BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a scanning exposure apparatus to which the present invention is applied.
FIG. 2 is a top view of the scanning exposure apparatus shown in FIG. 1.
FIG. 3A is a cross sectional view of the scanning exposure apparatus shown in FIG. 1.
FIG. 3B is a cross sectional view of an optical device box of the scanning exposure apparatus shown in FIG. 1.
FIG. 3C is a cross sectional view of a motor on which a polygon mirror is attached in the scanning exposure apparatus shown in FIG. 1.
FIG. 4 is a bottom view of the scanning exposure apparatus shown in FIG. 1.
FIG. 5 is a top view illustrating another state of the scanning exposure apparatus to which the present invention is applied.
FIG. 6A is a cross sectional view of the scanning exposure apparatus shown in FIG. 5.
FIG. 6B is a cross sectional view of an optical device box of the scanning exposure apparatus shown in FIG. 5.
FIG. 6C is a cross sectional view of a motor on which a polygon mirror is attached in the scanning exposure apparatus shown in FIG. 5.
FIG. 7 is a bottom view of the scanning exposure apparatus shown in FIG. 1.
FIG. 8 is a perspective view of another embodiment.
FIG. 9 illustrates an image forming apparatus to which the present invention is applied.
FIG. 10 illustrates the structure of the image forming apparatus.
FIG. 11 illustrates the scanning exposure apparatuses and relevant portions in FIG. 10.
FIG. 12 schematically illustrates the structure of scanning exposure apparatuses and relevant portions.
FIG. 13 illustrates a conventional scanning exposure apparatus.
FIG. 14 is a cross sectional view of the scanning exposure apparatus shown in FIG. 13.
FIG. 15 illustrates another type of conventional scanning exposure apparatus.
DESCRIPTION OF THE EMBODIMENTS
In the following, an exemplary embodiment of the present invention will be described.
FIG. 9 illustrates scanning exposure apparatuses and portions relevant thereto in an image forming apparatus according to an embodiment. In FIG. 9, a plurality of photosensitive drums 3 to 8 serving as image bearing members are provided in the vicinity of the scanning exposure apparatuses. Among the photosensitive drums, four photosensitive drums 3 to 8 are respectively associated with normally used colors, namely yellow (Y), magenta (M), cyan (C) and black (Bk) The other photosensitive drums 7 and 8 are associated with special colors that are added to enhance color reproduction. Among these additional drums, one photosensitive drum 7 is adapted to form a toner image with light magenta toner that has the same hue as and higher brightness than the magenta toner, and the other photosensitive drum 8 is adapted to form a toner image with light cyan toner that has the same hue as and higher brightness than the cyan toner. In this embodiment, image forming units including the photosensitive drums 3 to 8 are provided.
Near the plurality of photosensitive drums 3 to 8, there is provided an intermediate transfer belt 61, which is a belt member that transfers toner images formed on the photosensitive drums 3 to 8 onto a transfer sheet. The image forming units in this embodiment have the same structure except for the colors of the toners. Here, a description will be made of the image forming unit for yellow. In the vicinity of the photosensitive drum 3 are provided a charging member for charging the photosensitive drum 3, a developing unit for forming a toner image from an electrostatic latent image formed by exposure, a primary transfer member for transferring the toner image onto the intermediate transfer belt and a cleaning unit for cleaning residual toner. The charging member, the developing unit, the primary transfer member and the cleaning unit as described above are provided in each of the image forming units for respective colors in the same manner. Single color toner images formed in the respective units are superimposed on the intermediate transfer belt, and then they are transferred onto a recording material by a secondary transfer member. The toner images thus transferred are fixed by heat by a fixing unit. The intermediate transfer belt used in this embodiment is stretched between tension members. Details of the scanning exposure apparatus performing image exposure will be described later. To prevent an increase in the lateral size of the image forming apparatus and an increase in the area occupied by the image forming apparatus, two photosensitive drums 7 and 8 are provided on the side of the intermediate transfer belt, which serves as an intermediate transfer member, different from the side on which the other photosensitive drums 3 to 6 are provided. Specifically, the two photosensitive drums 7 and 8 are provided on the upper side with respect to the vertical direction and the other photosensitive drums 3 to 6 are provided on the lower side. To expose the photosensitive drums 3 to 6 disposed on the lower side, two scanning exposure apparatuses la are provided below the photosensitive drums 3 to 6. On the other hand, a scanning exposure apparatus 1b for exposing the two photosensitive drums 7 and 8 disposed on the upper side is provided above the photosensitive drums 7 and 8.
Embodiment 1
In the following, an embodiment will be described with reference to drawings.
