Image forming device and detachable process unit

An image forming device has a main casing and a cartridge accommodating portion in which a combined unit of first and second cartridges can be loaded. The first cartridge includes a pressing member movable between a first position in which the second cartridge is removed from the first cartridge and a second position in which the second cartridge is combined with the first cartridge. A moving member supported on the main casing is movable between a third position in which the combined unit is unloaded from the main casing and a fourth position in which the combined unit is loaded in the main casing. The pressing member disposed in the second position presses the moving member to move to the fourth position. A determination unit does not start image forming operations until a position detector provided on the main casing detects that the moving member is in the fourth position.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2009-130904 filed May 29, 2009. The entire content of the priority application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an image forming device, such as a laser printer, and a developing cartridge for use therein.

BACKGROUND

A conventional image forming device includes a main casing within which a process unit is detachably accommodated. In such an image forming device, the process unit is configured of a drum cartridge and a developing cartridge. The drum cartridge is detachably loadable in the main casing and includes a photosensitive drum. The developing cartridge is formed with a toner chamber for accommodating toner therein and is detachably mounted on the drum cartridge. In other words, the process unit can be separated into the drum cartridge and the developing cartridge, and the process unit as a whole is detachably loadable in the main casing of the image forming device.

The developing cartridge includes a developing roller for supplying the accommodated toner to the photosensitive drum. The drum cartridge has a drum frame on which a lever is provided as a pressing member so that the developing roller can be pressed against the photosensitive drum.

SUMMARY

In the above-described image forming device, when the process unit is unloaded from the main casing for a maintenance purpose, the process unit is separated into the drum cartridge and the developing cartridge. At this time, a careless user may bring the process unit back to the main casing in an incomplete state, i.e., only either one of the drum cartridge and the developing cartridge may possibly be brought back to the main casing.

Further, in case of replacing the developing cartridge with a new one in the process unit, the drum cartridge, which should not be replaced, may be thrown away together with the old developing cartridge. If this is the case, a new developing cartridge alone may be loaded in the main casing without the necessary drum cartridge.

In either case, the conventional image forming device cannot detect that the loaded process unit is incomplete since the developing cartridge is detachably mountable in the main casing via the drum cartridge. In other words, the above-described image forming device can hardly, if not impossible, distinguish a state where the drum cartridge alone is mounted in the main casing from a state where the drum cartridge is mounted in the main casing with the developing cartridge mounted on the drum cartridge.

As a result, the image forming device is allowed to start image forming operations, although a paper jam will result, even though either one of the drum cartridge and developing cartridge has not been loaded. Occurrence of the paper jam makes the user realize at that time that there is something wrong with the loaded process unit, i.e., either only one of the drum cartridge and the developing cartridge has been loaded in the main casing. However, desirably, occurrence of such error should be prevented as early as possible before a paper jam actually happens.

In view of the foregoing, it is an object of the present invention to provide an image forming device and a drum cartridge that would not allow image formation to be started until a complete process unit is detected to have been loaded in the image forming device.

In order to attain the above and other objects, the image forming device in accordance with the invention includes a main casing, a cartridge accommodating portion, a moving member, a position detector, and a determination unit. The cartridge accommodating portion is configured to detachably accommodate a first cartridge and a second cartridge. The second cartridge is able to be detachably combined with the first cartridge to form a combined unit. The first cartridge is provided with a pressing member movable between a first position and a second position. The pressing member is in the first position when the second cartridge is removed from the first cartridge, and in in the second position when the second cartridge is perfectly combined with the first cartridge. The moving member is supported on the main casing to be movable between a third position and a fourth position. The moving member is in the third position when the combined unit is unloaded from the main casing, and in the fourth position when the combined unit is loaded in the main casing. The pressing member disposed in the second position presses the moving member to move to the fourth position. The position detector is provided on the main casing and is configured to perform position detection of the moving member. The determination unit is configured not to start image forming operations until the position detector detects that the moving member is in the fourth position.

According to another aspect of the invention, there is provided a drum cartridge for an image forming device, the drum cartridge including a frame, a photosensitive drum, a pressing member, and a projection member. The frame has a mounting portion on which a developing cartridge is detachably mountable. The developing cartridge includes a developing roller. The photosensitive drum is rotatably supported on the frame. Developer is supplied to the photosensitive drum by the developing roller. The pressing member is supported on the frame at a position upstream of an accessing path along which the drum cartridge is loaded in the image forming device. The pressing member is movable between a first position and a second position. The pressing member is in the first position when the developing cartridge is dismounted from the drum cartridge and in the second position when the developing cartridge is mounted on the drum cartridge. The pressing member urges the developing roller against the photosensitive drum when the pressing member is in the second position. The projection member is supported on the pressing member and projects out of the frame. A position of the projection member is movable when the pressing member is moved from the first position to the second position.

DETAILED DESCRIPTION

An embodiment of the invention will be described with reference to the accompanying drawings. As shown inFIG. 1, the printer1has a main casing2in which a feeder section3and an image forming section4are disposed. In the front wall of the main casing2, a front cover5is hinged at the lower portion thereof to be capable of being opened. When the front cover5is opened, it is capable of accessing to the internal space2A of the main casing2. In this state, a process unit13(to be described later) can be loaded in the main casing2. When the front cover5is shut, accessing to the internal space2A of the main casing2becomes impossible.

