Paper sheet conveyance device and image forming device

Abstract

To provide a paper sheet conveyance device and an image forming device having a vibration suppressing effect.SOLUTION: A registration roller 21 is connected to a drive shaft 32 to transmit a driving force thereto, and includes: a rotation shaft 212 having an engagement part 212a on a connection side with the drive shaft 32; and a coupling 211 having an engaged hole 211a and attached to the rotation shaft 212 by inserting the engagement part 212a into the engaged hole 211a. The engagement part 212a and the engaged hole 211a have similar figures in a predetermined cross section perpendicular to a center axis of the rotation shaft 212, and the engaged hole 211a is larger in size than the engagement part 212a. When a driving force is transmitted from the coupling 211 to the rotation shaft 212, at the predetermined cross section, the engagement part 212a contacts an inner surface of the engaged hole 211a at three or more contact points, and the contact at the plurality of contact points limits a relative movement of the coupling 211 with respect to the rotation shaft 212.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to a paper transport device and an image forming apparatus using the same. [Background technology]

[0002] A paper transport device that transports paper to an image forming unit of an image forming apparatus is sometimes unitized and detachably attached to the image forming apparatus from the viewpoint of ease of assembly. In this case, to improve workability, a coupling that transmits rotational force to the paper transport roller may be provided with multiple pin engagement grooves for engaging with engagement pins provided on the paper transport roller (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-304776 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional paper transport devices, the method for fixing the coupling to the drive shaft is not disclosed, and if the rotation axis of the drive shaft to which the coupling is attached and the rotation axis of the paper transport roller are not aligned and offset due to the influence of component precision or assembly precision, the rotation force is not transmitted smoothly to the paper transport roller, generating vibrations, which may be transmitted to the image forming unit and cause image defects. Since the vibrations are particularly large when the rotation starts, it is necessary to suppress them.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a paper transport device and an image forming apparatus that can suppress the occurrence of vibrations and impacts when a paper transport roller rotates. [Means for solving the problem]

[0006] In order to solve the above problems, a first aspect of the present disclosure is a paper transport device that is detachably attached to an image forming device and has a paper transport roller that is connected to a drive shaft provided in the image forming device when attached to the image forming device to transmit a driving force, wherein the paper transport roller comprises a rotating shaft having an engaging portion on the connection side with the drive shaft, and a transmission member that has an engaged hole and is attached to the rotating shaft by inserting the engaging portion into the engaged hole and is connected to the drive shaft to transmit a driving force from the drive shaft to the rotating shaft, wherein the engaging portion and the engaged hole have similar shapes in a predetermined cross section perpendicular to the central axis of the rotating shaft, and the engaged hole is larger in size than the engaging portion, and when the driving force is transmitted from the transmission member to the rotating shaft, the engaging portion contacts the inner surface of the engaged hole at three or more contact points in the predetermined cross section, and the contact at the multiple contact points restricts the relative movement of the transmission member with respect to the rotating shaft.

[0007] According to the above configuration, when the driving force is transmitted from the transmission member to the rotating shaft, the relative movement of the transmission member with respect to the rotating shaft is restricted, so that no collision occurs between the engaging portion and the inner surface of the engaged hole, and vibration in the paper transport roller can be suppressed.

[0008] Furthermore, the paper transport device can be configured such that, when a driving force is transmitted from the transmission member to the rotation shaft, a closed area surrounded by multiple tangents to the multiple contact points is generated in the specified cross section.

[0009] In addition, in the above-mentioned paper conveying device, the transmission member has four engaging grooves formed in a cross shape when viewed from the axial direction of the rotating shaft, and the drive shaft has protrusions protruding from two locations 180° opposite each other on the side of the drive shaft, and the drive shaft and the transmission member can be configured to be connected by fitting the protrusions into two of the four engaging grooves.

[0010] In addition, in the above-mentioned paper conveying device, a screw hole is provided at the tip of the rotating shaft on the side connecting with the drive shaft, and the transmission member can be configured to be attached to the rotating shaft by inserting the engaging portion into the engaged hole and tightening a screw into the screw hole.

