Power transmission mechanism, fixing device, and image forming apparatus

Abstract

To prevent breakage of teeth when tooth tips collide with each other without elastically deforming a gear.SOLUTION: The power transmission mechanism 50 includes the gear having partly omitted teeth 53 provided with a teeth 53a only at a part of a peripheral edge portion thereof and rotationally driven, and the first gear 54 provided with a plurality of teeth 54a at a peripheral edge portion thereof, and engaged with the teeth 53a of the gear having partly omitted teeth 53 by rotation of the gear having partly omitted teeth 53 and rotationally driven with the rotation of the gear having partly omitted teeth 53. The first gear 54 is movable between a first position where a free end of a part of the teeth 54a among the plurality of teeth 54a and a free end of the teeth 53a of the gear having partly omitted teeth 53 collide with each other and a second position where the first gear 54 is more spaced from the gear having partly omitted teeth 53 than in the first position.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a power transmission mechanism, a fixing device, and an image forming apparatus. [Background technology]

[0002] Image forming apparatuses, such as multifunction peripherals (MFPs), are equipped with various power transmission mechanisms. Conventionally, a power transmission mechanism used, for example, in a paper feed roller drive system, includes a first gear and a second gear having a toothless portion (see, for example, Patent Document 1). In such a power transmission mechanism, when the teeth of the second gear, which has a toothless portion, mesh with the first gear, which has multiple teeth evenly spaced around its entire circumference, there is a possibility that the tooth tips of the first gear may collide with the tooth tips of the second gear. If the tooth tips of the first gear collide with the tooth tips of the second gear, neither the first nor the second gear can rotate normally. Therefore, if the rotation shaft of one gear is forcibly rotated, the teeth of each gear will be damaged. To prevent this, the power transmission mechanism disclosed in Patent Document 1 is configured so that the toothed portion located downstream of the toothless portion in the rotation direction of the second gear is elastically deformable. In other words, in conventional power transmission mechanisms, when the tooth tips of the first gear and the second gear collide when they mesh, the tooth portion of the second gear contracts and deforms radially to prevent damage to the teeth.

[0003] Incidentally, the above-mentioned power transmission mechanism is also installed in a fixing device, which is exposed to a high-temperature environment during operation. The power transmission mechanism installed in the fixing device must have sufficient heat resistance, and for example, PPS (polyphenylene sulfide) resin, which is a thermoplastic resin with particularly excellent heat resistance, is used. In addition to high heat resistance, PPS resin is also characterized by high dimensional stability. Therefore, PPS resin is suitable as a material for forming the gears of the power transmission mechanism.

[0004] However, on the other hand, PPS resin has the properties of being difficult to deform due to its lack of viscosity, and also of having low resistance to impact, which means that when PPS resin is used to form gears for power transmission mechanisms, it is not possible to adopt an elastically deformable structure like the above-mentioned conventional technology. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-50406 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve the above-mentioned problems of the related art, and aims to provide a power transmission mechanism, a fixing device, and an image forming apparatus that can prevent damage to the teeth when the tooth tips collide with each other without elastically deforming the gears. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the invention of claim 1 is a power transmission mechanism comprising: a partially-toothed gear having teeth formed only on a portion of its periphery and being driven to rotate; and a first gear having a plurality of teeth formed on its periphery, which meshes with the teeth of the partially-toothed gear as the partially-toothed gear rotates, and which is driven to rotate as the partially-toothed gear rotates; wherein the first gear is configured to be movable between a first position where the tips of some of the plurality of teeth collide with the tips of the teeth of the partially-toothed gear, and a second position that is farther from the partially-toothed gear than the first position.

[0008] The invention of claim 2 is characterized in that, in the power transmission mechanism of claim 1, the first gear is in the first position in an unconnected state in which the multiple teeth are not meshed with the teeth of the missing tooth gear, and as the missing tooth gear rotates, the tips of some of the multiple teeth collide with the tips of the teeth of the missing tooth gear at the first position, and then moves to the second position by receiving the rotational force of the missing tooth gear.

[0009] The invention of claim 3 is characterized in that, in the power transmission mechanism of claim 2, as the first gear moves to the second position, some of the teeth of the plurality of teeth enter a connected state in which they mesh with the teeth of the missing tooth gear.

[0010] The invention of claim 4 is characterized in that, in the power transmission mechanism of claim 3, the first gear rotates at the second position in the connected state in conjunction with the rotation of the missing tooth gear.

[0011] The invention of claim 5 is characterized in that, in the power transmission mechanism of claim 1, it further comprises a second gear that is arranged in mesh with the first gear, and the first gear rotates the second gear.

[0012] The invention of claim 6 is characterized in that, in the power transmission mechanism of claim 5, the movement direction of the first gear connecting the first position and the second position is approximately perpendicular to a line connecting the center of the first gear and the center of the second gear when the first gear is in the first position.

[0013] The invention of claim 7 is characterized in that, in the power transmission mechanism of claim 5, the second gear maintains a state of meshing with the first gear regardless of whether the first gear is in the first position or the second position.

[0014] An eighth aspect of the present invention provides the power transmission mechanism of the fifth aspect, characterized in that the rotational torque of the second gear is greater than the rotational torque of the first gear.

[0015] The invention of claim 9 is a power transmission mechanism of claim 1, further comprising a rotating shaft that rotatably holds the first gear, wherein the rotating shaft is inclined from the horizontal when the first gear is in the first position, and is in a horizontal position when the first gear moves to the second position.

