JP5768915B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method having a function of moving a sheet in a sheet width direction perpendicular to the sheet conveying direction before conveying the sheet to an image forming position.

  Conventionally, when a sheet, which is one of the recording media, is transported from the sheet feeding unit to an image forming position, the sheet may be shifted in the sheet width direction, which is a direction perpendicular to the sheet transport direction. Causes of this include, for example, non-uniformity of the roller diameter in the longitudinal direction of the roller due to errors in the manufacture of the roller that transports the paper, changes in the roller diameter due to aging of the roller, and deviation of the paper loaded in the paper feeder Is mentioned. As described above, when the position in the width direction of the paper is shifted, there arises a problem that an image is formed at a position different from the position desired by the user at the time of image formation.

  As a method for solving the above-described problem, that is, a method for accurately aligning an image and a sheet in consideration of a deviation of the sheet, resist swing is known.

  There exists patent document 1 as an example of a resist rocking | fluctuation. Patent Document 1 describes a registration roller pair disposed in front of an image forming position and an optical sensor disposed in the vicinity of the downstream side of the registration roller pair in the paper transport direction. Specifically, the registration roller pair can swing with the paper sandwiched in the paper width direction, and in the paper width direction with the paper sandwiched according to the offset amount of the paper obtained by the optical sensor. Rocks. As a result, the deviation of the sheet in the sheet width direction is corrected, so that the image and the sheet are aligned.

JP 2007-22680 A

  However, when the registration is swung, the registration roller pair is swung using the above-mentioned deviation amount as a command value. This command value and an actual measurement value that is a swing amount of the paper swung by the resist swing There is a difference. Therefore, there is a problem that it is difficult to accurately align the image and the paper.

  The present invention has been made in view of the above situation, and an object of the present invention is to provide a function of moving in a state where the paper is sandwiched in the paper width direction, and to accurately align the image and the paper. An object of the present invention is to provide an image forming apparatus and an image forming method.

The above object of the present invention is achieved by the following means.
(1) An image forming apparatus capable of double-sided printing in which an image is formed on the first side of the paper and then an image is formed on the second side of the paper on which the image is formed on the first side.
An image forming unit that forms an image on a sheet at an image forming position;
A transport path for transporting the paper to the image forming position;
Moving the paper in the paper width direction by moving in the paper width direction, which is upstream of the image forming unit with respect to the paper transport direction and sandwiching the paper, and perpendicular to the paper transport direction A pair of transport rollers to be displaced to
In duplex printing, before the transport roller pair moves, an image is formed on either the first surface or the second surface at the image forming position downstream of the transport roller pair in the paper transport direction. And the distance from the reference position in the paper width direction to the edge of the paper on the upstream side of the image forming position and the downstream side of the pair of transport rollers with respect to the paper transport direction. A control unit that determines a movement amount of the conveyance roller pair and performs control for moving the conveyance roller pair in the paper width direction by the determined movement amount;
The control unit determines the movement amount based on the distance when forming an image on the second surface to be larger than the movement amount based on the distance when forming an image on the first surface. An image forming apparatus.
(2) The control unit determines whether the image is formed on the first surface or the second surface at the image forming position downstream of the conveyance roller with respect to the sheet conveyance direction, and on the distance. In addition, the amount of movement is determined based on whether the transport roller is moved in the first direction or the second direction in the paper width direction. apparatus.
(3) A line sensor in which photoelectric conversion elements are arranged in a line, or an image sensor in which photoelectric conversion elements are arranged in a matrix,
The image forming apparatus according to (1) or (2), wherein the line sensor or the image sensor acquires a distance from a reference position in the paper width direction to an edge of the paper.
(4) A first condition for determining the movement amount when forming an image on the first surface based on the distance, and the movement amount when forming an image on the second surface based on the distance. A storage unit for storing in advance the second condition for determining
When forming an image on the first surface, the control unit determines the movement amount based on the first condition and the distance stored in advance in the storage unit, and forms an image on the second surface. When performing, said movement amount is determined based on said 2nd condition and said distance previously memorize | stored in the said memory | storage part, The said any one of (1)-(3) characterized by the above-mentioned Image forming apparatus.
(5) The control unit determines whether the image is formed on the first surface or the second surface at the image forming position downstream of the transport roller with respect to the paper transport direction, and on the distance. In addition, the amount of movement is determined based on at least one of humidity of a place where the image forming apparatus is placed, basis weight of the paper, and paper size of the paper. The image forming apparatus according to any one of to (3).
(6) The control unit according to any one of (1) to (5), wherein the movement amount is increased as a frictional force generated between the paper and the conveyance path is increased. The image forming apparatus described.
(7) The image forming apparatus according to (4), further including an adjustment unit that adjusts the first condition or the second condition stored in the storage unit.
(8) A plurality of paper feed trays are provided,
The image forming apparatus according to (7), wherein the adjustment unit is capable of individually adjusting the first condition or the second condition for each of the plurality of paper feed trays.
(9) Double-sided printing is possible in which an image is formed on the first side of the paper and then an image is formed on the second side of the paper on which the image is formed on the first side;
An image forming unit that forms an image on a sheet at an image forming position;
A transport path for transporting the paper to the image forming position;
Moving the paper in the paper width direction by moving in the paper width direction, which is upstream of the image forming unit with respect to the paper transport direction and sandwiching the paper, and perpendicular to the paper transport direction A pair of transport rollers to be displaced to
An image forming method in an image forming apparatus comprising:
In double-sided printing, whether the image is formed on the first surface or the second surface at the image forming position downstream of the transport roller with respect to the paper transport direction, the reference position in the paper width direction And the distance to the end of the sheet upstream of the image forming position and downstream of the pair of transport rollers with respect to the sheet transport direction is determined. Steps,
Moving the transport roller pair in the paper width direction by the determined amount of movement, and
In the determining step, the movement amount based on the distance when forming an image on the second surface is determined to be larger than the movement amount based on the distance when forming an image on the first surface. An image forming method.
(10) In the determining step, whether the image is formed on the first surface or the second surface at the image forming position downstream of the conveyance roller with respect to the sheet conveyance direction, the distance, In addition to the above, the moving amount is determined based on whether the transport roller is moved in the first direction or the second direction in the paper width direction. Forming method.
(11) The image forming apparatus includes a line sensor in which photoelectric conversion elements are arranged in a line, or an image sensor in which photoelectric conversion elements are arranged in a matrix.
(9) or (9), further comprising the step of obtaining a distance from a reference position in the paper width direction to the edge of the paper by the line sensor or the image sensor before the determining step. (10) The image forming method according to (10).
(12) The image forming apparatus includes a first condition for determining the amount of movement when forming an image on the first surface based on the distance, and the movement when forming an image on the second surface. A storage unit for storing in advance a second condition for determining the amount based on the distance;
When forming an image on the first surface, in the determining step, the movement amount is determined based on the first condition and the distance stored in advance in the storage unit, and an image is formed on the second surface. (9) to (11), wherein, when forming, the determining step determines the amount of movement based on the second condition and the distance stored in advance in the storage unit. The image forming method according to any one of the above.
(13) In the determining step, whether the image is formed on the first surface or the second surface at the image forming position downstream of the conveyance roller with respect to the sheet conveyance direction, the distance, In addition, the moving amount is determined based on at least one of humidity of a place where the image forming apparatus is placed, basis weight of the sheet, and sheet size of the sheet. The image forming method according to any one of (11) to (11).
(14) In any one of (9) to (13), in the determining step, the moving amount is increased as the frictional force generated between the paper and the transport path increases. The image forming method described in 1.
(15) The image forming method according to (12), further including a step of adjusting the first condition or the second condition stored in the storage unit.
(16) The image forming apparatus includes a plurality of paper feed trays,
The image forming method according to (15) above, wherein in the adjusting step, the first condition or the second condition can be individually adjusted for each of the plurality of paper feed trays.

