HK1110125B - Drive transmission mechanism and image forming device - Google Patents

Description

Drive transmission mechanism and image forming apparatus

Technical Field

The present invention relates to a drive transmission mechanism. The present invention also relates to an image forming apparatus in which an electrophotographic process unit having a shaft rotating mechanism is detachably attached to an apparatus main body. In particular, the present invention relates to a drive transmission mechanism for transmitting drive to a shaft rotation mechanism and an image forming apparatus using the drive transmission mechanism.

Background

Electrophotographic recording units are often used in image forming apparatuses. The image forming apparatus is realized as a copier, a facsimile machine, a printer, a so-called multifunction peripheral having these functions, or the like. The processing sections of the respective electrophotographic recording sections are unitized. The process unit (process cartridge) is detachably mounted on the apparatus main body. Examples of the process unit include a drum unit, a developing unit, and a unit in which both units are integrated. The drum unit unitizes the photoreceptor drum and its peripheral devices. The developing unit unitizes the developer container, the developing roller, the stirring/conveying screw, and the like. The processing unit is provided with a shaft rotating mechanism. The shaft rotation mechanism is, for example, a photosensitive drum, a developing roller, a screw for stirring and conveying the developer, or the like. The shaft rotating mechanism is rotated by receiving a driving force from a driving source in the apparatus main body. In addition, the processing unit is a consumable. Therefore, the process unit is periodically replaced and removed from the apparatus main body at the time of maintenance. Therefore, when the processing unit is mounted to the apparatus main body, a drive transmission mechanism is constructed between the drive source in the apparatus main body and the shaft rotation mechanism in the processing unit.

In addition, if the ease of attaching and detaching the processing unit is taken into consideration, the processing unit can be attached and detached horizontally along the axial direction of the shaft rotating mechanism from the side portion (including the front and rear or both side portions) of the apparatus main body. In this case, a driving member is provided on the rear side of the apparatus main body to be axially rotated by transmission of a driving force from a driving source. A driven-side member is mounted on the front side in the insertion direction of the process unit. When the process unit is inserted into the apparatus main body, the driving-side member and the driven-side member are coaxially combined. Thus, the drive is transmitted to the shaft rotating mechanism. Further, a coupling member is interposed between the driving-side member and the driven-side member so that the driving force can be transmitted therebetween even if there is an unavoidable axial displacement due to a machining tolerance or the like between the driving-side member and the driven-side member.

However, the axial misalignment between the driving member of the apparatus main body and the driven member of the processing unit occurs in 2 axial directions (in a plane perpendicular to the axis of the axis rotation mechanism, in 2 axial directions perpendicular to each other) in general. The conventional universal joint is fixed to only one of the driving member and the driven member, and thus absorbs only 1 axial displacement. In other conventional coupling mechanisms, the triangular prism-shaped protrusions twisted in the direction of rotation of the shaft are coupled to the recesses, and therefore, even if there is a 2-dimensional axial misalignment, drive can be transmitted from the driving-side member to the driven-side member. However, in the conventional coupling mechanism, in order to absorb the axial misalignment, stress deformation occurs in both the driving-side member and the driven-side member. Thus, it is predicted that the chronological rotational fatigue will occur.

In order to absorb the 2 axial displacements reasonably, it is conceivable to adopt a structure in which the coupling member is composed of a plurality of parts and the axial displacements are absorbed when the drive is transmitted from the driving-side member to the driven-side member. In this case, the number of parts increases and the number of assembly steps increases. Further, as a method of constituting the coupling member by a single member, it is possible to use a material (for example, an elastic material) which is deformable in 2 axial directions, but there is a difficulty in that the elastic material does not have strength enough to withstand a large stress to be applied.

Disclosure of Invention

According to the present invention, it is possible to transmit drive from the driving-side member to the driven-side member while reasonably absorbing 2 axial center shifts.

