Sheet transport device and image forming apparatus

Abstract

The present invention provides a sheet conveying device that reduces the decrease in applied pressure when pressurizing a driven roller toward a drive roller. [Solution] The device comprises a conveyor roller for conveying a sheet, a driven roller that moves in accordance with the rotation of the conveyor roller, a shaft that rotatably supports the driven roller, a plurality of first bearings that are located outside the driven roller in the width direction of the sheet perpendicular to the sheet conveying direction, have holes that engage with the shaft, and support the shaft, a second bearing that is located between the plurality of first bearings in the width direction, has holes that support the shaft, and a plurality of biasing means for biasing the plurality of first bearings and the second bearing, wherein the outer diameter of the first shaft portion of the shaft that engages with the plurality of first bearings is larger than the outer diameter of the second shaft portion of the shaft that engages with the second bearing, and the inner diameter of the holes in the plurality of first bearings and the second bearing is larger than the outer diameter of the first shaft portion.

Description

Technical Field

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[0001] The present invention relates to a sheet conveying device and an image forming apparatus including the sheet conveying device.

Background Art

[0002] As a sheet conveying device, a pair of conveying rollers that sandwich and convey a sheet includes a driving roller that rotates by receiving a driving force, and a driven roller that is driven to rotate by the rotation of the driving roller. The driven roller is pressed toward the driving roller by a biasing means such as a spring via a bearing. In Patent Document 1, as a configuration of the driven roller, two driven rollers are provided in the width direction of the sheet orthogonal to the sheet conveying direction, and include a shaft that pivotally supports the two driven rollers, a bearing that supports the shaft, and a compression spring. That is, it is composed of two driven rollers, one shaft, three bearings, and three compression springs. In recent years, there has been a demand for compatibility with a wide range of media, from ultra-thin sheets such as 45 gsm (grams per square meter) to 52 gsm to ultra-thick sheets with high stiffness such as 500 gsm. [[ID=X]]

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] [[ID=X]] However, in the configuration of the driven roller according to Patent Document 1, when there are three or more fitting portions where the shaft of the driven roller and the bearing are fitted, there is a possibility that a load is generated on the fitting portion between the bearing and the shaft with respect to a portion that regulates the pressing direction of some of the bearings. As a result, there may be a shortage of the pressing force for pressing the driven roller toward the driving roller, and there may be a conveyance failure in which a sheet with high stiffness cannot be conveyed.

[0005] Therefore, the object of the present invention is to provide a sheet conveying device that reduces the decrease in applied pressure when pressurizing a driven roller toward a drive roller. [Means for solving the problem]

[0006] One aspect of the invention for solving the above problems is a conveying roller for conveying a sheet, a driven roller that follows the rotation of the conveying roller, a shaft that rotatably supports the driven roller, a plurality of first bearings that are provided outside the driven roller in the width direction of the sheet perpendicular to the sheet conveying direction, have a hole that engages with the shaft, and support the shaft, a second bearing provided between the plurality of first bearings in the width direction, have the hole, and support the shaft, and a plurality of biasing means for biasing the plurality of first bearings and the second bearing, wherein the outer diameter of the first shaft portion of the shaft that engages with the plurality of first bearings is larger than the outer diameter of the second shaft portion of the shaft that engages with the second bearing, and the inner diameter of the hole of the plurality of first bearings and the second bearing is larger than the outer diameter of the first shaft portion. [Effects of the Invention]

[0007] The present invention makes it possible to reduce the decrease in applied pressure when pressurizing the driven roller toward the drive roller. [Brief explanation of the drawing]

