Power transmission device and image forming apparatus

Abstract

To miniaturize the components of the drive transmission mechanism. [Solution] The system comprises a reversal input gear 201 to which driving force is input from a drive source, a reversal output gear 203 to which driving force is output, a reversal switching gear 202 to which the rotation direction of the reversal output gear 203 is switched, a clutch unit 600 to which the rotation direction of the reversal output gear is set, and an internal holder unit 212 to which the driving force of the reversal input gear 201 is transmitted to the reversal output gear. The reversal input gear 201 has external teeth 201a to which driving force is input from a drive source and internal teeth 201b to which driving force is transmitted to the internal holder unit 212. The external teeth 201a and internal teeth 201b have the same number of teeth but different modules and are molded together as a single unit when the reversal input gear 201 is formed. The root of the external teeth 201a is located outward in the rotational radius direction compared to the root of the internal teeth 201b, and the positions of the teeth of the external teeth 201a and the teeth of the internal teeth 201b are offset with respect to the rotational direction of the reversal input gear 201.

Description

Technical Field

[0001] The present invention relates to a driving force transmission device and an image forming apparatus including the driving force transmission device.

Background Art

[0002] In an image forming apparatus having a configuration in which a plurality of rotators are rotationally driven by a rotational driving force in one direction, there is an image forming apparatus provided with a driving force switching mechanism for enabling only the rotational direction of some of the rotators to be switched in the reverse direction. For example, in Example 1, an image forming apparatus provided with a driving force switching mechanism using an internal gear has been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The driving force switching mechanism of the image forming apparatus described in Patent Document 1 above uses a gear that transmits driving force having the configuration shown in Figure 15. Figure 15 is a diagram illustrating the shape of the gears used as input gear and output gear. In Figure 15(a), the left side is a front view of the gear, and the right side is a cross-section of the gear shown on the left side when cut along line AA. Figure 15(b) is a perspective view showing the external shape of the gear shown in Figure 15(a). The gear shown in Figure 15 has an external gear 901a and an internal gear 901b, and the external gear 901a and the internal gear 901b are molded as a single unit. When the gear shown in Figure 15 is used as an input gear, the external gear 901a transmits driving force from the outside, and when it is used as an output gear, the external gear 901a transmits driving force to the outside. The internal teeth 901b of the gear are used to transmit driving force from the input gear to the output gear via an idler gear (not shown). In the gear shown in Figure 15, a gap g is provided between the external gear 901a and the internal gear 901b, which leads to the problem of the drive force switching mechanism becoming larger.

[0005] This invention was made under these circumstances and aims to miniaturize the components of a drive transmission mechanism. [Means for solving the problem]

[0006] To solve the above-mentioned problems, the present invention has the following configuration.

[0007] (1) A drive force transmission device for transmitting driving force from a drive source, comprising: an input gear to which driving force is input from the drive source; an output gear to which driving force is output; a switching gear to which the rotation direction of the output gear is switched; a rotation direction setting unit to set the rotation direction of the output gear; and an internal drive unit to which the driving force of the input gear is transmitted to the output gear, wherein the input gear has external teeth to which driving force is input from the drive source and internal teeth to which driving force is transmitted to the internal drive unit, the external teeth and the internal teeth have the same number of teeth but different modules, are molded together as a single unit when the input gear is formed, the root of the external teeth is located outward in the rotational radius direction from the root of the internal teeth, and the positions of the teeth of the external teeth and the teeth of the internal teeth are offset with respect to the rotation direction of the input gear.

[0008] (2) A drive force transmission device for transmitting driving force from a drive source, comprising: an input gear to which driving force is input from the drive source; an output gear to which driving force is output; a switching gear to which the rotation direction of the output gear is switched; and a rotation direction setting unit to set the rotation direction of the output gear, wherein the output gear has internal teeth to which driving force is input from the input gear and external teeth to which the input driving force is transmitted, the internal teeth and the external teeth have the same number of teeth but different modules, are molded together as a single unit when the output gear is molded, the roots of the external teeth are located outward in the rotational radius direction from the roots of the internal teeth, and the positions of the teeth of the external teeth and the teeth of the internal teeth are offset with respect to the rotation direction of the output gear.

[0009] (3) An image forming apparatus for forming an image on a recording material, comprising: an image forming unit for forming an image on one side of the recording material; a rotating body for transporting the recording material that has passed through the image forming unit; a drive force transmission device as described in (1) or (2) above; and a transport unit for transporting the recording material, whose transport direction has been reversed by the reversal of the rotation direction of the rotating body, to the upstream side of the image forming unit. [Effects of the Invention]

[0010] According to the present invention, the components of the drive transmission mechanism can be miniaturized. [Brief explanation of the drawing]

[0011] [Figure 1] Cross-sectional view showing the schematic configuration of the image forming apparatus in Examples 1-3 [Figure 2] Perspective view illustrating the configuration of the discharge reversal drive mechanism in Example 1. [Figure 3] Exploded perspective view illustrating the configuration of the inversion unit in Example 1. [Figure 4] A perspective view and a cross-sectional view illustrating the configuration of the reversing input gear in Example 1. [Figure 5] Front view and perspective view illustrating the internal configuration of the reversal unit of Example 1. [Figure 6] Front view and perspective view illustrating the drive switching operation of the reversal unit in Example 1. [Figure 7] Perspective view illustrating the operation of the discharge reversal drive mechanism of Example 1. [Figure 8] Perspective view illustrating the configuration of the discharge reversal drive mechanism in Example 2. [Figure 9] Exploded perspective view and cross-sectional view illustrating the configuration of the inversion unit in Example 2. [Figure 10] Front view and rear view illustrating the internal configuration of the inversion unit of Example 2. [Figure 11] Perspective view illustrating the operation of the discharge reversal drive mechanism in Example 2. [Figure 12] Perspective view illustrating the configuration of the discharge reversal drive mechanism in Example 3. [Figure 13] Exploded perspective view and cross-sectional view illustrating the configuration of the inversion unit in Example 3. [Figure 14] Perspective view illustrating the operation of the discharge reversal drive mechanism in Example 3. [Figure 15] Front view, cross-sectional view, and perspective view of a conventional gear. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described in detail below with reference to the drawings.

Example

[0013]

Configuration of Image Forming Apparatus

[0014] In FIG. 1, the apparatus main body 2 of the printer 1 includes an image forming unit 3 that forms an image by an electrophotographic method, and a sheet feeding device 10 for feeding a sheet S, which is a recording material, to the image forming unit 3. The image forming unit 3 includes a photosensitive drum 61 that forms a toner image, a transfer roller 31 that transfers the toner image formed on the photosensitive drum 61 to the sheet S, a charging roller 62 that charges the surface of the photosensitive drum 61 to a uniform potential, a developing device 63, and the like. Note that the photosensitive drum 61, the charging roller 62, and the developing device 63 are integrated as a process cartridge 60 and are configured to be detachable from the apparatus main body 2. In the sheet feeding device 10, the sheet S is stacked on the intermediate plate 13 and fed to the image forming unit 3 by the feeding roller 11.

[0015]

Image Forming Operation

[0016] Meanwhile, in the sheet feeding device 10, the feeding roller 11 is driven at a predetermined timing, and in conjunction with this, the intermediate plate 13, which is biased toward the feeding roller 11 by the pressing force of the coil spring 12, rotates upward in the figure. As a result, the leading edge of the sheet S loaded on the intermediate plate 13 in the direction of transport is pressed against the feeding roller 11 with a predetermined force. Here, the feeding roller 11 is controlled to rotate counterclockwise in the figure only during feeding, and the pressed sheet S is fed by frictional force. When multiple sheets S on the intermediate plate 13 are fed out simultaneously, the separation unit 14 separates only the uppermost sheet S on the intermediate plate 13, and it is transported downstream of the transport path.