[0011] In order to solve the above problem, an image forming apparatus according to a second aspect of the present disclosure is characterized by including the above-described paper transport device. [Effects of the Invention]

[0012] The paper conveying device and image forming device disclosed herein can prevent rotational irregularities and vibrations from occurring even if the rotational center lines of the paper conveying roller's rotational axis and the drive axis are offset by making the cross-sectional shapes of the engaging portion provided on the rotational axis of the paper conveying roller and the engaged portion that engages with the engaging portion provided on the transmission member that rotates in response to rotational force from the drive axis similar. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present disclosure. [Figure 2] FIG. 2 is a perspective view showing the appearance of a registration roller unit and a drive unit. [Figure 3] FIG. 2 is an exploded perspective view of the rear end of the registration roller. [Figure 4] FIG. 2 is an enlarged perspective view of a connection end portion between a registration roller and a drive shaft. [Figure 5] FIG. 4 is a cross-sectional view showing an example of a state in which a drive shaft is connected to a registration roller. [Figure 6] FIG. 10 is an exploded perspective view of the rear end of a registration roller in a conventional example. [Figure 7] 10A and 10B are diagrams illustrating hypothetical behavior of a coupling when a driving force is transmitted from a drive shaft to a registration roller in a conventional example. [Figure 8]10A and 10B are diagrams illustrating hypothetical behavior of a coupling when a driving force is transmitted from a drive shaft to a registration roller in the embodiment. [Figure 9] 10A and 10B are diagrams illustrating conditions under which the relative movement of the coupling with respect to the rotation shaft of the registration roller is limited when a driving force is transmitted. [Figure 10] 10A and 10B are diagrams illustrating conditions under which the relative movement of the coupling with respect to the rotation shaft of the registration roller is not restricted when the driving force is transmitted. [Figure 11] 10A and 10B are diagrams showing examples of shapes of an engaging portion and an engaged hole according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] [First embodiment] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Fig. 1 is a schematic diagram showing an embodiment of an image forming apparatus 10 of the present disclosure. Note that the image forming apparatus 10 shown in Fig. 1 is a color image forming apparatus having multiple process units, but the present disclosure is not limited to this and can also be applied to a monochrome image forming apparatus having a single process unit.

[0015] As shown in FIG. 1, the image forming apparatus 10 is configured to include a main body 11, a document reading unit 12, a document transport device 13, and a paper feed device 14. The main body 11 has an internal image forming unit for forming (printing) an image on recording paper. The document reading unit 12 is disposed above the main body 11 and reads the document when copying the document. In automatic reading mode, the document transport device 13 sequentially transports documents placed on a document set tray toward the document placement table of the document reading unit 12. The paper feed device 14 has at least one paper feed cassette for stocking recording paper, and separates recording paper one sheet at a time from a selected paper feed cassette and transports it toward the main body 11. The main body 11 forms an image on the recording paper sent from the paper feed device 14.

[0016] The image data handled by the image forming apparatus 10 corresponds to a color image using each of the colors black (K), cyan (C), magenta (M), and yellow (Y), or a monochrome image using a single color (e.g., black). Therefore, the image forming apparatus 10 has four process units Pa to Pd corresponding to black, cyan, magenta, and yellow as image forming sections. Each of the process units Pa to Pd forms a toner image corresponding to the image data using known electrophotographic technology.

[0017] The toner images formed in each process unit Pa to Pd are sequentially transferred and superimposed on the intermediate transfer belt 15. As a result, a color toner image is formed on the intermediate transfer belt 15. The color toner image on the intermediate transfer belt 15 is transferred onto a recording sheet by a transfer device 16, and the recording sheet is heated and pressed by a fixing unit 17 to fix the color toner image on the recording sheet.

[0018] The image forming apparatus 10 has a paper transport system consisting of a plurality of transport rollers. The paper transport system includes registration rollers (paper transport rollers) 21 for transporting recording paper in accordance with the image transfer timing. In the image forming apparatus 10 of this embodiment, the registration rollers 21 are included in a registration roller unit (paper transport device) 20 (described later), which is provided detachably with respect to the image forming apparatus 10. The registration roller unit 20 of this embodiment includes a transport roller 22 arranged upstream of the registration rollers 21. In this way, the registration roller unit 20 may, but does not have to, include transport rollers other than the registration rollers 21.

