Patent ID: 12248270

DESCRIPTION OF THE EMBODIMENTS

An image forming apparatus according to the present invention will be described in detail with reference to the drawings.

Example 1

FIGS.1and2are a schematic cross-sectional view and a schematic enlarged cross-sectional view of an image forming apparatus1according to Example 1 of the present invention. The image forming apparatus1of Example 1 is a monochrome laser beam printer that can form a monochrome image using an electrophotographic system. InFIGS.1and2, the front-back direction of the image forming apparatus1is the X direction, the width direction (width direction of the recording material S) is the Y direction, and the height direction (vertical direction when the image forming apparatus1is installed on a horizontal plane) is the Z direction. The right side ofFIGS.1and2is the front surface of the image forming apparatus1, and the left side thereof is the rear surface. The direction from the rear surface to the front surface of the image forming apparatus1is the +X direction, and the direction from the left to the right of the image forming apparatus1viewed from the front surface thereof (direction from this side to the other side of the paper) is the +Y direction, and the direction from the bottom to the top of the paper is the +Z direction.FIGS.1and2are diagrams of the image forming apparatus1viewed from the left side in the +Y direction.

The image forming apparatus1includes a drum type electrophotographic photosensitive member (hereafter photosensitive drum3) as an image bearing member. The photosensitive drum3is constituted of a cylinder-shaped drum body made of aluminum, nickel, or the like, on which a layer of photosensitive material, such as an organic photoconductor (OPC), amorphous selenium, and amorphous silicon, is formed. The photosensitive drum3is rotary-driven by a driving source at a predetermined speed. Around the photosensitive drum3, a charging roller4(charging member), a developing roller5(developing member) and a transfer roller6(transfer member) are disposed sequentially in the rotating direction. A scanner unit7(exposure apparatus) is disposed above the photosensitive drum3. The image forming apparatus1includes an apparatus main unit1A, and a process cartridge8that is detachable from the apparatus main unit1A. The photosensitive drum3, the charging roller4and the developing roller5are included inside the process cartridge8.

The image forming apparatus1also includes, in order along the transporting path of a recording material S, a cassette paper feeding unit9which loads recording materials S which are recording media (e.g. paper), a paper feeding roller10, a transporting roller11, a resist roller12, a fixing apparatus13, a discharging roller14and a paper delivery tray15.

An operation of the image forming apparatus1will be described. The photosensitive drum3is exposed by the scanner unit7at an exposure position P1. The photosensitive drum3, which is rotary-driven by the driving source, is uniformly charged to have a predetermined polarity and a predetermined potential by the charging roller4. The photosensitive drum3after charging is exposed by the scanner unit7at the exposure position P1 based on the image information, whereby an electrostatic latent image is formed on the photosensitive drum3. The electrostatic latent image is developed by the developing roller5, and is visualized as a developer image (toner image). The toner image on the photosensitive drum3is transferred to the recording material S (transfer target material) by the transfer roller6at a transfer position P2. The image forming apparatus1may transfer the toner image on the photosensitive drum3to the recording material S via an intermediate transfer material. In this case, the toner image on the photosensitive drum3is transferred to the intermediate transfer material (transfer target material) at the transfer position P2.

The recording material S is transported by the paper feeding roller10in the X direction from the cassette paper feeding unit9where the recording materials S are loaded and stored. The recording material S is transported to a transfer nip portion, which is formed by the transfer roller6and the photosensitive drum3, by way of the transporting roller11and the resist roller12. The toner image, which was transferred from the photosensitive drum3to the recording material S at the transfer nip portion, is heated and fixed by the fixing apparatus13. The recording material S, which passed the fixing apparatus13, is discharged onto the paper delivery tray15in the X direction via the discharging roller14.

A driving unit of the process cartridge8will be described.FIG.3is a side view of the image forming apparatus1, when the image forming apparatus1is viewed from the right side in the −Y direction. As illustrated inFIG.3, the process cartridge8has a first driving input unit16and a second driving input unit17.

The first driving input unit16of the process cartridge8receives power from a driving motor21, which is a driving source (describe later), and drives the photosensitive drum3of the process cartridge8. The photosensitive drum3is an example of a driven member, which is rotary-driven by power transmitted from the driving source.

The second driving input unit17of the process cartridge8is a driving input unit to drive the developing roller5of the process cartridge8, and is disposed separately from the driving input unit of the photosensitive drum3.

In the present embodiment, in the print operation (image forming operation), the photosensitive drum3is rotary-driven from the start to the end of transporting the recording material S. The developing roller5, on the other hand, is rotary-driven only during the developing period by a later mentioned developing switching mechanism50receiving the switching operation force from a developing contact/separation mechanism (not illustrated). Thereby toner consumption can be suppressed and life of a developing roller constituting the developing roller5can be extended.