[0017] The top sheet S, separated by the separation unit 14, is then transported to the resist unit 20 for skew correction, and subsequently transported by the resist unit 20 to the transfer unit 30, which is a nip section composed of a photosensitive drum 61 and a transfer roller 31. In the transfer unit 30, the toner image formed on the photosensitive drum 61 is transferred to the sheet S by the transfer roller 31. The sheet S, on which the toner image has been transferred, is then transported to the fuser unit 40. The fuser unit 40 includes a heating unit 41 for heating the toner image and a pressure roller 42 for applying pressure to the toner image onto the sheet S. In the fuser unit 40, the toner image is heated and pressured to fix it onto the sheet S.

[0018] [Single-sided printing mode and double-sided printing mode] Subsequently, in single-sided printing mode, where an image is formed on only one side of the sheet S, the sheet S with the fixed toner image is discharged onto the discharge tray 54 on the upper surface of the device body 2 by the discharge roller pair 50, which is a rotating body. The discharge roller pair 50 receives the driving force from the input section via a reversing unit 200, which will be described later, capable of switching the direction of rotation of the driving force from forward rotation (first rotation direction) to reverse rotation (second rotation direction) when outputting the driving force from the input section as a rotation in one direction.

[0019] On the other hand, in the case of double-sided printing mode, where images are formed on both sides of the sheet S, the sheet S, with one side printed, passes through the fuser unit 40 and is transported by the discharge roller pair 50 in the direction of discharge to the discharge tray 54. Then, at the timing when the rear end of the sheet S in the transport direction passes a predetermined position, the rotation direction of the discharge roller pair 50 reverses from forward rotation to reverse rotation. As a result, the sheet S is pulled back into the printer 1 and guided to the double-sided transport path R3 of the double-sided unit 80, which is a transport unit that transports the sheet S to the upstream side of the image forming section. Then, the sheet S is transported along the double-sided transport path R3 of the double-sided unit 80 by the double-sided transport roller pair 81 and transported toward the registration roller pair 21 in an inverted state. Then, as in the case of single-sided printing mode, a toner image is transferred to the back side of the sheet S by the transfer unit 30, and the toner image is fixed to the sheet S by the fuser unit 40. The sheet S, with images formed on both sides, is then discharged by the discharge roller pair 50 onto the discharge tray 54 on the upper surface of the device body 2.

[0020] [Overall configuration of the drive force reversal mechanism] Next, the drive force reversal mechanism (also called the drive force transmission mechanism) using the reversal unit 200 will be described. Figure 2 is a perspective view showing the overall configuration of the discharge reversal drive mechanism 90 that drives the discharge roller pair 50 described above. Figure 2(a) is a perspective view of the discharge reversal drive mechanism 90 when viewed from the direction toward the discharge roller pair 50 (front), and Figure 2(b) is a perspective view of the discharge reversal drive mechanism 90 when viewed from the discharge roller pair 50 side (rear). As shown in Figure 2, the discharge reversal drive mechanism 90 includes a discharge reversal input gear train 100, a reversal unit 200, and a clutch unit 600.

[0021] (Discharge inversion input gear train) The discharge reversal input gear train 100 is configured to be rotatable by receiving driving force from a drive motor (not shown), which is the drive source, via a drive gear train (not shown). The discharge reversal input gear train 100 includes a first discharge reversal input gear 101, a second discharge reversal input gear 102, and a third discharge reversal input gear 103. As shown in the enlarged view of Figure 2(b), the second discharge reversal input gear 102 and the third discharge reversal input gear 103 have convex and concave portions that engage with each other, and rotate as a single unit by engaging with each other.

[0022] (Inverted Unit) The reversing unit 200 has a reversing input gear 201, a reversing switching gear 202, and a reversing output gear 203. The reversing unit 200 switches the rotation (driving force) transmitted from the discharge reversing input gear train 100 to the reversing input gear 201 by switching the rotation state of the reversing switching gear 202 as follows: That is, the reversing unit 200 is configured to switch the direction of rotation of the rotation transmitted to the reversing input gear 201 to either forward rotation (clockwise rotation) or reverse rotation (counterclockwise rotation) and output it to the reversing output gear 203. A discharge roller gear 50b is provided at the end of the discharge roller shaft 50a that drives the discharge roller pair 50. Driving force is transmitted from the reversing output gear 203 to the discharge roller gear 50b, causing the discharge roller shaft 50a to rotate, and the rotation of the discharge roller shaft 50a causes the discharge roller pair 50 to rotate.

[0023] (Clutch unit) The clutch unit 600, which is the rotation direction setting unit, has a clutch input gear 601, a clutch fixing unit 602, a clutch output unit 604, and a clutch holding shaft 605. The clutch input gear 601 rotates due to the rotation (driving force) transmitted from the reversal switching gear 202. The clutch holding shaft 605 is fixed to the frame (not shown) so as not to rotate and is engaged with and integrated with the clutch output unit 604. Depending on the off or on state of the clutch signal of the clutch unit 600, the clutch input gear 601, the engaged and integrated clutch output unit 604, and the clutch holding shaft 605 switch between a connected state and an unconnected state. The clutch fixing unit 602 is held in place so as not to rotate by the fixing of the rotation stopper 603.

[0024] [Internal configuration of the inversion unit] The internal configuration of the reversing unit 200 will be explained using Figure 3. Figure 3 is an exploded perspective view of the reversing unit 200. Figure 3(a) is an exploded perspective view of the reversing unit 200 as seen from the direction toward the discharge roller pair 50 (front), and Figure 3(b) is an exploded perspective view of the reversing unit 200 as seen from the discharge roller pair 50 side (rear).

[0025] As shown in Figure 3, the reversal unit 200 includes a reversal input gear 201, a reversal switching gear 202, a reversal output gear 203, an internal idler gear 204, and an internal holder unit 212 which is an internal drive unit. The reversal input gear 201 is an input member that rotates due to the driving force transmitted from the discharge reversal input gear train 100 as described above. The reversal output gear 203 is an output member that outputs the driving force to the discharge roller gear 50b to rotate the discharge roller pair 50. The internal idler gear 204, which is an internal gear, is composed of two symmetrically arranged gear trains and is a drive transmission member for transmitting driving force from the reversal input gear 201 to the reversal output gear 203.

[0026] The internal holder unit 212 has a first internal holder 212a and a second internal holder 212b. The internal idler gear 204 described above is sandwiched between the first internal holder 212a and the second internal holder 212b of the internal holder unit 212 and is held rotatably. The internal holder unit 212 has a rotating support shaft that rotatably holds the reversal input gear 201 and also holds the reversal switching gear 202, and four rotating support shafts that support each of the internal idler gears 204.

[0027] The stopper holder 208 has a locking lever 209 and a compression spring 210. The stopper holder 208 is connected to the internal holder unit 212 so as to be an integral part of it. The locking lever 209 is rotatably held relative to the stopper holder 208 and can move to an engaged position (locked state) that locks the reversal input gear 201 to the stopper holder 208, or to an unengaged position (unlocked state) that does not lock it, by the biasing force of the compression spring 210. When the locking lever 209 moves to the engaged position, the reversal input gear 201, the stopper holder 208, and the internal holder unit 212 are integrated as described later. Furthermore, the reversal switching gear 202 is configured to switch between a rotating state and a rotation-stopped state depending on the state of the clutch unit 600, as described later, in order to control the operation of the locking lever 209.

[0028] [Gear configuration of the reverse input gear] The gear configuration of the reversing input gear 201 will be explained using Figure 4. Figure 4(a) is a perspective view of the reversing input gear 201 as seen from the reversing switching gear 202 side, and Figure 4(b) is a perspective view of the reversing input gear 201 as seen from the reversing output gear 203 side. In Figure 4(c), the left side is a side view of the reversing input gear 201 as seen from the side, and the center side is a cross-sectional view of the reversing input gear 201 as seen from the left (front) direction of the left side when the reversing input gear 201 is cut along line AA shown in the left side of the left side of the figure.

