Image forming apparatus

Abstract

To accurately perform calibration without reducing productivity.SOLUTION: An image forming apparatus comprises image forming units, an intermediate transfer belt, primary transfer rollers, a secondary transfer roller, image density sensors, and a sensor opposing member. When the length in the width direction of the primary transfer roller is defined as Wa, the length in the width direction of the sensor opposing member as Wb, the dimension in the width direction of the intermediate transfer belt as Wc, and the maximum dimension in the width direction of a sheet as Wd, the relationship of Wd≤Wa<Wb≤Wc or the relationship of Wd≤Wa<Wc≤Wb is satisfied. A transfer position of a test pattern image is a position on the inside in the width direction of the intermediate transfer belt at a predetermined distance from the end edge in the width direction of the intermediate transfer belt. The predetermined distance is twice or more of the distance in the width direction from the end edge in the width direction of the intermediate transfer belt to the end edge in the width direction of the primary transfer roller.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] The image forming apparatus includes an intermediate transfer belt. The intermediate transfer belt carries an image formed using toner and rotates to transfer the image onto a sheet. Such an image forming apparatus is disclosed in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-59336 A Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, to calibrate image density, etc., a test pattern image is transferred to the outer peripheral surface of the intermediate transfer belt at an end in the width direction perpendicular to the rotation direction of the intermediate transfer belt. Then, a reflective optical sensor as an image density sensor is used to detect the density of the test pattern image on the intermediate transfer belt, etc. With this method, calibration can be performed during execution of a print job, so productivity is not impaired.

[0005] However, if the end of the intermediate transfer belt in the width direction is deformed (for example, bent), the positional relationship between the intermediate transfer belt and the image density sensor may shift, which may cause an inconvenience that the detection by the image density sensor becomes inaccurate, i.e., an inconvenience that the calibration cannot be performed accurately.

[0006] The present invention has been made to solve the above problems, and an object thereof is to provide an image forming apparatus capable of accurately performing calibration related to image formation without reducing productivity.

Means for Solving the Problems

[0007] To achieve the above object, an image forming apparatus according to an aspect of the present invention includes an image forming unit having an image carrier and causing an image formed using toner to be carried on the image carrier, an endless intermediate transfer belt having an outer peripheral surface to which an image is primarily transferred from the image carrier and rotating while carrying the transferred image, a primary transfer roller rotatable about an axis extending in a width direction orthogonal to a rotation direction of the intermediate transfer belt and positioned inside the width direction from an edge in the width direction of the intermediate transfer belt and pressing against the image carrier via the intermediate transfer belt, a secondary transfer roller rotatable about an axis extending in the width direction and forming a transfer nip with an outer peripheral surface of the intermediate transfer belt and secondarily transferring an image to a sheet passing through the transfer nip, an image density sensor disposed at an interval from the outer peripheral surface of the intermediate transfer belt, irradiating light on the intermediate transfer belt, and outputting a value corresponding to an amount of reflected light from the intermediate transfer belt, and a sensor facing member disposed on an inner peripheral side of the intermediate transfer belt, extending in the width direction so as to cross a position facing the image density sensor, and contacting an inner peripheral surface of the intermediate transfer belt. When performing calibration related to image formation, the image forming unit primarily transfers a printed image to be secondarily transferred to a sheet to a transfer region of the intermediate transfer belt while primarily transferring a test pattern image to be a detection target of the image density sensor to a region outside the transfer region in the width direction. When the length in the width direction of the primary transfer roller is Wa, the length in the width direction of the sensor facing member is Wb, the dimension in the width direction of the intermediate transfer belt is Wc, and the maximum dimension in the width direction of the sheet is Wd, the relationship of Wd ≦ Wa < Wb ≦ Wc or the relationship of Wd ≦ Wa < Wc ≦ Wb is satisfied. The transfer position of the test pattern image is a position separated by a predetermined distance inward in the width direction from an edge in the width direction of the intermediate transfer belt. The predetermined distance is not less than twice the distance in the width direction from an edge in the width direction of the intermediate transfer belt to an edge in the width direction of the primary transfer roller.

Effects of the Invention

[0008] In the present invention, calibration related to image formation can be performed accurately without reducing productivity. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram of an image forming unit according to an embodiment. [Diagram 3] FIG. 2 is a diagram illustrating a primary transfer roller and its periphery according to an embodiment. [Figure 4] 1 is a block diagram of an image forming apparatus according to an embodiment. [Diagram 5] FIG. 2 is a diagram illustrating a sensor facing member and its periphery according to an embodiment. [Figure 6] 4A and 4B are diagrams illustrating the positions of print areas and test areas of an intermediate transfer belt according to an embodiment. [Figure 7] 11A and 11B are diagrams for explaining inconvenience caused by a deformed portion of the intermediate transfer belt riding on a sensor facing member; [Figure 8] 11A and 11B are diagrams for explaining meandering correction performed by a meandering correction mechanism according to an embodiment. [Figure 9] 5A and 5B are schematic diagrams of a meandering correction mechanism according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described using a tandem color laser printer as an example. Note that the present invention is not limited to printers, but can also be applied to multifunction machines that have a copy function, etc.