Each of the first driving input unit16and the second driving input unit17has a triangular coupling shape in order to transmit power. A different coupling shape may be used as long as the power can be transmitted, or power may be transmitted using a gear.

Now a gear train of the driving unit20, to drive the process cartridge8, will be described. The image forming apparatus1includes a pinion gear22(first gear) disposed on an output shaft of the driving motor21(driving source), a branching gear23(second gear) which engages with the pinion gear22, and a first driving input gear24which engages with the branching gear23. The branching gear23engages with a later mentioned gear teeth portion22aof the pinion gear22, and is driven by the pinion gear22. In the present embodiment, the first driving input gear24is disposed coaxially with the rotational axis of the photosensitive drum3(driven member). This means that the image forming apparatus1has a gear train constituted of at least one gear, to transmit power from the pinion gear22to the first driving input gear24.

In Example 1, a coupling shape, matching with the first driving input unit16of the process cartridge8, is formed at the tip of the first driving input gear24, so that the photosensitive drum3can be rotary-driven by the power transmission via the coupling shape. The branching gear23transmits the power of the driving motor21to an idler gear25. This power is transmitted to a second driving input gear26via a developing switching mechanism (developing clutch)50. A coupling shape, matching with the second driving input unit17of the process cartridge8, is formed at the tip of the second driving input gear26, so that the developing roller5can be rotary-driven by the power transmission via the coupling shape. In other words, the pinion gear22and the branching gear23are configured to drive the photosensitive drum3and the developing roller5.

A number of gear teeth of the driving unit20will be described next. As illustrated inFIG.2, the photosensitive drum3of the image forming apparatus1of Example 1 rotates in a rotation direction R, from an exposure position P1 where the laser light18enters from the scanner unit7. Here a drum rotation angle Θ, from the exposure position P1 to a transfer position P2 where the toner image is transferred to the recording material S, is assumed to be 151°. Generally the drum rotation angle Θ is not exactly 180°, but is slightly shifted because of such reasons as preventing reflection of incident light, the position of the scanner unit7, and process factors.

In order to transfer a high quality image without image distortion to a recording material S, it is preferable to suppress influence of rotation irregularity, when the photosensitive drum3rotates from the exposure position P1 to the transfer position P2, to transfer a toner image. The rotation irregularity in one cycle of the pinion gear22is influenced not only by gear accuracy, but also by axial runout of the driving motor21, and rotation irregularity of the driving motor21. In Example 1, influence of rotation irregularity caused by driving transmission is cancelled by performing driving transmission to the photosensitive drum3as follows.

In Example 1, the drum rotation angle Θ, when the photosensitive drum3rotates from the exposure position P1 to the transfer position P2, is set to 151°. Then a deceleration ratio is determined such that the branching gear23(a gear constituting the gear train engaged with the first driving input gear24) and the pinion gear22(the first gear) rotate an integral number of times while the photosensitive drum3and the first driving input gear24rotate by angle Θ. In other words, when the drum rotation angle is Θ and a number of teeth of the first driving input gear24is Z1, a number of teeth Z2, for the branching gear23to rotate n times, is Z2=Z1 (Θ/360n).

In the case of Example 1, a number of teeth Z1 of the first driving input gear24is 129, hence a number of teeth Z2 of the branching gear23becomes Z2=129 (151/360)=54.11, and the branching gear23rotates once when the number of teeth is 54. In the same manner, a number of teeth Z3 of the pinion gear22becomes Z3=129 (151/(360×3))=18.04, and the pinion gear22rotates 3 times when the number of teeth is 18. As a result, even if rotation irregularity is generated in the branching gear23or in the pinion gear22due to gear accuracy problem or the like, the rotation irregularity becomes the same at the exposure position P1 and the transfer position P2. Therefore influence of the rotation irregularity is cancelled in the image transferred onto the recording material S, and a high quality image without image distortion can be acquired.

Now the driving motor21and the pinion gear22will be described in detail.FIGS.4A and4Bare perspective views of the driving motor21and the pinion gear22.FIG.4Aindicates a state where the pinion gear22is mounted on the motor shaft21a, andFIG.4Bindicates a state where the pinion gear22is detached from the motor shaft21a.FIG.5Ais a cross-sectional view of the driving motor21and the pinion gear22sectioned at a plane which is perpendicular to the central axis line of a later mentioned parallel pin hole21hand includes the rotational axis of the motor shaft21a.FIG.5Bis a cross-sectional view of the pinion gear22and a parallel pin27sectioned at a plane indicated by the AA line inFIG.5A. The direction of the rotational axis of the motor shaft21ais called the axis line direction.