[0019] The registration rollers 21 and conveying rollers 22 included in the registration roller unit 20 are basically a pair of rollers consisting of a drive roller that rotates by receiving the rotational force of the drive motor 31, and a driven roller that contacts the drive roller and is rotated by the rotation of the drive roller. The image forming apparatus 10 of the present disclosure is characterized by a drive force transmission mechanism to the drive roller, so in the following description, when simply referring to the registration rollers 21, it refers to the drive roller. Furthermore, in the following description, an example is given in which the characteristics of the image forming apparatus 10 of the present disclosure are applied to the registration rollers 21, but a similar configuration can also be applied to the conveying rollers 22.

[0020] FIG. 2 is a perspective view showing the appearance of the registration roller unit 20 and a drive unit 30 provided with a drive motor 31 that transmits a rotational force to the registration rollers 21. As shown in FIG.

[0021] The registration roller unit 20 is detachably attached to the image forming apparatus 10. Fig. 2 shows the registration roller unit 20 removed from its attachment position in the image forming apparatus 10. The registration roller unit 20 is attached to the attachment position in the image forming apparatus 10 by moving it to the rear side in the front-to-rear direction of the image forming apparatus 10 (the direction of arrow A in Fig. 2), and can be removed from the attachment position in the image forming apparatus 10 by moving it to the front side from its attachment position.

[0022] Further, a coupling (transmission member) 211 that receives a rotational force from the drive motor 31 is attached to the rear end of the registration roller 21.

[0023] The drive unit 30 includes a drive motor 31 and a drive shaft 32 that rotates when the rotational force of the drive motor 31 is transmitted by a gear train (not shown), and is disposed rearward of the registration roller unit 20 within the image forming apparatus 10 .

[0024] When the registration roller unit 20 is attached to the attachment position of the image forming apparatus 10, the coupling 211 of the registration roller 21 is connected to the drive shaft 31 of the drive unit 30, allowing the drive motor 31 to drive the registration roller 21.

[0025] The mechanism for transmitting driving force to the registration roller 21 using the coupling 211 will be described below. Fig. 3 is an exploded perspective view of the rear end of the registration roller 21. As shown in Fig. 3, the registration roller 21 has a rotary shaft 212, and an engaging portion 212a for attaching the coupling 211 is formed at the rear end of the rotary shaft 212. A screw hole 212b is formed at the tip of the engaging portion 212a. The coupling 211 is formed with an engaged hole 211a that engages with the engaging portion 212a.

[0026] The coupling 211 is attached to the registration roller 21 by fastening a set screw 213 to a screw hole 212b in a state where an engaging portion 212a of the rotating shaft 212 is inserted into an engaged hole 211a of the coupling 211. When fastened to the screw hole 212b, the set screw 213 prevents the coupling 211 from coming off in the axial direction of the rotating shaft 212 and also serves as a starting point for precession of the coupling 211 relative to the rotating shaft 212, which will be described later.

[0027] FIG. 4 is an enlarged perspective view showing the registration roller 21 and the drive shaft 32 with the coupling 211 attached to the engagement portion 212a. The illustration shows the coupling 211 and the drive shaft 32 when the registration roller unit 20 is in a position immediately before being attached to the attachment position. As shown in FIG. 4, the coupling 211 has four engagement grooves 211b formed in a cross shape when viewed from the axial direction of the rotation shaft 212. More specifically, the coupling 211 has a cylindrical portion 211e that protrudes axially from a bottom portion 211d, in which the engagement holes 211a are formed, toward the rear side. The engagement grooves 211b are formed in the axial direction of this cylindrical portion and have a shape that is open on the rear side. Furthermore, a taper 211c is formed between two adjacent engagement grooves 211b on the rear end surface of the cylindrical portion 211e of the coupling 211. All of the tapers 211c are formed to be inclined in the same direction in the circumferential direction of the cylindrical portion. For example, in the example of FIG. 4, all of the tapers 211c are inclined from the rear side to the front side in the counterclockwise direction when viewed from the rear side.