[0008] [Figure 1] Schematic diagram of the image forming apparatus and feeding apparatus in an embodiment of the present invention. [Figure 2] Perspective view of the upper transport section in an embodiment of the present invention [Figure 3] A perspective view showing the open and closed state of the rotation guide of the upper transport section in an embodiment of the present invention. [Figure 4] Side view of a rotating guide in an embodiment of the present invention [Figure 5] Perspective view showing the pressure configuration of the driven roller in an embodiment of the present invention. [Figure 6] Cross-sectional view showing the pressure configuration of the driven roller in an embodiment of the present invention. [Figure 7] External view of the driven shaft in an embodiment of the present invention [Figure 8] Cross-sectional view of the bearing and shaft engaging with the outer stay in an embodiment of the present invention. [Figure 9] Cross-sectional view of the bearing and shaft engaging with the internal stay in an embodiment of the present invention. [Modes for carrying out the invention]

[0009] The best mode for carrying out the present invention will be described below with reference to the drawings. The embodiments described below are preferred embodiments of the present invention and therefore have various technically preferred limitations. However, the scope of the present invention is not unduly limited by the following description, and not all of the configurations described in these embodiments are essential components of the present invention.

[0010] <Image forming apparatus> First, the overall configuration of the image forming apparatus according to this embodiment will be described. Color image forming apparatuses are mainly classified into two types: a tandem system in which multiple image forming units are arranged side by side, and a rotary system in which they are arranged in a cylindrical shape. In addition, there are two types of transfer methods: a direct transfer method in which the toner image is transferred directly from the photoreceptor to the sheet material, and an intermediate transfer method in which the toner image is first transferred from the photoreceptor to an intermediate transfer unit before being transferred to the sheet material.

[0011] Figure 1 is a cross-sectional view of the image forming apparatus of this embodiment, which is an intermediate transfer tandem type image forming apparatus in which four color image forming units are arranged side by side on an intermediate transfer belt 506. The intermediate transfer method does not require the sheet material to be held on a transfer drum or transfer belt as in the direct transfer method, and can therefore handle a wide variety of transfer materials such as extra-thick paper and coated paper. Furthermore, its features of parallel processing in multiple image forming units and simultaneous transfer of full-color images make it suitable for achieving high productivity. The operation of the image forming apparatus 1 will be described below using Figure 1.

[0012] The image forming apparatus 1 is classified into a sheet transport section that transports sheets and an image forming section that forms images. The sheet transport section is further provided with a sheet feeding section 51, a merging transport section 54, a pre-skew correction transport section 50, a skew correction section 55, a branching transport section 59, a discharge tray 500, a reversal transport section 550, and a double-sided transport section 502. The image forming section consists of an image forming section 513 and a fixing section 58. A sheet feeding apparatus 2 is provided alongside the image forming apparatus 1 and will be described separately.

[0013] First, the sheets S are loaded onto a lifter plate 52 provided in the sheet feeding unit 51. The sheets S loaded onto the lifter plate 52 are fed by the feeding unit 53 in accordance with the image formation timing of the image forming unit 513. The feeding unit 53 can utilize methods such as friction separation using feeding rollers or separation and adsorption using air. In this embodiment, an air-based sheet feeding method is adopted. The sheets S sent out by the feeding unit 53 pass through the transport path 54a of the merging transport unit 54, and then through the pre-skew correction transport unit 50, before being transported to the skew correction unit 55. The pre-skew correction transport unit 50 is equipped with a detection unit 510 that detects the leading edge of the sheet S. This detection unit 510 measures the delay time or early arrival time of the sheet S, changes the transport speed of the sheet S accordingly, cancels the delay time or early arrival time, and then transports the sheet to the skew correction unit 55. Furthermore, the sheets fed from the sheet feeding device 2, which will be described later, are transported via the transport path 54c, through the pre-skew correction transport section 50, and then to the skew correction section 55.

[0014] Subsequently, the sheet is skewed in the skew correction unit 55 and then sent to the secondary transfer unit by the registration roller 7. The secondary transfer unit is a toner image transfer nip section to the sheet S formed by the substantially opposing secondary transfer inner roller 503 and secondary transfer outer roller 56, where a toner image is transferred to the sheet S by applying a predetermined pressure and electrostatic load bias.

