JPH11295633A - Rotary polygon mirror and optical scanning device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the cost of a device from being significantly increased as a whole even when the intensity of a beam required on the surface of an exposure object and that required for a sensor for detecting a synchronizing signal are different. SOLUTION: A beam emitted from a semiconductor laser 21 is reflected and deflected by a polygon mirror 30 and converged on a photoreceptor drum 50 through an (f θ) lens 40 so as to form a stop. The mirror 30 is formed by equally dividing the outside circumference thereof by 6 reflection surfaces 31. Besides, a 1st high-reflectivity area 31a and a 2nd low-reflectivity area 31b are formed at the respective surfaces 31. The beam made incident on the area 31a and reflected with relatively high reflectivity is reflected on a mirror 60 and made incident on the sensor for detecting a synchronizing signal 61. The beam reflected on the area 31b is provided with comparatively weak intensity and made incident on the drum 50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a rotating polygon mirror such as a polygon mirror and a scanning optical apparatus using the same.

[0002]

2. Description of the Related Art In an optical system of a conventional scanning optical apparatus, for example, as shown in FIG. 6, a beam emitted from a semiconductor laser 1 is collimated by a collimating lens 2, and then a position of a polygon mirror 4 by a cylindrical lens 3. To converge once in the sub-scanning direction, and converge the beam reflected and deflected by the polygon mirror 4 via the fθ lens 5 to form a spot for scanning in the main scanning direction y on the photosensitive drum 6 which is a surface to be exposed. I do.

On the emission side of the fθ lens 5, a mirror 7 for reflecting a beam emitted from the fθ lens 5 in an area before the spot on the photosensitive drum 6 enters the writing range W is arranged. A synchronization signal detection sensor 8 that outputs a synchronization signal at a position where the reflected beam is received.
Is provided. The point P0 on the photosensitive drum 6
Indicates the equivalent position of the spot when it is assumed that the beam reaches the photosensitive drum 6 without being reflected by the mirror 7 when the synchronization signal is output. Indicates that a signal is output. The synchronization signal is output for each scan (each time the reflection surface of the polygon mirror is switched), and the start position of the writing range W is defined as a point at which a predetermined time has elapsed from the output of the synchronization signal.

The optical elements from the semiconductor laser 1 to the fθ lens 5, the mirror 7 and the synchronizing signal detecting sensor 8 are arranged in a casing 10 constituting an optical system unit. Travels through the dustproof glass 9 attached to the opening of the casing 10 toward the photosensitive drum 6.

In determining the specifications of a scanning optical device such as a laser printer, the specifications of the sensitivity of the photosensitive drum, the voltage for charging the photosensitive drum, the size of the toner, and the like are determined first. In some cases, the spot size on the photosensitive drum, the beam intensity, and the like are determined in correspondence. On the other hand, the side that manufactures the optical system unit has a demand to share components as much as possible in a plurality of models having different specifications in the above-described specification determination process.

Therefore, conventionally, an optical system unit is designed according to a specification requiring a relatively high beam intensity, and when the optical system unit is applied to a specification requiring a low beam intensity, it is necessary to use a photoconductor from a semiconductor laser. N in the light path between the drums
An adjustment method such as arranging a D filter to attenuate the beam intensity is employed. However, when an ND filter is arranged between the semiconductor laser 1 and the polygon mirror 4, not only the intensity of the beam reaching the photosensitive drum 6 is attenuated, but also the intensity of the beam reaching the synchronization signal detecting sensor 8 is reduced. Since there is a possibility that the sensor does not respond and the synchronization signal is not output, or the sensor malfunctions and an accurate synchronization signal cannot be obtained, the dustproof glass 9 is coated with the ND.

[0007]

However, if the ND coating is applied to the dust-proof glass 9 having a relatively large area in a specification having a low beam intensity as in the above-mentioned conventional example, the dust-proof glass with the coat is provided. There is a problem that the cost of the glass becomes very high, which leads to a significant increase in the cost of the entire apparatus.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the related art, and is intended for a case where the beam intensity required on the exposure target surface is different from the beam intensity required for the synchronization signal detecting sensor. Further, it is an object (object) to provide a configuration of a rotary polygon mirror capable of coping with this without causing a significant increase in cost of the entire apparatus, and a scanning optical device using the rotary polygon mirror.

