Image forming apparatus

An image forming apparatus (1) includes an image carrier unit (15) and a positioning member (30) configured to position the image carrier unit (15) to the apparatus main body (2). The image carrier unit (15) has a concentric circumference part (51L), (51R) formed on a concentric circle with a rotating shaft (9a) of the image carrier (9) and the apparatus main body (2) has an edge part (42L), (42R) facing the concentric circumference part (51L), (51R) at the attachment position. The positioning member (30) has an intervening part (37) formed with an edge side abutment face (37a) facing the edge part (42L), (42R) of the apparatus main body (2) and a unit side abutment face (37b) facing the concentric circumference part (51L), (51R) of the image carrier unit (15).

TECHNICAL FIELD

The present invention relates to an image forming apparatus provided with a drum unit which supports an image carrier such as a photosensitive drum.

BACKGROUND

An image forming apparatus, such as a copying machine, a printer or a multifunction peripheral, is sometimes constructed such that an image carrier on which an electrostatic latent image is formed, such as a photosensitive drum, a charging device, a cleaning device or the like are integrated into a unit and this unit is attachably/detachably supported to an apparatus main body by sliding operation. In an image forming apparatus for full color, since the units for every color are provided, in order to prevent color displacement, each of the units needs to be positioned with respect to the apparatus main body with a high precision.

In order to position each of the units with respect to the apparatus main body, there may be a case in which a retainer made of a metal plate is used. The retainer is a positioning member having a bearing hole into which a front end of a rotating shaft of the image carrier of each unit is to be inserted. In such each unit, a rear end of the rotating shaft of the image carrier is inserted into a shaft supporting hole formed in the apparatus main body and the front end of the rotating shaft is held in the bearing hole of the retainer. Then, by positioning the retainer with respect to the apparatus main body, it makes possible to improve a precision of a relative position of each image carrier.

As a construction to position each unit by employing the retainer, in Patent Literature 1, there is proposed an image forming apparatus configured such that a front end of a rotating shaft of an image carrier is held in a shaft supporting hole formed in the retainer by self-weight. This image forming apparatus is further provided with a pressing member to press and position the rotating shaft held in the shaft supporting hole and a sliding member to slide the pressing member between a pressing position where the pressing member presses the rotating shaft and a non-pressing position where the pressing member comes into non-contact with the rotating shaft.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF INVENTION

Problems to be Solved by the Invention

However, in the image forming apparatus shown in the Patent Literature 1, when each unit is attached to the apparatus main body, it is necessary to slide each unit to an attachment position with respect to the apparatus main body, subsequently attach the retainer so as to support the rotating shafts of the image carriers in the respective bearing holes, and further slide the sliding members to the pressing position to position the rotating shafts.

Also, while the apparatus main body and the retainer are formed of the metal plate as described previously, the units are generally made of resin; and therefore, the units may be damaged because the apparatus main body or the retainer comes into contact with the units at the time of sliding of the units or at the time of attaching the retainer.

In the construction in which the retainer is used, there are problems that the construction becomes complicated, resulting in higher costs, and the work of attaching and detaching the units is complicated or difficult, resulting in poor workability, and further, the units are easily damaged.

The present invention has been made in view of the circumstance described above, and it is an object of the present invention to provide an image forming apparatus capable of positioning an image carrier unit with respect to an apparatus main body with a simple construction.

Means of Solving the Problems

An image forming apparatus according to the present invention includes: an image carrier unit configured to rotatably support an image carrier on which an electrostatic latent image is to be formed and attachable to or detachable from an apparatus main body; and a positioning member configured to position the image carrier unit with respect to the apparatus main body at an attachment position, wherein the image carrier unit has a concentric circumference part formed on a concentric circle with a rotating shaft of the image carrier, the apparatus main body has an edge part facing the concentric circumference part at the attachment position, the positioning member has an intervening part formed with an edge side abutment face facing the edge part of the apparatus main body and a unit side abutment face facing the concentric circumference part of the image carrier unit, and wherein the intervening part is intervened between the concentric circumference part of the image carrier unit and the edge part of the apparatus main body so that the image carrier unit is positioned with respect to the apparatus main body.

