Drive connection mechanism, and image forming apparatus having the drive connection mechanism

A drive connection mechanism has a sliding unit which is fixed to a drive shaft extending through the photoconductive drum, a convex coupling gear which has three coupling members fixed slidably to splines formed in the periphery of the sliding unit, a compressing spring which energizes the coupling gar, and a concave coupling gear which is provided in the drum to receive and fit the convex coupling gear. When the convex coupling gear is pressed to the concave coupling gear, a force from the tapered surface to the inside acts on each coupling member. Then, the bevel gear of the convex coupling gear is stuck to the bevel gear of the concave coupling gear, the internal gears of the convex coupling gear is stuck to the splines of the drive shaft, and the centers of the drive shaft and photoconductive drum are aligned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-193151, filed Jun. 30, 2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drive connection mechanism to connect a drive unit and a driven unit. In particular, the present invention relates to a drive connection mechanism to connect a photoconductive drum of a copier or printer and its drive shaft, and an image forming apparatus having the drive connection mechanism.

2. Description of the Related Art

In a known drive connection mechanism to connect a photoconductive drum of a copier to a drive shaft provided in a main body of a copier, a coupling gear is provided rotatably together with a drive shaft and slidably along the axial direction of the drive shaft. In the periphery of the coupling gear, outer bevel gear is formed coaxially with the drive shaft. The coupling gear is energized toward the distal end of the drive shaft by a compression spring fit to the drive shaft. At the corresponding end of the photoconductive drum, internal gears like a bevel gear are formed to engage with the external gears of the coupling gear.

Therefore, when connecting the drive shaft to the photoconductive drum, fit and push the coupling gear of the drive shaft in the internal gears of the photoconductive drum, and press the external gears of the coupling gear to the internal gears of the photoconductive drum by the restoring force of the compression spring. The external gears of the coupling gear are securely engaged with the internal gears of the photoconductive drum, the driving force of the drive shaft is transmitted to the photoconductive drum, and the photoconductive drum is driven by the drive shaft.

However, in the above-mentioned drive connection mechanism, as the coupling gear is provided slidably along the drive shaft, the coupling gear can be securely engaged with the internal gears of the photoconductive drum, but a clearance exists between the coupling gear and causes a backlash. Namely, the clearance causes a backlash when the driving force is transmitted from the drive shaft to the photoconductive drum.

To eliminate a backlash of the coupling gear to the drive shaft, the inventor of this application proposes a drive connection mechanism which divides the coupling gear having the above described form into three parts in the circumferential direction (Jpn. Pat. Appln. KOKAI Publication No. 8-87225).

The drive connection mechanism has an involute spline extending in the axial direction on the periphery of a drive shaft, and has grooves to engage with the involute spline inside each coupling gear divided into three. When three coupling gears are energized in the axial direction and pressed to the internal gears of the photoconductive drum by a compression spring, each coupling gear receives repulsion toward the drive shaft from the internal gears like a bevel gear of the photoconductive drum, and each coupling gear is pressed to the drive shaft by this repulsion. Therefore, each coupling gear is securely engages with the drive shaft, and the above-mentioned backlash can be decreased.

By using the above conventional drive connection mechanism, a backlash can be decreased and a driving force can be transmitted from the drive shaft to a photoconductive drum, but the centering of the photoconductive drum and drive shaft is insufficient, the photoconductive drum swings a little during rotation, and a satisfactory image is not formed.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide a drive connection mechanism which is configured to connect a drive unit to a driven unit without generating a backlash, enable accurate centering of the drive unit and driven unit, and transmit the rotation of the drive unit stably to the driven unit, and an image forming apparatus having the drive connection mechanism.

In order to achieve the above object, according to an embodiment of the invention, there is provided a drive connection mechanism comprising splines which are

formed parallel to each other with equal intervals, and

extended in an axial direction along the periphery of a drive shaft; a convex coupling gear which is provided with internal gears to engage with the splines, arranged rotatably together with the drive shaft through the internal gears and slidably in the axial direction of the drive shaft, provided with a first tapered surface inclined in the axial direction on an outer circumference remote from the drive shaft, the first tapered surface having a first bevel gear, and divided into several parts in the circumferential direction; an energizing member which energizes the convex coupling gear divided into several parts in the axial direction to converge the first tapered surface; and a concave coupling gear which is provided in the driven unit connected to the drive shaft, and a concave part having a second tapered surface opposite to the first tapered surface of each of the convex coupling gear divided into several parts, and has a second bevel gear to engage with the first bevel gear on the second tapered surface, wherein the first bevel gear of the convex coupling gear is stuck without a clearance to the second bevel gear of the concave coupling gear, the splines of the drive shaft are stuck without a clearance to the internal gears of the convex coupling gear, and the centers of the drive shaft and driven unit are automatically aligned, in the state that the convex coupling gear is pressed to the concave coupling gear by the force of the energizing member, and the drive shaft is connected to the driven unit.

