Image forming device

An image forming device is provided, which includes an interlocking mechanism that causes a cleaning unit to clean with a cleaning surface thereof a detection surface of a detection sensor for reading each detection pattern formed on an outer surface of a sheet-feeding endless belt, in conjunction with movement of a drawer, which holds a plurality of process cartridges, between an attachment position where a photoconductive drum included in each process cartridge faces an up-facing side of the outer surface of the endless belt and a replacement position where at least one of the process cartridges is outside a main body housing of the image forming device.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 from Japanese Patent Application No. 2010-219208 filed on Sep. 29, 2010. The entire subject matter of the application is incorporated herein by reference.

BACKGROUND

1. Technical Field

The following description relates to one or more image forming devices that include a belt unit having an endless belt, a plurality of process cartridges, arranged along the belt unit, each of which contains therein a specific color of recording agent used for color image formation, and a detection sensor configured to optically read a detection pattern formed on the endless belt with each recording agent.

2. Related Art

So far, as an image forming device that forms a color image, an image forming device has been known that includes a belt unit having an endless belt and a plurality of process cartridges, arranged along the belt unit, each of which contains therein toner used for color image formation.

The known image forming device has the plurality of process cartridges arranged on a surface of the endless belt in a tandem manner, and each of the process cartridges contains therein toner of a specific one of the colors, black (K), yellow (Y), magenta (M), and cyan (C). Further, the known image forming device forms a color image on a recording medium while sequentially transferring different color toner images in a superimposed manner. Accordingly, in order to assure favorable image quality, the known image forming device needs to control with a high accuracy a position where a toner image is superimposed on another toner image and a density of each toner image.

In consideration of the aforementioned regards, the known image forming device is configured to form a detection pattern with each color of toner on the endless belt and optically detect each detection pattern with an optical sensor which is disposed such that a detection surface thereof faces the surface of the endless belt. Therefore, by reading each detection pattern with the optical sensor, the known image forming device can appropriately correct the position where a toner image is to be superimposed on another toner image and the density of each toner image, and thus form a user-desired image of favorable image quality.

SUMMARY

In the known image forming device, a certain level of detection accuracy for detecting each detection pattern by the optical sensor is required to correct a positional deviation and an inadequate density of each toner image. As described above, since the detection surface of the optical sensor faces the endless belt, when toner used for the formation of the image or the detection pattern image is splashed, the detection surface is likely to be contaminated by the splashed toner. Such a contaminated detection surface might lead to a lowered level of detection accuracy for detection of the detection patterns and in a lowered level of quality of the image formed by the image forming device.

Accordingly, in order to assure favorable quality of the image formed by the image forming device, it is required to keep the detection surface of the optical sensor clean. In this respect, a user may be required to clean the detection surface of the optical sensor on user's own. In this case, however, favorable image quality might not certainly be assured as a moment to clean the detection surface is determined by the user. Further, the user could not clean the detection surface on user's own due to a problem concerning a positional relationship between the optical sensor and a different component.

Aspects of the present invention are advantageous to provide one or more improved techniques for an image forming device having process cartridges and an endless belt, which techniques make it possible to keep clean a detection surface of a detection sensor for reading each detection pattern formed on the endless belt.

According to aspects of the present invention, an image forming device is provided, which includes a main body housing, a plurality of process cartridges each of which accommodates recording agent of a specific one of colors used for image formation, a plurality of photoconductive drums each of which is configured such that an electrostatic latent image, to be developed with the recording agent of a specific one of the colors, is formed thereon, a belt unit including an endless belt wound around a pair of rollers inside the main body housing, the endless belt being configured such that an up-facing side of an outer surface thereof extends and travels in a predetermined direction, a drawer configured to hold the process cartridges and the photoconductive drums arranged along the predetermined direction above the belt unit, the drawer being movable between an attachment position where each photoconductive drum faces the up-facing side of the outer surface of the endless belt and a replacement position where at least one of the process cartridges is outside the main body housing, a pattern forming unit configured to form, on the up-facing side of the outer surface of the endless belt, a detection pattern corresponding to each color of the recording agent used for image formation, a detection sensor comprising a detection surface that faces the outer surface of the endless belt, the detection sensor being configured to read, through the detection surface, each detection pattern formed on the outer surface of the endless belt, a cleaning unit including a cleaning surface configured to be able to contact and clean the detection surface of the detection sensor, and an interlocking mechanism that causes the cleaning unit to clean the detection surface of the detection sensor with the cleaning surface in conjunction with movement of the drawer between the attachment position and the replacement position.

DETAILED DESCRIPTION

First Embodiment

Hereinafter, a laser printer1of a first embodiment according to aspects of the present invention will be described with reference toFIGS. 1 to 4. In the following description, an up-to-down direction (i.e., the vertical direction) and a front-to-rear direction (and a left-to-right direction) of the laser printer1will be defined as depicted in the relevant drawings for the sake of easy understanding of a relative positional relationship among elements included in the laser printer1. The laser printer1is a color laser printer configured to form a multicolor image on a sheet P using an electrophotographic technique.