In the following description, one end of the main casing2in which the front cover5is provided (left side inFIG. 1) will be referred to as “front side”, and the opposite side thereof (right side inFIG. 1) as “rear side”. The terms “right (side)” and “left (side)” will be used to refer to the side of the printer1as viewed from front. The terms “front”, “rear”, “right”, “left” and the like will also be used for the process unit13and a developing cartridge9(to be described later) to refer to the same sides as in the main casing2. The expression “widthwise direction” may be used to mean the left-to-right direction.

The feeder section3includes a sheet supply tray6, a sheet feed roller7, a sheet feed pad8, a pickup roller9, a pair of conveying rollers10, and a pair of registration rollers11. Sheets of paper P serving as a recording medium are stacked in the sheet supply tray6. The topmost sheet in the sheet supply tray6is fed toward the sheet feed roller7and the sheet feed pad8by the pickup roller9. The sheet P thus fed out is fed in between the sheet feed droller7and the sheet feed pad8, and then fed into a nip between the pair of conveying rollers10. The sheet P having passed between the pair of conveying rollers10is fed into a nip between the registration rollers11. The registration rollers11feed the sheet P toward a transfer position (to be described later) in the image forming section4at a prescribed timing.

The image forming section4includes a scanner unit12, the process unit13and a fixing unit14. The scanner unit12is disposed at the upper portion of the main casing2. The scanner unit12includes a laser source (not shown), a polygon mirror15, a plurality of lenses16and a plurality of reflection mirrors17. As shown by a dotted line, the scanner unit12irradiates a laser beam toward a photosensitive drum20(to be described later) contained in the process unit13.

The process unit13is disposed beneath the scanner unit12. The process unit13includes a drum cartridge18as one example of a photosensitive drum cartridge, and the developing cartridge19detachably mounted on the drum cartridge18. As descried, the drum cartridge18and the developing cartridge19can be loaded in or unloaded from the main casing2through loading or unloading the process unit13.

The photosensitive drum20is rotatably supported in the drum cartridge18. The drum cartridge18includes a scorotron type charger21, a transfer roller22, and a cleaning member35, which are disposed around the periphery of the photosensitive drum20. The developing cartridge19has a developer housing23in which disposed are an agitator24, a supply roller25, a developing roller26, and a thickness regulating blade27.

The developer housing23includes a toner accommodating chamber28and a developing chamber29which are arranged in the front-to-rear direction. The toner accommodating chamber28and the developing chamber29are in communication with each other at a communication port30. The toner accommodating chamber28accommodates non-magnetic single-component, positively-chargeable polymerization toner. The agitator24is rotatably disposed within the toner accommodating chamber28.

The supply roller25is rotatably disposed within the developing chamber29behind the communication port30. The developing roller26is rotatably disposed within the developing chamber29. The supply roller25is disposed in the rear side of the developing roller26and both are held in pressure contact with each other. The thickness regulating blade27is a plate-shaped member and extends in the left-to-right direction. The thickness regulating member27has a base portion fixed to the developer housing23and a free end held in pressure contact with the peripheral surface of the developing roller26.

The toner in the toner accommodating chamber28is agitated by the agitator24and conveyed to the supply roller24disposed in the developing chamber29through the communication port30. The toner conveyed to the supply roller25is then delivered to the developing roller26. At this time, the toner is frictionally charged to positive polarity at a portion between the supply roller25and the developing roller26to which a developing bias is applied. In this manner, the toner supplied to the developing roller26is subject to a thickness regulation by the thickness regulating blade27so that the toner layer bore on the peripheral surface of the developing roller26has a predetermined thickness.

On the other hand, as the photosensitive drum20rotates, the surface thereof is uniformed charged to positive polarity by the charger21. A laser beam emanated from the scanner unit12is irradiated onto the positively charged surface of the photosensitive drum20as indicated by a dotted line. The portions onto which the laser beam is irradiated form an electrostatic latent image. The laser beam is modulated based on image data and thus an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum20.

Rotations of the photosensitive drum20bring the electrostatic latent image to the position of the developing roller26. The positively charged toner bore on the developing roller26is attracted to the electrostatic latent image so that the electrostatic latent image is visualized with the toner image. The toner image bore on the surface of the photosensitive drum20is moved to a transfer position where the transfer roller22is located for allowing the toner image to be transferred to the sheet of paper P.

After the toner image has been transferred to the sheet of paper P, toner remaining on the photosensitive drum20is removed or collected by the developing roller26. The cleaning member removes paper dust or paper powder which comes from the sheet of paper P and adhered to the surface of the photosensitive drum2.

The fixing unit14is disposed at the rear side of the process unit13. The fixing unit14includes a heat roller31and a pressure roller32which is urged upward to the heat roller31to be in pressure contact with the heat roller31.

The sheet of paper P with the toner image thereon is brought into a nip between the heat roller31and the pressure roller32and passes therethrough, thereby fixing the toner image on the sheet of paper P with the pressure and heat applied thereto.

The sheet of paper P to which the toner image is fixed is conveyed toward the discharge roller33and discharged onto the discharge tray34formed on the upper surface of the main casing2.