[0016] The invention of claim 10 is characterized in that, in the power transmission mechanism of claim 9, it further comprises a pair of support plates that support both ends of the rotating shaft, and the support plate on the one end side to which the first gear is attached has a long hole formed therein that changes the rotating shaft between the inclined posture and the horizontal posture.

[0017] The invention according to claim 11 is the power transmission mechanism of claim 1, further comprising a biasing member that biases the first gear toward the first position.

[0018] The invention according to claim 12 is the power transmission mechanism of claim 1, wherein the missing tooth gear and the first gear are formed from PPS (polyphenylene sulfide) resin.

[0019] The invention of claim 13 is a fixing device comprising a first support portion that supports a heating roller, a second support portion that supports a pressure roller and is movable relative to the first support portion in a direction toward and away from the first support portion, a holding member that holds the second support portion and the first support portion in a state close to each other, a pressing portion that presses the second support portion and the first support portion in a direction separating them from each other against the holding force of the holding member, and a power transmission mechanism described in any of claims 1 to 12, wherein the power transmission mechanism is configured to operate the pressing portion to separate the second support portion and the first support portion from each other by rotating the missing tooth gear and rotating the first gear when the missing tooth gear and the first gear are in a connected state in which they are meshed with each other.

[0020] The invention of claim 14 is an image forming apparatus comprising the fixing device of claim 13 and a control unit that controls the power transmission mechanism, wherein the control unit drives the missing tooth gear to rotate when in a predetermined state, thereby separating the second support portion and the first support portion from each other.

[0021] The invention according to claim 15 is the image forming apparatus according to claim 13, characterized in that the predetermined state is a state in which execution of a print job has stopped.

[0022] The invention according to claim 16 is the image forming apparatus according to claim 13, characterized in that the predetermined state is a state in which a jam has occurred. [Effects of the Invention]

[0023] According to the present invention, it is possible to prevent damage to the teeth when the tooth tips collide with each other without elastically deforming the gears. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a conceptual diagram illustrating an overall configuration of an image forming apparatus in which a power transmission mechanism is mounted. [Figure 2] FIG. 2 is a perspective view showing a fixing device. [Figure 3] FIG. [Figure 4] 6A and 6B are diagrams illustrating changes in the fixing device due to a power transmission mechanism. [Figure 5] FIG. [Figure 6] 10A and 10B are diagrams showing the movement of a first gear attached to the outside of the support plate. [Figure 7] FIG. 10 is a diagram illustrating the displacement of a rotation axis. [Figure 8] 10A and 10B are diagrams illustrating the operation of the power transmission mechanism. [Figure 9] FIG. 10 is a diagram showing the direction of movement of the first gear relative to the second gear. [Figure 10] 10 is a diagram showing the direction of movement of the first gear in relation to the missing tooth gear. FIG. [Figure 11] 4 is a flowchart showing a procedure for drive control of the power transmission mechanism by the control unit. [Figure 12] 10A and 10B are diagrams illustrating an example of a biasing member that biases a first gear toward a first position. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Elements common to the embodiments described below are designated by the same reference numerals, and redundant description thereof will be omitted.

[0026] FIG. 1 is a conceptual diagram showing the overall configuration of an image forming apparatus 1 equipped with a power transmission mechanism 50 according to one embodiment of the present invention. The image forming apparatus 1 is configured as, for example, an MFP (Multifunction Peripheral) and has multiple functions, such as a scanning function and a printing function. The image forming apparatus 1 has a scanner unit 2 located at the top of the apparatus main body 1a. The scanner unit 2 optically reads an image of a document set by a user and generates image data. The image forming apparatus 1 has an operation panel 3 located in front of the scanner unit 2. The operation panel 3 is a user interface used by a user when using the image forming apparatus 1. The operation panel 3 displays an operation screen that can be operated by the user and accepts operations by the user. The image forming apparatus 1 also has a printer unit 4 located at the bottom of the apparatus main body 1a. The printer unit 4 forms an image on a sheet and outputs it.

[0027] 1, the printer unit 4 includes a paper feed conveyance unit 10, an image forming unit 20, and a fixing device 30. The printer unit 4 also includes a control unit 6 that controls the overall operation of the image forming apparatus 1.

[0028] The paper feed conveyance unit 10 feeds a sheet 9 from one of a plurality of paper feed trays 10a, 10b, and 10c, and conveys the sheet 9 along a conveyance path 13 formed inside the printer unit 4. The plurality of paper feed trays 10a, 10b, and 10c may each store different types of sheets 9, or may store the same type of sheets 9. Each of the paper feed trays 10a, 10b, and 10c is provided with a pickup roller 11 and a paper feed roller 12. The paper feed conveyance unit 10 drives the pickup roller 11 and paper feed roller 12 provided in one paper feed tray designated by the user, and feeds the sheet 9 toward the conveyance path 13. The paper feed conveyance unit 10 conveys the sheet 9 sent to the conveyance path 13 in the direction of arrow F1.

[0029] The transport path 13 is provided with a timing roller 15, a secondary transfer roller 16, a fixing device 30, and a paper discharge roller 18.

[0030] The timing roller 15 is composed of a pair of rollers. The timing roller 15 is a roller that adjusts the timing at which the sheet 9 is sent to the secondary transfer position by the secondary transfer roller 16. When the leading edge of the sheet 9 fed from the paper feed trays 10a, 10b, and 10c reaches the position of the timing roller 15, the paper feed conveying unit 10 temporarily stops the conveyance of the sheet 9. The paper feed conveying unit 10 then drives the timing roller 15 in accordance with the timing at which the image that has been primarily transferred onto the intermediate transfer belt 22 in the image forming unit 20 is conveyed to the secondary transfer position, and conveys the sheet 9 toward the secondary transfer roller 16. The image is secondarily transferred onto the sheet 9 sent out from the timing roller 15 as it passes through the secondary transfer position by the secondary transfer roller 16. The sheet 9 onto which the image has been secondarily transferred then proceeds toward the fixing unit 17.