As shown inFIG. 1, the laser printer1includes a substantially box-shaped main body housing2. Further, the laser printer1includes a feeding unit10, an image forming unit20, a conveying unit50, a scanning unit60, a fixing unit70, and a registration sensor unit80, all of which are housed in the main body housing2. The image forming unit20is disposed substantially in a center of an internal space of the main body housing2.

On an inner side face of each side of the main body housing2in the left-to-right direction (i.e., on each inner side face of the far and near sides of the main body housing2in the direction perpendicular to a plane ofFIGS. 1 to 3), a drawer guide3is formed to protrude horizontally toward the inside of the main body housing2. The drawer guides3guide a drawer40(included in the image forming unit20) when the drawer40is moved between an attachment position (seeFIG. 1) and a replacement position (seeFIG. 3).

As depicted inFIGS. 2 and 3, each drawer guide3includes a first guide surface3A, a second guide surface3B, and a stopper surface3C. The first guide surface3A is horizontal in both the front-to-rear direction and the left-to-right direction of the laser printer1. Further, the first guide surface3A is formed as a flat plane extending from a position near a front cover6toward a rear side in an elongated manner. The second guide surface3B is horizontal in the left-to-right direction, and formed as a flat plane extending obliquely downward to a rear side of the laser printer1. A front end of the second guide surface3B is continuous with a rear end of the first guide surface3A. With the first guide surface3A and the second guide surface3B, a bent guide surface is configured. The stopper surface3C is horizontal in the left-to-right direction of the laser printer1, and extends upward from a rear end of the second guide surface3B. The stopper surface3C has a role for positioning the drawer40, moved along the drawer guides3, in a predetermined attachment position (seeFIG. 1).

A catch tray5is formed above the main body housing2, such that the sheet P, with an image formed thereon by the image forming unit20, is ejected thereonto by ejection rollers75. The catch tray5is loaded with ejected sheets P stacked thereon. Further, the front cover6is provided at a front face of the main body housing2, to be open and closed while turning around a lower end of the front cover6. As illustrated inFIGS. 2 and 3, the front cover6is opened when the drawer40is to be pulled out of the main body housing2.

Subsequently, an explanation will be provided about the feeding unit10of the laser printer1. The feeding unit10is configured to feed the sheet P to the image forming unit20. The feeding unit10includes a feed tray11, a pickup roller12, a separation pad13, feed rollers14, and registration rollers15.

The feed tray11is detachably attached under the main body housing2and configured to accommodate a stack of sheets P. The pickup roller12is rotatably disposed in a position above a front end of the feed tray11and configured to pick up and feed a sheet P from the feed tray11toward the image forming unit20. The separation pad13is configured to provide the sheet P fed by the pickup roller12with a predetermined feeding resistance, and to separate and feed the sheet P on a sheet-by-sheet basis.

As shown inFIG. 1, the sheet P fed from the feed tray11is conveyed toward the catch tray5along a feeding route R. Namely, a feeding direction in which the sheet P is fed in the laser printer1is a direction extending from the feed tray11to the catch tray5along the feeding route R.

Two feed rollers14are rotatably disposed downstream relative to the separation pad13in the feeding direction. The feed rollers14provide a feeding force to the sheet P to be conveyed to the image forming unit20while bent substantially in a U-shape along the feeding route R.

Further, two registration rollers15are rotatably disposed downstream relative to the feed rollers14in the feeding direction. The registration rollers15are configured to contact a leading end of the sheet P fed by the feed rollers14and carry out skew correction for the sheet P, and then feed the sheet P further to the image forming unit20.

Subsequently, the image forming unit20of the laser printer1will be described. The image forming unit20is disposed substantially in a center of an internal space of the main body housing2, and configured to form a color image on the sheet P fed by the feeding unit10. The image forming unit20, which employs a direct tandem method, includes a plurality of process cartridges25K,25Y,25M, and25C and the drawer40.

The process cartridge25K is used to form a black image with toner of black (K). The process cartridge25Y is used to form a yellow image with toner of yellow (Y). The process cartridge25M is used to form a magenta image with toner of magenta (M). The process cartridge25C is used to form a cyan image with toner of cyan (C).

Further, the process cartridges25K,25Y,25M, and25C are arranged in the drawer40in the aforementioned order along a direction from a front side to a rear side of the drawer40.

Next, an explanation will be provided about the configurations of the process cartridges25K,25Y,25M, and25C. The process cartridges25K,25Y,25M, and25C use respective different colors of toner. However, in the other respects, the process cartridges25K,25Y,25M, and25C are configured in the same fashion. Accordingly, in the following description, each of the process cartridges25K,25Y,25M, and25C will be referred to as a “process cartridge25” in a generic manner.

