Belt device and image forming apparatus

Abstract

Even when the belt component is rotated, variations in the detection accuracy of the optical sensor that detects the surface of the belt component are minimized. [Solution] The device comprises a plurality of roller members 72-78 and a secondary transfer belt 71 (belt member) stretched between the plurality of roller members 72-78. A secondary transfer belt unit 70 (belt unit) is provided, which is configured to rotate around the rotation center 74a of the sensor-facing roller 74 among the plurality of roller members 72-78. A pressurizing mechanism 92 is provided that can adjust the contact pressure of the secondary transfer belt 71 against the intermediate transfer belt 8 (target body) by rotating the secondary transfer belt unit 70 around the rotation center 74a. Furthermore, an optical sensor 85 is provided that faces the sensor-facing roller 74 via the secondary transfer belt 71, without being linked to the rotation of the secondary transfer belt unit 70 by the pressurizing mechanism 92.

Description

[Technical Field]

[0001] This invention relates to a belt device equipped with belt members such as a secondary transfer belt, an intermediate transfer belt, and a transfer belt, and to an image forming apparatus such as a copier, printer, facsimile, or a multifunction device thereof that is equipped with the same. [Background technology]

[0002] Conventionally, image forming apparatuses such as copiers and printers are known to be equipped with optical sensors (toner image detection sensors) that detect toner images formed on the surface of belt members such as intermediate transfer belts and secondary transfer belts (see, for example, Patent Document 1).

[0003] More specifically, in the image forming apparatus described in Patent Document 1, an intermediate transfer belt (belt member) is stretched and supported by multiple roller members, and a toner image detection sensor (optical sensor) is installed so as to face one tension roller (roller member) via the intermediate transfer belt. The toner image formed on the surface of the intermediate transfer belt is detected by the toner image detection sensor, and adjustments such as image density and positional misalignment are made based on the detection result. [Overview of the project] [Problems that the invention aims to solve]

[0004] Conventional image forming apparatuses, when configured to allow the belt member to rotate (oscillate) in the contact and separation directions in order to vary the contact pressure of the belt member with respect to the object, can cause the relative position of the optical sensor to change due to the rotation of the belt member, potentially leading to variations in the detection accuracy of the optical sensor that detects the surface of the belt member. Such variations in the detection accuracy of the optical sensor can then affect the accuracy of control functions such as image density and positional misalignment based on the detection results of the optical sensor. Furthermore, in order to solve these problems, if the optical sensor is configured to move in conjunction with the rotation of the belt member so that its relative position to the belt member does not change due to the rotation of the belt member, the device will become larger and more expensive.

[0005] This invention was made to solve the above-mentioned problems, and aims to provide a belt device and an image forming apparatus in which the detection accuracy of the optical sensor that detects the surface of the belt member is less likely to vary even when the belt member is rotated. [Means for solving the problem]

[0006] The belt device in this invention comprises a plurality of roller members and a belt member stretched over the plurality of roller members, and further comprises a belt unit configured to be rotatable about the rotation center of one of the plurality of roller members, a pressurizing mechanism capable of adjusting the contact pressure of the belt member against an object by rotating the belt unit about the rotation center, and an optical sensor that faces the one roller member via the belt member without being linked to the rotation of the belt unit by the pressurizing mechanism. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a belt device and an image forming apparatus in which the detection accuracy of the optical sensor that detects the surface of the belt member is less likely to vary even when the belt member is rotated. [Brief explanation of the drawing]

[0008] [Figure 1] This is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention. [Figure 2] This is a diagram showing a magnified view of a portion of the image-making section. [Figure 3] This is a schematic diagram showing the vicinity of the intermediate transfer belt and the secondary transfer belt device. [Figure 4]This is a diagram showing the configuration of the secondary transfer belt device. [Figure 5] (A) A diagram showing the secondary transfer belt unit rotated toward the intermediate transfer belt, and (B) A diagram showing the secondary transfer belt unit rotated toward the side away from the intermediate transfer belt. [Figure 6] This is an enlarged view showing the optical sensor and the roller facing the sensor. [Figure 7] This diagram shows the secondary transfer belt unit and the pressurizing mechanism. [Figure 8] This diagram shows the sensor-facing roller and multiple optical sensors in the width direction. [Figure 9] This is an enlarged view showing an optical sensor and a roller facing the sensor as a comparative example. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments for carrying out this invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations will be simplified or omitted as appropriate.

[0010] First, the overall configuration and operation of the image forming apparatus 100 will be explained using Figures 1 and 2. Figure 1 is a schematic diagram showing a printer as an image forming apparatus, and Figure 2 is an enlarged view showing a part of its image-forming section. As shown in Figure 1, an intermediate transfer belt 8 (intermediate transfer body) is installed in the center of the image forming apparatus 100 as an image carrier. Opposite the intermediate transfer belt 8, image forming units 6Y, 6M, 6C, and 6K corresponding to each color (yellow, magenta, cyan, and black) are arranged side by side. Furthermore, an operation display panel (operation display unit) is installed on the top of the image forming apparatus 100 for displaying information related to the printing operation (image forming operation) and for performing operations.

[0011] Referring to FIG. 2, the image forming unit 6Y corresponding to yellow is composed of a photosensitive drum 1Y as a photoreceptor, a charging unit 4Y, a developing unit 5Y, a cleaning unit 2Y, a lubricant supply device 3, a charge removal unit, etc., arranged around the photosensitive drum 1Y. And on the photosensitive drum 1Y, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process, charge removal process) is performed, and a yellow image is formed on the photosensitive drum 1Y.

