Developing cartridge that includes member to be pressed by image-bearing-member cartridge

A process cartridge includes an image bearing member cartridge and a developing cartridge detachably installed in the image bearing member cartridge. The image bearing member cartridge has a pair of first and second side plates, a latent image bearing member, and a pressure member. The developing cartridge has a pair of third and fourth side plates and a pair of first and second light guides fixed at the third and fourth side plates, respectively. The pressure member presses side surfaces of the first and the second light guides, thereby urging the developing agent bearing member toward the latent image bearing member.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2008-247373 filed Sep. 26, 2008. The entire content of the priority application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an image forming device, and more particularly to an image forming device using a process cartridge.

BACKGROUND

Electrophotographic image forming devices typically use a process cartridge that is detachably mounted in the image forming device. One example of the process cartridge includes a drum cartridge incorporating a photosensitive drum therein, and a developing cartridge detachably mounted on the drum cartridge. The developing cartridge includes a developing roller that is urged toward the photosensitive drum by a pressure member. The developing cartridge further includes a toner chamber that accommodates toner therein. To detect an amount of toner remaining in the toner chamber, a toner amount detector is provided to the image forming device.

This type of process cartridge is advantageous in terms of cost, because the drum cartridge and the developing cartridge can be separately and independently replaced with new one. However, such an image forming device is disadvantageous in some points. For example, space for accommodating a member to be pressed by the pressure member is limited.

SUMMARY

In view of the foregoing, it is an object of the present invention to provide an improved image forming device, wherein space for accommodating a member to be pressed by a pressure member is preserved.

In order to attain the above and other objects, the invention provides a process cartridge detachably installable to a main frame of an image forming device. The main frame has a developing-agent amount detection unit including a light emitting element and a light receiving element. The process cartridge includes an image bearing member cartridge and a developing cartridge. The image bearing member cartridge includes a first casing having a pair of first and second side plates defining an accommodation portion, a latent image bearing member having a surface on which an electrostatic latent image is formed, and a pressure member. The latent image bearing member is supported to the first casing. The developing cartridge is detachably installed in the accommodation portion and includes a second casing having a pair of third and fourth side plates in confrontation with the first and second side plates, respectively, a developing agent bearing member rotatably supported to the second casing, and a pair of first and second light guides fixed to the third and fourth side plates, respectively. The pair of third and fourth side plates defines a chamber that stores a developing agent. The developing agent bearing member supplies the developing agent onto the latent image bearing member. The pair of first and second light guides are configured to introduce a light emitted from the light emitting element into the chamber and to direct the light from the chamber toward the light receiving element. Each of the first and second light guides has a fixed end portion having a first end surface and fixed to either of the third and fourth side plates, a free end portion having a second end surface and remote from the chamber, and a side surface extending in an axial direction of the developing agent bearing member. The pressure member presses the side surfaces, thereby urging the developing agent bearing member toward the latent image bearing member.

There is also provided a developing cartridge detachably installable in an image bearing member cartridge including a pressure member. The developing cartridge includes a cartridge casing, a developing agent bearing member, and a pair of first and second light guides. The cartridge casing has a pair of first and second side plates defining a chamber that stores a developing agent. The developing agent bearing member bears the developing agent supplied from the chamber and is rotatably supported to the cartridge casing. The pair of first and second light guides are fixed to the first and second side plates, respectively. The pair of first and second light guides are configured to introduce a light into the chamber and directing the light from the chamber. The first light guide has a fixed end portion fixed to the first side plate and a free end portion remote from the chamber. The free end portion has an end surface and a side surface that the pressure member of the image bearing member cartridge presses.

Further, there is also provided a developing cartridge detachably installable in an image bearing member cartridge including a pressure member. The developing cartridge includes a cartridge casing, a developing agent bearing member, a gear transmission mechanism, and a pair of first and second light guides. The cartridge casing has a pair of first and second side plates defining a chamber that stores a developing agent. The developing agent bearing member bears the developing agent supplied from the chamber, and is rotatably supported to the cartridge casing. The gear transmission mechanism is provided at the first side plate and transmits a driving force to the developing agent bearing member. The pair of first and second light guides are fixed to the first and second side plates, respectively, made from a transparent material, and configured to introduce a light into the chamber and directing the light from the chamber. The pair of first and second light guides are positioned in symmetrical relationship with each other with respect to a plane extending in a direction perpendicular to an axial direction of the developing agent bearing member. The first light guide has a fixed end portion fixed to the first side plate and a free end portion remote from the chamber. The free end portion has an end surface and a side surface that the pressure member of the image bearing member cartridge presses. A distance between the first side plate and the end surface is greater than a distance between the first side plate and an outer contour of the gear transmission mechanism.

