Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent a change in the surface resistivity of an intermediate transfer belt over a long period, and can continue high-quality image formation.SOLUTION: An image forming apparatus comprises: an endless intermediate transfer belt 31; a plurality of rollers; a density detection unit 11; and a positioning unit 12. The positioning unit 12 is arranged opposite to the density detection unit 11 on an inter peripheral side of the intermediate transfer belt 31, and is in contact with an inner peripheral surface of the intermediate transfer belt 31 to maintain the gap between the intermediate transfer belt 31 and the density detection unit 11 to be a predetermined interval. The positioning unit 12 has a support member 121 that is arranged opposite to the inner peripheral side of the intermediate transfer belt 31, and a nonwoven fabric 122 that has conductivity, and is laminated on an opposing surface of the support member 121 to the intermediate transfer belt 31 to be brought into contact with the inner peripheral surface of the intermediate transfer belt 31.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Electrophotographic image forming devices, such as copiers and printers, widely use devices that supply toner to an electrostatic latent image formed on the outer surface of a photosensitive drum and develop it to form a toner image that is later transferred to a sheet (recording medium). The density of the toner image formed by the image forming device changes over time for various reasons. For this reason, it is common to form a toner image (reference image) for density correction on the outer surface of the photosensitive drum or intermediate transfer belt, and then perform calibration by detecting the toner density of the toner image with a sensor to perform density correction. To perform appropriate density correction, it is important to maintain a constant distance between the sensor and the toner image.

[0003] The conventional image forming apparatus disclosed in Patent Document 1 includes a reading sensor that reads a toner image formed on the surface of an endless belt-like image holding member, and a backup member located on the back side of the image holding member facing the reading sensor. The backup member abuts against the image holding member so as to urge the image holding member toward the reading sensor, and the abutment surface with the image holding member is made of a low-friction soft material. This prevents uneven driving of the endless belt-like image holding member, ensuring stable movement of the image holding member and enabling the reading sensor to read the toner image with high accuracy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-14956 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the backing member that contacts the back side of the endless belt-shaped image-bearing member is an insulating member, there is a problem in that the surface resistivity of the image-bearing member decreases over time. This can lead to an insufficient amount of charge being supplied to the toner image, which can cause transfer failure and reduce image density. This raises concerns that good image formation cannot be achieved.

[0006] The present invention has been made in consideration of the above points, and aims to provide an image forming apparatus that can suppress changes in the surface resistivity of an intermediate transfer belt over a long period of time and can continue to form high-quality images. [Means for solving the problem]

[0007] To solve the above problems, the image forming apparatus of the present invention includes an endless intermediate transfer belt, a plurality of rollers, a density detection unit, and a positioning unit. The plurality of rollers rotatably support the intermediate transfer belt. The density detection unit outputs a detection value related to the toner density of a toner image transferred to the outer peripheral surface of the intermediate transfer belt. The positioning unit is disposed on the inner peripheral side of the intermediate transfer belt facing the density detection unit and contacts the inner peripheral surface of the intermediate transfer belt to maintain a predetermined gap between the intermediate transfer belt and the density detection unit. The positioning unit includes a support member disposed on the inner peripheral side of the intermediate transfer belt, and a conductive nonwoven fabric layered on the surface of the support member facing the intermediate transfer belt and in contact with the inner peripheral surface of the intermediate transfer belt. [Effects of the Invention]

[0008] According to the configuration of the present invention, since the nonwoven fabric in contact with the inner peripheral surface of the intermediate transfer belt is conductive, it is possible to suppress changes in the surface resistivity of the intermediate transfer belt over a long period of time, thereby enabling the image forming apparatus to continue forming high-quality images and achieving a longer lifespan. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a schematic cross-sectional front view of an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram showing the configuration of the image forming apparatus of FIG. 1. [Figure 3] 2 is a schematic cross-sectional front view of the periphery of a secondary transfer unit of the image forming apparatus of FIG. 1. [Figure 4] 10 is a graph showing the state of the surface resistivity of an intermediate transfer belt of an image forming apparatus of a comparative example. [Figure 5] 10 is a graph showing the change in surface resistivity of an intermediate transfer belt of an image forming apparatus according to an embodiment of the present invention; [Figure 6] 4 is an explanatory diagram showing the configuration of a bias application circuit in the vicinity of the secondary transfer unit in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following.