[0028] The drive shaft 32 has an engagement pin (protrusion) 321 that engages with the engagement groove 211b. The engagement pin 321 is provided so as to protrude from the outer circumferential surface of the drive shaft 32 in a direction perpendicular to the central axis of the drive shaft 32. In the present embodiment, the engagement pins 321 are provided so as to protrude from the outer circumferential surface of the drive shaft 32 at two locations. When the registration roller unit 20 is attached to the attachment position of the image forming apparatus 10, the engagement pin 321 is fitted into the engagement groove 211b of the coupling 211. Here, if the position of the engagement groove 211b relative to the position of the engagement pin 321 is misaligned in the circumferential direction of the rotation shaft 212, the taper 211c described above will first come into contact with the engagement pin 321. When a force to move the registration roller unit 20 to the mounting position acts on the contact portion between the taper 211c and the engaging pin 321, the drive shaft 32 on which the engaging pin 321 is mounted does not rotate because the drive motor 31 is stopped, but the taper 211c slides, causing the coupling 211 to rotate. This rotation guides the engaging pin 211b into the engaged groove 211b and engages with it. With the engaging pin 321 and the engaged groove 211b engaged in this manner, the rotational force of the drive shaft 32 is transmitted to the coupling 211 via the engaging pin 321 and the engaged groove 211b. The rotational force transmitted to the coupling 211 is also transmitted to the registration roller 21 via the engaged hole 211a and the engaging portion 212a.

[0029] As described above, of the four engaged grooves 211b formed in the coupling 211, the engaging pin 321 fits into only two engaged grooves 211b that are symmetrical about the axial center. However, by providing the four engaged grooves 211b in the coupling 211 and forming the taper 211c on the rear end surface of the cylindrical portion 211e of the coupling 211, the engaging pin 321 is smoothly guided into the engaged groove 211b along the taper 211c regardless of the positional relationship between the engaged groove 211b and the engaging pin 321 in the connection between the registration roller unit 20 and the drive unit 30. This makes it possible to smoothly attach the registration roller unit 20 to the attachment position.

[0030] 5 is a cross-sectional view showing an example of a state in which the coupling 211 attached to the registration roller 21 is connected to the drive shaft 32. Here, it is preferable that the central axis S1 of the rotation shaft 212 of the registration roller 21 and the central axis S2 of the drive shaft 32 are completely coaxial when the drive shaft 32 is connected to the registration roller 21. However, in reality, depending on the assembly accuracy of the unit, the central axis S1 and the central axis S2 do not always completely coincide on the same axis, and as shown in FIG. 5, an axial misalignment (offset ΔS) may occur between the central axis S1 and the central axis S2.

[0031] To ensure smooth transmission of driving force from the drive shaft 32 to the registration rollers 21 even when such an offset ΔS occurs, the coupling 211 is attached so as to be allowed to tilt with respect to the rotary shaft 212. Specifically, the shape of the engaged hole 211a in the coupling 211 as viewed from the axial direction (the shape of a predetermined cross section perpendicular to the central axis S1 of the rotary shaft 212) is similar to the shape of the engaging portion 212a of the rotary shaft 212, and is slightly larger than the engaging portion 212a. Therefore, a gap (play) is generated between the engaged hole 211a and the engaging portion 212a, and this gap (play) allows the coupling 211 to tilt with respect to the rotary shaft 212. Furthermore, in order to smoothly change the value of the tilt α when the drive shaft 32 rotates and the value of the tilt α changes, a biasing member 24 that biases the coupling 211 and a holding member 23 that rotates together with the rotating shaft 212 and abuts against the end of the biasing member 24 on the opposite side to the abutment portion with the coupling 211 may be provided. With this configuration, it becomes possible to smoothly tilt the coupling 211 even if the offset ΔS changes as the drive shaft 32 rotates.

[0032] 5, the axial center of the coupling 211 is inclined at an inclination angle α with respect to the central axis S1. By inclining the coupling 211 in this way, even when an offset ΔS occurs, the coupling 211 can connect the rotation shaft 212 of the registration roller 21 and the drive shaft 32. When the rotational driving force is transmitted from the drive shaft 32 to the rotation shaft 212 via the coupling 211, the coupling 211 oscillates (precesses) so as to maintain the inclination angle α, thereby enabling smooth transmission of the driving force from the drive shaft 32 to the registration roller 21.

