Image Forming Apparatus Comprising a Main Assembly Having a Top Frame Adapted to Swing Open and Closed With Respect to a Bottom Frame and Having Process Cartridge Detachably Mounted in the Main Assembly

The present invention relates to an image forming apparatus usable with a process cartridge which contains a photosensitive member and at least one of an image forming means such as a developing device, a cleaning device, and charger, which are integrally supported on the process cartridge. The image forming apparatus can produce on a recording material an image of characters and figures as in a computer, facsimile, personal computer, electrophotographhic copying machine and a word processor and the like.

An image forming apparatus usable with such a process cartridge has been made practicable, wherein the main apparatus is divisible or openable to allow easy mounting and dismounting of the process cartridge, such that the process cartridge is loaded on the upper frame of the main assembly.

In this type of the apparatus, since the cartridge is disposed with the major components of the optical system in the upper frame, the upper frame becomes heavy, with the result of a bulky supporting mechanism for the upper frame. Further, the vibration at the time of opening and closing the upper frame distorts the optical system, which leads to a non-uniform scanning operation and the inability to produce a sharp exposure of the image. Furthermore, the toner can be scattered from the cartridge.

Accordingly, it is a principal object of the present invention to provide an image forming apparatus wherein the above-described problems with the conventional image forming apparatus using a process cartridge are solved.

It is another object of the present invention to provide an accurate positioning mechanism for the optical member provided in the upper frame which is openable with respect to the bottom frame.

It is another object of the present invention to provide a simple mounting and dismounting mechanism for the process cartridge.

According to an embodiment of the present invention, an image forming apparatus is provided, which comprises a main assembly including a bottom, frame and a top frame which is capable of assuming closing and opening positions with respect to the bottom frame; a process cartridge detachably mountable into the main assembly and containing at least a photosensitive member and process means contributable to image formation on the photosensitive member; optical means provided in the bottom frame for applying light information to the photosensitive member of the cartridge; a positioning member provided in the bottom frame and engageable with the cartridge when the top frame assumes its closing position; and supporting means provided in the top frame to detachably support the cartridge.

When the apparatus comprises an upper frame openable with respect to the bottom frame, it is advantageous that the optical members such as mirrors or the like are positioned on the bottom frame by abutting the optical member to a positioning member provided on the bottom frame, as in the cartridge.

These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

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

FIG. 2 is a sectional view of the apparatus of FIG. 1 when top cover is opened.

FIG. 3 is a partial side elevation of a positioning mechanism of the present invention.

FIG. 4 is a plan view of the positioning mechanism shown in FIG. 3.

FIG. 5 is a perspective view seen from the bottom of a process cartridge.

FIG. 6 is a perspective view of a driving mechanism of the present invention.

FIGS. 7 and 8 are sectional views of an apparatus of the present invention provided with a reflection mirror.

FIG. 9 is a perspective view of FIG. 7 apparatus wherein the top frame is opened.

FIGS. 10 and 11 are partial side views, illustrating the reflection mirror of the present invention correctly positioned.

FIGS. 12 and 13 are sectional views of image forming apparatuses according to other embodiments of the present invention.

FIG. 14 is a partial side view, illustrating the positioning where a photosensitive belt is used.

Referring to FIG. 1, there is shown an image forming apparatus according to an embodiment of the present invention. The image forming apparatus is shown as being of such a type of image forming apparatus wherein an electrophotographic photosensitive member is scanned by a laser beam for image formation, as an example of the image forming apparatus.

FIG. 2 illustrates the same apparatus under a different condition, that is, when the top part of the apparatus is opened.