Effects of the Invention

By employing such a construction, since the image carrier unit can be positioned with respect to the apparatus main body only by attaching the positioning member to the apparatus main body, the work of attaching and detaching the image carrier unit can be easily carried out. Further, in a full color image forming apparatus, since the image carrier units for each color of toner are positioned in an apparatus main body by employing the positioning members with a same construction, a relative position precision between the image carrier units is enhanced and thus a color displacement can be reliably prevented. Also, since the concentric circumference parts formed on the concentric circle with the rotating shaft of the image carrier is employed for positioning of the image carrier unit with respect to the apparatus main body, a positioning precision of the image carrier itself can be enhanced.

THE MODE FOR CARRYING OUT THE INVENTION

Hereinafter, with reference to figures, an image forming apparatus according to an embodiment of the present disclosure will be described.

First, with reference toFIG. 1, an entire structure of a color printer1(image forming apparatus) will be described.FIG. 1is a schematic diagram schematically showing the color printer according to an embodiment of the present disclosure. In the following description, a front side of the sheet plane ofFIG. 1shows a front side of the color printer1and left and right directions are based on a direction viewed from the front side of the color printer1.

The color printer1is provided with a box-like shaped printer main body2. In a lower part of the printer main body2, a sheet feeding cassette3storing a sheet (not shown) and on an upper face of the printer main body2, an ejected sheet tray4is provided.

In a center part of the printer main body2, an intermediate transferring belt6is bridged between a plurality of rollers, and under the intermediate transferring belt6, an exposure device7containing a laser scanning unit (LSU) is arranged. Along the lower face of the intermediate transferring belt6, four image forming parts8for each color (for example, magenta, cyan, yellow and black) of toner are provided side by side in the left and right directions. In each image forming part8, a photosensitive drum9(image carrier) is rotatably provided. Around the photosensitive drum9, a charger10, a development unit11, a first transferring part12, a cleaning device13and a static eliminator14are arranged in the order of the first transferring process. The photosensitive drum9, the charger10and the cleaning device13are integrated into a drum unit (image carrier unit)15. Above the development units11, toner containers7for respective image forming parts8are provided for each color of the toner.

Along one side (the right side in the figure) of the printer main body2, a sheet conveying path18is formed extending from the sheet feeding cassette3to the sheet ejecting tray4. At the upstream end of the sheet conveying path18, a sheet feeding part19is provided, at the midstream portion of the sheet conveying path18, a second transferring part20is provided on one end (the right end in the figure) of the intermediate transferring belt6, at the downstream portion of the sheet conveying path18, a fixing device21is provided, and at the downstream end of the sheet conveying path18, a sheet ejecting port22is provided.

Next, the operation of forming an image by the color printer1having such a configuration will be described. When image data is inputted from a computer or the like connected to the color printer1, the image forming operation is carried out as follows.

After the surface of the photosensitive drum9is charged by the charger10, the exposure device7exposes the surface of the photosensitive drum9with a laser light (refer to an arrow P) to form an electrostatic latent image on the surface of the photosensitive drum9. The electrostatic latent image is then developed into a toner image of corresponding color by the developing unit11. The toner image is first-transferred on the intermediate transferring belt6at the first transferring part12. The above-mentioned operation is repeated in order by the image forming parts9, thereby forming a full color toner image onto the intermediate transferring belt6. Incidentally, toner and residual electric charge remained on the photosensitive drum9is removed by the cleaning device13and the static eliminator14, respectively.

On the other hand, the sheet fed from the sheet feeding cassette3by the sheet feeding part19or a bypass tray (not shown) is conveyed to the second transferring part20in a suitable timing for the above-mentioned image forming operation. Then, in the second transferring part20, the full color toner image on the intermediate transferring belt6is second-transferred onto the sheet. The sheet with the second-transferred toner image is conveyed to the downstream side along the sheet conveying path18to enter the fixing device21, and then, the toner image is fixed on the sheet in the fixing device21. The transfer sheet with the fixed toner image is ejected through the sheet ejecting port22to the ejected sheet tray4.