[0033] The gap between the engaged hole 211a and the engaging portion 212a is set so that the gap in the (extending) direction of the engaging pin 321 and the gap in the direction perpendicular to the engaging pin 321 are approximately the same.

[0034] In a connection between a coupling and a drive shaft attached to a registration roller such that the gap between the engaged hole 211a and the engaging portion 212a is different in the direction in which the engaging pin 321 extends and in the direction perpendicular to the engaging pin 321, there is a problem of vibration occurring when the registration roller is rotated. The principle of this vibration generation will be explained with reference to FIGS. 6 and 7. FIG. 6 is an exploded perspective view, viewed from the rear, of a registration roller 21′ and a coupling 211′ configured such that the gap between the engaged hole 211a and the engaging portion 212a is different in the direction in which the engaging pin 321 extends and in the direction perpendicular to the engaging pin 321. FIG. 7 is a virtual diagram illustrating the behavior of the coupling 211′ when driving force is transmitted from the drive shaft to the registration roller 21′. The coupling 211′ of the registration roller 21′ is connected to the drive shaft 32 in the same manner as the coupling 211 of the registration roller 21.

[0035] Vibrations in the registration roller 21' are caused by the shapes of the engaged hole 211a' in the coupling 211' and the engaging portion 212a' in the rotating shaft 212'. The shape of the engaging portion 212a' in FIG. 6 (cross-sectional shape as viewed from the axial direction) is commonly used for attaching a transmission member such as a gear to the end of a roller, and has a shape with notches on both sides of two parallel chords (hereinafter referred to as an I-shaped cross-sectional shape). By providing a flat portion on part of the cylindrical surface in this way, the rotational force received by the gear can be reliably transmitted to the roller. The shape of the engaged hole 211a' that engages with this I-shaped cross-sectional shape is similar to this shape and is slightly larger than the engaging portion 212a'.

[0036] Figure 7(a) is a view from the bottom 211d showing a state in which no driving force is being transmitted from the coupling 211' to the rotation shaft 212'. In the example of Figure 7, an offset ΔS occurs between the central axis S1 of the registration roller 21' and the central axis S2 of the drive shaft 32, and the coupling 211' receives a biasing force F1 toward the left side in the figure due to the offset ΔS. Therefore, in the state shown in Figure 7(a), the engaging portion 212a' is shifted to the right side inside the engaged hole 211a'.

[0037] When the drive shaft 32 starts to be driven from the state shown in Figure 7(a), the coupling 211' starts to rotate accordingly. In the example of Figure 7, the drive shaft 32 and the coupling 211' rotate clockwise. As the coupling 211' rotates, the engaging portion 212a' comes into contact with the inner surface of the engaged hole 211a' at three points, contact points P1 to P3 (see Figure 7(b)).

[0038] When the engaging portion 212a' comes into contact with the engaged hole 211a' at contact points P1 to P3, a driving force is transmitted from the coupling 211' to the rotating shaft 212' via these contact points P1 to P3, and the rotating shaft 212' starts to rotate together with the coupling 211'. Figures 7(c) and 7(d) show the states in which the coupling 211' has rotated 90° and 180° from the state in Figure 7(a), respectively.

[0039] Here, it is assumed that the relative positional relationship between the rotating shaft 212' and the coupling 211', in other words, the relative positional relationship between the engaging portion 212a' and the engaged hole 211a', does not change during the process shown in Figures 7(b) to 7(d). Therefore, during the process shown in Figures 7(b) to 7(d), contact points P1 to P3 between the engaging portion 212a' and the engaged hole 211a' do not change relative to the rotating shaft 212' and the coupling 211'. For this reason, in the state shown in Figure 7(d), the engaging portion 212a' is shifted to the left inside the engaged hole 211a', and a gap G is generated on the right side of the engaged hole 211a'.