  According to the present invention, the conveying roller pair moves in the paper width direction by a movement amount determined based on the state of the paper and the distance from the reference position in the paper width direction to the edge of the paper. As a result, the difference between the distance from the reference position in the paper width direction to the edge of the paper and the actual amount of paper movement due to the movement of the transport roller pair is smaller than when the paper state is not considered. As a result, it is possible to provide an image forming apparatus that can accurately align an image and a sheet.

1 is a schematic diagram of an image forming apparatus 1. FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus 1. FIG. FIG. 10 is an explanatory diagram when the acquisition unit 90 acquires a deviation amount ΔX of the paper P. FIG. 6 is a relationship diagram between a command value and an actual measurement value when a deviation amount ΔX is a command value. FIG. 6 is a classification diagram in which the paper P is classified into groups according to the state of the paper P in single-sided printing. FIG. 6 is a classification diagram in which paper P is classified into groups according to the state of the paper P in duplex printing. (1) It is a figure which shows the relationship between deviation | shift amount (DELTA) X and command value when the paper P classified into each group of (a), (2) a, (3) a is printed on one side. 3 is a flowchart illustrating a control procedure of a CPU 101 in a first image forming mode. It is the figure which showed an example of the display screen of the operation part 10 for adjustment of command value. It is a flowchart which shows the control procedure of CPU101 in a 2nd image formation mode.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present embodiment described below includes various technically preferable limitations for carrying out the present invention, but the scope of the invention is not limited to the following present embodiment and drawings. . In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from the actual ratios. The paper width direction that appears below is a direction that is perpendicular to the paper transport direction D, which is the travel direction of the paper passing through the transport unit 70 or the re-transport unit 80, and is the width direction of the paper. It is.

  FIG. 1 is a schematic diagram of an image forming apparatus 1 reflecting one aspect of the present invention.

  The image forming apparatus 1 includes an operation unit 10, an automatic document feeding unit 20, a reading unit 30, an image forming unit 40, a fixing unit 50, a paper feeding unit 60, a conveyance unit 70, a reconveying unit 80, and an acquisition unit 90. .

  The operation unit 10 includes, for example, a touch panel formed integrally with a display surface of an LCD (Liquid Crystal Display), a numeric keypad, various selection buttons, a determination button, and the like. The user can operate the operation unit 10 to perform settings relating to printing such as document setting, image quality setting, magnification setting, application setting, output setting, single-sided / double-sided setting, paper setting, and swing amount adjustment. Details of the operation unit 10 will be described below.

  The automatic document feeder 20 is also called an ADF (Auto Document Feeder), and includes an ADF paper feed tray 21 and an ADF discharge tray 22 and automatically feeds a document to read the document. The document set on the ADF paper feed tray 21 is conveyed to the position of the document reading slit glass 31 of the reading unit 30 described below when the determination button of the operation unit 10 is pressed, for example, and the image data of the document Is read. Thereafter, the document is discharged to the ADF discharge tray 22.

  The reading unit 30 includes a document reading slit glass 31, a platen glass 32, a CCD (Charge Coupled Device) 33, a plurality of lenses, and a light source, and is conveyed from the ADF paper supply tray 21 to the document reading slit glass 31. Image data of a document or a document placed on the platen glass 32 is acquired.