[0011] <Configuration of Image Forming Apparatus> The configuration of an image forming apparatus 100 according to this embodiment is shown in Fig. 1. The image forming apparatus 100 is placed on a flat floor surface FL. The up-down direction of the image forming apparatus 100 is perpendicular to the floor surface FL.

[0012] The image forming apparatus 100 includes a main transport path MP. The image forming apparatus 100 also includes a sheet cassette CA. The sheet cassette CA is detachable from the main body of the image forming apparatus 100. The sheet cassette CA accommodates sheets S to be used in a print job. The main transport path MP runs from a supply position P0 for the sheet S from the sheet cassette CA, through a transfer position P1 and a fixing position P2, to an output tray ET.

[0013] In a print job, a sheet S in a sheet cassette CA is supplied from a supply position P0 to a main transport path MP. The sheet S is transported along the main transport path MP. An image is formed using toner. The image is then printed on the sheet S during transport. In other words, a transfer process of the image onto the sheet S during transport is performed at a transfer position P1. A fixing process of the image onto the sheet S is performed at a fixing position P2.

[0014] The image forming apparatus 100 includes an image forming unit 1. There are four image forming units 1. The four image forming units 1 correspond to the colors cyan, magenta, yellow, and black, respectively. The four image forming units 1 form images using toner of the corresponding color. The following description focuses on one image forming unit 1 and explains its configuration, but the configurations of the four image forming units 1 are the same as each other. Therefore, the description of the configurations of the other image forming units 1 will be omitted, as the following description is incorporated herein.

[0015] Details of the image forming unit 1 are shown in FIG. 2. The image forming unit 1 is equipped with a photoconductor drum 11. The photoconductor drum 11 corresponds to an "image carrier." The photoconductor drum 11 is supported so as to be rotatable about an axis extending in one direction (a direction perpendicular to the paper surface of FIG. 2). The image forming unit 1 causes an image formed using toner to be carried on the outer circumferential surface of the photoconductor drum 11. The photoconductor drum 11 rotates carrying a toner image on its outer circumferential surface.

[0016] The image forming unit 1 further includes a charging device 12, an exposure device 13, a developing device 14, and a cleaning device 15. When the image forming unit 1 forms an image, the photoconductor drum 11 rotates. The charging device 12 charges the outer peripheral surface of the photoconductor drum 11. The exposure device 13 exposes the outer peripheral surface of the photoconductor drum 11 to light, and forms an electrostatic latent image on the outer peripheral surface of the photoconductor drum 11. The developing device 14 supplies toner to the outer peripheral surface of the photoconductor drum 11, and develops the electrostatic latent image into a toner image. The toner image on the outer peripheral surface of the photoconductor drum 11 is primarily transferred to an intermediate transfer belt 2, which will be described later. The cleaning device 15 removes toner that has not been transferred to the intermediate transfer belt 2 and remains on the outer peripheral surface of the photoconductor drum 11.

[0017] 1, the image forming apparatus 100 includes an intermediate transfer belt 2. The intermediate transfer belt 2 is an endless belt. The intermediate transfer belt 2 is supported so as to be rotatable. The intermediate transfer belt 2 is one component of an intermediate transfer unit.

[0018] In the following description, the rotation direction of the intermediate transfer belt 2 is referred to as the belt rotation direction, and the belt rotation direction is denoted by the symbol Dr. The direction perpendicular to the belt rotation direction Dr is referred to as the width direction, and the width direction is denoted by the symbol Dw. The width direction Dw is a direction perpendicular to the up-down direction of the image forming apparatus 100 (i.e., the horizontal direction). The width direction Dw corresponds to the main scanning direction, and the belt rotation direction Dr corresponds to the sub-scanning direction. In Figures 1 and 2, the direction perpendicular to the paper surface is the width direction Dw.

[0019] The intermediate transfer belt 2 includes, for example, a base layer and a rubber layer (i.e., an elastic layer) on the base layer. The base layer may be made of polyimide resin or PVDF (polyvinylidene fluoride) mixed with a conductive material such as an ion conductive material and conductive carbon to impart conductivity. The rubber layer may be made of hydrin rubber, chloroprene rubber, polyurethane rubber, or the like. A coating layer may be provided to protect the rubber layer. The coating layer may be made of acrylic, silicone, fluororesin, or the like.

[0020] The image forming apparatus 100 includes a plurality of tension rollers 3 as one component of the intermediate transfer unit. The plurality of tension rollers 3 are supported rotatably around an axis extending in the width direction Dw. The plurality of tension rollers 3 are disposed on the inner circumferential side of the intermediate transfer belt 2. The plurality of tension rollers 3 contact the inner circumferential surface of the intermediate transfer belt 2. The plurality of tension rollers 3 rotatably suspend the intermediate transfer belt 2. The number of tension rollers 3 to be installed is not particularly limited and may be appropriately changed depending on the size of the intermediate transfer belt 2, etc.