Next, the drum unit15will be described with reference toFIG. 2toFIG. 5.FIG. 2is a perspective view showing the front end part of the drum unit attached to the printer main body, viewed from the front side;FIG. 3is a perspective view showing the front end part of the drum unit attached to the printer main body, viewed from the right side;FIG. 4is a front view showing the drum unit attachment opening of the printer main body; andFIG. 5is a front view showing the drum unit.

The drum unit15is configured to be attachable to or detachable from the printer main body2by the sliding operation in an axial direction of a rotating shaft9aof a photosensitive drum9and is positioned at an attachment position by a positioning member30.

A framework of the printer main body2is constructed by a casing40made of a metal plate. The casing40is formed in a box shape, and as shown inFIG. 2andFIG. 3, has a front side plate40aand a rear side plate (not shown) which oppose to each other in the front and rear directions. The rear side plate is formed with a bearing hole to which the rotating shaft9aof the photosensitive drum9is inserted, at positions corresponding to respective photosensitive drums9of the drum units15. Also, the front side plate40ais formed with an elongated substantially rectangular opening41into which the drum units15or the development units11are to be inserted. The opening41is divided into an attachment section to which corresponding drum unit15is to be attached.

In each of the attachment sections of the opening41, as shown inFIG. 4, a flat trapezoidal notch42in a front view is formed along the upper edge. The notch42is formed symmetrically in the left and eight directions in a front view, and has a horizontal center edge42C, and a left edge42L and a right edge42R extending in a truncated reverse V-shape toward a left lower direction and a right lower direction from the left end and right end of the center edge42C, respectively. The left and right edges42L,42R extend in the reverse V-shape at a center angle θ. Above the center edge42C, a vertically long elongated hole43is formed.

In each of the attachment sections, as shown inFIG. 3, a pair of left and right rails44are bridged between the front and rear side plates under the opening41. The rails44are inclined slightly upward toward the rear direction. Also, on an inside face of the front side plate40a, a drum unit biasing mechanism45is provided under the opening41. The drum unit biasing mechanism45has a roller-shaped pressing member45aand a coil spring to bias the pressing member45aupward, and is configured to bias the drum unit15upward.

The drum unit15, as shown inFIG. 5, has a box-shaped casing50made of resin. Inside of the casing50, the photosensitive drum9is housed rotatably around the rotating shaft9a, and the charger10and the cleaning device13are housed at appropriate positions along the periphery of the photosensitive drum9. The rear end of the rotating shaft9aof the photosensitive drum9protrudes rearward from the casing50.

The casing50is formed with left and right concentric circumferences parts51L,51R formed on a concentric circle with the rotating shaft9aof the photosensitive drum9on the left and right sides of a horizontal flat plate part51C, respectively, on a part of the front end of the upper face. The left and right concentric circumferences parts51L,51R each have a same center angle (the center angle around the rotating shaft9aof the photosensitive drum9) and are formed symmetrically in the left and right directions.

Further, on the lower face of the casing50, a sliding part (not shown) engaging with the rail44of the casing40is provided extending in the front and rear directions. Furthermore, as shown inFIG. 3, on the front end of the lower face of the casing50, a protrusion55protruding downward is formed. A lower face of the protrusion55is formed to be flat.

The positioning member30will be described with reference toFIG. 6A,FIG. 6Bor the like.FIG. 6Ais a rear view of the positioning member andFIG. 6Bis a perspective view of the positioning member. The positioning member30, as shown inFIG. 2, is interposed between the notch42formed in the opening41of the front side plate40aof the casing40and the left and right concentric circumferences parts51L,51R of the casing50of the drum unit15. As shown inFIG. 6AandFIG. 6B, the positioning member30has a supporting part31provided at the center and arm pieces32L,32R extending in a truncated reverse V-shape from the lower side of the supporting part31and is made of resin (for example, polypropylene resin).