According to another embodiment of the invention, there is provided a drive connection mechanism comprising a substantially cylindrical sliding unit which is securely provided at the proximal end of a drive shaft extending through a driven unit with the distal end held rotatably, and has splines extended in an axial direction and formed parallel to each other with equal intervals in the outer circumference; a convex coupling gear which is provided with internal gears to engage with the splines of the sliding part, arranged rotatably together with the drive shaft through the internal gears and slidably in the axial direction of the drive shaft, provided with a first tapered surface inclined in the axial direction to converge toward the distal end on an outer circumference remote from the drive shaft, the first tapered surface having a first bevel gear, and divided into several parts in the circumferential direction; an energizing member which energizes the convex coupling gear divided into several parts in the axial direction toward the driven unit; and a concave coupling gear which is provided in the driven unit, and has a concave part having a second tapered surface opposite to the first tapered surface of each of the convex coupling gear divided into several parts, and a second bevel gear to engage with the first bevel gear on the second tapered surface.

According to still another embodiment of the invention, there is provided an image forming apparatus comprising a substantially cylindrical image holding unit; a drive unit for rotating the image holding unit; an image forming means for forming an image in the periphery of the image holding unit rotated by the drive unit; a transfer means for transferring the image formed on the periphery of the image holding unit by the image forming means to a transfer medium; and a drive connection mechanism which coaxially connects the drive shaft to transfer the driving force of the drive unit to the image holding unit, wherein the drive connection mechanism has splines which are formed parallel to each other with equal intervals, and extended in an axial direction along the periphery of the drive shaft; a convex coupling gear which is provided with internal gears to engage with the splines, arranged rotatably together with the drive shaft through the internal gears and slidably in the axial direction of the drive shaft, provided with a first tapered surface inclined in the axial direction to converge toward the image holding unit on an outer circumference remote from the drive shaft, the first tapered surface having a first bevel gear, and divided into several parts in the circumferential direction; an energizing member which energizes the convex coupling gear divided into several parts in the axial direction toward the image holding unit; a concave coupling gear which is provided in the image holding unit, and has a concave part having a second tapered surface opposite to the first tapered surface of each of the convex coupling gear divided into several parts, and a second bevel gear to engage with the first bevel gear on the second tapered surface; and the first bevel gear of the convex coupling gear is stuck without a clearance to the second bevel gear of the concave coupling gear, the splines of the drive shaft are stuck without a clearance to the internal gears of the convex coupling gear, and the centers of the drive shaft and image holding unit are automatically aligned, in the state that the convex coupling gear is pressed to the concave coupling gear by the force of the energizing member, and the drive shaft is connected to the image holding unit.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be explained in detail hereinafter with reference to the accompanying drawings.

FIG. 1is a schematic diagram of an internal structure of MFP (Multi-Functional Printer)1of an intermediate transfer system as an image forming apparatus according to an embodiment of the invention.FIG. 2is a diagrammatic sketch showing a drive transmission system of a rotary drive unit described later incorporated in the MFP1ofFIG. 1.FIG. 3is a schematic perspective view showing the rotary drive unit ofFIG. 2. In the description, the invention is applied to the MFP1, but the invention may be applied to other image forming apparatus, such as an electrophotographic digital copier.

As shown inFIG. 1, in the main body of MFP1, a photoconductive drum2as an image holding unit is provided rotatably in the clockwise direction. Around the photoconductive drum2, a charging unit3, a black color developing unit4, a rotary color developing unit5, a primary transfer roller6, and a cleaning unit7are sequentially provided along the rotating direction of the drum.

The charging unit3charges the surface of the photoconductive drum2. A laser beam L emitted from a laser unit8is radiated to the surface of the photoconductive drum2through a clearance between the charging unit3and black color developing unit4. By the radiation of laser beam L, the charged surface of the photoconductive drum2is exposed, and an electrostatic latent image is formed on the surface of the photoconductive drum2.