[0009]

The rotary polygon mirror according to the present invention is a rotary polygon mirror having a plurality of reflection surfaces formed on an outer periphery, wherein each reflection surface has a first area having a predetermined reflectance. And a second region having a reflectance different from that of the first region, wherein the first and second regions are distributed at the same ratio with respect to the total reflection surface.

According to the above arrangement, for example, the beam reflected by the first area is used for detecting the synchronization signal,
If the beam reflected by the region is guided to the exposure target surface, the reflectance of the first and second regions is set in accordance with the required beam intensity, so that the synchronization signal detection sensor and the exposure It is possible to cope with the case where the required beam intensity differs from the target surface.

[0011] For example, the first area is a high reflectivity area arranged on the front side in the rotational direction in each reflecting surface, and the second area is arranged on the rear side in the rotational direction from the first area. Low reflectance region. According to this configuration, a high intensity beam is obtained in the first part of the scanning range, and a low intensity beam is obtained in the subsequent range. Therefore,
This is effective when applied to a case where the beam intensity required for the synchronization signal detection sensor arranged at the first part of the scanning range is high and the beam intensity required for the scanning target surface is low. Note that the scanning range here means the entire range in which the beam reflected by each reflecting surface of the rotary polygon mirror scans, and the writing range that is the actual drawing range on the exposure target surface is included in this scanning range. Will be.

Further, a scanning optical device according to the present invention is
A light source, a rotating polygon mirror that reflects and deflects a beam emitted from the light source, and an imaging optical system that forms a spot by converging the beam reflected by the rotating polygon mirror on a scanning target surface,
A synchronization signal detection sensor that outputs a synchronization signal by receiving a beam emitted from the imaging optical system in a region before the spot enters the writing range on the scanning target surface, and each reflection surface of the rotary polygon mirror is A first area for reflecting the beam from the light source when the beam enters the synchronization signal detection sensor, and a second area for reflecting the beam from the light source when the beam reaches a writing range on the scanning target surface. And the reflectances of the first and second regions are set to be different from each other.

According to the above arrangement, the beam reflected on the first area of each reflecting surface is guided to the synchronization signal detecting sensor, and the beam reflected on the second area reaches the surface to be exposed. Therefore, by setting the reflectivity of the first and second regions in accordance with the required beam intensity, it is possible to cope with a case where the required beam intensity differs between the synchronization signal detection sensor and the exposure target surface. It is possible.

Further, when the reflectivity of the first area is set higher than the reflectivity of the second area, the beam intensity required for the synchronization signal detecting sensor is high, and the beam intensity required for the scanning target surface is high. Application to low strength is effective.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a rotary polygon mirror according to the present invention will be described below. FIG. 1 is an explanatory view showing an optical system of a scanning optical device to which the rotary reflecting mirror of the embodiment is applied, and FIG. 2 is a perspective view of a rotary polygon mirror used in the device of FIG. The scanning optical device of the embodiment is an exposure unit used in a laser printer, scans a laser beam that is ON / OFF modulated in accordance with an input drawing signal on a photosensitive drum that is a surface to be exposed, and outputs an electrostatic image. Form a latent image.

The optical system of the scanning optical apparatus according to the embodiment is shown in FIG.
As shown in FIG. 1, a semiconductor laser 21 as a light source, a collimator lens 22 for converting a beam emitted from the semiconductor laser 21 into parallel light, a cylindrical lens 23 having a positive power in the sub-scanning direction, a rotating polygonal surface for reflecting and deflecting the beam A polygon mirror 30 serving as a mirror, and a beam reflected and deflected by the polygon mirror 30
An fθ lens 40 is provided as an image forming optical system for forming a spot by converging on zero.

The polygon mirror 30 has six reflecting surfaces 31.
Are formed by equally dividing the outer circumference and rotate clockwise in the figure to deflect and scan the beam. On each reflection surface 31 of the polygon mirror 30, a first region 31a and a second region 31b having different reflectivities are formed.

