Image formation system

Abstract

To obtain an image formation system capable of estimating the tension of a conveying member by using a density measurement part for measuring the density of a toner image held on the surface of the conveying member.SOLUTION: An image formation system 10 includes an endless transfer belt 31 which moves in a direction determined with tension applied to convey a toner image held on a surface, a cleaning blade 76 coming into contact with the surface of the transfer belt 31 to clean the surface of the transfer belt 31, an optical sensor 72 for measuring the density of the toner image held on the surface of the transfer belt 31, and a CPU 101 of a control part 100. The CPU 101 estimates the tension of the transfer belt 31 on the basis of a measurement result obtained by measuring the surface of the transfer belt 31 by the optical sensor 72 in which the toner image is not held on the surface of the transfer belt 31.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] The following Patent Document 1 discloses an image forming device having a toner image forming means that forms a toner image using toner, a detection means that detects the amount of toner available in the toner image forming means, and a control means that causes the toner image forming means to form a toner image according to input image data and also causes the toner image forming means to form a toner band, which is a toner image for maintenance of the device, when a toner image according to the input image data has not been formed, and that, if the amount of toner detected by the detection means is less than a predetermined amount, reduces the amount of toner used in a toner band formed subsequently to be less than the amount used in a toner band formed before the toner band was formed.

[0003] The following Patent Document 2 discloses a density control method for an image forming device in which a control patch is created on an image carrier, the amount of reflected light from the portion of the control patch where toner is present and the amount of reflected light from the portion of the control patch where toner is not present are detected by a density sensor, and parameters that determine image density are controlled based on the detection results. In this density control method, a correction patch that achieves maximum density is created on the image carrier, and the amount of reflected light from the portion of the correction patch where toner is present and the amount of reflected light from the portion of the control patch where toner is not present are detected by a density sensor, and the sensitivity of the density sensor is calculated by calculating the ratio between the two. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-212936 A [Patent Document 1] Japanese Patent Application Publication No. 5-302892 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide an image forming system capable of estimating the tension of a transport member by using a density measuring unit that measures the density of a toner image held on the surface of the transport member. [Means for solving the problem]

[0006] The image forming system of the first embodiment comprises an endless transport member that moves in a predetermined direction under tension and transports a toner image held on its surface, a cleaning member that contacts the surface of the transport member and cleans the surface of the transport member, a concentration measurement unit that measures the concentration of the toner image held on the surface of the transport member, and at least one processor, wherein the processor estimates the tension of the transport member based on a measurement result obtained by measuring the surface of the transport member by the concentration measurement unit when no toner image is held on the surface of the transport member.

[0007] The image forming system of the second aspect is the image forming system described in the first aspect, and further includes an image forming unit that forms a toner image on a surface of the transport member, and the processor controls the band-shaped toner image formed by the image forming unit in an area of ​​the transport member that does not face the recording medium in accordance with the estimated tension of the transport member.

[0008] An image forming system according to a third aspect is the image forming system according to the second aspect, wherein the processor controls at least one of an amount of toner in the strip-shaped toner image and a supply frequency of the strip-shaped toner image.

[0009] An image forming system according to a fourth aspect is the image forming system according to the first aspect, wherein the density measuring unit is provided in a central portion in a width direction intersecting with a moving direction of the transport member.

[0010] An image forming system according to a fifth aspect is the image forming system described in the first aspect, further comprising an image forming unit that forms a toner image on a surface of the transport member, and the processor controls the image forming unit so that when the surface of the transport member is measured by the concentration measuring unit without a toner image being held on the surface of the transport member, the image forming unit does not adhere to the surface of the transport member from the image forming unit.

[0011] An image forming system according to a sixth aspect is the image forming system according to the fifth aspect, wherein the image forming unit includes an image carrier and a developing device that develops a latent image on a surface of the image carrier by adhering toner to the latent image, and when the concentration measuring unit measures the surface of the transport member in a state where no toner image is held on the surface of the transport member, the surface potential of the image carrier is made higher than the surface potential of the image carrier when a normal toner image is formed.

[0012] An image forming system according to a seventh aspect is the image forming system according to the first aspect, further comprising a transfer rotating body that contacts the transport member and transfers a toner image held on an image holder to the transport member, and when the concentration measuring unit measures the surface of the transport member in a state where no toner image is held on the surface of the transport member, the transfer rotating body is separated from the transport member.

[0013] An image forming system according to an eighth aspect is the image forming system according to the fifth aspect, further comprising a transfer rotating body that contacts the transport member and transfers a toner image held on an image holder to the transport member, and when the concentration measuring unit measures the surface of the transport member in a state where no toner image is held on the surface of the transport member, the transfer rotating body is separated from the transport member.

[0014] An image forming system according to a ninth aspect is the image forming system according to the first aspect, further comprising a reverse mode for moving the conveying member in a direction opposite to the determined direction, and the processor measures the surface of the conveying member using the concentration measuring unit immediately after the reverse mode, without a toner image being held on the surface of the conveying member.

[0015] An image forming system according to a tenth aspect is the image forming system described in the third aspect, wherein the processor increases the amount of toner in the band-shaped toner image when the difference between the maximum and minimum values ​​of the output of the concentration measuring unit is greater than or equal to a first threshold value, more than when the difference is less than the first threshold value.

[0016] An image forming system according to an eleventh aspect is the image forming system described in the tenth aspect, wherein when the difference between the maximum and minimum values ​​of the output of the concentration measuring unit is equal to or greater than a second threshold value that is greater than the first threshold value, the processor maintains or further increases the amount of toner in the band-shaped toner image when the difference is less than the second threshold value, and increases the frequency of supply of the band-shaped toner image compared to when the difference is less than the second threshold value. Effect of the Invention

[0017] According to the image forming system of the first aspect, the tension of the transport member can be estimated by using the density measuring unit that measures the density of the toner image held on the surface of the transport member.

[0018] According to the image forming system of the second aspect, the occurrence of cleaning defects can be suppressed compared to a case where an equivalent band-shaped toner image is formed without relying on estimation of the tension of the transport member.

[0019] According to the image forming system of the third aspect, the occurrence of poor cleaning can be suppressed compared to the case where the amount of toner in the belt-shaped toner image and the supply frequency of the belt-shaped toner image are the same.

[0020] According to the image forming system of the fourth aspect, the output value of the density measuring unit corresponding to the tension of the conveying member can be stably measured compared to a case where the density measuring unit is provided only on one end side in the width direction intersecting the movement direction of the conveying member.

[0021] According to the image forming system of the fifth aspect, the output value of the density measuring unit corresponding to the tension of the transport member can be measured stably, compared to a case where toner adheres to the transport member from the image forming unit.

[0022] According to the image forming system of the sixth aspect, when the surface of the conveying member is measured by the concentration measuring unit, it is possible to suppress toner from adhering to the image carrier from the developing device and further toner from the image carrier adhering to the conveying member, compared to the case where the surface potential of the image carrier is the same as that when a normal toner image is formed.

[0023] According to the image forming system of the seventh aspect, a decrease in tension of the transport member can be estimated earlier than when the surface of the transport member is measured by the concentration measurement unit while the transfer rotating body is in contact with the transport member.

[0024] According to the image forming system of the eighth aspect, it is possible to suppress toner from adhering to the transport member from the image carrier, compared to a case in which the surface of the transport member is measured by the concentration measuring unit while the transfer rotating body is in contact with the transport member.

[0025] According to the image forming system of the ninth aspect, a decrease in tension of the conveying member can be estimated earlier than when the surface of the conveying member is measured by a concentration measurement unit while the conveying member continues to move in a specified direction.

[0026] According to the image forming system of the tenth aspect, even if the difference between the maximum and minimum values ​​of the output of the concentration measurement unit becomes large, the occurrence of cleaning defects can be suppressed compared to when the amount of toner in the band-shaped toner image is the same.