The black color developing unit4supplies black (K) toner to the surface of the photoconductive drum2through a mug roller4a. By the supply of black toner, the electrostatic latent image on the photoconductive drum2is developed to a black visible image. A large-capacity black toner bottle9is prepared to supply the black toner to the black color developing unit4.

The color developing unit5has a yellow color developing part5Y, a magenta color developing part5M and a cyan color developing part5C, and is rotated clockwise at the position adjacent to the photoconductive drum2in the drawing. The yellow color developing part5Y has a mug roller5Yaseparable from the surface of the photoconductive drum2, and supplies yellow (Y) toner to the surface of the photoconductive drum2, when the mug roller5Yacomes in contact with the surface of the photoconductive drum2. The magenta color developing part5M has a mug roller5Maseparable from the surface of the photoconductive drum2, and supplies magenta (M) toner to the surface of the photoconductive drum2, when the mug roller5Macomes in contact with the surface of the photoconductive drum2. The cyan color developing part5C has a mug roller5Caseparable from the surface of the photoconductive drum2, and supplies cyan (C) toner to the surface of the photoconductive drum2, when the mug roller5Cacomes in contact with the surface of the photoconductive drum2.

The photoconductive drum2is rotated by one to several turns according to the number of electrostatic latent images formed on the periphery per 1 image. Whenever the photoconductive drum2is rotated, the toner of each color is supplied from the black developing unit4or color developing unit5, and the electrostatic latent image on the periphery is developed to the supplied toner color.

The primary transfer roller6is provided inside the endless conveying belt10(intermediate transfer unit) contacting the photoconductive drum2while moving, and at the position facing to the photoconductive drum2through the belt. The primary transfer roller6supplies appropriate electric charge to the rear side of the conveying belt10running in the counterclockwise direction in the drawing, and transfers a visible image of each color toner formed on the periphery of the photoconductive drum2to the surface of the conveying belt10.

The cleaning unit7cleans the surface of the photoconductive drum2after the visible image is transferred. The toner remained on the surface of the photoconductive drum2is removed by this cleaning.

The conveying belt10is wound and stretched around a drive roller11(rotary unit), a wind roller12, a driven roller13and a tension roller14, and moved in the counterclockwise direction in the drawing by rotating the drive roller11in the direction of the arrow in the drawing. The wind roller12acts to press the conveying belt10to the photoconductive drum2. The tension roller14is provided to adjust the tension of the conveying belt10.

A secondary roller20is provided at the position on the right of the conveying belt10and contacting the driven roller13through the belt in the drawing. Therefore, a paper sheet (transferred medium) supplied from a not-shown paper supply cassette to a nip between registration rollers21is fed to between the conveying belt10and secondary transfer roller20by the registration rollers21. In this time, the visible image on the conveying belt10is transferred to the paper sheet by the secondary transfer roller20. After the visible image is transferred, the paper sheet is fed to a fixing unit22. The fixing unit22heats and fuses the visible image transferred to the paper sheet, and fixes the image to the paper sheet. The paper sheet passed through the fixing unit22is ejected to an ejected paper tray24at the top of the MFP1through a guide gate23.

The secondary transfer roller20is provided separable from the conveying belt10, to come in contact with the conveying belt10only when the transfer is necessary, and separate from the conveying belt10when the transfer is unnecessary.

A cleaning unit25is provided at the left end of the conveying belt10and close to the drive roller11through the belt10in the drawing. The cleaning unit25is provided separable from the conveying belt10wound around the drive roller11, and cleans the conveying belt10when it comes in contact with the belt.

As shown inFIG. 2andFIG. 3, the rotary drive unit30is provided close to the rear side of the MFP1, and has a common drive motor31as a driving source of the photoconductive drum2and intermediate conveying belt10. The drive motor31is a servomotor with minimum vibration, a stepping motor with micro steps or a DC brush-less motor.

A motor drive gear33is provided integrally with an output shaft32of the drive motor31. The motor drive gear33engages with a belt driven gear36provided in a belt driving shaft35(drive shaft) for rotating the drive roller11, through a reduction gear mechanism34composing a multistage reduction gear train.