[0031] The image forming section 20 includes image forming units 21Y, 21M, 21C, and 21K corresponding to the colors yellow (Y), magenta (M), cyan (C), and black (K), respectively, and an intermediate transfer belt 22.

[0032] The image forming unit 21Y is a unit that forms a Y-color image. The image forming unit 21Y includes an image carrier 25, which is composed of a photosensitive drum or the like, a charger 26, an exposure device 27, and a developing device 28. The image carrier 25 has a photosensitive layer on the surface of a cylindrical body and rotates in a predetermined direction (clockwise). The charger 26, the exposure device 27, and the developing device 28 are arranged around the image carrier 25. The charger 26 charges the surface of the image carrier 25 to a predetermined charge. The exposure device 27 exposes the charged surface of the image carrier 25 based on image data, thereby forming an electrostatic latent image on the surface of the image carrier 25. The developing device 28 supplies a developer containing toner to the surface of the image carrier 25 and develops the electrostatic latent image with toner. As a result, an image (toner image) corresponding to the image data is formed on the surface of the image carrier 25. The other image forming units 21M, 21C, and 21K have the same configuration as image forming unit 21Y, and differ only in the color of toner that they supply to image carrier 25. In other words, multiple image forming units 21Y, 21M, 21C, and 21K having the same configuration are arranged at predetermined intervals in the horizontal direction.

[0033] The intermediate transfer belt 22 is an endless belt disposed above the image forming units 21Y, 21M, 21C, and 21K. The intermediate transfer belt 22 is stretched over a drive roller 23 disposed opposite the secondary transfer roller 16 and a driven roller 24 disposed a predetermined distance horizontally from the drive roller 23. As the drive roller 23 is driven to rotate counterclockwise, the intermediate transfer belt 22 circulates in the direction indicated by arrow F2. The intermediate transfer belt 22 comes into contact with the secondary transfer roller 16 at the position of the drive roller 23.

[0034] Primary transfer rollers 29 are provided inside the intermediate transfer belt 22 at positions facing each of the image forming units 21Y, 21M, 21C, and 21K. The primary transfer rollers 29 press the intermediate transfer belt 22 against the surfaces of the image carriers 25 of each of the image forming units 21Y, 21M, 21C, and 21K. In this state, a predetermined voltage is applied to the primary transfer rollers 29. As a result, the images (toner images) formed on the surfaces of the image carriers 25 are primarily transferred onto the intermediate transfer belt 22. Each of the image forming units 21Y, 21M, 21C, and 21K primarily transfers each of the Y, M, C, and K images onto the intermediate transfer belt 22 in order, superimposing them on top of each other. As a result, a color image is formed on the surface of the intermediate transfer belt 22. The image transferred onto the intermediate transfer belt 22 is secondarily transferred onto the sheet 9 at the position of the secondary transfer roller 16.

[0035] The fixing device 30 applies heat and pressure to the sheet 9 onto which the image has been secondarily transferred, thereby fixing the image to the sheet 9. The fixing device 30 has a heating roller 31 and a pressure roller 32. The heating roller 31 and the pressure roller 32 come into contact with each other to form a nip portion. The heating roller 31 and the pressure roller 32 sandwich the sheet 9 in the nip portion and apply heat and pressure to the sheet 9. The surface temperature of the heating roller 31 is heated by the control unit 6 to a fixing temperature appropriate for the type of sheet 9 (e.g., basis weight). The toner transferred to the sheet 9 is melted by the heating roller 31, and the melted toner is fixed to the sheet 9 by the pressure application by the pressure roller 32. The sheet 9 onto which the image has been fixed in the fixing device 30 is discharged via the paper discharge roller 18 onto the paper discharge tray 5 formed above the printer unit 4.

[0036] 2 is a perspective view showing the fixing device 30. The fixing device 30 has a first support part 33 that rotatably supports the heating roller 31 and a second support part 34 that rotatably supports the pressure roller 32.

[0037] The first support section 33 has a pair of support plates 35, 36 arranged at both ends of the heating roller 31 in the longitudinal direction, and the pair of support plates 35, 36 are connected to each other by a connecting member 37. The connecting member 37 traverses between the pair of support plates 35, 36, and connects and fixes the support plates 35, 36 to both ends of the connecting member 37. Therefore, the connecting member 37 holds the pair of support plates 35, 36 at a predetermined distance so that their relative positions do not change.

[0038] The pair of support plates 35, 36 are provided with bearings 42 that support end portions 43 of the heating roller 31. By mounting the end portions 43 of the heating roller 31 on the bearing portions 42, the pair of support plates 35, 36 rotatably support the heating roller 31. A heat source such as a halogen heater is built into the heating roller 31. Therefore, the bearing portions 42 are configured so that an electric cable can be connected to the heat source.

[0039] The second support portion 34 has a pair of side plates 38, 39 disposed at both longitudinal ends of the pressure roller 32, and a cover portion 40 connecting the pair of side plates 38, 39 and covering the outer peripheral surface of the pressure roller 32. For example, the pair of side plates 38, 39 and the cover portion 40 are integrally formed. The distance between the pair of side plates 38, 39 is wider than the distance between the pair of support plates 35, 36 of the first support portion 33. Therefore, the pair of side plates 38, 39 are disposed outside the pair of support plates 35, 36 of the first support portion 33. The pair of side plates 38, 39 are provided with bearing portions that support end portions 44 of the pressure roller 32. By attaching the end portions 44 of the pressure roller 32 to the bearing portions, the pair of side plates 38, 39 rotatably support the pressure roller 32.