  Specifically, when the automatic document feeder 20 is used, the documents are conveyed one by one from the bundle of documents placed on the ADF sheet feed tray 21 to the document reading slit glass 31 of the reading unit 30. The light source irradiates the original with light, and the CCD 33 receives the reflected light reflected from the original to read the image data of the original. When there is a document on the platen glass 32, the light source irradiates the document with light, and the CCD 33 receives reflected light reflected from the document, whereby the document image data is read. The image data acquired in this way is stored in the hard disk 104 described below.

  The image forming unit 40 includes a first image forming unit 40Y that forms a yellow image, a second image forming unit 40M that forms a magenta image, a third image forming unit 40C that forms a cyan image, and a black image A fourth image forming unit 40K for forming the first image. In addition, the image forming unit 40 uses the intermediate transfer belt ITB as a holding unit that holds images formed by the first image forming unit 40Y to the fourth image forming unit 40K, and the image on the intermediate transfer belt ITB on the paper P. A first nip creating roller 47 and a second nip creating roller 48 that form a nip portion N for transfer, and a cleaner unit 49 that collects toner remaining on the intermediate transfer belt ITB after transfer are also provided.

  The fixing unit 50 includes a heating roller 51, a fixing roller 52, a fixing belt 53 stretched by the heating roller 51 and the fixing roller 52, and a pressure roller 54 at a position facing the fixing roller 52 via the fixing belt 53. .

  Hereinafter, an electrophotographic method when the image forming unit 40 and the fixing unit 50 form an image on the paper P will be described. In this description, the first image forming unit 40Y will be described as a representative in order to perform the same functions from the first image forming unit 40Y to the fourth image forming unit 40K.

  The first image forming unit 40Y includes a photosensitive drum 41Y, a charging unit 42Y, an exposure unit 43Y, a developing unit 44Y, a transfer unit 45Y, and a cleaning unit 46Y. In the case of forming a yellow image, the photosensitive drum 41Y charged by the charging unit 42Y is exposed and scanned by a laser beam emitted from the exposure unit 43Y based on the image data. Thereby, an electrostatic latent image is formed on the photosensitive drum 41Y. Next, the photosensitive drum 41Y attracts yellow toner by the developing unit 44Y, and the transfer unit 45Y transfers (primary transfer) this image to the intermediate transfer belt ITB.

  Thereafter, the images of the respective colors formed by the second image forming unit 40M, the third image forming unit 40C, and the fourth image forming unit 40K are superimposed on the yellow image on the intermediate transfer belt ITB. The superimposed images are sent to the nip portion N while being held on the intermediate transfer belt ITB, and transferred (secondary transfer) onto a sheet P conveyed from a sheet feeding unit 60 described below. The fixing unit 50 applies heat and pressure to the paper P to fix the image on the paper P.

  The paper feed unit 60 serves as a storage unit to store various paper P, a plurality of paper trays 61 to 63, pickup rollers 61PR to 63PR for feeding the paper P from each paper tray, and paper in each paper tray. The roller 61FR-63FR for preventing double conveyance of P is provided. The paper tray 63 is a manual paper tray. The number of paper trays is not limited to three. In addition, a single or a plurality of large-capacity paper feeding devices that can store a large-capacity paper P may be installed as necessary.

  The transport unit 70 includes a transport path R1 from each of the paper trays 61, 62, and 63 to the nip N, a discharge transport path R2 for discharging the paper P from the fixing unit 50 to the outside of the image forming apparatus 1a, and a plurality of transport paths R2. It has conveyance roller pairs 71-79. The paper P fed from the paper feed unit 60 is transported to the nip portion N by a transport roller pair necessary for transport among the transport roller pairs 71 to 78 on the transport path R1, and subjected to secondary transfer. Thereafter, the paper P is transported to the fixing unit 50 where the fixing is performed. When the sheet P on which the image is fixed by the fixing unit 50 is discharged outside the apparatus, the pair of transport rollers 79 on the discharge transport path R2 discharges the sheet P to the outside of the apparatus.

  Among the transport roller pairs 71 to 79, the transport roller pair 76 is a roller pair for forming a loop on the paper P by abutting the paper P being transported against the transport roller pair 77, and is referred to as a loop creation roller pair. Is. Hereinafter, the conveyance roller pair 76 is referred to as a loop creation roller pair 76. The transport roller pair 77 is a roller pair that can swing in the paper width direction with the paper P sandwiched therebetween, and is referred to as a registration roller pair. Hereinafter, the conveyance roller pair 77 is referred to as a registration roller pair 77. The loop creation roller pair 76 and the registration roller pair 77 are provided with a mechanism for pressing and releasing the roller pair. This mechanism includes, for example, a cam in contact with the roller shaft and a motor for rotating the cam. Since this detailed description is well known, it will be omitted.

  The reconveying unit 80 includes a reconveying path R3 through which the paper P sent out from the fixing unit 50 circulates in the image forming apparatus 1 and is conveyed again to the nip N, and a reconveying roller as a plurality of reconveying roller pairs. Pair 81-89, loop creation roller pair 76, and registration roller pair 77 are included.

