JP2020086322A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily deform a rotating multifaceted mirror made of a resin, which is conventionally formed of a metal for cost reduction, and the deformation deteriorates the image quality of an output image. SOLUTION: A heat-dissipating protrusion 310 (heat-dissipating protrusion) is formed integrally with a polygon mirror 308 at an upper part and a lower part of a polygon mirror 308. The plurality of heat radiating protrusions 310 are provided so as to project from the back surface of the surface facing the rotor portion 302 at least in the direction of the rotation axis of the motor. In addition, a plurality of or a single protrusion 310 for heat dissipation may be provided so as to project from the surface facing the rotor 302 toward the rotation axis of the motor. On the surface facing the rotor portion 302, in addition to the heat radiating protrusion 310, a supported protrusion 315 as a supported portion supported by the rotor 302 is provided. [Selection diagram] Fig. 3

Description

The present invention relates to a polygon mirror used in an image forming apparatus such as a laser printer.

An optical scanning device used in an image forming apparatus such as a laser beam printer deflects a light beam (laser light) by a polygon mirror. The light beam deflected by the polygon mirror is guided onto the photosensitive drum rotating in a direction intersecting the scanning direction of the light beam to expose the photosensitive drum. The image forming apparatus forms an image on a recording sheet by developing an electrostatic latent image formed on a photosensitive drum by scanning with a light beam by a developing device and transferring the developed toner image onto the recording sheet.

The optical scanning device includes a motor having a rotor portion that supports the polygon mirror, and the rotation of the motor causes the polygon mirror to rotate. (See Patent Document 1).

Japanese Patent Laid-Open No. 10-96872

In the configuration of the related art, in recent years, for the purpose of cost reduction, a configuration in which the polygon mirror is formed of resin instead of the conventional metal is considered. On the other hand, the polygon motor that drives the polygon mirror generates heat from each part as it rotates. As an example, in the exciting coil, a current flows, so that copper loss and iron loss occur and heat is generated. Further, the bearing generates heat due to friction between the bearing and the shaft. These heat generations are applied to the polygon mirror via the rotor.

Resins often have a higher coefficient of thermal expansion than metals. Therefore, thermal deformation of the resin polygon mirror has a greater effect on the mirror surface than the conventional metal polygon mirror. When the thermal deformation of the polygon mirror affects the mirror surface, color shift occurs in the main scanning direction of the light beam due to magnification and write start position shift.

Therefore, an object of the present invention is to provide an image forming apparatus capable of suppressing the deformation of the mirror surface of the polygon mirror due to the heat from the rotor portion of the motor.

In order to solve the above problems, an image forming apparatus according to the present invention includes a photoconductor, a light source that emits a light beam for exposing the photoconductor, and a light beam emitted from the light source scans the photoconductor. A rotary polygon mirror for deflecting the light beam, and a motor having a rotor unit for supporting and rotating the rotary polygon mirror, wherein the rotary polygon mirror is made of resin. Is provided on the back surface of the surface of the rotary polygonal mirror facing the rotor portion for heat dissipation of the rotary polygonal mirror, and has a plurality of heat dissipation projections protruding in the rotation axis direction of the rotary polygonal mirror. Characterize.

Since the rotating polygonal mirror made of resin is provided with the plurality of heat dissipation projections, thermal deformation of the rotating polygonal mirror can be reduced.

FIG. 1 is a schematic configuration diagram of an image forming apparatus. 1 is a schematic configuration diagram of an optical scanning device. Schematic sectional view of a polygon motor. Top view of polygon motor. 6 is a schematic cross-sectional view of a polygon motor according to a second embodiment. FIG. FIG. 6 is a top view of the polygon motor according to the second embodiment. 6 is a schematic cross-sectional view of a polygon motor according to a third embodiment. FIG. FIG. 6 is a top view of the polygon motor according to the third embodiment. The figure explaining the restriction|limiting of the position of the heat dissipation protrusion.

(Example 1)
(Overall structure of image forming apparatus)
FIG. 1 is a sectional view showing a hardware configuration of the image forming apparatus 100 according to the first embodiment. The image forming apparatus 100 may be an image forming apparatus that forms a single color image, but here, it is assumed that an image forming apparatus that forms a multicolor image using toners (developers) of a plurality of colors. The image forming apparatus 100 may be, for example, a printing apparatus, a printer, a copying machine, a multifunction peripheral (MFP), or a facsimile apparatus. It should be noted that Y, M, C, and K at the end of the reference numerals indicate that the colors of the toners targeted by the corresponding members are yellow, magenta, cyan, and black, respectively. In the following description, reference symbols without Y, M, C, and K at the end are used when it is not necessary to distinguish colors.

