Image forming system

Abstract

To obtain an image forming system that can estimate the nip width of the charged portion on the image holder. [Solution] The image forming system 10 comprises a photoreceptor 22, a charging roll 62, a coil spring 86, a developing device 66, and a CPU 101. The CPU 101 maintains a state where the absolute value of the surface potential of the photoreceptor 22, which is charged by the charging roll 62, is lower than the absolute value of the developing potential of the developing device 66. In this state, the CPU 101 increases the absolute value of the potential of the charging roll 62 in a rectangular wave for a predetermined set time only, so that the absolute value of the surface potential of the photoreceptor 22 becomes higher than the absolute value of the developing potential. The set time is the time during which instantaneous discharge occurs on the photoreceptor 22 before and after the nip width of the charging roll 62, but no discharge occurs in the center of the nip width.

Description

Technical Field

[0001] The present disclosure relates to an image forming system.

Background Art

[0002] Patent Document 1 below discloses an image forming apparatus including a charging member, a latent image forming unit, a developing unit, and an optical sensor. The charging member is disposed in contact with or in proximity to a photoreceptor. The latent image forming unit forms an electrostatic latent image on the photoreceptor charged by the charging member. The developing unit attaches toner to the electrostatic latent image to visualize it. The voltage applying unit applies a voltage to the charging member. The optical sensor detects the reflection density of the surface of the photoreceptor. In the image forming apparatus, the voltage applied to the charging member can be changed, and the applied voltage output from the voltage applying unit can be changed according to the output ratio of the optical sensor before and after the change. Further, in the image forming apparatus, the optical sensor also serves as a toner density sensor, and the optical sensor is installed between the developing width end and the position corresponding to the toner density sensor in the longitudinal direction of the photoreceptor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present disclosure provides an image forming system capable of estimating the nip width of the charging unit on the image holding member.

Means for Solving the Problems

[0005] The image forming system according to the first embodiment includes a rotating image holder, a charging unit that rotates in contact with the image holder and charges the surface of the image holder by applying a charging bias, a pressing member that presses the charging unit against the image holder so as to create a nip width, a developing unit that develops the latent image formed on the surface of the image holder with toner, and at least one processor, wherein the processor instantaneously generates a discharge on the image holder before and after the nip width of the charging unit, while the absolute value of the potential of the charging unit is higher than the absolute value of the development potential of the image holder, for a set time when the absolute value of the surface potential of the image holder charged by the charging unit is lower than the absolute value of the development potential of the developing unit, and increases the absolute value of the potential of the charging unit in a rectangular wave manner so that the absolute value of the surface potential of the image holder is higher than the absolute value of the development potential.

[0006] The image forming system according to the second embodiment is the image forming system according to the first embodiment, wherein the charging part is a circular rotating body, the diameter of the charging part is d [mm], and the rotation speed of the image holder is v [mm / sec], and the set time t [ms] is, t = d / v × 2.92 ± 5% That is the case.

[0007] The image forming system according to the third embodiment is the image forming system according to the first embodiment, wherein the minimum value of the set time is the time required to reach the potential of the charged part, and the maximum value of the set time is less than or equal to the time at which there is no remaining section in the nip width that is not discharged.

[0008] The image forming system according to the fourth embodiment, in the image forming system according to the first embodiment, the processor predicts the nip width of the charged portion on the image holder according to a measurement value obtained by directly or indirectly measuring the width of the position where there is fouling toner while there is little fouling toner in the rotational direction of the image holder.

[0009] The image forming system according to the fifth embodiment is the image forming system according to the fourth embodiment, further comprising an intermediate transfer body for transferring toner from the surface of the image holder, and a density detection unit for detecting the density of the toner transferred to the intermediate transfer body.

[0010] The image forming system according to the sixth embodiment includes a detection unit for detecting the density of toner on the surface of the image holder, in the image forming system described in the fourth embodiment.

[0011] The image forming system according to the seventh embodiment is an image forming system according to the fifth or sixth embodiment, wherein the measurement of the toner density is performed only at a position corresponding to the axial end of the image holder.

[0012] The image forming system according to the eighth embodiment is the image forming system according to the fourth embodiment, wherein the processor performs a cleaning mode to clean the charged portion when the nip width of the charged portion corresponding to the measured value is greater than or equal to a threshold.

[0013] The image forming system according to the ninth embodiment is the image forming system according to the eighth embodiment, wherein the processor increases the frequency of the cleaning mode for cleaning the charged portion according to the nip width of the charged portion corresponding to the measured value.

[0014] The image forming system according to the tenth embodiment is an image forming system according to the eighth embodiment, wherein a cleaning member for cleaning the surface of the image holder is provided downstream of the transfer position for transferring the toner image on the surface of the image holder to a medium and upstream of the charging unit, and in the cleaning mode, the dirt from the charging unit is transferred to the image holder and the dirt from the image holder is removed by the cleaning member.

[0015] The image forming system according to the 11th embodiment, in the image forming system according to the 4th embodiment, the processor increases the absolute value of the potential of the charging part that charges the image holder during image formation compared to the normal absolute value of the potential of the charging part when the nip width of the charging part corresponding to the measured value is greater than or equal to a threshold.

[0016] The image forming system according to the 12th embodiment is an image forming system according to the first embodiment, in which the absolute value of the surface potential of the image holder charged by the charging unit is lower than the absolute value of the development potential of the developing unit, by lowering the absolute value of the potential of the charging unit without changing the development potential of the developing unit.

[0017] The image forming system according to the 13th embodiment is the image forming system according to the first embodiment, wherein the charging unit charges the image holder by adding an AC voltage to the DC voltage. [Effects of the Invention]

[0018] According to the image forming system of the first embodiment, the nip width of the charged portion on the image holder can be estimated.

[0019] According to the image forming system of the second embodiment, compared to the case where time t is longer than d / v × 2.92 + 5% or time t is shorter than d / v × 2.92 - 5%, it is possible to form a position where there is toner covering the charged portion corresponding to the nip width while there is less toner covering the image holder in the rotational direction.

[0020] According to the image forming system of the third embodiment, by increasing the absolute value of the potential of the charged part for a set time, it is possible to form a position where there is toner covering the nip width of the charged part while there is little toner covering in the rotational direction of the image holder.

[0021] According to the image forming system of the fourth embodiment, the nip width of the charged portion on the image holder can be estimated by measuring the width of the position where the fouling toner is present.

[0022] According to the image forming system of the fifth embodiment, the density of toner transferred to the intermediate transfer medium is detected by the density detection unit, thereby enabling the measurement of the width of the toner overlay while the amount of toner overlay is low.

[0023] According to the image forming system according to the sixth aspect, by directly detecting the toner density on the surface of the image carrier by the detection unit, the width of the fogged toner during the state with less fogged toner can be measured.

[0024] According to the image forming system according to the seventh aspect, compared with the case of measuring the toner density over the entire axial direction of the image carrier, it is easy to measure the width of the fogged toner in the rotational direction of the image carrier.

[0025] According to the image forming system according to the eighth aspect, compared with the case where the nip width of the charging unit to the image carrier is unknown, the occurrence of charging failure of the image carrier due to the charging unit can be suppressed.

