JPH0821969A - Scanning optical device - Google Patents

Abstract

PURPOSE:To prevent a ghost image from being formed on an image-formed surface in the case of detecting a write beginning position signal by a scanner unit. CONSTITUTION:After a light beam L emitted from a laser beam emitting part unit 20 provided in a housing case 30 passes through a rotary polygon mirror 27 and an ftheta lens 21 and is reflected by a mirror for a write beginning position signal 25, it is allowed to pass through a slit 44 being the thin gap of a slit body 35 and made incident on a write beginning position signal detecting sensor 26. In such a case, the light shielding walls 35a and 35b of the slit body 35 are formed to be inclined at a proper angle to the incident optical axis line of the light beam L. Thus, the light beam L reflected on the surfaces of the walls 35a and 35b in the slit body 35 is prevented from being directly reflected by the mirror 25 again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device,
More specifically, the present invention relates to the structure of a writing start position detection unit of an image forming apparatus that writes an image with a light beam in a scanning optical device.

[0002]

2. Description of the Related Art Conventionally, a scanning optical apparatus applied to an electrophotographic image forming apparatus such as a laser printer, a copying machine, a facsimile apparatus or the like has an upper surface open as disclosed in Japanese Utility Model Laid-Open No. 19194/1993. In a box-shaped housing case, a rotary polygonal mirror having a hexagonal shape in plan view as a deflector that is rotated by a motor attached to the bottom surface thereof and a lens group as a scanning optical system such as an fθ lens are fixedly provided. A laser unit including a semiconductor laser element as a light source and a collimating lens is attached to one side wall surface of the housing case, and a light beam emitted from the laser unit is modulated in accordance with image data and is rotated by a rotating polygon mirror. The light beam that has been irradiated onto the laser beam and is reflected here has its path changed by a mirror provided in the housing case through a lens group such as an fθ lens. The surface of the rotating photosensitive drum is scanned from the mirror through a window hole formed on one side of the housing case so as to be parallel to the rotation axis of the photosensitive drum, and light is condensed (imaged). Are known.

In the scanning optical device described in the above publication, a writing start position detecting mirror, a slit body, and an optical fiber as a writing start position detecting section are provided in the housing case. The light beam emitted from the laser unit is reflected by the writing position detecting mirror through the lens group, and then passes through the slit, which is a narrow gap in the slit body, to enter the optical fiber, and the other optical fiber. The photo sensor arranged at the end is used to obtain the write start position detection signal.

[0004]

However, the light shielding walls located on the left and right sides of the slit of the slit body have planes orthogonal to the optical axis of the light beam reflected by the writing start position detection mirror. Therefore, the light incident on the slit body is reflected by the surface of the light shielding wall, the light is reflected again by the writing position detecting mirror, and then by the rotary polygon mirror as the deflector, and Since the light enters the drum surface and forms an image, there is a problem that an unnecessary ghost image such as a black streak is generated in the image forming area.

In the above scanning optical device, the optical path reflected by the writing start position detecting mirror and directed to the writing start position detecting sensor and the optical path scanned for forming an image on the surface of the photosensitive drum are housing cases. Since the light beams that intersect in the same (shared) space inside and are scanned to form an image on the surface of the photosensitive drum do not reflect or interfere with the slit body or the writing position detection sensor, In order to secure the installation positions of the writing start position detection mirror and the writing start position detection sensor, there is a problem that the housing case becomes large.

The present invention has been made to solve the above technical problem, and an object of the present invention is to prevent a ghost image from being generated in an image forming area and to provide a compact scanning optical device. Is.

[0007]

In order to achieve the above object, the scanning optical apparatus according to the invention of claim 1 illuminates an image forming surface by deflecting a light beam emitted from a light source through a deflector. Then, the horizontal scanning is performed, the light beam incident on the scanning start end is reflected by the mirror, and is incident on the writing position signal detection sensor through the slit in the slit body to obtain the horizontal scanning synchronization signal. In the scanning optical device, the light shielding wall of the slit body arranged between the mirror and the writing position signal detection sensor is formed so as to be inclined at an appropriate angle with respect to the incident optical axis of the light beam.