[0027] According to the image forming system of the eleventh aspect, the occurrence of cleaning defects can be suppressed, compared to the case where there is one threshold value for the difference between the maximum and minimum values ​​of the output of the density measuring unit. [Brief description of the drawings]

[0028] [Figure 1A] 1 is a schematic diagram showing a configuration of an image forming system according to a first embodiment as viewed from the front side. [Figure 1B] 2 is an enlarged view showing a configuration in the vicinity of a transfer belt during normal driving of the image forming system according to the first embodiment. FIG. [Diagram 2] 1 is a block diagram showing a hardware configuration of an image forming system according to a first embodiment. [Diagram 3] 4 is an enlarged view showing a configuration near a transfer belt in a special measurement mode of the image forming system according to the first embodiment. FIG. [Figure 4A] FIG. 13 is a diagram illustrating the state of the tip of the cleaning blade when the tension of the transfer belt is high. [Figure 4B] FIG. 13 is a diagram illustrating a state of the tip of the cleaning blade when the tension of the transfer belt is reduced; [Diagram 5] 1 is a graph showing the relationship between time and the sensor output value when a transfer belt is measured by an optical sensor without holding a toner image in an image forming system according to a first embodiment, the graph showing an example when the tension of the transfer belt is high. [Figure 6] 1 is a graph showing the relationship between time and the sensor output value when a transfer belt is measured by an optical sensor without holding a toner image in an image forming system according to a first embodiment, and is a graph showing an example when the tension of the transfer belt decreases. [Figure 7] 11 is a graph showing the relationship between the amount of decrease in tension of the transfer belt and the peak-to-peak (PP) output of the optical sensor during normal driving of the image forming system according to the first embodiment and when the primary transfer roll is retracted. [Figure 8] 5 is a flowchart showing the flow of information processing handled by a control unit of the image forming system according to the first embodiment. [Figure 9] 4 is a diagram showing the width of a toner band relative to the peak-to-peak (PP) output of an optical sensor and the conditions of the frequency of supply of the toner band in the image forming system according to the first embodiment. FIG. [Figure 10]3A and 3B are diagrams illustrating an example of a toner band formed on the surface of a transfer belt in an image forming system according to the first embodiment, with the transfer belt in a developed state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, an embodiment of the present invention will be described. In the following description, the direction indicated by the arrow H in each drawing is the vertical direction, which is the device height direction, and the direction indicated by the arrow W is the horizontal direction, which is the device width direction. The direction perpendicular to each of the device height direction and device width direction in each drawing (the direction of the arrow D) is the device depth direction.

[0030] First Embodiment 1A is a front view showing the overall configuration of an image forming system 10 according to a first embodiment. In the first embodiment, the overall configuration of the image forming system 10 will first be described, and then the configuration of a transfer device, which is a main part of the system, will be described.

[0031] <Overall composition> 1A, an image forming system 10 according to the first embodiment is an electrophotographic apparatus including a toner image forming unit 20, a transfer device 30, a conveying device 40, a fixing device 50, and a control unit 100. In the following description of the overall configuration of the image forming system 10, unless otherwise specified, FIG. 1A will be referred to.

[0032] [Toner image forming section] The toner image forming unit 20 has a function of performing each process of charging, exposing, and developing to form a toner image (not shown) held by the transfer belt 31 described later on the transfer belt 31. Here, the toner image forming unit 20 is an example of an image forming unit. The toner image forming unit 20 is configured to include yellow, magenta, cyan, and black monochromatic units 20Y, 20M, 20C, and 20K. The monochromatic units 20Y, 20M, 20C, and 20K are respectively equipped with photoconductors 22Y, 22M, 22C, and 22K. The photoconductors 22Y, 22M, 22C, and 22K are examples of image carriers. When the image forming system 10 is viewed from the front side, the monochromatic units 20Y, 20M, 20C, and 20K are arranged in the order of description from the right side to the left side in the device width direction (below the transfer belt 31). Moreover, the polarity of the average charge amount of the toner (aggregation of particles that form a toner image) used in the first embodiment is, as an example, negative.

[0033] In the single-color units 20Y, 20M, 20C, and 20K, the components are similar except for the color of the toner, and therefore, when it is not necessary to distinguish the color of the toner, the symbols Y, M, C, and K following each component may be omitted in the description. Each of the single-color units 20Y, 20M, 20C, and 20K has, around the photoconductor 22 rotating in the direction indicated by the arrow, a charging device 62 for charging the photoconductor 22, and an exposure device 64 for exposing the photoconductor 22 charged by the charging device 62 to light to form a latent image on the photoconductor 22. Furthermore, each of the Y, 20M, 20C, and 20K has a developing device 66 having a developing roll 66A for developing the latent image formed on the photoconductor 22 by the exposure device 64 to form a toner image, and a cleaning device (not shown) having a cleaning blade for removing the toner remaining on the surface of the photoconductor 22 after the toner image is transferred to the transfer device 30.

[0034] The charging device 62, for example, charges the surface (photosensitive layer) of the photoconductor 22 to a negative polarity. A portion of the negatively charged surface of the photoconductor 22 that is irradiated with exposure light by the exposure device 64 assumes a positive polarity, and a latent image is formed on the surface of the photoconductor 22. Then, in the developing device 66, toner that has been frictionally charged to a negative polarity adheres to the latent image that assumes a positive polarity, and the latent image is developed. In this manner, a toner image is formed on the surface of the photoconductor 22.

[0035] [Transfer device] The transfer device 30 has a function of primarily transferring the toner images formed on the photoconductors 22Y, 22M, 22C, and 22K onto the transfer belt 31, and then transferring (secondarily transferring) the toner images held on the transfer belt 31 (i.e., formed on the transfer belt 31) onto the medium P. The medium P is an example of a recording medium, such as paper.

[0036] 1A and 1B, the transfer device 30 includes a transfer belt 31, a driving roll 32, a plurality of primary transfer rolls 34, a driven roll 36, a tension roll 37, a secondary transfer roll 38, an optical sensor 72, a support roll 74, and a cleaning blade 76. Here, the transfer belt 31 is an example of a transport member, the optical sensor 72 is an example of a concentration measuring unit, and the cleaning blade 76 is an example of a cleaning member.

[0037] [Transfer belt and driving roll] The transfer belt 31 is endless, wound around a drive roll 32 that rotates about an axis, and has a function of holding a toner image to be transferred to the medium P and rotating in a rotation direction (arrow A direction) by being driven by the driving force of the drive roll 32. In other words, the transfer belt 31 has a function of holding a toner image and transporting it in the rotation direction (arrow A direction). The transfer belt 31 holds the toner images that have been primarily transferred by each primary transfer roll 34 from the photoconductors 22Y, 22M, 22C, and 22K on which the toner images of each color have been formed.

[0038] 1A, when the image forming system 10 is viewed from the front side, the driven roll 36 is disposed below the driving roll 32, and the tension roll 37 is disposed above the driving roll 32 and on the right side in the device width direction. Furthermore, a support roll 74 is disposed below the tension roll 37. The transfer belt 31 is wound around the driving roll 32, the driven roll 36, the tension roll 37, and the support roll 74 to determine its posture. When the image forming system 10 is viewed from the front side, the posture of the transfer belt 31 is inclined such that the tension roll 37 and the support roll 74 are on the upper side and the driving roll 32 and the driven roll 36 are on the lower side in the device width direction.

[0039] [Primary transfer roll] When a transfer voltage is applied to the primary transfer roll 34, the primary transfer roll 34 has a function of transferring the toner images held on the photoreceptors 22Y, 22M, 22C, and 22K to the transfer belt 31. The primary transfer roll 34 contacts the inner surface of the transfer belt 31 and rotates around its axis. The primary transfer roll 34 is an example of a transfer rotating body.