A sheet conveying path36is formed within the main casing2for conveying the sheet of paper P therealong. The locus of the sheet of paper P being conveyed from the sheet supply tray6to the discharge tray34is indicated by a thick dotted line inFIG. 1. It can be understood that the thick dotted line is in coincidence with the sheet convey path. The sheet conveying path36is in a reversed S-shaped structure as viewed from the widthwise direction. When the sheet of paper P is conveyed along the sheet conveying path36, the paper P passes the pickup roller9, between the sheet supply roller7and the sheet supply pad8, between the pair of conveying rollers10, between the pair of registration rollers11, the transfer position, between the heat roller31and the pressure roller32, and the discharge roller33in the stated order. As described, the sheet conveying path36connects the sheet supply tray6and the discharge tray34.

Next, each of the drum cartridge18and the developing cartridge19will be described. As shown inFIG. 1, the drum cartridge18has a drum housing38in which the photosensitive drum20, charger21, transfer roller22and cleaning member35are accommodated.

As can be understood fromFIGS. 1 and 2, the drum housing38extends in the widthwise direction and is a hollow box that is flattened shape in the vertical or up-to-down direction. An inlet port39in communication with the internal space of the drum housing38is formed in the bottom wall37of the drum housing38at a central position in the front-to-rear direction. An outlet port40which is also in communication with the internal space of the drum housing38is formed in the rear wall44of the drum housing38.

Both the inlet port39and the outlet port40have a width wider than the paper width. The sheet of paper P forwarded by the registration rollers11enters into the drum housing38from the inlet port39. After passing through the transfer position, the sheet of paper P moves from the outlet port40to the fixing unit14. As is apparent from the above description, the channel between the inlet port39and the outlet port40is a part of the sheet conveying path36. Another part of the sheet conveying path36is located in the front side with respect to the inlet port39, where the upper registration roller11is rotatably disposed.

The internal space of the drum housing38is partitioned into the rear side drum accommodating chamber41and a cartridge accommodating chamber42. Both the drum accommodating chamber41and the cartridge accommodating chamber42are in communication with each other. The drum accommodating chamber41is defined by a ceiling wall48, bottom wall37, left wall46and right wall47of the drum housing38and includes a first space at the rear side of the cartridge accommodating chamber42and a second space surrounded by the rear wall44.

The drum accommodating chamber41accommodates the photosensitive drum20, charger21, transfer roller22, and cleaning member35. The photosensitive drum20is in a cylindrical shape having a center axis extending in the widthwise direction. In other words, the axial direction of the photosensitive drum20is in coincidence with the widthwise direction. Both ends in the widthwise direction of the photosensitive drum20are rotatably supported on the left wall46and right wall47of the drum housing38. A front part of the photosensitive drum surface is exposed to face the cartridge accommodating chamber42. As will be describe later with reference toFIG. 4, each of the left wall46and right wall47is formed with a guide groove49penetrating in the widthwise direction. As viewed from the widthwise direction, the guide slots49are formed in the left wall46and the right wall47at the upper end portion thereof and also at the central portion thereof in the front-to-rear direction. The guide slots49extend rearward and downward to a position close to the photosensitive drum20.

The transfer roller22is disposed below the photosensitive drum20and held in pressure contact with the photosensitive drum20. The transfer roller22has a longitudinal axis extending in the widthwise direction. Both axial ends of the transfer roller22are rotatably supported on the left wall46and right wall47of the drum housing38. A part37A of the bottom wall of the drum housing38is arcuately protruded downward to conform to the shape of the lower peripheral surface of the transfer roller22.

The cleaning member35is disposed at the rear side of the photosensitive drum20and secured to the front side surface of the rear wall44. The cleaning member35is held in contact with the photosensitive drum20. The charger21is disposed at the rear and diagonally upward position with respect to the photosensitive drum20. The charger21is supported on the upper portion of the rear wall44to be in spaced-apart relation with the surface of the photosensitive drum20and disposed in confrontation with the surface of the photosensitive drum20.

The cartridge accommodating chamber42is a part of the space defined by the ceiling wall48, bottom wall37, left wall46and right wall47, and surrounded by the part in the front side of the drum accommodating chamber41and the front wall45of the drum housing38. A part of the ceiling wall48defining the cartridge accommodating chamber42is formed with a continuous cutout portion which serves as a loading port43. The cartridge accommodating chamber42is exposed toward upward from the loading port43.

The developing cartridge19passes through the loading port43when the same is mounted on or dismounted from the drum cartridge18. The developing cartridge19mounted on the drum cartridge18is accommodated in the cartridge accommodating chamber42. A pair of pressing members50is provided to the front wall45of the drum housing38. The pressing members50are provided for urging the developing cartridge19mounted on the drum cartridge18rearward against the photosensitive drum20. Note that the pressing member50is not shown inFIG. 1. As shown inFIG. 2, the pressing members50are provided one at a right end and the other at a left end on the rear surface, i.e., the surface facing the cartridge accommodating chamber42, of the front wall45. In other words, the pressing members50are arranged in spaced apart relation in the widthwise direction of the front edge portion of the cartridge accommodating chamber42.