[0015] After a full-color toner image is secondarily transferred onto the sheet S, the sheet S is conveyed to the fixing unit 58 by the pre-fixing conveyance unit 57. The fixing unit 58 applies a predetermined pressing force by a roller or belt that substantially faces each other, and generally applies a heating effect by a heat source such as a heater to melt and fix the toner onto the sheet S.

[0016] The sheet S having the fixed image obtained in this way is discharged to the discharge tray 500 as it is by the branch conveyance unit 59, or the sheet is switched back by the reverse conveyance unit 550 and discharged to the discharge tray 500.

[0017] Also, when double-sided image formation that requires forming images on both sides of the sheet is needed, it is conveyed to the double-sided conveyance unit 502. The sheet S conveyed to the double-sided conveyance unit 502 is detected at its leading end by a detection unit that detects the leading end of the sheet S provided in the double-sided conveyance path, and the sheet is temporarily stopped in the double-sided conveyance path. After that, the sheet is made to wait (double-sided standby) until refeeding for forming the second-side image, and refeeding is performed based on the second-side image formation. After that, it is conveyed to the pre-skew correction conveyance unit 50 via the conveyance path 54b. Thereafter, image formation is performed on the second side of the sheet and discharged in the same manner as when printing an image on the first side of the sheet.

[0018] Regarding the conveyance process of the sheet S described above, an image formation process for forming an image on the sheet sent to the secondary transfer unit at the same timing will be described. Among the image formation units 513, the yellow (Y) image formation unit will be described. Therefore, the same image formation process is also performed for the other magenta (M), cyan (C), and black (Bk) image formation units.

[0019] The image forming unit 513 mainly consists of a photoreceptor 508, an exposure unit 511, a developer unit 510, a primary transfer unit 507, and a photoreceptor cleaner 509. The surface of the photoreceptor is uniformly charged beforehand by a charging unit (not shown). The photoreceptor 508 rotates in the direction of arrow A in the figure, and the exposure unit 511 emits light based on the image information signal that has been sent, and a latent image is formed via the diffraction means 512 and other appropriate means. The electrostatic latent image formed on the photoreceptor 508 in this way is developed by the developer unit 510, and a toner image is formed on the photoreceptor 508. After that, a predetermined pressure and electrostatic load bias are applied by the primary transfer unit 507, and the toner image is primary transferred onto the intermediate transfer belt 506. After that, any remaining toner on the photoreceptor 508 is collected by the photoreceptor cleaner 509 and prepared again for the next image formation.

[0020] Next, the intermediate transfer belt 506 will be described. The intermediate transfer belt 506 is stretched by rollers such as the drive roller 504, tension roller 505, and secondary transfer inner roller 503. The drive roller 504 is driven by a motor (not shown), and the intermediate transfer belt 506 is rotated in the direction of arrow B in the figure. Therefore, the image formation processes for each color, which are processed in parallel by the image forming units 513 of Y, M, C, and Bk mentioned above, are performed at the timing when they are superimposed on the upstream toner image that has been primary transferred onto the intermediate transfer belt 506. As a result, a full-color toner image is ultimately formed on the intermediate transfer belt 506 and transported to the secondary transfer unit.

[0021] As described above, the sheet S transport process and the image formation process for forming an image on the sheet S work in conjunction with each other to form an image on the sheet.

[0022] <Sheet feeding device> As shown in Figure 1, a feeding device 2 is located upstream of the transport path 54c of the image forming apparatus 1 and is connected to the image forming apparatus. This feeding device 2 has three feeding sections in the vertical direction, each with a configuration similar to the sheet feeding section 51 in the image forming apparatus, and is configured to feed sheets S from each feeding section. Of the three feeding sections, sheets S fed from the first feeding section 60U and the second feeding section 60M from the top are transported through the upper transport path α of the upper transport section 700. Sheets S fed from the third feeding section 60L from the top are transported through the lower transport path β. Sheets S fed from each feeding section are transported to the upstream skew correction section 61. Multiple pairs of transport rollers for transporting sheets are provided in the upper transport path α, the lower transport path β, and the upstream skew correction section 61.

