the control unit 50 moves the image writing position toward the back of the apparatus (upper side in the drawing) by the amount of deviation of the ideal fixing center Cf. Even if the position of the paper P entering the secondary transfer roller 16 moves in the paper width direction by this correction control, the image position formed on the paper P and the paper P should be formed on the paper P. Matching with the image position can be achieved.

  In step 6 (S6), the controller 50 starts feeding the paper P.

  The position control can also be performed by moving the pair of registration rollers 26 as described above. In this case, the execution order of Step 5 and Step 6 is reversed, and the pair of registration rollers 26 is moved while the paper P is held between the pair of registration rollers 26, as shown in FIG. 6C. Let For example, when the ideal fixing center Cf is shifted to the back side of the apparatus (upper side in the drawing) with respect to the transport path center Cst, the control unit 50 increases the back side of the apparatus (the amount of shift of the ideal fixing center Cf). The pair of registration rollers 26 are moved to the upper side in the drawing. Since the transport position of the paper P is shifted in the paper width direction by the pair of registration rollers 26, the paper P is started to be fed, passes through the pair of registration rollers 26, and is then fed to the fixing device 40. When P enters, the sheet conveyance center coincides with the fixing ideal center Cf. In this method, it is necessary to further perform control for correcting the image forming position by the image forming units 10Y, 10M, 10C, and 10K.

  As described above, in this embodiment, the image forming apparatus 1 includes the image forming units 10Y, 10M, 10C, and 10K that form an image and transfer the image onto the paper P, and the fixing device 40 that fixes the image on the paper P. And a control unit 50. Here, the control unit 50 has a function of acquiring the paper type for the paper P (paper type acquisition unit 50a), a function of acquiring the fixing ideal center Cf according to the paper type (position acquisition unit 50b), And a function (position control unit 50c) for performing position control for matching the sheet conveyance center and the fixing ideal center Cf.

  According to this configuration, by acquiring the fixing ideal center Cf unique to the fixing device 40 corresponding to the paper type, it is possible to make this coincide with the paper transport center. Thereby, it is possible to suppress the deviation of the sheet due to the characteristics unique to the fixing device. As a result, it is possible to suppress the occurrence of situations such as image bending and image damage due to contact with the guide plate, so that deterioration in image quality can be suppressed.

  In particular, for paper P having a long size in the paper conveyance direction, such as roll paper or long paper, the deviation of the paper P tends to be accumulated according to the conveyance distance. Therefore, in the image forming apparatus 1 using such paper P, it is effective to perform position control according to the present embodiment.

  In the present embodiment, the image forming apparatus 1 further includes a storage unit 51 that stores information defining the correspondence between the paper type and the ideal fixing center Cf. The control unit 50 acquires the ideal fixing center Cf by searching the storage unit 51 based on the acquired paper type.

  According to this configuration, since the storage unit 51 holds necessary information, the ideal fixing center Cf along the paper type can be appropriately acquired. However, the information about the ideal fixing center Cf does not need to be held by the image forming apparatus 1 itself, and may be acquired by a user or by communicating with an external device as necessary. .

  In the present embodiment, the paper type includes at least one of the size of the paper P, the thickness of the paper P, and the surface property of the paper P.

  The deviation of the paper P in accordance with the deviation of the ideal fixing center Cf is caused by the deviation of the pressure distribution acting on the paper P. Even if the pressure distribution is the same, the degree of deviation of the paper P differs depending on the paper type, so the ideal fixing center Cf differs depending on the paper type. For example, if the paper width of the paper P is small, the deviation of the paper P tends to increase. Further, the smaller the thickness of the paper P or the smoother the surface of the paper P, the larger the deviation of the paper P tends to be. As described above, by appropriately considering the paper type, that is, the parameter that affects the deviation of the paper P, the ideal fixing center Cf can be accurately acquired.

  In the present embodiment, the position control is control for moving the fixing device 40 in the paper width direction based on the ideal fixing center Cf before the paper P enters the fixing device 40.

  According to this configuration, the sheet conveyance center of the sheet P entering the fixing device 40 and the ideal fixing center Cf can be matched.

  In the present embodiment, the position control is control for moving the registration roller 26 in the paper width direction based on the ideal fixing center Cf while the paper P is held between the pair of registration rollers 26.