[0011] FIG. 1 is a schematic cross-sectional front view of an image forming apparatus 1 according to an embodiment. FIG. 2 is a block diagram showing the configuration of the image forming apparatus 1 shown in FIG. 1. FIG. 3 is a schematic cross-sectional front view of the periphery of a secondary transfer unit 33 of the image forming apparatus 1 shown in FIG. 1. An example of the image forming apparatus 1 according to this embodiment is a tandem color printer that transfers a toner image onto a sheet S using an intermediate transfer belt 31. The image forming apparatus 1 may be a so-called multifunction peripheral that has functions such as printing, scanning (image reading), and facsimile transmission.

[0012] As shown in Figures 1, 2 and 3, the image forming apparatus 1 includes a sheet supply unit 3, a sheet conveying unit 4, an exposure unit 5, an image forming unit 20, a transfer unit 30, a fixing unit 6, a sheet discharge unit 7, a control unit 8 and a memory unit 9, which are provided in its main body 2.

[0013] The sheet supply unit 3 is located at the bottom of the main body 2. The sheet supply unit 3 stores multiple sheets S before printing, and separates and sends out the sheets S one by one during printing. The sheet conveying unit 4 extends vertically along the side wall of the main body 2. The sheet conveying unit 4 conveys the sheet S sent out from the sheet supply unit 3 to the secondary transfer unit 33 and the fixing unit 6, and then discharges the sheet S after fixing from the sheet discharge port 4a to the sheet discharge unit 7. The exposure unit 5 is located above the sheet supply unit 3. The exposure unit 5 irradiates the image forming unit 20 with laser light controlled based on image data.

[0014] The image forming units 20 are disposed above the exposure unit 5 and below the intermediate transfer belt 31. The image forming units 20 include an image forming unit 20Y for yellow, an image forming unit 20C for cyan, an image forming unit 20M for magenta, and an image forming unit 20B for black. These four image forming units 20 have the same basic configuration. Therefore, in the following description, the identification symbols "Y," "C," "M," and "B" representing each color may be omitted unless otherwise specified.

[0015] The image forming unit 20 includes a photosensitive drum 21 that is supported so as to be rotatable in a predetermined direction (clockwise in FIGS. 1 and 3). The image forming unit 20 further includes a charging unit 22, a developing unit 23, and a drum cleaning unit 24 that are arranged around the photosensitive drum 21 along the direction of rotation of the photosensitive drum 21. A primary transfer unit 32 is arranged between the developing unit 23 and the drum cleaning unit 24.

[0016] The photosensitive drum 21 has a photosensitive layer formed on its outer circumferential surface. The charging unit 22 charges the outer circumferential surface of the photosensitive drum 21 to a predetermined surface potential. The exposure unit 5 exposes the outer circumferential surface of the photosensitive drum 21, which has been charged by the charging unit 22, to light, forming an electrostatic latent image of the original image on the outer circumferential surface of the photosensitive drum 21, with the charge attenuated. The developing unit 23 supplies toner to the electrostatic latent image on the outer circumferential surface of the photosensitive drum 21, developing it to form a toner image. Each of the four image forming units 20 forms a toner image of a different color. The drum cleaning unit 24 removes and cleans any toner remaining on the outer circumferential surface of the photosensitive drum 21 after the toner image has been primarily transferred to the outer circumferential surface of the intermediate transfer belt 31. In this way, the image forming unit 20 forms an image (toner image) that will later be transferred to the sheet S.