The multistage reduction gear mechanism34composes a first-stage reduction gear train by a first reduction gear37engaging with the motor drive gear33. A second stage intermediate reduction gear train is composed of a second reduction gear38provided coaxially with the first reduction gear37and the belt driven gear36engaging with the second reduction gear38.

A final stage third reduction gear39is provided coaxially with the belt driven gear36of the intermediate reduction gear train. The third reduction gear39directly engages with a final stage fourth reduction gear40. The final stage reduction gear train is composed as a reduction gear train for driving the photoconductive drum2.

Namely, the belt driven gear36engages with the fourth reduction gear40through the third reduction gear39, and the fourth reduction gear40is pivoted on a drum driving shaft41(drive shaft). A flywheel42is attached pivotally to the drum driving shaft41of the photoconductive drum2, and the photoconductive drum2can be rotated stably and smoothly without generating an uneven rotation by the inertial force of the flywheel42. InFIG. 2, each gear of the multistage reduction gear train composing the reduction gear mechanism34is expressed by a pitch circle indicated by a chain line.

Hereinafter, an explanation will be given on a drive connection mechanism according to an embodiment of the invention, which connects the drum driving shaft41and photoconductive drum2.FIG. 4is a sectional view of the drive connection mechanism connected with the photoconductive drum2and drum driving shaft41.FIG. 5is a perspective view of a convex connection member for connecting the photoconductive drum2and drum driving shaft41.FIG. 6shows three coupling members of the convex connection member viewed from the axial direction.

In this embodiment, the drum driving shaft41extends long and narrow from the rear side of MFP1to the front side, and penetrates through the center of the photoconductive drum2. The inserting end of the drum driving shaft41, or the front side end of the apparatus is held rotatably in the cabinet of MFP1.

As shown inFIG. 4andFIG. 5, the proximal end of the drum driving shaft41is provided with a convex connection member51of the drive connection mechanism for transmitting the rotary driving force of the drum driving shaft41to the photoconductive drum2. In other words, the convex connection member51is provided at the position acting at the rear side end of the photoconductive drum2after the drum driving shaft41is inserted into the photoconductive drum2. The convex connection member51includes a substantially cylindrical sliding unit511, and a convex coupling gear512fit slidably to the outside of the sliding unit511.

The sliding unit511is provided integrally with external gears511a(splines) extending in the axial direction, on the peripheral surface. The external gears511aare arranged parallel with equal intervals in the circumferential direction over the full length of the sliding unit511. The internal circumference diameter H1(refer toFIG. 5) of the sliding unit511is slightly smaller than the outside diameter H2(refer toFIG. 3) of the drum driving shaft41. The drum driving shaft41is pressed into the sliding unit511to fix them. Any method may be used to fix the sliding unit511to the drum driving shaft41. For example, an adhesive may be used to fix them.

The convex coupling gear512is divided into several parts in the circumferential direction. In this embodiment, the convex coupling gear512is divided into three same shape parts,512x,512yand512zas shown inFIG. 6. However, the number of dividing the convex coupling gear512is not limited to three, but may be optionally set.

Among the three same shaped coupling members, the coupling member512xhas internal gears512ain the internal circumference (the surface opposite to the sliding unit511), which are engaged with external gears511aprovided in the outer circumference of the sliding unit511. The internal gears512aextend in the same direction as the external gears511aof the sliding unit511, and have substantially the same shape as the external gears511a. Namely, the coupling member512xis rotatable as one body with the sliding unit511and slidable in the axial direction with respect to the sliding unit511, in the state that the internal gears512aare engaged with the external gears511a.

The coupling member512xhas a virtual tapered surface512bon the opposite side of the internal gears512a, or in the outer circumference remote from the drum driving shaft41. The virtual tapered surface512bis slightly inclined in the direction to converge toward the distal end of the drum driving shaft41. The virtual tapered surface512bhas a bevel gear512c(first bevel gear) consisting of gears with triangular cross sections arranged with equal intervals. Namely the bevel gear512cis slightly inclined in the direction to converge toward the distal end of the drum driving shaft41.

Three coupling members512a,512yand512zhave a certain clearance in the circumferential direction, in the state that they are stuck to the sliding unit511as shown inFIG. 4. Concretely, as described later in detail, comparing with a non-divided coupling gear612shown inFIG. 11(actually, a non-divided gear is not used), the convex coupling gear512of this embodiment divided into three parts lacks one bevel gear (total 3 gears) in the clearance between the divided three parts.