[0040] The second support portion 34 has a pair of side plate portions 38, 39, and the lower portions of the second support portion 34 are connected to the first support portion 33 by a fulcrum shaft 41. The fulcrum shaft 41 is a rotation axis for changing the relative position of the second support portion 34 and the first support portion 33. For example, when the first support portion 33 is fixed inside the image forming apparatus 1, the second support portion 34 rotates about the fulcrum shaft 41, thereby changing the position of the second support portion 34 relative to the first support portion 33. The second support portion 34 rotates about the fulcrum shaft 41, thereby moving relatively toward and away from the first support portion 33. When the second support portion 34 moves away from the first support portion 33, the pressure roller 32 and the heating roller 31 are released from their pressed-together state. On the other hand, when the second support portion 34 moves toward the first support portion 33, the pressure roller 32 and the heating roller 31 are joined to each other, forming a nip portion.

[0041] The upper portions of the pair of side plate portions 38, 39 of the second support portion 34 are connected to the first support portion 33 via a holding member 45. The holding member 45 is formed of an elastic member such as a compression coil spring. The holding member 45 urges the second support portion 34 in a direction that brings it closer to the first support portion 33, thereby holding the pressure roller 32 and the heat roller 31 in a state where they are joined together. The holding member 45 holds the second support portion 34 and the first support portion 33 in a state where they are close to each other, thereby forming a nip portion between the pressure roller 32 and the heat roller 31. This allows the sheet 9 on which an image has been formed to be subjected to a heat treatment and a pressure treatment, and the image can be fixed to the sheet.

[0042] The second support part 34 also has an inclined plate 46 at the center of the ends of the pair of side plate parts 38, 39, with the upper part inclined toward the first support part 33. This inclined plate 46 serves as an operating part when moving the second support part 34 away from the first support part 33.

[0043] The fixing device 30 has a power transmission mechanism 50 for driving the first support portion 33 and the second support portion 34 in a direction separating them from each other. The power transmission mechanism 50 is attached to the pair of support plates 35, 36 of the first support portion 33.

[0044] 3 is a perspective view showing the power transmission mechanism 50. The power transmission mechanism 50 includes a drive gear 51, a drive shaft 52, a missing tooth gear 53, a first gear 54, a second gear 56, and rotary shafts 55 and 57.

[0045] The drive gear 51 is a gear that is rotationally driven by a drive source such as a motor (not shown). The drive gear 51 is disposed on the outer side of the support plate 36. The drive source such as a motor drives the drive gear 51 to rotate in both forward and reverse directions within a predetermined angular range.

[0046] The drive shaft 52 is a rotating shaft having a drive gear 51 attached to one end and a missing tooth gear 53 attached to the other end. The drive shaft 52 is disposed so as to bridge between the support plate 35 and the support plate 36. The drive shaft 52 is rotated by the rotation of the drive gear 51.

[0047] The partially toothed gear 53 is a gear having teeth 53a formed only on a portion of its periphery and no teeth formed on the other portion. The partially toothed gear 53 is disposed on the outside of the support plate 35 and is connected to the other end of the drive shaft 52. Therefore, when the drive gear 51 is driven to rotate, the partially toothed gear 53 rotates in synchronization with the drive gear 51.

[0048] The first gears 54 are disposed in two locations, one on the outside of the support plate 35 and the other on the outside of the support plate 36. The two first gears 54 are connected by a rotating shaft 55. The rotating shaft 55 is disposed so as to bridge between the support plate 35 and the support plate 36 and rotatably supports the first gears 54 on the outside of the pair of support plates 35, 36. The first gear 54 is a gear with a plurality of teeth 54a formed at a predetermined pitch on its periphery. For example, the teeth 54a are formed around the entire periphery of the first gear 54. The first gear 54 disposed on the outside of the support plate 35 meshes with the teeth 53a of the missing tooth gear 53, thereby rotating in synchronization with the rotation of the missing tooth gear 53. At this time, the two first gears 54 rotate in synchronization. However, when the first gear 54 is not meshed with the teeth 53a of the missing tooth gear 53, the first gear 54 does not rotate even when the missing tooth gear 53 rotates.

[0049] Like the first gear 54, the second gear 56 is disposed in two locations, one on the outer side of the support plate 35 and the other on the outer side of the support plate 36. The two second gears 56 are connected by a rotating shaft 57. The rotating shaft 55 is disposed so as to bridge between the support plate 35 and the support plate 36 and rotatably supports the second gear 56 on the outer sides of the pair of support plates 35, 36. The second gear 56 is a gear having a plurality of teeth 56a formed at a predetermined pitch on its periphery. For example, the second gear 56 has teeth 56a formed only on a portion of its periphery, similar to the missing-tooth gear 53. However, the second gear 56 is maintained in a state in which the plurality of teeth 56a formed on its periphery are constantly meshed with the teeth 54a of the first gear 54. In other words, when the drive gear 51 is rotated by the drive source within a predetermined angle range, the teeth 56a of the second gear 56 do not disengage from the first gear 54.