  The acquisition unit 90 includes a sensor such as a line sensor in which photoelectric conversion elements are arranged in a line or an image sensor in which photoelectric conversion elements are arranged in a matrix. The acquisition unit 90 is located upstream of the nip portion N that is the image forming position with respect to the paper transport direction D and downstream of the registration roller pair 77. In other words, the acquisition unit 90 is provided on the conveyance path R1 between the nip portion N and the registration roller pair 77. The acquisition unit 90 acquires a deviation amount ΔX from an end portion reference position, which will be described later, to the end of the paper P with respect to the paper P conveyed from the registration roller pair 77. Details will be described below. The deviation amount ΔX acquired by the acquisition unit 90 is used to determine a command value when the registration roller pair 77 swings the registration. Here, the registration rocking means that the registration roller pair 77 moves in the paper width direction with the paper P sandwiched therebetween.

  FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus 1.

  The image forming apparatus 1 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, a hard disk 104, a network interface 105, an operation unit 10, an automatic document feeder 20, and a reading unit. 30, an image forming unit 40, a fixing unit 50, a paper feeding unit 60, a transport unit 70, a re-transport unit 80, and an acquisition unit 90. These are connected to each other via a bus B.

  The CPU 101 performs control of the above parts and various arithmetic processes according to a program. That is, the CPU 101 corresponds to the control unit of the present invention. As an example, the CPU 101 determines a command value when the registration roller pair 77 swings the registration based on a command value determination program stored in the ROM 102 or the hard disk 104.

  The ROM 102 stores various programs and various data. The RAM 103 temporarily stores programs and data as a work area. The hard disk 104 stores various programs including an operating system and various data. Examples of the program stored in the ROM 102 or the hard disk 104 include a program for translating PDL data received from a personal computer to generate bitmap format image data, and stored bitmap format image data. There are programs for editing or processing.

  The network interface 105 includes various interfaces such as a NIC (Network Interface Card), a MODEM (Modulator-DEModulator), and a USB (Universal Serial Bus), and connects to an external device. For example, the network interface 105 is connected to a personal computer that is an external device, and receives a page description language (PDL) that is a page description language from the personal computer. Note that there may be a plurality of external devices to be connected, and the external device may be a multifunction machine, a printer, a print server, or the like other than a personal computer.

  FIG. 3 is an explanatory diagram when the acquisition unit 90 acquires the deviation amount ΔX of the paper P. In FIG. 3, the paper width W is the width of the paper P in the paper width direction. The edge reference position a is an imaginary line that indicates the reference position of the edge of the paper P that is on the left side with respect to the paper transport direction D when viewed from above the image forming apparatus 1. The deviation amount ΔX is the shortest distance between the end reference position a indicating the end reference position and the paper P. That is, the offset amount ΔX indicates how much the sheet P is offset from the edge reference position a. In the present embodiment, when the deviation amount ΔX is positive, it indicates that the sheet P is shifted to the right side with respect to the sheet conveyance direction D from the edge reference position. Conversely, when the deviation amount ΔX is negative, it indicates that the paper P is shifted to the left side of the edge reference position in the paper conveyance direction D.

  Next, when the registration roller pair 77 is swung by using the deviation amount ΔX as a command value, there is a difference between the command value and an actual measurement value that is a swing amount of the paper swung by the resist swing. Will be described with reference to FIG. Note that the actual measurement values in FIG. 4 are values acquired by the acquisition unit 90 after the resist swinging.

  FIG. 4 is a relationship diagram between a command value and an actual measurement value when the deviation amount ΔX is a command value. The horizontal axis represents the command value, and the vertical axis represents the actual measurement value. A solid line K in the figure is a line showing a case where the command value and the actual measurement value are equal. Originally, it is preferable that the command value and the actual measurement value are equal as indicated by the solid line K, but the command value and the actual measurement value do not actually match.

The square and circle plots shown in FIG. 4 show the relationship between the command value and the actual measurement value when the basis weight of the paper is changed under the constant humidity and the constant paper size in the image forming apparatus 1. The solid line L and the solid line M are linear approximation curves of the respective plots. Specifically, the solid line L indicates a linear approximate curve of plain paper (for example, basis weight is 100 g / m ² ), and the solid line M indicates a linear approximate curve of thick paper (for example, basis weight is 200 g / m ² ). The inventors of the present invention have found that the difference between the command value and the actual measurement value increases as the basis weight increases. The inventors of the present invention have also found that when the paper size is changed under constant humidity and constant basis weight, the difference between the command value and the actual measurement value increases as the paper size increases. The inventors of the present invention have also found that when the humidity changes under a constant paper size and a constant basis weight, the difference between the command value and the actual measurement value increases as the humidity increases. Further, the inventors of the present invention can perform image formation only on the first surface of the paper P in single-sided printing and paper in double-sided printing even when all conditions of humidity, basis weight, and paper size are fixed. It has also been found that the command value differs from the actual measurement value when image formation is performed on the second surface which is the back surface of the first surface of P. From these experimental results, the inventors of the present invention have found that the cause of the mismatch between the command value and the actual measurement value is in the state of the paper P. Specifically, the frictional force generated between the sheet P and the conveyance path (for example, the conveyance path R1 or the re-conveyance path R3) in contact with the sheet P when the resist swings is the difference between the command value and the actual measurement value. The difference is affected.