The image forming apparatus 100 includes four image forming units (image forming stations) that form images (toner images) using toners of Y color, M color, C color, and K color, respectively. The image forming unit corresponding to each color includes photosensitive drums (photosensitive members) 102Y, 102M, 102C, and 102K, respectively. Around the photosensitive drums 102Y, 102M, 102C, 102K, charging units 103Y, 103M, 103C, 103K, optical scanning units (optical scanning devices) 104Y, 104M, 104C, 104K, and developing units 105Y, 105M, 105C, 105K. Are arranged respectively. A drum cleaning unit (not shown) is arranged around each of the photosensitive drums 102Y, 102M, 102C, and 102K.

An intermediate transfer belt (intermediate transfer member) 107, which is an endless belt, is disposed below the photosensitive drums 102Y, 102M, 102C, and 102K. The intermediate transfer belt 107 is stretched around a driving roller 108 and driven rollers 109 and 110. During image formation, the outer peripheral surface of the intermediate transfer belt 107 moves in the direction of the arrow shown in FIG. 1 as the drive roller 108 rotates. Primary transfer bias blades 111Y, 111M, 111C and 111K are arranged at positions facing the photosensitive drums 102Y, 102M, 102C and 102K via the intermediate transfer belt 107. The image forming apparatus 100 includes a secondary transfer bias roller 112 for transferring a toner image formed on the intermediate transfer belt 107 onto a sheet, and a fixing for fixing the toner image transferred onto the sheet to the sheet. And a section 113. The sheet may be referred to as recording paper, recording material, recording medium, paper, transfer material, transfer paper, or the like.

Next, the image forming process from the charging process to the developing process in the image forming apparatus 100 having the above configuration will be described. The image forming process executed by each image forming unit corresponding to each color is the same. Therefore, hereinafter, the image forming process in the image forming unit corresponding to the Y color will be described as an example, and the description of the image forming process in the image forming unit corresponding to the M color, the C color, and the K color will be omitted.

First, the charging unit 103Y of the image forming unit corresponding to the Y color charges the surface of the rotationally driven photosensitive drum 102Y. The optical scanning unit 104Y exposes the surface of the photosensitive drum 102Y by emitting a plurality of laser beams (light beams) and scanning the surface of the charged photosensitive drum 102Y with the plurality of laser beams. As a result, an electrostatic latent image is formed on the rotating photosensitive drum 102Y. The electrostatic latent image formed on the photosensitive drum 102Y is developed by the Y-color toner by the developing unit 105Y. As a result, a Y-color toner image is formed on the photosensitive drum 102Y. Further, in the image forming units corresponding to M color, C color, and K color, the M color, C color, and K color are formed on the photosensitive drums 102M, 102C, and 102K by the same process as the image forming unit corresponding to the Y color. Color toner images are formed respectively.

The image forming process after the transfer process will be described below. In the transfer process, first, the primary transfer bias blades 111Y, 111M, 111C, and 111K apply the transfer bias to the intermediate transfer belt 107, respectively. As a result, the four-color (Y, M, C, and K) toner images formed on the photosensitive drums 102Y, 102M, 102C, and 102K are transferred onto the intermediate transfer belt 107 in an overlapping manner.

The toner image formed of the four color toners formed on the intermediate transfer belt 107 in an overlapping manner is formed between the secondary transfer bias roller 112 and the intermediate transfer belt 107 as the outer peripheral surface of the intermediate transfer belt 107 moves. Of the secondary transfer nip portion. The sheet is conveyed from the paper feed cassette 115 to the secondary transfer nip portion at the timing when the toner image formed on the intermediate transfer belt 107 is conveyed to the secondary transfer nip portion. In the secondary transfer nip portion, the toner image formed on the intermediate transfer belt 107 is transferred onto the sheet by the action of the transfer bias applied by the secondary transfer bias roller 112 (secondary transfer).

After that, the toner image formed on the sheet is heated by the fixing unit 113 to be fixed on the sheet. The sheet on which the multicolor image is formed in this manner is discharged to the paper discharge unit 116.