[0029] As shown in Figures 4(a) and (b), the reversal input gear 201 has external teeth 201a to which driving force (rotation) is transmitted from the discharge reversal input gear train 100, and internal teeth 201b to which driving force (rotation) is transmitted to the internal idler gear 204 (Figure 3). As shown in Figure 4(c), the external teeth 201a and internal teeth 201b have the same number of teeth but different modules and are configured to overlap on the same plane. In this embodiment, the external teeth 201a are configured with module 0.7 / number of teeth 52, and the internal teeth 201b are configured with module 0.6 / number of teeth 52. By making the number of teeth of the external teeth 201a and internal teeth 201b of the reversal input gear 201 the same and configuring them to overlap on the same plane, the reversal input gear 201 has a shape that is symmetrical in all directions, as shown in the AA cross-sectional view of Figure 4(c). In this way, by making the external teeth 201a and internal teeth 201b of the reversing input gear 201 symmetrical, the resin can be flowed uniformly during molding, thereby improving the manufacturing accuracy of the gear. As a result, since the gap g shown in Figure 15 above does not occur, it becomes possible to mold a high-precision gear in a small space.

[0030] [Mechanism of reversing input gear, reversing output gear, and internal idler gear] Next, Figure 5 will be used to explain the meshing relationship between the reversal input gear 201, the reversal output gear 203, and the internal idler gear 204 in the reversal unit 200. Figure 5(a) is a diagram illustrating the meshing relationship between the reversal input gear 201 and the internal idler gear 204. In Figure 5(a), the left side is a front view of the reversal input gear 201 and the internal idler gear 204 as seen from the reversal output gear 203 side, and the right side is a perspective view of the reversal input gear 201 and the internal idler gear 204 as seen from the reversal output gear 203 side. Note that the reversal output gear 203 and the second internal holder 212b are omitted in Figure 5(a).

[0031] On the other hand, Figure 5(b) is a diagram illustrating the meshing relationship between the reversing output gear 203 and the internal idler gear 204. In Figure 5(b), the left side is a front view of the reversing output gear 203 and internal idler gear 204 as seen from the reversing input gear 201 side, and the right side is a perspective view of the reversing output gear 203 and internal idler gear 204 as seen from the reversing input gear 201 side. Note that the reversing input gear 201, the reversing switching gear 202, and the first internal holder 212a are not shown in Figure 5(b).

[0032] As shown in Figure 5(a), the reversal input gear 201 has external teeth 201a, internal teeth 201b, and a hole through which the shaft of the internal holder unit 212 is inserted, and is rotatably supported on the shaft of the internal holder unit 212 (Figure 3(a)). The external teeth 201a mesh with the discharge reversal input gear train 100 to input rotational driving force. The internal teeth 201b mesh with the first internal idler gear 204, which is the internal idler gear 204a, 204c. On the other hand, as shown in Figure 5(b), the reversal output gear 203 has external teeth 203a (Figure 3(b)), internal teeth 203b (Figure 3(a)), and a hole through which a shaft provided in the frame (not shown) is inserted, and is rotatably supported on the shaft provided in the frame (not shown). The external teeth 203a output rotational driving force to the discharge roller gear 50b. The internal tooth 203b meshes with the second internal idler gear 204, which consists of internal idler gears 204b and 204d. The first internal idler gear 204, which consists of internal idler gears 204a and 204c, meshes with the second internal idler gears 204b and 204d, respectively.

[0033] As shown in Figure 5(a), the first internal idler gears 204a and 204c mesh with the internal teeth 201b of the reversing input gear 201 and also mesh with the second internal idler gears 204 (204b and 204d). Furthermore, as shown in Figure 5(b), the second internal idler gears 204b and 204d mesh with the internal teeth 203b of the reversing output gear 203, thereby transmitting driving force from the reversing input gear 201 to the reversing output gear 203 via the internal idler gears 204.

[0034] As explained above, the reversing unit 200 receives driving force from the discharge reversing input gear train 100 to the external teeth 201a of the reversing input gear 201, and rotates in the direction of rotation R1 (Figure 5(a)) indicated by the arrow. In addition, the discharge roller gear 50b (Figure 2), which rotates the discharge roller pair 50, receives drive from the external teeth 203a of the reversing output gear 203. Therefore, when the rotation direction of the reversing output gear 203 is switched, the discharge roller pair 50 also follows suit and its rotation direction is switched.

[0035] [Rotation direction switching of the reversal unit] Next, using Figure 6, the operation of switching the rotation direction of the reversal output gear 203 of the reversal unit 200 will be explained. Figure 6(a) is a front view showing the reversal unit 200 when the rotation direction of the reversal output gear 203 is forward rotation. Figure 6(b) is a front view of the reversal unit 200 when it is rotating forward, with the reversal switching gear 202 omitted from the illustration of the reversal unit 200 shown in Figure 6(a). Figure 6(c) is a perspective view of the reversal unit 200 when it is rotating forward, with the reversal input gear 201, the reversal switching gear 202, and the first internal holder 212a omitted from the illustration of the reversal unit 200 shown in Figure 6(a).

[0036] Figures 6(a) to 6(c) show the state of the reversing unit 200 when the reversing gear 202 is in a state where it can rotate freely without being restricted by an external source (the clutch unit 600, as will be described later). In this case, as shown in Figure 6(a), the locking portion 209a (first locking portion) of the locking lever 209 of the stopper holder 208 is engaged with the locking portion 202a, which is a hole provided in the reversing gear 202.

[0037] As shown in Figure 6(b), the locking lever 209 of the stopper holder 208 receives the biasing force of the compression spring 210 because there is no rotational restriction by the reversal switching gear 202. As a result, the convex locking portion 209b (second locking portion) of the locking lever 209 engages with the concave locked portion 201c of the reversal input gear 201. The engagement of the locking portion 209b of the locking lever 209 with the locked portion 201c of the reversal input gear 201 causes the stopper holder 208 to be locked to the reversal input gear 201. Therefore, when the reversal input gear 201 rotates, the driving force of the reversal input gear 201 is transmitted via the locking portion 209a of the stopper holder 208 in a direction that biases the locked portion 202a of the reversal switching gear 202, thus driving the reversal switching gear 202 to rotate. On the other hand, the integrated stopper holder 208 and internal holder unit 212 rotate together with the reversal input gear 201, and no relative displacement occurs between the internal holder unit 212 and the reversal input gear 201. As a result, the internal idler gear 204, which is rotatably supported by the internal holder unit 212, is maintained in a stationary (fixed) state relative to the internal holder unit 212. Consequently, the internal idler gear 204, together with the reversal input gear 201 and the internal holder unit 212, rotates in the same direction as the RD1 direction indicated by the arrow (Figure 6(a), (b)) around the rotation axis of the reversal input gear 201. The driving force that rotates the reversal input gear 201 in the RD1 direction indicated by the arrow is transmitted to the reversal output gear 203 via the internal idler gear 204, which rotates in the same RD1 direction as the reversal input gear 201 and the internal holder unit 212 rotate together. In other words, as shown in Figure 6(c), the reversing output gear 203 rotates in the RD2 direction, which is the same direction as the RD1 direction, because its internal teeth 203b receive rotational driving force from the internal idler gear 204, which moves around while fixed to the internal holder unit 212.

[0038] Next, we will describe the operation of the reversal unit 200 when the reversal switching gear 202 is restricted by an external force (the clutch unit 600, which will be described later) and its rotation is stopped. Figure 6(d) is a front view showing the reversal unit 200 when the rotation direction of the reversal output gear 203 is reversed. Figure 6(e) is a front view of the reversal unit 200 when it is rotating in the reverse direction, with the reversal switching gear 202 omitted from the illustration of the reversal unit 200 shown in Figure 6(d). Figure 6(f) is a perspective view of the reversal unit 200 when it is rotating in the reverse direction, with the reversal input gear 201, the reversal switching gear 202, and the first internal holder 212a omitted from the illustration of the reversal unit 200 shown in Figure 6(d).

[0039] Figures 6(d) to 6(f) show the state of the reversal unit 200 when the reversal switching gear 202 is stopped from rotating due to external restriction (the clutch unit 600, which will be described later). As shown in Figure 6(d), the locking portion 209a of the locking lever 209 of the stopper holder 208 is engaged with the locked portion 202a of the reversal switching gear 202. Then, the locking portion 209b of the locking lever 209 engages with the locked portion 201c of the reversal input gear 201, thereby locking the stopper holder 208 to the reversal input gear 201. When the reversal input gear 201 rotates, the locking portion 209a of the stopper holder 208 rotates around the rotation axis of the reversal input gear 201, thereby biasing the locked portion 202a of the reversal switching gear 202. However, when the reversing gear 202 is stopped, if the locking portion 209a moves in a circular motion, the locked portion 202a of the stationary reversing gear 202 restricts the circular motion (rotation), and the locking portion 209a is biased in the opposite direction to the rotation direction of the reversing input gear 201. As a result, the pressure spring 210 pressing the locking portion 209a of the locking lever 209 is biased and compressed, causing the locking portion 209a to move inside the locked portion 202a of the reversing gear 202 in the direction M1 indicated by the arrow.