[0026] <000009​​​​​​​​​​​​​​​​​​​​​​​​​​​This is a side view showing the charging roll and the vicinity of the photoreceptor in the image forming system according to the first embodiment. [Figure 3] This is a cross-sectional view showing the nip width of the charging roll for the photoreceptor in the image forming system according to the first embodiment. [Figure 4] This graph shows the relationship between the axial position of the electrostatic roll and the nip width. [Figure 5] This graph shows the relationship between the nip width of the charging roll on the photoreceptor and the amount of external additive attached to the charging roll. [Figure 6] This is a block diagram showing the hardware configuration of the image forming system according to the first embodiment. [Figure 7] This is an explanatory diagram showing the potential of each part, the developer toner, and the output of the density sensor as time is used to detect the nip width of the charging roll on the photoreceptor. [Figure 8] This is an explanatory diagram showing the discharge state when a photoreceptor is charged by a charging roll. [Figure 9] (A) is an explanatory diagram showing the state of the charging roll, exposure apparatus, and primary transfer roll during normal image formation, and (B) is an explanatory diagram showing the state of the charging roll and photoreceptor during normal image formation. [Figure 10] (A) is an explanatory diagram showing the state of the charging roll, exposure apparatus, and primary transfer roll during the cleaning of the charging roll, and (B) is an explanatory diagram showing the state of the charging roll and photoreceptor during the cleaning of the charging roll. [Figure 11] This is a flowchart showing the information processing flow of the image forming system according to the first embodiment. [Figure 12] This is a schematic diagram showing the toner image forming section of the image forming system according to the second embodiment. [Modes for carrying out the invention]

[0032] The following describes embodiments for carrying out the present invention. In the following description, the direction indicated by arrow H in each drawing is the vertical direction, which is the device height direction, and the direction indicated by arrow W is the horizontal direction, which is the device width direction. The direction perpendicular to the device height direction and the device width direction in each drawing (the direction of arrow D) is the device depth direction.

[0033] [First Embodiment] Figure 1 is a front view showing the overall configuration of the image forming system 10 according to the first embodiment. In the first embodiment, the overall configuration of the image forming system 10 will be described first, and then the details regarding the nip width of the charging roll for the photoreceptor will be described.

[0034] <Overall configuration of the image forming system> The image forming system 10 of the first embodiment is an electrophotographic apparatus, as shown in Figure 1, comprising a toner image forming unit 20, a transfer device 30, a transport device 40, a fixing device 50, and a control unit 100. The following description of the overall configuration of the image forming system 10 will refer to Figure 1 unless otherwise specified.

[0035] [Toner image forming unit] The toner image forming unit 20 has the function of forming toner images on the photoreceptors 22Y, 22M, 22C, and 22K by performing charging, exposure, and development processes. The toner image forming unit 20 is composed of yellow, magenta, cyan, and black single-color units 20Y, 20M, 20C, and 20K. Each single-color unit 20Y, 20M, 20C, and 20K is equipped with a photoreceptor 22Y, 22M, 22C, and 22K, respectively. The photoreceptors 22Y, 22M, 22C, and 22K are examples of image holders. When viewing the image forming system 10 from the front side as shown in Figure 1, the single-color units 20Y, 20M, 20C, and 20K are arranged in the order listed above, from right to left in the width direction of the device (below the transfer belt 31). In the first embodiment, the polarity of the average charge amount of the toner used is negative, for example.

[0036] In the single-color units 20Y, 20M, 20C, and 20K, the components are the same except for the toner color. Therefore, when it is not necessary to distinguish the toner color, the designations Y, M, C, and K after each component may be omitted in the description. Each of the single-color units 20Y, 20M, 20C, and 20K has a charging roll 62, an exposure device 64, a developing device 66, and a cleaning blade 68 around a photoreceptor 22 that rotates in the direction indicated by the arrow. The charging roll 62 is an example of a charging part. The charging roll 62 rotates while in contact with the photoreceptor 22 and charges the photoreceptor 22 by applying a charging bias. The exposure device 64 exposes the photoreceptor 22 charged by the charging roll 62 to form a latent image on the photoreceptor 22. The developing device 66 is equipped with a developing roll 66A that develops the latent image formed on the photoreceptor 22 by the exposure device 64 with toner. The cleaning blade 68 removes toner remaining on the surface of the photoreceptor 22 after the toner image has been transferred to the transfer device 30. The developing device 66 is an example of a developing unit. The cleaning blade 68 is an example of a cleaning member.

[0037] The charging roll 62, for example, negatively charges the surface (photosensitive layer) of the photoreceptor 22. The negatively charged surface of the photoreceptor 22 exhibits positive polarity in the area irradiated with exposure light by the exposure device 64, and a latent image is formed on the surface of the photoreceptor 22. Then, toner that has been negatively triboelectrically charged in the developing device 66 adheres to the latent image that exhibits positive polarity, and the latent image is developed. As a result, a toner image is formed on the surface of the photoreceptor 22.

[0038] For example, the charging roll 62 is a circular rotating body. The charging roll 62 rotates in conjunction with the rotation of the photoreceptor 22. For example, a charging bias is applied to the charging roll 62, which is obtained by adding an AC voltage to a DC voltage. The charging roll 62 charges the photoreceptor 22 by adding an AC voltage to the DC voltage.

[0039] The cleaning blade 68 is located downstream of the primary transfer position that transfers the toner image on the surface of the photoreceptor 22 to the transfer belt 31, and upstream of the charging roll 62.

[0040] [Transfer device] The transfer device 30 has the function of first transferring the toner images formed on each photoreceptor 22Y, 22M, 22C, and 22K onto the transfer belt 31. Furthermore, the transfer device 30 has the function of secondarily transferring the toner images held on the transfer belt 31 onto the medium P. The medium P is an example of a recording medium, such as paper.

[0041] As shown in Figure 1, the transfer device 30 includes a transfer belt 31, a drive roll 32, a plurality of primary transfer rolls 34, a driven roll 36, and a tension roll 37. Furthermore, the transfer device 30 includes a secondary transfer roll 38, a concentration sensor 72, a support roll 74, and a cleaning blade 76. Here, the transfer belt 31 is an example of an intermediate transfer body, and the concentration sensor 72 is an example of a concentration detection unit.

[0042] The transfer belt 31 is endless and is wrapped around a drive roll 32 that rotates around an axis, and is driven by the drive roll 32 to rotate in a circumferential direction (direction of arrow A). In other words, the transfer belt 31 has the function of holding the toner image and transporting it in a circumferential direction (direction of arrow A). The transfer belt 31 holds the toner images that have been primary transferred by the primary transfer rolls 34 from the photoreceptors 22Y, 22M, 22C, and 22K on which the toner images of each color have been formed.

[0043] Furthermore, as shown in Figure 1, when the image forming system 10 is viewed from the front, a driven roll 36 is positioned below the driven roll 32, and a tension roll 37 is positioned above the driven roll 32 and to the right in the width direction of the device. In addition, a support roll 74 is positioned below the tension roll 37. The transfer belt 31 is then wrapped around the driven roll 32, driven roll 36, tension roll 37, and support roll 74 to determine its orientation.

[0044] (Primary transfer roll) The primary transfer roll 34 has the function of transferring the toner images held on the photoreceptors 22Y, 22M, 22C, and 22K to the transfer belt 31 when a transfer voltage is applied. The primary transfer roll 34 contacts the inner surface of the transfer belt 31 and rotates around its axis.

[0045] (Secondary transfer roll) The secondary transfer roll 38 has the function of transferring the toner image to the medium P by sandwiching the medium P between itself and a portion of the transfer belt 31 that is wrapped around the drive roll 32. The secondary transfer roll 38 is positioned on the opposite side of the drive roll 32 from the transfer belt 31, and together with the drive roll 32, it forms a nip N1 on the transfer belt 31.