According to the drive transmission mechanism of the present invention, the drive side member and the driven side member for rotating the shaft are coaxially coupled with each other with the coupling member interposed therebetween, and the shaft rotation of the drive side member is transmitted to the driven side member, thereby rotating the driven side member, wherein the drive transmission direction in the coupling portion of the drive side member and the coupling member and the drive transmission direction in the coupling portion of the coupling member and the driven side member are in a mutually perpendicular relationship, a gap is formed in the coupling portion of the drive side member and the coupling member and in the coupling portion of the coupling member and the driven side member, the gap enabling the drive side member and the coupling member, and the coupling member and the driven side member to be engaged in a state allowing mutual positional displacement in a direction perpendicular to the respective drive transmission directions, and the drive transmission end portion of the drive side member is provided with a bifurcated action protrusion having a symmetrical axial center and extending in the axial direction, the driven transmission end of the coupling member includes a recess for accommodating the operation projection, and a driven portion which is in contact with the operation portion of the operation projection during rotation and is symmetrical with respect to the axial center, and a gap for allowing the positional deviation is provided between the bifurcated operation projection and an inner wall surface of the recess.

According to the present invention, even if there are 2 axial offsets on the driving side member and the driven side member, the offsets are absorbed by the gaps of the respective coupling portions. Therefore, stress deformation does not occur in the driving member and the driven member, and reasonable driving transmission is performed. Further, since such a function is realized by the engagement relationship between the 1 coupling member and the driving-side member and the driven-side member, the number of parts and the number of assembling steps are not increased. Further, since the coupling member can be made of hard resin, metal, or the like, the strength of the component can be ensured.

In this case, it is preferable that the action portion of the action projection has a convex curved surface shape, and the action portion abuts against the acted-on portion of the coupling member in a substantially line contact state along the axial direction.

According to the preferred embodiment of the present invention, the driven member can be smoothly coupled to the driving member through the coupling member. At the same time, the gap portion absorbs 1 axial misalignment in the coupling. Also, the degree of freedom of relative movement between the acting portion of the acting projection and the acted-on portion of the coupling member is increased. Further, the frictional resistance at the contact portion can be reduced, and the generation of noise during driving can be suppressed.

Preferably, the driven-side member includes a shaft body having parallel tangential surfaces at a distal end portion thereof. An elliptical recess having parallel cross-sections for receiving the front end of the shaft body is formed at the drive transmitting end of the coupling member. Preferably, the major axis direction of the elliptical recess is perpendicular to the drive transmission action direction, and a gap portion for allowing positional displacement is formed between the shaft body tip and the inner wall surface of the recess in the major axis direction. The coupling structures of the driving-side member and the coupling member, and the coupling member and the driven-side member may be in an inverse relationship to the above.

According to a preferred embodiment of the present invention, the sliding contact movement of the distal end portion of the shaft body is allowed in the elliptical recess along the major axis direction, i.e., the tangential plane. This absorbs axial positional displacement between the coupling member and the shaft body.

An image forming apparatus of the present invention is an image forming apparatus in which an electrophotographic process unit including a shaft rotating mechanism is detachably mounted to an apparatus main body along a shaft of the shaft rotating mechanism, the image forming apparatus including a drive transmission mechanism for transmitting drive from a drive source in the apparatus main body to the shaft rotating mechanism by the drive transmission mechanism when the process unit is mounted to the apparatus main body, wherein in the drive transmission mechanism, a drive side member and a driven side member which rotate in a shaft direction are coaxially coupled with each other with a coupling member interposed therebetween, and the shaft rotation of the drive side member is transmitted to the driven side member to rotate the driven side member, and a drive transmission direction in the coupling portion of the drive side member and the coupling member is orthogonal to a drive transmission direction in the coupling portion of the coupling member and the driven side member, and a drive transmission direction in the coupling portion of the drive side member and the coupling member, And a gap is formed in the coupling parts of the coupling member and the driven-side member, the gap enabling the driving-side member and the coupling member, and the coupling member and the driven-side member to be engaged with each other in a state of allowing mutual positional displacement in a direction perpendicular to the respective driving transmission operation directions, the driving transmission end part of the driving-side member is provided with a bifurcated operation protrusion having axial symmetry and extending along the axial direction, the driven transmission end part of the coupling member is provided with a recess for accommodating the operation protrusion, and an operated part which is in contact with the operation part of the operation protrusion during rotation and is symmetrical with respect to the axial center, and the gap for allowing the positional displacement is provided between the bifurcated operation protrusion and an inner wall surface of the recess.