FIGS. 1 to 4 show one of the scanning exposure apparatuses la in FIG. 9. In this embodiment, the scanning exposure apparatus is an optical unit that can be detachably mounted on an image forming apparatus.
Referring to FIG. 4, an optical device box 20 has three body mount portions 20e, 20f and 20g provided on the upper and lower portions thereof. The body mount portions 20e, 20f and 20g have a circular hole 20h for positioning, an elongated hole 20j and three screw holes 20j. The three body mount portions are positioned by positioning pins (not shown) provided on the apparatus body and secured by screws, whereby the scanning exposure apparatus is fixedly mounted on the image forming apparatus. Here, reference is made to FIGS. 1 and 2. Laser units 21a and 21b for irradiating two photosensitive drums are mounted on a side wall of the optical device box 20. Each laser unit 21a, 21b has a semiconductor laser LD serving as a light source and a collimator lens CL that changes the laser beam into a parallel beam. Cylindrical lenses 22a and 22b are adapted to focus the laser beams emitted from the laser units 21a and 21b in linear shapes on a polygon mirror 23 that functions as a rotational polygon mirror. The polygon mirror 23 that functions as a rotational polygon mirror is fixed on the rotor of a motor 24 serving as a drive unit and rotates at high speed to thereby deflect the laser beams to scan photosensitive drums. FE lenses 25a, 26a and 25b, 26b serving as imaging members are provided to focus the laser beams emitted from the laser units 21a and 21b and deflected by the polygon mirror 23 onto two photosensitive members to thereby scan and expose the photosensitive members at a constant speed. The laser beams having passed through the fθ lenses are guided by turn back mirrors 27a and 27b respectively toward photosensitive drums provided above the scanning exposure apparatus. Light sensors 29a and 29b for controlling the timing of image writing are provided. A part of the laser beam deflected by the polygon mirror 23 is focused onto the light sensor 29a, 29b by a lens 28a, 28b. In the case where the polygon mirror 23 rotates clockwise in FIG. 2, the timing of image writing on the two photosensitive drums is controlled by detecting the laser beam from the laser unit 21a by means of the light sensor 29a. On the other hand in the case where the polygon mirror 23 rotates anticlockwise, the timing of image writing is controlled by detecting the laser beam from the laser unit 21b by means of the light sensor 29b.
As illustrated in FIGS. 3A, 3B and 3C, a lid member 30 seals the interior of the optical device box 20. The openings 30a and 30b are provided on the lid member 30 through which the laser beams guided by the turn back mirrors 27a and 27b toward the photosensitive drums exit. The openings 30a and 30b are sealed by dust-proof glasses 31a and 31b. Referring to the vertical orientation of the image forming apparatus, the surface having the lid 30 is facing upward in the image forming apparatus, and the surface opposite thereto is facing downward in the image forming apparatus and constitutes the bottom of the optical device box 20. A cap 32 has a structure for mounting on the optical device box 20 similar to that of the motor 24, and the cap 32 is attached to three motor mount portions 20c provided on the inner side of the optical device box 20.
In FIGS. 3A, 3B and 3C, the motor 24 is fixed to three motor mount portions 20b (first mount portions) provided on the outer side of the optical device box 20 from the downward (first direction) of the optical device box 20 (see FIG. 7). When the motor 24 is fixed, the outer circumference of a circular positioning portion (first engagement portion) 24a1 that is provided on the stator of the motor 24 and coaxial with the rotary shaft of the motor 24 fits or engages with the inner circumference of a cylindrical positioning portion 20a serving as a support portion provided on the optical device box 20, whereby the polygon mirror 23 attached on the rotor of the motor 24 is positioned. The circular positioning portion 24a1 of the motor 24 may be formed integrally with a bearing portion of the stator to constitute a bearing member. Thus, the motor 24 and the polygon mirror 23 can be positioned relative to the optical device box 20 with high precision.
As will be seen from FIG. 3A, optical components such as lenses and mirrors are supported on the base member of the optical apparatus that constitutes the base of the optical device box 20. The optical components are provided on the same side of the base member as the cylindrical positioning portion 20a. In this embodiment, the base member of the optical apparatus serves as an optical frame.
Here, a description will be made of the motor 24 with reference to FIG. 3C. The rotor 24c is supported by a bearing member (stator) 24a2 having a bearing portion of the rotor 24c or the driving shaft. The polygon mirror 23 rotates with the rotation of the rotor 24c. The stator 24a2 has the positioning portion 24a1 for positioning the polygon mirror 23 relative to the optical device box 20. The positioning portion 24a2 is molded integrally with the bearing portion. On the lower portion of the stator 24a2 is attached an electric board 24b for energizing the motor 24 to rotate the rotor 24c. The circular positioning portion 24a1 of the motor 24 may be formed integrally with the bearing portion of the stator to constitute the bearing member. Thus, the motor 24 and the polygon mirror 23 can be positioned relative to the optical device box 20 with high precision. The positioning portion 24a1 is circular in shape when seen from above.