[0046] The secondary transfer roll 38 rotates around its axis, and a transfer voltage is applied to the drive roll 32 from the power supply PS (see Figure 1). Thus, the secondary transfer roll 38 and the drive roll 32 transfer the toner image held by the transfer belt 31 to the medium P passing through the nip N1. The secondary transfer roll 38 is grounded.

[0047] (Tension Roll) The tension roll 37 has the function of applying tension to the transfer belt 31. The tension roll 37 rotates in association with the movement of the transfer belt 31 in the circumferential direction (direction of arrow A). The outer surface of the tension roll 37 is pressed against the inner surface of the transfer belt 31, thereby applying tension to the transfer belt 31. As a result, the transfer belt 31 moves in the circumferential direction (direction of arrow A) while under tension, conveying the toner image held on its surface.

[0048] (Support roll) The support roll 74 has the function of supporting the transfer belt 31 by contacting the inner surface of the transfer belt 31. The support roll 74 moves in conjunction with the circumferential movement of the transfer belt 31.

[0049] (Concentration sensor) The density sensor 72 has the function of measuring the density of the toner image transferred to 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. The density sensor 72 is positioned on the outer circumference of the transfer belt 31, facing the toner image forming unit 20 downstream in the circumferential direction of the transfer belt 31 and upstream of the driven roll 36.

[0050] As an example, the density sensors 72 are provided at both ends in the width direction intersecting the direction of movement of the transfer belt 31 (direction of arrow A). When measuring the toner density on the surface of the transfer belt 31 using the density sensors 72, the density sensors 72 irradiate the transfer belt 31 with light and detect the light reflected by the transfer belt 31. The output of the density sensors 72 is input to the control unit 100 (see Figure 1).

[0051] (Cleaning blade) The cleaning blade 76 has the function of contacting the surface of the transfer belt 31 and cleaning the surface of the transfer belt 31. The cleaning blade 76 is positioned downstream of the transfer position of the secondary transfer roll 38 in the circumferential direction (direction of arrow A) of the transfer belt 31. When the tip of the cleaning blade 76 contacts the surface of the transfer belt 31, any toner or other deposits remaining on the surface of the transfer belt 31 after the toner image has been secondary transferred are removed by the cleaning blade 76.

[0052] [Conveying equipment] The transport device 40 has the function of transporting the medium P contained in the medium storage section 42 along a transport path 46C including nip N1 and nip N2, and discharging it outside the housing of the image forming system 10. The transport device 40 comprises a discharge roll 46A and a plurality of transport roll pairs 46B.

[0053] [Fusing device] The fixing device 50 has the function of fixing the toner image transferred to the medium P by the transfer device 30 onto the medium P. The fixing device 50 is equipped with a heating roll 54 and a pressure roll 52. The fixing device 50 heats the medium P passing through the nip N2 formed by the heating roll 54 with the heating roll 54 and pressurizes it with the heating roll 54 and the pressure roll 52. This fixes the toner image onto the medium P.

[0054] [Control Unit] The control unit 100 has the function of controlling each component of the image forming system 10. The control unit 100 will be described later.

[0055] <Operation of the image forming system> Next, the operation of the image forming system 10 will be described.

[0056] When the image forming system 10 starts operating, the monochromatic units 20Y, 20M, 20C, and 20K of the toner image forming unit 20 form toner images of each color on the surface of the photoreceptors 22Y, 22M, 22C, and 22K through the processes of charging, exposure, and development. Specifically, the photoreceptor 22 is charged by the charging roll 62 and exposed by the exposure device 64, thereby forming a latent image on the surface of the photoreceptor 22. Furthermore, the latent image on the photoreceptor 22 is developed with toner by the development device 66. As a result, toner images of each color are formed on the surface of the photoreceptors 22Y, 22M, 22C, and 22K in the monochromatic units 20Y, 20M, 20C, and 20K.

[0057] In the image forming system 10, a primary transfer voltage is applied to the primary transfer rolls 34 of each color. The drive roll 32 rotates the transfer belt 31 in the direction of arrow A. As a result, the toner images of each color formed on the photoreceptors 22Y, 22M, 22C, and 22K are superimposed onto the transfer belt 31 and primary transferred.

[0058] Meanwhile, the transport device 40 transports the medium P contained in the medium storage unit 42 to the nip N1 so that the timing coincides with the arrival of the nip N1 at the portion of the transfer belt 31 where the toner images of each color have been primarily transferred. Then, when a transfer voltage is applied to the drive roll 32, an electric field is formed between the drive roll 32 and the secondary transfer roll 38, and the toner images of each color held on the transfer belt 31 are transferred to the medium P.

[0059] Furthermore, the transport device 40 transports the medium P onto which the toner images of each color have been transferred toward the nip N2 of the fuser device 50. The fuser device 50 then fixes the toner images of each color onto the medium P as it passes through the nip N2, forming an image on the medium P.

[0060] The image-forming medium P is discharged outside the device by the transport device 40. This completes the image-forming operation.

[0061] <Nip width of the electrostatic roll> Next, we will describe the nip width of the charging roll 62 for the photoreceptor 22.

[0062] Figure 2 shows a side view of the configuration near the charging roll 62, and Figure 3 shows a cross-sectional view of the configuration near the charging roll 62.

[0063] As shown in Figures 2 and 3, the charging roll 62 is positioned along the axial direction of the photoreceptor 22, and the charging roll 62 is in contact with the photoreceptor 22. On the side of the charging roll 62 opposite to the photoreceptor 22, a cleaning roll 80 is positioned to remove deposits from the surface of the charging roll 62. The cleaning roll 80 is positioned along the axial direction of the charging roll 62, and the cleaning roll 80 is in contact with the charging roll 62. Holding parts 82 are provided at both ends of the cleaning roll 80 in the axial direction to rotatably hold the shaft portion of the cleaning roll 80 (see Figure 2). Note that in Figure 2, the holding parts that rotatably hold the shaft portion 62A of the charging roll 62 and the holding parts that rotatably hold the shaft portion of the photoreceptor 22 are not shown.

[0064] As shown in Figure 2, for example, the holding portion 82 is supported by a symmetrical L-shaped support frame 84. The support frame 84 is pressed against the photoreceptor 22 by a coil spring 86. The coil spring 86 is an example of a pressing member. The coil spring 86 presses the charging roll 62 against the photoreceptor 22 so that a nip width NW is created (see Figure 3). Here, the nip width NW is the width over which the charging roll 62 is in contact with the photoreceptor 22 in the rotational direction of the photoreceptor 22 (arrow direction). For example, the charging roll 62 comprises a shaft portion 62A and a conductive elastic layer 62B formed around the shaft portion 62A. The charging roll 62 is pressed against the photoreceptor 22, creating a nip width NW of the charging roll 62. The coil spring 86 is provided at both ends of the cleaning roll 80 in the axial direction. For example, a coil spring 86 presses the charging roll 62 against the photoreceptor 22 via a cleaning roll 80.

[0065] Figure 4 is a graph showing the profile of the nip width NW of the charging roll 62 on the photoreceptor 22. Figure 4 shows the relationship between the axial position of the charging roll 62 and the nip width NW. Both axial ends of the charging roll 62 are pressed against the photoreceptor 22 by coil springs 86 (see Figure 2). Therefore, as shown in Figure 4, the nip width NW at both axial ends of the charging roll 62 is larger than the nip width NW at the axial center.