  Specifically, when the basis weight is different as the state of the paper P, the frictional force between the paper and the conveyance path increases as the basis weight increases, which becomes resistance when the resist swings. In addition, when the paper size is different as the state of the paper P, the frictional force increases as the contact area between the paper P and the conveyance path increases, which becomes a resistance when the resist swings. Further, when the surrounding humidity is different as the state of the paper P, the amount of water contained in the paper increases as the humidity increases, so that the frictional force increases and becomes a resistance when the resist swings. Further, there is a shape of the paper P when the deviation amount ΔX is acquired by the acquisition unit 90 as the state of the paper P. That is, the frictional force changes depending on whether the paper P is positioned on the transport path R1 or the re-transport path R3 when the registration is swung. For example, in the image forming apparatus 1, the transport path R1 and the re-transport path R3 merge in the vicinity of the transport roller 76, but the shape of the transport path before the merge has a curvature in the re-transport path R3 rather than the transport path R1. large. Therefore, the paper P is bent more greatly in the case where the second surface of the paper P is subjected to resist swinging than in the case where the first surface of the paper P is subjected to resist swinging in single-sided printing. The contact between the paper P and the re-transport path R3 is strengthened by the paper P. As a result, the frictional force between the paper P and the re-transport path R3 is higher than the frictional force between the paper P and the transport path R1. Therefore, the frictional force changes when the shape of the paper P when the deviation amount ΔX is acquired by the acquisition unit 90 is different.

  As described above, the state of the sheet P includes the humidity, the basis weight, the sheet size, and the shape of the sheet P when the deviation amount ΔX is acquired by the acquisition unit 90. However, in the following, for the sake of brevity, the paper size, basis weight, and the shape of the paper P when the deviation amount ΔX is acquired by the acquisition unit 90 will be handled.

  FIG. 5 is a classification diagram in which the paper P is classified into groups according to the state of the paper P in single-sided printing. Specifically, in the case of performing image formation only on the first surface of the paper P in single-sided printing, the paper P is determined according to the basis weight and the paper size (1) a, (2) a, (3) a There are three groups.

  Similarly, FIG. 6 is a classification diagram in which the paper P is classified into groups according to the state of the paper P in double-sided printing. Specifically, when image formation is performed on the second side, which is the back side of the first side of the paper P in double-sided printing, the paper P is (1) b, (2) according to the basis weight and the paper size. b and (3) are classified into three groups b. In addition, when image formation is performed on the first surface of the paper P in double-sided printing, three of (1) a, (2) a, and (3) a are applied.

The paper size in FIGS. 5 and 6 indicates the size of the paper P (paper width size) in the paper width direction. However, the paper size is not limited to this, and may be the size of the paper P in the paper transport direction D, for example. In single-sided printing and double-sided printing, the paper width size is divided into 200 mm and 300 mm, and the basis weight is divided into 120 g / m ² and 250 g / m ^2. These dividing positions depend on the specifications of the apparatus. It can be changed as appropriate.

  Next, the relationship between the deviation amount ΔX of the paper P and the command value in each group described above is shown. The command value data for the deviation amount ΔX is stored in advance in the hard disk 104, for example. That is, the hard disk 104 corresponds to the storage unit of the present invention. In the following description, since the description overlaps between single-sided printing and double-sided printing, only single-sided printing will be described.

  FIG. 7 is a diagram illustrating the relationship between the deviation amount ΔX and the command value when the sheets P classified into the groups (1) a, (2) a, and (3) a are printed on one side. The intercept n and intercept n ′ in the figure are values determined by, for example, rattling of the drive unit that drives the registration roller pair 77.

  First, the upper right region in FIG. 7 will be described. In this region, since the deviation amount ΔX is positive, the sheet P is shifted to the right side of the end reference position with respect to the sheet conveyance direction D. Therefore, at the time of the registration swing, the registration roller pair 77 swings in a direction (leftward with respect to the paper transport direction D) to return the paper P to the end reference position by the command value with the paper P being sandwiched. To do. The command value here is different from the deviation amount ΔX, and is a value larger than the deviation amount ΔX. Specifically, the command values of the lines corresponding to (1) a, (2) a, and (3) a are higher than the deviation amount ΔX. In (1) a, (2) a, and (3) a, the frictional force generated between the paper P and the transport path R1 increases as the number increases. Therefore, the slope m of the line corresponding to each of (1) a, (2) a, and (3) a increases as the number increases.

  Next, the lower left area of FIG. 7 will be described. In the lower left area of FIG. 7, the deviation amount ΔX is negative, so that the paper P is shifted to the left in the paper transport direction D from the edge reference position in the paper width direction. Therefore, at the time of the registration swing, the registration roller pair 77 swings in a direction (rightward with respect to the paper transport direction D) to return the paper P to the end reference position by the command value with the paper P being sandwiched. To do. The command value here is different from the deviation amount ΔX, and has a larger absolute value than the deviation amount ΔX. Specifically, the absolute values of the command values of the lines corresponding to (1) a ′, (2) a ′, and (3) a ′ are higher than the absolute value of the deviation amount ΔX. In (1) a ', (2) a', and (3) a ', the frictional force generated between the paper P and the transport path R1 increases as the number increases. For this reason, the slope m ′ of the line corresponding to each of (1) a, (2) a, and (3) a increases as the number increases.

  As described above, in the image forming apparatus 1, when the deviation amount ΔX is negative, the group of sheets P is not (1) a, (2) a, (3) a but (1) a ′, (2) a ′ and (3) a ′ are applied. This is because the direction in which the registration roller pair 77 swings changes depending on whether the deviation amount ΔX is positive or negative. That is, in (1) a ′, (2) a ′, and (3) a ′, it is considered that the frictional force between the paper P and the conveyance path changes due to the change in the swinging direction of the registration roller pair 77. ing. Note that the present invention is not limited to this, and the group of sheets P may be the same when the deviation amount ΔX is plus or minus.