In the present invention, the process unit may be a developing unit, and the shaft rotating mechanism may be a developing roller and/or a screw for stirring and conveying the developer. Further, the process unit may be a drum unit, the shaft rotation mechanism may be a photosensitive drum, a roller charger, a cleaning roller, or the like. Alternatively, the process unit may be an integral unit of the drum unit and the developing unit, and the shaft rotating mechanism may be the same mechanism.

According to the present invention, even if there are 2 axial misalignment in the drive side member on the apparatus main body side and the rotation mechanism on the process unit side, these 2 axial misalignment can be absorbed by the coupling member. For this reason, reasonable drive transmission can be performed. Further, the effect of facilitating the attaching and detaching operation of the processing unit by attaching and detaching the processing unit from the side portion of the apparatus main body is more effectively exhibited. In addition, it is more effective if the developing unit employs the above-described drive transmission mechanism. This is because the developing unit has a structure and functional characteristics in which a plurality of rotary mechanisms are incorporated and the rotary mechanisms are rotationally driven in a resin casing that contains developer.

Other features, elements, methods, steps, characteristics and advantages of the present invention will become more apparent from the following description of preferred embodiments of the present invention and the accompanying drawings to which the present invention relates.

Drawings

Fig. 1 is a schematic perspective view showing an example of an image forming apparatus using a drive transmission mechanism according to the present invention.

Fig. 2 is a vertical sectional view showing an example of an image forming apparatus using the drive transmission mechanism of the present invention.

Fig. 3 is a sectional view showing an example of the drive transmission mechanism according to the embodiment of the present invention, and shows a state before the drive transmission mechanism is established.

Fig. 4 is a cross-sectional view showing an example of the drive transmission mechanism according to the embodiment of the present invention, and shows a state after the drive transmission mechanism is established.

Fig. 5A is a cross-sectional view of fig. 4 taken along line X-X, and fig. 5B is a cross-sectional view taken along line Y-Y of fig. 4.

Fig. 6 is a diagram showing another embodiment of the present invention.

Detailed Description

The image forming apparatus 100 of fig. 1 and 2 is shown by way of example as a printer including an electrophotographic recording unit. The image forming apparatus 100 is not limited to this, and may be a transfer machine provided with an image reading device, a facsimile machine, or a so-called multifunction peripheral having both of these functions. In the apparatus main body 1 of the image forming apparatus 100, a recording paper feeding section 2, an electrophotographic image recording section 3, and a printed recording paper discharging section 4 are stacked in this order in the height direction. The paper feed portion 2 includes a paper feed cassette 201, a separation paper feed roller 202, and a separation pad 203. The paper feed cassette 201 can store a large number of sheets of recording paper in a stacked state and can be inserted into and removed from the apparatus main body 1. A separation paper feed roller 202 is provided at the front end portion in the paper feed direction of the paper feed cassette 201. The separation pad 203 is in elastic contact with the outer peripheral surface of the separation feed roller 202.

The image recording section 3 has a processing section and a fixing device 11 on the downstream side thereof. The processing section has a photosensitive drum 5. Around the photosensitive drum 5, a charger 6, an exposure unit 7 including an LED or the like, a developing unit 8, a transfer roller 9, and a residual toner removal device 10 are arranged in this order. These processing portions serve as processing units constituted by the drum unit 50 and the developing unit 80. The drum unit 50 removes the exposer 7 and the transfer roller 9, and collectively includes the photoreceptor drum 5, the charger 6, and the residual toner removing device 10. The developing unit 80 includes a developer container, an agitator, a developing roller, and the like. The drum unit 50 and the developing unit 80 can be attached to and detached from the apparatus main body 1 from the front side thereof, respectively, or in a state where both are coupled by some coupling means. In addition, all the processing sections except the exposure unit 7 and the transfer roller 9 can be collectively defined as a processing unit. Here, the front side of the apparatus main body 1 is the front side in the right oblique direction in fig. 1, and the rear side in the left oblique direction is the rear side. In the figure, the developing unit 80 is attached to the apparatus main body 1 from the front side. An openable and closable service door 101 is provided on the front surface of the apparatus main body 1. The maintenance door 101 is opened to allow the developer unit 80 to be inserted and mounted at a predetermined position in the apparatus main body 1. The paper feed cassette 201 can be inserted into and removed from the apparatus main body 1 from the front surface side. The mounting of the developer unit 80 will be described later.