The process cartridge25includes a known photoconductive drum26, an electrification device27, and a toner cartridge30. On the photoconductive drum26, an electrostatic latent image corresponding to a toner color of the process cartridge25is formed by the below-mentioned scanning unit60. Then, when toner is supplied to the electrostatic latent image, a toner image is formed on the photoconductive drum26. The photoconductive drum26is disposed such that a part thereof protrudes downward from a lower end of the drawer40and contacts a surface of a conveying belt53of the below-mentioned conveying unit50. The electrification device27is configured to charge the surface of the photoconductive drum26evenly and positively when the electrostatic latent image is formed on the surface of the photoconductive drum26. The photoconductive drum26and the electrification device27are integrally supported by and fixed to the drawer40, and can be replaced as expendable parts together with the drawer40.

The toner cartridge30includes a toner container31, a supply roller32, and a development roller33. The toner container31contains therein toner of a color corresponding to the process cartridge25. The supply roller32supplies the toner contained in the toner container31to the development roller33. The development roller33adjusts (regulates) the thickness of the toner supplied by the supply roller32to a predetermined thickness, with a layer thickness regulating blade. Further, the development roller33carries the toner with the thickness thereof adjusted and supplies the toner to the surface of the photoconductive drum26.

It is noted that the “toner cartridge30” is a generic term that represents each of four toner cartridges30K,30Y,30M, and30C. For example, the toner cartridge30included in the process cartridge25K is the toner cartridge30K with black toner contained in the toner container31thereof. In the same manner, the toner cartridges30Y,30M, and30C correspond to the process cartridges25Y,25M, and25C, respectively.

Next, an explanation will be provided about the drawer40included in the image forming unit20with reference toFIGS. 1 to 4. The drawer40is configured to support the process cartridges25K,25Y,25M, and25C arranged therein and to be drawn from a predetermined attachment position (seeFIG. 1) in the main body housing2.

The drawer40includes a drawer frame41, a front handle42, a rear handle43, and cam followers44. The drawer frame41, which constitutes a main body of the drawer40, is formed in a box shape with an open upper side and an open lower side. The front handle42is firmly attached to the drawer frame41at an upper front side of the drawer40. The front handle42is gripped by a user who moves the drawer40. The rear handle43is firmly attached to the drawer frame41at an upper rear side of the drawer40. The rear handle43is gripped by the user who moves the drawer40.

The cam follower44is rotatably supported to protrude horizontally outward in the left-to-right direction (toward a near side and a far side in the direction perpendicular to the plane ofFIG. 2), in a predetermined upper rear position on each side face of the drawer frame41in the left-to-right direction. Each cam follower44is configured to contact an upper face of a corresponding one of the drawer guides3and guide the drawer40along the drawer guide3when the drawer40is moved. It is noted that the cam followers44provided on both side faces of the drawer frame41in the left-to-right direction have their respective centers of axes on the same horizontal line.

As shown inFIG. 4, the drawer40has an operating member45at a lower rear end on a right side face (a near side face inFIG. 3) of the drawer frame41. The operating member45contributes to cleaning of a detection surface D of each registration sensor S in cooperation with a part of a below-mentioned registration sensor unit80. As illustrated inFIG. 5, the operating member45includes a case46, a contact member47, and a coil spring48. The case46is formed in a box shape having a through-hole on a lower surface, at a lower rear end of a right side face (a near side face inFIG. 4) of the drawer frame41. The contact member47and the coil spring48are housed inside the case46. The contact member47is formed in a pillar shape as high as a distance between a lower end of the drawer40at the time when the drawer40is located in the attachment position and a position near the registration sensor unit80. Accordingly, the contact member47contacts a part (a below-mentioned interlocking member) of the registration sensor unit80when the drawer40is located in the attachment position. The coil spring48is disposed in a position higher than an upper surface of the contact member47in the case46and configured to provide a downward biasing force to the contact member47.

Next, an explanation will be provided about the conveying unit50of the laser printer1. The conveying unit50is configured to form a color image on the sheet P in cooperation with the image forming unit20while conveying the sheet P fed by the feeding unit10toward the catch tray5. The conveying unit50is disposed in a position that is above the feeding unit10and under the image forming unit20. As depicted inFIG. 1, the conveying unit50includes a driving roller51, a driven roller52, a conveying belt53, and a plurality of transfer rollers55.

The conveying belt53is a looped endless belt wound around the pair of the driving roller51disposed at a lower rear end of the image forming unit20and the driven roller52disposed at a lower front end of the image forming unit20. The driving roller51is driven to rotate in synchronization with the registration rollers15and revolve the conveying belt53in a predetermined direction. An upper-facing outer surface of the conveying belt53, which extends substantially in the horizontal direction beneath the image forming unit20, constitutes a sheet conveying surface53A that conveys the sheet P along the feeding route R while contacting a down-facing side of the sheet P.

Each transfer roller55contacts a down-facing side opposite to the sheet conveying surface53A in a position to face a corresponding one of the photoconductive drums26across the sheet conveying surface53A. When a transfer voltage is applied to each transfer roller55at a predetermined moment, each transfer roller55transfers the toner image carried on the surface of the photoconductive drum26onto the sheet P being conveyed on the sheet conveying surface53A. Further, the conveying belt53, made of electrically conductive rubber, is charged by the transfer voltage applied to each transfer roller55. Thereby, the conveying belt53conveys the sheet P along the feeding route R, with the sheet P attracted to the sheet conveying surface53A by an electrostatic force.