FIG. 3shows the right side view of the pressing member50. The following description about the pressing member50will be made based on the posture depicted inFIG. 3. The pressing member50is of substantially a reversed (upside down) J-shape as viewed from the widthwise direction. From the functional viewpoint, the pressing member50can be divided into a pressing part55at an upper portion and an extension portion56extending downward from the pressing part55, although these two parts are integrally formed as one block.

As viewed from the widthwise direction, the pressing part55is of substantially a triangular shape with a front-to-rear length becoming thinner in higher or upward levels. The topmost portion of the pressing part55is rounded. The rear edge line of the pressing part55extends diagonally downward from the topmost rounded portion, and is bent and further extends diagonally downward with a sharper slope to the upper end position of the extension portion56. The front edge of the pressing part55extends substantially downward from the topmost rounded portion.

The pressing part55is formed with a concave portion55A at the lower surface thereof. A downwardly projecting boss57is formed in the concave portion55A to be integral with the pressing part55. The extension portion56extends linearly downward from the lower end of the pressing part55. The vertical or longitudinal length of the extension portion56is about two to three times as long as the vertical length of the pressing part55. The extension portion56has a lower end portion56A defined by a rear surface extending downward and a front surface extending diagonally downward. Stated differently, the extension portion56is of a cutter-knife shape and its knife edge portion is such a shape that its front-to-rear length becomes smaller as the vertical level goes down. A pressing shaft58is integrally formed with the extension portion56. The pressing shaft58extends in the widthwise direction and is provided in a position slightly upper from the vertical center of the extension portion56.

FIG. 4shows the drum cartridge18from which the developing cartridge19is detached. On the other hand,FIG. 5shows the developing cartridge19mounted on the drum cartridge18. As described above, the pressing members50are provided at the rear side surface of the front wall45of the drum housing38at the widthwise end portions (seeFIG. 2). The pressing member50is rotatable about the pressing shaft58which is supported by the right wall46and the left wall47.

As to the right side pressing member50, the boss57extends toward a right lower corner where the right wall47, front wall45and bottom wall37join together. A coil spring59is interposed between the boss57and the right lower corner. Similarly, the boss57of the left side pressing member50extends toward a left lower corner where the left wall46, front wall45and bottom wall37join together. Another coil spring59is interposed between the boss57and the left lower corner. The coil springs59urge the pressing member55in a rear upper direction, causing the pressing member50to incline in the rear upper direction.

The position of each pressing member50when placed as shown inFIG. 4will be referred to as the “first position”. Each pressing member50is placed in the first position by virtue of the associated coil spring59. The lower portion of the extension portion56of each pressing member50protrudes downward from the bottom wall37of the drum housing38to be outside the drum housing38. When the pressing member50is in the first position, the lower portion56A of the extension portion56projects toward the front lower side of the drum cartridge18.

On the other hand, when the developing cartridge19is mounted on the drum cartridge18, the pressing member50, which has been stayed in the first position, is rotated counterclockwise for a predetermined amount as viewed from the right side of the drum cartridge18, as shown inFIG. 5. The rotated position of the pressing member50will be referred to as the “second position”. Briefly, the pressing member50is rotatingly moved between the first position and the second position.

A drum grip51is integrally formed in the front upper portion of the front wall45and extends in the front side. The drum grip51is grasped by the user when the drum cartridge18(process unit13) is loaded in the main casing2.

The developer housing23of the developing cartridge19is elongated in the widthwise direction and a vertically flat shaped and hollow box. The developing cartridge19has a size and shape to be fittedly received at the cartridge accommodating chamber42.

A pressed member80is integrally formed to each of the left and right side surfaces of the developer housing23at their front end portions. The pressed member80is a boss projecting outward in the widthwise direction and is of substantially C-shaped with the rear side being open as viewed from the widthwise direction. The toner accommodating chamber28and the developing chamber29are disposed in the developer housing23and the former is located in front of the latter. The toner accommodating chamber28is of substantially circular shape as viewed from the widthwise direction. The circular shape of the toner accommodating chamber28follows the rotation locus of the agitator24. The bottom wall52of the developing housing23is downwardly circularly protruded to receive the lower portion of the toner accommodating chamber28.

The front wall53of the developer housing23extends upward from the front end of the bottom wall52. A developer grip54is integrally formed with the front wall53at the upper end portion thereof. The developer grip54extends frontward and upward from the upper end portion of the front wall53. The developer grip54is grasped by the user when the developing cartridge19is mounted on or dismounted from the drum cartridge18or when the process unit13is loaded in or unloaded from the main casing2.

Rotational shafts of the agitator24, supply roller25and the developing roller26extend in the widthwise direction. As shown inFIG. 5, the axial ends of the rotation shaft of the developing roller26project outward from the developer housing23. As best shown inFIG. 7, the rear peripheral surface of the developing roller26is partly projected from the developer housing23. When the developing cartridge19is mounted on the drum cartridge18and received at the cartridge accommodating chamber42, the rear peripheral surface of the developing roller26is brought into contact with the front peripheral surface of the photosensitive drum20having been partly projected into the cartridge accommodating chamber42. With this structure, toner bore on the developing roller26can be supplied to the electrostatic latent image formed on the surface of the photosensitive drum20.