[0021] One of the multiple tension rollers 3 is connected to a belt motor BM (see FIG. 4). In the following description, the tension roller 3 connected to the belt motor BM is referred to as a drive roller, and the drive roller is denoted by the reference symbol 30. The drive roller 30 rotates by a driving force transmitted from the belt motor BM. The intermediate transfer belt 2 rotates in response to the rotation of the drive roller 30. The other tension rollers 3 rotate in response to the intermediate transfer belt 2.

[0022] The image forming apparatus 100 includes primary transfer rollers 4 as one component of the intermediate transfer unit. There are four primary transfer rollers 4. One primary transfer roller 4 is assigned to each of the colors cyan, magenta, yellow, and black. Each primary transfer roller 4 is disposed on the inner circumferential side of the intermediate transfer belt 2. Each primary transfer roller 4 faces a photoconductor drum 11 carrying an image of the corresponding color via the intermediate transfer belt 2. Each primary transfer roller 4 is pressed against the photoconductor drum 11 carrying an image of the corresponding color via the intermediate transfer belt 2.

[0023] 3, each primary transfer roller 4 is located inside the edge 2a of the intermediate transfer belt 2 in the width direction Dw. Of both end edges 4a of each primary transfer roller 4 in the width direction Dw, the edge 4a on one side is located inside the edge 2a on one side in the width direction Dw of the intermediate transfer belt 2, and the edge 4a on the other side is located inside the width direction Dw of the edge 2a on the other side in the width direction Dw of the intermediate transfer belt 2. Each primary transfer roller 4 contacts the inner circumferential surface of the intermediate transfer belt 2 between both end edges 2a of the intermediate transfer belt 2 in the width direction Dw.

[0024] Further, each primary transfer roller 4 is supported rotatably around an axis extending in the width direction Dw on the inner peripheral side of the intermediate transfer belt 2. For example, the image forming apparatus 100 includes a pair of unit frames Fr as components of the intermediate transfer unit. The pair of unit frames Fr face each other in the width direction Dw with the intermediate transfer belt 2 therebetween. One end and the other end of a rotating shaft 40 are rotatably supported by each of the pair of unit frames Fr. One rotating shaft 40 is assigned to each primary transfer roller 4. Each primary transfer roller 4 is attached to the corresponding rotating shaft 40. Each primary transfer roller 4 rotates together with the corresponding rotating shaft 40.

[0025] 3 corresponds to a cross section of the primary transfer roller 4 and its periphery cut by a plane parallel to the width direction Dw. Fig. 3 is a schematic illustration of the primary transfer roller 4 and its periphery, and does not directly show the actual dimensions and shapes.

[0026] Returning to FIG. 1, the image forming apparatus 100 includes a secondary transfer roller 5. The secondary transfer roller 5 is supported rotatably about an axis extending in the width direction Dw. The secondary transfer roller 5 is in pressure contact with the outer circumferential surface of the intermediate transfer belt 2 at a transfer position P1. The secondary transfer roller 5 sandwiches the intermediate transfer belt 2 between itself and the drive roller 30, and forms a transfer nip between itself and the outer circumferential surface of the intermediate transfer belt 2. This forms the transfer nip at the transfer position P1. The main transport path MP passes through the transfer nip.

[0027] In a print job, a sheet S is transported toward a transfer position P1 (i.e., a transfer nip). The sheet S passes through the transfer nip during transport. The intermediate transfer belt 2 contacts the sheet S during transport downstream of the contact position with each photoconductor drum 11 in the belt rotation direction Dr.

[0028] Each image forming unit 1 forms an image using toner of a corresponding color. Each primary transfer roller 4 primarily transfers the image onto the outer circumferential surface of the intermediate transfer belt 2.

[0029] The intermediate transfer belt 2 rotates while carrying on its outer circumferential surface the images that are primarily transferred from the photoreceptor drums 11. While the sheet S is passing through the transfer nip, the sheet S comes into contact with the outer circumferential surface of the intermediate transfer belt 2. A transfer voltage is applied to the secondary transfer roller 5 from a transfer voltage power source (not shown). The secondary transfer roller 5 forms a transfer electric field between itself and the intermediate transfer belt 2, thereby performing a second transfer of the image onto the sheet S that is passing through the transfer nip.

[0030] The image forming apparatus 100 includes a cleaning unit 200. The cleaning unit 200 faces the outer circumferential surface of the intermediate transfer belt 2 downstream of the transfer position P1 in the belt rotation direction Dr. The cleaning unit 200 cleans the outer circumferential surface of the intermediate transfer belt 2.

[0031] The image forming apparatus 100 includes a fixing unit FX. The fixing unit FX includes a heating roller and a pressure roller. The fixing unit FX is disposed at a fixing position P2. The heating roller has a built-in heater. The pressure roller is in pressure contact with the heating roller. The heating roller and the pressure roller are in pressure contact with each other to form a fixing nip at the fixing position P2.