  According to this configuration, the sheet conveyance center of the sheet P entering the fixing device 40 and the ideal fixing center Cf can be matched.

  In the present embodiment, the position control is a control for moving the pair of side end regulating plates 21a and 23a in the sheet width direction based on the ideal fixing center Cf prior to the feeding of the sheet P.

  According to this configuration, the sheet feeding center of the sheet P entering the fixing device 40 and the ideal fixing center Cf can be matched.

  The position control further includes control for correcting the image forming position by the image forming units 10Y, 10M, 10C, and 10K.

  According to this configuration, the image forming position can be corrected according to the movement of the paper P. Thereby, an image can be formed at an appropriate position on the paper P.

  Further, in the present embodiment, the ideal fixing center Cf detects the position of the sheet side edge parallel to the sheet conveyance direction for the sheet P passing through the fixing device 40, and based on the shift amount of the side edge position. Has been decided.

  According to this configuration, the ideal fixing center Cf can be appropriately determined from the actual behavior of the paper P.

  In this embodiment, the ideal fixing center Cf is determined based on the amount of bending of the read image obtained by reading the image on the paper P that has passed through the fixing device 40.

  According to this configuration, the ideal fixing center Cf can be appropriately determined from the locus of the image formed on the paper P.

  In the present embodiment, reading of an image is started from a position that has advanced a predetermined distance from the leading edge of the paper P. Here, the predetermined distance is a distance from the transfer position (transfer nip) by the image forming units 10Y, 10M, 10C, and 10K to the fixing device 40 (fixing nip).

  According to this configuration, it is possible to read an image only in a region where the deviation of the paper P is reflected. Thereby, the fixing ideal center Cf can be determined efficiently and appropriately.

(Second Embodiment)
FIG. 7 is a block diagram illustrating a configuration of a control system of the image forming apparatus 1 according to the second embodiment. The image forming apparatus 1 according to the second embodiment will be described below. The image forming apparatus 1 according to the second embodiment is different from that of the first embodiment in that the control unit 50 performs swing control of the fixing device 40 from the viewpoint of protecting each fixing roller 41. It has a function (swing control unit 50d). This swing control is control for swinging the fixing device 40 in the sheet width direction between sheets. That is, the swing control is performed by moving the fixing device 40 in the paper width direction before the succeeding sheet P arrives when the preceding sheet P passes, so that the succeeding sheet P is located at a position different from the preceding sheet P. And the passage position of the sheet edge is shifted for each sheet.

  FIG. 8 is an explanatory diagram showing the concept of swing control in the image forming apparatus 1 according to the second embodiment. Normally, when swing control is performed, the center position of the fixing device is moved from the center of the sheet conveyance to the back side or the front side of the device. On the other hand, in the present embodiment, the ideal fixing center Cf is taken into consideration, and the ideal fixing center Cf of the fixing device 40 is moved to the back side of the apparatus or the front side of the apparatus starting from the sheet conveyance center.

  Further, in a situation where the ideal fixing center Cf is moved from the sheet conveyance center by the swing control, the sheet P conveyed along the sheet conveyance center becomes the ideal fixing center Cf when passing through the fixing device 40. There is a possibility of moving towards.

  FIG. 9 is an explanatory diagram showing an outline of the swing control and the fixing control. Therefore, in the present embodiment, the control unit 50, after passing the preceding paper P, before the subsequent paper P enters the fixing device 40, the entrance position of the preceding paper P and the entrance of the subsequent paper P The fixing device 40 is moved so that the position is different (oscillation control). When the leading edge of the succeeding paper P enters the fixing device 40 after the fixing device 40 is swung, the control unit 50 waits until the trailing edge of the paper P passes through the transfer nip until the transport path center Cst ( The fixing device 40 is moved so that the ideal fixing center Cf coincides with the (paper transport center) (position control).

  According to this configuration, when the conveyance path center Cst and the ideal fixing center Cf are deviated, the sheet P moves to the ideal fixing center Cf, but the fixing device 40 is moved to the conveyance path center Cst (paper conveyance center). ) To cancel each other's movements. Therefore, the sheet conveyance center is maintained at the conveyance path center Cst, and the deviation of the sheet P can be suppressed. Thereby, both position control and swing control can be achieved. As a result, it is possible to appropriately protect the fixing device 40 while suppressing the deviation of the paper P.