The driving motor21includes the motor shaft21a, which is an output shaft to output power transmitted to the photosensitive drum3. The material of the motor shaft21ais preferably metal. The pinion gear22(first gear) is disposed on the motor shaft21a. The motor shaft21aincludes a first shaft diameter portion21b, which is a large diameter portion having a first outer diameter, a second shaft diameter portion21c, which is a small diameter portion having a second outer diameter that is smaller than the first outer diameter, and a third shaft diameter portion21d, which has a third outer diameter that is smaller than the second outer diameter.

The first shaft diameter portion21b(large diameter portion) includes the parallel pin hole21h, which is a through hole penetrating the motor shaft21ain the direction intersecting with (perpendicular to) the rotational axis of the motor shaft21a. The parallel pin27is inserted into the parallel pin hole21hso as to protrude from the parallel pin hole21h. In Example 1, the parallel pin27, which is longer than the length of the parallel pin hole21h, is inserted into the parallel pin hole21h, but the parallel pin27, which is shorter than the parallel pin hole21h, may be inserted so as to protrude from one edge of the parallel pin hole21h. In this case, another parallel pin27, which protrudes from the other edge of the parallel pin hole21h, may be inserted. Instead of the parallel pin, a spring pin or a pin having a polygonal cross-section may be used.

The second shaft diameter portion21cis disposed at a position corresponding to the gear teeth portion22aof the pinion gear22in the axis line direction of the motor shaft21a, and supports the pinion gear22. An E-ring28is disposed in the third shaft diameter portion21d, so that the pinion gear22does not come off in the motor shaft21adirection. The radius of the corner portion at the boundary of the first shaft diameter portion21band the second shaft diameter portion21cincreases along the axis line in the direction from the second shaft diameter portion21cto the first shaft diameter portion21b. Specifically, in the corner portion at the boundary of the first shaft diameter portion21band the second shaft diameter portion21c, a corner R shape21e, of which diameter increases in the direction from the second shaft diameter portion21cto the first shaft diameter portion21b, is disposed. The corner R shape21ecan prevent the stress concentration of radial load F1 due to the later mentioned driving transmission, and enhance the strength of the motor shaft21a.

The motor shaft21ais held via a bearing21g, which is a bearing to rotatably support the motor shaft21a, and can rotate with respect to a mounting metal plate21f, to mount the driving motor21on the apparatus main unit1A of the image forming apparatus1. In Example 1, the outer diameter of the portion of the motor shaft21asupported by the bearing21gis the same as the outer diameter (first outer diameter) of the first shaft diameter portion21bwhich is the large diameter portion.

The pinion gear22has a first portion (large inner diameter portion)22b1which includes a first opening22c1having a first diameter, a second portion (small inner diameter portion)22b2which includes a second opening22c2having a second diameter which is smaller than the first diameter, and a contact surface22ewhich is in contact with the E-ring28. In other words, the first portion22b1of the pinion gear22may be called a first cylindrical portion having a cylindrical shape of which inner diameter is the first diameter, and the second portion22b2may be called a second cylindrical portion having a cylindrical shape of which inner diameter is the second diameter. The first portion22b1and the second portion22b2are disposed in positions shafted from each other in the axis line direction of the motor shaft21a, and the first portion22b1is closer to the motor main unit21mof the driving motor21than the second portion22b2. The motor main unit21mhouses a rotor, a stator and the bearing21g. The length of the first portion22b1is shorter than the length of the second portion22b2in the axis line direction of the motor shaft21a.

The pinion gear22is mounted on the motor shaft21asuch that the first shaft diameter portion21bis inserted into the first opening22c1and the second shaft diameter portion21cis inserted into the second opening22c2. In Example 1, the first diameter of the first opening22c1is larger than the first outer diameter of the first shaft diameter portion21b, and a gap exists between the inner peripheral surface of the first portion22b1constituting the first opening22c1and the first shaft diameter portion21b. Specifically, the diameter of the first opening22c1is 6.4 mm, and the outer diameter of the first shaft diameter portion21bis 6 mm.

The first portion22b1is located at a position corresponding to the first shaft diameter portion21bof the motor shaft21ain the axis line direction, and includes, on the inner periphery side: the first opening22c1; and a parallel pin receiving portion22d, which is an engaging portion to be engaged with the parallel pin27protruding from the parallel pin hole21h. In Example 1, the parallel pin receiving portion22dis a depressed portion. By the parallel pin27fitting with the parallel pin hole21h, rotation of the pinion gear22around the rotational axis of the motor shaft21ais restricted. When the parallel pin receiving portion22dcontacts with the parallel pin27, the rotational driving force is transmitted from the parallel pin27to the gear teeth portion22a, which is disposed on the outer peripheral surface of the second portion22b2.