[0040] As a result, as shown in Figure 6(e), the locking lever 209 is released from its engagement with the locked portion 201c of the reversal input gear 201. This restricts the rotation of the stopper holder 208, which holds the locking lever 209, and the internal holder unit 212, which is integrated with the stopper holder 208, causing them to stop rotating. Therefore, the driving force input to the reversal input gear 201, which rotates the reversal input gear 201 in the direction of RD1 indicated by the arrow, is transmitted to the reversal output gear 203 via the internal idler gear 204, which is rotatably supported inside the internal holder unit 212, which has stopped rotating.

[0041] As shown in Figure 6(f), the first internal idler gears 204a and 204c, which are the first internal idler gears 204, mesh with the internal teeth 201b of the reversal input gear 201 and therefore rotate in the same direction as the reversal input gear 201. On the other hand, the second internal idler gears 204b and 204d, which are the second internal idler gears 204, mesh with the first internal idler gears 204a and 204c, respectively, and therefore rotate in the opposite direction to the reversal input gear 201. The reversal output gear 203 rotates in the opposite direction to the reversal input gear 201 because its internal teeth 203b mesh with the second internal idler gears 204b and 204d. Thus, when the reversing gear 202 is stopped rotating, the direction of rotation of the rotational drive force is reversed between the two corresponding internal idler gears 204, and the reversing output gear 203 is driven to rotate in the RD3 direction, which is opposite to the direction of rotation of the reversing input gear 201.

[0042] [Switching operation of the rotation direction of the discharge roller pair] Next, the switching operation of the rotation direction of the discharge roller pair 50 will be explained using Figure 7. Figures 7(a) and (b) are perspective views illustrating the rotation direction of the gears of each unit constituting the discharge reversal drive mechanism 90 when the clutch signal to the clutch unit 600 is in the off state (power outage state). The arrows in Figures 7(a) and (b) indicate the rotation direction of each gear. On the other hand, Figures 7(c) and (d) are perspective views illustrating the rotation direction of the gears of each unit constituting the discharge reversal drive mechanism 90 when the clutch signal to the clutch unit 600 is in the on state (power supply state). The arrows in Figures 7(c) and (d) indicate the rotation direction of each gear, and gears for which the rotation direction is not indicated (for example, the clutch input gear 601) are in a stopped rotation state.

[0043] As shown in Figures 7(a) and (b), when the clutch signal to the clutch unit 600 is off and the clutch unit 600 is experiencing a power outage, the connection between the clutch input gear 601 and the clutch holding shaft 605 is released and they are not connected. As a result, the clutch input gear 601 receives rotation from the reversing gear 202 and becomes rotatable. Consequently, the reversing input gear 201, the reversing gear 202, and the reversing output gear 203 rotate in the same direction, and the discharge roller pair 50 rotates in the forward direction.

[0044] On the other hand, as shown in Figures 7(c) and 7(d), when the clutch signal input to the clutch unit 600 is switched to the ON state, the clutch unit 600 is powered, and the clutch input gear 601 and the clutch holding shaft 605 are connected. Since the clutch holding shaft 605 is fixed to the frame (not shown) so as not to rotate, the clutch input gear 601 and the reversing gear 202 stop rotating simultaneously. When the reversing gear 202 stops rotating, the rotation direction of the reversing output gear 203 is switched by the internal structure of the reversing unit 200 described above. As the rotation direction of the reversing output gear 203 is switched, the rotation direction of the discharge roller gear 50b and the discharge roller pair 50, which mesh with the external teeth 203a of the reversing output gear 203, is also switched, and the discharge roller pair 50 rotates in the reverse direction, causing the sheet S to flow back into the inside of the device.

[0045] As described above, the discharge reversal drive mechanism 90 of this embodiment is a mechanism that switches the drive of the discharge roller pair 50 between forward and reverse rotation using a drive motor (not shown) with a unidirectional rotational drive force. As mentioned above, by using the reversal input gear 201 that constitutes the reversal unit 200 of this embodiment, it is possible to miniaturize the discharge reversal drive mechanism 90 and improve the precision of its rotation.

[0046] In this embodiment, a configuration was used in which the sheet S is transported by a discharge roller pair 50, but a configuration in which the sheet S is transported by a triple roller pair with rollers positioned above and below the rollers is also acceptable. Alternatively, a configuration using two sets of roller pairs is also acceptable: a discharge roller pair that discharges the sheet S outside the main body 2 of the printer 1, and a reversing roller pair that switches the sheet S back inside the machine.

[0047] Furthermore, in this embodiment, a configuration was used to disconnect the clutch holding shaft 605 and the clutch input gear 601, but a configuration may also be used to disconnect the clutch input gear 601 from the guide member of the seat S. Also, in this embodiment, a clutch was used to disconnect the clutch holding shaft 605 and the clutch input gear 601, but instead of a clutch, a solenoid or other actuator may be used. For example, a configuration may be used in which a claw shape is provided instead of the gear portion of the reversal switching gear 202, and the rotation stop state of the reversal switching gear may be switched by switching between an engaged state and an unengaged state with the claw portion of the movable plate of the solenoid.

[0048] As described above, according to this embodiment, the components of the drive transmission mechanism can be miniaturized. [Examples]

[0049] Example 2 describes an exhaust reversal drive mechanism having a configuration different from that of the exhaust reversal drive mechanism described in Example 1.

[0050] [Configuration of the image forming apparatus] The printer 1 in Example 2, which is an image forming apparatus, differs from the printer 1 in Example 1, which uses the discharge reversal drive mechanism 90, in that it uses the discharge reversal drive mechanism 90A, which will be described later, as the discharge reversal drive mechanism that drives the discharge roller pair 50. In the printer 1 of Example 2, the other configurations of the printer 1 described in Example 1, the image forming operation, and the sheet transport operation during single-sided and double-sided printing are the same as those of the printer 1 in Example 1, and will not be described here.

[0051] [Overall configuration of the drive force reversal mechanism] Figure 8 is a perspective view showing the overall configuration of the discharge reversal drive mechanism 90A that drives the discharge roller pair 50. Figure 8(a) is a perspective view of the discharge reversal drive mechanism 90A as seen from the direction toward the discharge roller pair 50 (front), and Figure 8(b) is a perspective view of the discharge reversal drive mechanism 90A as seen from the discharge roller pair 50 side (rear). As shown in Figure 8, the discharge reversal drive mechanism 90A includes a discharge reversal input gear 104, a reversal unit 200B, a clutch drive train 500, and a clutch unit 600. The discharge reversal input gear 104 is configured to be rotatable by receiving driving force from a drive motor (not shown) via a drive gear train (not shown).

[0052] The reversal unit 200B includes a reversal input gear 201B, a reversal switching gear 202B, and a reversal output gear 203B. The reversal unit 200B switches the rotation state of the reversal switching gear 202B. This switches the direction of rotation of the rotation transmitted from the discharge reversal input gear 104 to the reversal input gear 201B to either forward rotation (clockwise) or reverse rotation (counterclockwise), and outputs it to the reversal output gear 203B.

[0053] A discharge roller gear 50b is provided at the end of the discharge roller shaft 50a, which drives the discharge roller pair 50. Driving force is transmitted from the reversing output gear 203B to the discharge roller gear 50b, causing the discharge roller shaft 50a to rotate, and the rotation of the discharge roller shaft 50a causes the discharge roller pair 50 to rotate.