[0032] In a print job, the sheet S passes through the fixing position P2. That is, the sheet S is sandwiched in the fixing nip. The fixing unit FX heats the sheet S as it passes through the fixing position P2. Pressure is applied to the sheet S at the fixing position P2. The fixing unit FX applies heat and pressure to the sheet S to fix the toner image to the sheet S. The sheet S after the fixing process is discharged to an output tray ET.

[0033] The image forming apparatus 100 includes a transport unit, the reference numerals of which are omitted. The transport unit includes a transport roller pair. The transport roller pair includes a pair of rollers. The pair of rollers has a transport nip between the rollers. The transport roller pair rotates to transport the sheet S that has entered the transport nip. The transport unit transports the sheet S along a main transport path MP. The transport unit also transports the sheet S along a double-sided printing transport path DP, which will be described later.

[0034] The image forming apparatus 100 is capable of executing a double-sided print job in which an image is printed on both sides of a sheet S, in addition to a single-sided print job in which an image is printed on only one side of the sheet S. In order to execute a double-sided print job, the image forming apparatus 100 is provided with a double-sided print transport path DP.

[0035] The double-sided printing transport path DP branches off from the main transport path MP at a branching position P3 downstream of the fixing position P2 in the sheet transport direction of the main transport path MP, and merges with the main transport path MP at a merging position P4 upstream of the transfer position P1 in the sheet transport direction of the main transport path MP.

[0036] When the job to be executed is a single-sided print job, the sheet S passes through the transfer nip only once, and a single transfer process is performed on the sheet S while it is passing through the transfer nip. After the first transfer process, the sheet S is discharged directly onto the discharge tray ET.

[0037] When the job to be executed is a double-sided printing job, the sheet S passes through the transfer nip twice in order to perform the transfer process once on each of the front and back sides of the sheet S. Specifically, when the sheet S passes through the transfer nip for the first time, the transfer process is performed on one side of the sheet S. After the first transfer process, the sheet S is switched back after the rear end of the sheet S passes through the branch position P3 and before the sheet S is completely discharged onto the discharge tray ET. As a result, the rear end of the sheet S is drawn into the double-sided printing transport path DP.

[0038] Thereafter, the sheet S is transported along the double-sided printing transport path DP. Then, the sheet S on the double-sided printing transport path DP is returned to the main transport path MP from the junction position P4. The sheet S returned to the main transport path MP is transported along the main transport path MP and passes through the transfer nip again. At this time, the orientation of the front and back surfaces of the sheet S is reversed to the orientation when it passed through the transfer nip the previous time. As a result, when the sheet S passes through the transfer nip for the second time, a transfer process is performed on the other side of the sheet S that is opposite to the one side.

[0039] As shown in Fig. 4, the image forming apparatus 100 includes a control unit 10. The control unit 10 includes processing circuits such as a CPU and an ASIC. The control unit 10 also includes storage devices such as a ROM and a RAM. The control unit 10 controls a print job executed by the image forming apparatus 100. The control unit 10 controls a belt motor BM to rotate the intermediate transfer belt 2 appropriately.

[0040] The image forming apparatus 100 includes a communication unit 101. The communication unit 101 includes a communication circuit, a communication memory, a communication connector, and the like. The communication unit 101 is communicably connected to an external device via a network such as a LAN. An example of the external device is a user terminal. A personal computer (PC), a smartphone, a tablet computer, and the like can serve as the user terminal.

[0041] The control unit 10 communicates with an external device using the communication unit 101. For example, print data of a print job is transmitted from an external device (user terminal) to the image forming apparatus 100. The print data includes image data to be printed in the print job. The control unit 10 controls the print job based on the print data.

[0042] The image forming apparatus 100 includes an operation panel 102. The operation panel 102 includes a touch screen. The operation panel 102 receives settings, instructions, and the like from a user. The operation panel 102 is connected to the control unit 10. The control unit 10 detects the settings, instructions, and the like received by the operation panel 102 from the user.

[0043] The image forming apparatus 100 also includes an image density sensor 6. The image density sensor 6 is used to detect the density and transfer position of an image transferred to the outer circumferential surface of the intermediate transfer belt 2. The image density sensor 6 is connected to a control unit 10. The control unit 10 detects an output value of the image density sensor 6.

[0044] The image density sensor 6 is disposed at a distance from the outer peripheral surface of the intermediate transfer belt 2. The image density sensor 6 is a reflective optical sensor, and has a light emitting section and a light receiving section. The image density sensor 6 irradiates light toward the outer peripheral surface of the intermediate transfer belt 2, and outputs a value according to the amount of light reflected from the outer peripheral surface of the intermediate transfer belt 2 (specifically, a test area 22 described later). The image density sensor 6 changes its output value depending on whether an image is present or not at the detection position. The image density sensor 6 also changes its output value depending on the density of the image present at the detection position. The detection position of the image density sensor 6 is a position of the intermediate transfer belt 2 that faces the image density sensor 6, and is a position where the light of the image density sensor 6 is irradiated.