[0017] The transfer unit 30 includes an intermediate transfer belt 31, primary transfer units 32Y, 32C, 32M, and 32B, a secondary transfer unit 33, and a belt cleaning unit 34. The intermediate transfer belt 31 is disposed above the four image forming units 20. The intermediate transfer belt 31 is supported so as to be rotatable in a predetermined direction (counterclockwise in FIGS. 1 and 3), and is an endless intermediate transfer body onto which toner images formed on the outer circumferential surfaces of the photosensitive drums 21 in each of the four image forming units 20 are sequentially superimposed and primarily transferred. The four image forming units 20 are disposed in a so-called tandem arrangement, lined up in a row from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 31.

[0018] Primary transfer units 32Y, 32C, 32M, and 32B are disposed above image forming units 20Y, 20C, 20M, and 20B of the respective colors, with intermediate transfer belt 31 sandwiched therebetween. Secondary transfer unit 33 is disposed upstream of fixing unit 6 in the sheet conveying direction of sheet conveying unit 4, and downstream of four image forming units 20Y, 20C, 20M, and 20B in the rotation direction of intermediate transfer belt 31. Belt cleaning unit 34 is disposed downstream of secondary transfer unit 33 in the rotation direction of intermediate transfer belt 31.

[0019] The primary transfer unit 32 transfers the toner image formed on the outer circumferential surface of the photosensitive drum 21 onto the intermediate transfer belt 31. In other words, the toner image is primarily transferred onto the outer circumferential surface of the intermediate transfer belt 31 at the primary transfer units 32Y, 32C, 32M, and 32B for each color. Then, as the intermediate transfer belt 31 rotates, the toner images of the four image forming units 20 are successively superimposed and transferred onto the intermediate transfer belt 31 at a predetermined timing, thereby forming a color toner image on the outer circumferential surface of the intermediate transfer belt 31 in which toner images of four colors, yellow, cyan, magenta, and black, are superimposed.

[0020] The color toner image on the outer circumferential surface of the intermediate transfer belt 31 is transferred to the sheet S, which is fed synchronously by the sheet conveying unit 4, at a secondary transfer nip formed in the secondary transfer unit 33. The belt cleaning unit 34 removes and cleans the toner and other adhering matter remaining on the outer circumferential surface of the intermediate transfer belt 31 after the secondary transfer. In this way, the transfer unit 30 transfers (records) the toner image formed on the outer circumferential surface of the photosensitive drum 21 onto the sheet S.

[0021] The fixing unit 6 is disposed above the secondary transfer unit 33. The fixing unit 6 fixes the toner image to the sheet S by applying heat and pressure to the sheet S onto which the toner image has been transferred.

[0022] The sheet discharge section 7 is disposed above the transfer section 30. The sheet S on which the toner image has been fixed and printing has been completed is transported to the sheet discharge section 7. The sheet discharge section 7 takes out the printed sheet (printed material) from above.

[0023] The control unit 8 includes a CPU, an image processing unit, and other electronic circuits and electronic components (none of which are shown). Based on control programs and data stored in the storage unit 9, the CPU controls the operation of each component provided in the image forming apparatus 1 to perform processing related to the functions of the image forming apparatus 1. The sheet supply unit 3, the sheet conveying unit 4, the exposure unit 5, the image forming unit 20, the transfer unit 30, and the fixing unit 6 each receive individual commands from the control unit 8 and print on the sheet S in cooperation with each other.

[0024] The storage unit 9 is configured by combining a non-volatile storage device (not shown) such as a program ROM (Read Only Memory) or a data ROM, and a volatile storage device (not shown) such as a RAM (Random Access Memory).

[0025] Next, a detailed description will be given of the configuration around the transfer unit 30. The transfer unit 30 includes an intermediate transfer device 40 shown in Figures 1 and 3. The intermediate transfer device 40 includes an intermediate transfer belt 31, a drive roller (first support roller) 41, a tension roller 42, a support roller (second support roller) 43, and four primary transfer rollers 32r.