Referring back to FIG. 1, the image forming apparatus comprises a laser scanner 14 of a known structure which scans the photosensitive drum 12. Since the laser beam carries image signals, the photosensitive drum 12 is exposed to an image. The photosensitive drum is rotatable in the direction indicated by an arrow, during which time it is uniformly charged by a corona charger 10. After being uniformly charged thereby, the photosensitive drum 12 is exposed to the image-modulated laser beam by the laser scanner 14, so that an electrostatic latent image is formed on the photosensitive drum 12, which image is in turn developed by the toner of the developing device 11. In this example, a process cartridge 9 is illustrated as containing as a unit the photosensitive drum 12, the developing device 11, cleaning device 13 and the charger 10 which are supported on a frame. A transfer material or sheet 1 on which the image is to be recorded, is fed to the surface of the photosensitive drum 12 by a feeding roller 2, a registration roller 3 and transfer material guiding plates 4. At an image transfer station, the toner image formed on the photosensitive drum 12 is transferred to the thus fed transfer sheet by a transfer charter 5. Thereafter, the transfer sheet is separated from the photosensitive drum 12, and is then transported to an image fixing device 6, where the image now transferred onto the transfer sheet is fixed into a permanent image. Finally, the transfer sheet is discharged out of the image forming apparatus onto a tray above the cover 8 constituting a part of the top frame B. The sheet discharging is effected by a couple of the discharging rollers 7. The toner which has not been transferred onto the transfer sheet but which remains on the photosensitive drum 12 is removed therefrom by the cleaning device 13 and is collected.

The apparatus further comprises a pre-exposure lamp 15, a hinge 16 constituting a rotational axis of the cover 8, a spring 17 for urging the process cartridge 9 downwardly, a positioning block 18a for engaging with and supporting end shafts 12a and 12b of the photosensitive drum 12 and an abutting block 19 for stopping the rotation of the process cartridge 9.

As is best seen in FIG. 2, the top frame B and the bottom frame A of the apparatus are divisible or openable by pivotable or rotational action about the hinge 16. More particularly, in this embodiment, the top frame B can be rotated upwardly. The top frame contains the discharging rollers 7, the pre-exposure lamp 15, the process cartridge 9, the guide 9A for guiding the cartridge, the spring 17 and other elements. The bottom frame contains the feeding roller 2, the registration roller 3, the transfer sheet guides, the image fixing device 6, a laser scanner 14 for constituting the major part of the optical system, the positioning block 18a and the abutting block 19 and other elements. The cartridge 9 may be mounted into or dismounted from the apparatus in the direction of an axis of the photosensitive drum 12.

In FIG. 2, the process cartridge 9 is shown as simply bearing against the guide 9a in the top frame B, and it is urged downwardly by the spring 17 so that it does not easily come out of the guide 9a with the aid of an unshown stopper. In this state, the process cartridge is easily raised upwardly if it is pushed upwardly against the force of the spring 17.

When the top frame or cover is closed (FIG. 1), the shafts 12a provided at longitudinal opposite ends of the photosensitive drum 12 engage the groove of the positioning block 18a provided in the bottom frame. A part of the frame of the process cartridge 9 engages the abutting block 19 for positioning and supporting the frame of the cartridge, by which the frame of the process cartridge 9 is prevented from rotating. Further, a transfer guide plate 4 is fixed to the positioning block 18a, the transfer guide plate 4 is fixed, and the relative positional relation between the photosensitive drum 12 and the transfer guide plate 4 is automatically assured only by closing the top frame.

FIG. 5 is a perspective view seen from the bottom, of the process cartridge. The cartridge includes a gear 12b for transmitting the driving force from the main assembly to the photosensitive drum 12. The gear is fixed to an end of the photosensitive drum 12.

FIG. 6 is a perspective view illustrating the driving mechanism for the photosensitive drum 12. As will be understood from this Figure, the above-described gear 12b of the photosensitive drum meshes with a driving gear C provided in the bottom frame A so that the driving force from the bottom frame A is transmitted to the photosensitive drum 12 through those gears.

FIG. 7 illustrates an image forming apparatus according to another embodiment of the present invention. In this apparatus, a reflection mirror 14a as a part of the optical means is contained in the top frame, in addition to the scanner disposed in the bottom frame A. The reflection mirror 14a is fixedly secured to a mirror holder 14c.

As shown in FIG. 10, opposite end portions of the mirror holder 14c are engaged with and supported by a hook 14d in the opening of the side wall of the top frame. Also provided is an urging spring 14b having an end fixed to the top frame and the other end acting on the top surface of the mirror 14a so as to urge it substantially downwardly.