The developing unit 80 is a developing device of a two-component developer type. A developer including toner and a carrier is accommodated in a developer housing 81 which is formed of resin and also serves as a developer container. The toner and the carrier are agitated/conveyed by 2 parallel agitating/conveying screws 82, 83. The supply paddle 84 supplies the developer to the developing roller 85 to which the bias is applied. A magnetic sensor 86 is provided outside the developer housing 81. The toner concentration (mixing ratio of toner and carrier) in the developer housing 81 is detected by the magnetic sensor 86. The toner hopper 12 is provided at a position spaced from the developer unit 80. When the magnetic sensor 86 detects a decrease in the toner concentration in the developer housing 81, the toner is replenished into the developer housing 81 via the screw conveyor (tube screw) 13. An agitator 121 and a feed screw 122 are disposed in the toner hopper 12.

A switching gate 401, a discharge roller pair 402, and a discharge tray 403 are provided downstream of the fixing device 11. The switching gate 401, the discharge roller pair 402, and the discharge tray 403 constitute the discharge portion 4. A resist roller pair 14 is disposed in the vicinity of the upstream side of the processing section. The recording sheets are separated one by one from the sheet feeding cassette 201 by the action of the separation sheet feeding roller 202 and the separation pad 203 and are sequentially fed out. The recording paper is stopped by the pair of resist rollers 14. Then, the recording paper is introduced into the mating portion between the photosensitive drum 5 and the transfer roller 9. The photoreceptor drum 5 is uniformly charged on its surface by the charger 6 while rotating in the direction indicated by the arrow in fig. 2. An optical image based on image information is irradiated onto the surface of the photosensitive drum 5 by an exposure device 7. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 5. The electrostatic latent image is formed by changing the potential of the light irradiated portion and maintaining the potential of the other portion due to the characteristics of the photoconductor on the surface of the photoconductor drum 5.

The electrostatic latent image is successively developed as a toner image by the developing unit 8 to which a bias voltage is applied. The toner image reaches the mating portion of the photosensitive drum 5 and the transfer roller 9. At the time of this development, at a portion where the potential changes due to the light irradiation, the toner is attracted to the photosensitive drum 5 due to the potential difference with the developing unit 8, and a black image is formed. In the other part, the toner is not attracted to form a white image. In this way, a black-and-white toner image based on the image information is formed. The resist roller pair 14 performs resist control and rotation control so that the recording paper is guided to the mating portion in synchronization with the toner image on the surface of the photosensitive drum 5.

The transfer roller 9 is biased. The transfer roller 9 is aligned with the photosensitive drum 5. The transfer roller 9 is rotated in the direction of the arrow (direction facing the photosensitive drum 5) and is transported while sandwiching the recording paper. During this time, the toner image on the surface of the photoreceptor drum 5 is transferred onto the recording paper. The toner remaining on the surface of the photoreceptor drum 5 is removed and collected by the residual toner removing device 10. The recording paper with the toner image transferred is introduced into the fixing device 11, and the toner image is fixed as a permanent image on the recording paper. Thereafter, the recording paper pushes up the switching gate 401, and is discharged onto the discharge tray 403 via the discharge roller pair 402. The series of feeding of the recording paper is performed along the main feeding path P as follows: after the paper feed cassette 201, the paper feed cassette stands up substantially vertically (upright), and is U-turned in the discharge roller pair 402 in a direction substantially 180 degrees from the feeding direction in order from the paper feed cassette 201. With such a design structure, the entire device can be miniaturized.