[0040] [Secondary transfer roll] The secondary transfer roll 38 has a function of nipping the medium P with a part of the transfer belt 31 wound around the drive roll 32, and transferring the toner image to the medium P. The secondary transfer roll 38 is disposed on the opposite side of the drive roll 32 with the transfer belt 31 in between, and forms a nip N1 with the transfer belt 31 together with the drive roll 32.

[0041] The secondary transfer roll 38 rotates around its axis, and a transfer voltage is applied to the drive roll 32 from a power source PS (see FIG. 1A). As a result, the secondary transfer roll 38 and the drive roll 32 transfer the toner image carried by the transfer belt 31 to the medium P passing through the nip N1. The secondary transfer roll 38 is connected to ground.

[0042] [Tension roll] The tension roll 37 has a function of applying tension (i.e., tension) to the transfer belt 31. The tension roll 37 rotates in accordance with the movement of the transfer belt 31 in the rotation direction (arrow A direction). As shown in FIG. 1B, the tension roll 37 includes a tension applying section 78. As an example, the tension applying section 78 includes a coil spring 78A and a support 78B. One end of the coil spring 78A contacts both axial ends of the shaft section 37A of the tension roll 37, and the other end of the coil spring 78A is supported by the support 78B. The outer peripheral surface of the tension roll 37 is pressed against the inner surface of the transfer belt 31 by the biasing force of the coil spring 78A, thereby applying tension to the transfer belt 31. As a result, the transfer belt 31 moves in the rotation direction (arrow A direction) while being tensioned, and conveys the toner image held on the surface.

[0043] [Support Roll] The support roll 74 has a function of supporting the transfer belt 31 by contacting the inner surface of the transfer belt 31. The support roll 74 rotates in accordance with the rotation of the transfer belt 31.

[0044] The transfer device 30 includes a moving section 80 (see FIG. 2) that moves the support roll 74 and the four primary transfer rolls 34 in a direction intersecting the transfer belt 31. The moving section 80 moves the support roll 74 and the four primary transfer rolls 34 to a first position P1 (see FIG. 1B) where the support roll 74 and the four primary transfer rolls 34 contact the inner surface of the transfer belt 31, and to a second position P2 (see FIG. 3) where the support roll 74 and the four primary transfer rolls 34 are retracted from the inner surface of the transfer belt 31. As an example, the moving section 80 is a hydraulic cylinder that moves a support (not shown) that rotatably supports the support roll 74 and the four primary transfer rolls 34. The moving section 80 may be any other member as long as it is a device that moves a support (not shown) that rotatably supports the support roll 74 and the four primary transfer rolls 34, and may be, for example, a rack and pinion. Furthermore, the moving section 80 is not limited to a configuration that moves the support roll 74 and the four primary transfer rolls 34 together, but may be configured to move the support roll 74 and the four primary transfer rolls 34 individually.

[0045] The image forming system 10 has, as measurement modes by the optical sensor 72, a normal density measurement mode in which a toner image is formed on the surface of the transfer belt 31 and the density of the toner image is measured by the optical sensor 72, and a special measurement mode in which the surface of the transfer belt 31 is measured by the optical sensor 72 to estimate the tension of the transfer belt 31. As an example, in the density measurement mode, the moving unit 80 moves the support roll 74 and the four primary transfer rolls 34 to a first position P1 (see FIG. 1B). Note that, during normal driving to form an image on the medium P, the support roll 74 and the four primary transfer rolls 34 are moved to the first position P1 (see FIGS. 1A and 1B). Also, as an example, in the special measurement mode, the moving unit 80 moves the support roll 74 and the four primary transfer rolls 34 to a second position P2 (see FIG. 3). As a result, in the special measurement mode, the support roll 74 and the four primary transfer rolls 34 are separated from the transfer belt 31.

[0046] [Optical sensor] The optical sensor 72 has a function of measuring the density of the toner image held on the surface of the transfer belt 31 by irradiating the transfer belt 31 with light and detecting the light reflected by the transfer belt 31. Specifically, in a normal density measurement mode, a toner image is formed on the surface of the transfer belt 31 by the toner image forming unit 20, and the density of the toner image on the surface of the transfer belt 31 is measured by the optical sensor 72. As shown in FIGS. 1A and 1B, the optical sensor 72 is disposed on the outer periphery of the transfer belt 31 at a position downstream of the toner image forming unit 20 in the rotation direction of the transfer belt 31 and upstream of the driven roll 36 so as to face the position. As an example, the setting values ​​of each member of the toner image forming unit 20 are adjusted based on the measurement result of the density of the toner image.

[0047] The optical sensor 72 is provided at the center of the width direction intersecting with the moving direction (direction of arrow A) of the transfer belt 31. In the first embodiment, the optical sensor 72 is provided at the center of the transfer belt 31 in the device depth direction. As an example, the optical sensor 72 is provided in the middle when the transfer belt 31 is divided into three in the device depth direction. Under normal conditions when the tension of the transfer belt 31 is as intended, the tension in the center of the transfer belt 31 in the width direction (device depth direction) is most stable, so this portion is measured by the optical sensor 72.

[0048] The optical sensor 72 is disposed at a position slightly shifted upstream in the rotation direction of the transfer belt 31 (the direction of the arrow A) from the direction perpendicular to the axial direction of the driven roll .

[0049] In the special measurement mode, the optical sensor 72 irradiates the transfer belt 31 with light and detects the light reflected by the transfer belt 31, without a toner image being held on the surface of the transfer belt 31. The output of the optical sensor 72 is input to the control unit 100 (see FIG. 1A).

[0050] [Cleaning blade] The cleaning blade 76 has a function of contacting the surface of the transfer belt 31 and cleaning the surface of the transfer belt 31. The cleaning blade 76 is an example of a cleaning member. The cleaning blade 76 is disposed downstream of the secondary transfer roll 38 in the rotation direction (arrow A direction) of the transfer belt 31. When the tip of the cleaning blade 76 contacts the surface of the transfer belt 31, the cleaning blade 76 removes deposits such as toner remaining on the surface of the transfer belt 31 after the toner image is secondarily transferred.

[0051] The cleaning blade 76 is disposed on the opposite side of the transfer belt 31 to the tension roll 37 , and is in contact with the surface of the transfer belt 31 wrapped around the tension roll 37 .

[0052] The cleaning blade 76 is a plate-like member, and is disposed so that the surface direction of the cleaning blade 76 intersects with the surface of the transfer belt 31. The cleaning blade 76 is supported by a support member (not shown), and the tip of the cleaning blade 76 is directed upstream in the rotation direction (direction of arrow A) of the transfer belt 31. This makes it easier for the cleaning blade 76 to remove toner adhering to the surface of the transfer belt 31.

[0053] [Transportation device] The transport device 40 has a function of transporting the medium P stored in the medium storage unit 42 through a transport path 46C including nips N1 and N2 described below, and discharging the medium P to the outside of the housing of the image forming system 10. The transport device 40 includes a delivery roll 46A and a plurality of transport roll pairs 46B.

[0054] [Fixing device] The fixing device 50 has a function of fixing the toner image transferred to the medium P by the transfer device 30 to the medium P. The fixing device 50 includes a heating roll 54 and a pressure roll 52. The fixing device 50 heats the medium P passing through a nip N2 formed by the heating roll 54 and the pressure roll 52 with the heating roll 54, and applies pressure with the heating roll 54 and the pressure roll 52 to fix the toner image to the medium P.

[0055] [Control Unit] The control unit 100 has a function of controlling each component other than the control unit 100 that configures the image forming system 10. FIG.

[0056] 2, the image forming system 10 includes a control unit 100, a toner image forming unit 20, a transfer device 30, a conveying device 40, a fixing device 50, and an optical sensor 72. The image forming system 10 further includes motors 84 for driving the rolls of each unit. The transfer device 30 includes a motor 82 for the drive roll 32 and a moving unit 80.