According to a second aspect of the present invention, in the scanning optical device according to the second aspect, an optical path from the deflector side to the mirror is provided in the housing case in which the deflector, the slit body, and the writing position signal detection sensor are mounted. And a partition for separating the optical path from the mirror to the slit body.

[0009]

Next, an embodiment of the present invention will be described. FIG. 1 is a schematic sectional side view of a laser beam printer 1 as an image forming apparatus, FIG. 2 is a sectional side view of a scanning optical device, and FIG. 3 is a bottom view showing an arrangement relationship of components inside a housing case 30. A paper feed cassette 3 as a paper feed unit is detachably mounted on one side of the main body case 2 of the printer 1 of this embodiment, and is stacked in the paper feed cassette 3 by a paper feed roller 4 and a separation pad 5. Sheets P as recording media are separated one by one and sent to the image forming unit 9 via the pair of feeding rollers 6.

The image forming unit 9 includes a rotating photosensitive drum 7 as a photosensitive member and a transfer roller 8 as a transfer means.
In the case, a developing device unit 12 including a toner cartridge 10 and a developing roller 11 located near the paper feed cassette 3 side, a charging device 13 on the lower surface side of the photosensitive drum 7, a cleaning device 14 and the like are included in a kit. Stored in a single unit.

A fixing device 17 including a pressing roller 15 and a heating roller 16 is arranged on the discharge side of the image forming unit 9. Below the image forming unit 9, a downward open box-shaped housing case 30 in the scanner unit 18 as a scanning optical device for scanning the laser beam toward the lower surface of the photosensitive drum 7 is provided.
0a on the upper side of the flat plate portion 2b of the main frame 2a in the main body case 2 and the sealing material 42 such as sponge material
And the top plate 30a of the housing case 30 that is mounted via the
The main frame 2a is detachably attached to both left and right sides through tie bars 40 and 41 attached to the upper surface.

A laser emitted from a scanner unit 18, which will be described later, according to image data transmitted from an external device such as a host computer (not shown) on the surface of the photosensitive drum 7 which has been precharged by the charging device 13. An electrostatic latent image is formed on the surface (image forming surface) of the photoconductor drum 7 by forming an image of light, and then the developing roller 11 is rotated to supply the charged powdery toner to the latent image. After the development for converting the toner image into a visible image is performed, the toner image is transferred onto the sheet P supplied to the transfer portion between the photosensitive drum 7 and the transfer roller 8, and then the heating in the fixing device 17 is performed. After passing between the roller 16 and the pressing roller 15, heat and pressure are applied to the transferred toner image to fix the toner image on the paper P. After that, the paper is discharged to the paper discharge tray 63 via the paper discharge roller pair 62.

A control board 60 and a high-voltage board 61 for applying a high voltage to the charging device 13 and the transfer roller 8 are arranged below the main frame 2a. Next, regarding the configuration of the scanner unit 18, FIG.
~ Will be described with reference to FIG. Figure 3 is III-II of Figure 2.
FIG. 1 is a view from the direction of arrow I, which is a downward open box type and is a bottom view of the inside of a housing case 30 made of glass reinforced plastic in which short glass fibers are mixed.

In the scanner unit 18, the laser emitting unit 20 and the rotary polygon mirror 27, f as a deflector.
A component including a θ lens 21, a cylindrical lens 22, a folding mirror 23, a writing position signal (BD) mirror 25, a slit body 35, a condenser lens 36, a writing position signal detection (BD) sensor 26 such as a light receiving element, etc. , The top plate 3 in the downward open box type housing case 30.
It is configured to be fixed to the inner surface (lower surface) of 0a.