Mounting the developing cartridge19on and dismounting the same from the drum cartridge18are performed at places outside the main casing2. Specifically, in order to mount the developing cartridge19on the drum cartridge18, the developing cartridge19is moved to the upper position of the drum cartridge18while grasping the developing grip54. Then, the developing cartridge19is further moved to rear and lower side and pushed into the cartridge accommodating chamber42through the loading port43of the drum housing38. At this time, the axial ends of the rotation shaft of the developing roller26are brought into engagement with the guide groove49formed in the drum. housing38to allow the developing roller26to be guided by the guide groove49. The developing cartridge19is thus moved to the rear lower side, resulting in accommodation into the cartridge accommodating chamber42.

As the developing cartridge19is about to be received at the cartridge accommodating chamber42, the left and right pressed members80(seeFIG. 5) formed to the developing cartridge19are brought into abutment with the corresponding pressing members55held in the first position, causing the pressing members50to start rotating counterclockwise against the urging force imparted thereon by the coil springs59as viewed from the right side.

After that, as shown inFIG. 5, when the axial ends of the rotation shaft of the developing roller26have reached to the deepest portion (rear end portion) of the guide groove49, the developing cartridge19is no longer movable. This completes loading of the developing cartridge19into the cartridge accommodating chamber42. At this time, rotations of the pressing members50are stopped and the pressing members50are brought to the second position shown inFIG. 5. With the operation described above, fabrication of the process unit is complete for ready to use.

When the developing cartridge19is mounted on the drum cartridge18, the developing cartridge19is positioned at the bottom wall37of the drum housing38, and the rotation shaft of the developing roller26engages the deepest portion of the guide groove49. As such, the developing cartridge19is vertically positioned relative to the drum cartridge18

The pressing members50are upwardly oriented in a larger degree in the second position than in the first position. When the pressing members50are in the second position, the pressing portion55is oriented to the rear side in a degree larger than when the pressing members50are in the first position (seeFIG. 4). The lower portion56A of the extension portion56protruding downward from the bottom wall37of the drum housing38is oriented to the rear side in a larger degree in the first position than in the second position. The urging force of the coil springs59is still imparted upon the pressing members50located at the second position, thus potential movability of the pressing members50to the first position is outstanding. The pressing portions55of the pressing members50are biased to move backward and thus urge the pressed members80rearward.

The developing cartridge19mounted on the drum cartridge18is urged rearward by the urging force applied by the pressing members50to the pressed members80, resulting that the developing roller26is held in pressure contact with the photosensitive drum20accommodated in the drum cartridge18. That is, the pressing members50serve to urge the developing roller26against the photosensitive drum20in the second position. The developing cartridge19is urged rearward by the pressing members50and the developing roller26disposed in the front side of the photosensitive drum20is in pressure contact with the photosensitive drum20, thereby achieving positioning of the developing cartridge in the front-to-rear direction relative to the drum cartridge18.

When the developing cartridge19is dismounted from the drum cartridge18, the developing cartridge19is pulled to the front upward direction while grasping the developer grip54. Dismounting the developing cartridge19from the drum cartridge18completes when the developing cartridge19is lifted through the loading port43formed in the drum housing38. Upon completion of dismounting the developing cartridge19, the pressing members50return to the first position (seeFIG. 4) by virtue of the urging force of the coil springs59.

As shown inFIG. 1, the feed unit60is disposed in the internal space2A of the main casing2. The feed unit60is vertically sandwiched by the sheet supply tray6and the process unit13. The feed unit60includes the sheet supply roller7, pickup roller9, rear-side conveying roller10, lower-side registration roller11and unit frame61for rotatably supporting those rollers. The feed unit60is a part of the feeder section3.

The unit frame61is a hollow, plate-shaped member that is substantially rectangular in plan view. Specifically, the unit frame61has a widthwise length slightly longer than that of the sheet of paper P, and a longitudinal length being about two third (⅔) with respect to the front-to-rear length of the sheet supply tray6. The thickness of the unit frame61is held even over the entire length, however, the front edge portion is slightly thicker than the remaining part. The front edge portion of the unit frame61has an arcuate cross-section protruding frontward as viewed from the widthwise direction.

The sheet feed roller7and the pickup roller9are supported on the lower surface of the front end portion of the unit frame61, the rear side conveying roller10is supported on the front surface of the front end portion of the unit frame61, and the lower side registration roller11is supported on the upper surface of the front end portion of the unit frame61. On the other hand, the front side conveying roller10and the sheet feed pad8are supported on the front wall of the main casing2. The upper side registration roller11is supported on the drum cartridge18as described previously.

The feed unit60is integrally formed with the main casing2. A part of the conveying path36is defined by a space between the feed unit60and the front wall of the main casing2and between the feed unit60and the process unit13. The process unit13loaded in the main casing2is positioned relative to the main casing2when the process unit13is placed on the feed unit60. Specifically, a downwardly protruded portion71is formed substantially centrally in the front-to-rear direction in the upper surface of the unit frame61of the feed unit60. The downwardly protruded portion37A formed in the bottom wall37of the drum housing38is fittingly placed in the downwardly protruded portion71of the unit frame61. The process unit13fitted to the unit frame61is thus positioned relative to the main casing2.

A moving member62(indicated by a dotted line inFIG. 6) is provided on the upper surface of the unit frame61at the front end thereof and also at the front side of the lower side registration roller11, i.e., the upstream side in the sheet conveying direction. InFIG. 5, the pressing member50is depicted with hatching.