[0050] The second gear 56 has a pressing portion 58 on the opposite side of the portion where the teeth 56a are formed, when the rotation axis 57 is used as the reference. The pressing portion 58 is joined to the inclined plate 46 of the second support portion 34. As the second gear 56 rotates, the pressing portion 58 presses the inclined plate 46, moving the second support portion 34 away from the first support portion 33.

[0051] 4A and 4B are diagrams showing changes in the fixing device 30 due to the power transmission mechanism 50. Fig. 4A shows a state in which the second support portion 34 approaches the first support portion 33, and the heating roller 31 and the pressure roller 32 are pressed together to form a nip. Fig. 4B shows a state in which the second support portion 34 moves away from the first support portion 33, and the nip between the heating roller 31 and the pressure roller 32 is released.

[0052] When a print job is executed in the image forming apparatus 1, the fixing device 30 is in the state shown in FIG. 4(a). That is, the heating roller 31 and the pressure roller 32 are pressed against each other to form a nip. The control unit 6 then drives the heat source of the heating roller 31 and controls it so that the surface temperature of the heating roller 31 reaches a predetermined fixing temperature. At this time, as shown in FIG. 4(a), the missing tooth gear 53 waits in an initial position where the teeth 53a are disengaged from the teeth 54a of the first gear 54. For example, the initial position is a position where the missing tooth gear 53 is rotated so that the teeth 53a of the missing tooth gear 53 face away from the first gear 54, as shown in FIG. 4(a).

[0053] For example, if a jam occurs in the fixing device 30 during execution of a print job and the print job is stopped, the control unit 6 drives the drive source to rotate the missing tooth gear 53, as shown in FIG. 4B. When the missing tooth gear 53 rotates and the tooth 53a of the missing tooth gear 53 meshes with the tooth 54a of the first gear 54, the missing tooth gear 53 rotates the first gear 54, which in turn rotates the second gear 56. As the second gear 56 rotates around the rotation shaft 57, the contact point between the pressing portion 58 and the inclined plate 46 moves upward, and the pressing portion 58 presses the inclined plate 46. As a result, the second support portion 34 moves away from the first support portion 33 against the holding force of the holding member 45, and the nip between the heating roller 31 and the pressure roller 32 is released. This allows the sheet 9 jammed in the fixing device 30 to be removed. After the jam is cleared, the drive source rotates the missing tooth gear 53 in the opposite direction to return it to its initial position, causing the first support portion 33 and the second support portion 34 to approach each other again, and pressing the heating roller 31 and the pressure roller 32 together.

[0054] When a print job is executed in the image forming apparatus 1, the heating roller 31 and the pressure roller 32 reach a high temperature. Therefore, for example, after the execution of the print job is completed, if the heating roller 31 and the pressure roller 32 continue to be in a pressed state without being driven to rotate, creep deformation may occur in the heating roller 31 and the pressure roller 32. Therefore, it is preferable that the control unit 6 drive the drive source of the missing tooth gear 53 to release the pressed state between the heating roller 31 and the pressure roller 32 when the image forming apparatus 1 is in a predetermined state. The predetermined state is, for example, a state in which the execution of the print job has stopped. Stopping a print job includes an emergency stop due to a jam or the normal completion of the print job.

[0055] In the fixing device 30 configured as described above, the missing-tooth gear 53, the first gear 54, and the second gear 56 are used in a high-temperature environment. Therefore, the missing-tooth gear 53, the first gear 54, and the second gear 56 are required to have higher heat resistance than when used in a power transmission mechanism for a sheet 9 conveyance system. Therefore, the power transmission mechanism 50 of this embodiment uses, for example, PPS (polyphenylene sulfide) resin, which is a thermoplastic resin with particularly excellent heat resistance, as the material for forming the missing-tooth gear 53, the first gear 54, and the second gear 56. However, PPS resin has properties that make it difficult to deform and has low resistance to impact. Therefore, when the missing-tooth gear 53 engages with the first gear 54, if the tip of the tooth 53 a of the missing-tooth gear 53 collides with the tip of the tooth 54 a of the first gear 54, one or both of the teeth 53 a, 54 a are likely to be damaged.

[0056] Therefore, the power transmission mechanism 50 of this embodiment has a structure for preventing damage to the missing tooth gear 53 and the first gear 54. This will be described in detail below.

[0057] 5 is a diagram showing support plate 35. Support plate 35 is provided with bearing hole 35a that rotatably supports drive shaft 52, bearing hole 35b that rotatably supports rotation shaft 55, and bearing hole 35c that rotatably supports rotation shaft 57. Support plate 35 also has bearing hole 35d that rotatably supports fulcrum shaft 41.

[0058] Bearing hole 35a, which supports drive shaft 52, is a circular hole slightly larger than the outer diameter of drive shaft 52. Bearing hole 35c, which supports rotating shaft 57, is also a circular hole slightly larger than the outer diameter of rotating shaft 57. In contrast, bearing hole 35b, which supports rotating shaft 55, is an elongated hole having a predetermined length in the direction indicated by the arrow in FIG. 5. Bearing hole 35b supports inserted rotating shaft 55 so that it can move along the longitudinal direction of the elongated hole. In other words, the axis of rotating shaft 55 supported by support plate 35 is displaceable. For example, bearing hole 35b in this embodiment is formed as an elongated hole having a predetermined length in the diagonal vertical direction.

[0059] Furthermore, support plate 36 on the opposite side facing support plate 35 is also provided with a plurality of bearing holes at positions similar to bearing holes 35a, 35b, 35c, and 35d of support plate 35. However, the bearing holes in support plate 36 that support rotating shaft 55 are not elongated holes as shown in Fig. 5, but are provided as circular holes that are slightly larger than the outer diameter of rotating shaft 55. Therefore, the axis of rotating shaft 55 supported by support plate 36 does not displace.