A laser light emitting unit 20 in which a semiconductor laser as a light source and a collimating lens (both not shown) are built in a block body 28 is arranged on one side far from the photosensitive drum 7 and on the top plate 30a. It is fixed to the bottom surface with screws. A printed wiring board 29 is provided on the back surface of the block body 28.
Is installed. A rotary polygon mirror 27 such as a six-sided mirror that rotates in the direction of arrow A in FIG. 4 by a drive motor 31 fixed to the inner surface of the top plate 30a is incident from the laser emitting unit 20 toward this mirror surface. The optical axis of the light beam is arranged so as to be substantially parallel to the rotation axis of the photosensitive drum 7. The light beam L reflected by the mirror surface of the rotary polygon mirror 27 has a mounting member 32 made of a leaf spring at both ends.
After passing through the fθ lens 21 and the cylindrical lens 22 fixed to the top plate 30a via a, 32b, 33a, and 33b, the light is reflected by the folding mirror 23 toward the lower surface of the photosensitive drum 7. The top plate 30a of the housing case 30 is provided with a long window hole 34 in a portion near the lower surface of the photosensitive drum 7 in parallel with the axis of the photosensitive drum 7, and a glass plate covering the window hole 34. The deflected light beam L is scanned on the lower surface of the photoconductor drum 7 along the axial direction of the photoconductor drum 7 through the light-transmitting cover plate 24.

In the fθ lens 21, the distance from the optical axis of the lens 21 to the image spot on the surface of the photosensitive drum 7 is the principal ray reflected by the reflecting surface of the rotary polygon mirror 27 which is a deflector. Deflection angle θ formed by the optical axis of fθ lens 21
It has the characteristic of being proportional to. As shown in FIGS. 3 and 4, a writing position signal mirror (BD (Beam Detector) mirror) fixed by a leaf spring (not shown) in the vicinity of one end in the longitudinal direction of the folding mirror 23. ) 25 are arranged. The optical path from the rotary polygon mirror 27 to the writing position signal mirror 25 and the slit body 35, the condenser lens 36, and the writing position signal detection sensor 26, which are reflected by the writing position signal mirror 25 and will be described later. It is separated from the optical path that reaches it by a partition wall 43, and only the light beam L reflected by the writing position signal mirror 25 is directed to the slit body 35, and the rotary polygon mirror 27.
The light beam L from is diffusely reflected by the inner surface of the peripheral side wall 30b and the partition wall 43, and is then shielded so as not to enter the slit body 35, the condenser lens 36, and the writing position signal detection sensor 26.

In the illustrated embodiment, the partition wall 43 is arranged substantially parallel to one side wall (right side in FIGS. 3 and 4) of the housing case 30. In addition, as shown in FIGS. 4 to 6, the slit body 35 made of synthetic resin extends in a direction substantially perpendicular to the inner surface of the top plate 30a of the housing case 30 and has both left and right light shielding walls 35a having a substantially L-shaped cross section. ，
35b, a narrow slit 44 formed between the left and right light-shielding walls 35a, 35b and extending substantially perpendicular to the inner surface of the top plate 30a, and the left and right light-shielding walls 35a, 3b.
5b connected to the base plate 35c along the inner surface of the top plate 30a, and the slit body 35 for adjusting the position of the slit 44.
a) A boss 35d that serves as a central position for rotating with respect to the mounting recess 45 on the inner surface.

4 and 5 show the surfaces of the left and right light shielding walls 35a and 35b on the side where the light beam L reflected by the writing position signal mirror 25 enters the slit 44. Specifically, after adjusting so as to be inclined at an appropriate angle with respect to the incident optical axis of the light beam L, the boss 35d of the slit body 36 and / or the substrate 35a is fixed to the inner surface of the top plate 30a with an adhesive. To do.

With this structure, the write start position signal (BD signal) for detecting the write start position of the light beam L emitted from the laser emitting unit 20 in the horizontal direction of the photosensitive drum 7 is rotated. Polyhedral mirror 27, fθ
The rotary polygon mirror 27 rotates in the direction of arrow A in FIG. 4 when inputting to the write position signal detection sensor 26 via the path of the lens 21, the cylindrical lens 22, the write position signal mirror 25, the slit body 35, and the condenser lens 36. As the light beam L is reflected by the writing position signal mirror 25, the partition wall 43 from the side closer to the peripheral side wall 30b in FIG.
Scan by angle θ1 in the direction. And the light beam L
At the moment when the light enters into the edge of the slit 44 and a predetermined or more light energy is incident on the write position signal detection sensor 26, the write position signal detection is performed.