More concretely, as shown inFIG. 6, each of the three coupling members512x,512yand512zhas the same number of internal gear512ain the inner circumference, and the same number of bevel gear512cin the outside tapered surface512b. In this embodiment, each of the coupling members512x,512yand512zhas ten internal gears512aand fourteen bevel gears512c.

When making the coupling members512x,512yand512zout of metal, they can be formed by sintering by using the same mold. When using resin for forming the coupling members512x,512yand512z, a common mold for injection molding can be used. The manufacturing cost can be decreased by making the divided coupling members in the same shape, and by using a common mold.

Back toFIG. 4, an e-ring44is fit to the drum driving shaft41as a stopper to control movement of the convex coupling gear512in the axial direction. The e-ring44controls the movement of the coupling member in the axial direction by contacting the end portions remote from the flywheel42of the three coupling members512x,512yand512zpressed by a compression spring52(en energizing member) described later toward the end of the axial direction.

The photoconductive drum2functioning as a driven unit of the invention includes a cylindrical photosensitive member2amade by forming photosensitive material on an aluminum roller surface, and flanges2band2cwhich are provided at both ends of the photosensitive member2aand hold the photosensitive member2asubstantially in a cylindrical form. At the central portion of one flange2bpositioned at the proximal end of the drum driving shaft41, a concave part which engages with the convex coupling gear512provided in the drum driving shaft41, that is, a concave coupling gear201is provided. The concave coupling gear201forms a drive connection mechanism, incorporating with the sliding unit511and convex coupling gear512.

The concave coupling gear201has a virtual tapered surface202opposite to the virtual tapered surface512bof the convex coupling gear512. The tapered surface202has a bevel gear202ato engage with the bevel gear512cof the convex coupling gear512. In this embodiment, the bevel gear202ahas substantially the same shape as the bevel gear512cof the convex coupling gear512, and the two bevel gears are stuck to each other when arranged in the state shown inFIG. 4.

An e-ring43is fit to the drum driving shaft41as a stopper to lock the proximal end of the compression spring52. In other words, the e-ring43is provided between the sliding unit511and flywheel42, and the compression spring52is provided between the e-ring43and convex coupling gear512. Therefore, the proximal end of the compression spring52is controlled by the e-ring43, and the compression spring52functions to press the convex coupling gear512to the concave coupling gear201of the photoconductive drum2.

Therefore, as shown inFIG. 4, by penetrating the drum driving shaft41through the center of the photoconductive drum2, holding the distal end of the shaft rotatably in the cabinet of MFP1, and fitting the convex coupling gear512of the drum driving shaft41into the concave coupling gear202provided in the flange2bof the photoconductive drum2, three coupling members512x,512yand512zprovided slidably to the sliding unit511are pressed by the compression spring52upward (front side) in the drawing toward the concave coupling gear201. In this time, a force directing inward the drum driving shaft41from the tapered surface202of the concave coupling gear (in the direction of the arrow in the drawing) acts on each of the divided coupling members512x,512yand512z, and the coupling members512x,512yand512zare pressed inward toward the sliding unit511.

The bevel gears512cof the three coupling members512x,512yand512zare stuck to and engaged with the bevel gear202aof the concave coupling gear201, and the internal gears512aof the coupling members512x,512yand512zare stuck to and engaged with the external gears511aof the sliding unit511.

Therefore, the driving force from the drum driving shaft41can be surely and stably transmitted to the photoconductive drum2through the convex connection member51and concave coupling gear201(i.e., the drive connection mechanism). Namely, by adopting the drive connection mechanism of this embodiment, a backlash is eliminated almost completely, a vibration of the photoconductive drum2during rotation of the drum is decreased, and a jitter in a copy image is prevented.

Particularly, according to the drive connection mechanism of this embodiment, the bevel gear202aof the concave coupling gear201has substantially the same shape as the bevel gear512cof the convex coupling gear512, and the internal gears512aof the convex coupling gear512have substantially the same shape as the external gears511aof the sliding unit511. Therefore, the centers of the drum driving shaft41and photoconductive drum2can be automatically aligned, by sticking the coupling members512x,512yand512zto the concave coupling gear201and sliding unit511as described above.

Use of the drive connection mechanism of this embodiment prevents a troublesome vibration of the photoconductive drum2caused by deviation of the center of the drum driving shaft41from the center of the photoconductive drum2during rotation of the drum, and forms a good image.