The illustrated image forming apparatus 100 has a double-sided recording function. A reverse feeding path P1 merging with the main feeding path P is arranged from the mounting position of the switching gate 401 of the main feeding path P to the upstream side of the resist roller pair 14. The discharge roller pair 402 can rotate forward and backward. Further, the pair of conveying rollers 15 and 16 is disposed on the reverse feeding path P1. In the case of double-sided recording, when a recording sheet for single-sided recording is conveyed along the main feed path P and the trailing edge of the recording sheet reaches the discharge roller pair 402, the discharge roller pair 402 is temporarily stopped to sandwich the trailing edge of the recording sheet. Next, the discharge roller pair 402 is reversed, and the recording paper is conveyed from the rear end thereof on the reverse feed path P1 by the conveying roller pairs 15, 16. The recording paper merges with the main feeding path P and reaches the resist roller pair 14. The recording paper is stopped by the resist roller pair 14 and is guided to the mating portion between the photosensitive drum 5 and the transfer roller 9. During this time, an image is recorded on the back side of the recording paper. The recording paper having been subjected to the double-sided recording is then discharged onto the discharge tray 403 along the main feeding path P in the same manner as described above.

The image forming apparatus 100 also has a manual function of recording paper. A manual feed tray 17 that can be opened and closed vertically is provided on the side of the apparatus main body 1. The manual paper feed tray 17 is closed when not in use as shown by the 2-dot chain line in fig. 2. The manual feed tray 17 can be opened and closed by holding the handle 171. A separation paper feed roller 172 and a separation pad 173 are disposed in elastic contact with the front end of the manual paper feed tray 17. Further downstream thereof, a manual feed path P2 that merges with the main feed path P is connected.

When image recording is performed using the manual feed tray 17, the manual feed tray 17 is opened by the handle 171. A recording sheet is placed on the manual feed tray 17, and the manual feed roller 172 is operated by an appropriate start operation. The recording sheets on the manual feed tray 17 are separated one by the action of the separation feed roller 172 and the separation pad 173 and are sequentially fed out. The recording paper is transported on the manual feed path P2, and merges with the main feed path P. Thereafter, the recording paper is stopped by the resist roller pair 14, guided to the mating portion between the photosensitive drum 5 and the transfer roller 9, and recorded. In the case of performing double-sided recording on a recording sheet manually fed, the recording sheet is conveyed on the reverse feeding path P1 by reversing the discharge roller pair 402. As described above, recording is performed on the back surface of the recording paper. The recording paper on which recording is completed is discharged onto a discharge tray 403 by a discharge roller pair 402.

Next, the drive transmission mechanism to the developing unit 80 will be described in detail with reference to fig. 3 to 5. Mounting boards 102 and 103 as a part of the rear side body are provided on the rear side of the apparatus main body 1. The studs 1801, 1901 are fixed to the mounting substrate 102 by screwing. The studs 1801, 1901 are attached along the axial centers L1, L2 of the shafts (shaft bodies) 831, 851 of the agitating/conveying screw 83 of the developing unit 80 and the developing roller 85, which are attached in the hollow arrow direction. Transmission gear members (driving side members) 18 and 19 are supported by the studs 1801 and 1901 so as to be rotatable about the axis. The transmission gear members 18 and 19 are used to rotationally drive the screw 83 and the developing roller 85. These transmission gear members 18 and 19 have gear portions 181 and 191. The gear portions 181, 191 mesh with idler gears 302, 303, 304, respectively. The idler gears 302, 303, and 304 are connected to an output gear 301 of a motor (drive source) 300 fixedly provided on the mounting substrate 102. In this way, a drive transmission system from the motor 300 to the transmission gear members 18, 19 is formed. The idler gears 302, 303, and 304 are supported by unillustrated studs that are mounted between the mounting boards 102 and 103 so as to be rotatable about axes. However, the number of the components is not limited to the number of the drawings, and the components are designed to be appropriate. Although not shown between the mounting boards 102 and 103, a drive transmission system for driving the shaft rotation mechanism of the other processing unit is also provided in the same manner.