  The image forming apparatus according to the embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the invention. .

  For example, when the fixing device is moved, it is not necessary to move the entire device, and only a pair of fixing rollers may be moved. Further, as long as the sheet is moved upstream of the fixing device, the position control may be performed not only by the registration rollers but also by other transport rollers or a dedicated moving mechanism.

  Further, as a specific example of the position control, a method of automatically moving the fixing device or the paper has been described. However, the position control may simply display information on the ideal fixing position to the user. In this case, referring to the information, the user himself / herself moves the fixing device or the pair of side end regulating plates, so that the paper transport position and the ideal fixing position can be matched.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10Y-10K Image forming part 11Y-11K Photosensitive drum 12Y-12K Optical writing part 15 Intermediate transfer belt 16 Secondary transfer roller 20 Paper conveyance part 21 Paper tray 21a Side edge regulating plate 22 Paper feed part 23 Supply Paper tray 23a Side edge regulating plate 24 Paper feed unit 26 Registration roller 40 Fixing device 50 Control unit 50a Paper type acquisition unit 50b Position acquisition unit 50c Position control unit 50d Swing control unit 51 Storage unit

Claims (12)

In an image forming apparatus including an image forming unit that forms an image and transfers the image to a sheet,
A fixing device for fixing an image on paper;
A paper type acquisition unit for acquiring the paper type related to the paper;
Based on the paper type acquired by the paper type acquisition unit, a position acquisition unit that acquires an ideal fixing position that is an ideal paper conveyance position unique to the fixing device;
A position control unit that performs position control for making the sheet conveyance position coincide with the ideal fixing position acquired by the position acquisition unit;
An image forming apparatus comprising: A storage unit for storing information defining a correspondence relationship between the paper type and the ideal fixing position;
The image forming apparatus according to claim 1, wherein the position acquisition unit acquires the ideal fixing position by searching the storage unit based on the paper type acquired by the paper type acquisition unit. apparatus.   The image forming apparatus according to claim 1, wherein the paper type includes at least one of a paper size, a paper thickness, and a paper surface property.   4. The control according to claim 1, wherein the position control is control for moving the fixing device in a paper width direction based on the ideal fixing position before the paper enters the fixing device. 5. The described image forming apparatus. It further has a pair of registration rollers that convey the paper to the transfer position by the image forming unit,
4. The control according to claim 1, wherein the position control is a control for moving the registration roller in a sheet width direction based on the ideal fixing position while the sheet is held between the pair of registration rollers. The image forming apparatus described in any of the above. For the paper fed to the transport path, it further has a pair of side edge regulating plates that regulate the position of the paper side edge parallel to the paper transport direction,
4. The control according to claim 1, wherein the position control is control for moving the pair of side end regulating plates in the paper width direction based on the ideal fixing position prior to paper feeding. 5. An image forming apparatus as described above.   The image forming apparatus according to claim 5, wherein the position control further includes control for correcting an image forming position by the image forming unit. A swing control unit for performing swing control for swinging the fixing device in the paper width direction between the papers;
2. The swing control unit according to claim 1, wherein the swing control unit performs the swing control by moving the fixing ideal position from a reference position on a transport path for transporting paper. Image forming apparatus. The swing control unit is configured so that an entry position of the preceding sheet and an entry position of the succeeding sheet are different from each other before the succeeding sheet enters the fixing device after the preceding sheet passes. While moving the fixing device,
When the leading edge of the succeeding sheet enters the fixing device, the position control unit is configured to detect the ideal fixing position with respect to the reference position on the transport path until the trailing edge of the sheet passes through the transfer nip. The image forming apparatus according to claim 8, wherein the fixing device is moved so as to match each other.   The ideal fixing position is determined on the basis of a deviation amount of the side end position of a sheet passing through the fixing device by detecting a position of the side end of the sheet parallel to the sheet conveyance direction. Item 10. The image forming apparatus according to any one of Items 1 to 9.   10. The image forming according to claim 1, wherein the ideal fixing position is determined based on a bending amount of the read image obtained by reading an image on a sheet that has passed through the fixing device. apparatus. Reading of the image is started from a position that has advanced a predetermined distance from the leading edge of the paper,
The image forming apparatus according to claim 11, wherein the predetermined distance is a distance from a transfer position by the image forming unit to the fixing device.

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