[0026] The intermediate transfer belt 31 is an endless belt rotatably mounted on a plurality of rollers. In this embodiment, these rollers include a drive roller 41 and a tension roller 42. A primary transfer roller 32r is disposed above each of the four image forming units 20Y, 20C, 20M, and 20B, with the intermediate transfer belt 31 between them. Each of the four primary transfer rollers 32r is disposed in a position facing the photosensitive drum 21 with the intermediate transfer belt 31 sandwiched therebetween, and is in contact with the inner circumferential surface of the intermediate transfer belt 31.

[0027] The intermediate transfer belt 31 is a seamless belt made of a dielectric resin material containing conductive carbon. The surface resistivity of the intermediate transfer belt 31 is 9.5 [log Ω / □] or more and 10.5 [log Ω / □] or less.

[0028] The drive roller 41 is disposed downstream of the four primary transfer portions 32Y, 32C, 32M, and 32B in the rotation direction of the intermediate transfer belt 31. In other words, the drive roller 41 is disposed between the four primary transfer portions 32Y, 32C, 32M, and 32B and a density detection portion 11 (described later) in the rotation direction of the intermediate transfer belt 31. The drive roller 41 contacts the inner circumferential surface of the intermediate transfer belt 31 and rotatably supports the intermediate transfer belt 31. The drive roller 41 receives power from a drive motor (not shown) and rotates the intermediate transfer belt 31 counterclockwise in FIGS. 1 and 3 .

[0029] The drive roller 41 is disposed adjacent to the secondary transfer unit 33. A secondary transfer roller 33r is disposed in the secondary transfer unit 33. The secondary transfer roller 33r is disposed opposite the drive roller 41 with the intermediate transfer belt 31 sandwiched therebetween, and is in contact with the outer circumferential surface of the intermediate transfer belt 31. The secondary transfer roller 33r performs a second transfer of the toner image that has been primarily transferred onto the outer circumferential surface of the intermediate transfer belt 31 onto the sheet S that passes between the intermediate transfer belt 31 and the secondary transfer roller 33r.

[0030] The tension roller 42 is disposed upstream of the four primary transfer portions 32Y, 32C, 32M, and 32B in the rotation direction of the intermediate transfer belt 31. The tension roller 42 rotates counterclockwise in FIG. 1 in accordance with the rotation of the intermediate transfer belt 31. Both axial ends of the tension roller 42 are biased by a pair of tension springs (not shown) in a direction away from the drive roller 41, i.e., leftward in FIGS. 1 and 3. This applies a predetermined tension to the intermediate transfer belt 31.

[0031] The support rollers 43 are disposed between the four primary transfer units 32Y, 32C, 32M, and 32B and the drive roller 41 in the rotation direction of the intermediate transfer belt 31. The support rollers 43 contact the inner circumferential surface of the intermediate transfer belt 31 and rotatably support the intermediate transfer belt 31.

[0032] The four primary transfer rollers 32r are disposed above the four image forming units 20, respectively, with the intermediate transfer belt 31 between them. Each primary transfer roller 32r is disposed opposite a photosensitive drum 21 with the intermediate transfer belt 31 sandwiched therebetween, and is in contact with the inner circumferential surface of the intermediate transfer belt 31 to rotatably support the intermediate transfer belt 31. Each primary transfer roller 32r sequentially superimposes the toner images formed on the outer circumferential surfaces of the four photosensitive drums 21 onto the outer circumferential surface of the intermediate transfer belt 31.

[0033] The image forming apparatus 1 further includes a density detection unit 11 and a positioning unit 12.

[0034] The density detection unit 11 is located downstream of the secondary transfer unit 33 in the rotation direction of the intermediate transfer belt 31, and is disposed above the intermediate transfer belt 31 at a distance from the intermediate transfer belt 31. The density detection unit 11 faces the outer peripheral surface of the intermediate transfer belt 31 in the vertical direction.

[0035] The density detection unit 11 includes a reflective optical sensor (not shown) having a light-emitting unit including a light-emitting element such as an LED (Light Emitting Diode) and a light-receiving unit including a light-receiving element such as a photodiode. The light-emitting unit irradiates detection light at a predetermined angle toward the toner image that has been primarily transferred onto the outer circumferential surface of the intermediate transfer belt 31. The light-receiving unit receives the detection light (reflected light) that is irradiated by the light-emitting unit toward the toner image and reflected by the toner image.