The moving member62is formed integrally from a detection shaft63extending in the widthwise direction within the unit frame61, a first segment64at the left end of the detection shaft63, a second segment65at the right end of the detection shaft63, and a third segment66downwardly projected from the center of the detection shaft63. The third segment66serves as a detected section.

The detection shaft63is disposed below the right side of the conveying path36formed between the process unit13and the feed unit60. The detection shaft63is rotatably supported by the unit frame61, and the moving member62is rotatable about the detection shaft63.

The first segment64of the moving member62is a rod-shaped member projecting upward from the detection shaft63. The upper end of the first segment64is within the conveying path36. The first segment64is positioned upstream of the registration rollers11and downstream of the conveying roller10with respect to the conveying direction of the sheet of paper P (seeFIG. 1).

The second segment65of the moving member62is a rod-shaped member projecting upward from the detection shaft63. The second segment65is spaced apart rightward from the conveying path36and the upper portion of the second segment65is located above the unit frame61. The third segment65is also a rod-shaped member and is located within the unit frame61. A position detector67is disposed within the unit frame61, which operates in cooperation with the third segment66.

The position detector67includes a light emitting section68and a light receiving section69. The light emitting section68and the light receiving section69are upstanding posture on the lower wall of the unit frame61and arranged in spaced-apart relation with each other in the widthwise direction. The light emitting section68and the light receiving section69are in confrontation with each other and are not in contact with the moving member62. The light emitting section68emits detection light as indicated by a dotted line inFIG. 6and the light receiving section69receives the detection light if a light path70from the light emitting section68to the light receiving section69is not interrupted.

Depending upon the rotated position of the moving member62, the third segment66of the moving member62is either placed between the light emitting section68and the light receiving section69to interrupt the light path70or placed out of the light path70to allow the detection light to receive at the light receiving section69. Depending upon whether the light path70is interrupted by the third segment66, the position detector67detects the position of the moving member62.

As the moving member62rotates about the detection shaft63, the moving member62is selectively placed in a third position (seeFIG. 4), a fourth position indicated by a solid line inFIG. 5, and a fifth position indicated by a dotted line inFIG. 5. When the moving member62is in the third position as shown inFIG. 4, the first and second segments64,65are diagonally oriented front/up-ward, and the third segment66horizontally rearward. When the moving member62is held in such a position, the third segment66is out of the light path70and does not interrupt the detection light to be received at the light receiving section69. When the moving member62is in the fourth position as shown inFIG. 5, the first and second segments64,65are oriented upward, and the third segment66diagonally rear/down-ward. When the moving member62is held in such a position, the third segment66is disposed between the light emitting section68and the light receiving section69to interrupt the detection light. When the moving member62is in the fifth position as shown by a dotted line inFIG. 5, the first and second segments64,65are diagonally oriented rear/up-ward, and the third segment66downward. At this time, the third segment66is out of the light path70.

Referring toFIGS. 4 and 5, the moving member62sequentially takes the third, fourth and fifth positions when rotated clockwise as viewed from the right side. The moving member62is urged to be in the third position as shown inFIG. 4by an urging member (not shown).

When the process unit13is unloaded from the main casing2, the moving member62is in the third position and the position detector67detects such a positioning. To load the process unit13into the main casing2, the user first opens the front cover5, grasps the drum grip51and the developer grip54to bring the process unit13into the internal space2A of the main casing2. When the process unit13is further brought forward into the main casing2, the downwardly protruded portion37A formed in the bottom wall37of the drum cartridge18is brought into engagement with the corresponding protruded portion71formed in the unit frame61. At this time, the lower end portion56A of the extension portion56of the right side pressing member50is brought into abutment with the second segment65of the moving member62held in the third position. As a result, the moving member62rotates clockwise as viewed from the right side against the urging force applied by the urging member (not shown).

When the protruded portion37A of the drum cartridge18is engaged with the corresponding protruded portion71of the unit frame61, the process unit13is no longer movable forwardly. This completes loading the process unit13in the main casing2. At this time, rotations of the moving member62stop and the moving member62is placed in the fourth position. That is, when the process unit12is loaded in the main casing2, the moving member62is brought to the fourth position by the pressing member50placed in the second position. At this time, the process unit12is brought into abutment with the pressing member50.

In this manner, when the moving member62is moved from the third position to the fourth position, the third segment66of he moving member62moves into the light path70to interrupt the detection light. The position detector67thus detects that the moving member62is in the fourth position. It should be noted that a CPU90functioning as a determination unit is disposed in the main casing2as shown inFIG. 1. The CPU90determines that the process unit13is loaded in the main casing2based on the detection result indicating that the moving member62is in the fourth position.

On the other hand, to unload the process unit13from the main casing2, the process unit13is drawn frontward while gripping the drum grip51and the developer grip54. When the process unit13is completely unloaded from the main casing2, the moving member62returns to the third position by the urging force imparted by the urging member (not shown), and the position detector67detects that the moving member62has moved to the third position.

A major part of the process unit13is loaded in or unloaded from the main casing2through a space95above a reference line96(seeFIG. 4). The moving member62is located below the reference line96wherever the position of the moving member62may be.