[0060] FIG. 6 is a diagram showing movement of the first gear 54 attached to the outside of the support plate 35. The first gear 54 attached to the outside of the support plate 35 moves in conjunction with the rotation shaft 55. FIG. 6(a) shows a state in which the first gear 54 is in a first position. This first position is a state in which the rotation shaft 55 is at one end (lower position) of the bearing hole 35b in the longitudinal direction. FIG. 6(b) shows a state in which the first gear 54 is in a second position. This second position is a state in which the rotation shaft 55 is at the other end (upper position) of the bearing hole 35b in the longitudinal direction. The first gear 54 held on the outside of the support plate 35 is movable between the first position shown in FIG. 6(a) and the second position shown in FIG. 6(b).

[0061] 7A and 7B are diagrams illustrating the displacement of the rotation shaft 55. FIG. 7A shows the orientation of the rotation shaft 55 when the first gear 54 is in the first position. When the first gear 54 is in the first position, the rotation shaft 55 is not parallel to the horizontal line H, but is tilted. In other words, when the first gear 54 is in the first position, the rotation shaft 55 is held in an orientation that is not perpendicular to the pair of support plates 35, 36.

[0062] 7(b) shows the orientation of the rotation shaft 55 when the first gear 54 is in the second position. When the first gear 54 is in the second position, the rotation shaft 55 is in a horizontal orientation parallel to the horizontal line H. In other words, when the first gear 54 is in the first position, the rotation shaft 55 is held in an orientation perpendicular to the pair of support plates 35, 36.

[0063] As described above, the power transmission mechanism 50 has a configuration that allows the first gear 54 to move between the first position and the second position. With this configuration, the power transmission mechanism 50 can prevent damage to the teeth 53a of the missing tooth gear 53 and the teeth 54a of the first gear 54.

[0064] 8(a) to 8(d) are diagrams illustrating the operation of the power transmission mechanism 50. First, as shown in Fig. 8(a), with the missing tooth gear 53 in the initial position, the power transmission mechanism 50 drives the drive gear 51 to rotate, causing the missing tooth gear 53 to rotate in the R direction. When the teeth 53a of the missing tooth gear 53 are not in contact with the teeth 54a of the first gear 54, there is no change in the first gear 54 and the second gear 56. At this time, the first gear 54 is in the first position.

[0065] As shown in FIG. 8( b), when the missing tooth gear 53 rotates, the tooth 53 a of the missing tooth gear 53 abuts against the tooth 54 a of the first gear 54, which is in the first position. That is, the tip of the tooth 53 a of the missing tooth gear 53 collides with the tip of the tooth 54 a of the first gear 54. When the tooth tips of the missing tooth gear 53 and the first gear 54 collide with each other, the rotational force of the missing tooth gear 53 is not transmitted as a force that rotates the first gear 54. When the missing tooth gear 53 rotates in the R direction with the tooth tips of the missing tooth gear 53 and the first gear 54 colliding, the rotational force of the missing tooth gear 53 is transmitted to the first gear 54 as a force F that pushes the first gear 54 up in the longitudinal direction of the bearing hole 35 b. As a result, the first gear 54 moves from the first position to the second position.

[0066] 8(c) shows a state in which the first gear 54 has moved to the second position. As the first gear 54 moves to the second position, the first gear 54 moves away from the missing tooth gear 53. Therefore, the impact caused by a collision between the missing tooth gear 53 and the first gear 54 is absorbed by the first gear 54 moving away from the missing tooth gear 53. In other words, by moving the first gear 54 from the first position to the second position, the power transmission mechanism 50 prevents damage to the teeth 53a of the missing tooth gear 53 and the teeth 54a of the first gear 54.

[0067] When the first gear 54 moves from the first position to the second position, it moves while maintaining a state of meshing with the second gear 56. In other words, when the first gear 54 moves from the first position to the second position, it moves in a direction away from the missing tooth gear 53 while maintaining a substantially constant distance from the second gear 56.

[0068] 9 is a diagram showing the movement direction of the first gear 54 in relation to the second gear 56. As shown in FIG. 9, the movement direction M of the first gear 54 is approximately perpendicular to a line L connecting the center 54c of the first gear 54 and the center 56c of the second gear 56 when the first gear 54 is in the first position. The elongated hole of the bearing hole 35b is formed along this movement direction M. By making the movement direction M of the first gear 54 approximately perpendicular to the line L connecting the center 54c of the first gear 54 and the center 56c of the second gear 56, the first gear 54 moves from the first position to the second position while maintaining meshing with the second gear 56.

[0069] Fig. 10 is a diagram showing the movement direction of the first gear 54 in relation to the missing tooth gear 53. As shown in Fig. 10, the movement direction M of the first gear 54 is set between a tangent direction L1 and a normal direction L2 of a circle at a junction P1 with the missing tooth gear 53. More preferably, as shown in Fig. 10, the movement direction M of the first gear 54 is set between the tangential direction L1 and a middle line L3 that bisects the angle between the tangential direction L1 and the normal direction L2. As a result, the first gear 54 moves appropriately from the first position to the second position as the missing tooth gear 53 rotates.

[0070] The second gear 56 is joined to the second support portion 34, and therefore a load is applied in the rotational direction. Therefore, the rotational torque of the second gear 56 is greater than the rotational torque of the first gear 54. Therefore, when the first gear 54 moves from the first position to the second position, the second gear 56 does not rotate. Furthermore, when the first gear 54 moves from the first position to the second position, the second gear 56 restricts the rotation of the first gear 54.