[0054] The clutch drive train 500 includes a clutch idler gear 501, a first clutch transmission gear 505, a second clutch transmission gear 506, and a torque limiter 507. The first clutch transmission gear 505 rotates by receiving a driving force from a drive motor (not shown) via the drive gear train (not shown). The rotation (driving force) of the first clutch transmission gear 505 is transmitted to the reversing changeover gear 202B via the torque limiter 507, the second clutch transmission gear 506, and the clutch idler gear 501. The reversing changeover gear 202B is configured to rotate in the same direction and at the same speed as the reversing input gear 201B. In addition, the rotation (driving force) of the first clutch transmission gear 505 is also transmitted to the clutch input gear 601 via the torque limiter 507 and the second clutch transmission gear 506.

[0055] The clutch unit 600, like in Embodiment 1, includes a clutch input gear 601, a clutch fixing part 602, a clutch output part 604, and a clutch holding shaft 605. The clutch input gear 601 rotates due to the rotation (driving force) transmitted from the clutch second transmission gear 506. The clutch holding shaft 605 is fixed to a frame (not shown) so as not to rotate and is engaged with and integrated with the clutch output part 604. Depending on whether the clutch signal of the clutch unit 600 is ON (power supply state) or OFF (power outage state), the connected state and disconnected state of the clutch input gear 601 and the integrated clutch output part 604 and clutch holding shaft 605 are switched. The clutch fixing part 602 is held in place so as not to rotate by the fixing of the rotation stopper 603.

[0056] [Internal configuration of the inversion unit] The internal configuration of the reversing unit 200 will be explained using Figure 9. Figure 9 is an exploded perspective view of the reversing unit 200B. Figure 9(a) is an exploded perspective view of the reversing unit 200B viewed from the direction toward the discharge roller pair 50 (front), and Figure 9(b) is an exploded perspective view of the reversing unit 200B viewed from the discharge roller pair 50 side (rear).

[0057] As shown in Figures 9(a) and (b), the reversing unit 200B includes a reversing input gear 201B, a reversing switching gear 202B, a reversing output gear 203B, and an internal idler gear 204B. The reversing input gear 201B is an input member that rotates upon receiving the driving force transmitted from the discharge reversing input gear 104 described above, and has a sun gear 201Ba that drives the internal idler gear 204B, which will be described later. The reversing output gear 203B is an output member that outputs driving force to the discharge roller gear 50b that rotates the discharge roller pair 50. The reversing switching gear 202B has a rotating shaft that holds the reversing input gear 201B and the reversing output gear 203B, and a rotating shaft 202Ba that holds the internal idler gear 204B. The internal idler gear 204B consists of a pair of symmetrically arranged gears and is a drive transmission member for transmitting the driving force (rotation) of the reversing input gear 201B to the reversing output gear 203B.

[0058] Furthermore, in Figure 9(c), the left-hand diagram is a side view of the reversing output gear 203B as seen from the side, and the center diagram is a cross-sectional view of the reversing output gear 203B as seen from the left (front) direction of the left-hand diagram, when the gear is cut along line AA shown in the left-hand diagram. As shown in Figure 9(c), the reversing output gear 203B has internal teeth 203Bb that receive rotation (driving force) from the internal idler gear 204B, and external teeth 203Ba that transmit rotation (driving force) to the discharge roller gear 50b (Figure 8). The external teeth 203Ba and internal teeth 203Bb have the same number of teeth but different modules, and are arranged to overlap on the same plane. For example, in this embodiment, the external teeth 203Ba are composed of module 0.5 / number of teeth 43, and the internal teeth 203Bb are composed of module 0.4 / number of teeth 43. In this way, by making the number of teeth of the external teeth 203Ba and the internal teeth 203Bb the same and configuring them to overlap on the same plane, the reversing output gear 203B has a symmetrical shape in all directions, as shown in the AA cross-sectional view of Figure 9(c). By making the external teeth 201Ba and the internal teeth 201Bb of the reversing output gear 203B symmetrical in this way, the resin can be flowed uniformly during molding, thereby improving the manufacturing accuracy of the gear. As a result, since the gap g shown in Figure 15 above does not occur, it becomes possible to mold a high-precision gear in a small space.

[0059] [Rotation direction switching of the reversal unit] Next, using Figure 10, we will explain the operation of the rotation direction switching of the reversal output gear 203B of the reversal unit 200B. Figures 10(a) and (b) are front and rear views showing the operation of the reversal unit 200B when the reversal switching gear 202B is rotating. On the other hand, Figures 10(c) and (d) are front and rear views showing the operation of the reversal unit 200B when the reversal switching gear 202B is stopped rotating. Note that the reversal output gear 203B is not shown in Figures 10(a) and (c), and the reversal input gear 201B and the reversal switching gear 202B are not shown in Figures 10(b) and (d).

[0060] As shown in Figure 10, the internal idler gear 204B is rotatably positioned on a pair of rotating shafts 202Ba provided on the reversing switching gear 202B and meshes with the sun gear 201Ba located at the center of the reversing input gear 201B. The internal idler gear 204B also meshes with the internal teeth 203Bb provided on the reversing output gear 203B. As a result, the driving force (rotation) of the reversing input gear 201B is transmitted to the reversing output gear 203B via the sun gear 201Ba, the pair of internal idler gears 204B, and the internal teeth 203Bb.

[0061] As shown in Figures 10(a) and (b), when the reversing gear 202B is rotating, the driving force (rotation) from the clutch first transmission gear 505 is transmitted to the reversing gear 202B, causing it to rotate in the same direction and at the same rotational speed as the reversing input gear 201B. In other words, the reversing gear 202B and the reversing input gear 201B are in a state equivalent to rotating as a single unit. Since no relative displacement occurs between the reversing gear 202B and the reversing input gear 201B, the internal idler gear 204B, which is rotatably supported by the reversing gear 202B, is maintained in a stationary state (fixed state) relative to the reversing gear 202B. Therefore, the internal idler gear 204B moves in a circular motion around the rotation axis of the reversing input gear 201B in the same direction as the RD6 direction indicated by the arrow, together with the reversing input gear 201B and the reversing gear 202B. The rotational driving force in the RD6 direction input to the reversal input gear 201B is transmitted to the reversal output gear 203B via the internal idler gear 204B, which rotates in the same direction as the reversal input gear 201B and the reversal switching gear 202B rotate together. That is, as shown in Figure 10(b), the reversal output gear 203B receives rotational driving force from the internal idler gear 204B, which rotates in a circular motion with its internal teeth 203Bb fixed to the reversal switching gear 202B. As a result, the reversal output gear 203B rotates in the RD7 direction, which is the same direction as the RD6 direction.

[0062] On the other hand, as shown in Figure 10(c), when the reversing gear 202B is stopped, the rotation (driving force) of the reversing input gear 201B is transmitted to the internal idler gear 204B which meshes with the sun gear 201Ba. As a result, the internal idler gear 204B rotates around the rotation axis 202Ba in the RD9 direction, which is opposite to the RD6 direction of the reversing input gear 201B. Then, as shown in Figure 10(d), the internal teeth 203Bb of the reversing output gear 203B mesh with the internal idler gear 204B, so the internal teeth 203Bb rotate in the RD8 direction, which is the same rotation direction as the RD9 direction of the internal idler gear 204B. In other words, the driving force of the reversing input gear 201B is output to the reversing output gear 203B as a rotational driving force in the RD8 direction, which is opposite to the RD6 direction in which the reversing input gear 201B rotates. In this embodiment, the rotational direction of the rotational drive force is changed between the sun gear 201Ba and the internal idler gear 204B.

[0063] [Switching operation of the rotation direction of the discharge roller pair] Next, the switching operation of the rotation direction of the discharge roller pair 50 will be explained using Figure 11. Figures 11(a) and (b) are perspective views illustrating the rotation direction of the gears of each unit constituting the discharge reversal drive mechanism 90A when the clutch signal to the clutch unit 600 is in the off state (power outage state). The arrows in Figures 11(a) and (b) indicate the rotation direction of each gear. On the other hand, Figures 11(c) and (d) are perspective views illustrating the rotation direction of the gears of each unit constituting the discharge reversal drive mechanism 90A when the clutch signal to the clutch unit 600 is in the on state (power supply state). The arrows in Figures 11(c) and (d) indicate the rotation direction of each gear, and gears for which the rotation direction is not indicated (e.g., clutch input gear 601) are in a stopped rotation state.