[0057] The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, a storage 104, and an input / output interface 105. Each component is connected to each other via a bus 109 so as to be able to communicate with each other.

[0058] The CPU 101 is a central processing unit that executes various programs and controls each part. The CPU 101 is an example of a processor. That is, the CPU 101 reads a program from the ROM 102 or the storage 104, and executes the program using the RAM 103 as a working area. The CPU 101 controls each of the above components and performs various arithmetic processing according to the program recorded in the ROM 102 or the storage 104. In the first embodiment, an information processing program is stored in the ROM 102 or the storage 104.

[0059] The ROM 102 stores various programs and various data. The RAM 103 temporarily stores programs or data as a working area. The storage 104 is configured with an HDD (Hard Disk Drive) or an SSD (Solid State Drive) and stores various programs including an operating system and various data. The storage 104 stores a printer driver program. The CPU 101 reads the printer driver program from the storage 104 and executes the program to function as the printer driver.

[0060] The input / output interface 105 is an interface for communicating with each device mounted in the image forming system 10. The control unit 100 is connected to the toner image forming unit 20, the transfer device 30, the conveying device 40, the fixing device 50, the optical sensor 72, and the motors 84 via the input / output interface 105.

[0061] The output value, which is the measurement value measured by the optical sensor 72, is input to the control unit 100.

[0062] The CPU 101 of the control unit 100 controls the toner image forming unit 20, the transfer device 30, the conveying device 40, the fixing device 50, and the motors 84.

[0063] In the image forming system 10, in the specific measurement mode, the optical sensor 72 measures the surface of the transfer belt 31 in a state where no toner image is held on the surface of the transfer belt 31. The CPU 101 estimates the tension of the transfer belt 31 based on the measurement result obtained by measuring the surface of the transfer belt 31 with the optical sensor 72. A method of estimating the tension of the transfer belt 31 will be described later.

[0064] The CPU 101 controls the toner band TB formed by the toner image forming unit 20 in an area 90A (see FIG. 10) of the transfer belt 31 that does not face the medium P, according to the estimated tension of the transfer belt 31. The toner band TB is an example of a band-shaped toner image. The CPU 101 controls at least one of the amount of toner in the toner band TB and the supply frequency of the toner band TB.

[0065] <Image formation operation> Next, an image forming operation using the image forming system 10 of the first embodiment will be described with reference to FIG. 1A.

[0066] When the control unit 100 receives image data for forming an image from an external device (for example, a personal computer), the control unit 100 converts the image data into image data for each color. Then, the control unit 100 causes the toner image forming unit 20 (the monochromatic units 20Y, 20M, 20C, and 20K constituting the toner image forming unit 20) to perform the processes of charging, exposing, and developing, and causes the photoconductors 22Y, 22M, 22C, and 22K to form toner images of each color.

[0067] Next, the control unit 100 causes the primary transfer rolls 34 to primarily transfer the toner images of each color formed on the photoreceptors 22Y, 22M, 22C, and 22K onto the transfer belt 31 rotating in the rotation direction.

[0068] Meanwhile, the control unit 100 controls the conveying device 40 to convey the medium P contained in the medium containing unit 42 to the nip N1 so as to coincide with the timing at which the areas on the transfer belt 31 where each toner image has been primarily transferred reach the nip N1.

[0069] Next, the control unit 100 applies a transfer voltage to the drive roll 32, causing the drive roll 32 and the secondary transfer roll 38 to form an electric field for transferring the toner image held on the transfer belt 31 to the medium P, and transfers the toner image to the medium P passing through the nip N1.

[0070] Next, the control unit 100 controls the conveying device 40 to convey the medium P onto which the toner images of each color have been transferred toward the nip N2 of the fixing device 50. As the medium P passes through the nip N2, the toner images of each color are fixed to the medium P (an image is formed on the medium P).

[0071] Then, the medium P on which the toner images of each color have been fixed (the medium P on which the images have been formed) is discharged outside the apparatus by the conveying device 40, and the image forming operation is completed.

[0072] <Issues with the image forming system in the comparative example> Here, the problems with the image forming system of the comparative example will be described. Although not shown in the drawings, the image forming system of the comparative example is configured to perform only normal density measurement in which a toner image is formed on the surface of a transfer belt and the density of the toner image is measured by an optical sensor. The other configurations of the image forming system of the comparative example are similar to those of the image forming system 10 of the first embodiment. That is, the image forming system of the comparative example does not have a special measurement mode using an optical sensor as in the image forming system 10 of the first embodiment.

[0073] In the image forming system of the comparative example, the tension (i.e., tension) of the transfer belt may decrease over time due to dirt or wear powder on the tension applying portion of the transfer belt. In a configuration in which a cleaning blade faces a tension roll with the transfer belt sandwiched between them, when the tension of the transfer belt decreases, the surface of the transfer belt before entering the cleaning blade becomes unstable, and the behavior of the tip of the cleaning blade may vary.

[0074] Here, the behavior of the tip of the cleaning blade will be specifically described with reference to Figures 4A and 4B. Figure 4A is an explanatory diagram for explaining the first state of the transfer belt 152, the tension applying section 78, and the cleaning blade 156, and shows a state in which the behavior of the tip of the cleaning blade 156 is stable.

[0075] 4A, the endless transfer belt 152 is wound around a drive roll 158 and a tension roll 37, and the tension roll 37 applies tension to the transfer belt 152 by a tension applying section 78. The tension roll 37 and the tension applying section 78 have the same configuration as the transfer device 30 of the first embodiment. The cleaning blade 156 is disposed opposite the tension roll 37 across the transfer belt 152, and a tip of the cleaning blade 156 is in contact with the transfer belt 152. The tip of the cleaning blade 156 is in contact with the surface of the transfer belt 152 while facing upstream in the rotation direction (direction of arrow A) of the transfer belt 152.

[0076] When the transfer belt 152 moves in the rotation direction (the direction of the arrow A), a tension force F1 acts on the transfer belt 152 in the rotation direction downstream of the contact portion with the tension roll 37, and a braking force F2 acts on the transfer belt 152 in the opposite direction to the rotation direction at the contact portion with the cleaning blade 156. In the first state shown in Fig. 4A, the tension of the transfer belt 152 applied from the tension applying unit 78 and the tension roll 37 is high, and the tension force F1 is greater than the braking force F2. Therefore, the surface of the transfer belt 152 is stable, and the behavior of the tip of the cleaning blade 156 in contact with the surface of the transfer belt 152 is stable.

[0077] 4B is an explanatory diagram for explaining the second state of the transfer belt 152, the tension applying unit 78, and the cleaning blade 156, and is a diagram showing a state in which the behavior of the tip of the cleaning blade 156 is unstable. As shown in FIG. 4B, when the tension of the transfer belt 152 decreases due to dirt or wear powder on the tension applying unit 78, the tension force F1 and the braking force F2 become close to each other, so that the surface of the front side (upstream side) of the cleaning blade 156 in the rotation direction (arrow A direction) of the transfer belt 152 becomes unstable. Therefore, the behavior of the tip of the cleaning blade 156 that contacts the surface of the transfer belt 152 becomes unstable, and the tip of the cleaning blade 156 may wear out, causing cleaning defects.

[0078] <Estimation of Transfer Belt Tension in First Embodiment> The image forming system 10 of the first embodiment shown in Fig. 1A has a special measurement mode in which the optical sensor 72 measures the surface of the transfer belt 31 in a state in which no toner image is held on the surface of the transfer belt 31. In the special measurement mode, the optical sensor 72 irradiates the transfer belt 31 with light and detects the light reflected by the transfer belt 31. The output value, which is the measurement value of the optical sensor 72, is input to the CPU 101 (see Fig. 2) of the control unit 100. The CPU 101 estimates the tension of the transfer belt 31 based on the measurement result obtained by measuring the surface of the transfer belt 31 with the optical sensor 72.