DETAILED DESCRIPTION

An image forming device according to a first embodiment of the present invention will be described with reference toFIGS. 1 through 10. The first embodiment pertains to a laser printer1. The terms “upward”, “downward”, “upper”, “lower”, “above”, “below”, “right”, “left”, “front”, “rear” and the like will be used throughout the description assuming that the laser printer1is disposed in an orientation in which it is intended to be used.

As shown inFIG. 1, the laser printer1has a main frame2in which a sheet supply section4for supplying a sheet3and an image forming section5for forming an image on the sheet3are provided. The main frame2has a front opening6(FIG. 2) for attachment and detachment of a process cartridge20. A front door7is provided for opening and closing the front opening6.

The sheet supply section4is provided in a lower portion of the main frame2, and includes a sheet supply tray9and a sheet supply mechanism. The sheet supply tray9is detachably installed in the main frame2for accommodating therein a stack of cut sheets3. The sheet supply mechanism includes a sheet supply roller10, a separation pad11, a pickup roller12, a pinch roller13, and a pair of registration rollers14. The sheet supply roller10and the separation pad11are positioned above a front end portion of the sheet supply tray9. The pickup roller12is positioned immediately rearward of the sheet supply roller10. The pinch roller13is positioned immediately frontward of and lower than the sheet supply roller10. The pair of registration rollers14are vertically arrayed at a position above and rearward of the sheet supply roller10. Rotation of the pickup roller12feeds an uppermost sheet3in the sheet supply tray9, and the sheet supply roller10and the separation pad11nip the sheet3therebetween for separating the uppermost sheet3from the remaining sheet stack. Then, the sheet3is supplied to the image forming section5by the pinch roller13and the pair of registration rollers14.

The image forming section5includes a scanner unit19, the process cartridge20, and a fixing unit21. The scanner unit19includes a polygon mirror22, an fθ lens23, a reflection mirrors24,26, and a lens25. As shown by a broken line, a laser beam emitted from a laser light source (not shown) based on image data is deflected at the polygon mirror22, passes through the fθ lens23, is reflected at the reflection mirror24, passes through the lens25, is bent downward by the reflection mirror26, and is irradiated onto a surface of a photosensitive drum92assembled to the process cartridge20.

The process cartridge20is positioned below the scanner unit19and is detachably attached to the main frame2(FIG. 2). As shown inFIGS. 3 through 5, the process cartridge20includes a drum cartridge27and a developing cartridge28detachably attached to the drum cartridge27.

The developing cartridge28can be detached from and attached to the main frame2integrally with the drum cartridge27. Further, the developing cartridge28is detachable from and attachable to the main frame2while the drum cartridge27is installed in the main frame2.

As shown inFIG. 1, the developing cartridge28is partitioned into a toner chamber30and a developing chamber36. A toner supply port58is defined between the toner chamber30and the developing chamber36. An agitator46is provided inside the toner chamber30. Disposed inside the developing chamber36are a toner supply roller31, a developing roller32, and a blade33. Toner accommodated in the toner chamber30is agitated by the agitator46and is discharged into the developing chamber36through the toner supply port58. Then, the toner is supplied to the developing roller32by the rotation of the toner supply roller31. At this time, the toner is triboelectrically charged with positive polarity between the toner supply roller31and the developing roller32to which a developing bias is applied.

The toner supplied onto the developing roller32is subjected to thickness regulation by the blade33. Thus, a toner layer of uniform thickness is carried on the developing roller32.

The drum cartridge27includes the photosensitive drum92, a scorotron charger93, a transfer roller94, and a cleaning brush95. The surface of the photosensitive drum92is uniformly charged with positive polarity by the scorotron charger93while the photosensitive drum92rotates. Then, the surface is exposed to a high-speed scanning of laser beam from the scanner unit19to form an electrostatic latent image on the surface. A visible toner image corresponding to the latent image is formed on the surface of the photosensitive drum92by supplying positively charged toner from the developing roller32.