In other words, the image forming apparatus1includes a rotation restricting portion which is disposed at a position corresponding to the first shaft diameter portion21bin the axis line direction, and restricts rotation of the pinion gear22with respect to the motor shaft21a. Thereby power is transmitted from the motor shaft21ato the pinion gear22. At least a part of the first shaft diameter portion21bfunctions as the rotation restricting portion. In Example 1, the rotation restricting portion includes the parallel pin hole21hand the parallel pin27. By disposing the rotation restricting portion at a position corresponding to the first shaft diameter portion21bin the axis line direction, the force for driving the branching gear23and the reaction force received from the branching gear23act on the first shaft diameter portion21b, which is thicker than the second shaft diameter portion21c. Therefore compared with the case of disposing the rotation restricting portion at a position corresponding to the second shaft diameter portion21c, a larger force can be transmitted to the pinion gear22. Further, by forming the parallel pin hole21hin the first shaft diameter portion21b, the strength of the motor shaft21acan be better maintained compared to the case of forming the parallel pin hole21hin the second shaft diameter portion21c.

The gear teeth portion22a, which engages with the branching gear23, is disposed on the outer peripheral surface of the second portion22b2, and the inner peripheral surface thereof is supported by the second shaft diameter portion21cof the motor shaft21a. Specifically, the inner peripheral surface of the second portion22b2constituting the second opening22c2is in contact with the second shaft diameter portion21c. In Example 1, the second shaft diameter portion21cis press-fitted in the second opening22c2.

The contact surface22eis an end surface that is vertical to the axis line direction of the motor shaft21a, and is disposed on the edge of the second portion22b2.

The parallel pin27receives rotating force from the parallel pin hole21hdisposed in the first shaft diameter portion21bof the driving motor21, and transmits the power to the parallel pin receiving portion22dof the pinion gear22. When the pinion gear22, mounted on the driving motor21, transmits power to the branching gear23, the motor shaft21areceives radial load F1, in accordance with the pressure angle of the gear teeth portion22a, from the pinion gear22. The pinion gear22is a helical gear, hence the thrust load F2, which is generated based on the helical gear torsion angle and rotation direction, is received by the side surface of the third shaft diameter portion21dof the motor shaft21afrom the contact surface22eof the pinion gear22via the E-ring28.

Now the motor shaft21awill be described in detail.FIGS.6A to6Care cross-sectional views of the driving motor21, sectioned at a plane which is vertical to the rotational axis of the motor shaft21a, and which passes through the center of the parallel pin hole21h,321hor421h.FIGS.6D to6Eare cross-sectional views of the driving motor21sectioned at a plane which includes the rotational axis of the motor shaft21a.FIG.6Ais a cross-sectional view sectioned at the A-A line inFIG.6D,FIG.6Bis a cross-sectional view sectioned at the B-B line inFIG.6E, andFIG.6Cis a cross-sectional view sectioned at the C-C line inFIG.6F.FIGS.6A and6Dindicate a configuration of Example 1, andFIGS.6B,6C,6E and6Findicate configurations of the motor shafts321aor421aof comparative examples.FIG.7Ais a perspective view of the motor shaft21aof Example 1.FIG.7Bindicates each stress generated in the parallel pin holes21h,321h,421hand the corner R shape21ewhen the motor shaft21areceives the radial load F1, and the indicated values are values assuming the stress generated in the parallel pin hole421hinFIG.6Cis 1.

Specific dimensions will be described with reference toFIG.6A.FIG.6Aindicates a portion of the motor shaft21aof Example 1, where the first shaft diameter portion21bis less than Φ 7 mm, and the second shaft diameter portion21cis less than Φ5 mm. Specifically, the first shaft diameter portion21bis Φ 6 mm, the second shaft diameter portion21cis Φ 4.2 mm, and the corner R shape21eis R 0.5 mm. InFIG.6B, the first shaft diameter portion321bis Φ 4.2 mm, where the parallel pin hole321his disposed in the first shaft diameter portion321b, and the pinion gear22is supported in the first shaft diameter portion321b. InFIG.6C, the first shaft diameter portion421bis Φ 6 mm, where the parallel pin hole421his disposed in the first shaft diameter portion421b, and the pinion gear22is supported in the first shaft diameter portion421b. The parallel pin hole of the parallel pin hole21h,321hor421his less than 3 mm, and is specifically Φ 2 mm. A value determined by dividing the diameter of the parallel pin hole21h,321hor421hby the outer diameter of the second shaft diameter portion21cis more than 0.4, and a value determined by dividing the diameter of the parallel pin hole21h,321hor421hby the outer diameter of the first shaft diameter portion21bis less than 0.4.

The inner diameter of the bearing21gof the driving motor21is Φ 6 mm, and the outer diameter of the portion of the motor shaft21a,321aor421asupported by the bearing21gis Φ 6 mm. Since the outer diameter of the first shaft diameter portion21bor421bis Φ 6 mm, which is the same as the portion supported by the bearing21g, the processing amount (time and cost) to acquire the motor shaft21aor421acan be reduced.