As in this embodiment, the surfaces of the left and right light shielding walls 35a and 35b that sandwich the slit 44 are not perpendicular to the incident optical axis of the light beam L that scans in the direction of arrow B in FIG. Since the light beams L are inclined by an appropriate angle, the light beam L reflected by the surfaces of the left and right light shielding walls 35a, 35b does not directly return to the writing position signal mirror 25 to be reflected again. Therefore, after the light beam L is reflected by the surface orthogonal to the incident optical axis as in the conventional technique and directly returns from the writing position signal mirror 25 to the rotary polygon mirror 27, the surface of the photosensitive drum 7 ( (Image formation side)
There is no phenomenon in which an unnecessary ghost image is generated by being incident on the image forming area.

Incidentally, the left and right light-shielding walls 35a, 35b.
The light beam L reflected by the surface of the
Even after returning to the writing position signal mirror 25 after repeating the diffused reflection on the inner surface of 0b, the light energy is greatly attenuated (a few tenths to a few tenths). There is no light energizing enough to form a latent image on the surface of the, and the ghost image as described above is not generated.

Further, a slit 44 is formed in the light shielding wall 35a or 35b which is inclined by an appropriate angle with respect to the incident optical axis of the light beam L which is scanned in the direction of arrow B in FIG.
By piercing, the incident light strikes the edge corner of the slit 44, and the rising edge of the light beam L (signal) incident on the writing position signal detection sensor 26 becomes sharp,
An accurate and stable detection signal can be obtained.

Further, as shown in FIG. 5, the slit body 3
On the inner surface of the peripheral side wall 30b in the vicinity of which 5 is arranged, there is provided a ridge 46 projecting so as to approach one of the light shielding walls 35b of the slit body 35 and parallel to the extending direction of the slit 44. As a result, of the light beam L traveling from the writing position signal mirror 25 toward the slit body 35, the light beam L approaching the inner surface of the peripheral side wall 30b.
However, even if it enters the light blocking wall 35b of the slit body 35 without being disturbed, it is disturbed at the location of the ridge 46 and diffusely reflected, so that it directly enters the condenser lens 36 and is used as a write start position signal. There is no false detection.

As in the embodiment shown in FIG. 9, if the light receiving surface of the writing position signal detecting sensor 26 such as a light receiving element is arranged at an appropriate angle with respect to the incident optical axis of the light beam L. It is possible to prevent the reflected light on the light receiving surface of the sensor 26 from directly returning to the writing position signal mirror 25. In this way, the laser drive substrate (printed wiring board) 37 for processing the horizontal synchronizing signal input to the writing position signal detection sensor 26 and driving the laser emitting unit 20 is directed downward from the inner surface of the top plate 30a. The rib 38 is fixed to the end surface of the protruding rib by a screw 38. In this case, as shown in FIGS. 3, 7 and 8, the condenser lens 36 is located between the writing position signal mirror 25 and the writing position signal detection sensor 26, and the surrounding side wall 30.
It is fitted into the pair of mounting grooves 47a, 47b formed between the inner surface of b and the partition wall 43 and having a substantially U shape in plan view without rattling, and the printed wiring board 37 prevents the printed wiring board 37 from falling off. Further, by directly fixing the foot of the writing position signal detection sensor 26 to the printed wiring board 37 by soldering or the like, the mounting work can be extremely simplified as compared with the mounting of the writing position signal detection sensor 26 alone.

As another embodiment, the housing case 30
It goes without saying that the laser light emitting unit 20 and the write start position signal detection sensor 26 may be fixed to one outer side of the peripheral side wall. Further, it goes without saying that the present invention can also be applied to a scanning optical device in an electrophotographic image forming apparatus such as a facsimile or a copying machine, and other optical devices used for image processing and the like.