  As described above, in the image forming apparatus 1, the command value is determined based on the state of the paper P and the deviation amount ΔX. Therefore, the difference between the deviation amount ΔX and the command value is smaller than when the registration roller pair 77 is swung with the deviation amount ΔX itself as the command value (when the state of the paper P is not considered). As a result, it is possible to provide an image forming apparatus that can accurately align an image and a sheet.

  Next, two image forming modes for adjusting the command value provided in the image forming apparatus 1 will be described. These image forming modes are stored in the ROM 102 or the hard disk 104 as a command value determination program. The difference between the two image forming modes is in the adjustment method of the command value m.

  FIG. 8 is a flowchart showing a control procedure of the CPU 101 in the first image forming mode. In the first image forming mode, the command value is manually adjusted by the user.

  First, the CPU 101 acquires information about the state of the paper P when the user determines a paper to be used for image formation (S801). For example, when a determination button for instructing the CPU 101 to execute image formation via the operation unit 10 is pressed by the user, the CPU 101 determines the sheet P used for image formation and relates to the state of the sheet P. Information is acquired from the hard disk 104. In addition, when the user selects the paper P or the paper feed unit 60 to be used by the user via the operation unit 10, the CPU 101 determines the paper P used for image formation, and stores information regarding the state of the paper P on the hard disk 104. May be obtained from When receiving the PDL data from the personal computer, the CPU 101 determines the paper P to be used for image formation from the received PDL data, and acquires information on the state of the paper from the hard disk 104.

The CPU 101 confirms whether the basis weight is 120 g / m ² or more (S802). When the basis weight is less than 120 g / m ² (“No” in S802), the CPU 101 confirms whether the paper width size is 300 mm or more (S803). If the paper width size is less than 300 mm in S803 (“No” in S803), the CPU 101 confirms whether or not double-sided printing is performed (S804). In S804, when it is single-sided printing instead of double-sided printing (“No” in S804), the CPU 101 determines the group of paper P as (1) a (S805). On the other hand, in the case of duplex printing in S804 (“Yes” in S804), the CPU 101 determines that the first side group of the paper P is (1) a and the second side group is (1) b (S806). .

When the basis weight is 120 g / m ² or more in S802 (“Yes” in S802), the CPU 101 further checks whether the basis weight is 250 g / m ² or more (S807). If the basis weight is less than 250 g / m ² (“No” in S807), the CPU 101 confirms whether the paper width size is 300 mm or more (S808). If the paper width size is less than 300 mm in S808 (“No” in S808), or if the paper width size is 300 mm or more in S803 (“Yes” in S803), the CPU 101 confirms whether or not duplex printing is performed ( S809). In S809, when the printing is single-sided printing instead of double-sided printing (“No” in S809), the CPU 101 determines the group of the paper P as (2) a (S810). On the other hand, if double-sided printing is performed in S809 (“Yes” in S809), the CPU 101 determines that the first side group of the paper P is (2) a and the second side group is (2) b (S811). .

When the basis weight is 250 g / m ² or more in S807 (“Yes” in S807) or the paper width size is 300 mm or more in S808 (“Yes” in S808), the CPU 101 determines whether double-sided printing is performed. Confirm (S812). If the printing is not single-sided printing but single-sided printing in S812 (“No” in S812), the CPU 101 determines the group of paper P as (3) a (S813). On the other hand, if double-sided printing is performed in S812 (“Yes” in S812), the CPU 101 determines the group of the first side of the paper P as (3) a and the group of the second side as (3) b (S814). .

  After the CPU 101 determines the group of sheets P as described above, the CPU 101 executes a test print to adjust the command value (S815). Then, the CPU 101 waits until the inclination m, inclination m ′, intercept n, and intercept n ′ for determining the command value via the operation unit 10 are determined by the user (S816). That is, the CPU 101 waits until the command value is adjusted by the user. During standby (“No” in S816), the user designates the inclination m, the inclination m ′, the intercept n, and the intercept n ′ with reference to the test print result and the screen displayed on the operation unit 10. The display screen of the operation unit 10 for adjusting the command value will be described below.

  When the user specifies the slope m, slope m ′, intercept n and intercept n ′ in S816 (“YES” in S816), the CPU 101 controls each part of the image forming apparatus 1 and starts image formation (S817). ). The CPU 101 calculates a command value based on the value specified in S816 when the image is formed in S817. Thereafter, the CPU 101 confirms whether all image formation has been completed (S818). If all image formations are not completed in S818 (No in S818), the CPU 101 continues to perform image formation (S817). On the other hand, if all image formation has been completed in S818 (Yes in S818), the CPU 101 ends execution of the program relating to the first image formation mode.

  FIG. 9 is a diagram illustrating an example of a display screen of the operation unit 10 for adjusting the command value. The operation unit 10 includes various setting buttons 101 for performing basic settings relating to image formation, a copy button 102 as a determination button for executing image formation, a scan button 103 for executing scanning and faxing, copying and scanning. A reset button 104 for resetting all the cancellations and settings, a comment column 105 for displaying a user operation support comment, and a display screen 110 for informing the user of a screen as necessary are provided.

  Here, various items displayed on the display screen 110 in S816 of FIG. 8 will be described. These items are displayed when the user designates various setting buttons 101 and then designates, for example, a button relating to the setting of the paper feed tray. The display screen 110 includes a paper feed tray specifying unit 111, a paper size specifying unit 112, a basis weight specifying unit 113, a swing amount adjusting unit (command value adjusting unit) 114, a front swing amount adjusting unit 115, a back swing amount adjusting unit 116, A description unit 117, a cancel button 118, and an OK button 119 are provided. A paper feed tray designating unit 111 designates a paper feed tray to be set. The paper size designation unit 112 and the basis weight designation unit 113 are for setting the paper size and the basis weight for the paper feed tray designated by the paper feed tray designation unit 111, respectively. These can be set roughly, such as more than a certain value or less than a certain value, or detailed values can be specified.