In the bottom frame, there is provided a mirror stopper having an inclined surface for engaging the bottom surfaces of the mirror holder 14c at the opposite ends, thus positioning the mirror 14a with respect to the mirror stopper, as shown in FIG. 11.

Referring back to FIG. 7, the bottom frame contains a scanner table 14f for supporting the laser scanner 14. The scanner table is integral with the drum shaft support 18a and the mirror stopper and is made of a reinforced plastic of polycarbonate with glass fibers, thus assuring the dimensional and positional accuracy and also assuring mechanical strength.

FIG. 9 is a perspective view of the apparatus when the top frame is in the open position.

Because of the structures described above, when the top frame is in its closing position, accurate positioning can be accomplished among the laser scanner 14 as the light source, the registration roller couple 3, which is the keystone of the transfer sheet transportation, the photosensitive drum 12 and the reflection mirror 14a, in conjunction with the bottom frame. Additionally, mechanical strength is increased by the integral frame structure, and moreover, the vibration can be reduced greatly.

Referring back to FIG. 7, the process cartridge is inserted into the top frame in the direction indicated by an arrow C.

FIG. 8 illustrates the apparatus of FIG. 7 when the top frame is in its closing position, and the image forming operation is performed.

FIG. 10 illustrates the positioning of the reflection mirror 14a with respect to the mirror stopper 14e, as will be understood from the foregoing description.

FIG. 11 shows the state of mirror 14a after it has been positioned, as will be understood from the foregoing description.

In this embodiment, as will be understood, the shaft defining the rotational axis of the photosensitive member in the process cartridge is engaged with the positioning member provided in the bottom frame, by which the very accurate positioning is accomplished between the major part of the optical system and the process cartridge, which should be accurately positioned with the major part of the optical system. Additionally, the transfer guide plate, the transfer charter and other elements may be correctly positioned automatically and simultaneously, by providing similar mechanisms if desired. It should be noted that the major part of the optical system is not provided in the top frame, and therefore, the mechanism for rotatably connecting the top and bottom frames may be of a relatively simple structure, thus providing an image forming apparatus which is not heavy and which is easy for the operator to handle.

The apparatus shown in FIG. 7 includes the reflection mirror. Even in this structure, the process cartridge and the reflection mirror are correctly positioned with respect to the bottom frame when the top frame assumes its closing position, without employing a complicated structure for the top frame and without increasing the dimensions of the device. Additionally, various image forming means such as the laser scanner as the light source, the reflection mirror, the registration roller couple and the photosensitive drum in the process cartridge are provided in the top frame substantially as a unit, whereby they are correctly positioned with high accuracy, so that the image quality can be maintained high.

In the foregoing description of the embodiments, the process cartridge is loadable into the top frame, However, it is a possible alternative that, as shown in FIG. 12, the process cartridge is supported on a supporting member 18b or 19 provided in the bottom frame A, and it is urged by a spring 17 provided in the top frame when the apparatus is closed, thus positioning the process cartridge.

As shown in FIG. 13, sheet original scanner may be used in place of the laser scanner 14. In the FIG. 13 apparatus, the original to be copied is transported by transporting rollers by a slit glass 21. During the transportation, the original 24 is illuminated by a lamp 22, and the light reflected by the original is imaged by an imaging lens 23 and focused on the surface of the photosensitive drum 12, so that the photosensitive drum 12 is exposed to the slit image of the original. Those optical means are securely fixed on the bottom frame A. It is possible that the mirror 14a as used in FIG. 7 embodiment may be used in the top frame.

As shown in FIG. 14, it is possible to use a photosensitive member in the form of a belt in place of the photosensitive drum. The above descriptions apply to the case of photosensitive belt 12b. The rotational axis of the photosensitive drum corresponds to the rotational axis 12d of a roller 12c for supporting the photosensitive drum. It is desirable that the roller 12c is disposed close to the exposure position with the view to correct positioning. As for the process cartridge, it contains as a unit two or more means to be used for image formation. For example, it may contain the photosensitive member and the developing device; the photosensitive member and the cleaning device; or the photosensitive member and the developing means and the cleaning means. The structures shown in FIGS. 13a-13f of U.S. Pat. No. 4462677 assigned to the assignee of the present application are usable with the present invention.

While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.