InFIG.6A, it is assumed that21h1is a line formed when a plane, which is vertical to the rotational axis of the motor shaft21aand passes through the center of the parallel pin hole21h, intersects with the inner peripheral surface of the parallel pin hole21h. P3 is an intersection between the line21h1and the outer peripheral surface of the first shaft diameter portion21b.21h2is a line that contacts the outer peripheral surface of the first shaft diameter portion21bat the intersection P3. Θ1 is an angle formed by the line21h1and the line21h2. InFIG.6Bas well, lines321h1and321h2, an intersection P33 and an angle Θ2are defined in the same manner with respect to the parallel pin hole321hand the first shaft diameter portion321b. InFIG.6Cas well, lines421h1and421h2, an intersection P43 and an angle Θ1 are defined in the same manner with respect to the parallel pin hole421hand the first shaft diameter portion421b. InFIGS.6A and6C, the dimensional relationship between the first shaft diameter portion and the parallel pin hole is the same, hence the same angle Θ1 is formed. Angles Θ1 and Θ2 become more acute as the diameters of the first shaft diameter portions21b,321band421bbecome smaller.

FIGS.7A and7Bindicate the analysis results of the shapes inFIGS.6A to6C.FIG.7Ais an enlarged view of the motor shaft21ainFIGS.4A and4B. When a radial load F1 is received, stress is generated in the parallel pin hole edge P3 of the parallel pin hole21hand the corner R shape portion P4 of the corner R shape21e.FIG.7Bindicates the results. InFIG.7B, the stress in each portion is indicated by a value assuming the stress generated in the parallel pin hole edge P43 of the parallel pin hole421hinFIG.6Cis 1.

InFIG.6B, the angle Θ2 is a sharper acute angle than Θ1, and the stress generated in the parallel pin hole edge P33 becomes 4.29 times compared withFIG.6C. This means that the motor shaft321ainFIG.6Bcan support the pinion gear22with a smaller shaft diameter compared withFIG.6C, but receives more stress, which drops strength. In order to perform driving with the same stress asFIG.6Cin the configuration inFIG.6B, the radial load F1 needs to be 1/4.29, and it is difficult to transmit power when load is high.

InFIG.6C, the first shaft diameter portion421bis Φ 6 mm, hence stress generated in the parallel pin hole edge P43 is small. However in the case of the configuration inFIG.6C, the second portion22b2, where the gear teeth portion22aof the pinion gear22is disposed, is supported in the first shaft diameter portion421b, hence the portion supported by the second portion22b2becomes thicker compared withFIGS.6A and6B. In this case, an increase in the outer diameter of the outer peripheral surface, where the gear teeth portion22ais disposed, can be suppressed by decreasing the thickness of the second portion22b2of the pinion gear22. The material of the pinion gear22is resin, and is polyacetal resin (POM) in the present embodiment. In Example 1, the pinion gear22is formed by injection molding. The thickness of the gear teeth portion22aof the pinion gear22and the thickness of the second portion22b2corresponding to the gear teeth portion22aare preferably 1 to 1.5 mm, considering the fluidity of the resin, sink marks after molding, component strength, and the like. Therefore if the difference between Φ 6 mm and Φ 4.2 mm (0.9 mm in the case of the radius) is compensated by decreasing the thickness of the second portion22b2of the pinion gear22, the thickness becomes too thin. If the thickness of the second portion22b2is increased in accordance with the shaft diameter of the portion supporting the pinion gear22, a pitch circle diameter of the gear teeth portion22aalso increases, hence the peripheral speed of the gear teeth portion22aof the pinion gear22increases, and operating sound also increases. Further, in order to cancel the above mentioned image distortion of the driving system up to the pinion gear22and the branching gear23, a number of gear teeth Z1 of the first driving input gear24and a number of gear teeth Z2 of the branching gear23need to be increased respectively, which results in an increase in the size of the image forming apparatus1.

In the case of using a small pinion gear22, the length, when the outer diameter of the first shaft diameter portion21bis subtracted from the root circle diameter of the gear teeth portion22aof the pinion gear22, is less than 2 mm. Specifically, the root circle diameter of the gear teeth portion22ais 6.6 mm, and the difference from the outer diameter 6 mm of the first shaft diameter portion21bis 0.6 mm. In this case, if the second portion22b2is supported by the shaft having the same thickness as the first shaft diameter portion21b, the thickness of the second portion22b2up to the root circle of the gear teeth portion22ais 0.3 mm. In other words, it is difficult to support the second portion22b2while maintaining the thickness of the second portion22b2.