The toner image carried on the surface of the photosensitive drum92is transferred to the sheet3by the transfer bias applied to the transfer roller94when the sheet3passes between the photosensitive drum92and the transfer roller94. Paper dust transferred from the sheet3to the photosensitive drum92can be removed by the cleaning brush95applied with cleaning bias.

The fixing unit21includes a heat roller183and a pressure roller184for thermally fixing the toner image onto the sheet3while the sheet3passes between the heat roller183and the pressure roller184. The sheet3with the toner image fixed thereon is conveyed along a discharge path185that diagonally upwardly extends from the fixing unit21, and is discharged by discharge rollers186onto a discharge tray187formed at an upper surface of the main frame2.

Next, the developing cartridge28will be described in detail. As shown inFIG. 5, the developing cartridge28includes a developing cartridge casing29made from a resin such as a polystyrene. In the developing cartridge casing29, the developing chamber36and the toner chamber30shown inFIG. 1are arrayed in the front-to-rear direction.

The developing cartridge casing29has a boxy shape having five almost-closed sides and one open end where the developing roller32is positioned. As shown inFIG. 6, a pair of left and right side plates38,39are provided at lateral positions of the developing cartridge casing29. The toner chamber30is defined between the left and right side plates38,39.

As shown inFIG. 8, the agitator46is provided at a center portion of the toner chamber30when viewing from the lateral side of the developing cartridge casing29. The agitator46includes a rotation shaft59whose axial end portions are rotatably supported to the left and right side plates38,39, and an agitation blade60extending radially outwardly from the rotation shaft59.

The toner supply roller31has a roller shaft62protruding laterally outwardly and rotatably supported to the side plates38,39. The developing roller32has a roller shaft64and a roller body65formed on the roller shaft64(FIG. 7). The roller shaft64protrudes laterally outwardly and rotatably supported to the left and right side plates38,39. The developing roller32is in pressure contact with the toner supply roller31. A rear part of an outer periphery of the developing roller32protrudes outward from the open end of the developing cartridge casing29.

As shown inFIGS. 5 through 7, a gear transmission mechanism45is provided at the left side plate38for transmitting driving force to the developing roller32, the toner supply roller31, and the agitator46. A gear cover77is fixed to the left side plate38for covering the gear transmission mechanism45. Another gear cover77is fixed to the right side plate39.

As shown inFIG. 7, the gear transmission mechanism45includes an input gear68and drive gears69,71, and72directly or indirectly meshingly engaged with the input gear68. The input gear68has a center portion provided with a coupling member74exposed through an opening of the gear cover77(FIGS. 3 and 5). The coupling member74is adapted to be coupled to a main coupling member (not shown) connected to a drive source (not shown) at the main frame2when the process cartridge20is loaded to the main frame2and rotatable together with the rotation of the main coupling member. The drive gear69is coaxially fixed to the rotation shaft59of the agitator46, and the drive gear71is coaxially fixed to the roller shaft64of the developing roller32. The drive gear72is coaxially fixed to the roller shaft62of the toner supply roller31. Thus, the agitator46, the developing roller32, and the toner supply roller31are rotated upon rotation of the input gear68.

Each axial end portion of the roller shaft64of the developing roller32protrudes laterally outward beyond the left or right side plate38,39and rotatably supports a sleeve64A (FIG. 6) thereon. Each sleeve64A is supported by the drum cartridge27as will be described later.

As shown inFIG. 10, light guides85,85are disposed at the left and right side plates38,39. The light guides85are made from a transparent material and positioned in symmetrical relationship with each other with respect to an imaginary center plane P1extending perpendicular to the axial direction of the roller shaft64.

More specifically, each of the left and right side plates38,39is formed with a hole through which each light guide85is inserted from the toner chamber30side so that the light guide85protrudes laterally outward beyond the left or right side plate38,39. The light guides85have laterally inner end portions853A,853B and laterally outer end portions856A,856B. The laterally inner end portions853A,853B are provided with flanges851that are in abutment with and fixed to the left and right side plates38,39by fuse-bonding or an adhesive. The laterally outer end portions856A,856B have side surfaces855,855extending in the lateral direction. The side surfaces855,855are adapted to be pressed by pressure members149when the developing cartridge28is assembled to the drum cartridge27. Each gear cover77has an opening77A through which each light guide85extends outward.