[0071] The first gear 54 moves from the first position to the second position while its rotation is restricted by the second gear 56. The missing tooth gear 53 rotates, but the first gear 54 does not rotate. Therefore, when the first gear 54 moves to the second position, the teeth 53a of the missing tooth gear 53 and the teeth 54a of the first gear 54 mesh with each other, as shown in FIG. 8(c). In other words, by moving away from the missing tooth gear 53, the first gear 54 properly meshes with the missing tooth gear 53 without receiving a strong impact.

[0072] When the teeth 53a of the missing tooth gear 53 and the teeth 54a of the first gear 54 mesh with each other, the power transmission mechanism 50 transmits the rotational force of the missing tooth gear 53 to the first gear 54, causing the first gear 54 to rotate. At this time, the first gear 54 rotates at the second position. When the first gear 54 is in the second position, the rotation shaft 55 is in a horizontal position. Therefore, when the first gear 54 rotates at the second position, the rotation shaft 55 rotates smoothly. Then, as shown in FIG. 8(d), the rotational force of the missing tooth gear 53 is transmitted to the second gear 56 via the first gear 54, causing the second gear 56 to rotate. As a result, the pressing portion 58 provided on the second gear 56 presses the second support portion 34, moving the second support portion 34 away from the first support portion 33. As the second support portion 34 moves away from the first support portion 33, the pressure contact state between the heating roller 31 and the pressure roller 32 is released.

[0073] Thereafter, when the heating roller 31 and the pressure roller 32 are pressed together again, the partly tooth-missing gear 53 is driven to rotate in the direction opposite to the R direction. The partly tooth-missing gear 53 then returns to the initial position shown in FIG. 8(a). When the partly tooth-missing gear 53 returns to the initial position, the teeth 53a formed on the partly tooth-missing gear 53 disengage from the first gear 54. Accordingly, the first gear 54 returns from the second position to the first position under its own weight.

[0074] 11 is a flowchart showing the procedure of drive control of the power transmission mechanism 50 by the control unit 6. For example, when the image forming apparatus 1 is in a powered state, the control unit 6 repeatedly executes the process based on FIG.

[0075] When the control unit 6 starts this process, it determines whether the image forming apparatus 1 is in a predetermined state (step S10). For example, the control unit 6 determines that the image forming apparatus 1 is in the predetermined state when execution of a print job has stopped. If it determines that the image forming apparatus 1 is in the predetermined state (YES in step S10), the control unit 6 drives the missing tooth gear 53 to rotate from its initial position in a predetermined direction (direction R shown in FIG. 8) (step S11). As a result, the missing tooth gear 53 rotates, and when the missing tooth gear 53 and the first gear 54 mesh with each other, the first gear 54 moves from the first position to the second position. Therefore, the missing tooth gear 53 and the first gear 54 mesh with each other without damaging the teeth 53a and 54a, causing the second gear 56 to rotate. As a result, the heating roller 31 and the pressure roller 32 separate, and the nip portion is opened.

[0076] Next, the control unit 6 determines whether the predetermined state has been resolved (step S12). If the predetermined state has been resolved (YES in step S12), the control unit 6 rotates the missing tooth gear 53 in the reverse direction and returns it to its initial position (step S13). This brings the heating roller 31 and the pressure roller 32 into close contact with each other at a predetermined pressure. This state means that the image forming apparatus 1 is ready to execute a print job. Therefore, for example, if a print job has been temporarily suspended due to a jam, the print job will resume after the missing tooth gear 53 returns to its initial position.

[0077] As described above, the power transmission mechanism 50 of this embodiment includes the missing-tooth gear 53, which has teeth 53a formed only on a portion of its periphery, and the first gear 54, which has multiple teeth 54a formed on its periphery. The missing-tooth gear 53 and the first gear 54 are initially in an unconnected state, i.e., not meshed with each other. The missing-tooth gear 53 is driven to rotate from its initial state, and enters a connected state in which it meshes with the first gear 54, causing the first gear 54 to rotate. The first gear 54 is movable between a first position where the tips of some of the multiple teeth 54a collide with the tips of the teeth 53a of the missing-tooth gear 53, and a second position that is farther from the missing-tooth gear 53 than the first position. Therefore, when the teeth 53a of the missing-tooth gear 53 collide with the teeth 54a of the first gear 54 while the first gear 54 is in the first position, the first gear 54 moves to the second position, thereby entering a connected state in which it properly meshes with the missing-tooth gear 53. Therefore, the power transmission mechanism 50 can rotate the first gear 54 by meshing the missing tooth gear 53 with the first gear 54 without damaging the missing tooth gear 53 and the first gear 54.

[0078] Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above embodiment. In other words, various modifications can be applied to the present invention. Below, several modifications related to the present invention will be described.

[0079] For example, in the above embodiment, when the tooth 53a formed on the missing tooth gear 53 disengages from the first gear 54 as the missing tooth gear 53 returns to its initial position, the first gear 54 returns from the second position to the first position under its own weight. That is, in the above embodiment, the bearing hole 35b that moves the first gear 54 is formed diagonally in the vertical direction, so the first gear 54 returns from the second position to the first position under its own weight. However, the bearing hole 35b is not necessarily formed in the vertical direction. Therefore, the power transmission mechanism 50 may be configured to include a biasing member that returns the first gear 54 from the second position to the first position when the tooth 53a formed on the missing tooth gear 53 disengages from the first gear 54.