After the transfer of the toner image to the intermediate transfer belt 107 is completed, the toner remaining on the photosensitive drums 102Y, 102M, 102C and 102K is removed by a drum cleaning unit (not shown). When the series of image forming processes is completed in this way, the image forming process for the next sheet is started continuously.

(Structure of optical scanning device)
FIG. 2 is a conceptual diagram showing the configuration of the optical scanning unit 104. The optical scanning unit 104 includes a laser light source 201, a collimator lens 202, a polygon motor unit 300, a polygon mirror (rotary polygonal mirror) 308, a motor unit 301, an fθ lens (scanning lens) 205, a beam detection (BD) sensor 206, and the like. To be done. The polygon motor unit 300 has a polygon mirror 308 and a motor unit 301. The motor unit 301 rotationally drives the polygon mirror 308. The polygon mirror 308 is made of resin such as polycarbonate (PC). The polygon mirror 308 rotates about the rotation line of the polygon motor and has a plurality of reflecting surfaces (deflection surfaces) that are mirror surfaces along the rotation direction. The mirror surface is formed by depositing metal powder on the resin main body. The polygon mirror 308 of this embodiment has four reflecting surfaces as shown in FIG. 2, but the number of reflecting surfaces may be other than four. The laser light emitted from the laser light source 201 is incident on each reflection surface and is deflected as the polygon mirror 308 rotates. In the present embodiment, the laser light source 201 is an example of a light source that emits a light beam to expose the photosensitive drum 102. The polygon mirror 308 is an example of a rotary polygon mirror that deflects the light beam on any one of a plurality of reflecting surfaces while rotating so that the light beam scans the photosensitive drum 102.

A laser light source (hereinafter, simply referred to as “light source”) 201 is driven by a drive current supplied from a laser driver (not shown). The light source 201 is supplied with a drive current from the laser driver, emits light, and emits a laser beam (light beam) having a light amount corresponding to the drive current. The light source 201 includes N (N is a natural number) laser diodes (LDs) as light emitting elements (light emitting points). In the image forming apparatus 100 of the present embodiment, N is an integer of 2 or more, that is, the multi-beam method in which the photosensitive drum 102 is scanned with a plurality of laser beams emitted from a plurality of LDs is used. In the following, a case where N=2 and the light source 201 includes two LDs LD1 and LD2 will be described as an example.

The collimator lens 202 shapes the laser light emitted from the light source 201 into parallel light. The laser beam L1 that has passed through the collimator lens 202 is incident on any one of a plurality of reflecting surfaces of the polygon mirror 308, and is reflected by the incident reflecting surface. The polygon mirror 308 is rotationally driven by the motor unit 301 so as to rotate in the arrow direction of FIG. The polygon mirror 308 is rotationally driven so as to rotate at a constant speed (constant angular speed) while the laser beam scans the surface of the photosensitive drum 102 to form an electrostatic latent image. The polygon mirror 308 reflects the laser light on each reflecting surface while rotating so that the incident laser light L1 is deflected at continuous angles.

The laser light deflected by the polygon mirror 308 enters the fθ lens 205. By passing through the fθ lens 205, the laser light forms an image on the surface of the photosensitive drum 102 to form a beam spot, and the photosensitive drum 102 is scanned at a constant speed in the main scanning direction. As a result, an electrostatic latent image 210 is formed on the photosensitive drum 102. The main scanning direction is a direction parallel to the surface of the photosensitive drum 102 and orthogonal to the moving direction of the surface of the photosensitive drum 102. The sub-scanning direction is the moving direction of the surface of the photosensitive drum 102 (direction orthogonal to the main scanning direction).

The optical scanning unit 104 includes a BD sensor 206 at a position on the scanning start side of the laser light in the scanning path of the laser light that has passed through the fθ lens 205. The BD sensor 206 is used as an optical sensor for detecting laser light. When the laser light is incident on the BD sensor 206 in each scanning cycle of the laser light, the BD sensor 206 generates and outputs a detection signal (BD signal) indicating that the laser light has been detected. The BD signal can be used as a synchronization signal that serves as a reference for the image writing timing in the main scanning direction. The light source 201 is controlled to forcibly emit light during a certain period during which the laser light can enter the BD sensor 206, in order to output a BD signal from the BD sensor 206 in each scanning cycle of the laser light.

(Structure of polygon motor unit)
Next, the polygon motor unit 300 will be described with reference to FIG. FIG. 3 is a sectional view of the polygon motor unit 300. The polygon motor unit 300 includes a motor unit 301, a polygon mirror 308, and a spring 309.