[0064] As shown in Figures 11(a) and (b), when the clutch signal to the clutch unit 600 is off and the clutch unit 600 is experiencing a power outage, the connection between the clutch input gear 601 and the clutch holding shaft 605 is released and they are not connected. Therefore, the rotation of the clutch second transmission gear 506 is transmitted to the clutch input gear 601, causing it to rotate. Consequently, the rotation from the clutch first transmission gear 505 is transmitted to the reversing switching gear 202B via the clutch idler gear 501, causing it to rotate in the same direction and at the same speed as the reversing input gear 201B. As a result, as described above, the reversing input gear 201B and the reversing switching gear 202B rotate together, causing the reversing output gear 203B to also rotate in the same direction via the internal idler gear 204B, and the discharge roller pair 50 rotates in the forward direction.

[0065] On the other hand, as shown in Figures 11(c) and (d), when the clutch signal input to the clutch unit 600 switches from the off state to the on state, the clutch unit 600 is powered. As a result, the clutch input gear 601 and the clutch holding shaft 605 become connected. Since the clutch holding shaft 605 is fixed to the frame (not shown) so as not to rotate, the rotation of the clutch second transmission gear 506, the clutch idler gear 501, and the reversing switching gear 202B stops simultaneously. At this time, the torque limiter 507 prevents the transmission of torque above a predetermined level, and although the clutch first transmission gear 505 rotates, the drive train downstream of the clutch second transmission gear 506 stops. Then, as the reversing switching gear 202B stops rotating, the rotation direction of the reversing output gear 203B is switched by the internal structure of the reversing unit 200B described above. When the rotation direction of the reversing output gear 203B is switched, the rotation direction of the discharge roller gear 50b and the discharge roller pair 50, which mesh with the external teeth 203Ba of the reversing output gear 203B, is also switched, and the discharge roller pair 50 rotates in the reverse direction, causing the sheet S to flow back into the inside of the device.

[0066] As described above, the discharge reversal drive mechanism 90A of this embodiment is a mechanism that switches the rotation direction of the discharge roller pair 50 in both forward and reverse directions using the driving force of a drive motor (not shown) that rotates in one direction. As mentioned above, by using the reversal output gear 203B that constitutes the reversal unit 200B of this embodiment, it is possible to miniaturize the drive mechanism and improve the precision of rotation. Furthermore, since this embodiment omits the locking lever 209 of Embodiment 1, there are fewer parts that operate after the state of the clutch signal of the clutch unit 600 is switched. Because there are fewer operating parts, the operating time when the state of the clutch signal is switched is shortened, and therefore Embodiment 2 has the advantage that the response time for switching the rotation direction of the discharge roller pair 50 is faster than that of Embodiment 1.

[0067] In this embodiment, a configuration was used in which the sheet S is transported by a discharge roller pair 50, but a configuration in which the sheet S is transported by a triple roller pair with rollers positioned above and below the rollers is also acceptable. Alternatively, a configuration using two sets of roller pairs is also acceptable: a discharge roller pair that discharges the sheet S outside the main body 2 of the printer 1, and a reversing roller pair that switches the sheet S back inside the machine.

[0068] In this embodiment, the rotation direction of the reversing output gear 203B is switched by switching the reversing input gear 201B and the reversing switching gear 202B to either a state where they rotate in the same direction and at the same rotational speed, or a state where their rotation has stopped. As for other configurations, for example, the rotation direction of the reversing switching gear 202B may be reversed, or it may be rotated at a different speed than the reversing input gear 201B, thereby being used as a mechanism to switch the rotation direction and rotational speed of the reversing output gear 203B. Alternatively, the reversing output gear 203B may be rotated in the same direction, and only the rotational speed may be switched.

[0069] Furthermore, in this embodiment, a configuration was used in which the clutch holding shaft 605 and the clutch input gear 601 are disconnected, but a configuration in which the clutch input gear 601 and the guide member of the seat S are disconnected may also be used. Also, in this embodiment, a clutch was used as the configuration for disconnecting the clutch holding shaft 605 and the clutch input gear 601, but instead of a clutch, a solenoid or other actuator may be used, for example.

[0070] As described above, according to this embodiment, the components of the drive transmission mechanism can be miniaturized. [Examples]

[0071] In Example 3, we will describe an exhaust reversal drive mechanism that differs from the exhaust reversal drive mechanism described in Example 1 in the configuration of the reversal switching gear and clutch unit.

[0072] [Configuration of the image forming apparatus] The printer 1 in Example 3, which is an image forming apparatus, differs from the printer 1 in Example 1, which uses the discharge reversal drive mechanism 90, in that it uses the discharge reversal drive mechanism 90B, which will be described later, as the discharge reversal drive mechanism that drives the discharge roller pair 50. In the printer 1 of Example 3, the other configurations of the printer 1 described in Example 1, the image forming operation, and the sheet transport operation during single-sided and double-sided printing are the same as those of the printer 1 in Example 1, and will not be described here.

[0073] [Overall configuration of the drive force reversal mechanism] Figure 12 is a perspective view showing the overall configuration of the discharge reversal drive mechanism 90B that drives the discharge roller pair 50. Figure 12(a) is a perspective view of the discharge reversal drive mechanism 90B when viewed from the direction toward the discharge roller pair 50 (front), and Figure 12(b) is a perspective view of the discharge reversal drive mechanism 90B when viewed from the discharge roller pair 50 side (rear). As shown in Figure 12, the discharge reversal drive mechanism 90B includes a reversal unit 200C and a clutch unit 600A.

[0074] The clutch unit 600A includes a clutch input gear 601 (first drive gear), a clutch fixing part 602, a clutch output gear 606 (second drive gear), and a torque limiter 607. The clutch input gear 601 is driven by a drive motor (not shown) via a drive gear train (not shown) and is configured to be rotatable. The torque limiter 607 is fixed to a frame (not shown) in a non-rotatable manner and applies a predetermined load to the clutch output gear 606. The coupling state of the clutch input gear 601 and the clutch output gear 606 is switched depending on whether the clutch signal of the clutch unit 600A is ON (power supply state) or OFF (power outage state). The clutch input gear 601 and the clutch output gear 606 are configured with the same number of teeth. The clutch fixing part 602 is held in place so as not to rotate by fixing a rotation stopper 603.

[0075] The reversal unit 200C comprises a reversal input gear 201, a reversal switching gear 202C, and a reversal output gear 203. By switching the rotation state of the reversal switching gear 202C, the reversal unit 200C switches the direction of rotation (driving force) transmitted to the reversal input gear 201 to either forward rotation (clockwise) or reverse rotation (counterclockwise) and outputs it to the reversal output gear 203. The reversal input gear 201 and the reversal switching gear 202C have the same number of teeth.

[0076] A discharge roller gear 50b is provided at the end of the discharge roller shaft 50a, which drives the discharge roller pair 50. Driving force is transmitted from the reversing output gear 203 to the discharge roller gear 50b, causing the discharge roller shaft 50a to rotate, and the rotation of the discharge roller shaft 50a causes the discharge roller pair 50 to rotate.

[0077] [Internal configuration of the inversion unit] The internal configuration of the reversing unit 200 will be explained using Figure 13. Figure 13 is an exploded perspective view of the reversing unit 200C. Figure 13(a) is an exploded perspective view of the reversing unit 200C as seen from the direction toward the discharge roller pair 50 (front), and Figure 13(b) is an exploded perspective view of the reversing unit 200C as seen from the discharge roller pair 50 side (rear).

[0078] As shown in Figures 13(a) and (b), the reversal unit 200C includes a reversal input gear 201, a reversal switching gear 202C, a reversal output gear 203, an internal idler gear 204, and an internal holder unit 212. The reversal input gear 201 is an input member that rotates upon receiving the driving force (rotation) transmitted from the clutch input gear 601, as described above. The reversal output gear 203 is an output member that outputs the driving force to the discharge roller gear 50b to rotate the discharge roller pair 50. The internal idler gear 204 consists of two symmetrically arranged gear trains and is a drive transmission member for transmitting drive from the reversal input gear 201 to the reversal output gear 203.