The transmission gear members 18 and 19 are provided with operation projections 182 and 192 projecting from the developing unit side end (drive transmission end). The action projections 182, 192 are axially symmetrical bifurcated members. Parallel tangential surfaces 833, 853 are formed at driven-side tip portions (shaft body tip portions) 832, 852 of shafts 831, 851 of the stirring/conveying screw 83 and the developing roller 85. Coupling members 20, 21 are attached to the shaft body tip portions 832, 852 so as not to come out. The coupling members 20 and 21 have recesses 201 and 211 and acted-upon portions 202 and 212 formed at their drive-transmitted end portions. The recesses 201, 211 receive the acting protrusions 182, 192. The acted portions 202 and 212 are axisymmetrical and abut against the acting portions 1821 and 1921 of the acting projections 182 and 192 during rotation. The acted portions 202 and 212 are formed in the concave portions 201 and 211 so as to protrude from the inner peripheral wall portions thereof in the center direction. The gear members 18, 19 receive the driving force of the motor 300 and rotate in the arrow a direction as shown in fig. 5A. When the gear members 18 and 19 are coupled to the coupling members 20 and 21, the acting portions 1821 and 1921 act on the acted-on portions 202 and 212 in the direction of arrow b in the figure due to the rotation. Thus, the coupling members 20 and 21 also rotate in the same direction "a". Between the action protrusions 182, 192 and the inner wall surfaces of the recesses 201, 211, a gap D1 for allowing mutual positional displacement in a direction perpendicular to the action direction b is secured.

On the other hand, as shown in fig. 5B, recesses 203, 213 having elliptical cross-sectional shapes for accommodating shaft body tip portions 832, 852 are formed at the drive transmission end portion (the end portion on the screw 83 and the developing roller 85) of the coupling member 20. The shaft body tip portions 832 and 852 are inserted gently through the elliptical recesses 203 and 213. The parallel tangential surfaces 833, 853 formed on the outer peripheries of the shaft body tip portions 832, 852 are along the major axis direction of the elliptical recesses 203, 213. When the gear members 18 and 19 and the coupling members 20 and 21 are coupled and the drive is transmitted from the motor 300, the coupling members 20 and 21 rotate in the arrow a direction. Due to the rotation of the coupling members 20 and 21, the linear wall portions of the elliptical recesses 203 and 213 act as the acting portions 204 and 214 in the direction of the arrow c on the tangential surfaces 833 and 853. Thus, the shaft body tip portions 832 and 852 rotate in the same direction "a". The direction c in which the coupling members 20, 21 act on the shaft body distal end portions 832, 852 is perpendicular to the long axis direction of the elliptical concave portions 203, 213, and is perpendicular to the direction b in which the gear members 18, 19 act on the coupling members 20, 21. In the major axis direction of the elliptical recesses 203, 213, a gap D2 is formed between the shaft body tip portions 832, 852 and the curved inner wall surfaces thereof to allow positional displacement in a direction perpendicular to the working direction c.

The developing unit 80 is inserted into a predetermined portion of the apparatus main body 1 as indicated by an outlined arrow in fig. 1 and 3. As a result, the screw 83 and the developing roller 85, which are driven-side members, are coupled to the gear members 18 and 19, which are driving-side members, via the coupling members 20 and 21. In this way, a drive transmission mechanism for transmitting the rotational drive force of the motor 300 to the screw 83 and the developing roller 85 is established. Fig. 4 shows a state in which the drive transmission mechanism is established. The axial centers of the gear members 18 and 19 and the axial centers L1 and L2 of the screw 83 and the developing roller 85 may be slightly offset from the planes perpendicular to the axial centers L1 and L2 due to machining tolerances or the like, but this is unavoidable.

Fig. 5A and 5B show the coupling portions of the gear members 18 and 19 and the coupling members 20 and 21, and the coupling portions of the coupling members 20 and 21 and the shaft body tip portions 832 and 852, respectively. In fig. 5A and 5B, when the direction axis perpendicular to the acting direction B is defined as the x-axis and the direction axis perpendicular to the acting direction c is defined as the y-axis, the axial center shift occurs on the plane formed by the x-axis and the y-axis. When such axial displacement occurs between the axial centers of the gear members 18 and 19 and the axial centers L1 and L2 of the screw 83 and the developing roller 85 during coupling, the gear members 18 and 19 and the coupling members 20 and 21 can be moved relative to each other in the x-axis direction due to the presence of the gap D1. Thus, positional displacement in the x-axis direction can be absorbed. In the coupling relationship between the coupling members 20 and 21 and the shaft body distal end portions 832 and 852, the presence of the gap D2 allows mutual sliding contact movement in the y-axis direction. Thus, the positional shift in the y-axis direction can be absorbed. Therefore, even if the gear members 18 and 19, the screw 83, and the developing roller 85 have the axial center shift in the 2-dimensional direction as described above, the coupling members 20 and 21 absorb the composite axial center shift in the 2 axial directions. Therefore, these drive transmission couplings are performed reasonably without generating stress deformation or the like in both members. Therefore, the fatigue of the rotor does not occur with time.