As described above, the sliding unit511is securely fixed to the drum driving shaft41by press-fitting, and the power from the drum driving shaft41can be surely transmitted to the photoconductive drum2. Particularly, the sliding unit511is formed to the necessary length by using the material different from the drum driving shaft41, and the spline511acan be easily machined, and the apparatus can be configured at a low price.

Contrarily, when providing spline511afor sliding the coupling members512x,512yand512zwith respect to the drum driving shaft41by carving directly in the drum driving shaft41, it is necessary to form the spline511aover the full length of the drum driving shaft41. This is difficult, and increases the manufacturing cost. To decrease the cost, it is considerable to use a mold for forming the drum driving shaft41having the spline511aover the full length. However, in this case, engagement with the coupling members512x,512yand512zmay become worse.

Therefore, according to this embodiment, prepare the sliding unit511capable of slidably mounting the coupling members512x,512yand512zas a member different from the drum driving shaft41, and fix it securely to the drum driving shaft41by press-fitting. The manufacturing labor and cost can be decreased thus, and the driving force of the motor can be stably and securely transmitted to the photoconductive drum2.

The drum driving shaft41is fixed to the sliding unit by press-fitting, but other common fixing methods such as bonding, welding and screw-fitting may be used.

Next, an explanation will be given on a structure to prevent swinging of the convex coupling gear512with reference toFIG. 7andFIG. 8.FIG. 7is a perspective view of the convex coupling gear512provided with a swing prevention structure.FIG. 8shows the convex coupling gear512viewed from the axial direction.

The convex coupling gear512has projections501at the end-faces of the divided coupling members512x,512yand512zopposite to each other. The projections501are provided at the position to permit interference with each other at the opposite end-faces of the divided coupling members512x,512yand512z. The height of the projections501is set to the level that the coupling members512x,512yand512zdo not come in contact with each other in the normal state stuck closely to the sliding unit511.

The projections501control the coupling members512x,512yand512zmoving in the circumferential direction when the photoconductive drum2is coupled to the drum driving shaft41. More precisely, once the projections501contact at their distal ends as the coupling members512x,512yand512zmove in the circumferential direction, the coupling members512x,512yand512zcan no longer move at all.

Even if the coupling members512x,512yand512zswing while the photoconductive drum2is being coupled to the drum-driving shaft41, the swing can be minimized. The coupling members512x,512yand512zcan therefore easily mesh with the concave coupling gear201.

Suppose the coupling members512x,512yand512zhave no projections501. Then, they are much spaced from one another and can move for a relatively long distant in the circumferential direction. They inevitably swing in the circumferential direction. If the swing increases to some extend, the coupling members can hardly mesh with the concave coupling gear201. This is why the projections501should be provided on the opposing ends of the coupling members512x,512yand512z.

Next, an explanation will be given on another characteristic structure of the coupling members512x,512yand512zof this embodiment with reference toFIG. 9andFIG. 10.FIG. 9is a perspective view of one representative coupling member512x.FIG. 10is a sectional view of the coupling member along the axial direction. The other coupling members512yand512zhave the same characteristic structure.

The coupling member512xaccording to this embodiment has two large-diameter portions502and503(staged portion) having no internal gears512aat both ends in the axial direction. These large-diameter portions502and503do not interfere with the spline511aof the sliding unit511, and act as follows.

When two e-rings43and44explained inFIG. 4are fit to the drum driving shaft41, the e-rings may contact and damage the part near the end portion in the axial direction of the sliding unit511. In this case, a burr may be generated in the spline511aformed in the periphery of the sliding unit511, affecting the slidability with respect to the coupling members512x,512yand512z. Namely, the internal gears512aof the coupling members512x,512yand512zare easily get caught by the spline511ain the part close to the end portion in the axial direction of the sliding unit511.

Therefore, in this embodiment, large-diameter portions502and503are formed at both ends of the coupling members512x,512yand512z, so that the internal gears of the coupling members512x,512yand512zdo not contact the part close to both ends of the axial direction where there is a high possibility of damaging the spline511. This prevents deterioration of the slidability in all movable ranges of the coupling members512x,512yand512z.

Next, a first modification of the convex coupling gear512will be explained with reference toFIG. 11toFIG. 13.FIG. 11shows a virtual coupling gear612not divided in the circumferential direction, viewed from the axial direction.FIG. 12shows a coupling gear512′ according to a first modification, viewed from the axial direction.FIG. 13is a partially magnified view of the characteristic part of the coupling gear512′ ofFIG. 12.