The motor is attached to the positioning portion provided on the base member shown in FIG. 3B. In this embodiment, when the motor 24 is attached to the optical device box 20, the polygon mirror 23 side of the motor 24 is first inserted into the positioning portion 24a1. Accordingly, the outer diameter of the positioning portion 24a1 is designed to be larger than the rotational diameter of the polygon mirror 23. With this structure, the drive axis of the motor 24 and the center axis of the positioning portion 24a1 are substantially aligned with each other.
FIG. 3A illustrates the state in which the motor 24 has been attached to the optical device box 20.
When this optical device box 20 is mounted in the image forming apparatus, the rotational polygon mirror 23 can be disposed above the motor 24 with respect to the vertical direction in the image forming apparatus.
In the surrounding of the polygon mirror 23, there is the cylindrical positioning portion 20a provided on the optical device box 20. Nevertheless, the polygon mirror 23 and the rotor 24c of the motor 24 will not interfere with the positioning portion 20a when they rotate, since the inner diameter of the positioning portion 20a is designed to be larger than the diameter of the circumscribed circle of the polygon mirror 23 and the outer diameter of the rotor 24c. The cylindrical positioning portion 20a of the optical device box 20 has two apertures 20d for allowing the laser beams coming from the laser units 21a and 21b and the laser beams deflected and scanned by the polygon mirror 23 to pass therethrough.
In the following, a description will be made of the scanning exposure apparatus 1b with reference to FIGS. 5 to 7. In this embodiment, the scanning exposure apparatus is a unit that is detachably mounted on the image forming apparatus.
The scanning exposure apparatus 1b is mounted on the image forming apparatus body with the orientation inverse to the scanning exposure apparatus la with respect to the vertical direction. The scanning exposure apparatus 1b performs scanning exposure of the two photosensitive drums disposed below it. The scanning exposure apparatus 1b differs from the scanning exposure apparatus 1a only in the manner in which the polygon mirror 23, motor 24 and cap 32 are attached to the optical device box 20, and the structure of the scanning exposure apparatus 1b other than those mentioned above is the same as the structure of the scanning exposure apparatus 1a.
Referring to FIG. 6A to 6C, the motor 24 is fixed to three motor mount portions 20c (second mount portions) provided on the inner side of the optical device box 20 from the downward (second direction) of the optical device box 20 (see FIG. 2). Thus, the surface having the lid 30 is facing downward in the image forming apparatus and constitutes the bottom surface of the optical device box 20. The motor 24 is attached from the bottom side. When the motor 24 is attached, the outer circumference of the circular positioning portion (second engagement portion) 24a1 that is provided on the stator 24a2 of the motor and coaxial with the rotary shaft fits or engages with the inner circumference of the cylindrical positioning portion 20a provided on the optical device box 20. In this way, the outer circumference of the positioning portion 24a1 of the motor 4 fits with the inner circumference of the positioning portion 20a of the optical device box 20, whereby the polygon mirror 23 attached to the rotor 24c of the motor 24 is positioned. In connection with this, since the circular positioning portion 24a1 fits with the positioning portion 20a which has a coaxes with the rotation axis of the polygon mirror and the same inner circumference, comparing to the case of the scanning exposure apparatus 1a is mounted, the position of the polygon mirror 23 is positioned in the same position relationship relative to the optical device box. The circular positioning portion 24a1 and the cylindrical positioning portion 20a constitute the position maintaining mechanism according to the present invention. Thanks to this position maintaining mechanism, the motor 24 can be maintained in the same position irrespective of the orientation of the scanning optical apparatus disposed on the body of the image forming apparatus. The position maintaining mechanism according to the present invention is not limited to the combination of the circular positioning portion 24a1 of the motor 24 and the cylindrical positioning portion 20a of the optical device box 20 as described above. The positioning portion 24a1 may have a different structure provided that it can maintain the motor 24 in the same position even when the optical device box 20 is mounted on the image forming apparatus upside down. With the above feature, the drive axis and the center axis of the positioning portion 24a1 are substantially aligned with each other.
As will be seen from FIG. 6A, optical components such as lenses and mirrors are supported on the optical frame on the same side as the cylindrical positioning member 20a.
FIG. 6C illustrates the motor 24 having a polygon mirror. The motor 24 is the same as the motor 24 in the exposure apparatus 1a. Accordingly, a common type of motors 24 can be used in spite that the directions of the laser emitted from the exposure apparatus 1 and the exposure apparatus 1b are opposite.