Fig. 6 shows another embodiment of the present invention. That is, the cross-sectional shapes of the action portions 1821, 1921 of the action projections 182, 192 on the gear members 18, 19 are convex curved surface shapes. The acting portions 1821, 1921 are in contact with the acted-on portions 202, 212 of the coupling members 20, 21 in a substantially line contact state in the axial direction. Accordingly, the degree of freedom of relative movement between the operating portions 1821, 1921 of the operating projections 182, 192 and the operated portions 202, 212 of the coupling members 20, 21 is increased. Further, the frictional resistance at the contact portion can be reduced, and the generation of noise during driving can be effectively suppressed. Such curved surface processing may be performed on both ends of the cut surfaces 833, 853 of the shaft body tip portions 832, 852. Therefore, the frictional resistance is reduced at the sliding contact portions between the straight inner wall surfaces of the elliptical concave portions 203, 213 and the cut surfaces 833, 853. Since other configurations are the same as those of the above embodiment, the same reference numerals are given to common portions, and the description thereof will be omitted.

In the above embodiment, the gear members 18 and 19 formed with the coupling members 20 and 21 interposed therebetween, and the drive transmission mechanism of the screw 83 and the developing roller 85 have the same configuration. Accordingly, fig. 5A, 5B and 6 show the joint between the gear member 19 and the developing roller 85 in fig. 4, as well as the joint between the gear member 18 and the screw 83, in cross-sectional views taken along the X-X line and the Y-Y line. However, the configurations of both may be different without departing from the present invention. The drive transmission mechanism may be configured to transmit drive to the other screw 82, the paddle 84, or the like, with the coupling members 20 and 21 as described above interposed therebetween. Alternatively, the drive may be transmitted from the screw 83 or the developing roller 85 to the screw 82, the paddle 84, and the like through a suitable idler gear (not shown) on the opposite side of the developing unit 80. Further, a gear portion may be formed on either of the coupling members 20 and 21 to transmit drive through the gear portion. In the above embodiment, the drive transmission mechanism of the shaft rotation mechanism of the developing unit 80 was described, but the drive transmission mechanism of the present invention may be applied to the shaft rotation mechanism of the drum unit 50.

While the preferred embodiments of the present invention have been illustrated in detail, it will be apparent to those skilled in the art that the invention is capable of modification in various forms and many embodiments in addition to the specific embodiments and details set forth above. It is therefore intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.

Claims (10)

1. A drive transmission mechanism in which a drive-side member and a driven-side member that rotate by a shaft are coaxially coupled with each other with a coupling member interposed therebetween, and the shaft rotation of the drive-side member is transmitted to the driven-side member to rotate the driven-side member shaft,

the driving transmission direction of the driving side member and the coupling portion of the coupling member is perpendicular to the driving transmission direction of the coupling portion of the coupling member and the driven side member,

gaps are formed in the coupling portions of the driving-side member and the coupling member and in the coupling portions of the coupling member and the driven-side member, the gaps enabling the driving-side member and the coupling member, and the coupling member and the driven-side member to engage in a state allowing mutual positional displacement in a direction perpendicular to the respective drive transmission acting directions,

the drive transmission end of the drive side member is provided with action projections which are axially symmetrical and are bifurcated along the axial direction,

the driven transmission end of the coupling member is provided with a recess for accommodating the acting projection and a driven part which is in contact with the acting part of the acting projection during rotation and is symmetrical relative to the axis,

a gap for allowing the positional deviation is provided between the bifurcated action projection and the inner wall surface of the recess.