[0036] The concentration detection unit 11 outputs the level of the detection light received by the light receiving unit as a detection value (voltage value) related to the toner concentration, thereby deriving the amount of toner in the toner image primarily transferred onto the outer circumferential surface of the intermediate transfer belt 31 and detecting the toner concentration of the toner image. When there is no toner on the outer circumferential surface of the intermediate transfer belt 31, the detection light emitted from the light emitting unit is specularly reflected without being diffusely reflected by the toner, and more of it is incident on the light receiving unit. This increases the detection value (voltage value) related to the toner concentration. As the amount of toner on the outer circumferential surface of the intermediate transfer belt 31 increases, more light is diffusely reflected by the toner, and the amount of light incident on the light receiving unit gradually decreases. In other words, the detection value (voltage value) related to the toner concentration gradually decreases.

[0037] In this way, the concentration detection unit 11 detects the toner concentration by irradiating detection light from the light-emitting unit toward the toner image, reflecting it off the toner image, and receiving it at the light-receiving unit, and outputting a detection value related to the toner concentration of the toner image that has been primarily transferred onto the outer surface of the intermediate transfer belt 31.

[0038] The positioning unit 12 is disposed opposite the concentration detection unit 11 on the inner peripheral side of the intermediate transfer belt 31. The positioning unit 12 contacts the inner peripheral surface of the intermediate transfer belt 31 to maintain a predetermined gap between the intermediate transfer belt 31 and the concentration detection unit 11. The positioning unit 12 includes a support member 121 and a nonwoven fabric 122.

[0039] The support member 121 is disposed facing the inner circumferential side of the intermediate transfer belt 31. The support member 121 is made of, for example, a metal plate having a substantially U-shaped cross section when viewed from the axial direction of the drive roller 41, and extends along the axial direction. The portion of the support member 121 facing the inner circumferential surface of the intermediate transfer belt 31 is formed in a substantially flat plate shape having a facing surface that extends in the movement direction of the intermediate transfer belt 31 and the axial direction of the drive roller 41.

[0040] The nonwoven fabric 122 is layered on the surface of the support member 121 facing the intermediate transfer belt 31, and is in contact with the inner circumferential surface of the intermediate transfer belt 31. Specifically, the nonwoven fabric 122 is in surface contact with the inner circumferential surface of the intermediate transfer belt 31 in the movement direction of the intermediate transfer belt 31 and the axial direction of the drive roller 41. The thickness of the nonwoven fabric 122 is, for example, 0.2 mm or more and 2 mm or less. The nonwoven fabric 122 is also electrically conductive.

[0041] Next, an example will be described. Fig. 4 is a graph showing the state of the surface resistivity of the intermediate transfer belt of the image forming apparatus of the comparative example. Fig. 5 is a graph showing the change in the surface resistivity of the intermediate transfer belt 31 of the image forming apparatus 1 of the example. In each of the image forming apparatus of the example and the image forming apparatus of the comparative example, the influence of the configuration of the nonwoven fabric 122 of the positioning unit 12 on the change in the surface resistivity of the intermediate transfer belt 31 was evaluated.

[0042] As described above, the nonwoven fabric 122 of the positioning section 12 of the example is conductive, whereas the nonwoven fabric 122 of the positioning section 12 of the comparative example is insulating.

[0043] 4 showing the comparative example, the horizontal axis indicates the position in the axial direction of the intermediate transfer belt 31, and the vertical axis indicates the surface resistivity of the intermediate transfer belt 31. In the comparative example, the insulating nonwoven fabric 122 of the positioning unit 12 is in contact with an area Ps that is 15 to 20 mm from one end (position 0 mm) in the axial direction of the intermediate transfer belt 31.

[0044] In the comparative example, it can be seen that the surface resistivity of the intermediate transfer belt 31 is lower in the region Ps than in the surrounding area as shown in Figure 4. It is thought that the contact of the insulating nonwoven fabric with the intermediate transfer belt 31 causes dielectric breakdown due to frictional charging in the region Ps of the intermediate transfer belt 31, resulting in a decrease in the surface resistivity.