[0066] Figure 5 is a graph showing the relationship between the nip width NW and the amount of external additive adhering to the photoreceptor 22. The developer contains external additives. As shown in Figure 5, when the nip width NW of the charging roll 62 to the photoreceptor 22 increases, the external additive is more likely to adhere to the charging roll 62. If the nip width NW of the charging roll 62 to the photoreceptor 22 is, for example, 0.39 [mm] or less, poor follow-through is likely to occur when the charging roll 62 rotates in response to the rotation of the photoreceptor 22. Also, if the amount of external additive adhering to the charging roll 62 is, for example, 0.7 [mg] or more, poor charging of the photoreceptor 22 by the charging roll 62 is likely to cause toner fouling on the photoreceptor 22. In this example, when the nip width NW of the charging roll 62 to the photoreceptor 22 is, for example, 0.55 [mm] or more, the amount of external additive adhering to the charging roll 62 increases. In this case, poor charging of the photoreceptor 22 by the charging roll 62 makes it easier for toner to be generated on the photoreceptor 22 due to fouling. For this reason, if the nip width NW of the charging roll 62 on the photoreceptor 22 is, for example, 0.55 [mm] or more, it is desirable to remove any adhering substances such as external additives from the charging roll 62.

[0067] <Hardware configuration of the image forming system> Figure 6 is a block diagram showing the hardware configuration of the image forming system 10. Figure 6 omits hardware configurations that are not relevant to the main parts of this disclosure.

[0068] As shown in Figure 6, the image forming system 10 includes a control unit 100, a power supply 120 for the charging roll, an exposure device 64, a developing device 66, a power supply 124 for the primary transfer roll, motors 126, and a density sensor 72. The developing device 66 is equipped with a power supply 122 for the developing roll. Furthermore, the motors 126 drive the rolls in each part of the image forming system 10.

[0069] The control unit 100 comprises a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, storage 104, and an input / output interface 105. Each component is connected to the others via a bus 109 so that they can communicate with each other.

[0070] The CPU 101 is a central processing unit that executes various programs and controls various parts. The CPU 101 is an example of a processor. Specifically, the CPU 101 reads a program from the ROM 102 or 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 calculations according to the program recorded in the ROM 102 or storage 104. In the first embodiment, an information processing program is stored in the ROM 102 or storage 104.

[0071] ROM 102 stores various programs and data. RAM 103 temporarily stores programs or data as a working area. Storage 104 consists of an HDD (Hard Disk Drive) or SSD (Solid State Drive) and stores various programs, including the operating system, and various data. The printer driver program is stored in storage 104. The CPU 101 reads the printer driver program from storage 104 and functions as a printer driver by executing the program.

[0072] The input / output interface 105 is an interface for communicating with each device mounted on the image forming system 10. The control unit 100 is connected via the input / output interface 105 to the power supply 120 for the charging roll, the exposure device 64, the developing device 66, the power supply 124 for the primary transfer roll, the motors 126, and the density sensor 72.

[0073] The output value, which is the measured value obtained by the concentration sensor 72, is input to the control unit 100.

[0074] The power supply 120 for the charging roll applies a charging bias (i.e., a charging voltage) to the charging roll 62. This charges the photoreceptor 22.

[0075] The developing roll power supply 122 applies a developing voltage to the developing roll 66A. During normal image formation, the application of the developing voltage to the developing roll 66A causes the latent image on the photoreceptor 22 to be developed by the toner, forming a toner image.

[0076] The primary transfer roll power supply 124 applies a primary transfer voltage to the primary transfer roll 34. During normal image formation, the primary transfer voltage applied to the primary transfer roll 34 causes the toner image on the surface of the photoreceptor 22 to be transferred to the transfer belt 31.

[0077] The CPU 101 of the control unit 100 controls the power supply 120 for the charging roll, the exposure device 64, the developing device 66, the power supply 124 for the primary transfer roll, and the motors 126 in the single-color units 20Y, 20M, 20C, and 20K of the toner image forming unit 20.

[0078] The CPU 101 performs a nip width detection mode to detect the nip width NW of the charging roll 62 on the photoreceptor 22. For example, at the timing of density adjustment after the image forming system 10 has printed a predetermined number of sheets, between 50 and 100 sheets, the CPU 101 switches from the normal image forming mode to the nip width detection mode.

[0079] The CPU 101 performs cleaning of the charged roll 62 according to the detection result of the nip width NW of the charged roll 62 obtained by the nip width detection mode.

[0080] <Detection of the nip width of the electrostatic roll> Next, we will describe the process of detecting the nip width NW of the charging roll 62 on the photoreceptor 22.

[0081] Figure 7 shows the potential of each part, the developing toner of the photoreceptor 22, and the output of the density sensor 72 as time is detected when detecting the nip width NW of the charging roll 62 on the photoreceptor 22. As shown in Figure 7, in the nip width detection mode, the CPU 101 sets the absolute value of the surface potential 136A of the photoreceptor 22 charged by the charging roll 62 to be lower than the absolute value of the developing potential 132 of the developing device 66. For example, by setting the absolute value of the potential of the charging roll 62 (i.e., the potential of the charging bias) 134A to be lower than the absolute value of the developing potential 132, the CPU 101 sets the absolute value of the surface potential 136A of the photoreceptor 22 to be lower than the absolute value of the developing potential 132 of the developing device 66.

[0082] As an example, the developing potential 132 of the developing device 66 is set to -500V, and the surface potential 136A of the photoreceptor 22 is set to -400V. As an example, the potential of the charging roll 62 (i.e., the potential of the charging bias) 134A is set to -450V. This results in a state where the absolute value of the surface potential 136A of the photoreceptor 22 charged by the charging roll 62 (e.g., 400V) is lower than the absolute value of the developing potential 132 of the developing device 66 (e.g., 500V).

[0083] As an example, in nip width detection mode, the absolute value of the potential 134A of the charging roll 62 is lowered without changing the development potential 132 of the developing device 66 as in normal image formation mode. This results in a state where the absolute value of the surface potential 136A of the photoreceptor 22 charged by the charging roll 62 is lower than the absolute value of the development potential 132 of the developing device 66.

[0084] As shown in Figure 7, the CPU 101 increases the absolute value of the potential 134B of the charging roll 62 in a square wave manner so that the absolute value of the surface potential 136B of the photoreceptor 22 is higher than the absolute value of the developing potential 132 of the developing device 66, but only for a predetermined set time. The set time is the time during which instantaneous discharge occurs before and after the nip width NW of the charging roll 62 on the photoreceptor 22, but no discharge occurs in the center of the nip width NW.

[0085] As an example, the potential 134B of the charging roll 62 is set to a square wave between -700V and -800V, and the surface potential 136B of the photoreceptor 22 is set to -600V. As a result, the absolute value of the surface potential 136B of the photoreceptor 22 (e.g., 600V) becomes higher than the absolute value of the developing potential 132 of the developing device 66 (e.g., 500V).

[0086] As shown in Figure 8, the charged roll 62 discharges before and after the nip width NW between it and the photoreceptor 22 (see discharge state ED shown in Figure 8). That is, discharge occurs in the space between the charged roll 62 and the photoreceptor 22 before and after the nip width NW. Therefore, as shown in Figure 7, if the absolute value of the potential 134B of the charged roll 62 is instantaneously increased, no discharge occurs within the nip width NW, and the absolute value of the surface potential 136A of the photoreceptor 22 does not increase. As an example, the surface potential 136A of the photoreceptor 22 in the area where no discharge occurs is -400V.