2. The drive transmission mechanism according to claim 1,

the action portion of the action protrusion has a convex curved surface shape, and the action portion is in contact with the acted-on portion of the coupling member along the axial direction in a substantially line contact state.

3. The drive transmission mechanism according to claim 1,

the driven member is provided with a shaft body having parallel tangential surfaces at the tip end portion,

the coupling member has an elliptical recess having parallel cross-sections at a drive transmitting end portion thereof for receiving a front end portion of the shaft body,

the elliptical recess has a major axis direction perpendicular to a drive transmission action direction at the coupling portion between the driven-side member and the coupling member, and the gap for allowing positional displacement is provided between the shaft body tip and the recess in the major axis direction.

4. The drive transmission mechanism according to claim 2,

the driven member is provided with a shaft body having parallel tangential surfaces at the tip end portion,

the coupling member has an elliptical recess having parallel cross-sections at a drive transmitting end portion thereof for receiving a front end portion of the shaft body,

the elliptical recess has a major axis direction perpendicular to a drive transmission action direction at the coupling portion between the driven-side member and the coupling member, and the gap for allowing positional displacement is provided between the shaft body tip and the recess in the major axis direction.

5. An image forming apparatus in which an electrophotographic process unit having a shaft rotating mechanism is detachably mounted on an apparatus main body along a shaft of the shaft rotating mechanism,

the image forming apparatus includes a drive transmission mechanism for transmitting drive from a drive source in the apparatus main body to the shaft rotation mechanism when the process unit is mounted to the apparatus main body,

in the above drive transmission mechanism, the drive side member and the driven side member that rotate by the shaft are coaxially coupled with each other with the coupling member interposed therebetween, and the shaft rotation of the drive side member is transmitted to the driven side member to rotate the driven side member shaft,

the driving transmission direction of the driving side member and the coupling portion of the coupling member is perpendicular to the driving transmission direction of the coupling portion of the coupling member and the driven side member,

gaps are formed in the coupling portions of the driving-side member and the coupling member and in the coupling portions of the coupling member and the driven-side member, the gaps enabling the driving-side member and the coupling member, and the coupling member and the driven-side member to engage in a state allowing mutual positional displacement in a direction perpendicular to the respective drive transmission acting directions,

the drive transmission end of the drive side member is provided with action projections which are axially symmetrical and are bifurcated along the axial direction,

the driven transmission end of the coupling member is provided with a recess for accommodating the acting projection and a driven part which is in contact with the acting part of the acting projection during rotation and is symmetrical relative to the axis,

a gap for allowing the positional deviation is provided between the bifurcated action projection and the inner wall surface of the recess.

6. The image forming apparatus according to claim 5,

the action portion of the action protrusion has a convex curved surface shape, and the action portion is in contact with the acted-on portion of the coupling member along the axial direction in a substantially line contact state.

7. The image forming apparatus according to claim 5,

the driven member is provided with a shaft body having parallel tangential surfaces at the tip end portion,

the coupling member has an elliptical recess having parallel cross-sections at a drive transmitting end portion thereof for receiving a front end portion of the shaft body,

the elliptical recess has a major axis direction perpendicular to a drive transmission action direction at the coupling portion between the driven-side member and the coupling member, and the gap for allowing positional displacement is provided between the shaft body tip and the recess in the major axis direction.

8. The image forming apparatus according to claim 6,

the driven member is provided with a shaft body having parallel tangential surfaces at the tip end portion,

the coupling member has an elliptical recess having parallel cross-sections at a drive transmitting end portion thereof for receiving a front end portion of the shaft body,

the elliptical recess has a major axis direction perpendicular to a drive transmission action direction at the coupling portion between the driven-side member and the coupling member, and the gap for allowing positional displacement is provided between the shaft body tip and the recess in the major axis direction.

9. The image forming apparatus according to claim 5,

the process unit is a developing unit, and the shaft rotating mechanism is a developing roller.

10. The image forming apparatus according to claim 5,

the processing unit is a developing unit, and the shaft rotating mechanism is a screw for stirring and conveying the developer.