Subsequently, the scanning unit60of the laser printer1will be described. The scanning unit60is disposed in a top area inside the main body housing2. The scanning unit60includes, for each toner color, a laser source, a polygon mirror, an fθ lens, and reflection mirrors. The scanning unit60forms an electrostatic latent image (to be developed with toner of a corresponding one of the colors) on each photoconductive drum26of the image forming unit20. Specifically, a laser beam emitted by the laser source is deflected by the polygon mirror and transmitted through the fθ lens. After that, an optical path of the laser beam is turned back and bent down by the reflection mirrors. Thereby, each laser beam is rendered incident onto the surface of the photoconductive drum26of a corresponding one of the process cartridges25K,25Y,25M, and25C, such that the electrostatic latent image is formed on the surface of the photoconductive drum26.

Subsequently, the fixing unit70of the laser printer1will be described. The fixing unit70is disposed in a downstream position on the feeding route R relative to the image forming unit20and the conveying unit50in the feeding direction. The fixing unit70fixes the toner image transferred on the sheet P by the image forming unit20and the conveying unit50. As shown inFIG. 1, the fixing unit70includes a heating roller71and a pressing roller72. The heating roller71is disposed at a side of an image-formed surface of the sheet P on which the toner image is formed. The heating roller71rotates in synchronization with the conveying belt53and feeds the sheet P while heating the toner transferred on the sheet P. The pressing roller72is disposed in a position to face the heating roller71across the sheet P. The pressing roller72is rotated in accordance with movement of the sheet P while pressing the sheet P against the heating roller71. Thereby, the fixing unit70fixes onto the sheet P the toner transferred on the sheet P by heating the toner, and feeds the sheet P downstream in the feeding direction on the feeding route R.

The feeding route R is curved upward substantially in a U-shape in a downstream position relative to the fixing unit70in the feeding direction. Two ejection rollers are rotatably disposed just upstream relative to the catch tray5that is disposed in the most downstream position on the feeding route R. The ejection rollers75eject onto the catch tray5the sheet P fed via the fixing unit70with the image formed thereon,

As shown inFIG. 1, the laser printer1includes the registration sensor unit80in a position, between a rear end of the conveying unit50and the fixing unit70, which position is slightly lower than the sheet conveying surface53A of the conveying unit50, inside the main body housing2. The registration sensor unit80is provided with registration sensors S and configured to detect detection patterns formed on the surface of the conveying belt53(on the side of the sheet conveying surface53A) and transmit a detection signal to a controller (not shown) of the laser printer1, as described below. Thereby, the laser printer1can correct a positional deviation and an inadequate density of each toner image that might be caused in image formation, when the controller thereof takes various kinds of control based on the result of the detection of the detection patterns with the registration sensors S. A configuration of the registration sensor80will be described in detail with reference to relevant drawings.

Subsequently, an explanation will be provided about operations to be performed for image formation in the laser printer1. When performing an image forming operation, the laser printer1controls the image forming unit20to form a detection pattern with the toner of each color (each of black (K), yellow (Y), magenta (M), and cyan (C)) in predetermined positions (at both sides in a width direction of the conveying belt53) on the surface of the conveying belt53. After that, the laser printer1revolves the conveying belt53by driving the driving roller51to rotate, and detects the detection pattern of each toner color formed on the surface of the conveying belt53with the registration sensors S of the registration sensor unit80. Then, the laser printer1corrects a positional deviation and an inadequate density of each toner image that might be caused in a subsequently-performed image forming operation, based on the result of the detection of the detection patterns with the registration sensors S.

When launching the image forming operation of forming an image on the sheet P, initially, the laser printer1drives the feeding unit10and the conveying unit50to convey the sheet P to the image forming unit20. At that time, in the image forming unit20, the surface of each photoconductive drum26is charged evenly and positively by the electrification device27, and then exposed to the laser beam emitted by the scanning unit60. Thereby, on the surface of each photoconductive drum26, an electrostatic latent image (to be developed with toner of a corresponding one of the colors) is formed based on print data.

Due to the rotation of the supply roller32and the development roller33, the toner in the toner container31is held and carried on the development roller33. When the development roller33faces and contacts the photoconductive drum26, the toner is supplied to the electrostatic latent image formed on the surface of the photoconductive drum26. Thereby, the electrostatic latent image on the surface of the photoconductive drum26is rendered visible, and a toner image is carried in an inverted fashion on the surface of the photoconductive drum26.

After that, the toner image carried on the surface of the photoconductive drum26is transferred onto the sheet P by a transfer voltage applied to the transfer roller55. Then, when the sheet P with the toner image transferred thereon is fed to the fixing unit70, the toner image is thermally fixed onto the sheet P by the heating roller71and the pressing roller72. Finally, the sheet P with the image formed thereon is fed out of the fixing unit70and ejected onto the catch tray5. Thus, the laser printer1ends the image forming operation.