[0045] 5 showing an example, the horizontal axis indicates the cumulative number of printed sheets of the image forming apparatus 1, and the vertical axis indicates the surface resistivity of the intermediate transfer belt 31. In FIG.

[0046] In the example, as shown in Fig. 5, it can be seen that the surface resistivity of the intermediate transfer belt 31 does not decrease substantially even after printing 600,000 sheets. In this way, according to the configuration of this embodiment, the nonwoven fabric 122 in contact with the inner circumferential surface of the intermediate transfer belt 31 is conductive, so that changes in the surface resistivity of the intermediate transfer belt 31 can be suppressed over a long period of time. Therefore, it becomes possible for the image forming apparatus 1 to continue forming high-quality images, and a longer life can be achieved.

[0047] In addition, the contact pressure between the support member 121 and the intermediate transfer belt 31 via the nonwoven fabric 122 is 1 [N / m 2 ] or more, and further, it is preferable that the thickness of the nonwoven fabric 122 in the direction facing the intermediate transfer belt 31 is 0.2 mm or more, and that the amount of change in thickness when in contact with the intermediate transfer belt 31 is 0.1 mm or less. With this configuration, the thickness of the nonwoven fabric 122 is unlikely to change due to the tension of the intermediate transfer belt 31, so the distance between the sensor of the concentration detection unit 11 and the toner image on the intermediate transfer belt 31 can be kept constant for a long period of time. This makes it possible to continuously perform appropriate concentration correction.

[0048] Furthermore, it is preferable that the dynamic friction coefficient of the nonwoven fabric 122 is 0.2 or less on the surface that comes into contact with the intermediate transfer belt 31. With this configuration, the intermediate transfer belt 31 that comes into contact with the nonwoven fabric 122 is slippery, and it is possible to prevent the nonwoven fabric 122 from braking the drive of the intermediate transfer belt 31. Therefore, even if the nonwoven fabric 122 is in constant contact, it is possible to continue to drive the intermediate transfer belt 31 smoothly, and high-quality image formation can be continued.

[0049] Furthermore, since the nonwoven fabric 122 has a cleaning function, it is possible to remove toner, dust, etc. adhering to the inner peripheral surface of the intermediate transfer belt 31. This makes it possible to suppress wear on the inner peripheral surface of the intermediate transfer belt 31. It is also possible to suppress the toner, dust, etc. adhering to the inner peripheral surface of the intermediate transfer belt 31 from adhering to the outer peripheral surface of the drive roller 41. This makes it possible to prevent adverse effects on the rotational drive of the intermediate transfer belt 31 by the drive roller 41.

[0050] Next, the configuration of the bias application circuit around the secondary transfer unit 33 will be described in detail. Fig. 6 is an explanatory diagram showing the configuration of the bias application circuit around the secondary transfer unit 33 in Fig. 3. In this embodiment, the nonwoven fabric 122 of the positioning unit 12 has a surface resistivity of, for example, 6 [log Ω / □] or less. As shown in Fig. 6, the image forming apparatus 1 includes a bias application unit 13 and a feedback unit 14.

[0051] The bias application unit 13 includes a power supply unit 131 and is electrically connected to the drive roller 41. The bias application unit 13 applies a secondary transfer bias to the drive roller (first support roller) 41. The control unit 8 controls the bias application unit 13 so that a predetermined output current I1 is output to the drive roller 41.

[0052] The output current I1 to the drive roller 41 includes a secondary transfer current It required for secondary transfer that flows into the secondary transfer roller 33r, an inflow current I2 that flows into the support member 121 via the intermediate transfer belt 31, and an inflow current I3 that flows into the support roller (second support roller) 43 via the intermediate transfer belt 31.