The main frame2has a light emitting element301and a light receiving element302. It is preferable that the laterally outer end portions856A,856B come into opposition and as close as possible to the light emitting element301and the light emitting element302, respectively, when the process cartridge20is loaded to the main frame.

When detecting the residual toner amount, a sensor light L from the light emitting element301enters the light guide85at the right side plate37from the laterally outer end portion856A and then is directed into the toner chamber30through the light guide85. The sensor light L passed through the toner chamber30enters the light guide85at the left side plate36from the laterally inner end portion853B and is directed to the light receiving element302.

The light guide85positioned at the left side plate38has a length between an inner end E1and an outer end E2that is greater than a distance between the inner end E1and the gear cover77. Further, the length of the light guide85is greater than a distance between the inner end E1and an outer contour of the gear transmission mechanism45on a side of the gear cover77. With this structure, the outer end E2can be positioned remote from grease impregnated in the gear transmission mechanism45.

The drum cartridge27has a left side plate96and a right side plate97. The length between the inner end E1and the outer end E2is greater than a distance between the inner end E1and the left side plate96. Also, a length between an inner end E3and an outer end E4is greater than a distance between the inner end E3and the right side plate97.

Next, a structure of the drum cartridge27will be described in detail with reference toFIGS. 5 and 9. The drum cartridge27includes a drum cartridge casing91made from a resin such as polystyrene. The drum cartridge casing91defines a drum accommodating portion102and a developing cartridge accommodating portion103those arrayed in the front-to-rear direction. The drum accommodating portion102accommodates therein the photosensitive drum92, the scorotron charger93, and the transfer roller94. The drum cartridge casing91has a boxy shape having an upper open end through which the developing cartridge28is assembled.

The photosensitive drum92includes a drum shaft125and a drum body (not shown) rotatable about the drum shaft125. The drum shaft125is supported to the left and right side plates96,97. The transfer roller94is positioned below the photosensitive drum92and its rotation shaft (not shown) is rotatably supported to the left and right side plates96,97. Each left end portion of each shaft of the photosensitive drum92and the transfer roller94is integrally fixed with a gear (not shown) meshedly engaged with the gear transmission mechanism45at the developing cartridge28. Thus, the photosensitive drum92and the transfer roller94are driven by the drive source (not shown) at the main frame2.

The left and right side plates96,97are formed with a pair of recesses101. The pair of recesses101are aligned with each other in the lateral direction for receiving therein the light guides85,85of the developing cartridge28. As shown inFIG. 5, each of the recesses101is defined by a front surface, a rear surface, a bottom surface, and a top opening. The pressure member149is provided along the front surface of each recess101, and is biased rearward (toward the photosensitive drum92) by a spring (not shown). Each pressure member149has a slant guide surface extending to the bottom of the recess101.

Each of the left and right side plates96,97is formed with a roller guide115and a shaft receiving portion116positioned rearward of and contiguous with the roller guide115. The roller guide115and the shaft receiving portion116together form a recess like configuration. The roller guide115has a guide surface extending toward the drum shaft125of the photosensitive drum92. The roller guide115has an upper open end for introducing the sleeve64A (FIG. 6) of the developing roller32into the shaft receiving portion116along the guide surface. A lock lever153is provided at the drum cartridge casing91for locking assembly of the developing cartridge28to the drum cartridge27. Further, the drum cartridge casing91is provided with a boss150, and the main frame2has a positioning member166(FIG. 1) engageable with the boss150for positioning the drum cartridge27relative to the main frame2.

Next, assembling procedure of the developing cartridge28to the drum cartridge27will be described. As shown inFIG. 5, the developing cartridge28is positioned above the developing cartridge accommodating portion103of the drum cartridge27. The sleeves64A at the end portions of the roller shaft64of the developing roller32are inserted into the roller guides115and guided along the guide surfaces of the roller guides115until the sleeves64A abut rearmost end surfaces of the shaft receiving portions116.

Then, the developing cartridge28is pivotally moved downward about the sleeves64A, so that a front end portion of the developing cartridge28can be positioned into the developing cartridge accommodating portion103. With this pivotal movement, the light guides85are inserted into the recesses101.

At this time, the side surfaces855of the light guides85come into abutment with the pressure members149and are guided toward the bottoms of the recesses101along the slant surfaces of the pressure members149.