Next, an explanation will be provided about operations of moving the drawer40of the laser printer1between the attachment position and the replacement position, with reference to the relevant drawings. As shown inFIG. 1, when the drawer40is located in the attachment position, the drawer40is substantially in a horizontal state above the conveying unit50. At this time, each cam follower44disposed at an upper rear side of the drawer frame41is halted in contact with the stopper surface3C of a corresponding one of the drawer guides3. Further, when the drawer40is in the attachment position, each photoconductive drum26contacts the sheet conveying surface53A of the conveying belt53and faces a corresponding one of the transfer rollers55across the conveying belt53.

Further, as depicted inFIGS. 2 and 3, the drawer40can be pulled toward a front side of the main body housing2when the front cover6is open. A specific explanation will be provided about operations to be performed when the drawer40is moved from the attachment position (seeFIG. 1) to the replacement position (seeFIG. 3).

Initially, in the open state of the front cover6, the user grips the front handle42and pulls the drawer40toward the front side of the main body housing2. Thereby, each cam follower44rotates and moves obliquely upward along the second guide surface3B. Accordingly, the drawer40is drawn obliquely upward along the second guide surface3B. Consequently, the drawer40comes into a position higher than the attachment position (seeFIG. 1), such that each photoconductive drum26is in a position higher than and obliquely away from a corresponding one of the transfer rollers55(seeFIG. 2).

When the drawer40is pulled from the state as shown inFIG. 2toward the front side of the main body housing2, each cam follower44moves from the second guide surface3B to the first guide surface3A, and rotates and moves horizontally along the first guide surface3A. Therefore, the drawer40is pulled out from the main body housing2horizontally along the first guide surface3A (seeFIG. 3). Then, the drawer40comes into the replacement position (seeFIG. 3) when the cam follower44rotates and moves on the first guide surface3A and at least one of the toner cartridges30(e.g., the toner cartridge30K) comes into a position outside the main body housing2. As illustrated inFIG. 3, when the drawer40is in the replacement position, the user is able to detach or attach a toner cartridge30.

Subsequently, an explanation will be provided about operations to be performed when the drawer40is attached to the main body housing2. When the drawer40is attached to the attachment position in the main body housing2, the user places the cam follower44on the first guide surface3A and inserts the drawer40toward a rear side of the main body housing2. Thereby, the cam follower44rotates and moves horizontally along the first guide surface3A, such that the drawer40moves horizontally along the first guide surface3A.

Further, when the drawer40is inserted into a rear side in the main body housing2, the cam follower44moves from the first guide surface3A to the second guide surface3B, and then rotates and moves obliquely downward along the second guide surface3B. Thereafter, when moving along the second guide surface3B, the cam follower44contacts the stopper surface3C and halted thereby. At this time, the drawer40is supported to be kept horizontal in the attachment position such that the photoconductive drums26face the respective transfer rollers55across the conveying belt53.

Thus, the laser printer1is configured such that the user can easily carry out maintenance for the process cartridges25K,25Y,25M, and25C provided to the drawer40and replacement of the toner cartridges30K,30Y,30M, and30C.

Next, a detailed explanation will be provided about a configuration of the registration sensor unit80of the first embodiment, with reference to the relevant drawings. As described above, the registration sensor unit80is configured to detect the detection pattern formed with each color of toner in the predetermined positions at both sides in a width direction of the conveying belt53on the surface of the conveying belt53. Further, the registration sensor unit80includes the registration sensors S, a sensor case81, protection films82, a cover member83, a biasing member84, and an interlocking member85(seeFIGS. 6 and 7).

The sensor case81has a long side that is slightly longer than a width of the conveying belt53. The sensor case81is disposed in a predetermined position (seeFIG. 1) inside the main body housing2such that the long side thereof is parallel to a width direction (the left-to-right direction) of the conveying belt53. The sensor case81has an inclined surface extending from a side face of the sensor case81at a side near the conveying unit50toward an upper rear side of the main body housing2.

On the inclined surface, the registration sensors S, each of which has the detection surface D, are disposed in respective two positions, corresponding to the positions where the detection patterns are formed, at both sides in the width direction of the conveying belt53(seeFIG. 7). The detection surface D of each registration sensor S includes a detection section, which has a light emitting portion and a light receiving portion, and the protection film82. Further, the detection surface D of each registration sensor S faces the surface of the conveying belt53. The light emitting portion of the detection section of each registration sensor S is provided, e.g., with an light emitting diode (LED) and configured to emit light toward the surface of the conveying belt53. The light receiving portion of the detection section of each registration sensor S is provided, e.g., with a phototransistor and configured to receive light reflected by the surface of the conveying belt53. Hence, each registration sensor S detects the detection patterns formed on the surface of the conveying belt53by receiving, with the light receiving portion, the light emitted by the light emitting portion and then reflected by the surface of the conveying belt53. Each protection film82is formed from a translucent (or transparent) film material and disposed in a position closer to the conveying belt53than the detection section so as to cover the detection section (seeFIGS. 7 to 9B).