The supporting part31is formed in a hexagonal flat plate shape in a front view. On the center portion of the rear face of the supporting part31, a supporting shaft33protruding rearward is formed. The supporting shaft33is formed of a pair of halves obtained by vertically dividing a three-stepped shaft with a gap extending in a vertical direction. Further, on the rear face of the supporting part31, an upper shaft34protruding rearward is formed above the supporting shaft33. A height of the upper shaft34is formed to be lower than a height of the supporting shaft33. Furthermore, along the lower edge of the supporting part31, a step part35bending rearward is formed.

The left arm piece32L and the right arm piece32R are provided in a truncated reverse V-shape in a front view so as to extend in the lower left direction and the lower right direction from the left end and the right end of the front edge of the step part35, respectively. The left arm piece32L and the right arm piece32R have proximal parts32aextending downward from the left end and the right end of the front edge of the step part35and main body parts32bextending linearly from tip ends of the proximal parts32ain an oblique left lower direction and an oblique right lower direction, respectively. In the left and right arm pieces32L,32R, an angle θ between the main body parts32bis formed to be equal to the angle θ between the left and right edges42L,42R (refer toFIG. 4) in the notch42of the opening41of the casing40. The main body part32bis formed with an elongated rectangular-shaped front tongue piece36extending upward along a portion close to the proximal part32a. Further, on the rear face of the main body part32b, an intervening part37is formed.

The intervening part37is flat-plate shaped elongated along the main body32band has a flat upper face (edge side abutment face)37aand a flat lower face (unit side abutment face)37b. The upper face37aand the lower face37bare formed in parallel to each other. As an example, an interval t (a thickness of the intervening part37) between the upper face37aand the lower face37bis 1 mm and a tolerance in a thickness direction of the intervening part37is ±0.02 mm or less. In addition, a length of the intervening part37in the front and rear directions is formed to be longer than a thickness of the front side plate40aof the casing40. The intervening part37is provided along the lower edge of the main body part32bon the rear face of the main body part32bof each of the left and right arm pieces32L,32R. In the left and right arm pieces32L,32R, an angle between the upper faces37aof the intervening parts37and an angle between the lower faces37bof the intervening parts37are equal to the angle θ between the main body parts32b.

On the rear face of the intervening part37, a rear tongue piece38extending upward is formed. The rear tongue piece38has a rectangular shape which is smaller in width than the front tongue piece36. The front tongue piece36and the rear tongue piece38are parallel to each other and are shifted in the left and right directions in a front view. Further, the front tongue piece36and the rear tongue piece38are perpendicular to the upper and lower faces37a,37bof the intervening part37.

A method of attaching the drum unit15to the printer main body2by employing the positioning member30having the above construction will be described with reference toFIG. 7toFIG. 9or the like.FIG. 7is a perspective view showing the positioning member supported to the printer main body, viewed from the rear side;FIG. 8Ais a front view showing the drum unit before biased by the drum unit biasing mechanism;FIG. 8Bis a front view showing the drum unit after biased by the drum unit biasing mechanism; andFIG. 9is a front view enlarging and showing the vicinity of the positioning member at the attachment position.

When the drum unit15is attached to the printer main body2, first, the positioning member30is caused to be supported to the casing40of the printer main body2. At this juncture, as shown inFIG. 7, the supporting shaft33of the positioning member30is caused to be inserted from the front side into the elongated hole43formed above the opening41formed in the front sideplate40aof the casing40. The supporting shaft33can be supported to the elongated hole43movably in the vertical direction and swingably in the left and right directions by deforming each of the halves inward. Incidentally, at this juncture, the supporting shaft33is inserted into a position close to the lower end of the elongated hole43.

In addition, when the left and right edges42L,42R of the notch42are respectively fitted between the front tongue pieces36and the rear tongue pieces38of the left and right arm pieces32L,32R, the upper faces37aof the intervening parts37of the left and right arm pieces32L,32R respectively face the left and right edges42L,42R of the notch42at predetermined intervals. Also, the rear faces of the front tongue pieces36of the left and right arm pieces32L,32R face the front face of the front side plate40aand the front faces of the rear tongue pieces38face the rear face of the front side plate40a.