Upon completion of assembly of the developing cartridge28into the drum cartridge27, the pressure members149press the side surfaces855of the light guides85rearward (toward the photosensitive drum92), so that the developing roller32is urged toward the photosensitive drum92. Therefore, the developing roller32can be positioned at a given position with respect to the photosensitive drum92in such a manner that the developing roller32is in contact with or spaced away from the photosensitive drum92by a predetermined distance. Then, the lock lever153is operated to lock the position of the developing cartridge28relative to the drum cartridge27. In this case, the left side plates96and38are facing with each other, and the right side plates97and39are facing with each other. Further, the light guides85are out of contact with the bottom surfaces of the recesses101.

In this manner, the developing cartridge28is assembled to the drum cartridge27to provide the process cartridge20. Upon loading the process cartridge20to the main frame2, the boss150is engaged with the positioning member166at the main frame2, thereby positioning the process cartridge20relative to the main frame2as shown inFIG. 1.

As described above, the pressure members149press the side surfaces855of the light guides85protruding beyond the left and right side plates38,39to urge the developing roller32toward the photosensitive drum92. Since the light guides85,85are positioned symmetrical with each other with respect to the plane P1extending perpendicular to the axis of the developing roller32, balanced force in the lateral direction can be applied to the developing roller32, enabling desirable developing operation.

Next, detection of toner amount remaining in the toner chamber30will be described. As shown inFIG. 10, the light emitting element301and the light receiving element302are disposed in confrontation with each other. A light emitting diode (LED) is used as the light emitting element301, for example. The light emitting element301emits the sensor light L toward the light receiving element302, and the light receiving element302receives the sensor light L. Based on the sensor light L received at the light receiving element302, the light receiving element302outputs an electrical signal having a level corresponding to the amount of sensor light L received at the light receiving element302. In this embodiment, the light emitting element301is disposed in a left-side side wall of the main casing2and the light receiving element302in a right-side side wall of the main casing2. However, the light emitting element301and the light receiving element302may be disposed in reversed relation.

The light emitting element301, the light guides85, and the light receiving element302are brought into alignment with one another along a line parallel to the axial direction of the roller shaft64when the process cartridge20is properly positioned with respect to the main casing2. The remaining toner amount detection is commenced when the laser printer1is powered ON or at a predetermining timing, such as, at a time before starting a printing operation.

The sensor light L emitted from the light emitting element301enters the light guide85at the right side plate39from the outer end portion856A and advances toward the toner chamber30while being diffuse-reflected inside the light guide85.

The sensor light L is then outputted from the inner end portion853A of the light guide85and irradiated into the toner chamber30. Then, the sensor light L is incident upon the inner end portion853B of the light guide85at the left side plate38. The sensor light L advances toward the outer end portion856B of the light guide85while being diffuse-reflected inside the light guide85, and is outputted from the outer end portion856B of the light guide85. The light receiving element302detects the sensor light L and outputs an electrical signal corresponding to the amount of light received thereat. When a large amount of toner remains in the toner chamber30, a small amount of light is received at the light receiving element302. In this case, the light receiving element302outputs a low-level electrical signal. Conversely, when a small amount of toner remains in the toner chamber30, a large amount of light is received at the light receiving element302. Accordingly, the light receiving element302outputs a high-level electrical signal. The amount of toner remaining in the toner chamber30can be detected based on the level of the electrical signal.

As described above, the right-side light guide85projects beyond the right side plate97of the drum cartridge casing91toward the light emitting element301, so that the outer end portion856A of the light guide85is positioned in proximity with the light emitting element301. The above is also true with respect to the positional relation between the outer end portion856B of the left-side light guide85and the light receiving element302. Thus, the sensor light L from the light emitting element301can effectively reach the light receiving element302and can be used for the detection of the toner with no substantial loss of light caused by diffusion. As a result, detection of the remaining toner amount can be accurately performed. Further, because the outer end portion856B of the light guide85projects further outward than the gear transmission mechanism45, it is unlikely that the outer end portion856B is polluted by grease scattering from the gears68,69,71and72of the gear transmission mechanism45, and therefore the sensor light L is substantially free from diffusion.

The light guides85are also used as members to be pressed by the pressure members149so that the developing roller32is urged toward the photosensitive drum92. It is therefore not necessary to separately provide members to be pressed by the pressure members149and to preserve space for such members, thereby preventing the developing cartridge28from being large-sized.