[0079] 5 is a graph showing an example of the relationship between time and the output value of the optical sensor 72 when the surface of the transfer belt 31 is measured by the optical sensor 72, and shows the measurement results when the tension of the transfer belt 152 is high. As shown in Fig. 5, during normal times when the tension of the transfer belt 152 is high, there is little fluctuation in the output value of the optical sensor 72, and the output value is stable.

[0080] 6 is a graph showing another example of the relationship between time and the output value of the optical sensor 72 when the surface of the transfer belt 31 is measured by the optical sensor 72, and shows the measurement results when the tension of the transfer belt 152 decreases. As shown in FIG. 6, when the tension of the transfer belt 152 decreases, the fluctuation in the output value of the optical sensor 72 becomes large.

[0081] Therefore, in the image forming system 10 of the first embodiment, the CPU 101 estimates the tension (i.e., tension) of the transfer belt 31 by calculating the peak-to-peak (PP, i.e., the difference between the maximum and minimum values ​​of the output of the optical sensor 72) of the output of the optical sensor 72.

[0082] FIG. 7 is a graph showing the relationship between the amount of decrease in tension of the transfer belt 31 and the peak-to-peak (PP) output of the optical sensor 72. As shown in FIG. 7, as the tension of the transfer belt 31 decreases, the peak-to-peak (PP) output of the optical sensor 72 increases. A first curve 170 shows the relationship between the amount of decrease in tension and the peak-to-peak (PP) output of the optical sensor 72 during normal driving (see FIG. 1B) in which the four primary transfer rolls 34 and the support roll 74 are in contact with the transfer belt 31. A second curve 172 shows the relationship between the amount of decrease in tension and the peak-to-peak (PP) output of the optical sensor 72 when the four primary transfer rolls 34 and the support roll 74 are retracted from the transfer belt 31 (i.e., when separated from the transfer belt 31, see FIG. 3).

[0083] In the second curve 172, when the amount of decrease in tension of the transfer belt 31 is the same, the peak-to-peak (PP) of the output of the optical sensor 72 becomes larger than in the first curve 170. The reason for this will be explained below.

[0084] As shown in FIG. 1B, when the four primary transfer rolls 34 and the support roll 74 are in contact with the transfer belt 31, the detection surface (i.e., the range of the belt surface that is detected) R1 of the transfer belt 31 by the optical sensor 72 is between the driven roll 36 and the primary transfer roll 34 in the black monochrome unit 20K.

[0085] On the other hand, as shown in FIG. 3, when the four primary transfer rolls 34 and the support roll 74 are withdrawn from the transfer belt 31, the detection surface R2 of the transfer belt 31 by the optical sensor 72 (i.e., the range of the belt surface to be detected) is between the driven roll 36 and the tension roll 37. When the four primary transfer rolls 34 and the support roll 74 are withdrawn from the transfer belt 31, the tension of the transfer belt 31 does not change. When the distance of the detection surface R2 of the transfer belt 31 increases, the surface of the transfer belt 31 is easily unstable. For this reason, by making the surface of the transfer belt 31 unstable only in the special measurement mode in which the optical sensor 72 measures the surface of the transfer belt 31, the influence of the slack of the tension roll 37 is not attenuated compared to the state in which the primary transfer roll 34 and the like are in contact. In other words, the sensitivity of the tension to the surface of the transfer belt 31 is increased compared to the state in which the primary transfer roll 34 and the like are in contact. For this reason, it becomes easier to directly detect the surface of the transfer belt 31, and slack of the transfer belt 31 (i.e., a decrease in tension) can be detected early.

[0086] Therefore, in the image forming system 10 of the first embodiment, in the special measurement mode, the optical sensor 72 measures the surface of the transfer belt 31 in a state in which the four primary transfer rolls 34 and the support roll 74 are retracted (i.e., separated) from the transfer belt 31. Then, based on the measurement result of the surface of the transfer belt 31, the tension of the transfer belt 31 is estimated. For example, when the peak-to-peak (PP) output of the optical sensor 72 is greater than a threshold value, a decrease in the tension of the transfer belt 31 can be detected.

[0087] When the transfer belt 31 is not loose or has little looseness, the output value of the optical sensor 72 is within a normal range both during normal driving and when the primary transfer roll 34 and the like are retracted.

[0088] <Toner Band Control in First Embodiment> The CPU 101 controls the toner band TB to be formed on the surface of the transfer belt 31 as shown in FIG. 10 according to the estimated tension of the transfer belt 31. The toner band TB is an example of a belt-shaped toner image, and is a lubricating toner to be supplied to the transfer belt 31. The transfer belt 31 has an area 90B facing the medium P and an area 90A between the two areas 90B that does not face the medium P. The CPU 101 controls the toner band TB to be formed in the area 90A of the transfer belt 31 that does not face the medium P by the toner image forming unit 20. When the toner band TB is formed, the applied voltages of the secondary transfer roll 38 and the driving roll 32 are controlled so that the toner band TB is not transferred from the transfer belt 31 to the medium P. By forming the toner band TB on the surface of the transfer belt 31, when the transfer belt 31 moves in the rotation direction (arrow A direction), the toner constituting the toner band TB is removed by the cleaning blade 76. This makes it possible to suppress the progress of wear at the tip of the cleaning blade 76.

[0089] Fig. 9 is a table showing an example of the width of the toner band TB relative to the peak-to-peak (PP) output of the optical sensor 72 and the frequency of supply of the toner band TB. The table shown in Fig. 9 is stored, for example, in the storage 104 (see Fig. 2). The CPU 101 controls the toner band TB formed on the transfer belt 31 based on this table.

[0090] 9, when the peak-to-peak (PP) output of the optical sensor 72 is smaller than a first threshold value (e.g., 5), the width of the toner band TB is set to 5 mm, and the frequency of supplying the toner band TB is set to once every 50 prints. The width of the toner band TB is the width along the rotation direction (arrow A direction) of the transfer belt 31.

[0091] Also, when the peak-to-peak (PP) of the output of the optical sensor 72 is equal to or greater than a first threshold value (e.g., 5) and less than a second threshold value (e.g., 20), the width of the toner band TB is set to 10 mm, and the supply frequency of the toner band TB is not changed (i.e., once every 50 prints). Also, when the peak-to-peak (PP) of the output of the optical sensor 72 is equal to or greater than a second threshold value (e.g., 20), the width of the toner band TB is maintained at 10 mm, and the supply frequency of the toner band TB is increased (i.e., once every 25 prints).

[0092] In the special measurement mode (i.e., when the surface of the transfer belt 31 is measured by the optical sensor 72 in a state where no toner image is held on the surface of the transfer belt 31), the CPU 101 controls the toner image forming unit 20 so that toner does not adhere to the surface of the transfer belt 31 from the toner image forming unit 20. In the first embodiment, in the special measurement mode, the CPU 101 makes the surface potential of the photoconductor 22 higher than the surface potential of the photoconductor 22 when a normal toner image is formed. Specifically, by controlling the charging voltage applied to the charging device 62, the surface potential of the photoconductor 22 is made higher (for example, about 30 V higher) than the surface potential of the photoconductor 22 when a normal toner image is formed. As an example, the charging device 62 charges the surface of the photoconductor 22 to a negative potential higher than the surface potential of the photoconductor 22 when a normal toner image is formed.

[0093] <Action and Effects> Next, the operation of the first embodiment will be described.

[0094] 8 is a flowchart showing the flow of information processing handled by the control unit 100. The CPU 101 reads out an information processing program from the ROM 102 or the storage 104, loads it into the RAM 103, and executes it to perform information processing.