The difference between the root circle diameter of the gear teeth portion22aof the pinion gear22and the diameter of the second opening22c2is preferably at least 2 mm and not more than 3 mm, considering at least one of the fluidity of the resin, sink marks after molding, component strength, or the like. The thickness of the second portion22b2up to the root circle of the gear teeth portion22acan be ensured to be 1 mm to 1.5 mm. In Example 1, the root circle diameter of the gear teeth portion22aof the pinion gear22is 6.6 mm, and the diameter of the second opening22c2is 4.2 mm.

In Example 1 inFIG.6A, the stress factor of the parallel pin hole edge P3 is about the same asFIG.6C(1.1 times). By disposing the corner R shape21eat the corner between the first shaft diameter portion21band the second shaft diameter portion21c, the stress factor of the corner R shape portion P4 becomes about the same asFIG.6C(1.04 times). As a result, the shaft diameter of the second shaft diameter portion21ccan be thin, likeFIG.6B, the peripheral speed of the pinion gear22can be decreased, and an increase in operation sound can be suppressed. Further, power can be transmitted with a high load similar toFIG.6C. Furthermore, the above mentioned image distortion of the driving system up to the pinion gear22and the branching gear23can be cancelled, hence there is no need to increase the number of gear teeth Z1 of the first driving input gear24and the number of gear teeth Z2 of the branching gear23, and the size of the image forming apparatus1does not increase very much.

As described above, in Example 1, the first shaft diameter portion21band the second shaft diameter portion21care disposed on the motor shaft21a, whereby the peripheral speed of the pinion gear22can be decreased, and power can be transmitted with high load while keeping the operation sound low.

Further, in the case where the drum rotation angle of the photosensitive drum3, from the exposure position P1 to the transfer position P2, is Θ, the gear trains of the branching gear23and the pinion gear22can be configured so as to rotate for an integral number of times while the photosensitive drum3rotates for this angle, without increasing the size of the gears. Therefore the image distortion on the recording material S is cancelled, and a high quality image can be acquired while suppressing the increase in the size of the apparatus.

As a result, the strength of the motor shaft can be increased and power can be transmitted with high load without increasing the size of the apparatus, and the image forming apparatus1that can acquire a high quality image while suppressing the operation sound is implemented.

Whereas the present invention has been described with reference to a concrete embodiment, the present invention is not limited to the above embodiment. The branching gear23is one gear in the above description, but a step gear may be used such that an output side gear, which transmits driving to the first driving input gear24, has a number of teeth with which the above mentioned branching gear23rotates for an integral number of times, and an input side gear, to which driving is transmitted from the pinion gear22, rotates for a same integral number of times as the pinion gear22. Thereby a similar effect can be acquired.

The driving unit20drives the process cartridge8in the above description, but even in the case where another driven member, such as a roller to transport the recording material S, is driven as well, the effect of enhancing the strength of the motor shaft21awhile suppressing an increase in operation sound can be acquired.

The pinion gear22is retained by the E-ring28in the above description, but the pinion gear22may be secured by press fitting, adhesion, or the like, as long as the pinion gear22can be retained. Further, if the thrust load F2 is generated toward the parallel pin27by changing the torsion angle or the rotation direction of the helical gear, the E-ring28is not required.

Dimensions of the first shaft diameter portion21b, the second shaft diameter portion21c, the parallel pin hole21hand the corner R shape21eare indicated above using concrete numeric values, but these are examples for explanatory purposes. A threshold of the stress may be determined considering actual operation conditions (e.g. load condition, shaft material, life of product), and dimensions may be appropriately determined such that the stress generated in each portion does not exceed the threshold.

The corner R shape21eis disposed at the corner between the first shaft diameter portion21band the second shaft diameter portion21cin the above description, but the corner C chamfering shape may be formed in according with the stress.

The pinion gear22is the helical gear in the above description, but a driving unit20may be a pulley that drives a toothed belt, as long as the driving transmission can be performed.

Example 2

Example 2 of the present invention will be described next with reference toFIGS.8A and8BandFIGS.9A to9F. A composing element the same as Example 1 will be denoted with a same reference sign, and detailed description thereof will be omitted.FIGS.8A and8Bare diagrams depicting a driving motor221and a pinion gear222of Example 2, and correspond toFIGS.4B and5Bof Example 1 respectively. A main difference of Example 2 from Example 1 is the configuration of the pinion gear222and the motor shaft221a.

The motor shaft221a, which is an output shaft of the driving source, includes: a first shaft diameter portion221bwhich is a large diameter portion having a first outer diameter; a second shaft diameter portion221cwhich is a small diameter portion having a second outer diameter that is smaller than the first outer diameter; and a third shaft diameter portion221dhaving a third outer diameter that is smaller than the second outer diameter.

The second shaft diameter portion221csupports the pinion gear222at a second portion222b2, where a gear teeth portion222aof the pinion gear222is disposed.