Next, a second embodiment of the invention will be described. The second embodiment pertains to a process cartridge to which the present invention is applied. It is to be noted that like parts or like portions as those in the first embodiment are designated by like reference numerals, and duplicate description is omitted with respect to the arrangement same as that described with reference to the first embodiment.

A developing cartridge280shown inFIGS. 11 and 12differs from the developing cartridge28of the first embodiment in the shape of light guides. More specifically, the developing cartridge280of the second embodiment includes a pair of light guides850(only one light guide850on the left side is shown inFIG. 12) positioned in symmetrical relationship with each other with respect to the plane P1(FIG. 10).

Each light guide850is right-angled at two portions. For the sake of explanation, the light guide850will be described while dividing it into three portions including a first portion extending parallel to the roller shaft64of the developing roller32and including the inner end portion853B, a second portion extending parallel to the roller shaft64of the developing roller32and including the outer end portion856B, and a third portion859extending in a direction substantially orthogonal to the first and second portions. The third portion859has smoothly curved portions858each for joining the third portion859with either the first portion or the second portion. The first portion of the light guide850penetrates in part into either the left or right side plate38,39at a right angle with respect thereto and is fixed thereto.

With the above-described shape of the light guide850, the sensor light L entered the light guide850can pass through the light guide850without being refracted outside the light guide850at the curved portions858. The inner end portions853A,853B of the light guides850are in confrontation with each other and arranged on a line parallel to the roller shaft64of the developing roller32.

The light guides850may be fixed to the left and right side plates38,39during the production of the left and right side plates38,39by, for example, burying extended head portions851into the left and right side plates38,39.

In a drum cartridge270of the second embodiment, the outer end portion856A,856B of each light guide850is positioned closer to the developing roller32than the inner end portion853A,853B. As such, the pressure members149and the recesses101are provided in positions closer to the photosensitive drum92as compared with the drum cartridge27of the first embodiment. Each pressure member149urges the side surface855near the outer end portion856A,856B of each light guide850. The side surface855extends in an axial direction of the roller shaft64. That is, the position in which the light guide850is pressed is closer to the photosensitive drum92than the position in which the light guide85is pressed.

The bending direction of the light guides850may be determined arbitrarily, and the positions in which the light guides850are pressed by the pressure members147may be freely changed. Further, a position of the toner chamber30at which the sensor light L enters or is outputted from the toner chamber30can also be freely changed. Accordingly, there is no limitation in arranging the light emitting element301and the light receiving element302within the main frame2, and thus the design choice of the laser printer can be improved.

Next, a third embodiment of the invention will be described with reference toFIG. 13. A developing cartridge2800of the third embodiment includes a pair of light guides8500(only one light guide8500on the left side is shown inFIG. 13) positioned in symmetrical relationship with each other with respect to the plane P1(FIG. 10). Each light guide8500includes a window8600made from a transparent material and a hollow cylindrical projection3800projecting outward from either the left or right side plate38,39. The window8600is fitted into a through-hole formed in the left or right side plate38,39. The projection3800surrounds an outer part of an outer periphery of the window8600.

Similar to the light guide85described with reference to the first embodiment, the projection3800projects outward beyond both the gear cover77and the left or right side plate96,97. The projection3800has a side surface8550extending in a direction parallel to the roller shaft64of the developing roller32. The side surface8550is pressed by the pressure member149of the drum cartridge27.

At the time of detection of the residual toner amount, the sensor light L emitted from the light emitting element301passes through the projection3800and the window8600of the light guide8500on the right side, the toner chamber30, and the window8600and the projection3800of the light guide8500on the left side, and is received at the light receiving element302.

Surrounding the outer periphery of the window8600, the projection3800prevents grease scattered from the gear transmission mechanism45from clinging onto the window8600. Hence., toner amount detecting accuracy is not degraded by the foreign matter clinging to the window8600. Further, the sensor light L passes through the projection3800while being reflected inside the projection3800so that the leakage of the sensor light L is not likely to occur. With the structure described above, highly accurate toner amount detection can be performed. Similar to the first and second embodiments, it is not necessary to provide a separate member to be pressed by the pressure member149because the projection3800plays a role of such a member.

While the invention has been described in detail and with reference to specific embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

For example, although the gear transmission mechanism45is only provided at the left side plate38in the above described embodiments, the gear transmission mechanism45may be provided at both the left and right side plates38and39.