[0095] The timing of execution of the special measurement mode is determined in advance, for example, to perform measurement once every time one sheet is printed. When executing the special assumed mode, the CPU 101 causes the moving unit 80 to move the four primary transfer rolls 34 and the support roll 74 away from the transfer belt 31.

[0096] When processing in the special measurement mode is started, CPU 101 measures the surface of transfer belt 31 with optical sensor 72 in a state where there is no toner image on the surface of transfer belt 31 (i.e., a state where no toner image is held) (step S301). Specifically, transfer belt 31 is moved in the circulating direction (the direction of arrow A), and no toner image is formed on the surface of transfer belt 31 by toner image forming unit 20. In this state, optical sensor 72 irradiates light onto transfer belt 31 and receives light reflected from transfer belt 31. The output value (i.e., the measurement value) of optical sensor 72 is input to CPU 101.

[0097] The CPU 101 determines whether the peak-to-peak (PP) of the output of the optical sensor 72 is smaller than a first threshold value (step S302). Specifically, the CPU 101 calculates the peak-to-peak (PP) of the output within a set time from the output value of the optical sensor 72, and determines whether the peak-to-peak (PP) of the output is smaller than a first threshold value. The CPU 101 reads a table (see FIG. 9) stored in the storage 104, and determines whether the peak-to-peak (PP) of the output of the optical sensor 72 is smaller than a first threshold value (e.g., 5).

[0098] If the peak-to-peak (PP) output of the optical sensor 72 is smaller than the first threshold value (step S302: YES), the CPU 11 supplies a lubricating toner band TB to the transfer belt 31 with a set amount of toner and frequency (step S303). For example, based on the table shown in Fig. 9, the CPU 11 supplies the toner band TB to the surface of the transfer belt 31 so that the width of the toner band TB is 5 mm and the supply frequency of the toner band TB is once every 50 sheets printed.

[0099] If the peak-to-peak (PP) of the output of the optical sensor 72 is equal to or greater than the first threshold value (step S302: NO), the CPU 101 determines whether the peak-to-peak (PP) of the output of the optical sensor 72 is smaller than a second threshold value (step S304). For example, the CPU 101 determines whether the peak-to-peak (PP) of the output of the optical sensor 72 is smaller than a second threshold value (e.g., 20) based on the table shown in FIG.

[0100] When the peak-to-peak (PP) output of the optical sensor 72 is smaller than the second threshold value (step S304: YES), the CPU 11 increases the amount of toner compared to when the output is smaller than the first threshold value, maintains the frequency, and supplies the lubricating toner band TB to the transfer belt 31 (step S305). For example, based on the table shown in Fig. 9, the CPU 11 sets the width of the toner band TB to 10 mm, increases the amount of toner compared to normal, and maintains the frequency of supplying the toner band TB at once every 50 sheets printed (state A).

[0101] If the peak-to-peak (PP) output of the optical sensor 72 is equal to or greater than the second threshold (step S304: NO), the CPU 11 increases the amount and frequency of toner supply to the transfer belt 31 compared to when the PP output is less than the first threshold (step S306). For example, based on the table shown in Fig. 9, the CPU 11 sets the width of the toner band TB to 10 mm, increases the amount of toner compared to normal, and increases the frequency of supply of the toner band TB to once every 25 sheets printed (state B). This ends the processing based on the information processing program handled by the control unit 100.

[0102] In the image forming system 10, both the toner amount in the toner band TB and the supply frequency of the toner band TB are controlled, but it is also possible to control either the toner amount in the toner band TB or the supply frequency of the toner band TB.

[0103] The image forming system 10 described above is provided with an optical sensor 72 that measures the density of a toner image held on the surface of the transfer belt 31. The CPU 101 estimates the tension of the transfer belt 31 based on the measurement result obtained by measuring the surface of the transfer belt 31 with the optical sensor 72 in a state where no toner image is held on the surface of the transfer belt 31. Therefore, in the image forming system 10, the tension of the transfer belt 31 can be estimated using the optical sensor 72 that measures the density of a toner image held on the surface of the transfer belt 31.

[0104] Furthermore, in the image forming system 10, the CPU 101 controls the toner band TB formed by the toner image forming unit 20 in the area 90A of the transfer belt 31 that does not face the medium P, according to the estimated tension of the transfer belt 31. As a result, the toner band TB is formed on the surface of the transfer belt 31, and the behavior of the tip of the cleaning blade 76 that contacts the transfer belt 31 is stabilized, and the progress of wear of the cleaning blade 76 is suppressed. For example, if the cleaning blade 76 becomes worn, there is a concern that poor cleaning may occur. Therefore, in the image forming system 10, occurrence of cleaning defects can be suppressed compared to a case where an equivalent toner band is formed without relying on an estimation of the tension of the transfer belt.

[0105] Furthermore, in the image forming system 10, the CPU 101 controls at least one of the amount of toner in the toner band TB and the supply frequency of the toner band TB. In the first embodiment, the CPU 101 controls both the amount of toner in the toner band TB and the supply frequency of the toner band TB. Therefore, in the image forming system 10, the occurrence of cleaning defects can be suppressed compared to a case where the amount of toner in the toner band and the supply frequency of the toner band are the same.

[0106] In the image forming system 10, the optical sensor 72 is provided at the center of the width direction intersecting with the moving direction of the transfer belt 31. When the tension of the transfer belt 31 is as intended, the tension of the center of the width direction of the transfer belt 31 is most stable. For example, the tension roll 37 that contacts the transfer belt 31 may have a crown shape in which the diameter of the axial center is larger than the diameter of both ends in the axial direction. When the tension roll 37 is crown-shaped, the tension of the center of the width direction of the transfer belt 31 is stable. Note that even if the tension roll 37 is not crown-shaped, the tension of the center of the width direction of the transfer belt 31 is stable. The optical sensor 72 is provided at the center of the width direction of the transfer belt 31 where the tension of the transfer belt 31 is most stable. Therefore, in the image forming system 10, the output value of the optical sensor 72 corresponding to the tension of the transfer belt 31 can be stably measured compared to a case in which the optical sensor is provided only at one end of the width direction intersecting with the moving direction of the transfer belt.

[0107] Furthermore, in the image forming system 10, the CPU 101 controls the toner image forming unit 20 so that when the surface of the transfer belt 31 is measured by the optical sensor 72 in a state where no toner image is held on the surface of the transfer belt 31, the toner image forming unit 20 does not adhere to the surface of the transfer belt 31. This prevents the surface of the transfer belt 31 from becoming dirty, improving the measurement accuracy of the optical sensor 72. Therefore, in the image forming system 10, the output value of the optical sensor 72 corresponding to the tension of the transfer belt 31 can be stably measured compared to a case where toner adheres to the transfer belt from the toner image forming unit.

[0108] The image forming system 10 also includes a developing device 66 that develops the latent image on the surface of the photoconductor 22 by adhering toner to the latent image. In the image forming system 10, when the surface of the transfer belt 31 is measured by the optical sensor 72 in a state where no toner image is held on the surface of the transfer belt 31, the surface potential of the photoconductor 22 is made higher than the surface potential of the photoconductor 22 during normal toner image formation. This makes it difficult for toner to move from the developing roll 66A of the developing device 66 to the photoconductor 22. Therefore, in the image forming system 10, it is possible to suppress toner from adhering from the developing device 66 to the photoconductor 22 and further from the photoconductor 22 to the transfer belt 31, compared to a case where the surface potential of the photoconductor is set to the same potential as that during normal toner image formation when the surface of the transfer belt is measured by the optical sensor.