  The swing amount adjustment unit 114 is for adjusting the inclination m, the inclination m ′, the intercept n, and the intercept n ′. That is, the swing amount adjusting unit 114 corresponds to the adjusting unit of the present invention. When the swing amount adjusting unit 114 is designated by the user, a front swing amount adjusting unit 115, a back swing amount adjusting unit 116, and an explanation unit 117 are displayed in the display screen 110. Then, for example, the user adjusts the command value with the front rocking amount adjusting unit 115 or the back rocking amount adjusting unit 116 while referring to the explanation unit 117. In the front rocking amount adjustment unit 115, after the user touches the area on the right side of each of the inclination m, the inclination m ', the intercept n, and the intercept n', the user inputs a value with the numeric keypad on the lower right. When the value input is completed, the calculation result is automatically displayed in the area to the right of “Y” or “Y ′”. Then, the user confirms whether the adjustment of the command value is appropriate with reference to this result. Thereafter, by specifying the OK button 119, the inclination m, the inclination m ', the intercept n, and the intercept n' are determined, and the adjustment of the command value is completed. On the other hand, when canceling the adjustment of the command value, the user designates the cancel button 118. Further, the adjustment of the command value relating to the second surface, which is the back surface of the first surface of the paper P, is performed by the user specifying the back rocking amount adjustment unit 116.

  Finally, the second image forming mode will be described. FIG. 10 is a flowchart showing a control procedure of the CPU 101 in the second image forming mode. In the second image forming mode, the command value is automatically adjusted by the CPU 101.

  About S901-S914, since it is the same as that of S801-S814, description is abbreviate | omitted. After the group of paper P is determined by the CPU 101 in S901 to S914, the CPU 101 executes image formation for adjusting the command value (S915). Then, the CPU 101 executes registration rocking for the paper P conveyed from the paper feed unit 60 (S916), and then confirms the amount of deviation of the paper P after the resist rocking by the acquisition unit 90 (S917). . Then, the CPU 101 determines the inclination m, the inclination m ′, the intercept n, and the intercept n for the next sheet to be conveyed from the difference between the command value used in the registration swing in S916 and the deviation amount acquired in S917. 'Is determined (S918). That is, the CPU 101 adjusts the command value on behalf of the user. Thereafter, the CPU 101 confirms whether all image formation has been completed (S919). If all image formations have not been completed in S919 (No in S919), the CPU 101 continues to perform image formation using the command value adjusted in S918 (S915). On the other hand, if all image formation has been completed in S919 (Yes in S919), the CPU 101 ends the execution of the program relating to the second image formation mode.

  Thus, the image forming apparatus 1 can adjust the command value manually or automatically. Therefore, even when the command value is not correct, it is possible to improve the accuracy of alignment between the image and the paper. When the command value is manually adjusted, the command value can be adjusted while visually confirming the result of alignment between the image and the paper, so that the user's specific request can be satisfied. On the other hand, when the command value is automatically adjusted, the command value is sequentially applied to the next paper P used for the adjustment, so that it is possible to flexibly cope with the humidity change due to the season.

  Although the present embodiment has been described above, the specific configuration is not limited to that shown in the embodiment, and modifications and additions within the scope not departing from the gist of the present invention are included in the present invention. It is.

  In the present embodiment, the command value is larger than the deviation amount ΔX with respect to the deviation amount ΔX, but is not limited thereto. For example, depending on the specifications of the apparatus, the deviation amount ΔX may be a small value in the case of thin paper or plain paper (paper whose basis weight is smaller than that of thick paper).

  In the present embodiment, the group classification is divided between single-sided printing and double-sided printing according to the state of the paper P, but the same group is applied to single-sided printing and double-sided printing. May be.

  In this embodiment, an image forming apparatus that forms a color image on a sheet is described. However, the present invention may be applied to an image forming apparatus that forms a monochrome image on a sheet.

  In this embodiment, the image forming apparatus in which the image forming method is the electrophotographic method has been described. However, the present invention may be applied to an ink jet type image forming apparatus.

  The means and method for performing various processes in the image forming apparatus 1 according to the present embodiment can be realized by either a dedicated hardware circuit or a programmed computer. The program may be provided by a computer-readable paper such as a flexible disk and a CD-ROM, or may be provided online via a network such as the Internet. In this case, the program recorded on the computer-readable paper is usually transferred to and stored in a storage unit such as a hard disk. The program may be provided as a single application software, or may be incorporated in the software of the apparatus as one function of the printing system.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Operation part 20 Automatic document feeder 30 Reading part 40 Image forming part 40Y 1st image forming part 40M 2nd image forming part 40C 3rd image forming part 40K 4th image forming part N Nip part ITB Intermediate transfer Belt 50 Fixing unit 60 Paper feeding unit 70 Conveying unit 74 Conveying roller pair 75 Conveying roller pair 76 Loop creating roller pair 77 Registration roller pair 80 Reconveying unit 101 CPU
102 ROM
103 RAM
104 Hard disk 105 Network interface a Edge reference position ΔX Misalignment

Claims (16)