[0045] Here, as shown in FIG. 5, the image forming apparatus 100 includes a sensor facing member 7. The sensor facing member 7 is disposed on the inner circumferential side of the intermediate transfer belt 2. The sensor facing member 7 contacts the inner circumferential surface of the intermediate transfer belt 2. The sensor facing member 7 suppresses deformation of the detection position of the image density sensor 6 on the intermediate transfer belt 2, thereby backing up detection by the image density sensor 6. In FIG. 5, the light emitted by the image density sensor 6 (including reflected light) is typically indicated by dotted arrows. The same applies to FIG. 7, which will be referred to in the following description.

[0046] 5 corresponds to a cross section of the sensor facing member 7 and its periphery cut by a plane parallel to the width direction Dw. Fig. 5 is a schematic illustration of the sensor facing member 7 and its periphery, and does not directly show the actual dimensions and shapes, etc. The same applies to Fig. 7 referred to in the following description.

[0047] For example, the sensor facing member 7 is a roller, and is supported rotatably about an axis extending in the width direction Dw. The roller serving as the sensor facing member 7 may have the same configuration as the tension roller 3. In other words, the sensor facing member 7 may function as the tension roller 3. In other words, one of the multiple tension rollers 3 may function as the sensor facing member 7.

[0048] The sensor facing member 7 may be made of a member different from the roller. For example, the sensor facing member 7 may be a sheet metal member. In this case, the sheet metal member as the sensor facing member 7 is suspended from one of a pair of unit frames Fr to the other so as to contact the inner circumferential surface of the intermediate transfer belt 2. In order to reduce frictional resistance with the intermediate transfer belt 2 and to release static electricity, a conductive sheet (for example, nonwoven fabric) may be attached to the sheet metal member and the conductive sheet may be brought into contact with the inner circumferential surface of the intermediate transfer belt 2.

[0049] The sensor facing member 7 is disposed so that a portion thereof faces the image density sensor 6 across the intermediate transfer belt 2. In other words, the sensor facing member 7 extends in the width direction Dw so as to cross a position facing the image density sensor 6 across the intermediate transfer belt 2. In further other words, the sensor facing member 7 has a facing portion 70 that faces the image density sensor 6 across the intermediate transfer belt 2.

[0050] By providing the sensor facing member 7, the detection position of the image density sensor 6 on the intermediate transfer belt 2 is supported by the facing portion 70. In other words, deformation such as bending can be suppressed from occurring on the intermediate transfer belt 2 at the detection position of the image density sensor 6.

[0051] The image density sensor 6 is used in the calibration described below. To perform this calibration accurately, it is necessary for the image density sensor 6 to perform accurate detection. For this reason, it is preferable to suppress deformation of the detection position of the image density sensor 6 on the intermediate transfer belt 2.

[0052] <Calibration Overview> The control unit 10 performs calibration of the image formation by the image forming unit 1 in order to keep the quality of the output image constant. As part of the calibration, the control unit 10 performs a process of correcting the density and color shift of the output image. To this end, the control unit 10 detects the density of the image transferred to the outer circumferential surface of the intermediate transfer belt 2 based on the output value of the image density sensor 6. The control unit 10 also detects the transfer position (in other words, positional misalignment) of the image transferred to the outer circumferential surface of the intermediate transfer belt 2 based on the output value of the image density sensor 6.

[0053] When performing calibration, the control unit 10 causes each image forming unit 1 to form a test pattern image TP used for the calibration. Each image forming unit 1 forms the test pattern image TP using toner and performs primary transfer onto the intermediate transfer belt 2. The test pattern image TP is the detection target of the image density sensor 6. Therefore, to perform accurate calibration, it is necessary to detect the density of the test pattern image TP with high accuracy.

[0054] It should be noted that the test pattern image TP is not printed on the sheet S. For example, the test pattern image TP includes an image used for density correction and an image used for color shift correction. In the drawings, the test pattern image TP is indicated by a black area.

[0055] When performing density correction, the control unit 10 causes each image forming unit 1 to form a test pattern image TP used for density correction. For example, each image forming unit 1 forms a plurality of patches having different densities as the test pattern image TP used for density correction, and secondarily transfers the test pattern image TP to the intermediate transfer belt 2. The control unit 10 detects the densities of the plurality of patches of each color based on the output value of the image density sensor 6. If the detected density is lower than the target density, the control unit 10 performs a correction to make the printed image darker, and if the detected density is higher than the target density, the control unit 10 performs a correction to make the printed image lighter. In the density correction, the development bias, transfer bias, etc. may be corrected.

[0056] When performing color misregistration correction, the control unit 10 causes each image forming unit 1 to form a test pattern image TP used for color misregistration correction. For example, each image forming unit 1 forms lines inclined at 45° to the main scanning direction as the test pattern image TP used for color misregistration correction in the main scanning direction, and transfers it to the intermediate transfer belt 2. Also, each image forming unit 1 forms lines parallel to the main scanning direction as the test pattern image TP used for color misregistration correction in the sub-scanning direction, and transfers it to the intermediate transfer belt 2. The control unit 10 detects the line intervals of each color based on the output value of the image density sensor 6. The control unit 10 corrects the exposure start position so that the line intervals of each color become the target intervals.