[0109] In addition, in the image forming system 10, when the surface of the transfer belt 31 is measured by the optical sensor 72 in a state where no toner image is held on the surface of the transfer belt 31, the primary transfer roll 34 is separated from the transfer belt 31 (see FIG. 3). As shown in FIG. 3, the detection surface R2 of the transfer belt 31 is expanded, so that the surface of the transfer belt 31 becomes unstable and the effect of the decrease in the tension of the transfer belt 31 is less likely to attenuate compared to when the primary transfer roll 34 is in contact with the transfer belt 31, making it easier to directly detect the surface of the transfer belt 31. Therefore, in the image forming system 10, the decrease in the tension of the transfer belt 31 can be estimated earlier compared to when the surface of the transfer belt is measured by the optical sensor while the primary transfer roll is in contact with the transfer belt.

[0110] Furthermore, by separating the primary transfer roll 34 from the transfer belt 31, toner is less likely to adhere from the photoconductor 22 to the transfer belt 31. Therefore, in the image forming system 10, it is possible to suppress toner from adhering to the transfer belt 31 from the photoconductor 22, compared to a case in which the surface of the transfer belt 31 is measured by an optical sensor while the primary transfer roll is kept in contact with the transfer belt.

[0111] Furthermore, in the image forming system 10, when the peak-to-peak (PP) output of the optical sensor 72 is equal to or greater than the first threshold value, the CPU 101 increases the amount of toner in the toner band TB more than when it is less than the first threshold value. Therefore, in the image forming system 10, even if the difference between the maximum and minimum values ​​of the optical sensor output becomes large, the occurrence of cleaning defects can be suppressed compared to when the amount of toner in the band-shaped toner image is the same.

[0112] Furthermore, in the image forming system 10, when the peak-to-peak (PP) output of the optical sensor 72 is equal to or greater than a second threshold value that is greater than the first threshold value, the CPU 101 maintains the amount of toner in the toner band TB when it is less than the second threshold value, and increases the frequency of supply of toner band TB compared to when it is less than the second threshold value. Therefore, in the image forming system 10, the occurrence of cleaning defects can be suppressed compared to when there is one threshold value for the difference between the maximum and minimum values ​​of the optical sensor output.

[0113] Second Embodiment Next, an image forming apparatus according to a second embodiment will be described. Note that the same components as those in the first embodiment are given the same reference numerals and the description thereof will be omitted.

[0114] The image forming system 10 of the second embodiment has a reverse mode in which the transfer belt 31 moves in a direction opposite to a specified direction (arrow A direction). In the reverse mode, the CPU 101 rotates the motor 82 (see FIG. 2) for the driving roll 32 in a direction opposite to that during normal driving, thereby moving the transfer belt 31 in a direction opposite to the specified direction (arrow A direction). The CPU 101 measures the surface of the transfer belt 31 by the optical sensor 72 in a state in which no toner image is held on the surface of the transfer belt 31 immediately after the reverse mode. Then, the CPU 101 estimates the tension of the transfer belt 31 based on the measurement result obtained by measuring the surface of the transfer belt 31. "Immediately after the reverse mode" refers to, for example, within 10 seconds after the transfer belt 31 is switched from reverse rotation to forward rotation. Other configurations of the image forming system 10 of the second embodiment are the same as those of the image forming system 10 of the first embodiment.

[0115] In the image forming system 10 of the second embodiment, in addition to the actions and effects of the same configuration as the image forming system 10 of the first embodiment, the following actions and effects can be obtained.

[0116] The image forming system 10 of the second embodiment has a reverse mode in which the transfer belt 31 is moved in the direction opposite to a specified direction (the direction of the arrow A). The CPU 101 measures the surface of the transfer belt 31 by the optical sensor 72 in a state in which no toner image is held on the surface of the transfer belt 31 immediately after the reverse mode. In the reverse mode, the transfer belt 31 is moved in the direction opposite to the specified direction (the direction of the arrow A) to create a state in which the surface of the transfer belt 31 is easy to move, and the effect of loosening of tension is easily felt on the surface of the transfer belt 31 (i.e., the sensitivity of the tension to the surface of the transfer belt 31 is increased).

[0117] Therefore, in the image forming system 10, a decrease in tension of the transfer belt 31 can be estimated earlier than when the surface of the transfer belt is measured by an optical sensor while the transfer belt continues to move in a specified direction.

[0118] <Supplementary explanation> In the image forming systems 10 of the first and second embodiments, one optical sensor 72 is provided, but the present disclosure is not limited thereto, and multiple (two or more) optical sensors 72 may be provided. When multiple optical sensors 72 are provided, the output values ​​or peak-to-peak output of the multiple optical sensors 72 may be compared, and the tension of the transfer belt 31 may be estimated from the largest output value or peak-to-peak output.

[0119] In the image forming system 10 of the first embodiment, the surface potential of the photoconductor 22 is set higher in the special assumed mode than the surface potential of the photoconductor 22 during normal toner image formation, but the present disclosure is not limited to this configuration. For example, the potential of the developing roll 66A of the developing device 66 may be lowered to make it difficult for toner to be transferred from the developing roll 66A to the photoconductor 22. This makes it difficult for toner to adhere to the transfer belt 31 from the photoconductor 22.

[0120] Furthermore, in the image forming systems 10 of the first and second embodiments, the shape of the toner band TB, the length of the toner band TB in the moving direction of the transfer belt 31, and the supply frequency of the toner band TB can be changed without departing from the spirit of the present invention.

[0121] The above-described processing of the image forming system 10 can also be realized by a dedicated hardware circuit. In this case, the processing may be executed by a single piece of hardware or by multiple pieces of hardware.

[0122] The program for operating the image forming system 10 may be provided by a computer-readable recording medium such as a Universal Serial Bus (USB) memory, a flexible disk, or a Compact Disc Read Only Memory (CD-ROM), or may be provided online via a network such as the Internet. In this case, the program recorded in the computer-readable recording medium is usually transferred to and stored in a memory or storage. The program may be provided as a standalone application software, or may be incorporated into the software of each device of the image forming system 10 as one function of the system.

[0123] Although the present invention has been described in detail with respect to a specific embodiment, it will be apparent to those skilled in the art that the present invention is not limited to such an embodiment, and that various other embodiments are possible within the scope of the present invention.

[0124] <Additional Notes> Preferred aspects of the present disclosure will be described below.

[0125] (((1))) an endless conveying member that moves in a predetermined direction while being tensioned, and conveys a toner image held on a surface of the endless conveying member; a cleaning member that comes into contact with a surface of the conveying member and cleans the surface of the conveying member; a density measuring unit that measures the density of the toner image held on the surface of the conveying member; at least one processor; The processor estimates the tension of the transport member based on a measurement result obtained by measuring the surface of the transport member by the concentration measuring unit in a state where no toner image is held on the surface of the transport member.

[0126] (((2))) an image forming unit that forms a toner image on a surface of the conveying member, The image forming system described in (((1))), wherein the processor controls a band-shaped toner image formed by the image forming unit in an area of ​​the transport member that does not face the recording medium, in accordance with the estimated tension of the transport member.

[0127] (((3))) The image forming system according to (((2))), wherein the processor controls at least one of an amount of toner in the strip-shaped toner image and a supply frequency of the strip-shaped toner image.

[0128] (((4))) The image forming system according to any one of (((1))) to (((3))), wherein the density measuring unit is provided at a center portion in a width direction intersecting with a moving direction of the conveying member.

[0129] (((5))) an image forming unit that forms a toner image on a surface of the conveying member, The image forming system described in any one of (((1))) to (((4))), wherein when the surface of the conveying member is measured by the concentration measuring unit without a toner image being held on the surface of the conveying member, the processor controls the image forming unit so that toner does not adhere to the surface of the conveying member from the image forming unit.

[0130] (((6))) the image forming unit includes an image carrier and a developing device that develops a latent image on a surface of the image carrier by applying toner thereto; The image forming system described in (((5))), wherein, when the surface of the transport member is measured by the concentration measuring unit in a state where no toner image is held on the surface of the transport member, the surface potential of the image carrier is made higher than the surface potential of the image carrier when a normal toner image is formed.