Incidentally, as described previously, the length of the intervening part37in the front and rear directions is formed to be longer than the thickness of the front side plate40aof the casing40. Also, the supporting shaft33can be moved inside the elongated hole43in the front and rear directions by deforming inward. This makes it possible to move the positioning member30in the front and rear directions between a position at which the rear faces of the front tongue pieces36of the left and right arm pieces32L,32R abut against the front face of the front side plate40aand another position at which the front faces of the rear tongue pieces38abut against the rear face of the front side plate40a.

Namely, the positioning member30is supported in the front sideplate40aso as to be movable in the vertical direction and swingable in the left and right directions and further movable in the front and rear directions.

Next, the drum unit15is caused to be positioned to corresponding attachment section of the opening41formed in the front side plate40aof the casing40, a slider provided on the lower face of the casing50is caused to engage with the rail44(refer toFIG. 3) bridged between the front and rear side plates of the casing40and then is caused to slide rearward along the rail44. When the drum unit15slides up to the rear end of the rail44, the rotating shaft9aof the photosensitive drum9protruding from the rear face of the casing50is inserted into the bearing hole formed in the rear side plate. Incidentally, as described previously, since the rail44is inclined slightly upward toward the rear side, the drum unit15does not interfere with the transferring belt6during the sliding of the drum unit15.

When the drum unit15slides up to the rear end of the rail44, as shown inFIG. 8A, the left and right concentric circumferences parts51L,51R provided on the front end portion of the upper face of the casing50are respectively positioned below the lower faces37bof the intervening parts37of the left and right arm pieces32L,32R of the positioning member30. Further, as shown inFIG. 4, the protrusion55provided on the lower face of the casing50abuts against the upper face of the pressing member45aof the drum unit biasing mechanism45provided on the front side plate40aand biases the front end of the drum unit15upward.

When the front end of the drum unit15is biased upward, as shown inFIG. 8B, the left and right concentric circumferences parts51L,51R of the casing50move upward and abut against the lower faces37bof the respective intervening parts37of the positioning member30. At this juncture, the supporting shaft33of the positioning member30swings in the left and right directions. This causes apexes of the left and right concentric circumferences parts51L,51R of the casing50to abut against the lower faces37bof the intervening parts37. The intervening parts37are pushed upward by the left and right concentric circumferences parts51L,51R of the casing50. In the positioning member30, the supporting shaft33moves upward inside the elongated hole43.

Incidentally, while the positioning member30moves upward, since the front tongue piece36and the rear tongue piece38respectively provided at the left and right arm pieces32L,32R prevent the positioning member30from swinging in the front and rear directions, the intervening parts37are pushed up in a substantially parallel posture with the left and right edges42L,42R. The positioning member30moves upward until the upper faces37aof the intervening parts37respectively abut against the left and right edges42L,42R of the notch42in the opening41of the front side plate40a.

Afterwards, as shown inFIG. 9, the upper faces37aof the intervening parts37of the positioning member30abut against the left and right edges42L,42R of the front side plate40aand also the apexes of the left and right concentric circumferences parts51L,51R of the casing50abut against the lower faces37bof the intervening parts37. In this manner, an interval between the left and right edges42L,42R of the front side plate40aand the respective left and right concentric circumferences parts51L,51R of the casing50is regulated to the thickness t of the intervening part37. In addition, the drum unit15is supported at a total of three positions including an abutment position between the pressing member45aof the drum unit biasing mechanism45and the lower face of the protrusion55of the casing50and another two abutment positions between the apexes of the left and right concentric circumferences parts51L,51R of the drum unit15and the lower faces37bof the intervening parts37of the positioning member30.

As has been described hereinabove, in the color printer1according to the embodiment, if the positioning member30is mounted to each elongated hole43formed above the opening41of the casing40, only the sliding operation of the drum unit15through the opening41at corresponding attachment section makes it possible to position the drum unit15with respect to the printer main body2by the positioning member30. Therefore, since the work of detaching or attaching the retainer as in the prior art is unrequired, the work of attaching or detaching the drum unit15can be made easy and a structure of the color printer1can be simplified. Also, since the opening41is formed in the front side plate40aof the casing40, the sliding operation of each drum unit15or the positioning operation with respect to the printer main body2by employing the positioning member30can be easily carried out. Further, since each drum unit15is positioned by employing the positioning member30having a same structure, the precision of the relative position of each drum unit15can be enhanced and therefore degradation in image quality, such as color displacement, at the time of forming a color image does not occur.