[0087] The setting time for increasing the absolute value of the potential 134B of the charged roll 62 using a square wave is set, for example, as follows: When the diameter of the charging roll 62 is d [mm] and the rotation speed of the photoreceptor 22 is v [mm / sec], the set time t [ms] is: t = d / v × 2.92 ± 5% That is the case.

[0088] For example, when the diameter d of the charging roll 62 is φ12 [mm] and the rotation speed v of the photoreceptor 22 is 175 [mm / sec], the set time t [ms] will be 0.2 ± 5% [ms].

[0089] The minimum setting time is the time it takes to reach the required potential of the charged roll 62 at 134B, and the maximum setting time is the time at which there is no remaining undischarged section in the nip width NW.

[0090] For example, the minimum setting time is 0.15 ms, which is the time it takes for the potential of the charging roll 62 to rise from -600V to -900V when the rotation speed is 175 mm / sec. Also, for example, the maximum setting time is 0.3 mm / 175 mm / sec = 1.7 ms, assuming a minimum assumed nip width of 0.3 mm. For example, with the diameter and hardness of the charging roll 62 in the first embodiment, the assumed minimum nip width is 0.3 mm. Note that in the rotation direction of the photoreceptor 22, once the pre-discharge start positions before and after the nip width NW reach the post-discharge start position, there will be no areas that are not discharged.

[0091] For the above-mentioned set time only, by increasing the absolute value of the potential 134B of the charging roll 62 in a square wave, a region with a low absolute value of the surface potential 136A of the photoreceptor 22 is formed between the region with a high absolute value of the surface potential 136B of the photoreceptor 22. The region with a high absolute value of the surface potential 136B of the photoreceptor 22 and the region with a low absolute value of the surface potential 136A of the photoreceptor 22 correspond to the "latent image" in the nip width detection mode. As a result, as shown in Figure 7, the developing toner of the photoreceptor 22 developed by the developing device 66 is formed in the region where the absolute value of the surface potential 136A of the photoreceptor 22 is lower than the absolute value of the developing potential 132. That is, since toner is negative polarity, the developing toner is formed in the region where the surface potential 136A of the photoreceptor 22 is -400V. The position P2 where there is fouling toner (i.e., developing toner) during the state S1 in which there is little fouling toner in the rotational direction of the photoreceptor 22 corresponds to the nip width NW.

[0092] The fouling toner (i.e., developing toner) on the surface of the photoreceptor 22 is first transferred to the transfer belt 31, and the fouling toner (i.e., developing toner) on the transfer belt 31 is measured by the density sensor 72. As shown in Figure 7, the output of the density sensor 72 corresponds to the nip width NW. In other words, the density sensor 72 measures the width of the position P2 where the fouling toner (i.e., developing toner) is located during the state S1 where there is little fouling toner. The CPU 10 predicts the nip width NW of the charging roll 62 to the photoreceptor 22 according to the measurement value of the width of the position P2 where the toner (i.e., developing toner) is located, measured by the density sensor 72. In this example, the fouling toner (i.e., developing toner) on the surface of the photoreceptor 22 is first transferred to the transfer belt 31, so the fouling toner (i.e., developing toner) on the surface of the photoreceptor 22 is measured indirectly by the density sensor 72.

[0093] As an example, the density of the fouling toner (i.e., developing toner) on the transfer belt 31 is measured by the density sensor 72 approximately 10 times consecutively, and the nip width NW is predicted using the average value.

[0094] The density sensor 72 is positioned opposite both axial ends of the transfer belt 31, as described above. The density sensor 72 measures the toner density only at the position corresponding to the axial end of the photoreceptor 22. Based on the measurement from the density sensor 72, the CPU 10 predicts the nip width NW of the charging roll 62 at the axial end of the photoreceptor 22.

[0095] <Cleaning the electrostatic roller> Next, we will explain how to clean the electrostatic roll 62.

[0096] The CPU 101 performs a cleaning mode to clean the charged roll 62 when the nip width NW of the charged roll 62, which corresponds to the measurement value of the concentration sensor 72, is greater than or equal to a threshold. The cleaning mode is an example of a cleaning mode.

[0097] The threshold is set to, for example, 0.55. As mentioned above, if the nip width NW is 0.55 [mm] or more, the amount of external additive adhering to the charging roll 62 increases, and the amount of toner fouling on the photoreceptor 22 increases due to poor charging (see Figure 5). Therefore, by setting the threshold to, for example, 0.55 and cleaning the charging roll 62, the amount of toner fouling on the photoreceptor 22 can be reduced.

[0098] Before explaining the cleaning mode, let's describe an example of normal image formation. As shown in Figure 9(A), during normal image formation, after the primary transfer roll 34 is de-staticized, the photoreceptor 22 is charged by the charging roll 62, and the photoreceptor 22 is exposed or de-staticized by the exposure device 64. As a result, the latent image formed on the surface of the photoreceptor 22 is developed by the toner on the developing roll 66A. The toner image on the photoreceptor 22 is transferred to the transfer belt 31 by the primary transfer roll 34.

[0099] As shown in Figure 9(B), during normal image formation, the absolute value of the potential of the photoreceptor 22 becomes low, and the absolute value of the potential of the charging roll 62 becomes high. Therefore, any substances such as external additives adhering to the surface of the charging roll 62 are less likely to move to the photoreceptor 22.

[0100] As shown in Figure 10(A), in cleaning mode, the relationship between the potential of the photoreceptor 22 and the potential of the charging roll 62 is reversed. For example, the output of the primary transfer roll 34 is turned off, the output of the charging roll 62 is turned off, and the output of the exposure device 64 is turned off. As a result, as shown in Figure 10(B), the absolute value of the potential of the photoreceptor 22 increases, and the absolute value of the potential of the charging roll 62 decreases. For example, the potential of the photoreceptor 22 is -600V to -700V. Therefore, dirt on the surface of the charging roll 62 (i.e., deposits such as external additives) is transferred to the photoreceptor 22. Dirt on the surface of the photoreceptor 22 (i.e., deposits such as external additives) is removed by the cleaning blade 68. Alternatively, the dirt on the surface of the photoreceptor 22 (i.e., deposits such as external additives) may be transferred to the transfer belt 31 and removed by the cleaning blade 76.

[0101] Furthermore, when the nip width NW of the charging roll 62 corresponding to the measurement value of the density sensor 72 is above a threshold, the CPU 101 increases the absolute value of the potential of the charging roll 62 that charges the photoreceptor 22 during image formation, compared to the absolute value of the potential of the normal charging roll 62. By increasing the absolute value of the potential of the charging roll 62 compared to the absolute value of the potential of the normal charging roll 62, it is possible to suppress charging defects (i.e., fogging of the photoreceptor 22) that occur due to a wide nip width NW of the charging roll 62 and the progression of contamination. For example, the absolute value of the potential of the charging roll 62 is set to be +10V higher than the absolute value of the potential of the normal charging roll 62. This makes it less likely for charging defects (i.e., fogging of the photoreceptor 22) to occur due to the nip width NW of the charging roll 62 being non-uniform in the axial direction.

[0102] <Operation of the image forming system 10> Figure 11 is a flowchart showing the information processing flow of the image forming system 10. In the image forming system 10, information processing is performed by the CPU 101 reading an information processing program from the ROM 102 or storage 104, loading it into the RAM 103, and executing it.

[0103] As shown in Figure 11, the CPU 101 performs a detection sequence for the nip width NW of the charging roll 62 on the photoreceptor 22 (step S301).