[0057] <Test pattern image transfer position> As shown in Fig. 6, the intermediate transfer belt 2 has a print area 21 and a test area 22. In other words, the outer peripheral surface of the intermediate transfer belt 2 is divided into the print area 21 and the test area 22. In Fig. 6, in order to clarify the print area 21 and the test area 22, the boundary between the print area 21 and the test area 22 is indicated by a dashed line. Note that Fig. 6 is a plan view of the intermediate transfer belt 2 as viewed in its thickness direction.

[0058] The area between both ends of the intermediate transfer belt 2 in the width direction Dw is the printing area 21. Also, each area of ​​the intermediate transfer belt 2 at both ends in the width direction Dw is the test area 22. In other words, the area sandwiched in the width direction Dw between a pair of test areas 22 is the printing area 21. In yet other words, the areas on both sides of the printing area 21 in the width direction Dw (i.e., the areas outside the printing area 21 in the width direction Dw) are the test areas 22. The printing area 21 corresponds to the "transfer area." The test area 22 corresponds to the "area outside the transfer area in the width direction."

[0059] Each image forming unit 1 forms a printed image using toner and primarily transfers the printed image to the printing area 21. The printed image is the image to be secondarily transferred to the sheet S. Also, each image forming unit 1 forms a test pattern image TP using toner and primarily transfers the test pattern image TP to the test area 22. When calibration is executed, each image forming unit 1 primarily transfers the printed image to the printing area 21 while primarily transferring the test pattern image TP to the test area 22. Thereby, since a printing job can be executed in parallel with the execution of calibration, productivity does not decrease. Note that when only calibration is executed, in addition to the test area 22, the test pattern image TP may be transferred to the printing area 21.

[0060] Here, the centers of the primary transfer roller 4, the sensor facing member 7, the intermediate transfer belt 2, and the sheet S in the respective width directions Dw thereof coincide with each other. Also, when the length of the primary transfer roller 4 in the width direction Dw is Wa (see FIG. 3), the length of the sensor facing member 7 in the width direction Dw is Wb (see FIG. 5), the dimension of the intermediate transfer belt 2 in the width direction Dw is Wc (see FIG. 6), and the maximum dimension of the sheet S in the width direction Dw (in other words, the dimension of the sheet S in the width direction Dw of the maximum size that can be used in the image forming apparatus 100) is Wd, it is configured to satisfy the relationship of Wd ≦ Wa < Wb ≦ Wc.

[0061] In the reference drawings, for the sake of convenience, Wb < Wc is shown, but Wb = Wc may also be the case. Also, although not shown, it may be configured to satisfy the relationship of Wd ≦ Wa < Wc ≦ Wb. Note that in the reference drawings, the dimension Wd of the sheet S in the width direction Dw is not shown in order to make the drawings easier to view. For example, the dimension Wd of the sheet S in the width direction Dw may be the same as the dimension Wp of the printing area 21 in the width direction Dw.

[0062] Since the intermediate transfer belt 2 is larger in the width direction Dw than the primary transfer roller 4, the end of the intermediate transfer belt 2 in the width direction Dw protrudes outward in the width direction Dw from the primary transfer roller 4. Therefore, the end of the intermediate transfer belt 2 in the width direction Dw is pressed relatively stronger from its inner periphery side toward its outer periphery side than other parts. As a result, as shown in FIG. 3, the end of the intermediate transfer belt 2 in the width direction Dw is deformed. For example, the end of the intermediate transfer belt 2 in the width direction Dw is bent toward the inner periphery side of the intermediate transfer belt 2. The intermediate transfer belt 2 is likely to bend from the part that contacts the edge 4a in the width direction Dw of the primary transfer roller 4 as a starting point. In the following description, the end of the intermediate transfer belt 2 in the width direction Dw is denoted by reference numeral 20, and the part is referred to as the belt deformed part 20.

[0063] In addition, since the sensor facing member 7 is larger in the width direction Dw than the primary transfer roller 4, an edge 7a of the sensor facing member 7 in the width direction Dw protrudes outward in the width direction Dw beyond the edge 4a in the width direction Dw of the primary transfer roller 4. In the sensor facing member 7, an edge 7a on one side in the width direction Dw protrudes outward in the width direction Dw beyond the edge 4a on one side in the width direction Dw of the primary transfer roller 4, and an edge 7a on the other side in the width direction Dw protrudes outward in the width direction Dw beyond the edge 4a on the other side in the width direction Dw of the primary transfer roller 4. As a result, the belt deformed portion 20 rides up on the sensor facing member 7 as shown in FIG.