[0040] Furthermore, the coupling 211' receives a biasing force F1 toward the left side in the figure due to the offset ΔS. Therefore, when the rotation shaft 212' and the coupling 211' reach the state shown in FIG. 7(d), the coupling 211' moves parallel to the left side due to the biasing force F1. As a result, P3 in FIG. 7(d) is no longer the contact point, and P3' in FIG. 7(e) becomes the new contact point. At this time, a collision occurs between the engaging portion 212a' and the inner surface of the engaged hole 211a' at the contact point P3'. Such a collision occurs every time the registration roller 21' rotates 180°, causing vibration in the registration roller 21'.

[0041] Next, the principle of vibration suppression in the registration roller 21 of this embodiment will be described with reference to Fig. 8. Fig. 8 is a virtual diagram for explaining the behavior of the coupling 211 when the driving force is transmitted from the drive shaft 32 to the registration roller 21.

[0042] In this embodiment, vibration in the registration roller 21 is suppressed by the shapes of the engaging portion 212a and the engaged hole 211a. Specifically, as shown in Figures 3 and 8, the shape of the engaging portion 212a (cross-sectional shape as viewed from the axial direction) is a substantially cross shape (hereinafter referred to as a cross-cut shape) in which four L-shaped notches are provided at equal intervals in the circumferential direction of a circle. The shape of the engaged hole 211a is similar to this shape and is slightly larger in size than the engaging portion 212a.

[0043] Figure 8(a) shows a state in which the drive shaft 32 is not being driven. When the drive shaft 32 starts to be driven from the state shown in Figure 8(a), the coupling 211 starts to rotate (clockwise in this case). The rotation of the coupling 211 causes the engaging portion 212a to come into contact with the inner surface of the engaged hole 211a at four contact points P1 to P4 (see Figure 8(b)).

[0044] When the engaging portion 212a comes into contact with the engaged hole 211a at contact points P1 to P4, a driving force is transmitted from the coupling 211 to the rotating shaft 212 via these contact points P1 to P4, and the rotating shaft 212 starts to rotate together with the coupling 211. Figures 8(c) and 8(d) show states where the coupling 211 has rotated 90° and 180°, respectively, from the state in Figure 8(a).

[0045] In the registration roller 21 in which the engaging portion 212a and the engaged hole 211a are cross-cut shaped, when a driving force is transmitted from the coupling 211 to the rotary shaft 212, the engaging portion 212a comes into contact with the inner surface of the engaged hole 211a at four contact points P1 to P4, thereby restricting the relative movement (translation) of the coupling 211 with respect to the rotary shaft 212. In this way, when a driving force is transmitted, the relative movement (translation) of the coupling 211 with respect to the rotary shaft 212 is restricted, so that no collision occurs between the engaging portion 212a and the inner surface of the engaged hole 211a, and vibration in the registration roller 21 can be suppressed.

[0046] The conditions under which the relative movement (translation) of the coupling 211 with respect to the rotating shaft 212 is limited when a driving force is transmitted from the coupling 211 to the rotating shaft 212 are explained as follows. As shown in FIG. 9 , in the registration roller 21 of this embodiment, contact points P1 to P4 are generated between the engaging portion 212a and the engaged hole 211a, thereby transmitting the driving force. Here, if tangents to the contact points P1 to P4 are denoted by L1 to L4, respectively, a closed area surrounded by the tangent lines L1 to L4 is generated. Thus, when multiple (three or more) contact points are generated between the engaging portion 212a and the engaged hole 211a when a driving force is transmitted, and a closed area surrounded by multiple tangent lines to these multiple contact points is generated, the relative movement (translation) of the coupling 211 with respect to the rotating shaft 212 is limited. This movement restriction effect of the coupling 211 is obtained even when there is an offset ΔS between the central axis S1 and the central axis S2 and the coupling 211 is subjected to a biasing force F1 due to the offset ΔS.

[0047] For comparison, consider the registration roller 21' described above. As shown in FIG. 10, the registration roller 21' has an engaging portion 212a' and an engaged hole 211a' with an I-shaped cross section. Contact points P1 to P3 are generated between the engaging portion 212a' and the engaged hole 211a'. If the tangents to the contact points P1 to P3 are L1 to L3, respectively, no closed area surrounded by the tangent lines L1 to L3 is generated. Specifically, in the state shown in FIG. 10, the tangent lines L1 and L2 are parallel to each other, so the right side of the area surrounded by the tangent lines L1 to L3 is open, and the engaging portion 212a' can move parallel to the right inside the engaged hole 211a'.