The cover member83includes cleaners83A, a shaft83B, and a projection83C. The cover member83is supported to be rotatable around the shaft83B between a first position and a second position. It is noted that the first position is a position where the cover member83covers the detection surface D of each registration sensor S (seeFIGS. 6,8B, and9B). The second position is a position to which the cover member83is turned upward such that the detection surface D of each registration sensor S is exposed to face the surface of the conveying belt53(seeFIGS. 7,8A, and9A).

Each cleaner83A is configured with a sponge formed by foaming synthetic resin, and disposed on a surface, of the cover member83, which faces a corresponding one of the detection surfaces D when the cover member83is in the first position. The cleaner83A has a cleaning surface slightly larger than the detection surface D, so as to contact an entire area of the detection surface D when the cover member83is in the first position (seeFIG. 9A). The cleaner83A moves up and down in contact with the detection surface D, as the cover member83moves between the first position and the second position. Accordingly, the laser printer1can wipe a contamination (such as toner and paper dust) off the detection surface D when the cover member83moves between the first position and the second position.

The projection83C is formed to protrude outward (in a rightward direction of the main body housing2) in a predetermined position on a right side face of the cover member83. The projection83C causes the cover member83to turn and move from the first position to the second position while contacting the interlocking member85.

The biasing member84is configured with a twist spring, and inserted in the shaft83B. The biasing member84urges the cover member83in a direction from the second position to the first position by an elastic force of the biasing member84.

The interlocking member85is formed substantially in a V-shape, and provided with a first contact portion85A, a second contact portion85B, and a rotational shaft85C. The interlocking member85is supported at a bending point of its V-shape by the rotational shaft85C, to be rotatable around the rotational shaft85C on the right side face of the sensor case81. The first contact portion85A is located at a front side relative to the rotational shaft85C (i.e., to be closer to the conveying unit50than the rotational shaft85C) in the interlocking member85. The first contact portion85A contacts the contact member47of the operating member45when the drawer40is in the attachment position. The second contact portion85B is located at a rear side relative to the rotational shaft85C in the interlocking member85. The second contact portion85B contacts the projection83C of the cover member83. Accordingly, the laser printer1can move the cover member83between the first position and the second position in conjunction with the turning of the interlocking member85.

Subsequently, a detailed explanation will be provided about an operation of cleaning the detection surface D in response to movement of the drawer40in the laser printer1of the first embodiment, with reference toFIGS. 8A,8B,9A and9B. Firstly, a case where the drawer40moves from the attachment position to the replacement position will be described.

When the drawer40is in the attachment position, the contact member47of the operating member45contacts the first contact portion85A of the interlocking member85from above. Thus, the gravity applied to elements such as the drawer40and each process cartridge25acts on the first contact portion85A, and thereby the interlocking member85turns clockwise around the rotational shaft85C and comes into such a position as shown inFIG. 8A. At this time, as the second contact portion85B contacts the projection83C of the cover member83, the cover member83comes into the second position in conjunction with the turning of the interlocking member85(seeFIG. 8A). Accordingly, when the drawer40is in the attachment position, the detection surface D of each registration sensor S is exposed to face the surface of the conveying belt53of the conveying unit50without being shielded by the cover member83(seeFIG. 9A). Thereby, when the drawer40is in the attachment position to allow execution of image formation, the laser printer1can detect the detection patterns formed on the surface of the conveying belt53by the detection surface D of each registration sensor S, and thus correct a positional deviation and an inadequate density of each toner image based on the result of the detection of the detection patterns.

Next, an explanation will be provided about a case where the drawer40moves from the attachment position to the replacement position. As described above, when beginning to move from the attachment position, the drawer40is pulled along the second guide surfaces3B while moving upward. Hence, the contact member47of the operating member45comes to be away from the first contact portion85A of the interlocking member85, in response to the movement of the drawer40. Here, the cover member83is urged in the direction from the second position to the first position by the elastic force of the biasing member84. When the operating member45is away from the first contact portion85A, the force applied to the first contact portion85A dissolves, such that the projection83C of the cover member83pushes down the second contact portion85B of the interlocking member85with the elastic force of the biasing member84. Consequently, the cover member83turns around the shaft83B from the second position to the first position (seeFIG. 8B). When the cover member moves from the second position to the first position, each cleaner83A moves down in contact with the detection surface D of a corresponding one of the registration sensors S (seeFIG. 9B). Thereby, the laser printer1can clean the detection surfaces D of the registration sensors S with the cleaners83A in response to the drawer40moving from the attachment position to the replacement position.

Further, when the cover member83is in the first position, the detection surfaces D of the registration sensors S are covered with the cover member83and the cleaners83A (seeFIG. 9B). Accordingly, even though toner and/or paper dust are splashed into the main body housing2, the laser printer1can protect the detection surfaces D from the toner and/or the paper dust in response to the drawer40moving from the attachment position to the replacement position.

Subsequently, an explanation will be provided about a case where the drawer40moves from the replacement position to the attachment position. As described above, when the drawer40is in the replacement position, the cover member83is located in the first position to cover the detection surfaces D of the registration sensors S with the cleaners83A (seeFIGS. 8B and 9B). When moved from the replacement position to the attachment position, the drawer40moves down along the second guide surfaces3B of the drawer guides3. At this time, since the drawer40moves down along the second guide surfaces3B, the contact member47certainly comes into contact with the first contact portion85A of the interlocking member85from above.