In the third shaft diameter portion221d, an E-ring28is disposed so that the pinion gear222does not come off in the motor shaft221adirection.

The radius of the corner at the boundary of the first shaft diameter portion221band the second shaft diameter portion221cincreases along the axis line in the direction from the second shaft diameter portion221cto the first shaft diameter portion221b. Specifically, a corner R shape221ehas a shape of which the diameter increases in the direction from the second shaft diameter portion221cto the first shaft diameter portion221b. Thereby concentration of the stress of the radial load F1, caused by the later motioned driving transmission, can be prevented.

The motor shaft221ais held via a bearing221g, which is a bearing to rotatably support the motor shaft221a, and can rotate with respect to a mounting metal plate221f, to mount the driving motor21on the apparatus main unit1A of the image forming apparatus1. An outer diameter of a portion of the motor shaft221asupported by the bearing221gis the same as the outer diameter (first outer diameter) of the first shaft diameter portion221b.

In Example 2 as well, the image forming apparatus1is disposed at a position corresponding to the first shaft diameter portion221bin the axis line direction, and includes a rotation restricting portion which restricts the rotation of the pinion gear222with respect to the motor shaft221a. Thereby power is transmitted from the motor shaft221ato the pinion gear222. Here at least a part of the first shaft diameter portion221bfunctions as the rotation regulating portion. Specifically, the first shaft diameter portion221bof Example 2 includes, on the outer peripheral surface, a D-shaped portion221k, which is an outer peripheral flat portion which is parallel with the rotational axis of the motor shaft221a, and of which distance from the rotational axis is shorter than a half the length of the first outer diameter (radius of the first shaft diameter portion221b). A cross-section of the area where the D-shaped portion221kis disposed, sectioned vertically to the rotational axis of the motor shaft221a(first shaft diameter portion221b) is D-shaped. The D-shaped portion221khas a three-dimensional shape partially cutting the first shaft diameter portion221b, but it is not always necessary to manufacture it by cutting.

The pinion gear222includes: a first portion222b1including a first opening222c1having a first diameter; a second portion222b2including a second opening (not illustrated) having a second diameter which is smaller than the first diameter; and a contact surface222ewhich contacts with the E-ring28. A gear teeth portion222a, which engages with the branching gear23, is disposed on the outer peripheral surface of the second portion222b2. The second portion222b2is supported by the second shaft diameter portion221cof the motor shaft221a. The second portion222b2, the second shaft diameter portion221c, the contact surface222e, and the gear teeth portion222ahave the same shapes as the second portion22b2, the second shaft diameter portion21c, the contact surface22e, and the gear teeth portion22aof Example 1 respectively. The diameter of the first opening222c1is 6.4 mm.

The first portion222b1is located at a position corresponding to the first shaft diameter portion221bof the motor shaft221ain the axis line direction. The inner peripheral surface thereof includes a D-shaped hole222f, which is an inner peripheral flat portion parallel with the rotational axis of the pinion gear222, and of which distance from the rotational axis is shorter than the half the length of the first diameter. The rotation of the pinion gear222with respect to the motor shaft221ais restricted by contact between the D-shaped portion221k(outer peripheral flat portion) and the D-shaped hole222f(inner peripheral flat portion). The D-shaped hole222fof the pinion gear222contacts with the D-shaped portion221kof the motor shaft221a, and the rotational force is transmitted from the D-shaped portion221kto the gear teeth portion222a, which is disposed on the outer peripheral surface of the second portion222b2.

Now the motor shaft221awill be described in detail.FIG.9Ais a cross-sectional view of the motor shaft221aof Example 2, sectioned at a plane vertical to the rotational axis.FIG.9Bis a cross-sectional view of a motor shaft521aof a comparative example, sectioned at a plane vertical to the rotational axis, corresponding toFIG.9A.FIG.9Cis a cross-sectional view of the motor shaft221aof Example 2, sectioned at a plane that includes the rotational axis.FIG.9Dis a cross-sectional view of the motor shaft521aof a comparative example, sectioned at a plane that includes the rotational axis.FIG.9Eis a perspective view of the motor shaft221aof Example 2.FIG.9Fis a perspective view of the motor shaft521aof the comparative example.

Specific dimensions will be described with reference toFIG.9A. In the motor shaft221aof Example 2, the first shaft diameter portion221bis Φ 6 mm, the second shaft diameter portion221cis Φ 4.2 mm, and the corner R shape221eis R 0.5 mm. A distance L1, from the rotational axis to the outer peripheral flat portion of the D-shaped portion221k, is 2.3 mm, which is smaller than the radius R1 of the first shaft diameter portion221band is larger than the radius of the second shaft diameter portion221c. In the comparative example inFIG.9B, the first shaft diameter portion521bis Φ 4.2 mm, and the pinion gear222is supported by the first shaft diameter portion521b. A distance L2, from the rotational axis lien of the first shaft diameter portion521bto the outer peripheral flat portion of the D-shaped portion521k, is 1.5 mm, which is smaller than the radius R5 of the first shaft diameter portion521b. The inner diameter of the bearing221gof the driving motor221is Φ 6 mm, and the outer diameter of the portion of the motor shaft221asupported by the bearing221gis Φ 6 mm. Since the outer diameter of the first shaft diameter portion221bis the same as the outer diameter Φ 6 mm of the portion supported by the bearing221g, the process amount (time and cost) to acquire the motor shaft221acan be reduced.