[0080] FIG. 12 illustrates an example of a biasing member 60 that biases the first gear 54 toward the first position. As shown in FIGS. 12(a) and 12(b), the biasing member 60 is, for example, a torsion coil spring. One end of the spring is fixed, and the other end engages with the first gear 54 to bias the first gear 54. For example, as shown in FIG. 12(b), when the first gear 54 moves to the second position, the biasing member 60 tightens, biasing the first gear 54 toward the first position. This biasing force returns the first gear 54 from the second position shown in FIG. 12(b) to the first position shown in FIG. 12(a). Therefore, the biasing member 60 can forcibly return the first gear 54 from the second position to the first position as the teeth 53a formed on the missing-tooth gear 53 disengage from the first gear 54.

[0081] Furthermore, the power transmission mechanism 50 in the above embodiment is exemplified as including the second gear 56. However, the second gear 56 is not an essential component in the present invention.

[0082] Furthermore, in the above embodiment, the case where the power transmission mechanism 50 is mounted on the fixing device 30 of the image forming apparatus 1 has been exemplified. However, the scope to which the above-described power transmission mechanism 50 can be applied is not limited to the fixing device 30, and is not limited to the image forming apparatus 1.

[0083] Furthermore, in the above embodiment, an example has been described in which the missing tooth gear 53 and the first gear 54 are formed from PPS resin. However, in the power transmission mechanism 50 having the above-described structure, the missing tooth gear 53 and the first gear 54 may be formed from a material other than PPS resin. [Explanation of symbols]

[0084] 1. Image forming device 6 Control Unit 30 Fixing device 33 1st support part 34 Second support part 35,36 Support plate 35b Bearing hole (long hole) 45 Retaining member 50 Power transmission mechanism 53 Missing Tooth Gear 54 First Gear 56 2nd Gear 58 Pressing section 60 biasing member

Claims

1. a gear with teeth formed only on a portion of its periphery that is driven to rotate; a first gear having a plurality of teeth formed on a peripheral edge thereof, which meshes with the teeth of the missing tooth gear as the missing tooth gear rotates, and which is rotationally driven in accordance with the rotation of the missing tooth gear; Equipped with A power transmission mechanism characterized in that the first gear is configured to be movable between a first position where the tips of some of the plurality of teeth and the tips of the teeth of the missing tooth gear collide with each other, and a second position that is farther from the missing tooth gear than the first position.

2. 2. The power transmission mechanism of claim 1, wherein the first gear is in the first position in an unconnected state in which the plurality of teeth are not meshed with the teeth of the missing tooth gear, and as the missing tooth gear rotates, tips of some of the plurality of teeth collide with tips of the teeth of the missing tooth gear at the first position, and then receives the rotational force of the missing tooth gear and moves to the second position.

3. 3. The power transmission mechanism according to claim 2, wherein, as the first gear moves to the second position, some of the plurality of teeth of the first gear mesh with the teeth of the missing-tooth gear.

4. 4. The power transmission mechanism according to claim 3, wherein the first gear rotates at the second position in accordance with rotation of the missing tooth gear in the connected state.

5. a second gear provided in mesh with the first gear; Further provided with 2. The power transmission mechanism according to claim 1, wherein the first gear rotates the second gear.

6. 6. The power transmission mechanism according to claim 5, wherein a movement direction of the first gear connecting the first position and the second position is approximately perpendicular to a line connecting a center of the first gear and a center of the second gear when the first gear is at the first position.

7. 6. The power transmission mechanism according to claim 5, wherein the second gear maintains a state of meshing with the first gear regardless of whether the first gear is in the first position or the second position.

8. 6. The power transmission mechanism according to claim 5, wherein the rotational torque of the second gear is greater than the rotational torque of the first gear.

9. a rotation shaft that rotatably holds the first gear; Further provided with 2. The power transmission mechanism according to claim 1, wherein the rotating shaft is inclined from the horizontal when the first gear is in the first position, and is in a horizontal position when the first gear moves to the second position.

10. a pair of support plates supporting both ends of the rotary shaft; Further provided with 10. The power transmission mechanism according to claim 9, wherein the support plate on one end of the pair of support plates to which the first gear is attached has a long hole formed therein, which changes the rotation shaft between the inclined posture and the horizontal posture.

11. a biasing member that biases the first gear toward the first position; The power transmission mechanism according to claim 1 , further comprising:

12. 2. The power transmission mechanism according to claim 1, wherein the partly toothed gear and the first gear are made of PPS (polyphenylene sulfide) resin.

13. a first support portion that supports the heating roller; a second support portion that supports a pressure roller and is movable relative to the first support portion in a direction toward or away from the pressure roller; a holding member that holds the second support portion and the first support portion in a state where they are close to each other; a pressing portion that presses the second support portion and the first support portion in a direction separating them from each other against the holding force of the holding member; A power transmission mechanism according to any one of claims 1 to 12; Equipped with The power transmission mechanism rotates the missing tooth gear and the first gear in a connected state in which the missing tooth gear and the first gear are meshed with each other, thereby operating the pressing portion and separating the second support portion and the first support portion from each other.

14. The fixing device according to claim 13 ; a control unit that controls the power transmission mechanism; Equipped with The image forming apparatus is characterized in that the control unit drives the missing tooth gear to rotate in a predetermined state, thereby separating the second support unit and the first support unit from each other.

15. 15. The image forming apparatus according to claim 14, wherein the predetermined state is a state in which execution of a print job has stopped.

16. 15. The image forming apparatus according to claim 14, wherein the predetermined state is a state in which a jam has occurred.

Images