[0023] The upstream skew correction unit 61 corrects the skew of the leading edge of the sheet by abutting it against the nip of the transport roller pair to form a loop, and aligning the leading edge of the sheet with the nip of the roller pair. The sheet, whose skew has been corrected in the upstream skew correction unit 61, is then transported to the image forming apparatus 1.

[0024] The sheets transported from the feeding device 2 to the image forming apparatus 1 are fed from each feeding unit in accordance with the image forming timing of the image forming apparatus, similar to the sheet feeding unit 51 of the image forming apparatus 1. When the sheet is transported to the horizontal transport path after passing through the upper transport path α or the lower transport path β, the leading edge of the sheet is detected by a detection unit installed in the horizontal transport path that detects the leading edge of the sheet.

[0025] Within the horizontal transport path, when the detection unit detects the leading edge of the sheet, it temporarily stops the sheet. Then, the sheet is fed again in accordance with the image forming timing of the image forming apparatus 1. This makes it possible to correct for variations in transport timing. After that, the sheet is transported to the image forming apparatus 1.

[0026] <Upper transport unit configuration> Next, the upper conveying section 700 will be explained using Figures 2, 3, and 4. Figure 2 is a perspective view of the upper conveying section 700. Figure 3 is a front view of the upper conveying section 700, where Figure 3(a) shows the rotating guide 701 in the closed position and Figure 3(b) shows the rotating guide 701 in the open position. Figure 4 is a side view of the rotating guide 701, showing the state with the cover attached to the rotating guide removed.

[0027] The upper transport path α is composed of a fixed guide 708 fixed to the housing of the sheet feeding device and a rotating guide 701 that is rotatable relative to the fixed guide. When the rotating guide 701 is closed, the sheet is ready for transport. When the rotating guide 701 is open, the system is configured to remove any sheets that have accumulated in the upper transport path α in the event of a jam.

[0028] Here, the opening and closing mechanism for the rotating guide 701 will be described. The rotating guide 701 has a hinge portion 702 on the rear side of the sheet feeding device, and hooks 703a and 703b are provided above and below the rotating guide 701 on the front side of the sheet feeding device. Furthermore, the hooks 703a and 703b are connected to a hook shaft 705, and an operating lever 704 is attached to the hook shaft 705. As a result, when the user operates the operating lever 704, the hooks 703a and 703b rotate around the hook shaft 705 as the pivot point. In addition, a hook hooking member (not shown) is attached to the fixed guide 708, and when the hooks 703a and 703b engage with the hook hooking member, the rotating guide 701 is positioned in the sheet feeding position as shown in Figure 3(a). When the user operates the operating lever 704, disengaging the hook and rotating the pivot guide 701, the upper transport path α is exposed to the outside, as shown in Figure 3(b). When the pivot guide 701 is in the open position, an open space is formed on the front side of the transport path α.

[0029] Furthermore, as shown in Figures 3 and 4, the upper transport path α has three pairs of transport rollers arranged in the sheet feeding direction. The fixed guide 708 is provided with drive rollers 709a, 709b, and 709c, which are driven and rotated by a drive source (not shown). On the other hand, the rotating guide 701 has a plurality of driven rollers 710a, 710b, and 710c that follow the rotation of the drive rollers.

[0030] The driven roller 710a is equipped with a biasing means to bias it toward the driven roller 709a. This makes it possible to form a nip pressure between the driven roller 709a and the driven roller 710a when the rotating guide 701 is closed, as shown in Figure 3(a), thereby obtaining a conveying force for transporting the sheet. The same applies to the driven rollers 709b, 709c and the driven rollers 710b, 710c. On the other hand, when the rotating guide 701 is open, as shown in Figure 3(b), the nip between the driven roller and the driven roller is separated.