[0012] Note that the other three image forming units 6M, 6C, and 6K have substantially the same configuration as the image forming unit 6Y corresponding to yellow, except that the color of the toner used is different, and images corresponding to their respective toner colors are formed. Hereinafter, the description of the other three image forming units 6M, 6C, and 6K will be appropriately omitted, and only the description of the image forming unit 6Y corresponding to yellow will be given.

[0013] Referring to FIG. 2, the photosensitive drum 1Y is rotationally driven counterclockwise by a drive motor. And at the position of the charging unit 4Y, the surface of the photosensitive drum 1Y is uniformly charged (this is the charging process). After that, the surface of the photosensitive drum 1Y reaches the irradiation position of the laser beam L emitted from the exposure unit 7, and an electrostatic latent image corresponding to yellow is formed by exposure scanning in the width direction (the direction perpendicular to the paper surface in FIGS. 1 and 2, which is the main scanning direction) at this position (this is the exposure process).

[0014] After that, the surface of the photosensitive drum 1Y reaches the position facing the developing unit 5Y, and the electrostatic latent image is developed at this position, and a yellow toner image is formed (this is the developing process). After that, the surface of the photosensitive drum 1Y reaches the position facing the intermediate transfer belt 8 and the primary transfer roller 9Y, and the toner image formed on the surface of the photosensitive drum 1 is primarily transferred to the surface of the intermediate transfer belt 8 at this position (this is the primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drum 1Y.

[0015] After that, the surface of the photoreceptor drum 1Y reaches the position facing the cleaning unit 2Y, and the untransferred toner remaining on the photoreceptor drum 1Y at this position is collected into the cleaning unit 2Y by the cleaning blade 2a (this is the cleaning process). Here, inside the cleaning unit 2Y, a lubricant supply device 3 (a lubricant supply device for the photoreceptor), which consists of a lubricant supply roller 3a, a solid lubricant 3b, a compression spring 3c (biasing member), etc., is installed. Then, the lubricant is scraped off little by little from the solid lubricant 3b by the lubricant supply roller 3a that rotates in the clockwise direction in Fig. 2, and the lubricant is supplied to the surface of the photoreceptor drum 1Y by the lubricant supply roller 3a. Finally, the surface of the photoreceptor drum 1Y reaches the position facing the charge elimination unit, and the residual potential on the photoreceptor drum 1 is removed at this position. Thus, a series of imaging processes performed on the photoreceptor drum 1Y is completed.

[0016] In addition, the above-described imaging process is also performed in the other imaging units 6M, 6C, 6K in the same manner as in the yellow imaging unit 6Y. That is, the laser light L based on the image information is irradiated onto the photoreceptor drums 1M, 1C, 1K of each imaging unit 6M, 6C, 6K from the exposure unit 7 disposed above the imaging unit. Specifically, the exposure unit 7 emits the laser light L from a light source and irradiates it onto the photoreceptor drum while scanning the laser light L with a polygon mirror driven to rotate through a plurality of optical elements. Note that a plurality of LEDs arranged side by side in the width direction may be used as the exposure unit 7. After that, the toner images of each color formed on the photoreceptor drums 1M, 1C, 1K through the developing process by each developing unit 5M, 5C, 5K are superposed and primarily transferred onto the intermediate transfer belt 8. Thus, a color image is formed on the intermediate transfer belt 8.

[0017] Here, the intermediate transfer belt 8 is stretched and supported by a plurality of roller members 16 to 22, 80, and is endlessly moved in the direction of the arrow in Fig. 3 by the rotational drive of one roller member (drive roller 16) by a drive motor. The four primary transfer rollers 9Y, 9M, 9C, and 9K each have an intermediate transfer belt 8 sandwiched between them and the photoreceptor drums 1Y, 1M, 1C, and 1K to form a primary transfer nip. A transfer voltage (primary transfer bias) with the opposite polarity to the toner polarity is then applied to the primary transfer rollers 9Y, 9M, 9C, and 9K. The intermediate transfer belt 8 then travels in the direction of the arrow, sequentially passing through the primary transfer nips of the primary transfer rollers 9Y, 9M, 9C, and 9K. In this way, the toner images of each color on the photoreceptor drums 1Y, 1M, 1C, and 1K are superimposed onto the surface of the intermediate transfer belt 8 and primary transferred (this is the primary transfer process).

[0018] Subsequently, the intermediate transfer belt 8, on which the toner images of each color have been superimposed and primary transferred, reaches a position opposite the secondary transfer belt 71, which acts as a transfer rotating body. At this position, the secondary transfer opposing roller 80 sandwiches the intermediate transfer belt 8 and the secondary transfer belt 71 between itself and the secondary transfer roller 72, forming a secondary transfer nip. The four toner images formed on the intermediate transfer belt 8 are then secondary transferred onto a sheet P, such as paper, which has been transported to the position of this secondary transfer nip (this is the secondary transfer process). At this time, untransferred toner remains on the intermediate transfer belt 8 that has not been transferred to the sheet P.

[0019] Subsequently, the intermediate transfer belt 8 reaches the intermediate transfer cleaning unit 10. At this position, any untransferred toner or other deposits adhering to the surface of the intermediate transfer belt 8 are removed. Furthermore, the intermediate transfer belt 8 reaches the position of the lubricant supply device 30, which acts as an intermediate transfer lubricant supply device. At this position, lubricant is supplied to the surface of the intermediate transfer belt 8. Thus, the series of transfer processes performed on the intermediate transfer belt 8 are completed.