When the contact member47contacts the first contact portion85A, the gravity applied to elements containing the drawer40and each process cartridge25acts on the first contact portion85A. At this time, the elastic force of the biasing member84acts on the second contact portion85B of the interlocking member85via the projection83C of the cover member83. However, since the force applied by the operating member45is greater than the elastic force of the biasing member84, the interlocking member85turns clockwise around the rotational shaft85C. Then, in conjunction with the interlocking member85turning, the second contact portion85B pushes up the projection83C, such that the cover member83turns around the shaft83B from the first position to the second position (seeFIG. 8A).

As mentioned above, when the cover member83is in the first position, each cleaner83A contacts the detection surface D of a corresponding one of the registration sensors S (seeFIG. 9B). Therefore, when the cover member83moves from the first position to the second position, the cleaner83A moves downward in contact with the detection surface D of the registration sensor S. Thereby, the laser printer1can clean the detection surfaces D of the registration sensors S with the cleaners83A in response to the movement of the drawer40from the replacement position to the attachment position.

As describe above, according to the laser printer1of the first embodiment, when the drawer40is moved between the attachment position and the replacement position, it is possible to move the cover member83between the first position and the second position by cooperation between the contact member47of the operating member45included in the drawer40and the biasing member84and the interlocking member85included in the registration sensor unit80. The cover member83includes the cleaners83A, which are provided to be able to contact with the detection surfaces D of the registration sensors S, respectively (seeFIGS. 9A and 9B). Accordingly, in conjunction with the movement of the cover member83between the first position and the second position, the cleaners83A move in contact with the detection surfaces D, so as to clean the detection surfaces D.

Namely, in response to the movement of the drawer40between the attachment position and the replacement position, the laser printer1can clean the detection surfaces D of the registration sensor unit80and keep clean the detection surfaces D that exert an influence on the reading accuracy for reading the detection patterns. Further, the drawer40is periodically moved between the attachment position and the replacement position, e.g., at the time for replacement of a toner cartridge30. Therefore, the laser printer1can periodically clean the detection surfaces D and keep the detections surfaces D clean even though the user is not careful about cleaning the detection surfaces D. Consequently, the laser printer1can maintain a high level of detection accuracy for detecting the detection patterns with the registration sensor unit80. Thus, it is possible to appropriately correct a positional deviation and an inadequate density of each toner image that might be caused in image formation and to maintain favorable image quality.

Further, in the laser printer1, the attachment position of the drawer40is a position, lower than the replacement position, where the surface of each photoconductive drum26contacts the upper surface of the conveying belt53(seeFIGS. 1 to 3). When moving from the replacement position to the attachment position, the drawer40moves obliquely downward along the second guide surfaces3B to be in the attachment position. At this time, the gravity applied to elements containing the drawer40and each process cartridge25acts on the interlocking member85. Thus, according to the laser printer1, it is possible to certainly clean the detection surfaces D in response to the movement of the drawer40from the replacement position to the attachment position.

Further, each detection surface D is configured with the protection film82that is formed from a transparent film material and disposed to cover the detection section. Each cleaner83A is provided to be able to contact the surface of the protection film82. Accordingly, when the detection surfaces D is cleaned with the cleaners83A, the laser printer1can prevent the detection section from being damaged by the cleaners83A.

Further, in the laser printer1, the registration sensor unit80is disposed in such a position as to be able to optically read the detection patterns formed on the surface of the conveying belt53, at a rear side in the direction in which the drawer40moves from the replacement position to the attachment position in the main body housing2(seeFIGS. 1 to 3). Namely, in the laser printer1, the registration sensor unit80is disposed in such a position that a user's hand cannot reach there and the user can hardly clean the detection surfaces D. Even in such a case, the laser printer1can clean the detection surfaces D of the registration sensor unit80with the cleaners83A in response to the movement of the drawer40.

Second Embodiment

Subsequently, a second embodiment will be described with reference toFIG. 10. In the second embodiment, the basic configuration of the laser printer1is the same as that in the first embodiment. Therefore, an explanation about the basic configuration of the laser printer1will be omitted. The second embodiment is different from the first embodiment with respect to the configuration of the registration sensor unit80. Hence, in the following description, a registration sensor unit80of the second embodiment will be described.

FIGS. 10A and 10Bare front views showing a portion around a right end of the registration sensor unit80in the second embodiment.FIG. 10Cis a top view of the registration sensor unit80in the second embodiment. A configuration of a portion around a left end of the registration sensor unit80is substantially the same as that around the right end, except for left-right reversal. Thus, in the following description, a portion around the right end of the registration sensor unit80will be described.

As illustrated inFIGS. 10A to 10C, the registration sensor unit80of the second embodiment includes the same registration sensors S, sensor case81, and protection films82as exemplified in the first embodiment. Further, the registration sensor unit80of the second embodiment includes a slide cover member86, and an interlocking mechanism87, instead of the cover member83, the biasing member84, and the interlocking member85in the first embodiment.