[0048] In the registration roller 21 of this embodiment, when the driving force is transmitted from the coupling 211 to the rotating shaft 212, the relative movement (parallel movement) of the coupling 211 with respect to the rotating shaft 212 is restricted, so that no collision occurs between the engaging portion 212a and the inner surface of the engaged hole 211a, and vibration in the registration roller 21 can be suppressed.

[0049] Second Embodiment In the first embodiment, the engaging portion 212a and the engaged hole 211a are exemplified as having a substantially cross-cut shape. However, in the registration roller 21 of the present disclosure, the shapes of the engaging portion 212a and the engaged hole 211a are not limited to this and may be, for example, a regular polygon. In the case of a regular polygon, a square shape as shown in FIG. 11 is particularly preferable.

[0050] 11, even when the shape of the engaging portion 212a and the engaged hole 211a is square, if the tangents to the contact points P1 to P4 are L1 to L4, a closed area surrounded by the tangents L1 to L4 is generated. In other words, the condition that the relative movement (translation) of the coupling 211 with respect to the rotating shaft 212 is limited when transmitting a driving force is satisfied. Furthermore, when the engaging portion 212a is square, it is easier to form the screw hole 212b at the tip of the engaging portion 212a than when the engaging portion 212a is an equilateral triangle, and it is easier to attach the coupling 211 to the rotating shaft 212 by fastening the screw 213 than when the engaging portion 212a is an equilateral triangle.

[0051] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be determined based on the claims. [Explanation of symbols]

[0052] 10 Image forming device 20 Registration roller unit (paper transport device) 21 Registration roller (paper transport roller) 211 Coupling (transmission component) 211a Engaged hole 211b Engaged groove 211c tapered 212 Rotation axis 212a Engagement part 212b screw hole 213 Screw 30 Drive Unit 31 Drive motor 32 Drive shaft 321 Engagement pin (protrusion) P1~P4 contact points L1~L4 Tangent line

Claims

1. A paper transport device that is detachably mounted to an image forming apparatus and has a paper transport roller that is connected to a drive shaft provided in the image forming apparatus when the paper transport device is mounted to the image forming apparatus to transmit a driving force thereto, The paper transport roller is a rotating shaft having an engagement portion on a connection side with the drive shaft; a transmission member having an engaged hole, which is attached to the rotating shaft by inserting the engaging portion into the engaged hole, and which is connected to the drive shaft to transmit a driving force from the drive shaft to the rotating shaft; the engaging portion and the engaged hole have similar shapes in a predetermined cross section perpendicular to a central axis of the rotating shaft, and the engaged hole is larger in size than the engaging portion; A paper transport device characterized in that when a driving force is transmitted from the transmission member to the rotating shaft, the engagement portion contacts the inner surface of the engaged hole at three or more contact points in the specified cross section, and the contact at the multiple contact points limits the relative movement of the transmission member with respect to the rotating shaft.

2. 2. The paper transport device according to claim 1, A paper transport device, characterized in that, when a driving force is transmitted from the transmission member to the rotation shaft, a closed area surrounded by a plurality of tangents to the plurality of contact points is generated in the specified cross section.

3. 2. The paper transport device according to claim 1, The transmission member has four engaged grooves that are formed in a cross shape when viewed in the axial direction of the rotation shaft, The drive shaft has protrusions provided so as to protrude from two locations on a side surface of the drive shaft that are opposed to each other by 180 degrees, The paper transport device according to claim 1, wherein the drive shaft and the transmission member are connected to each other by fitting the protrusion into two of the four engaged grooves.

4. 2. The paper transport device according to claim 1, A screw hole is provided at a tip of the rotating shaft on a side connected to the drive shaft, The sheet transport device according to claim 1, wherein the transmission member is attached to the rotation shaft by inserting the engagement portion into the engaged hole and fastening a screw into the screw hole.

5. An image forming apparatus comprising the paper transport device according to claim 1 .

Images