[0079] The internal holder unit 212 has a first internal holder 212a and a second internal holder 212b. The internal idler gear 204 described above is sandwiched between the first internal holder 212a and the second internal holder 212b of the internal holder unit 212 and is held rotatably. The internal holder unit 212 has a rotating support shaft that rotatably holds the reversal input gear 201 and also holds the reversal switching gear 202C, and four rotating support shafts that support each of the internal idler gears 204. Furthermore, the internal holder unit 212 and the reversal switching gear 202C are connected to form an integrated unit.

[0080] Furthermore, in Figure 13(c), the left-hand diagram is a side view of the reversal input gear 201 as seen from the side, and the center diagram is a cross-sectional view of the reversal input gear 201 as seen from the left (front) direction of the left-hand diagram, when the reversal input gear 201 is cut along line AA shown in the left-hand diagram. As shown in Figure 13(c), the reversal input gear 201 has external teeth 201a to which driving force (rotation) is transmitted from the clutch input gear 601, and internal teeth 201b to which driving force (rotation) is transmitted to the internal idler gear 204. As shown in Figure 13(c), the external teeth 201a and internal teeth 201b have the same number of teeth but different modules and are configured to overlap on the same plane. In this embodiment, the external teeth 201a are configured with module 0.7 / number of teeth 52, and the internal teeth 201b are configured with module 0.6 / number of teeth 52. In this way, by making the number of teeth of the external teeth 201a and internal teeth 201b of the reversing input gear 201 the same and configuring them to overlap on the same plane, the reversing input gear 201 has a shape that is symmetrical in all directions, as shown in the cross-sectional view of Figure 13(c)AA. By making the external teeth 201a and internal teeth 201b of the reversing input gear 201 symmetrical in all directions, the resin can be flowed uniformly during molding, thereby improving the manufacturing accuracy of the gear. As a result, since the gap g shown in Figure 15 above does not occur, it becomes possible to mold a high-precision gear in a small space.

[0081] [Switching operation of the rotation direction of the discharge roller pair] Next, the switching operation of the rotation direction of the discharge roller pair 50 will be explained using Figure 14. Figures 14(a) and (b) are perspective views illustrating the rotation direction of the gears of each unit constituting the discharge reversal drive mechanism 90B when the clutch signal to the clutch unit 600 is in the ON state (power supply state). The arrows in Figures 14(a) and (b) indicate the rotation direction of each gear. Figure 14(c) is a perspective view of the reversal unit 200C in forward rotation, with the reversal input gear 201, reversal switching gear 202C, and the first internal holder 212a of the internal holder unit 212 omitted from the illustration of the reversal unit 200C shown in Figure 14(a).

[0082] As shown in Figures 14(a) and (b), when the clutch signal to the clutch unit 600A is ON and the clutch unit 600 is receiving power, the clutch input gear 601 and the clutch output gear 606 are connected. Therefore, the clutch output gear 606 rotates at the same speed as the clutch input gear 601. The clutch input gear 601 and the clutch output gear 606 have the same number of teeth, and the reversing input gear 201 and the reversing switching gear 202C that mesh with the clutch input gear 601 and the clutch output gear 606 also have the same number of teeth. As a result, the reversing input gear 201 and the reversing switching gear 202C also rotate at the same speed, resulting in operation similar to when the reversing input gear 201 and the reversing switching gear 202C rotate as a single unit.

[0083] As described in Example 1, as shown in Figure 14(c), the internal idler gear 204, together with the reversing input gear 201 and the reversing switching gear 202C, rotates in the same RD2 direction as the reversing input gear 201, around the rotation axis of the reversing input gear 201. The second internal idler gears 204b and 204d mesh with the internal teeth 203b of the reversing output gear 203, and rotate in the same RD2 direction as the reversing input gear 201 due to the internal idler gears 204b and 204d. As the reversing output gear 203 rotates in the same RD2 direction as the reversing input gear 201, the discharge roller pair 50 rotates in the forward rotation direction.

[0084] On the other hand, Figures 14(d) and (e) are perspective views illustrating the rotation direction of the gears of each unit constituting the discharge reversal drive mechanism 90B when the clutch signal to the clutch unit 600 is in the off state (power outage state). The arrows in Figures 14(d) and (e) indicate the rotation direction of each gear, and gears for which the rotation direction is not indicated (e.g., clutch output gear 606) are in a stopped rotation state. Figure 14(f) is a perspective view of the reversal unit 200C in reverse rotation, with the reversal input gear 201, reversal switching gear 202C, and the first internal holder 212a of the internal holder unit 212 omitted from the illustration of the reversal unit 200C shown in Figure 14(d).

[0085] As shown in Figures 14(c) and (d), when the clutch signal to the clutch unit 600A is off and the clutch unit 600 is experiencing a power outage, the connection between the clutch input gear 601 and the clutch output gear 606 is released. As a result, the clutch output gear 606 stops due to the load received from the torque limiter 607. When the rotation of the clutch output gear 606 stops, the rotation of the reversing switching gear 202C, which is meshed with the clutch output gear 606, also stops, and the rotation of the internal holder unit 212, which is integrated with the reversing switching gear 202C, also stops. Consequently, as described in Embodiment 1, as shown in Figure 14(f), the rotation (driving force) input to the reversing input gear 201 is transmitted to the reversing output gear 203 via the internal idler gear 204, which is rotatably supported by the stopped internal holder unit 212.

[0086] As shown in Figure 14(f), the first internal idler gears 204a and 204c, which are the first internal idler gears 204, mesh with the internal teeth 201b of the reversal input gear 201 and therefore rotate in the same direction as the reversal input gear 201. On the other hand, the second internal idler gears 204b and 204d, which are the second internal idler gears 204, mesh with the first internal idler gears 204a and 204c and therefore rotate in the opposite direction to the reversal input gear 201. The reversal output gear 203 rotates in the opposite direction to the reversal input gear 201 because its internal teeth 203b mesh with the second internal idler gears 204b and 204d. In this way, the direction of rotation of the rotational driving force is reversed between the two corresponding internal idler gears 204. As a result, the reversing output gear 203 rotates in the RD3 direction, which is opposite to the rotation direction of the reversing input gear 201, and the discharge roller pair 50 rotates in the reverse direction, causing the sheet S to flow back into the device. As described above, the rotation direction of the discharge roller pair 50 can be switched by switching between the power supply state and the power outage state of the clutch unit 600A.

[0087] As described above, the discharge reversal drive mechanism 90B of this embodiment is a mechanism that switches the rotation direction of the discharge roller pair 50 in both forward and reverse directions using the driving force of a drive motor (not shown) that rotates in one direction. As mentioned above, by using the reversal input gear 201 that constitutes the reversal unit 200C of this embodiment, it is possible to miniaturize the drive mechanism and improve the precision of rotation. In this embodiment, the number of components is reduced compared to Embodiment 2, which has the advantage of making the entire unit smaller.

[0088] In this embodiment, a configuration was used in which the sheet S is transported by a discharge roller pair 50, but a configuration in which the sheet S is transported by a triple roller pair with rollers positioned above and below the rollers is also acceptable. Alternatively, a configuration using two sets of roller pairs is also acceptable: a discharge roller pair that discharges the sheet S outside the main body 2 of the printer 1, and a reversing roller pair that switches the sheet S back inside the machine.

[0089] In this embodiment, the rotation direction of the reversing output gear 203B is switched by switching the reversing input gear 201 and the reversing switching gear 202C to either a state where they rotate in the same direction and at the same rotational speed, or a state where their rotation is stopped. As for other configurations, for example, the rotation direction of the reversing switching gear 202C may be reversed, or it may be rotated at a different speed than the reversing input gear 201, and this may be used as a mechanism to switch the rotation direction and rotational speed of the reversing output gear 203. Alternatively, the reversing output gear 203 may be rotated in the same direction, and only the rotational speed may be switched. Furthermore, in this embodiment, a torque limiter 607 was used to maintain the rotation-stopped state of the clutch output gear 606 in the event of a power outage of the clutch unit 600, but a configuration that maintains the rotation-stopped state using, for example, a second clutch or a solenoid may also be used.