[0064] In this configuration, it is assumed that the detection position of the image density sensor 6 is the belt deformed portion 20 as shown in FIG. 7. In other words, it is assumed that the transfer position of the test pattern image TP is the belt deformed portion 20. In this case, the belt deformed portion 20 rides up onto the sensor facing member 7, and the positional relationship between the detection position of the image density sensor 6 and the transfer position of the test pattern image TP is shifted. Specifically, the distance from the image density sensor 6 to the test pattern image TP is shifted. Also, the transfer surface of the test pattern image TP is significantly inclined with respect to the light emission surface of the image density sensor 6 (i.e., the angle is shifted). If the distance and angle are shifted between the detection position of the image density sensor 6 and the transfer position of the test pattern image TP, it becomes difficult to accurately detect the density and transfer position of the test pattern image TP.

[0065] Therefore, in this embodiment, the test pattern image TP is primarily transferred to a position that is almost not affected by the deformation of the intermediate transfer belt 2.

[0066] 5 and 6, the transfer position of the test pattern image TP is a position spaced a predetermined distance Lp inward in the width direction Dw from the edge 2a of the intermediate transfer belt 2 in the width direction Dw. The predetermined distance Lp is at least twice the distance L in the width direction Dw from the edge 2a of the intermediate transfer belt 2 in the width direction Dw to the edge 4a of the primary transfer roller 4 in the width direction Dw.

[0067] In this embodiment, both sides of the print area 21 in the width direction Dw of the intermediate transfer belt 2 are secured as the test area 22, and the transfer position of the test pattern image TP is located at a predetermined distance Lp (≧2L) inward in the width direction Dw from the edge 2a of the intermediate transfer belt 2 in the width direction Dw. This makes it possible to suppress deviations in the distance and angle between the detection position of the image density sensor 6 and the transfer position of the test pattern image TP even if the end of the intermediate transfer belt 2 in the width direction Dw is deformed, as shown in FIG. 5. As a result, it is possible to accurately perform calibration related to image formation by the image forming unit 1 without reducing productivity.

[0068] In this embodiment, the image forming unit 1 primarily transfers the test pattern image TP to both a position on the outer circumferential surface of the intermediate transfer belt 2 that is a predetermined distance Lp inward in the width direction Dw from the edge 2a on one side in the width direction Dw, and a position on the inner side in the width direction Dw from the edge 2a on the other side in the width direction Dw (see FIG. 6). This allows the density and transfer position of the test pattern image TP to be confirmed for both ends of the intermediate transfer belt 2 in the width direction Dw, so that calibration can be performed in more detail.

[0069] <Correction of intermediate transfer belt meandering> 8, the image forming apparatus 100 includes a meandering correction mechanism 8. The meandering correction mechanism 8 corrects meandering of the intermediate transfer belt 2. The meandering correction mechanism 8 is connected to a correction target roller 31 among the multiple tension rollers 3, and tilts a rotation axis 300 of the correction target roller 31 to correct the meandering of the intermediate transfer belt 2. For example, when the intermediate transfer belt 2 shifts to one side in the width direction Dw (here, the left side in the drawing), the meandering correction mechanism 8 tilts the rotation axis 300 of the correction target roller 31 downward and to the left.

[0070] The configuration of the meandering correction mechanism 8 is not particularly limited. The amount of meandering of the intermediate transfer belt 2 may be detected, and the inclination of the rotation axis 300 of the correction target roller 31 may be changed based on the detection result (first embodiment). Furthermore, when the intermediate transfer belt 2 meanders, the inclination of the rotation axis 300 of the correction target roller 31 may be automatically changed (second embodiment).

[0071] In the first embodiment, although not shown, the meandering correction mechanism 8 includes a meandering amount detection unit that detects the meandering amount of the intermediate transfer belt 2. The configuration of the meandering amount detection unit is not particularly limited. The meandering amount detection unit outputs a value according to the end position of the intermediate transfer belt 2 in the width direction Dw. The meandering amount detection unit may be a transmission type optical sensor including a light emitting unit and a light receiving unit that face each other in the vertical direction with the end of the intermediate transfer belt 2 in the width direction Dw sandwiched therebetween. The meandering amount detection unit may also be a CIS. The control unit 10 receives the output value of the meandering amount detection unit. The control unit 10 detects the meandering amount of the intermediate transfer belt 2 based on the output value of the meandering amount detection unit.

[0072] In the first embodiment, although not shown, the meandering correction mechanism 8 includes a correction motor connected to the rotation shaft 300 of the correction target roller 31, and a connecting member connecting the rotation shaft 300 and the correction motor. The connecting member is a gear, a cam, or the like. When the correction motor is driven, an end of the axial direction (i.e., the width direction Dw) of the rotation shaft 300 moves in the vertical direction, and the rotation shaft 300 tilts. The control unit 10 controls the correction motor. The control unit 10 tilts the rotation shaft 300 of the correction target roller 31 based on the amount of meandering of the intermediate transfer belt 2, thereby correcting the meandering of the intermediate transfer belt 2.

[0073] In the second embodiment, as shown in FIG. 9, the rotation shaft 300 of the correction target roller 31 is rotatably supported by a bearing 81 having an inclined portion 81a on its outer periphery. The bearing 81 is movable in the axial direction of the rotation shaft 300 (i.e., the width direction Dw). The bearing 81 is disposed on the outer side of the belt guide 80 in the width direction Dw. The inclined portion 81a of the bearing 81 is formed so as to be inclined downward toward the outer side in the width direction Dw. A main body guide 82 is disposed above the inclined portion 81a of the bearing 81. The main body guide 82 is fixed to, for example, a frame (not shown) of the intermediate transfer unit, protrudes downward from the main body, and abuts against the inclined portion 81a of the bearing 81.