The driving transmission of the motor shaft221aor521ais performed in a portion near the intersection P5 or P55 (edge of the D-shaped portion221kor521k), between the outer peripheral flat portion of the D-shaped portion221kor521kof the first shaft diameter portion221bor521band the outer peripheral surface of the first shaft diameter portion221bor521b. The load F3 or F4 that is applied to a portion near the intersection P5 or P55 (edge of the D-shaped portion221kor521k) is applied in a direction vertical to the outer peripheral flat portion of the D-shaped portion221kor521k. If the torque of the transmitted power is the same, the load is in inverse proportion to the radius of the portion to which this load is applied. Since the radius of the portion to which the load is applied is R1 (3 mm) or R5 (2.1 mm), the load is F3=2.1/3×F4. In other words, in order to apply a load the same asFIG.9Ato the outer peripheral flat portion of the first shaft portion and the inner peripheral flat portion of the pinion gear222in the configuration ofFIG.9B, the torque must be 2.1/3, and power cannot be transmitted while load is high.

Here it is assumed that the first shaft diameter portion521binFIG.9Bis changed from Φ 4.2 mm to Φ 6 mm, and the distance L2, from the rotational axis to the outer peripheral flat portion of the D-shaped portion521k, is changed from 1.5 mm to 2.3 mm. If such modifications are performed, the load applied to the outer peripheral flat portion of the D-shaped portion of the first shaft diameter portion and the inner peripheral flat portion of the D-shaped hole of the pinion gear becomes F3, which is the same asFIG.9A. However in this case, the pitch circle diameter of the gear teeth portion222aof the pinion gear222becomes large, hence the peripheral speed of the gear teeth portion222aof the pinion gear222increases, and the operation sound increases. Further, in order to cancel the above mentioned image distortion of the driving system up to the pinion gear222and the branching gear23, a number of gear teeth Z1 of the first driving input gear24and a number of gear teeth Z2 of the branching gear23must be increased respectively, and the size of the image forming apparatus1is increased thereby.

In Example 2 inFIG.9A, the load F3 applied to the outer peripheral flat portion of the D-shaped portion221kof the first shaft diameter portion221band the inner peripheral flat portion of the D-shaped hole222fof the pinion gear222can be smaller than the configuration inFIG.9B. Further, the outer diameter of the second shaft diameter portion to support the pinion gear222can be the same as the configuration inFIG.9B. Therefore just like Example 1, the peripheral speed of the gear teeth portion of the pinion gear can be decreased, and an increase in the operation sound can be suppressed, while power can still be transmitted with high load. Further, by using the driving unit20the same as Embodiment 1, a number of gear teeth Z1 of the first driving input gear24and a number of gear teeth Z2 of the branching gear23need not be increased respectively. Therefore the above mentioned image distortion of the driving system up to the pinion gear222and the branching gear23can be cancelled, and the size of the image forming apparatus1is not increased. Furthermore, driving transmission can be performed without using the parallel pin27of Example 1, hence a number of components can be reduced.

As described above, in Example 2, the first shaft diameter portion221band the second shaft diameter portion221care disposed on the motor shaft221a, the D-shaped portion221kis disposed in the first shaft diameter portion221b, and the D-shaped hole222fmatching with the D-shaped portion221kis disposed in the pinion gear222. Thereby the effect similar to Example 1 can be acquired. In Example 2, the parallel pin27is unnecessary, hence a number of components can be reduced.

Whereas the present invention has been described with reference to a specific embodiment, the present invention is not limited to the above embodiment. For example, the shapes of the D-shaped portion221kof the first shaft diameter portion221band the D-shaped hole222fof the first portion222b1are not limited to a D shape, and may be an I shape that cuts two surfaces, for example, as long as the rotation of the pinion gear222, with respect to the motor shaft221a, can be restricted by the contact of [these portions].

According to the present disclosure, in the image forming apparatus having a driven member which is rotary-driven by power transmitted from a drive source, the strength of the output shaft can be ensured to be operated with high torque, while preventing an increase of the size of the gear, which is mounted on the output shaft of the driving source.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2022-131867, filed on Aug. 22, 2022, which is hereby incorporated by reference herein in its entirety.