[0031] <Configuration of the driven roller> Figures 5 and 6 show the pressure configuration of the driven roller relative to the drive roller. Figure 5 is a perspective view, and Figure 6 is a cross-sectional view from the front.

[0032] The driven roller 710 comprises two driven rollers 245 arranged in the width direction of the sheet, perpendicular to the sheet conveying direction, which rotate in accordance with the rotation of the drive roller 241, and a driven shaft 242 that rotatably supports the two driven rollers 245. In addition, four bearings 247 that have holes to support the driven shaft 242 are provided at inner and outer positions in the width direction relative to each driven roller 245. A biasing part 246 is provided to bias each bearing 247 toward the drive roller 241. In this embodiment, a compression spring is used for the biasing part.

[0033] The system includes an outer stay 243, which is a first support part, and an inner stay 244, which is a second support part, that support the bearing 247 and the biasing part 246. The outer stay 243 contacts and supports the bearing 247 and the biasing part 246 on the widthwise outer side of each driven roller 245, and the inner stay 244 contacts and supports the bearing 247 and the biasing part 246 on the widthwise inner side of each driven roller 245. One end of the outer stay 243 and the inner stay 244 are attached to and fixed to a part of the rotation guide.

[0034] As in this embodiment, by arranging the compression springs 246 in four locations, the spring constant per spring can be reduced, which makes it possible to reduce variations in the applied pressure that the driven roller 245 applies to the drive roller 709, and thus provide a stable applied pressure.

[0035] <Mechanism to prevent improper pressure application of driven rollers> Figure 7 is a perspective view of the driven shaft 242 according to this embodiment of the present invention. As shown in Figure 7, the driven shaft 242 has a first shaft portion, which is an outer diameter portion 242a with a large outer diameter of the shaft, and a second shaft portion, which is an outer diameter portion 242b with a small outer diameter of the shaft.

[0036] The portion of the driven shaft 242 that engages with the hole in the bearing 247 of the outer stay 243 is the outer diameter portion 242a. The portion of the driven shaft 242 that is positioned in the bearing 247 of the inner pressure stay 242 is the outer diameter portion 242b. In other words, in order to use the four compression springs 248 and bearings 247 in common, a difference in the outer diameter of the driven shaft 242 is provided, as shown in Figure 7.

[0037] In this embodiment, the outer diameter of the outer diameter portion 242a is φ5, and the outer diameter of the outer diameter portion 242b is φ4.6. The inner diameter of the bore of the bearing 247 is φ5. Specifically, the outer diameter φ5 of the outer diameter portion 242a has an H10 tolerance, and the inner diameter φ5 of the bore of the bearing 247 has an f9 tolerance, resulting in a so-called "clearance fit." In contrast, the inner diameter φ5 of the bore of the bearing 247 and the outer diameter portion 242b φ4.6 are configured to have a clearance of ±0.2 mm.

[0038] In other words, in this embodiment, where the driven shaft 242 is rotatably supported by four bearings 247, there is a clearance between the bearing 247 on the widthwise side of each driven roller 245 and the driven shaft 242. The bearing 247 on the widthwise side of each driven roller 245 and the driven shaft 242 are fitted in a "clearance fit" configuration. As a result, the driven shaft 242 is supported by the bearings 247 at two points on the outside and at two points on the inside with clearance, thus eliminating twisting of the driven shaft 246.

[0039] When a driven shaft of the same outer diameter is used for the four compression springs 246 and bearings 247, there are four fitting points. Due to part tolerances, the driven shaft of the same outer diameter is mounted twisted, reducing the sliding performance of the outer stay 243 and inner stay 244 and the bearing 247 in the pressurizing direction. As a result, the driven roller may be mounted at an angle in the front and rear of the pressurizing direction, or the driven roller may not reach the predetermined position due to the reduced sliding performance, leading to conveying failures due to insufficient pressurizing force. To solve this, the twisting of the driven shaft 246 can be eliminated by reducing the fitting configuration from four points to two.