[0074] In the second mode, if the intermediate transfer belt 2 does not meander, the rotating shaft 300 does not tilt (see the upper diagram in FIG. 9). When the intermediate transfer belt 2 meanders and the belt guide 80 is pushed toward one side in the width direction Dw by the intermediate transfer belt 2, the bearing 81 moves to one side in the width direction Dw together with the belt guide 80 (see the lower diagram in FIG. 9). At this time, the inclined portion 81a of the bearing 81 abuts against the main body guide 82, so that the rotating shaft 300 tilts. This corrects the meandering of the intermediate transfer belt 2.

[0075] Although not shown, there is a configuration in which a deviation prevention guide is used. In this configuration, a deviation prevention guide is provided at the end of the intermediate transfer belt 2 in the width direction Dw. As a result, when the intermediate transfer belt 2 moves in the width direction Dw, the deviation prevention guide comes into contact with the tension roller 3, and the intermediate transfer belt 2 does not move any further in the width direction Dw. However, in this configuration, it is necessary to enlarge the intermediate transfer belt 2 in the width direction Dw to ensure the installation position of the deviation prevention guide, which increases the size of the intermediate transfer unit. In other words, the image forming apparatus 100 increases in size.

[0076] On the other hand, in a configuration using the meandering correction mechanism 8, it is not necessary to provide a deviation prevention guide for the intermediate transfer belt 2. This makes it possible to prevent the image forming apparatus 100 from becoming large.

[0077] The embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is indicated by the claims, not by the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0078] 1 Image forming section 2 Intermediate transfer belt 2a edge 3 Tension roller 4 Primary transfer roller 4a Edge 5 Secondary transfer roller 6 Image density sensor 7 Sensor facing member 8. Meandering correction mechanism 11 Photoconductor drum (image carrier) 40 Rotational Axis 100 Image forming device Dr Belt rotation direction (rotation direction) Dw Width direction L distance Lp predetermined distance TP test pattern image

Claims

1. an image forming section having an image carrier and causing an image formed using toner to be carried on the image carrier; an endless intermediate transfer belt having an outer peripheral surface to which the image is primarily transferred from the image carrier and rotating while carrying the transferred image; a primary transfer roller that is rotatable about an axis extending in a width direction perpendicular to a rotation direction of the intermediate transfer belt, that is located inside an edge of the intermediate transfer belt in the width direction, and that is in pressure contact with the image carrier via the intermediate transfer belt; a secondary transfer roller that is rotatable about an axis extending in the width direction, forms a transfer nip between itself and an outer peripheral surface of the intermediate transfer belt, and secondarily transfers the image onto a sheet passing through the transfer nip; an image density sensor that is disposed at a distance from an outer peripheral surface of the intermediate transfer belt, that irradiates the intermediate transfer belt with light, and that outputs a value corresponding to the amount of light reflected from the intermediate transfer belt; a sensor facing member that is disposed on an inner peripheral side of the intermediate transfer belt, extends in the width direction so as to cross a position facing the image density sensor, and contacts the inner peripheral surface of the intermediate transfer belt; When performing calibration related to the formation of the image, the image forming unit primarily transfers a print image to be secondarily transferred to the sheet onto a transfer area of ​​the intermediate transfer belt, while primarily transferring a test pattern image to be detected by the image density sensor onto an area outside the transfer area in the width direction, When the length of the primary transfer roller in the width direction is Wa, the length of the sensor facing member in the width direction is Wb, the dimension of the intermediate transfer belt in the width direction is Wc, and the maximum dimension of the sheet in the width direction is Wd, a relationship of Wd≦Wa<Wb≦Wc or a relationship of Wd≦Wa<Wc≦Wb is satisfied, a transfer position of the test pattern image is a position spaced a predetermined distance inward in the width direction from an edge of the intermediate transfer belt in the width direction, an image forming apparatus, the predetermined distance being equal to or greater than twice the distance in the width direction from an edge of the intermediate transfer belt in the width direction to an edge of the primary transfer roller in the width direction;

2. 2. The image forming apparatus of claim 1, wherein when performing the calibration, the image forming unit primarily transfers the test pattern image to both a position on the outer surface of the intermediate transfer belt that is spaced a predetermined distance inward in the width direction from an edge on one side of the width direction of the intermediate transfer belt, and a position that is spaced a predetermined distance inward in the width direction from an edge on the other side of the width direction of the intermediate transfer belt.

3. A plurality of tension rollers that rotatably tension the intermediate transfer belt; The image forming apparatus according to claim 1 , further comprising a meandering correction mechanism that corrects meandering of the intermediate transfer belt by tilting a rotation axis of any one of the plurality of tension rollers.

Images