An image forming apparatus capable of double-sided printing that forms an image on a second surface of the paper after an image is formed on the first surface of the paper,
An image forming unit that forms an image on a sheet at an image forming position;
A transport path for transporting the paper to the image forming position;
Moving the paper in the paper width direction by moving in the paper width direction, which is upstream of the image forming unit with respect to the paper transport direction and sandwiching the paper, and perpendicular to the paper transport direction A pair of transport rollers to be displaced to
In duplex printing, before the transport roller pair moves, an image is formed on either the first surface or the second surface at the image forming position downstream of the transport roller pair in the paper transport direction. And the distance from the reference position in the paper width direction to the edge of the paper on the upstream side of the image forming position and the downstream side of the pair of transport rollers with respect to the paper transport direction. A control unit that determines a movement amount of the conveyance roller pair and performs control for moving the conveyance roller pair in the paper width direction by the determined movement amount;
The control unit determines the movement amount based on the distance when forming an image on the second surface to be larger than the movement amount based on the distance when forming an image on the first surface. An image forming apparatus.   In addition to the distance and whether the image is formed on the first surface or the second surface at the image forming position downstream of the transport roller with respect to the paper transport direction, the control unit, The image forming apparatus according to claim 1, wherein the amount of movement is determined based on whether the transport roller is moved in a first direction or a second direction in the paper width direction. A line sensor in which photoelectric conversion elements are arranged in a line, or an image sensor in which photoelectric conversion elements are arranged in a matrix,
The image forming apparatus according to claim 1, wherein the line sensor or the image sensor acquires a distance from a reference position in the sheet width direction to an end of the sheet. The first condition for determining the amount of movement when forming an image on the first surface based on the distance, and the amount of movement when forming an image on the second surface are determined based on the distance. A storage unit for storing in advance the second condition for
When forming an image on the first surface, the control unit determines the movement amount based on the first condition and the distance stored in advance in the storage unit, and forms an image on the second surface. 4. The image formation according to claim 1, wherein the movement amount is determined based on the second condition and the distance stored in advance in the storage unit. apparatus.   In addition to the distance and whether the image is formed on the first surface or the second surface at the image forming position downstream of the transport roller with respect to the paper transport direction, the control unit, 4. The movement amount is determined based on at least one of humidity of a place where the image forming apparatus is placed, basis weight of the paper, and paper size of the paper. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the control unit increases the movement amount as a frictional force generated between the sheet and the conveyance path increases.   The image forming apparatus according to claim 4, further comprising an adjustment unit that adjusts the first condition or the second condition stored in the storage unit. With multiple paper trays,
The image forming apparatus according to claim 7, wherein the adjustment unit is capable of individually adjusting the first condition or the second condition for each of the plurality of paper feed trays. After the image is formed on the first side of the paper, double-sided printing is possible in which an image is formed on the second side of the paper on which the image is formed on the first side,
An image forming unit that forms an image on a sheet at an image forming position;
A transport path for transporting the paper to the image forming position;
Moving the paper in the paper width direction by moving in the paper width direction, which is upstream of the image forming unit with respect to the paper transport direction and sandwiching the paper, and perpendicular to the paper transport direction A pair of transport rollers to be displaced to
An image forming method in an image forming apparatus comprising:
In double-sided printing, whether the image is formed on the first surface or the second surface at the image forming position downstream of the transport roller with respect to the paper transport direction, the reference position in the paper width direction And the distance to the end of the sheet upstream of the image forming position and downstream of the pair of transport rollers with respect to the sheet transport direction is determined. Steps,
Moving the transport roller pair in the paper width direction by the determined amount of movement, and
In the determining step, the movement amount based on the distance when forming an image on the second surface is determined to be larger than the movement amount based on the distance when forming an image on the first surface. An image forming method.   In the determining step, in addition to the distance and whether the image is formed on the first surface or the second surface at the image forming position downstream of the transport roller with respect to the paper transport direction. The image forming method according to claim 9, wherein the amount of movement is determined based on whether the transport roller is moved in a first direction or a second direction in the paper width direction. The image forming apparatus includes a line sensor in which photoelectric conversion elements are arranged in a line, or an image sensor in which photoelectric conversion elements are arranged in a matrix.
11. The method according to claim 9, further comprising: obtaining a distance from a reference position in the paper width direction to an edge of the paper by the line sensor or the image sensor before the determining step. The image forming method described. The image forming apparatus includes: a first condition for determining the amount of movement when forming an image on the first surface based on the distance; and the amount of movement when forming an image on the second surface. A storage unit for storing in advance a second condition for determining based on the distance;
When forming an image on the first surface, in the determining step, the movement amount is determined based on the first condition and the distance stored in advance in the storage unit, and an image is formed on the second surface. 12. When forming, in the step of determining, the amount of movement is determined based on the second condition and the distance stored in advance in the storage unit. The image forming method according to one item.   In the determining step, in addition to the distance and whether the image is formed on the first surface or the second surface at the image forming position downstream of the transport roller with respect to the paper transport direction. The movement amount is determined based on at least one of humidity of a place where the image forming apparatus is placed, basis weight of the paper, and paper size of the paper. The image forming method according to any one of the above.   The image forming method according to claim 9, wherein, in the determining step, the movement amount is increased as a frictional force generated between the sheet and the conveyance path increases. .   The image forming method according to claim 12, further comprising a step of adjusting the first condition or the second condition stored in the storage unit. The image forming apparatus includes a plurality of paper feed trays,
The image forming method according to claim 15, wherein in the adjusting step, the first condition or the second condition can be individually adjusted for each of the plurality of paper feed trays.

Images