[0040] Note that ±0.2 mm is a value assumed from the mounting position tolerance of the outer stay 243 and inner stay 244 in this embodiment. The difference between the ideal outer diameter portion 242a and the outer diameter portion 242b is preferably the sum of the total tolerances of the parts that cause twisting when the driven shaft 242 of the driven roller 710 is mounted.

[0041] Next, we will describe the configuration of the driven shaft and bearing when the driven roller is nipped onto the drive roller. Figure 8 shows a cross-sectional view of the bearing and driven shaft supported by the outer stay, and Figure 9 shows a cross-sectional view of the bearing and driven shaft supported by the inner stay. From Figure 8, the relationship between the hole in the bearing 247 located in the outer stay 243 and the axis of the outer diameter portion 242a of the driven shaft 242 is a fit 249, with a gap of approximately a small difference. From Figure 9, the relationship between the hole in the bearing 247 located in the inner stay 244 and the axis of the outer diameter portion 242b of the driven shaft 242 has a clearance of play 251. When the shape of the compression spring 246 and the bearing 247 are used in common, the clearance of play 251 as shown in Figure 9 reduces the load on the compression spring 246. Therefore, at the contact portion 252 (spring mounting surface) of the outer stay 243 where the compression spring contacts, it protrudes toward the drive roller by the difference of the clearance of play. This makes it possible to reduce the applied pressure when the driven roller is nipped by the drive roller, and also to reduce the twisting of the driven shaft.

[0042] An example was given in which the driven shaft 242 is held at four points by four bearings 247. However, the number of bearings is not limited. For example, the driven shaft 242 may be held by three bearings. [Explanation of Symbols]

[0043] 710 Driven roller 709 Drive Roller 242 Driven axis 242a Outer diameter part 242b Outer diameter part 243 Stay outside 244 Stay inside 245 Driven roller 246 Compression spring 247 Bearing 249 Fitting and interlocking 251 Gap rattle 252 Mounting surface for the spring of the outer stay

Claims

1. A conveyor roller for transporting the sheet, A driven roller that moves in accordance with the rotation of the aforementioned conveying roller, A shaft that rotatably supports the driven roller, A plurality of first bearings are provided on the outside of the driven roller in the width direction of the sheet, perpendicular to the sheet conveying direction, and have holes that engage with the shaft, and support the shaft. A second bearing is provided between the plurality of first bearings in the width direction, has the hole portion, and pivotally supports the shaft, The system comprises a plurality of biasing means for biasing the plurality of first bearings and the plurality of second bearings, The outer diameter of the first shaft portion that engages with the plurality of first bearings on the shaft is larger than the outer diameter of the second shaft portion that engages with the second bearing on the shaft. The inner diameter of the holes in the plurality of first bearings and the second bearings is larger than the outer diameter of the first shaft portion. A sheet conveying device characterized by the following features.

2. The gap between the hole and the shaft in the plurality of first bearings is smaller than the gap between the hole and the shaft in the second bearing. The sheet conveying device according to feature 1.

3. The holes and shafts in the plurality of first bearings are engaged with each other in a fitting relationship. The sheet conveying device according to feature 2.

4. Multiple driven rollers are provided, The sheet conveying device according to claim 1, characterized in that the second bearing is provided between the plurality of driven rollers in the width direction.

5. It comprises a plurality of support parts that support one end of the plurality of biasing means, In the second support portion that supports the second biasing means that biases the second bearing, the contact portion that contacts the second biasing means protrudes toward the drive roller more than the contact portion that contacts the first biasing means in the first support portion that supports the plurality of first biasing means that bias the first bearing. The sheet conveying device according to feature 1.

Images