[0104] Specifically, after performing a predetermined number of prints, the CPU 101 switches from the normal image formation mode to the nip width detection mode. As shown in Figure 7, the CPU 101 maintains a state where the absolute value of the surface potential 136A of the photoreceptor 22 charged by the charging roll 62 is lower than the absolute value of the development potential 132 of the developing device 66. In this state, the CPU 101 increases the absolute value of the potential 134B of the charging roll 62 in a square wave for a predetermined set time only, so that the absolute value of the surface potential 136B of the photoreceptor 22 becomes higher than the absolute value of the development potential 132 of the developing device 66. The set time is the time during which instantaneous discharge occurs before and after the nip width NW of the charging roll 62 on the photoreceptor 22, but no discharge occurs in the center of the nip width NW. As a result, a region with a low absolute value of the surface potential 136A of the photoreceptor 22 is formed between the regions with a high absolute value of the surface potential 136B of the photoreceptor 22.

[0105] As a result, the developing toner of the photoreceptor 22 developed by the developing device 66 is formed in areas where the absolute value of the surface potential 136A of the photoreceptor 22 is lower than the absolute value of the developing potential 132 (see Figure 7). The position P2 where there is fouling toner (i.e., developing toner) during the state S1 in which there is little fouling toner in the rotational direction of the photoreceptor 22 corresponds to the nip width NW.

[0106] Next, the fouling toner (i.e., developing toner) on the surface of the photoreceptor 22 is first transferred to the transfer belt 31, and the fouling toner (i.e., developing toner) on the transfer belt 31 is measured by the density sensor 72. The CPU 10 predicts the nip width NW of the charging roll 62 to the photoreceptor 22 according to the measurement value of the width of the position P2 where the toner (i.e., developing toner) is located, as measured by the density sensor 72.

[0107] As shown in Figure 11, the CPU 101 determines whether the nip width NW is greater than or equal to a threshold (step S302). As mentioned above, the threshold is, for example, 0.55.

[0108] If the nip width NW is greater than or equal to a threshold (step S302: YES), the CPU 101 performs a cleaning sequence for the charged roll 62 (step S303).

[0109] Specifically, the CPU 101 switches to the cleaning mode for the charging roll 62. As shown in Figure 10(A), for example, the output of the primary transfer roll 34 is turned off, the output of the charging roll 62 is turned off, and the output of the exposure device 64 is turned off. As a result, as shown in Figure 10(B), the absolute value of the potential of the photoreceptor 22 increases and the absolute value of the potential of the charging roll 62 decreases. This causes the dirt on the surface of the charging roll 62 (i.e., deposits such as external additives) to be transferred to the photoreceptor 22, and the dirt on the surface of the photoreceptor 22 (i.e., deposits such as external additives) is removed by the cleaning blade 68.

[0110] As shown in Figure 11, if the nip width NW is not greater than or equal to the threshold (step S302: NO), the CPU 101 terminates processing based on the information processing program of the image forming system 10.

[0111] This completes the processing based on the information processing program of the image forming system 10.

[0112] In the image forming system 10 described above, the nip width NW of the charging roll 62 on the photoreceptor 22 can be estimated.

[0113] Furthermore, in the image forming system 10, when the diameter of the charging roll 62 is d [mm] and the rotation speed of the photoreceptor 22 is v [mm / sec], the set time t [ms] is: t = d / v × 2.92 ± 5% That is the case. Therefore, in the image forming system 10, compared to the case where time t is longer than d / v × 2.92 + 5%, the position P2 where there is toner fouling corresponding to the nip width NW of the charging roll can be formed while there is less toner fouling in the rotational direction of the photoreceptor 22 (see Figure 7). Also, in the image forming system 10, compared to the case where time t is shorter than d / v × 2.92 - 5%, the position P2 where there is toner fouling corresponding to the nip width NW of the charging roll can be formed while there is less toner fouling in the rotational direction of the photoreceptor 22 (see Figure 7).

[0114] Furthermore, in the image forming system 10, the minimum set time is the time required to reach the necessary potential of the charging roll 62, and the maximum set time is less than or equal to the time at which there is no remaining section in the nip width NW that is not discharged. Therefore, in the image forming system 10, by increasing the absolute value of the potential of the charging roll 62 only for the set time, it is possible to form a position P2 where there is toner fouling opposite the nip width NW of the charging roll 62 while there is little toner fouling in the rotational direction of the photoreceptor 22 (see Figure 7).

[0115] Furthermore, in the image forming system 10, the CPU 101 predicts the nip width NW of the charging roll 62 to the photoreceptor 22 based on a measurement value indirectly obtained by measuring the width of the position P2 where there is toner fouling in the rotational direction of the photoreceptor 22. Therefore, the image forming system 10 can estimate the nip width NW of the charging roll 62 to the photoreceptor 22 based on the measurement value of the width of the position P2 where there is toner fouling.

[0116] Furthermore, the image forming system 10 includes a transfer belt 31 for transferring toner from the surface of the photoreceptor 22, and a density sensor 72 for detecting the density of the toner transferred to the transfer belt 31. Therefore, the image forming system 10 can measure the width of the toner overhang while there is little toner overhang by detecting the density of the toner transferred to the transfer belt 31 with the density sensor 72.

[0117] Furthermore, in the image forming system 10, toner density is measured only at positions corresponding to the axial ends of the photoreceptor 22. Therefore, in the image forming system 10, it is easier to measure the width of toner fouling in the rotational direction of the photoreceptor 22 compared to when toner density is measured over the entire axial direction of the photoreceptor.

[0118] Furthermore, the CPU 101 performs a cleaning mode to clean the charging roll 62 when the nip width NW of the charging roll 62, which corresponds to the measurement value of the density sensor 72, is greater than or equal to a threshold. Therefore, the image forming system 10 can suppress the occurrence of charging defects of the photoreceptor 22 caused by the charging roll 62, compared to the case where the nip width of the charging roll to the photoreceptor is unknown.

[0119] Furthermore, the image forming system 10 is equipped with a cleaning blade 68 for cleaning the surface of the photoreceptor 22, located downstream of the transfer position where the toner image on the surface of the photoreceptor 22 is transferred to the transfer belt 31, and upstream of the charging roll 62. In cleaning mode, dirt on the charging roll 62 is transferred to the photoreceptor 22, and the cleaning blade 68 removes the dirt from the photoreceptor 22. Therefore, in the image forming system 10, dirt on the charging roll 62 can be removed from the photoreceptor 22 by the cleaning blade 68.

[0120] Furthermore, when the nip width NW of the charging roll 62 corresponding to the measurement value of the density sensor 72 is greater than or equal to a threshold, the CPU 101 increases the absolute value of the potential of the charging roll 62 that charges the photoreceptor 22 during image formation compared to the absolute value of the potential of the normal charging roll 62. As a result, in the image forming system 10, the occurrence of charging defects of the photoreceptor 22 by the charging roll 62 is suppressed compared to the case where the potential of the charging roll during image formation is constant.

[0121] Furthermore, in the image forming system 10, the state in which the absolute value of the surface potential of the photoreceptor 22 charged by the charging roll is lower than the absolute value of the development potential of the developing device 66 is achieved by lowering the absolute value of the potential of the charging roll 62 without changing the development potential of the developing device 66. Therefore, in the image forming system 10, the cost of the output substrate of the developing device 66 can be reduced compared to the case where the development potential of the developing device is changed.

[0122] Furthermore, in the image forming system 10, the charging roll 62 charges the photoreceptor 22 by adding an AC voltage to the DC voltage. Therefore, in the image forming system 10, the surface potential of the photoreceptor 22 is stabilized compared to the case where the surface of the photoreceptor is charged with DC voltage alone.