[0020] Referring to Figure 1, the sheet P that is transported to the secondary transfer nip position is transported from the paper feeding section 26 located below the main body of the device 100, via the paper feeding roller 27 and the pair of registration rollers 28, etc. More specifically, the paper feeding unit 26 stores multiple sheets P, such as transfer paper, stacked on top of each other. When the paper feeding roller 27 is driven to rotate counterclockwise in Figure 1, the top sheet P is fed via the first transport path K1 towards the space between the register rollers 28.

[0021] The sheet P, transported by the register roller pair 28 (timing roller pair), temporarily stops at the position of the roller nip of the register roller pair 28, where the rotational drive has been stopped. Then, in time with the color image on the intermediate transfer belt 8, the register roller pair 28 is driven to rotate, and the sheet P is transported toward the secondary transfer nip. In this way, the desired color image is transferred onto the sheet P.

[0022] Subsequently, the sheet P onto which the color image has been transferred at the secondary transfer nip is transported by the secondary transfer belt 71, separated from the secondary transfer belt 71, and then transported to the fixing unit 50 by the transport belt 60. At this position, the color image transferred to the surface is fixed onto the sheet P by heat and pressure from the fixing belt and pressure rollers (this is the fixing process). Subsequently, the sheet P is discharged from the device via the second transport path K2 by the paper discharge roller pair. The sheet P discharged from the device by the paper discharge roller pair is sequentially stacked on the stacking section as output images. Thus, the series of image formation processes in the image forming apparatus are completed.

[0023] Here, as shown in Figure 1, the image forming apparatus 100 in this embodiment is equipped with a double-sided transport device 40 that transports the sheet P toward the secondary transfer nip in order to transfer the toner image on the intermediate transfer belt 8 to the back side of the sheet P after the toner image has been transferred to the front side by the secondary transfer nip (transfer nip). Specifically, when the "double-sided printing mode," which prints on both sides of sheet P (the front and back sides), is selected, sheet P, after the fixing process on the front side is completed, is not ejected as is, as when the "single-sided printing mode" is selected. Instead, it is guided to the third transport path K3 in the double-sided transport device 40, where its transport direction is reversed, and then transported again via the fourth transport path K4 towards the position of the secondary transfer nip (secondary transfer belt device 69). At the position of the secondary transfer nip, an image is formed on the back side of sheet P (secondary transfer) by the same image forming process (image forming operation) as described above. After that, it undergoes a fixing process in the fixing unit 50 and is discharged from the image forming device main body 100 via the second transport path K2.

[0024] Next, Figure 2 will provide a more detailed explanation of the configuration and operation of the developing unit 5Y (developing device) in the image-making section. The developing unit 5Y consists of a developing roller 51Y facing the photoreceptor drum 1Y, a doctor blade 52Y facing the developing roller 51Y, two transport screws 55Y disposed within the developer storage unit, a density detection sensor 56Y for detecting the toner concentration in the developer, and the like. The developing roller 51Y consists of a magnet fixed inside and a sleeve that rotates around the magnet. A two-component developer G, consisting of a carrier and toner, is stored within the developer storage unit.

[0025] The developing unit 5Y, configured in this way, operates as follows: The sleeve of the developing roller 51Y rotates in the direction of the arrow in Figure 2. The developer G, which is supported on the developing roller 51Y by the magnetic field formed by the magnet, moves along the developing roller 51Y as the sleeve rotates. Here, the developer G in the developing unit 5Y is adjusted so that the proportion of toner in the developer G (toner concentration) is within a predetermined range. Specifically, when a low toner concentration is detected by the toner concentration sensor installed in the developing unit 5Y, new toner is supplied to the developing unit 5Y from the toner container 58 so that the toner concentration is within the predetermined range. Subsequently, the toner supplied from the toner container 58 into the developer container is mixed and agitated with the developer G by two transport screws 55Y, circulating between the two isolated developer containers (movement in the direction perpendicular to the paper plane in Figure 2). The toner in the developer G is then attracted to the carrier by triboelectric charging and, together with the carrier, is supported on the developer roller 51Y by the magnetic force formed on the roller 51Y.

[0026] The developer G supported on the developing roller 51Y is transported in the direction of the arrow in Figure 2 to the position of the doctor blade 52Y. At this position, the amount of developer G on the developing roller 51Y is adjusted to the appropriate level, and then it is transported to the position opposite the photoreceptor drum 1Y (the developing area). Then, the toner is attracted to the latent image formed on the photoreceptor drum 1Y by the electric field formed in the developing area. After that, the developer G remaining on the developing roller 51Y reaches above the developer storage section as the sleeve rotates, and at this position it is detached from the developing roller 51Y. The toner container 58 is detachably (replaceable) installed in the developing unit 5Y (image forming apparatus 100). When the new toner contained inside the toner container 58 is depleted, it is removed from the developing unit 5Y (image forming apparatus 100) and replaced with a new one.

[0027] Next, the intermediate transfer belt device in this embodiment will be described in detail using Figure 3 and other figures. Referring to Figure 3, the intermediate transfer belt device consists of an intermediate transfer belt 8 as the target body (image carrier), four primary transfer rollers 9Y, 9M, 9C, and 9K, a drive roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning opposing roller 20, a lubricant opposing roller 21, a backup roller 22, an intermediate transfer cleaning section 10, a lubricant supply device 30 as an intermediate transfer lubricant supply device, a secondary transfer opposing roller 80, and the like.

[0028] The intermediate transfer belt 8 contacts four photoreceptor drums 1Y, 1M, 1C, and 1K, each carrying a toner image of a different color, to form a primary transfer nip. The intermediate transfer belt 8 is stretched and supported primarily by eight roller members (a drive roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning opposing roller 20, a lubricant opposing roller 21, a backup roller 22, and a secondary transfer opposing roller 80).

[0029] In this embodiment, the intermediate transfer belt 8 is constructed by dispersing a conductive material such as carbon black in a single or multiple layer of PVDF (vinyldenine fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc. The intermediate transfer belt 8 has a volume resistivity of 10 6 ~10 13 Ωcm, surface resistivity of the back side of the belt is 10 7 ~10 13 It is adjusted to be in the range of Ωcm. Also, the intermediate transfer belt 8 is set to have a thickness in the range of 20 to 200 μm. In this embodiment, the thickness of the intermediate transfer belt 8 is about 60 μm, and the volume resistivity is 10 9 It is set to approximately Ωcm. Furthermore, a release layer can be coated onto the surface of the intermediate transfer belt 8 if necessary. In this case, fluororesins such as ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinyldenine fluoride), PEA (perfluoroalkoxy fluoropolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and PVF (vinyl fluoride) can be used as the coating material, but are not limited to these.

[0030] The primary transfer rollers 9Y, 9M, 9C, and 9K are in contact with their respective photoreceptor drums 1Y, 1M, 1C, and 1K via the intermediate transfer belt 8. Specifically, the yellow transfer roller 9Y is in contact with the yellow photoreceptor drum 1Y via the intermediate transfer belt 8, the magenta transfer roller 9M is in contact with the magenta photoreceptor drum 1M via the intermediate transfer belt 8, the cyan transfer roller 9C is in contact with the cyan photoreceptor drum 1C via the intermediate transfer belt 8, and the black transfer roller 9K is in contact with the black photoreceptor drum 1K via the intermediate transfer belt 8.

[0031] The drive roller 16 is positioned downstream of the intermediate transfer belt in the direction of travel relative to the four photoreceptor drums, and is positioned so as to contact the inner surface of the intermediate transfer belt 8 when the intermediate transfer belt 8 is wrapped around it at a winding angle of approximately 120 degrees. The drive roller 16 is rotated clockwise in Figure 3 by a drive motor Mt1 controlled by the control unit 90. As a result, the intermediate transfer belt 8 travels in a predetermined direction (clockwise in Figure 3).

[0032] The driven roller 17 is positioned upstream of the intermediate transfer belt 8 in the direction of travel relative to the four photoreceptor drums, and is positioned so as to contact the inner surface of the intermediate transfer belt 8 when the intermediate transfer belt 8 is wrapped around it at a winding angle of approximately 180 degrees. The portion of the intermediate transfer belt 8 from the driven roller 17 to the drive roller 16 is set to be approximately horizontal. The driven roller 17 rotates in a clockwise direction as the intermediate transfer belt 8 travels, as shown in Figure 3.

[0033] The tension roller 19 is in contact with the outer circumferential surface of the intermediate transfer belt 8. The pre-transfer roller 18, cleaning opposing roller 20, lubricant opposing roller 21, backup roller 22, and secondary transfer opposing roller 80 are in contact with the inner circumferential surface of the intermediate transfer belt 8. Between the secondary transfer opposing roller 80 and the lubricant opposing roller 21, an intermediate transfer cleaning section 10 (cleaning blade) is installed so as to contact the cleaning opposing roller 20 via an intermediate transfer belt 8. Between the cleaning opposing roller 20 and the tension roller 19, a lubricant supply device 30 (intermediate transfer lubricant supply device) is installed so as to contact the lubricant opposing roller 21 via an intermediate transfer belt 8. The lubricant supply device 30 consists of a lubricant supply roller, solid lubricant, and a compression spring (biasing member), similar to the lubricant supply device 3 for the photoreceptor drum. The lubricant supply roller, which rotates counterclockwise as shown in Figure 3, scrapes off small amounts of lubricant from the solid lubricant, and the lubricant is supplied to the surface of the intermediate transfer belt 8 by the lubricant supply roller. The roller members 17-22 and 80, excluding the drive roller 16, all rotate in the clockwise direction as the intermediate transfer belt 8 moves, as shown in Figure 3.

[0034] Referring to Figure 4, the secondary transfer opposing roller 80 is in contact with the secondary transfer roller 72 (secondary transfer belt device 69) via the intermediate transfer belt 8 and the secondary transfer belt 71. The secondary transfer opposing roller 80 has a cylindrical core made of stainless steel or the like, with a volume resistance of 10 on its outer surface. 7 ~10 8 An elastic layer 83 (with a layer thickness of approximately 5 mm) is formed from NBR rubber with a hardness of approximately Ω and a hardness (JIS-A hardness) of approximately 48 to 58 degrees.

[0035] Furthermore, in this embodiment, the secondary transfer opposing roller 80 is electrically connected to the power supply unit 99 (bias output means), and a secondary transfer bias of approximately -5kV is applied from the power supply unit 99. This secondary transfer bias applied to the secondary transfer opposing roller 80 is for secondary transfer of the toner image primary transferred to the surface of the intermediate transfer belt 8 onto the sheet P that is transported to the secondary transfer nip, and is a secondary transfer bias (DC voltage) with the same polarity as the toner (negative polarity in this embodiment). As a result, the toner carried on the toner-carrying surface (outer peripheral surface) of the intermediate transfer belt 8 is electrostatically moved from the secondary transfer opposing roller 80 side toward the secondary transfer device 70 side by the secondary transfer electric field.

[0036] Hereinafter, referring to FIG. 4, the secondary transfer belt device 69 as a belt device will be described. Referring to FIG. 4, the secondary transfer belt device 69 is installed so as to face the intermediate transfer belt 8 (intermediate transfer belt device). The secondary transfer belt device 69 is composed of a secondary transfer belt unit 70 as a belt unit, a pressing mechanism 92, an optical sensor 85, and the like. Further, the secondary transfer belt unit 70 is composed of a secondary transfer belt 71 as a belt member, a secondary transfer roller 72, a separation roller 73, a sensor facing roller 74, a first tension roller 75, a second tension roller 76, a third tension roller 77, a fourth tension roller 78, and the like.

[0037] The secondary transfer belt 71 (belt member) is an endless belt stretched and supported by seven roller members (the secondary transfer roller 72, the separation roller 73, the sensor facing roller 74, and the first to fourth tension rollers 75 to 78), and is formed of substantially the same material as the intermediate transfer belt 8. The secondary transfer belt 71 (belt member) abuts on the intermediate transfer belt 8 (object) to form a secondary transfer nip as a transfer nip, and conveys the sheet P sent out from the secondary transfer nip.

[0038] The secondary transfer roller 72 forms a secondary transfer nip by sandwiching the intermediate transfer belt 8 and the secondary transfer belt 71 between it and the secondary transfer facing roller 80. The secondary transfer roller 72 has an elastic layer with a hardness (Asker C hardness) of about 40 to 50 degrees formed (coated) on a hollow core made of stainless steel, aluminum, etc. The elastic layer of the secondary transfer roller 72 can be formed in a solid or foamed sponge shape by dispersing a conductive filler such as carbon or containing an ionic conductive material in a rubber material such as polyurethane, EPDM, or silicone. In the present embodiment, the elastic layer has a volume resistance of 10 6.5 ~10 7.5 Ω and is set to about that value. In the present embodiment, the secondary transfer roller 72 is grounded. Furthermore, the secondary transfer roller 72 is driven to rotate counterclockwise in Figure 4 by a drive motor (not shown) controlled by the control unit 90, causing the secondary transfer belt 71 to rotate (travel) counterclockwise in Figures 3 and 4. Consequently, a plurality of roller members 73 to 78 that contact the inner (or outer) surface of the secondary transfer belt 71 rotate in response.

[0039] The separation roller 73 is positioned downstream of the secondary transfer nip in the conveying direction of the sheet P. The sheet P, which is sent out from the secondary transfer nip, is conveyed along the secondary transfer belt 71 which runs counterclockwise as shown in Figure 4, and then, at the position of the separation roller 73, is separated from the secondary transfer belt 71 by the secondary transfer belt 71, which has a curved surface formed along the outer circumference of the separation roller 73 (curvature separation). The sensor-facing roller 74 is a roller member that faces the optical sensor 85 via the secondary transfer belt 71, which will be explained in detail later. Furthermore, in this embodiment, the secondary transfer belt 71 is tensioned and supported by seven roller members 72 to 78, and only the third tension roller 77 is configured to contact the outer circumferential surface of the secondary transfer belt 71. However, the number of roller members that tension and support the secondary transfer belt 71, and the number and position of roller members that contact the outer circumferential surface of the belt, are not limited to those of this embodiment.

[0040] The characteristic configuration and operation of the secondary transfer belt device 69 as a belt device in this embodiment will be described in detail below with reference to Figures 4 to 8, etc. As explained earlier, in this embodiment, the secondary transfer belt device 69, which is a belt device, is composed of a secondary transfer belt unit 70 as a belt unit, a pressurizing mechanism 92, an optical sensor 85, and the like. As shown in Figure 4, the secondary transfer belt unit 70, as a belt unit, is provided with a plurality of roller members (seven roller members in total: a secondary transfer roller 72, a separation roller 73, a sensor-facing roller 74, and first to fourth tension rollers 75 to 78) and a secondary transfer belt 71 as a belt member stretched over the plurality of roller members 72 to 78. The secondary transfer belt 71, as a belt component, is pressed against the secondary transfer opposing roller 80 via the intermediate transfer belt 8, which is the target object.

[0041] Referring to Figures 4 to 6, the secondary transfer belt unit 70 is configured to be rotatable (oscillating) around the rotation center 74a of one of the multiple roller members 72 to 78 (which is the sensor-facing roller 74). As explained earlier, among the multiple roller members 72 to 78, the secondary transfer roller 72, which is a separate roller member from the sensor-facing roller 74 (one roller member), is pressed against the intermediate transfer belt 8 via the secondary transfer belt 71.

[0042] The pressurizing mechanism 92 is configured to adjust the contact pressure of the secondary transfer belt 71 (belt member) against the intermediate transfer belt 8, which is the target object, by rotating the secondary transfer belt unit 70 (belt unit) around the rotation center 74a (which is the rotation center of the sensor-facing roller 74). For details, please refer to Figure 7. The pressurizing mechanism 92 consists of a cam 93 that contacts the bottom of the unit case 70a of the secondary transfer belt unit 70, and a motor (not shown) that rotates the cam 93. Meanwhile, seven roller members 72 to 78 are rotatably held in the unit case 70a via bearings, and a drive motor (not shown) that rotates the secondary transfer roller 72 is also fixedly installed. Then, the motor control by the control unit 90 rotates the cam 93 to the desired position (the position in the rotational direction), thereby adjusting the contact pressure (nip pressure of the secondary transfer nip) of the secondary transfer belt 71 (secondary transfer roller) against the intermediate transfer belt 8 (secondary transfer opposing roller 80).

[0043] Specifically, as shown in Figure 5(A), when the secondary transfer belt unit 70 is rotated counterclockwise around the rotation center 74a by the pressurizing mechanism 92, the nip pressure of the secondary transfer nip increases. Conversely, as shown in Figure 5(B), when the secondary transfer belt unit 70 is rotated clockwise around the rotation center 74a by the pressurizing mechanism 92, the nip pressure of the secondary transfer nip decreases. Furthermore, the state in which the nip pressure of the secondary transfer nip decreases includes the state in which the secondary transfer belt 71 is completely separated from the intermediate transfer belt 8 and the nip pressure becomes 0, as shown in Figure 5(B).

[0044] More specifically, in this embodiment, when the thickness of the sheet P being transported (passed through) to the secondary transfer nip is thick, the pressurizing mechanism 92 is controlled by the control unit 90 so that the nip pressure of the secondary transfer nip is lower compared to when the sheet is thin. This ensures good transportability of the sheet P in the secondary transfer nip, regardless of the thickness of the sheet P. Furthermore, if the type of sheet P (paper type) being transported (passed through) to the secondary transfer nip is of low transferability, the pressurizing mechanism 92 is controlled by the control unit 90 to increase the nip pressure of the secondary transfer nip compared to when the sheet P has high transferability. This ensures good transferability in the secondary transfer nip regardless of the type of sheet P. Furthermore, when the image area ratio (the percentage of the effective image area occupied by the image portion) of the toner image (image) secondarily transferred to the sheet P is low, the pressurizing mechanism 92 is controlled by the control unit 90 so that the nip pressure of the secondary transfer nip is lower compared to when the image area ratio is high. This ensures stable transfer performance at the secondary transfer nip regardless of the size of the image area ratio. Furthermore, information regarding the thickness and type of sheet P can be acquired by the control unit 90 based on information about sheet P entered by the user through the operation display panel 95. In addition, information regarding the image area ratio can be acquired by the control unit 90 based on information written by the exposure unit 7.

[0045] Furthermore, in this embodiment, as shown in Figure 5(B), the secondary transfer belt 71 is configured to be completely separated from the intermediate transfer belt 8. The primary reason for controlling the system to be in this state is when the image forming apparatus 100 is not performing any printing operations (image forming process), such as when the device is stopped or after printing is completed. By implementing this control, it is possible to mitigate problems such as elastic strain caused by the intermediate transfer belt 8 and the secondary transfer belt 71 constantly being in contact.

[0046] Referring to Figures 4 to 7, in this embodiment, the optical sensor 85 is configured to face the sensor-facing roller 74 (a single roller member that serves as the rotation center) via the secondary transfer belt 71 (belt member), without being linked to the rotation of the secondary transfer belt unit 70 (belt unit) by the pressurizing mechanism 92. More specifically, the optical sensor 85 is a reflective photosensor in which the light-emitting element and the light-receiving element are arranged to face the outer surface of the belt, and is fixedly installed on the pressurizing mechanism 92 as shown in Figure 7. In other words, the optical sensor 85 is not fixedly installed on the secondary transfer belt unit 70, but is fixedly installed on the pressurizing mechanism 92, which is not linked to the rotation of the secondary transfer belt unit 70.

[0047] In this embodiment, the image pattern (a toner image for image adjustment) formed on the intermediate transfer belt 8 by the image formation process described above is transferred not to the sheet P, but to the secondary transfer belt 71 at a timing different from that of normal image formation, such as before the start of printing or between sheets of paper. The image pattern (or background) is then optically detected by the optical sensor 85. Based on the results detected by the optical sensor 85, various conditions during the secondary transfer process (such as secondary transfer bias, nip pressure of the secondary transfer nip, and rotation speed of the secondary transfer roller 72) are adjusted. This optimizes the transfer efficiency (image density) in the secondary transfer process and reduces positional misalignment of the secondary transfer image on the sheet P.

[0048] As described above, in this embodiment, the optical sensor 85 is installed so as to face the roller member (sensor-facing roller 74) whose rotation center is the rotation center 74a of the secondary transfer belt unit 70, and the optical sensor 85 is fixed so as not to move in conjunction with the rotation of the secondary transfer belt unit 70. As a result, even when the secondary transfer belt 71 (secondary transfer belt unit 70) is rotated, variations in the detection accuracy of the optical sensor 85 that detects the surface of the secondary transfer belt 71 are less likely to occur, and the secondary transfer belt device 69 is less likely to become large and expensive. More specifically, as shown in Figure 9(A), if the secondary transfer belt unit is configured to rotate with a pivot point different from the rotation center of the sensor-facing roller 174 (for example, the rotation center of the first tension roller 75), the rotation of the secondary transfer belt unit will cause a change in the orientation of the optical sensor 185, which is fixedly installed in the pressurizing mechanism, relative to the secondary transfer belt 71 (sensor-facing roller 174). As a result, variations occur in the detection accuracy of the optical sensor 185 that detects the surface of the secondary transfer belt 71, and the accuracy of control such as image density and positional deviation based on the detection results of the optical sensor 85 also deteriorates. Furthermore, as shown in Figure 9(B), if the optical sensor 285 is configured to move in conjunction with the rotation of the secondary transfer belt unit so that the relative position of the optical sensor 285 with respect to the secondary transfer belt 71 (sensor-facing roller 274) does not change due to the rotation of the secondary transfer belt unit, then it becomes necessary to install a member to hold the optical sensor 285 and to secure space for the swinging of that member, which would result in a larger and more expensive secondary transfer belt device. In contrast, in this embodiment, the optical sensor 85 is installed so as to face the sensor-facing roller 74, whose rotation center is the rotation center 74a of the secondary transfer belt unit 70, and the optical sensor 85 is fixed so as not to move in conjunction with the rotation of the secondary transfer belt unit 70, thus making such problems less likely to occur.

[0049] Referring to Figure 6, when viewed in a cross-section perpendicular to the rotation center 74a, the sensing surface 85a of the optical sensor 85 is configured to be perpendicular to the virtual normal S passing through the rotation center 74a of the sensor-facing roller 74 (one roller member). In other words, the optical sensor 85 is positioned such that its detection surface 85a (light-receiving surface) faces the sensor-facing roller 74 in the direction normal to the sensor. This improves the detection accuracy of the optical sensor 85 that detects the surface of the secondary transfer belt 71 compared to the case where the detection surface 85a of the optical sensor 85 is tilted instead of being perpendicular to the virtual normal S.

[0050] Furthermore, referring to Figure 6, in this embodiment, as the secondary transfer belt unit 70 (belt unit) rotates due to the pressurizing mechanism 92, the winding range θ (the range in which the belt contacts) of the secondary transfer belt 71 on the sensor-facing roller 74 (one roller member) is displaced. Specifically, in Figure 6, when the secondary transfer belt unit 70 rotates from the position shown by the solid line to the position shown by the dashed line, the winding range θ of the secondary transfer belt 71, shown by the solid line, also displaces (rotates) to the winding range θ' shown by the dashed line, centered around the rotation center 74a. In this embodiment, even if the secondary transfer belt unit 70 rotates due to the pressurizing mechanism 92 and the winding range θ(θ') is displaced, the optical sensor 85 is configured to face the sensor-facing roller 74 (one roller member) within the winding range θ(θ') via the secondary transfer belt 71. That is, even if the secondary transfer belt unit 70 rotates, the optical sensor 85 will always face the rotation center 74a of the sensor-facing roller 74 via the secondary transfer belt 71 (winding range) (the detection surface 85a will be perpendicular to the virtual normal S). As a result, even when the secondary transfer belt unit 70 is rotated, variations in the detection accuracy of the optical sensor 85 that detects the surface of the secondary transfer belt 71 are less likely to occur.

[0051] In particular, in this embodiment, the pressurizing mechanism 92 is configured to rotate the secondary transfer belt unit 70 (belt unit) within a predetermined range of rotation. In other words, the pressurizing mechanism 92 is not configured to allow the secondary transfer belt unit 70 to rotate without limit; rather, there are upper and lower limits to the rotation range of the secondary transfer belt unit 70. Specifically, the shape of the cam 93 is set, or a stopper portion that can contact the secondary transfer belt unit 70 is provided, so that the rotation range of the secondary transfer belt unit 70 is predetermined. Furthermore, even when the secondary transfer belt unit 70 rotates within a predetermined rotation range, the optical sensor 85 is always positioned to face the sensor-facing roller 74 via the secondary transfer belt 71 within the winding range θ. As a result, even when the secondary transfer belt unit 70 is rotated, variations in the detection accuracy of the optical sensor 85 that detects the surface of the secondary transfer belt 71 are less likely to occur.

[0052] Here, as shown in Figure 8, in this embodiment, multiple optical sensors 85 can be installed at intervals along the axial direction of the rotation center 74a of the sensor-facing roller 74 (the left-right direction in Figure 8). In this configuration, when adjusting the conditions during the secondary transfer process as described above, the image pattern (or background) formed on the secondary transfer belt 71 can be detected in the width direction (axial direction) by multiple optical sensors 85. Therefore, based on the results detected by the multiple optical sensors 85, the conditions during the secondary transfer process can be adjusted accurately in the width direction.

[0053] As described above, the secondary transfer belt device 69 in this embodiment comprises a plurality of roller members 72 to 78 and a secondary transfer belt 71 (belt member) stretched over the plurality of roller members 72 to 78, and also includes a secondary transfer belt unit 70 (belt unit) configured to be rotatable around the rotation center 74a of one of the plurality of roller members 72 to 78 (sensor-facing roller 74). Furthermore, a pressurizing mechanism 92 is provided that can adjust the contact pressure of the secondary transfer belt 71 against the intermediate transfer belt 8 (target body) by rotating the secondary transfer belt unit 70 around the rotation center 74a. In addition, an optical sensor 85 is provided that faces the sensor-facing roller 74 via the secondary transfer belt 71, without being linked to the rotation of the secondary transfer belt unit 70 by the pressurizing mechanism 92. As a result, even when the secondary transfer belt 71 (secondary transfer belt unit 70) is rotated, variations in the detection accuracy of the optical sensor 85 that detects the surface of the secondary transfer belt 71 are less likely to occur.

[0054] In this embodiment, the present invention was applied to an image forming apparatus 100 using a repulsive transfer method, in which the power supply unit 99 is configured to apply a secondary transfer bias to the secondary transfer opposing roller 80. However, the present invention can also be applied to an image forming apparatus using an attractive transfer method, in which the power supply unit is configured to apply a secondary transfer bias to the secondary transfer roller 72. In that case, the secondary transfer bias will have the opposite polarity to that of the repulsive transfer method. Furthermore, the present invention can also be applied to an image forming apparatus that uses both repulsive and attractive transfer methods. Furthermore, in this embodiment, the present invention was applied to a belt device 69 using a secondary transfer belt 71 as the belt member. However, the present invention is not limited to this, and can also be applied to belt devices using, for example, an intermediate transfer belt 8 or a transfer belt as the belt member. Furthermore, in this embodiment, the present invention was applied to an image forming apparatus 100 that forms a color image. However, the present invention can also be applied to an image forming apparatus that forms only a monochrome image. Furthermore, even in such cases, the same effects as those of this embodiment can be obtained.