[0026]

As described above, claim 1
The scanning optical device of the invention described above deflects a light beam emitted from a light source through a deflector to irradiate an image forming surface to perform horizontal scanning, and a light beam incident on a scanning start end thereof is reflected by a mirror. A scanning optical device configured to reflect and enter a writing position signal detection sensor through a slit in a slit body to obtain a horizontal scanning synchronization signal, wherein the scanning optical device is provided between the mirror and the writing position signal detection sensor. The light shielding wall of the slit body to be arranged is formed so as to be inclined at an appropriate angle with respect to the incident optical axis of the light beam.

Therefore, the light beam reflected by the surface of the light shielding wall in the slit body inclined by an appropriate angle with respect to the incident optical axis of the light beam is not directly reflected again by the writing position signal mirror. Therefore, after the light beam is reflected on the surface orthogonal to the incident optical axis as in the conventional technique and directly returns from the writing position signal mirror to the deflector, it is unnecessary in the image forming area of the image forming surface. Since a phenomenon of generating a large ghost image does not occur, an effect that a good quality image can be obtained is obtained.

According to a second aspect of the present invention, in the scanning optical apparatus according to the first aspect, the optical path from the deflector side to the mirror is provided in the housing case in which the deflector, the slit body and the writing position signal detection sensor are mounted. And a partition for separating the optical path from the mirror to the slit body. Therefore, even if the optical path for irradiating the light beam to the vicinity of the writing position with respect to the image forming surface and the optical path for irradiating the light beam as the writing position signal to the mirror are substantially parallel to each other, During irradiation,
Even if it is diffusely reflected by the inner wall surface of the housing case, it is shielded by the partition wall, and the detection of the writing position signal is stable. Moreover, by providing the partition wall, as described above,
The installation positions of the mirror and the writing position signal detection sensor can be devised so that the optical path from the deflector side to the vicinity of the writing position on the image forming surface and the optical path from the mirror to the slit body are arranged substantially in parallel. In addition, the housing case can be made compact.

[Brief description of drawings]

FIG. 1 is a schematic side sectional view of a laser printer.

FIG. 2 is a side sectional view of a scanning optical device.

FIG. 3 is a view taken along the line III-III in FIG.

FIG. 4 is a plan sectional view of an essential part.

5 is an enlarged cross-sectional view of the main parts of FIG.

6 is a sectional view taken along the line VI-VI of FIG.

FIG. 7 is an enlarged plan view of an arrangement portion of a condenser lens and a writing start position signal detection sensor.

8 is a sectional view taken along the line VIII-VIII of FIG.

FIG. 9 is a plan view of another embodiment.

[Explanation of symbols]

 1 Printer 18 Scanner Unit 20 Laser Light Emitting Unit 21 fθ Lens 23 Folding Mirror 24 Cover Plate 25 Mirror for Writing Position Signal 26 Writing Position Signal Detection Sensor 27 Rotating Polyhedral Mirror 30 Housing Case 30b Peripheral Side Wall 35 Slits 35a, 35b Left and Right Shading Wall 36 Condenser lens 43 Partition wall 44 Slit

Claims (2)

[Claims] 1. A light beam emitted from a light source is deflected by a deflector to irradiate an image forming surface to perform horizontal scanning, and a light beam incident on a scanning start end is reflected by a mirror to form a slit. In a scanning optical apparatus configured to obtain a horizontal scanning synchronization signal by being incident on a writing position signal detection sensor through a slit in a body, the slit body disposed between the mirror and the writing position detection sensor shields light. A scanning optical device, wherein the wall is formed so as to be inclined at an appropriate angle with respect to an incident optical axis line of the light beam. 2. A partition that separates an optical path from the deflector side to the mirror and an optical path from the mirror to the slit body is provided in a housing case in which the deflector, the slit body, and the writing position signal detection sensor are mounted. The optical device according to claim 1, wherein: