Image forming apparatus

An image forming apparatus includes: a photosensitive drum; a process frame from which the photosensitive drum is detachable; an apparatus body from which the process frame is removable; a drum shaft including one end constituting a free end, and another end supported by the apparatus body, and transmitting rotational driving force to the photosensitive drum; and a fixing member configured to stop movement of the photosensitive drum, wherein the one end of the drum shaft is configured to penetrate through and protrude from the photosensitive drum, the photosensitive drum includes a first annular protruding portion, the process frame includes a bearing part, the fixing member includes a second annular protruding portion, the one end of the drum shaft is pivotally supported by the fixing member, and the first annular protruding portion of the photosensitive drum is pivotally supported by the second annular protruding portion of the fixing member.

The entire disclosure of Japanese Patent Application No. 2016-024055 filed on Feb. 10, 2016 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

Description of the Related Art

In a conventional image forming apparatus, since a photosensitive drum is directly supported by a bearing part, when the photosensitive drum is replaced, it is necessary to be disassembled, and its maintenance has not been easy (for example, see JP 05-289588 A).

Therefore, a technology has been devised for ensuring detachment easiness of the photosensitive drum by using: a process frame from which the photosensitive drum is detachable; an apparatus body from which the process frame is removable; a drum shaft including one end constituting a free end and the other end supported by the apparatus body and transmitting rotational driving force to the photosensitive drum; and a fixing member for stopping movement of the photosensitive drum in an axial direction of the drum shaft.

Here, to ensure detachment easiness of the photosensitive drum, it is necessary to provide a fitting gap between the photosensitive drum and the drum shaft, between the drum shaft and the fixing member, and the like. In the process frame, in addition to the photosensitive drum, an imaging unit is also arranged including a developing device, a charging unit, a cleaning device, and the like. The imaging unit is longer than the photosensitive drum in an insertion/removal direction of the process frame to ensure the maximum image area.

As a result, the process frame and the fixing member also become long, and influence is increased of part accuracy of a contact portion of the photosensitive drum and the fixing member (for example, squareness with respect to the drum shaft), and there is a problem that deviation to one side of the fitting gap (a phenomenon in which the fitting gap comes to one side in a radial direction from the contact portion as a point of origin) is caused.

Further, it is necessary to increase contact force to the fixing member and the photosensitive drum to inhibit the photosensitive drum from idly rotating on the drum shaft, and there is a problem that bending is caused of the drum shaft from the contact portion as a point of origin.

SUMMARY OF THE INVENTION

The present invention has been made to solve the problems associated with the above conventional technology, and it is an object to provide an image forming apparatus capable of inhibiting runout of the photosensitive drum while ensuring detachment easiness of the photosensitive drum.

The above object of the present invention is achieved by the following solutions.

(1) To achieve the above mentioned object, according to an aspect, an image forming apparatus reflecting one aspect of the present invention comprises:

a photosensitive drum;

a process frame from which the photosensitive drum is detachable;

an apparatus body from which the process frame is removable;

a drum shaft including one end constituting a free end, and another end supported by the apparatus body, and transmitting rotational driving force to the photosensitive drum; and

a fixing member configured to stop movement of the photosensitive drum in an axial direction of the drum shaft, wherein

the one end of the drum shaft is configured to penetrate through and protrude from the photosensitive drum,

the photosensitive drum includes a first annular protruding portion configured to surround an outer circumference of the one end of the drum shaft,

the process frame includes a bearing part configured to support the fixing member,

the fixing member includes a second annular protruding portion configured to surround an outer circumference of the first annular protruding portion of the photosensitive drum,

the one end of the drum shaft is pivotally supported by the fixing member supported by the bearing part, and

the first annular protruding portion of the photosensitive drum is pivotally supported by the second annular protruding portion of the fixing member supported by the bearing part.

(2) The image forming apparatus of Item. 1, wherein the bearing part is preferably arranged to face a region in which the one end of the drum shaft, the first annular protruding portion of the photosensitive drum, and the second annular protruding portion of the fixing member overlap with each other.

(3) The image forming apparatus of Item. 1 or 2, wherein an end portion of the first annular protruding portion of the photosensitive drum in a removal direction in which the photosensitive drum is removed from the drum shaft, is preferably in contact with the fixing member at a position of the removal direction side from an end portion of the bearing part in the removal direction.

(4) The image forming apparatus of any one of Items. 1 to 3, wherein the apparatus body preferably includes a bearing part configured to support the other end of the drum shaft.

(5) The image forming apparatus of any one of Items. 1 to 4, preferably further comprising a fastening member configured to fasten the photosensitive drum and the drum shaft together through the fixing member.

(6) The image forming apparatus of Item. 5, wherein

the fixing member preferably includes a through-hole communicating with the second annular protruding portion,

the one end of the drum shaft preferably includes a recess portion in which a screw thread is formed,

the fastening member preferably includes a protruding portion penetrating the through-hole of the fixing member and being inserted to the recess portion of the drum shaft, and

the protruding portion of the fastening member preferably includes a screw thread to be screwed into the screw thread of the recess portion of the drum shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples. Incidentally, dimensional ratios of the drawings are exaggerated for convenience of description, and may be different from actual ratios.

FIG. 1is a sectional view for explaining an image forming apparatus according to an embodiment of the present invention.

An image forming apparatus100illustrated inFIG. 1is a monochrome copier, and includes a control unit105, an image reading unit110, an operation display unit120, an image forming unit125, a transfer unit175, a fixing unit180, a sheet feeding unit185, a sheet conveying unit190, and a communication interface195.

The control unit105includes: a control circuit configured from a microprocessor for executing control of the above units and various types of calculation processing according to a program, and the like; and a storage unit to be used for storing various programs and data, and each function of the image forming apparatus100is exerted by causing the control unit105to execute a program corresponding to the function.

The image reading unit110is used for generating image data of a document to be copied, and includes a light source112, an optical system114, and an imaging element116. The light source112emits light to the document placed on a reading surface118, and its reflection light is focused via the optical system114on the imaging element116moved to a reading position. The imaging element116is configured from, for example, a linear image sensor, and generates (performs photoelectric conversion) an electrical signal depending on reflection light intensity. The electrical signal generated is input to the image forming unit125after image processing. The image processing includes A/D conversion, shading correction, filter processing, and image compression processing. Incidentally, the image reading unit110can be provided with an auto document feeder (ADF), as needed.

The operation display unit120is configured from, for example, a liquid crystal display (LCD) and a keyboard. The LCD is an output unit to be used for presenting a device configuration, a progress state of a print job, an occurrence state of an error, and a setting currently changeable, to a user. The keyboard is used when the user performs character input, various settings, and various instructions (inputs) such as a start instruction, and includes a plurality of keys configured from, for example, a select key for specifying a size of a sheet P, a numeric key for setting the number of copies and the like, a start key for instructing to start operation, and a stop key for instructing to stop operation.

The image forming unit125is used for forming an image on the sheet P that is a recording medium by using an electrophotographic process, and includes a process frame140and an optical writing unit173. Developing powder for the electrophotographic process is configured from, for example, non-magnetic toner and magnetic carriers.

The process frame140includes a photosensitive drum130and an imaging unit. The imaging unit includes a developing device170, a charging unit171, and a cleaning device172.

The photosensitive drum130is an image carrier including a hollow cylindrical main body part (base) and a photosensitive layer, and is configured to rotate at a predetermined speed. The main body part (base) is configured from, for example, metal such as aluminum. The photosensitive layer is configured from, for example, resin such as polycarbonate containing an organic photo conductor (OPC).

The developing device170is a unit for developing an electrostatic latent image formed on the photosensitive drum130and visualizing the image with toner.

The charging unit171includes a corona discharge electrode arranged around the photosensitive drum130, and charges a surface of the photosensitive drum130with ions to be generated.

The cleaning device172is used for maintaining an excellent surface state of the photosensitive drum130by scraping (removing) toner remaining on the surface of the photosensitive drum130after a toner image is transferred to the sheet P.

The optical writing unit173incorporates an optical scanner174, and, based on input image data from the image reading unit110, exposes the photosensitive drum130charged to decrease an electrical potential of a portion exposed, and forms a charge pattern (electrostatic latent image) corresponding to the image data. Incidentally, the optical writing unit173can be arranged in the process frame140, as needed.

The transfer unit175includes a transfer roller176. The transfer roller176is pressed against the photosensitive drum130to form a transfer nip, and is driven to rotate in accordance with rotation of the photosensitive drum130. While the sheet P passes through the transfer nip, the toner image carried on the photosensitive drum130is transferred to the sheet P by a function of a transfer electric field generated by a transfer voltage applied to the transfer roller176.

The fixing unit180includes a fixing roller181and a pressing roller182. The fixing roller181is positioned at a side in which a toner image to be fixed on the sheet P is arranged, and includes a heater for heating the sheet P. The pressing roller182is positioned at an opposite side to the fixing roller181through the sheet P, and is elastically urged to press the sheet P. While the toner image transferred onto the sheet P passes between the fixing roller181and the pressing roller182, the sheet P is pressed and heated, and the toner image is melted and fixed. The fixing roller181can be configured by a plurality of rollers including a roller having a heater, and a roller not having a heater.

The sheet feeding unit185is used for accommodating the sheet P on which the image is to be formed, and includes, for example, a sheet feeding cassette186, a feeding roller187, and a handling roller188. The sheet feeding cassette186is configured to be detachable from the sheet feeding unit185. The feeding roller187and the handling roller188are configured to feed the sheet out one by one from the sheet feeding cassette186to the sheet conveying unit190.

The sheet conveying unit190is used for conveying the sheet P accommodated in the sheet feeding unit185via the image forming unit125, the transfer unit175, and the fixing unit180. The sheet conveying unit190can be provided with a sheet reversing unit for ejecting the sheet P while reversing the front and back of the sheet P, or forming images on both surfaces of the sheet P, as needed. Incidentally, a sheet ejection roller192and a sheet ejection tray194are used for ejecting the sheet P to the outside of the apparatus.

The communication interface195is an extension device configured from a so-called LAN board, and is used for adding to the image forming apparatus100a communication function for executing transmission/reception of data via a network. The data to be received is, for example, a print job.

The network includes various networks such as: a local area network (LAN) for connecting computers and network devices to each other with the standard such as Ethernet (registered trademark), token ring, or fiber-distributed data interface (FDDI); a wide area network (WAN) for connecting the LANs to each other with a dedicated line; the Internet; and a combination thereof. The network protocol is, for example, transmission control protocol/internet protocol (TCP/IP).

Next, a fixing structure of the process frame and the photosensitive drum is described in detail.

FIGS. 2A to 2Dare schematic diagrams for explaining the process frame and the photosensitive drum illustrated inFIG. 1, andFIG. 2Aillustrates mounting of the photosensitive drum to the process frame,FIG. 2Billustrates a guide protruding from an apparatus body,FIG. 2Cillustrates insertion of the process frame to the apparatus body, andFIG. 2Dillustrates fixing of the photosensitive drum mounted on the process frame. In the figures, the developing device170, the charging unit171, and the cleaning device172are omitted.

The process frame140is configured so that the photosensitive drum130is detachable from the process frame140, and includes a frame142having a bearing part144(FIG. 2A). The bearing part144is provided to support a fixing member described later.

The photosensitive drum130includes flange portions132,138respectively positioned at both ends of the hollow cylindrical main body part (base). Each of the flange portions132,138includes an opening, and is configured so that one end151of a removal direction side of a drum shaft150described later is able to extend in an axial direction AD1of the photosensitive drum130, and to penetrate the inside of the photosensitive drum130.

An apparatus body101is configured so that the process frame140is removable from the apparatus body101, and includes a guide145, the drum shaft150, bearing parts157,158, and a drive device159.

The guide145is provided to facilitate insertion of the process frame140to the apparatus body101, and is configured to be able to protrude from the apparatus body101(FIG. 2B).

The drum shaft150is provided to transmit rotational driving force to the photosensitive drum130, and includes the one end151positioned at the removal direction side, and another end156positioned at an insertion direction side. Incidentally, an axial direction AD2of the drum shaft150coincides with the axial direction AD1of the photosensitive drum130in a state in which the process frame140is inserted to the apparatus body101.

The other end156of the insertion direction side is supported by the bearing parts157,158, and is coupled to the drive device159. The drive device159is configured to rotationally drive the other end156. The support structure of the other end156of the drum shaft150is not limited to the form using the bearing parts157,158.

The one end151of the removal direction side constitutes a free end, and is configured to protrude from the flange portion132through the inside of the photosensitive drum130in the state in which the process frame140is inserted to the apparatus body101(FIG. 2C).

Incidentally, as described later, it is configured so that the one end151of the removal direction side is in contact with a fixing member160for stopping movement of the photosensitive drum130in the axial direction AD2of the drum shaft150, and the photosensitive drum130and the drum shaft150are fastened by a fastening member167through the fixing member160(FIG. 2D). Therefore, the other end156of the drum shaft150is rotationally driven by the drive device159, whereby the photosensitive drum130fastened to the drum shaft150is rotated.

Next, a fixing structure of the photosensitive drum using the fixing member and the fastening member is described in detail.

FIG. 3is a sectional view for explaining the fixing structure of the removal direction side of the photosensitive drum.

As illustrated inFIGS. 2A to 2DandFIG. 3, the drum shaft150includes a drum shaft body150A, a step portion152, and a reduced diameter portion153. The reduced diameter portion153is a portion having a smaller outer circumferential diameter than that of the drum shaft body150A. The reduced diameter portion153includes an end surface154in which a recess portion155is formed. The recess portion155includes an inner circumferential surface in which a screw thread is formed. The step portion152is a portion in which the outer circumferential diameter decreases when viewed from the drum shaft body150A toward the removal direction side, and is an annular surface. Further, the step portion152is configured to be in contact with the inner side surface of the flange portion132of the photosensitive drum130. Incidentally, a predetermined clearance C1is set between the outer circumference of the drum shaft body150A and the flange portion132of the photosensitive drum130.

The flange portion132of the photosensitive drum130includes a step portion134and an annular protruding portion (first annular protruding portion)135. The step portion134is a portion in which an outer circumferential diameter of the flange portion132decreases when viewed from the drum shaft body150A toward the removal direction side, and is an annular surface. The annular protruding portion135is configured to surround a part of the outer circumference of the reduced diameter portion153, in a place apart from the step portion152by a predetermined distance in the axial direction AD2of the drum shaft150(a portion protruding from the photosensitive drum130).

The fixing member160is a substantially cylindrical member, and includes an annular protruding portion (second annular protruding portion)162positioned proximal to the photosensitive drum130from the step portion165in the axial direction AD2of the drum shaft150, and a base portion166positioned at a distal side from the photosensitive drum130.

The annular protruding portion162is configured to surround the outer circumference of the annular protruding portion135of the photosensitive drum130, and an end surface162A of the annular protruding portion162is in contact with the step portion134of the flange portion132of the photosensitive drum130. Therefore, the fixing member160is capable of stopping movement of the photosensitive drum130in the axial direction AD2of the drum shaft150.

The base portion166includes a through-hole161communicating with the annular protruding portion162, and an end surface166A being in contact with the fastening member167.

Here, the fixing member160has an inner diameter size changing in the middle thereof, and includes step portions163,165. The step portion163is configured to have an inner diameter size smaller than that of the end surface162A of the annular protruding portion162when viewed from the drum shaft body150A toward the removal direction side, and not to be in contact with an end surface136of the annular protruding portion135in the flange portion132of the photosensitive drum130. The step portion165is configured to define a boundary between the annular protruding portion162and the base portion166, and to have an inner diameter size smaller than that of the step portion163and larger than that of the through-hole161, and not to be in contact with the end surface154of the reduced diameter portion153of the drum shaft150.

The bearing part144of the process frame140is arranged to face (surround) the outer circumference of the annular protruding portion162of the fixing member160.

The fastening member167is a substantially columnar member, and includes a step portion168and a protruding portion169.

The step portion168is configured to be a portion in which an outer circumferential diameter increases when viewed from the protruding portion169toward the removal direction side, and to be an annular surface, and to be in contact with the end surface166A of the base portion166of the fixing member160. The protruding portion169is configured to include a screw thread in the outer circumference thereof, and to be able to be inserted to the recess portion155of the end surface154in the reduced diameter portion153of the drum shaft150through the through-hole161of the base portion166of the fixing member160. The screw thread of the protruding portion169is set to be screwed into the screw thread of the recess portion155of the end surface154in the reduced diameter portion153of the drum shaft150. Incidentally, a predetermined clearance C2is set between the outer circumference of the protruding portion169and the through-hole161of the base portion166of the fixing member160.

Therefore, when the protruding portion169of the fastening member167is inserted to the recess portion155of the one end151of the drum shaft150, and the screw threads are screwed together, in a state in which the end surface162A of the annular protruding portion162of the fixing member160is in contact with the step portion134of the flange portion132of the photosensitive drum130, the step portion168of the fastening member167is in contact with the end surface166A of the base portion166of the fixing member160, and the step portion152of the one end151of the drum shaft150is in contact with the inner side surface of the flange portion132of the photosensitive drum130.

Therefore, the fixing member160and the photosensitive drum130are clamped by the fastening member167and the drum shaft150. That is, the fastening member167is able to fasten the photosensitive drum130and the drum shaft150together through the fixing member160.

At this time, since the fixing member160is supported by the bearing part144of the process frame140, the photosensitive drum130fastened to the drum shaft150is rotated by the drive device159by rotationally driving the other end156of the drum shaft150.

Incidentally, the one end151of the drum shaft150is pivotally supported by the fixing member160supported by the bearing part144of the process frame140, and the annular protruding portion135of the flange portion132of the photosensitive drum130is pivotally supported by the annular protruding portion162of the fixing member160supported by the bearing part144of the process frame140(a region is included in which the one end of the drum shaft, the first annular protruding portion of the photosensitive drum, and the second annular protruding portion of the fixing member overlap with each other). Therefore, influence is reduced of bending of the drum shaft150and deviation to one side of the fitting gap, and runout of the photosensitive drum130is inhibited.

In particular, the bearing part144of the process frame140is arranged to face the overlap region and the region is positioned at the inside of the bearing part144of the process frame140for supporting the fixing member160, so that the influence is further reduced of bending of the drum shaft150and deviation to one side of the fitting gap.

Next, Modifications 1 to 3 according to the embodiment of the present invention are described in order.

FIG. 4is a sectional view for explaining Modification 1 according to the embodiment of the present invention.

The fixing structure of the photosensitive drum is not limited to the form illustrated inFIG. 3. For example, as illustrated inFIG. 4, the fixing structure can be configured so that the end surface136(end portion) of the annular protruding portion135of the photosensitive drum130in the axial direction AD2of the drum shaft150, is in contact with the step portion163of the fixing member160at a position of the axial direction AD2side of the drum shaft150from the end portion of the bearing part144in the axial direction AD2, and, in the axial direction AD2, a length of the bearing part144is within a length of the annular protruding portion135.

In this case, a contact portion (base point of deviation of fitting gap) between the annular protruding portion135of the photosensitive drum130and the fixing member160is outside the bearing part144of the process frame140(distal side from the photosensitive drum130), so that the influence is further reduced of bending of the drum shaft150and deviation to one side of the fitting gap. Incidentally, in this aspect, the step portion134of the flange portion132of the photosensitive drum130is configured not to be in contact with the end surface162A of the annular protruding portion162of the fixing member160.

FIG. 5is a sectional view for explaining Modification 2 according to the embodiment of the present invention As illustrated inFIG. 5, it is also possible to arrange the bearing part144of the process frame140at a position spaced apart in the axial direction AD2of the drum shaft150from the region in which the one end151of the drum shaft150, the annular protruding portion135of the flange portion132of the photosensitive drum130, and the annular protruding portion162of the fixing member160overlap with each other.

FIG. 6is a sectional view for explaining Modification 3 according to the embodiment of the present invention.

The image forming apparatus100is not limited to the form of the monochrome copier, and can be, for example, a multi-function peripheral (MFP) including a copy function, a printer function, and a scan function, illustrated inFIG. 6.

In this case, an image forming apparatus100A includes, for example, an image forming unit125A for forming a yellow (Y) color image, an image forming unit125B for forming a magenta (M) color image, an image forming unit125C for forming a cyan (C) color image, and an image forming unit125D for forming a black (K) color image, and each of the image forming units includes the process frame140and the optical writing unit173.

Next, performance regarding to drum swing and drum holding force is described.

FIG. 7is a table for explaining performance evaluation results regarding to the drum swing and the drum holding force of Example 1, Example 2, and Comparative Examples 1 to 3, andFIGS. 8 to 10are sectional views for explaining Comparative Examples 1 to 3 shown inFIG. 7. Incidentally, codes A, B, and F indicate excellent, acceptable, and practically unacceptable levels, respectively.

Example 1 corresponds to the form illustrated inFIG. 3; the one end151of the drum shaft150is pivotally supported by the fixing member160supported by the bearing part144of the process frame140, the annular protruding portion135of the flange portion132of the photosensitive drum130is pivotally supported by the annular protruding portion162of the fixing member160supported by the bearing part144of the process frame140, and the bearing part144of the process frame140is arranged to face the region in which the one end151of the drum shaft150, the annular protruding portion135of the flange portion132of the photosensitive drum130, and the annular protruding portion162of the fixing member160overlap with each other. Example 2 corresponds to the form illustrated inFIG. 4, and, in comparison with Example 1, is further configured so that the end surface136(end portion) of the annular protruding portion135of the photosensitive drum130is in contact with the step portion163of the fixing member160at a position of the axial direction AD2side from the end portion of the bearing part144, in the axial direction AD2of the drum shaft150.

Comparative Examples 1 to 3 correspond to the forms illustrated inFIGS. 8 to 10, respectively. Incidentally, in Comparative Examples 1 to 3, similar reference numerals are used for members including similar functions as those of the present embodiments, and descriptions thereof are omitted to avoid redundancy.

Specifically, in Comparative Example 1, an end surface262A of an annular protruding portion262of a fixing member260is in contact with a step portion234of an annular protruding portion235in a flange portion232of a photosensitive drum, to stop movement of the photosensitive drum, and an end surface254of a reduced diameter portion253in one end251of a drum shaft is not in contact with a step portion265of a fixing member260.

A step portion268of a fastening member267is in contact with an end surface266A of a base portion266of the fixing member260. A protruding portion269of the fastening member267is inserted to a recess portion255of the reduced diameter portion253in the one end251of the drum shaft, through a through-hole261of the fixing member260, and a screw thread of the protruding portion269and a screw thread of the recess portion255are screwed together. Thus, the fastening member267fastens the photosensitive drum and the drum shaft together through the fixing member260. Incidentally, a predetermined clearance C3is set between the outer circumference of the protruding portion269of the fastening member267and the through-hole261of the base portion266of the fixing member260.

A bearing part244of a frame242of a process frame is arranged to face (surround) the outer circumference of the annular protruding portion262of the fixing member260at a position spaced apart from the annular protruding portion235of the flange portion232of the photosensitive drum.

Comparative Example 2 illustrated inFIG. 9is generally different from. Comparative Example 1 in that the end surface254of the reduced diameter portion253in the one end251of the drum shaft is in contact with the step portion265of the fixing member260. Incidentally, a spring member239is configured from, for example, a bending washer, or a web washer, and is positioned between the inner side surface of the flange portion232of a photosensitive drum230and a step portion252of the drum shaft to apply holding force to the drum shaft by being squashed a predetermined amount.

Comparative Example 3 illustrated inFIG. 10is generally different from Comparative Example 1 in that the bearing part244of the frame242of the process frame is arranged in the vicinity of the photosensitive drum230.

Next, performance regarding to drum swing and drum holding force of each of Example 1 and Example 2 is described.

As illustrated inFIG. 7, Example 1, in which the average and maximum of drum swing are respectively 38.1 μm and 60 μm and influence of fitting gap and bending is inhibited, is evaluated as A. In addition, since drum clamping force is large and robustness is high to thick sheet shock noise and tip shift, drum clamping force is evaluated as A.

Example 2, in which the average and maximum of drum swing are respectively 32.4 μm and 49 μm and influence of fitting gap and bending is further inhibited in comparison with Example 1, is evaluated as A. In addition, since drum clamping force is large and robustness is high to thick sheet shock noise and tip shift, drum clamping force is evaluated as A.

Next, performance regarding to drum swing and drum holding force of each of Comparative Examples 1 to 3 is described.

As illustrated inFIG. 7, Comparative Example 1, in which the average and maximum of drum swing are respectively 65.7 μm and 104 μm and runout due to fitting gap is not inhibited, is evaluated as F. It is estimated that bending is increased by fastening force of the fastening member, and as a result, runout is increased. In addition, since clamping force is large and robustness is high to thick sheet shock noise and tip shift, drum clamping force is evaluated as A.

Comparative Example 2, in which the average and maximum of drum swing are respectively 38.9 μm and 68 μm and are improved in comparison with those of Comparative Example 1 but runout due to fitting gap is not sufficiently inhibited, is evaluated as B. In addition, since clamping force is relatively small and robustness is low to thick sheet shock noise and tip shift, drum clamping force is evaluated as B.

Comparative Example 3, in which the average and maximum of drum swing are respectively 36.7 μm and 65 μm and are slightly improved in comparison with those of Comparative Example 2 but runout due to fitting gap is not sufficiently inhibited, is evaluated as B. In addition, since clamping force is large and robustness is high to thick sheet shock noise and tip shift, drum clamping force is evaluated as A.

That is, regarding to drum swing and drum holding force, each of Example 1 and Example 2 obtains an excellent result, without being evaluated as B or F, different from Comparative Examples 1 to 3.

As described above, in the present embodiments, the photosensitive drum is detachable from the process frame that is removable from the apparatus body, so that attaching/detaching of the photosensitive drum is easy. In addition, the one end of the drum shaft is pivotally supported by the fixing member supported by the bearing part, and the first annular protruding portion of the photosensitive drum is pivotally supported by the second annular protruding portion supported by the fixing member of the bearing part (a region is included in which the one end of the drum shaft, the first annular protruding portion of the photosensitive drum, and the second annular protruding portion of the fixing member overlap with each other), so that influence is reduced of bending of the drum shaft and deviation to one side of the fitting gap, and runout of the photosensitive drum is inhibited. Therefore, the image forming apparatus can be provided capable of inhibiting runout of the photosensitive drum while ensuring detachment easiness of the photosensitive drum.

The present invention is not limited to the embodiments described above, and can be variously modified within the scope of appended claims. For example, the image forming apparatus is not limited to the monochrome copier or the MFP, and can be a machine specifically for printing, or a facsimile machine.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustrated and example only and is not to be taken byway of limitation, the scope of the present invention being interpreted by terms of the appended claims.