[0131] (((7))) a transfer rotor that contacts the transport member and transfers the toner image held on the image carrier to the transport member; The image forming system according to any one of (((1))) to (((4))) and (((6))), wherein when the surface of the transport member is measured by the concentration measuring unit in a state where no toner image is held on the surface of the transport member, the transfer rotating body is separated from the transport member.

[0132] (((8))) a transfer rotor that contacts the transport member and transfers the toner image held on the image carrier to the transport member; The image forming system according to (((5))), wherein when the surface of the transport member is measured by the concentration measuring unit in a state where no toner image is held on the surface of the transport member, the transfer rotating body is separated from the transport member.

[0133] (((9))) a reverse mode in which the conveying member is moved in a direction opposite to the determined direction; The image forming system of any one of (((1))) to (((8))), wherein the processor measures the surface of the conveying member using the concentration measuring unit in a state where no toner image is held on the surface of the conveying member immediately after the reverse mode.

[0134] (((10))) The processor, The image forming system described in (((3))) wherein when the difference between the maximum and minimum values ​​of the output of the concentration measuring unit is equal to or greater than a first threshold, the amount of toner in the band-shaped toner image is increased more than when the difference is smaller than the first threshold.

[0135] (((11))) The processor, The image forming system described in (((10))) wherein, when the difference between the maximum and minimum values ​​of the output of the concentration measuring unit is equal to or greater than a second threshold value that is greater than the first threshold value, the amount of toner in the band-shaped toner image when the difference is smaller than the second threshold value is maintained or further increased, and the frequency of supply of the band-shaped toner image is increased compared to when the difference is smaller than the second threshold value.

[0136] According to the image forming system described in (((1))), the tension of the transport member can be estimated using a density measuring unit that measures the density of a toner image held on the surface of the transport member.

[0137] According to the image forming system described in (((2))), the occurrence of cleaning defects can be suppressed compared to a case in which an equivalent band-shaped toner image is formed without relying on estimation of the tension of the transport member.

[0138] According to the image forming system described in (((3))), the occurrence of cleaning defects can be suppressed compared to the case where the amount of toner in the belt-shaped toner image and the supply frequency of the belt-shaped toner image are the same.

[0139] According to the image forming system described in (((4))), the output value of the density measuring unit corresponding to the tension of the conveying member can be stably measured, compared to a case where the density measuring unit is provided only on one end side in the width direction that intersects with the movement direction of the conveying member.

[0140] According to the image forming system described in (((5))), the output value of the concentration measuring unit corresponding to the tension of the transport member can be measured stably, compared to a case where toner adheres to the transport member from the image forming unit.

[0141] According to the image forming system described in (((6))), when the surface of the transport member is measured by the concentration measuring unit, it is possible to suppress toner from adhering to the image carrier from the developing device and further toner from the image carrier to the transport member, compared to a case in which the surface potential of the image carrier is the same as that during the formation of a normal toner image.

[0142] According to the image forming system described in (((7))), a decrease in tension of the transport member can be estimated earlier than when the surface of the transport member is measured by the concentration measuring unit while the transfer rotor is in contact with the transport member.

[0143] According to the image forming system described in (((8))), it is possible to suppress toner from adhering to the transport member from the image carrier, compared to a case in which the surface of the transport member is measured by the concentration measuring unit while the transfer rotating body is in contact with the transport member.

[0144] According to the image forming system described in (((9))), a decrease in tension of the transport member can be estimated earlier than when the surface of the transport member is measured by a concentration measuring unit while the transport member continues to move in a specified direction.

[0145] According to the image forming system described in (((10))), even if the difference between the maximum and minimum values ​​of the output of the concentration measurement unit becomes large, the occurrence of cleaning defects can be suppressed compared to when the amount of toner in the band-shaped toner image is the same.

[0146] According to the image forming system described in (((11))), the occurrence of cleaning defects can be suppressed compared to when there is only one threshold value for the difference between the maximum and minimum values ​​of the output of the density measuring unit. [Explanation of symbols]

[0147] 3 Transfer belt 10. Image forming system 20 Toner image forming unit (an example of an image forming unit) 22 Photoconductor (an example of an image carrier) 31 Transfer belt (an example of a conveying member) 34 Primary transfer roll (an example of a transfer rotor) 66 Developing device 72 Optical sensor (an example of a concentration measurement unit) 76 Cleaning blade (an example of a cleaning material) 101 CPU (an example of a processor) P media (an example of a recording medium) TB Toner band (an example of a band-shaped toner image)

Claims

1. an endless conveying member that moves in a predetermined direction while being tensioned, and conveys a toner image held on a surface of the endless conveying member; a cleaning member that comes into contact with a surface of the conveying member and cleans the surface of the conveying member; a density measuring unit that measures the density of the toner image held on the surface of the conveying member; At least one processor; The processor estimates the tension of the transport member based on a measurement result obtained by measuring the surface of the transport member by the concentration measuring unit in a state where no toner image is held on the surface of the transport member.

2. an image forming unit that forms a toner image on a surface of the conveying member, 2 . The image forming system according to claim 1 , wherein the processor controls a band-shaped toner image formed by the image forming unit in an area of ​​the transport member that does not face the recording medium, in accordance with the estimated tension of the transport member.

3. 3. The imaging system of claim 2, wherein the processor controls at least one of an amount of toner in the toner strip image and a frequency of delivery of the toner strip image.

4. 2. The image forming system according to claim 1, wherein the density measuring section is provided at a center portion in a width direction intersecting with a moving direction of the transport member.

5. an image forming unit that forms a toner image on a surface of the conveying member, 2. The image forming system of claim 1, wherein the processor controls the image forming unit so that toner does not adhere to the surface of the transport member from the image forming unit when the concentration measuring unit measures the surface of the transport member without a toner image being held on the surface of the transport member.

6. the image forming unit includes an image carrier and a developing device that develops a latent image on a surface of the image carrier by applying toner thereto; 6. The image forming system according to claim 5, wherein when the surface of the transport member is measured by the concentration measuring unit in a state where no toner image is held on the surface of the transport member, the surface potential of the image carrier is made higher than the surface potential of the image carrier when a normal toner image is formed.

7. a transfer rotor that contacts the transport member and transfers the toner image held on the image carrier to the transport member; 2. The image forming system according to claim 1, wherein the transfer rotator is separated from the transporting member when the density measuring unit measures the surface of the transporting member in a state where no toner image is held on the surface of the transporting member.

8. a transfer rotor that contacts the transport member and transfers the toner image held on the image carrier to the transport member; 6. The image forming system according to claim 5, wherein the transfer rotator is separated from the transporting member when the density measuring unit measures the surface of the transporting member in a state where no toner image is held on the surface of the transporting member.

9. a reverse mode in which the conveying member is moved in a direction opposite to the determined direction; 2 . The image forming system according to claim 1 , wherein the processor measures the surface of the transport member with the density measuring unit in a state where no toner image is held on the surface of the transport member immediately after the reverse mode.

10. The processor, 4. The image forming system according to claim 3, wherein when the difference between the maximum and minimum values ​​of the output of said density measuring unit is equal to or larger than a first threshold, the amount of toner in said band-shaped toner image is increased more than when the difference is smaller than the first threshold.

11. The processor, 11. An image forming system as described in claim 10, wherein when the difference between the maximum and minimum values ​​of the output of the concentration measuring unit is equal to or greater than a second threshold value that is greater than the first threshold value, the amount of toner in the band-shaped toner image when the difference is less than the second threshold value is maintained or further increased, and the frequency of supply of the band-shaped toner image is increased compared to when the difference is less than the second threshold value.

Images