In detail, since the drum unit15is supported at a total of three positions including an abutment position between the pressing member45aof the drum unit biasing mechanism45and the lower face of the protrusion55of the casing50and another two abutment positions between the apexes of the left and right concentric circumferences parts51L,51R of the drum unit15and the lower faces37bof the intervening parts37of the positioning member30, the drum unit15can be precisely positioned with respect to the printer main body2.

Further, at the abutment position between the pressing member45aof the drum unit pressing mechanism45and the lower face of the protrusion55of the casing50, a part on the circumferential face of the roller-shaped pressing member45aabuts against the flat lower face. In addition, at the another two abutment positions between the left and right concentric circumferences parts51L,51R of the casing50and the lower faces37bof the intervening parts37, a part on the circumferential face of each of the left and right circumferences parts51L,51R abuts against the flat lower face37bof the intervening part37. Thus, since each contact area of the three abutment positions is formed to be extremely small, the positioning precision by supporting at these three positions is improved more remarkably.

Furthermore, since the drum unit15is positioned by the left and right concentric circumferences parts51L,51R of the drum unit15that is concentric with the rotating shaft9aof the photosensitive drum9, the positioning precision of the photosensitive drum9can be enhanced in particular.

Still furthermore, since the intervening parts37of the positioning member30each have a high tolerance in the thickness direction, intervals between the left and right concentric circumferences parts51L,51R of the drum unit15and the respective left and right edges42L,42R of the front side plate40aof the casing40can be managed with a high precision. Therefore, the drum unit15can be positioned with respect to the printer main body2with a high precision.

Still furthermore, since the positioning member30made of resin is provided so as to cover the notch42of the opening41of the casing40, the casing50of the drum unit15less frequently comes into direct contact with the edge of the opening41of the casing40during the sliding operation of the drum unit15and, therefore, it becomes possible to reduce risk of damage on the drum unit15.

In addition, since the supporting shaft33of the positioning member30can be varied in the diameter within a certain degree by elastically deforming inward in the diametrical direction, the position of the supporting shaft33can be adjusted for every printer1.

Next, with reference toFIG. 10, another embodiment of the positioning member will be described. In this embodiment, at the center of each intervening part37of the positioning member30, an aperture61extending in the left and right directions is formed. Between the left and right side faces of each aperture61, a rotating shaft extending in parallel with each arm piece32is provided. Around the rotating shaft, a roller62is rotatably supported. The rollers62protrude upward and downward from the upper face37aand the lower face37bof the intermediate part37, respectively.

Also, along each of the left and right edges42L,42R of the casing40, a depression64in which the upper portion of the roller62is housed is formed at a position to corresponding roller62of the positioning member30attached to the casing40. By forming the depression64, the rollers62do not come into contact with the left and right edges42L,42R.

In this construction, when the drum unit15is biased upward by the drum unit biasing mechanism45, the left and right concentric circumferences parts51,51R each abut against an outer circumferential face of the roller62. Therefore, when the drum unit15is caused to slide along the rail44at the time of attaching or detaching the drum unit15, since the casing50comes into contact with the rollers62, the sliding property between the casing50and the positioning member30can be enhanced. Hence, the sliding operation of the drum unit15can be smoothly carried out.

The embodiment was described in a case of applying the configuration of the present disclosure to the printer1. On the other hand, in another embodiment, the configuration of the disclosure may be applied to another image forming apparatus, such as a copying machine, a facsimile or a multifunction peripheral, except for the printer1.

While the preferable embodiment and its modified example of the image forming apparatus of the present disclosure have been described above and various technically preferable configurations have been illustrated, a technical range of the disclosure is not to be restricted by the description and illustration of the embodiment. Further, the components in the embodiment of the disclosure may be suitably replaced with other components, or variously combined with the other components. The claims are not restricted by the description of the embodiment of the disclosure as mentioned above.