Unlike the convex coupling gear512, the convex coupling gear512′ has an involute spline or square spline in the internal circumference, instead of the internal gears512a. For example, as shown inFIG. 12, the coupling gear512′ of this modification is composed of three coupling members612x,612yand612zhaving an involute spline612ain the internal circumference. In this case, the sliding unit511to be fit in the coupling members612x,612yand612zneed to have an involute spline corresponding to the involute spline612ain the outer circumference.

The coupling members612x,612yand612zcan be obtained by machining the shape of the virtual non-divided coupling gear612, as shown inFIG. 11. The virtual coupling gear612mentioned here is not actually manufactured and used, but referred to for the explanation convenience.

The virtual coupling gear612has a bevel gear612jof the quantity of an integer multiple of the number of dividing the gear (hereinafter called a dividing number), and internal gears612kof the quantity of an integer multiple of the dividing number. In other words, the quantity of dividing the virtual non-divided convex coupling gear612as shown inFIG. 11is a common divisor of the numbers of teeth of the bevel gear612jand internal gears612k.

The coupling gear512′ of this modification is divided into three parts, and the virtual convex coupling gear612before dividing has 36 bevel gears612jand 15 internal gears612k, for example. By setting the numbers of teeth of the bevel gear612jand internal gears612kto an integer multiple of the dividing number, the convex coupling gear512′ can be composed of the same shape coupling members612x,612yand612z. This permits use of a common mold for manufacturing the coupling members612x,612yand612z, and decreases the manufacturing cost.

Further, the bevel gear612jand internal gears612kof the coupling members612x,612yand612zcan be retained in the complete form. Namely, the teeth formed in the involute spline612ainside the coupling members612x,612yand612z, and virtual tapered surface612bare divided at the groove between the teeth without missing in the halfway of the teeth.

In other words, in the virtual convex coupling gear612inFIG. 11, one tooth of the bevel gear612jand internal gears612kare removed at the divided portion as indicated by the broken line inFIG. 12, and the complete form is retained without missing a tooth at the divided end portion.

In this case, as shown inFIG. 12, the number of teeth of the bevel gear612jand internal gears612kare identical to the dividing number, and the intersection of the virtual line K passing through the divided position coincides with the center point of the coupling members612x,612yand612z(i.e., the center point P of the non-divided virtual convex coupling gear612).

As shown inFIG. 13, the following relationship is established between the tooth bottom size Q1of one bevel gear612jand the tooth bottom size Q2of one internal gears612k. Assuming that the tooth bottom sizes of two internal gears612kare Q3(Q2×2), Q3>Q1>Q2is established. As shown inFIG. 13, the tooth bottom size is the arc length connecting the concave bottoms of adjacent teeth in a virtual circle around the central point P of the coupling members612x,612yand612z. The tooth bottom size is established when replaced by a circle pitch (refer to JIS (Japanese Industrial Standard) B1603). It is also established that circle pitch of two internal gears612k>circle pitch of one bevel gear612j>circle pitch of one internal gear612k.

Therefore, the coupling members612x,612yand612zcan have a perfect gear form in the involute spline612aand tapered part612b, as shown inFIG. 12. The stress applied to the bevel gear612jand internal gears612kcan be evenly dispersed, and the strength of the coupling members612x,612yand612zcan be ensured.

FIG. 14shows a second modification of the convex gear512according to this embodiment. In this coupling gear712, two coupling members612xand612yout of three coupling members612x,612yand612zof the first modification coupling gear512′ are not divided, but combined in one body. Namely, this convex coupling gear712has a coupling member712xcombining two coupling members612xand612y, and a coupling member712y.

By forming some coupling members to be divided as one body as described above, the number of parts is decreased, the manufacturing process is simplified, and the manufacturing cost is decreased.

Further, in the above-mentioned embodiment, one compression spring52shown inFIG. 4is used as an energizing member to press the convex coupling gear512to the concave coupling gear201. The number of compressing spring is not limited to one. For example, as shown inFIG. 15, three compression springs800may be provided to press independently the coupling members512x,512yand512z. In this case, at the proximal ends of the pressing direction of the coupling members512x,512yand512z, projected bar-shaped guide members515x,515yand515zare provided.