[0123] In the first embodiment, the toner density was measured once by the density sensor 72, and a cleaning mode was performed once to clean the charging roll 62 according to the nip width NW of the charging roll 62 corresponding to the measured value. However, this disclosure is not limited to this configuration. The CPU 101 may increase the frequency of the cleaning mode to clean the charging roll 62 according to the nip width of the charging roll 62 corresponding to the measured value of the density sensor 72. For example, the cleaning mode may be performed two or more times for each measurement of the width of the fouled toner. As a result, the image forming system 10 can suppress the occurrence of charging defects of the photoreceptor 22 by the charging roll 62 compared to the case where the cleaning mode is performed once for each measurement of the width of the fouled toner.

[0124] [Second Embodiment] Next, the image forming system according to the second embodiment will be described. Note that components identical to those in the first embodiment described above will be given the same numbers and their descriptions will be omitted.

[0125] Figure 12 shows the toner image forming unit 401 of the image forming system 400 according to the second embodiment. As shown in Figure 12, the toner image forming unit 401 of the image forming system 400 includes a photoreceptor 402 that rotates in the direction of the arrow. The photoreceptor 402 is an example of an image holder. The image forming system 400 also includes a charging roll 62, an exposure device 64, a developing device 404, a transfer roll 406, and a cleaning blade 68 around the photoreceptor 402. Furthermore, the image forming system 400 includes a density sensor 420. The developing device 404 is an example of a developing unit.

[0126] In the image forming system 400, a transfer roll 406 is positioned below the photoreceptor 402 in the vertical direction. The transfer roll 406 directly transfers the toner image formed on the surface of the photoreceptor 402 to a medium P that is transported between the photoreceptor 402 and the transfer roll 406. The medium P is, for example, paper. A density sensor 420 is an example of a detection unit. The density sensor 420 is positioned between the developing device 404 and the transfer roll 406 in the rotational direction of the photoreceptor 402. The density sensor 420 detects the density of toner on the surface of the photoreceptor 402. As an example, the density sensor 420 is positioned opposite both ends of the photoreceptor 402 in the axial direction.

[0127] Furthermore, the other components of the image forming system 400 are the same as those of the mono-color unit of the toner image forming section 20 of the image forming system 10 of the first embodiment. The image forming system 400 includes a nip width detection mode for detecting the nip width NW of the charging roll 62 to the photoreceptor 402. In addition, the image forming system 400 includes a cleaning mode for cleaning the charging roll 62 according to the nip width NW.

[0128] The image forming system 400 of the second embodiment has the following effects in addition to the effects of having the same configuration as the image forming system 10 of the first embodiment.

[0129] In the image forming system 400, the density of toner on the surface of the photoreceptor 402 is directly detected by the density sensor 420. The density sensor 420 can measure the width of the toner overlay on the surface of the photoreceptor 402 when there is little toner overlay. In the image forming system 400, the nip width NW of the charging roll 62 to the photoreceptor 402 can be predicted according to the width of the toner overlay and the directly measured value.

[0130] 〔supplementary explanation〕 The image forming systems of this disclosure are not limited to the image forming systems 10,400 described in the first and second embodiments, and various modifications are possible. In the first embodiment, density sensors 72 were provided at positions facing the transfer belt 31 corresponding to both axial ends of the photoreceptor 22, but this disclosure is not limited to this configuration. For example, if a profile of the charging roll 62 on the photoreceptor 22 is obtained, the nip width NW at the axial end of the charging roll 62 can be predicted, and therefore the position of the density sensor 72 can be changed.

[0131] Similarly, in the second embodiment, the density sensor 420 was provided at positions facing both axial ends of the photoreceptor 402, but the disclosure is not limited to this configuration. For example, if a profile of the charging roll 62 on the photoreceptor 402 is obtained, the nip width NW at the axial end of the charging roll 62 can be predicted, and therefore the position of the density sensor 420 can be changed.

[0132] Furthermore, in the first embodiment, the configuration of the coil spring 86 for pressing the charging roll 62 against the photoreceptor 22 can also be changed.

[0133] Furthermore, the processing of the image forming systems 10 and 400 described above can also be implemented by dedicated hardware circuits. In this case, the processing may be performed on a single piece of hardware or on multiple pieces of hardware.

[0134] Furthermore, the program for operating the image forming systems 10 and 4300 may be provided on a computer-readable recording medium such as a USB (Universal Serial Bus) memory, flexible disk, or CD-ROM (Compact Disc Read Only Memory), or it may be provided online via a network such as the Internet. In this case, the program recorded on the computer-readable recording medium is usually transferred to and stored in memory or storage. This program may also be provided as a standalone application software, or it may be incorporated into the software of each device as a function of the image forming systems 10 and 400.

[0135] Although the present invention has been described in detail with respect to specific embodiments, it will be apparent to those skilled in the art that the present invention is not limited to these embodiments, and that various other embodiments are possible within the scope of the present invention.

[0136] [Note] The following are preferred embodiments of this disclosure.

[0137] (((1))) A rotating image holder, A charging unit that rotates while in contact with the image holder and charges the surface of the image holder by applying a charging bias, A pressing member that presses the charged portion against the image holder so that a nip width is created, A developing unit that develops a latent image formed on the surface of the image holder using toner, At least one processor, Equipped with, The aforementioned processor, An image forming system comprising: when the absolute value of the surface potential of the image holder charged by the charging unit is lower than the absolute value of the development potential of the developing unit, instantaneous discharge is generated on the image holder before and after the nip width of the charging unit, and the absolute value of the potential of the charging unit is increased in a rectangular wave manner only for a set time during which no discharge occurs in the center of the nip width, so that the absolute value of the surface potential of the image holder becomes higher than the absolute value of the development potential.

[0138] (((2))) The aforementioned charging part is a circular rotating body, When the diameter of the charged part is d [mm] and the rotation speed of the image holder is v [mm / sec], The aforementioned set time t[ms] is, t = d / v × 2.92 ± 5% The image forming system according to claim 1.

[0139] (((3))) The image forming system according to (((1))) or (((2))), wherein the minimum value of the setting time is the time required to reach the potential of the charged part, and the maximum value of the setting time is less than or equal to the time at which no discharge remains in the nip width.

[0140] (((4))) The aforementioned processor, An image forming system according to any one of (((1))) to (((3))), wherein the nip width of the charged portion on the image holder is predicted according to a measurement value obtained by directly or indirectly measuring the width of the position where there is fouling toner while there is little fouling toner in the rotational direction of the image holder.

[0141] (((5))) An intermediate transfer body for transferring toner from the surface of the image holder, A concentration detection unit for detecting the concentration of toner transferred to the intermediate transfer medium, The image forming system according to (((4))) having

[0142] (((6))) The image forming system according to (((4))), further comprising a detection unit for detecting the concentration of toner on the surface of the image holder.

[0143] (((7))) The image forming system according to (((5))) or (((6))), wherein the measurement of the toner concentration is performed only at a position corresponding to the axial end of the image holder.

[0144] (((8))) The aforementioned processor, The image forming system according to (((4))), wherein a cleaning mode is performed to clean the charged portion when the nip width of the charged portion corresponding to the measured value is greater than or equal to a threshold.

[0145] (((9))) The aforementioned processor, The image forming system according to ((8))) which increases the frequency of the cleaning mode for cleaning the charged portion according to the nip width of the charged portion corresponding to the measured value.