[0090] In the above-described embodiments 1 to 3, an image forming apparatus to which the present invention is applied was described using an image forming apparatus that forms an image on a sheet S by an electrophotographic image forming process as an example, but the present invention is not limited thereto. For example, it may be an image forming apparatus that forms an image on a sheet S by an inkjet image forming process that forms an image by ejecting ink liquid from a nozzle. Also, in the above-described embodiments, a printer's ejection reversal unit was described as an example of a transport device that switches the transport direction of the sheet S, but the present invention is not limited thereto. For example, the present invention may be used in other switchback mechanisms of an image forming apparatus, such as an automatic document feeder (ADF) that can automatically feed originals or a post-processing device that performs post-processing on the sheet S.

[0091] Furthermore, although the above-described embodiment described a configuration in which the reversing unit drives a guide member that guides the sheet S and a pair of reversing rollers that discharge the sheet S, the present invention is not limited thereto. For example, the present invention may be applied to a configuration in which the reversing unit operates a feeding mechanism (such as raising and lowering a loading plate, raising and lowering feeding rollers, and rotating feeding rollers) or an image forming process mechanism (such as rotating a photosensitive drum and developing rollers).

[0092] As described above, according to this embodiment, the components of the drive transmission mechanism can be miniaturized. [Explanation of Symbols]

[0093] 201 Reversal Input Gear 202 Reverse gear 203 Reversing Output Gear 212 Internal holder unit 600 Clutch Unit

Claims

1. A power transmission device that transmits power from a power source, An input gear to which driving force is input from the aforementioned drive source, The output gear that delivers driving force, A switching gear that switches the rotation direction that drives the output gear, A rotation direction setting unit for setting the rotation direction of the output gear, An internal drive unit that transmits the driving force of the input gear to the output gear, Equipped with, The input gear has external teeth to which driving force is input from the drive source, and internal teeth to which driving force is transmitted to the internal drive unit. The external teeth and internal teeth have the same number of teeth but different modules, and are molded together as a single unit when the input gear is formed. The root of the external tooth is located outward in the radial direction of rotation compared to the root of the internal tooth. Regarding the rotation direction of the input gear, the positions of the teeth of the external gear and the internal gear are misaligned. A drive force transmission device characterized by the following features.

2. The internal drive unit has a first internal gear and a second internal gear, The first internal gear and the second internal gear are rotatably held on a support shaft provided in the internal drive unit. The first internal gear meshes with the internal teeth of the input gear and receives driving force from the input gear. The drive force transmission device according to claim 1, characterized in that the second internal gear meshes with the first internal gear and the output gear to transmit drive force to the output gear.

3. The holder is connected to the internal drive unit, with the input gear in between. The holder has a first locking portion that engages with the switching gear, and a second locking portion that switches between a locked state in which it is engaged with a locking portion provided on the input gear, and an unlocked state in which it is not engaged with the locking portion. The drive force transmission device according to claim 2, characterized in that when the second locking portion is in the locked state, the switching gear is driven together with the input gear, and when the second locking portion is in the unlocked state, the switching gear is not driven.

4. The drive force transmission device according to claim 3, characterized in that the rotation direction setting unit sets the switching gear to a rotatable state or a rotation-stopped state, thereby setting the rotation direction of the output gear to a first rotation direction that is the same as the rotation direction of the input gear, or a second rotation direction that is opposite to the first rotation direction.

5. The drive force transmission device according to claim 4, characterized in that when the rotation direction setting unit sets the switching gear to a rotatable state, the second locking unit is set to the locked state, the input gear, the switching gear, and the internal drive unit are driven together, and the output gear is driven in the first rotation direction by the second internal gear.

6. The drive force transmission device according to claim 5, characterized in that when the rotation direction setting unit sets the switching gear to a rotation stop state, the second locking unit is set to the unlocked state, the first internal gear is driven by the internal teeth of the input gear, and the output gear is driven in the second rotation direction by the second internal gear.

7. The rotation direction setting unit has a gear meshed with the switching gear, and the switching gear is set to a rotatable state or a rotation-stopped state by setting the gear to a rotatable state or a rotation-stopped state, as described in claim 6.

8. A first drive gear that meshes with the input gear and inputs the driving force from the drive source to the input gear, A second drive gear meshes with the aforementioned switching gear, has the same number of teeth as the first drive gear, and, when connected to the first drive gear, rotates in the same direction as the first drive gear to drive the switching gear. The drive force transmission device according to claim 2, characterized by comprising:

9. The drive force transmission device according to claim 8, characterized in that the rotation direction setting unit is set to a connected state in which the first drive gear and the second drive gear are connected, or to an unconnected state in which the first drive gear and the second drive gear are not connected, thereby setting the rotation direction of the output gear to a first rotation direction which is the same as the rotation direction of the input gear, or to a second rotation direction which is the opposite of the first rotation direction.

10. When the rotation direction setting unit sets the first drive gear and the second drive gear to a connected state, the input gear, the switching gear, and the internal drive unit are driven together as a single unit. The drive force transmission device according to claim 9, characterized in that the output gear is driven in the first rotational direction by the second internal gear.

11. The drive force transmission device according to claim 10, characterized in that when the rotation direction setting unit sets the first drive gear and the second drive gear to an unconnected state, the first internal gear is driven by the internal teeth of the input gear, and the output gear is driven in the second rotation direction by the second internal gear.

12. A power transmission device that transmits power from a power source, An input gear to which driving force is input from the aforementioned drive source, The output gear that delivers driving force, A switching gear that switches the rotation direction that drives the output gear, A rotation direction setting unit for setting the rotation direction of the output gear, Equipped with, The output gear has internal teeth to which the driving force from the input gear is input, and external teeth to which the input driving force is transmitted. The internal teeth and external teeth have the same number of teeth but different modules, and are molded together as a single unit when the output gear is formed. The root of the external tooth is located outward in the radial direction of rotation compared to the root of the internal tooth. Regarding the rotation direction of the output gear, the positions of the teeth of the external gear and the internal gear are misaligned. A drive force transmission device characterized by the following features.

13. The switching gear has an internal gear that is rotatably held on a support shaft provided on the switching gear, The input gear has external teeth to which driving force is input from the drive source, and a sun gear that transmits the driving force to the internal gear. The drive force transmission device according to claim 12, characterized in that the internal teeth of the output gear mesh with the internal gear.

14. The drive force transmission device according to claim 13, characterized in that the rotation direction setting unit sets the rotation direction of the output gear to a first rotation direction, which is the same as the rotation direction of the input gear, or to a second rotation direction, which is the opposite of the first rotation direction, by setting the switching gear to a rotatable state or a rotation-stopped state.

15. The aforementioned switching gear meshes with a drive gear that receives driving force from a drive source different from the aforementioned drive source, The drive gear drives the switching gear at the same rotational speed and in the same rotational direction as the input gear, as described in claim 14.

16. The drive force transmission device according to claim 15, wherein the rotation direction setting unit has a gear meshed with the drive gear, and by setting the gear to a rotatable state or a rotation-stopped state, the switching gear meshed with the drive gear is set to a rotatable state or a rotation-stopped state.

17. When the rotation direction setting unit sets the gear to a state in which it can rotate, the input gear, The drive force transmission device according to claim 16, characterized in that the switching gear and the output gear are driven together, and the output gear is driven in the first rotational direction by the internal gear.

18. When the rotation direction setting unit sets the gear to a rotation stop state, the internal gear, The drive force transmission device according to claim 17, characterized in that the input gear is driven by the sun gear, and the output gear is driven in the second rotation direction by the internal gear.

19. An image forming apparatus for forming an image on a recording material, An image forming unit that forms an image on one side of the recording material, A rotating body for transporting the recording material that has passed through the image forming unit, A drive force transmission device according to any one of claims 1 to 18, which is capable of switching the forward and reverse direction of rotation of the rotational drive force transmitted to the rotating body, A transport unit transports the recording material, whose transport direction has been reversed by the reversal of the rotation direction of the rotating body, to the upstream side of the image forming unit. An image forming apparatus characterized by comprising:

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