FIG. 6B illustrates the structure of the frame of the optical device box 20 on which the motor has not been attached. As described before, when the motor 24 is attached, the polygon mirror side of the motor 24 is first inserted into the optical device box.
When the optical device box is mounted on the image forming apparatus, the rotational polygon mirror can be disposed on the upper side of the motor with respect to the vertical direction in the image forming apparatus.
In this embodiment, the first engagement portion and the second engagement portion are integral portion that constitutes the positioning portion. Since the center line of the first engagement portion and the center line of the second engagement portion are substantially aligned with each other, positional variations of the drive axis among optical units can be made small even if the motors are mounted differently on the first fitting portion and second fitting portion.
Although in this embodiment the positioning portion and the base member are integral, the positioning portion may be provided as a positioning member separate from the base member, and the positioning member may be attached to the base member. In this case also, the same advantageous effects can be achieved.
The cap 32 attached to the three motor mount portions 20b provided on the outer side of the optical device box 20 can seal the optical device box 20 and prevent dust from entering the optical device box 20.
In the case of the scanning exposure apparatus 1b, the motor is mounted upside down relative to the optical device box 20. Accordingly, the polygon mirror 23 rotates in the reverse direction when seen from the photosensitive drum side. However, as described before, the timing of image writing can be controlled by selecting a suitable light sensor among the light sensors 29a and 29b according to the rotation direction.
FIG. 8 illustrates a scanning exposure apparatus 1c as another embodiment of the scanning exposure apparatus. The scanning exposure apparatus 1c differs from the scanning exposure apparatus 1a in the structure of the optical device box 40 and the provision of a light sensor 29 for detecting the timing of image writing.
The optical device box 40 has a cylindrical positioning portion 40a to which the circular positioning portion 24a1 of the motor 24 is to be fitted, in a similar manner as with the optical device box 20 of the scanning exposure apparatus 1a. The cylindrical positioning portion 40a is molded integrally with the frame of the optical device box 40. The inner diameter of the cylindrical positioning portion 40a of the optical device box 40 is larger than the diameter of the circumscribed circle of the polygon mirror 23 and the outer diameter of the rotor of the motor 24. Consequently, the cylindrical positioning portion 40a will not interfere with the polygon mirror 23 nor the rotor of the motor 24 when they rotate. The cylindrical positioning portion 40a of the optical device box 40 has two cut-away portions 20d for allowing the laser beams coming from the laser units 21a and 21b and the laser beams deflected and scanned by the polygon mirror 23 to pass therethrough. Due to the presence of the cut-away portions 40d, the upper portion of the cylindrical positioning portion 40a does not form a continuous cylinder, but it can position the circular positioning portion 24a1.
The laser beam emitted from the laser unit 21b is deflected and scanned by the polygon mirror 23, and a part of the laser beam thus scanned is focused by a lens 28 onto the light sensor 29. With this position of the light sensor, the polygon mirror 23 rotates anticlockwise when seen from the photosensitive drum side. In the case where the motor 24 is mounted upside down on the optical device box 40, the direction of rotation of the motor 24 is reversed, whereby timing of image writing can be controlled.
In the above described embodiment, the image forming apparatus uses a plurality of scanning exposure apparatuses each of which exposes a plurality of photosensitive drums to laser beams that are emitted from a plurality of light sources and deflected and scanned by one polygon mirror. However, it will be easily understood that the present invention can be effectively applied to an image forming apparatus that uses a plurality of scanning exposure apparatuses each of which exposes one photosensitive drum to a laser beam that is emitted from one light source and deflected and scanned by one polygon mirror.
In the above described embodiments, the outer diameter of the positioning portion is designed to be larger than the rotational diameter of the rotational polygon mirror. However, what is required is that the positioning portion can be positioned relative to the optical frame by a stationary portion having a bearing portion, or more preferably, a stationary portion molded integrally with a bearing portion, and the size of the positioning portion is not limited to that of the discloses embodiments.
Although in the above described embodiments the image forming units with the photosensitive drums 7 and 8 are adapted to form light color toner images, the toners used in the image forming units are not limited to them. An image forming unit that forms an image of white toner, transparent toner or other special color toner may also be used.
As per that above, in the image forming apparatus in which the motor is positioned relative to a base member by a bearing member of the motor, precision of scanning by rotation polygon mirrors in the first exposure apparatus that performs exposure from below with respect to the vertical direction and in the second exposure apparatus that performs exposure from above with respect to the vertical direction can be improved.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2006-147381, filed May 26, 2006 which is hereby incorporated by reference herein in its entirety.
Patent Application
20070273748