The motor unit 301 includes a rotor unit including a rotor 302, a rotary magnet 303, and a shaft 305, and a stator unit including a bearing 306, an exciting coil 304, and a substrate 307. The rotor 302 (rotor portion) is integrated with the rotary magnet 303 and the shaft 305. The S-pole and the N-pole of the rotary magnet 303 are alternately magnetized, and are fixed inside the rotor 302. A plurality of exciting coils 304 are installed at positions facing the rotary magnet 303. The bearing 306 and the exciting coil 304 are fixed to the substrate 307. The shaft 305 is supported by a bearing 306 composed of a ball bearing, a metal bearing, a dynamic pressure bearing, or the like. A spring receiving portion 312 is formed on the polygon mirror 308. The spring 309 contacts the convex portion formed on the upper portion of the shaft 305 and the spring receiving portion 312 formed on the upper portion of the polygon mirror 308, respectively. It is regulated.

FIG. 4 shows a top view of the polygon mirror surface in the polygon motor unit 300. FIG. 3 shows a cross section taken along the line A-A′ in FIG. The structure in which the spring 309 is pressed against the spring receiving portion 312 is shown in the drawing.

Next, the heat dissipation method in this embodiment will be described.

In FIGS. 3 and 4, heat radiation protrusions 310 (heat radiation protrusions) are formed integrally with the polygon mirror 308 on the upper and lower portions of the polygon mirror 308. The plurality of heat dissipation protrusions 310 are provided so as to protrude from the back surface of at least the surface facing the rotor portion 302 toward the rotation axis direction of the motor. In addition, a plurality or a single radiating projection 310 for heat radiation may be provided so as to project from the surface facing the rotor 302 in the direction of the rotation axis of the motor. On the surface facing the rotor portion 302, a supported projection portion 315 as a supported portion supported by the rotor 302 is provided in addition to the heat dissipation projection portion 310. The shape of the protrusion 310 in this embodiment is cylindrical, but may be prismatic, conical, or pyramidal. By forming the plurality of protrusions 310 integrally with the polygon mirror 308, the surface area of the polygon mirror 308 is increased and the heat radiation effect is enhanced. In addition, the surface of the protrusion 310 has a fine uneven shape and a jagged shape, so that the surface area is further increased, and the heat dissipation effect can be expected to be improved.

The location where the protrusion 310 is to be installed needs to be installed inside the polygon mirror inscribed circle 314 on the polygon mirror 308. The reason for this necessity will be described with reference to FIG. FIG. 9 shows a state in which the protrusion 310 is installed outside the inscribed circle 314 of the polygon mirror and a defect occurs. In the figure, as the polygon mirror 308 rotates, the protrusion 310 also rotates in the CW direction. At this time, turbulence of the airflow occurs behind the rotation of the protrusion 310. The turbulence of the airflow reaches the side surface of the polygon mirror 308 behind the protrusion 310.

On the other hand, minute dust is floating inside the scanner unit 104. A part of this minute dust may be entrained in this air flow, hit against the upper surface or side surface of the polygon mirror 308, and be fixed. When a part of the minute dust adheres to the mirror portion on the side surface of the polygon mirror 308, it causes a decrease in reflectance, which in turn causes a problem of a decrease in image density.

In order to avoid this problem, the plurality of protrusions 310 are installed inside the polygon mirror inscribed circle 314 on the polygon mirror 308, which is indicated by the dotted line. This makes it possible to reduce the adverse effect of the turbulent flow generated by the protrusion 310 on the side surface of the polygon mirror 308. Further, the protrusion 310 formed on the lower surface of the polygon mirror 308 is also installed inside the inscribed circle 314 of the polygon mirror.

With the above configuration, by providing the protrusion 310 on the polygon mirror 308, the surface area of the polygon mirror 308 increases, and the heat generated from the motor unit 301 can be effectively dissipated, so that the deformation of the polygon mirror 308 can be reduced. it can. Therefore, it is possible to suppress the image quality deterioration due to the color shift due to the magnification of the light beam in the main scanning direction and the writing start position shift, and the focus shift of the light beam to the drum surface in the sub scanning direction. Further, in the present embodiment, the protrusion 310 is integrally formed on both the upper surface and the lower surface of the polygon mirror 308. It is possible to

(Example 2)
Next, a second embodiment will be described. 5 and 6 are a cross-sectional view and a top view of the polygon mirror unit 300 according to the second embodiment of the present invention. FIG. 5 shows a cross section taken along the line AA′ in FIG.