[0146] (((10))) Downstream of the transfer position where the toner image on the surface of the image holder is transferred to the medium, and upstream of the charging unit, a cleaning member is provided for cleaning the surface of the image holder. The image forming system according to ((8)) in which, in the cleaning mode, the dirt on the charged part is transferred to the image holder, and the dirt on the image holder is removed by the cleaning member.

[0147] (((11))) The aforementioned processor, The image forming system according to (((4))), wherein when the nip width of the charging portion corresponding to the measured value is greater than or equal to a threshold, the absolute value of the potential of the charging portion that charges the image holder during image formation is increased to a value greater than the normal absolute value of the potential of the charging portion.

[0148] (((12))) The image forming system according to any one of (((1))) to (((11))) in which the absolute value of the surface potential of the image holder charged by the charging unit is lower than the absolute value of the development potential of the developing unit, by lowering the absolute value of the potential of the charging unit without changing the development potential of the developing unit.

[0149] (((13))) The image forming system according to any one of (((1))) to (((12))), wherein the charging unit charges the image holder by adding an AC voltage to the DC voltage.

[0150] According to the image forming system described in (((1))), the nip width of the charged portion on the image holder can be estimated.

[0151] According to the image forming system of (((2))), compared to the case where time t is longer than d / v × 2.92 + 5% or time t is shorter than d / v × 2.92 - 5%, it is possible to form a position where there is toner covering the charged portion corresponding to the nip width while there is less toner covering the image holder in the rotational direction.

[0152] According to the image forming system described in (((3))), by increasing the absolute value of the potential of the charged part for a set time, it is possible to form a position where there is fouling toner opposite to the nip width of the charged part while there is little fouling toner in the rotational direction of the image holder.

[0153] According to the image forming system described in (((4))), the nip width of the charged portion on the image holder can be estimated by measuring the width of the position where the toner fouling is present.

[0154] According to the image forming system described in (((5))), the density of the toner transferred to the intermediate transfer medium is detected by the density detection unit, which allows for the measurement of the width of the toner overlay while the amount of toner overlay is low.

[0155] According to the image forming system described in (((6))), the density of toner on the surface of the image holder can be directly detected by the detection unit, thereby allowing the width of the toner overhang to be measured while the amount of toner overhang is low.

[0156] According to the image forming system described in (((7))), it is easier to measure the width of the toner fouling in the rotational direction of the image holder compared to measuring the toner density over the entire axial direction of the image holder.

[0157] According to the image forming system described in (((8))), the occurrence of charging defects of the image holder by the charging part can be suppressed compared to the case where the nip width of the charging part on the image holder is unknown.

[0158] According to the image forming system described in (((9))), compared to the case where the cleaning mode is performed once each time the width of the fouled toner is measured, the occurrence of charging defects in the image holder due to the charged part is suppressed.

[0159] According to the image forming system (((10))), dirt on the charged portion can be removed by the cleaning member of the image holder.

[0160] According to the image forming system described in (((11))), the occurrence of charging defects in the image holder by the charged part is suppressed compared to the case where the potential of the charged part is constant during image formation.

[0161] According to the image forming system described in (((12))), the cost of the output substrate of the developing unit can be reduced compared to the case where the developing potential of the developing unit is changed.

[0162] According to the image forming system described in (((13))), the surface potential of the image holder is stabilized compared to the case where the surface of the image holder is charged with DC voltage alone. [Explanation of Symbols]

[0163] 10 Image Forming Systems 22 Photoreceptor (an example of an image-retaining element) 31. Transfer belt (an example of an intermediate transfer body) 62. Charging Roll (Example of a Charging Section) 66 Developing device (an example of a developing unit) 68 Cleaning blade (an example of a cleaning component) 72. Concentration Sensor (Example of a concentration detection unit) 86. Coil spring (an example of a pressing member) 101 CPU (an example of a processor) 132 Development Potential 134A Potential of a Charged Roll 134B Potential of a charged roll 136A Surface potential of a photoreceptor (an example of the surface potential of an image-retaining material) 136B Surface potential of a photoreceptor (an example of the surface potential of an image-retaining material) 400 Image Forming Systems 402 Photoreceptor (an example of an image-retaining element) 404 Developing device (an example of a developing unit) 420 Concentration Sensor (Example of Detection Unit) NW Nip width

Claims

1. A rotating image holder, A charging unit that rotates while in contact with the image holder and charges the surface of the image holder by applying a charging bias, A pressing member that presses the charged portion against the image holder so that a nip width is created, A developing unit that develops a latent image formed on the surface of the image holder using toner, At least one processor, Equipped with, The aforementioned processor, An image forming system comprising: when the absolute value of the surface potential of the image holder charged by the charging unit is lower than the absolute value of the development potential of the developing unit, instantaneous discharge is generated on the image holder before and after the nip width of the charging unit, and the absolute value of the potential of the charging unit is increased in a rectangular wave manner only for a set time during which no discharge occurs in the center of the nip width, so that the absolute value of the surface potential of the image holder becomes higher than the absolute value of the development potential.

2. The aforementioned charging part is a circular rotating body, When the diameter of the charged part is d [mm] and the rotation speed of the image holder is v [mm / sec], The aforementioned set time t [ms] is, t=d / v×2.92±5% The image forming system according to claim 1.

3. The image forming system according to claim 1, wherein the minimum value of the setting time is the time required to reach the potential of the charged part, and the maximum value of the setting time is less than or equal to the time at which no discharge section remains in the nip width.

4. The aforementioned processor, The image forming system according to claim 1, wherein the nip width of the charged portion on the image holder is predicted according to a measurement value obtained by directly or indirectly measuring the width of the position where there is fouling toner while the fouling toner is low in the rotational direction of the image holder.

5. An intermediate transfer body for transferring toner from the surface of the image holder, A concentration detection unit for detecting the concentration of toner transferred to the intermediate transfer medium, The image forming system according to claim 4, having the following features.

6. The image forming system according to claim 4, further comprising a detection unit for detecting the concentration of toner on the surface of the image holder.

7. The image forming system according to claim 5 or claim 6, wherein the measurement of the toner concentration is performed only at a position corresponding to the axial end of the image holder.

8. The aforementioned processor, The image forming system according to claim 4, wherein a cleaning mode is performed to clean the charged portion when the nip width of the charged portion corresponding to the measured value is greater than or equal to a threshold.

9. The aforementioned processor, The image forming system according to claim 8, wherein the frequency of the cleaning mode for cleaning the charged portion is increased according to the nip width of the charged portion corresponding to the measured value.

10. Downstream of the transfer position where the toner image on the surface of the image holder is transferred to the medium, and upstream of the charging unit, a cleaning member is provided for cleaning the surface of the image holder. The image forming system according to claim 8, wherein in the cleaning mode, the dirt on the charged portion is transferred to the image holder, and the dirt on the image holder is removed by the cleaning member.

11. The aforementioned processor, The image forming system according to claim 4, wherein when the nip width of the charging portion corresponding to the measured value is greater than or equal to a threshold, the absolute value of the potential of the charging portion that charges the image holder during image formation is increased to a value greater than the normal absolute value of the potential of the charging portion.

12. The image forming system according to claim 1, wherein the absolute value of the surface potential of the image holder charged by the charging unit is lower than the absolute value of the development potential of the developing unit, by lowering the absolute value of the potential of the charging unit without changing the development potential of the developing unit.

13. The image forming system according to claim 1, wherein the charging unit charges the image holder by adding an AC voltage to the DC voltage.

Images