The slide cover member86is disposed near the detection surface D of the registration sensor S, to be able to slide in the width direction (i.e., the left-to-right direction) along the inclined surface (seeFIGS. 10A and 10B). The slide cover member86includes a cleaner86A, an elongated hole86B, and an elastic member86C. In the slide cover member86, the cleaner86A is disposed on a surface that faces the detection surface D at an end near the center in the width direction. The cleaner86A is configured with a sponge in the same manner as exemplified in the first embodiment, and a cleaning surface thereof is provided to be able to contact the detection surface D (seeFIG. 10C). Accordingly, the laser printer1of the second embodiment can clean the detection surface D with the cleaner86A in response to sliding movement of the slide cover member86.

The elongated hole86B is formed to be open in a position adjacent to the cleaner86A at an end side of the sensor case81in the width direction. When the slide cover member86is made slide toward a central side of the sensor case81in the width direction, the detection surface D is exposed through the elongated hole86AB so as to read the detection patterns (seeFIG. 10B). The elastic member86C is configured to, by its elastic force, return the slide cover member86, which has been moved to the central side of the sensor case81in the width direction, to an initial position on an end side of the sensor case81in the width direction.

The interlocking mechanism87includes a drawer contact member87A and a cover slide gear87B. When the drawer40is in the attachment position, the drawer87A is pushed down by the operating member45. Further, the drawer contact member87A is formed in a shape of a rack gear having teeth on a side face closer to the center of the sensor case81in the width direction (i.e., on a side face on the viewers' right hand inFIGS. 10A and 10B).

The cover slide gear87B is rotatably disposed in a position closer to the center of the sensor case81in the width direction than the drawer contact member87A, at an end side of the sensor case81in the width direction. The cover slide gear87B includes a first gear section and a second gear section. The first gear section has teeth formed on a circumferential surface thereof to engage with the teeth formed on the side face of the drawer contact member87A. The second gear section has teeth formed on a circumferential surface thereof to engage with up-facing teeth of the slide cover member86that are formed at an end of the slide cover member86in the width direction.

Subsequently, an explanation will be provided about an operation of cleaning the detection surface D in the second embodiment. Initially, a case where the drawer40moves from the replacement position to the attachment position will be described. In this case, the registration sensor unit80is in a state as shown inFIG. 10Auntil the drawer40reaches the attachment position. When the drawer40reaches the attachment position, the drawer contact member87A is pushed down by the operating member45. Thereby, the cover slide gear87B is rotated counterclockwise, such that the slide cover member86moves toward the center of the sensor case81in the width direction. As depicted inFIGS. 10A and 10B, the cleaner86A moves toward the center of the sensor case81in the width direction while contacting the detection surface D. Accordingly, in the second embodiment as well, the laser printer1can clean the detection surface D in response to the movement of the drawer40. In addition, when the slide cover member86is located at the central side of the sensor case81in the width direction, the elongated hole86B is located opposite the detection surface D. Thereby, as the detection surface D is exposed through the elongated hole86B, the laser printer1can read the detection patterns formed on the conveying belt53.

Next, an explanation will be provided about a case where the drawer40moves from the attachment position to the replacement position. In this case, since the drawer40is in the attachment position, the registration sensor unit80is in a state as shown inFIG. 10B. When the drawer40starts moving from the attachment position, the drawer contact member87A is released from the force applied by the operating member45. The elastic member86C applies, to the slide cover member86, an elastic force to urge the slide cover member86toward the end side of the sensor case81in the width direction. Hence, by the elastic force of the elastic member86C, the slide cover member86is moved to slide toward the end side of the sensor case81in the width direction. As shown inFIGS. 10A and 10B, the cleaner86A moves toward the end side of the sensor case81in the width direction while contacting the detection surface D. Accordingly, in the second embodiment as well, the laser printer1can clean the detection surface D in response to the movement of the drawer40. When the slide cover member86moves toward the end side of the sensor case81in the width direction, the cover slide gear87B rotates clockwise to move up the drawer contact member87A. Thereby, when the drawer40comes in the attachment position again, the registration sensor unit80can carry out the aforementioned operation.

As described above, in the laser printer1of the second embodiment as well, the same effects as described in the first embodiment can be provided. Namely, the laser printer1of the second embodiment can as well clean the detection surface D of the registration sensor S with the cleaner86A in conjunction with the movement of the drawer40from the replacement position to the attachment position.

In the aforementioned embodiments, a method to directly transfer the toner image from the photoconductive drums26onto the sheet P is applied. However, a method to transfer the toner image from the photoconductive drums26onto the sheet P indirectly via an intermediate transfer belt may be applied.

Further, in the aforementioned embodiments, each detection surface D is configured with the protection film82. However, various transparent elements may be applied instead of the protection film82. For instance, a cover glass may be applied instead of the protection film82. Further, a brush may be applied instead of the cleaners83A and86A as exemplified in the aforementioned embodiment.