The coupling members512x,512yand512zused in this embodiment have a module 0.5, transition coefficient 0.4 and pressure angle 20°, and number of teeth15(refer to JIS (Japanese Industrial Standard) B1603).

Explanation will now be given on an embodiment using the drive connection mechanism of the invention in another part of MFP1. An explanation will be given on an embodiment using the drive connection mechanism in a connection part of the drive roller11of the conveying belt10with reference toFIG. 3andFIG. 16.FIG. 16is a partially magnified view of a connection part for connecting the belt driving shaft35and drive roller11.

As shown inFIG. 3andFIG. 16, the belt driving shaft35is provided with a convex connection member52having substantially the same structure as the convex connection member51. At one end of a rotation shaft11aof the drive roller11, a concave connection member53to be connected with the convex connection member52is provided.

The belt driving shaft35is securely provided with sliding unit521as in the above described embodiment. A convex coupling gear522is slidably fit to the sliding unit521. The convex coupling gear522is composed of coupling members522x,522yand522z(three in this embodiment). Each of the coupling members522x,522yand522zhas a virtual tapered surface522aon the outside. The tapered surface522ais provided with bevel gear522bwith equal internals.

A compression spring54is fit to the belt driving shaft35as an energizing member to press the coupling members522x,522yand522ztoward the concave connection member54. Though not shown in the drawing, the coupling members522x,522yand522zare configured not to come off the sliding unit35even if pressed by the compression spring54.

The rotation shaft11aof the drive roller11is provided with the concave connection member (concave coupling gear)53. The concave coupling gear53has a tapered surface53ain the internal circumference, opposite to the tapered surface522aof the convex coupling gear522. On the tapered surface53a, bevel gear53bare provided to engage with the bevel gear522bformed on the tapered surface522aof the convex coupling gear522. Namely, the coupling members522x,522yand522zare stuck to the concave coupling gear53, in the state that the bevel gear522band bevel gear53bare engaged.

By sticking the tapered surface522aof the convex coupling gear522to the tapered surface53aof the concave coupling gear53and fitting the convex coupling gear522to the concave coupling gear53, the shaft center11bof rotation shaft11aof the drive roller11is automatically aligned with the shaft center35aof the belt driving shaft35. Namely, as in the above described embodiment, the centers of the belt driving shaft35and drive roller11are automatically aligned by adopting the drive connection mechanism.

By pressing the convex coupling gear522into the concave coupling gear53by the compression spring54, repulsion toward inside is acted on the coupling members522a,522yand522z. Namely, the coupling members522a,522yand522zare pressed to the center of the belt driving shaft35.

Then, the bevel gear522bof the convex coupling gear522are securely engaged with the bevel gear53bof the concave coupling gear53provided in the drive roller11, the coupling members522a,522yand522zare pressed to the center of the belt driving shaft35by the repulsion between the tapered surfaces522aand53a, and the clearance between the coupling members522a,522yand522zand the sliding unit521is filled.

Therefore, the centers of the drive roller11and belt driving shaft35are automatically aligned. Further, by adopting the drive connection mechanism of this embodiment, the driving force from the belt driving shaft35is stably and securely transmitted to the drive roller11through the convex connection member54and concave coupling gear53, a vibration generated in the drive roller11during the rotation of the drive roller is decreased, and a jitter does not occur in a copy image.

As described above, a backlash is eliminated not only from the photoconductive drum2, but also from the connection part in the drive roller11, a color matching accuracy is increased, and a jitter and color shift caused by deviation of the drive roller11are prevented in a toner transfer image that is overlaid on the conveying belt10.

For example, in the example described hereinbefore, the invention is applied to a part for connecting a photoconductive drum and drive shaft, and a part for connecting a drive roller of a conveying belt to a drive shaft. The invention may be applied to any other drive transmission systems.

In a color copier having photoconductive drums for each color (cyan, magenta, yellow and black), the drive connection mechanism of the described embodiment can be used for the photoconductive drum for each color.

The drive connection mechanism of the invention may be used for a drive roller, which transmits power to a conveying belt to convey a transfer medium (paper) to transfer a developer image from a photoconductive drum.

Further, the drive connection mechanism may be used for a drive roller of a belt type transfer unit.

In any case, by using the drive connection mechanism according to the embodiment of the invention for a drive connection mechanism in a developer image transfer process, a jitter and color shift in a copy image can be decreased, and a good image can be formed.