[0055] It is clear that the present invention is not limited to this embodiment, and that this embodiment can be modified as appropriate within the scope of the technical concept of the present invention, in addition to what is suggested here. Furthermore, the number, position, shape, etc. of the constituent members are not limited to this embodiment, and can be set to a number, position, shape, etc. that is suitable for carrying out the present invention. [Explanation of symbols]

[0056] 1Y, 1M, 1C, 1K Photoconductor drum (photoconductor), 8. Intermediate transfer belt (target body), 69 Secondary transfer belt device (belt device), 70 Secondary transfer belt unit (belt unit), 70a Unit Case (Enclosure), 71 Secondary transfer belt (belt component), 72 Secondary transfer roller (roller component), 74 Sensor-facing roller (roller component), 74a Center of rotation (axis of rotation), 80 Secondary transfer opposing roller, 85 Optical sensors, 85a detection surface, 92 Pressurization mechanism, 93 cam, 100 Image forming apparatus (image forming apparatus main unit), θ, θ' are the wrapping range (wrapping angle), and S is the virtual normal.

[0057] Furthermore, the embodiments of the present invention can also be, for example, combinations of appendices 1 to 8 as follows. (Note 1) A belt unit comprising a plurality of roller members and a belt member stretched over the plurality of roller members, and configured to be rotatable about the rotation center of one of the plurality of roller members, A pressurizing mechanism is provided that allows adjustment of the contact pressure of the belt member against an object by rotating the belt unit around the rotation center, Without being linked to the rotation of the belt unit by the pressurizing mechanism, an optical sensor is positioned opposite the one roller member via the belt member, A belt device characterized by having the following features. (Note 2) The belt device according to Appendix 1, characterized in that, when viewed in a cross-section perpendicular to the rotation center, the detection surface of the optical sensor is configured to be perpendicular to the virtual normal passing through the rotation center of one of the roller members. (Note 3) As the belt unit rotates due to the pressurizing mechanism, the winding range of the belt member on one of the roller members is displaced. The belt device according to Appendix 1 or Appendix 2, characterized in that even if the belt unit rotates due to the pressurizing mechanism and the winding range is displaced, the optical sensor faces the one roller member via the belt member within the winding range. (Note 4) The belt device according to Appendix 3, characterized in that the pressurizing mechanism is configured to rotate the belt unit within a predetermined range of rotation. (Note 5) The belt device according to any one of the appendices 1 to 4, characterized in that the optical sensor is fixedly installed on the pressurizing mechanism. (Note 6) The belt device according to any one of the appendices 1 to 5, characterized in that the optical sensors are installed in multiple locations at intervals along the axial direction of the rotation center. (Note 7) The belt member is a secondary transfer belt that presses against a secondary transfer opposing roller via the intermediate transfer belt which is the target object, Of the plurality of roller members, one roller member different from the one roller member is a secondary transfer roller that presses against the intermediate transfer belt via the secondary transfer belt. The belt device according to any one of the appendices 1 to 6, characterized in that the optical sensor is a reflective photosensor. (Note 8) An image forming apparatus characterized by being equipped with a belt device as described in any of Appendix 1 to Appendix 7. [Prior art documents] [Patent Documents]

[0058] [Patent Document 1] Japanese Patent Publication No. 2011-180284

Claims

1. A belt unit comprising a plurality of roller members and a belt member stretched over the plurality of roller members, and configured to be rotatable about the rotation center of one of the plurality of roller members, A pressurizing mechanism is provided that allows adjustment of the contact pressure of the belt member against an object by rotating the belt unit around the rotation center, Without being linked to the rotation of the belt unit by the pressurizing mechanism, an optical sensor is positioned opposite one of the roller members via the belt member, A belt device characterized by having the following features.

2. The belt device according to claim 1, characterized in that, when viewed in a cross-section perpendicular to the rotation center, the detection surface of the optical sensor is configured to be perpendicular to a virtual normal passing through the rotation center of one of the roller members.

3. As the belt unit rotates due to the pressurizing mechanism, the winding range of the belt member on one of the roller members is displaced. The belt device according to claim 1 or 2, characterized in that even if the belt unit rotates due to the pressurizing mechanism and the winding range is displaced, the optical sensor faces the one roller member via the belt member within the winding range.

4. The belt device according to claim 3, characterized in that the pressurizing mechanism is configured to rotate the belt unit within a predetermined range of rotation.

5. The belt device according to claim 1 or 2, characterized in that the optical sensor is fixedly installed on the pressurizing mechanism.

6. The belt device according to claim 1 or 2, characterized in that a plurality of optical sensors are installed at intervals along the axial direction of the rotation center.

7. The belt member is a secondary transfer belt that presses against a secondary transfer opposing roller via the intermediate transfer belt which is the target object, Of the plurality of roller members, one roller member different from the one roller member is a secondary transfer roller that presses against the intermediate transfer belt via the secondary transfer belt. The belt device according to claim 1 or 2, characterized in that the optical sensor is a reflective photosensor.

8. An image forming apparatus characterized by comprising the belt device described in claim 1 or claim 2.

Images