In a state where the pressing member50is in the second position and the moving member62is in the fourth position, line lengths A and B on the vertical cross section as shown inFIG. 5will be defined as follows. The line length A is defined as a length between a first contact point X and the first rotation center of the pressing member (center axis58A of the pressing shaft58). The first contact point X is defined as a contact point between the pressed member80of the developing cartridge19and the pressing potion55of the pressing member50. The second line length B is defined as a length between a second contact point Y and the first rotation center. The second contact point Y is defined as a contact point between the lower end portion56A of the pressing member50and the second segment65of the moving member62in the fourth position. It should be noted that the second line length B is set longer than the first line length A.

A third contact point Z is defined as a contact point between the second segment65of the moving member62in the fourth position and the lower end portion56A of the pressing member50in the second position. A third line length C is defined as a length between the third contact point Z and a second rotation center. The second rotation center is a center axis63A of the detection shaft63. A fourth line length D is defined as a line length between the third segment66(strictly, the end66A of the third segment66farthest from the axial center63A) of the moving member62and the center axis63A of the detection shaft63. It should be noted that the fourth line length D is longer than the third line length C. As viewed from the widthwise direction, the third segment66is disposed at the opposite side of the third contact point Z with respect to the center axis63A of the detection shaft63. The second and third contact points Y and Z are in coincidence with each other as viewed from the widthwise direction.

The printer1is ready for printing when the process unit13is loaded in the main casing2and the front cover5is closed. When printing is performed, a sheet of paper P (which is an example of a recording medium) passes through the conveying path36. When the sheet of paper P is conveyed to the moving member62placed in the fourth position as indicated by a solid line, the sheet P is brought into contact with and overrides the first segment64. This causes the moving member62to rotate clockwise as viewed from the right side against the urging force imparted by the urging member (not shown). As a result, the moving member62moves from the fourth position to the fifth position as indicated by a dotted line.

The third segment66that has been placed in the light path70when the moving member62is in the fourth position is moved out of the light path70resulting from the movement of the moving member62from the fourth position to the fifth position. The position detector67detects that the moving member62has moved to the fifth position. As described previously, the first segment64of the moving member62that is projected into the conveying path36is positioned upstream of the registration rollers11with respect to the sheet conveying direction. Based on the detection result obtained from the position detector67indicating that the moving member62is in the fifth position, the CPU90determines a timing at which the registration rollers11convey the sheet of paper in contact with the first segment64toward the transfer position. The registration rollers11convey the paper P toward the transfer position at the timing determined by the CPU90. In this sense, the moving member62functions as a passage detector for detecting passage of the sheet of paper P at a prescribed point in the conveying path36.

As described above, the moving member (passage detector)62detects passage of the paper P along the conveying path36with the first segment64thereof. Upon detection of the passage of the paper P, the moving member (passage detector)62moves to the fifth position in which the first segment64is placed within the unit frame61of the feed unit60and out of the conveying path so as not to bother the passage of paper P in the conveying path36.

When the paper P has passed the first segment64, the moving member passage detector)62is rotated counterclockwise by the force of the urging member (not shown) and returned to the fourth position. The moving member62stops at the fourth position as it is brought into abutment with the lower end portion56A of the pressing member50disposed at the second position. The position detector67thus detects that the moving member62is in the fourth position.

As described in detail above, the pressing member50is provided in the drum cartridge18to be movable between the first position and the second position. The pressing member50is placed in the first position when the developing cartridge19is dismounted from the drum cartridge18whereas the pressing member50is placed in the second position when the developing cartridge19is perfectly mounted on the drum cartridge18. The moving member62and the position detector67are provided in the main casing2. The moving member62is in the third position when the process unit (the drum cartridge18on which the developing cartridge19is mounted) is unloaded from the main casing2. On the other hand, the moving member62is moved to the fourth position when a perfectly assembled process unit is loaded in the main casing2. At this time, the pressing member50placed in the second position is brought into abutment with the moving member62, causing the moving member62to move to the fourth position. The position detector67detects the position of the moving member62.

The CPU90determines that the drum cartridge18on which the developing cartridge19is mounted is loaded in the main casing2based on the detection result of the position detector67indicating that the moving member62is in the fourth position. The pressing member50is not placed in the second position but in the first position if the developing cartridge19is not mounted on the drum cartridge18. Accordingly, the moving member62is not moved to the fourth position but remains in the third position if only the drum cartridge18is loaded in the main casing2. The CPU90thus determines that either one of the two cartridges is loaded in the main casing2but the remaining one of the cartridges is not loaded therein based on the detection result from the position detector67indicating that the moving member62is in the third position.

When the drum cartridge18is not loaded in the main casing2but only the developing cartridge19is loaded therein, the pressing member50is not present so that the moving member62is not brought to the fourth position but remains in the third position. Based on the detection result from the position detector67, the CPU90determines that either one of the two cartridges is loaded in the main casing2but the remaining one of the cartridges is not.

The main casing2is provided with an informing unit91for informing the user of various errors (seeFIG. 1). When the CPU90detects an error (for example, at least one of the drum cartridge18and the developing cartridge19has been loaded in the main casing2), the informing unit91informs the user about the occurrence of the error with a prescribed method before the image formation is performed (for example, when the front cover5is closed). Such a prescribed method may include a warning lamp, a warning sound or an error display. In this way, the informing unit91prompts the user to remove the error as early as possible once the error has occurred.