[0053] The feedback unit 14 electrically connects the support member 121 and the support roller 43 to the bias application unit 13. When the secondary transfer bias is applied to the drive roller 41, the feedback unit 14 returns the inflow currents I2 and I3 that flow from the drive roller 41 to the support member 121 and the support roller 43 via the intermediate transfer belt 31 to the bias application unit 13. The feedback unit 14 is also grounded via an electrical resistor 132.

[0054] The above configuration can prevent a shortage of the secondary transfer current It required for the secondary transfer of the toner image onto the sheet S, which is caused by the currents I2 and I3 flowing into the support member 121 and the support roller 43. Therefore, the feedback unit 14 can apply an appropriate secondary transfer bias. In other words, high-quality image formation can be achieved.

[0055] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and various modifications can be made without departing from the spirit of the invention. [Industrial Applicability]

[0056] The present invention can be used in an image forming apparatus. [Explanation of symbols]

[0057] 1. Image forming device 8 Control Unit 11 Concentration detection unit 12 Positioning part 13 Bias application section 14 Feedback section 20 Image forming unit 21 Photosensitive drum 30 Transfer unit 31 Intermediate transfer belt 32 Primary transfer unit 32r Primary transfer roller 33 Secondary transfer unit 33r Secondary transfer roller 40 Intermediate transfer device 41 Drive roller (first support roller) 42 Tension roller 43 Support roller (second support roller) 121 Support member 122 Nonwoven fabric

Claims

1. an endless intermediate transfer belt; a plurality of rollers around which the intermediate transfer belt is rotatably supported; a density detection unit that outputs a detection value relating to the toner density of the toner image transferred onto the outer peripheral surface of the intermediate transfer belt; a positioning unit that is disposed on the inner peripheral side of the intermediate transfer belt so as to face the density detection unit and that contacts the inner peripheral surface of the intermediate transfer belt to maintain a predetermined gap between the intermediate transfer belt and the density detection unit; Equipped with The positioning unit is a support member disposed opposite to the inner circumferential side of the intermediate transfer belt; a conductive nonwoven fabric layered on a surface of the support member facing the intermediate transfer belt and in contact with the inner circumferential surface of the intermediate transfer belt; An image forming apparatus comprising:

2. The contact pressure between the support member and the intermediate transfer belt through the nonwoven fabric is 1 [N / m ２ ] and 2. The image forming apparatus according to claim 1, wherein the nonwoven fabric has a thickness of 0.2 mm or more in a direction facing the intermediate transfer belt, and a thickness change amount upon contact with the intermediate transfer belt of 0.1 mm or less.

3. 2. The image forming apparatus according to claim 1, wherein the nonwoven fabric has a dynamic friction coefficient of 0.2 or less on the surface that comes into contact with the intermediate transfer belt.

4. a primary transfer unit that is disposed upstream of the density detection unit with respect to the rotation direction of the intermediate transfer belt and that primarily transfers the toner image formed on the outer peripheral surface of the photosensitive drum onto the outer peripheral surface of the intermediate transfer belt; a first support roller disposed between the density detection unit and the primary transfer unit, the first support roller supporting the intermediate transfer belt so as to be rotatable; a second support roller disposed between the primary transfer unit and the first support roller, and supporting the intermediate transfer belt so as to be rotatable; a secondary transfer roller disposed opposite the first support roller with the intermediate transfer belt interposed therebetween, and configured to perform a second transfer of the toner image, which has been primarily transferred onto the outer peripheral surface of the intermediate transfer belt, onto a sheet passing between the intermediate transfer belt and the secondary transfer roller; a bias applying unit that applies a secondary transfer bias to the first support roller; a feedback section that electrically connects the support member and the second support roller with the bias application section, and returns to the bias application section a current that flows from the first support roller through the intermediate transfer belt into the support member and the second support roller when the secondary transfer bias is applied to the first support roller; The image forming apparatus according to claim 1 , further comprising:

5. 5. The image forming apparatus according to claim 4, wherein the feedback section is grounded via an electric resistor.

6. 2. The image forming apparatus according to claim 1, wherein the nonwoven fabric has a surface resistivity of 6 [log Ω / □] or less.

Images