In the figure, the protrusion 310 is in contact with the inscribed circle of the polygon mirror 308 or is formed in a circular arc inside. Others are the same as the first embodiment.

Since the shape of the protrusion 310 in the vicinity of the point where the inscribed circle and the mirror surface contact each other is arcuate, it is possible to suppress the occurrence of turbulence as compared with the first embodiment. It is possible to further reduce contamination of the mirror surface with respect to dust.

(Example 3)
Next, a third embodiment will be described. 7 and 8 are a sectional view and a top view of a polygon mirror unit 300 according to the third embodiment of the present invention. FIG. 7 shows a cross section taken along the line AA′ in FIG. The configuration of the protrusion 310 will be described with reference to FIG.

First, the rotation direction of the polygon mirror 308 is clockwise (CW). The protruding portion 310 is installed from the outer peripheral portion to the inner peripheral portion of the polygon mirror 308. At this time, the outer peripheral end of the polygon mirror 308 is defined as a. The end of the inner peripheral portion of the polygon mirror 308 is defined as b. Further, the center of the polygon mirror 308 is c. When the CW direction, which is the rotation direction of the polygon mirror 308, is positive, the relationship of ∠acb>0 is established.

With this configuration, when the polygon mirror 308 is rotationally driven, the airflow generated from the protrusion 310 becomes an airflow flowing from the inside to the outside of the polygon mirror 308. In FIG. 7, the flow of this air flow is shown by the arrow. Since the inside of the polygon mirror 308 has a negative pressure, it can be seen that the protrusion 310 has a rectifying function of sucking the airflow from the upper portion of the shaft 305 and flowing out in the peripheral direction of the polygon mirror 308. This rectified airflow further improves the heat dissipation effect.

Further, the inertia of the resin polygon mirror is smaller than that of the metal polygon mirror. Therefore, the controllability of the motor may be affected, the stability may decrease, and the jitter may increase. However, by rectifying this air flow, a load is evenly applied to the polygon motor. This results in an increase in the rotation torque, which can be offset by a decrease in inertia, thereby preventing a decrease in stability and an increase in jitter.

100 image forming apparatus 102 photosensitive drum 103 charging section 104 optical scanning section 105 developing section 107 intermediate transfer belt 108 driving rollers 109, 110 driven roller 111 primary transfer bias blade 113 fixing section 201 laser light source 202 collimator lens 205 fθ lens 206 beam detection sensor 210 electrostatic latent image 300 polygon motor unit 301 motor unit 302 rotor 303 rotary magnet 304 exciting coil 305 shaft 306 bearing 307 substrate 308 polygon mirror 309 spring 310 protrusion 310 312 spring receiving portion 314 line showing the inscribed circle of the polygon mirror

Claims (5)

A photoconductor,
A light source that emits a light beam for exposing the photoconductor,
A rotating polygon mirror that deflects the light beam so that the light beam emitted from the light source scans the photoconductor,
A motor having a rotor portion that supports the rotating polygon mirror and rotates,
The rotating polygon mirror is made of resin,
The rotary polygon mirror is provided on the back surface of the surface of the rotary polygon mirror facing the rotor portion for heat radiation of the rotary polygon mirror, and a plurality of heat radiation projections protruding in the rotation axis direction of the rotary polygon mirror. An image forming apparatus comprising: On a surface facing the rotor portion, a supporting projection portion supported by the rotor, and a plurality of heat radiation projection portions different from the plurality of heat radiation projection portions provided on the back surface of the surface facing the rotor portion, The image forming apparatus according to claim 1, further comprising: The image forming apparatus according to claim 1, wherein the plurality of heat dissipation protrusions are provided inside an inscribed circle of the rotary polygon mirror. The image forming apparatus according to claim 1, wherein the plurality of heat dissipation protrusions formed on the rotary polygon mirror form an arc along a rotation direction of the rotary polygon mirror. The motor includes a rotor unit,
A pressing spring for fixing the rotary polygon mirror to the rotor portion,
2. The pressing spring is fixed to the rotation shaft of the motor so as not to overlap the plurality of heat radiation projections when the rotary polygon mirror is viewed from the rotation axis direction. Image forming device.

Images