In the above-described embodiment, a first distance A from a first contact point X between the pressing member in the second position and the pressed member80to a first rotation center58A of the pressing member is equal to or shorter than a second distance B from a second contact point Y between the moving member62and the pressing member50to the first rotation center58A. A third distance C from a third contact point Z between the pressing member50in the second position and the moving member62to a second rotation center63A of the moving member62is equal to or shorter than a fourth distance D between a portion disposed in opposite side of the third contact point Z relative to the second rotation center63A, the portion being detected by the position detector, and the second rotation center. As such, even if the amount of displacement of the pressing member50between the first position and the second position is small (in the embodiment described, the rotation angle of the pressing member50between the first position and the second position is about 9 degrees), the second contact point Y of the pressing member50, which point is relatively largely displaced or rotated, is brought into abutment with the third contact point Z. Thus, the movement of the moving member62between the third position and the fourth position is assured. Furthermore, even if the amount of displacement of the moving member62between the third position and the fourth position is small, positional detection of the moving member62by the position detector67can be assured because the third segment66to be detected by the position detector67is relatively largely displaceable as compared with other segments of the moving member62.

In other words, augmenting a small displacement of the pressing member50enables accurate detection of the first and second positions of the pressing member50and the third and fourth positions of the moving member62.

A modification is shown inFIGS. 8 and 9.FIG. 8shows a state in which a drum cartridge and a developing cartridge are separated andFIG. 9shows a state in which the developing cartridge is mounted on the drum cartridge.

The embodiment described above employs an optical sensor as the position sensor67as shown inFIG. 6. The modification employs a contact switch as the position sensor as shown inFIGS. 8 and 9. The position sensor67in accordance with the modification is configured from a lever85disposed immediately below the lower end portion56A of the pressing member50when the process unit13is loaded in the main casing2. The lever85is deformable and capable of moving between the third position and the fourth position. The third and fourth positions of the lever85correspond to the third and fourth positions of the moving member62described in the embodiment.FIG. 8shows that the lever85is in the third position where the lever85extends rear-up-ward.FIG. 9shows that the lever85is in the fourth position where the lever85extends rear-down-ward. When the pressing member50is in the second position (seeFIG. 9), the lower end portion56A of the pressing member50is oriented downward as compared to the case where the pressing member50is in the first position (seeFIG. 8). Similar to the moving member62according to the above-described embodiment, the lever85also functions as a moving member.

The position sensor67is rendered OFF in which the position sensor67is in an electrically disconnected state when the lever85is in the third position. On the other hand, the position sensor67is rendered ON in which the position sensor67is in an electrically disconnected state when the lever85is moved to the fourth position. The position of the lever85is detected based on whether or not the position sensor67is ON or OFF, i.e., whether the position sensor67is in the electrically connected state or disconnected state. The relation between the positions of the lever85and the ON and OFF states of the position sensor67can be reversed. Specifically, the position sensor67may be rendered ON in which the position sensor67is in an electrically connected state when the lever85is in the fourth position. On the other hand, the position sensor67may be rendered OFF in which the position sensor67is in an electrically disconnected state when the lever85is in the third position.

With the above-described structure according to the first embodiment, when only the drum cartridge18or only the developing cartridge19is loaded in the main casing2, the lower end portion56A of the pressing member50is apart from the lever85and thus the lever85remains in the third position. Thus, the position detector67is OFF, based on which it can be detected that the lever85is in the third position.

On the other hand, when the drum cartridge18on which the developing cartridge19is mounted, i.e., the completed process unit13, is loaded in the main casing2, the lower end portion56A of the pressing member50in the second position is brought into contact with the lever85, causing the lever85to press downward. As a result, the lever85is moved to the fourth position and thus the position detector67is rendered ON, based on which it can be detected that the lever85is in the fourth position.

The modification is advantageous in that the position of the lever5can be easily detected depending upon whether or not the contact switch acting as the position detector67is rendered ON or OFF.

While the above-described embodiment shows a monochromatic laser printer as one embodiment, the present invention is applicable not only to such a laser printer but also a color laser printer or other types of color image forming devices. Further, the above-described embodiment employs an exposure unit for exposing the photosensitive drum20to laser beam. Another type of exposure unit may be employed instead. For example, the exposure unit may include a plurality of LEDs aligned along the longitudinal axis of the photosensitive drum20, in which the LEDs are selectively lit based on image data instead of scanning the laser beam modulated based on image data.

In the above described embodiment and modifications, the present invention has been applied to the process unit13(the drum cartridge18and the developing cartridge19). However, the present invention may also encompass other combinations of cartridges, such as a toner cartridge that accommodates toner therein and a developing unit that includes a developing roller and a supply roller for supplying toner to the developing roller.

Further, the printer1is provided with the informing unit91for informing the user of errors. However, the printer1may not have the informing unit91. In the latter case, an informing unit may be provided on a computer to which the printer1is connected. Upon detection of an error, the printer1outputs a signal to the computer to indicate occurrence of the error. In response to such an error signal, the computer informs the user of the error with a prescribed method (an error display, for example).