Lens 40 is composed of two lenses, a first lens 41 and a second lens 42, arranged from the polygon mirror 30 side. On the emission side of the second lens 42, a spot on the photosensitive drum 50 is
A mirror 60 that reflects a beam emitted from the fθ lens 40 is arranged in a region just before the mirror
A synchronization signal detection sensor 61 that outputs a synchronization signal is provided at a position where the beam reflected at 0 is received. A point P0 on the photosensitive drum 50 indicates an equivalent position of a spot when it is assumed that the beam reaches the photosensitive drum 50 without being reflected by the mirror 60 when the synchronization signal is output, This indicates that the synchronization signal is output before the spot enters the writing range W defined between the writing start position P1 and the writing end position P2.

The optical elements from the semiconductor laser 21 to the fθ lens 40, the mirror 60 and the synchronizing signal detecting sensor 61 are composed of a casing 1 constituting an optical system unit.
The dustproof glass 70 is mounted on an opening of a casing 100 formed between the fθ lens 40 and the photosensitive drum 50.

According to the above configuration, the semiconductor laser 21
Is diverged by the collimator lens 22 to be collimated light, passes through the cylindrical lens 23, converges in the sub-scanning direction near the polygon mirror 30, and is reflected and deflected by the polygon mirror 30, and then in the sub-scanning direction. Is incident on the fθ lens 40 as divergent light and substantially parallel light in the main scanning direction. lens 40 has a relatively weak positive power in the main scanning direction as a whole, has a relatively strong positive power in the sub-scanning direction, and scans the beam reflected and deflected by the polygon mirror in the main scanning and sub-scanning directions. In both directions. The beam emitted from the fθ lens passes through the dustproof glass 70, and a spot is formed on the photosensitive drum 50 to scan in the main scanning direction y.

In the scanning optical device of the embodiment, the beam intensity required for the synchronization signal detection sensor 61 is high, and the beam intensity required for the photosensitive drum 50 is relatively low. To accommodate such required beam intensity differences,
On a reflection surface 31 of the polygon mirror 30, a first area 31a and a second area 31b having different reflectivities are formed.

That is, as shown in FIG. 2, the polygon mirror 30 has a first area 3 in which each reflection surface 31 is disposed on the front side in the rotation direction and has a relatively high reflectance.
1a and a second region 31b having a relatively low reflectivity
And the first and second regions 31a and 31b are distributed at the same ratio (for example, an area ratio of 1: 9) with respect to the total reflection surface.

The difference in the reflectance between the first area 31a and the second area 31b is realized by, for example, the difference in the coat applied to the reflection surface. A polygon mirror used for a scanning optical device such as a laser printer is generally made of aluminum, and is formed by applying a reflection-enhancing coating of magnesium or the like to a reflecting surface formed by cutting. Therefore,
The first area 31a is provided with a reflection enhancing coat, and the second area 31b is simply provided with a rust prevention coat only.
The reflectance of the first region 31a is relatively set to the second region 31b.
Can be higher than the reflectance.

Hereinafter, changes in the beam due to the rotation of the polygon mirror 30 will be described with reference to FIGS. FIG.
4 shows an optical path when the beam is received by the synchronization signal detecting sensor 61, that is, when the beam is assumed to be located at the synchronization signal output point P0 on the photosensitive drum 50. FIGS. Indicates an optical path when the writing position P1 is located at the writing start position P1 and the writing end position P2 on the photosensitive drum 50.

When the polygon mirror 30 is at the rotation position shown in FIG. 3, the beam incident from the semiconductor laser 21 side is a first area 31a of the reflection surface 31 of the polygon mirror 30.
, Is reflected at a relatively high reflectance, is converged by the fθ lens 40, is reflected by the mirror 60, and is incident on the synchronization signal detecting sensor 61. Since the intensity of the beam incident on the synchronization signal detection sensor 61 is relatively high, the synchronization signal can be reliably output even when the detection sensitivity of the synchronization signal detection sensor 61 is low.

When the polygon mirror 30 rotates clockwise from the state shown in FIG. 3, the beam incident from the semiconductor laser 21 enters the second area 31b of the reflection surface 31, as shown in FIG. At a low reflectance, f
While being converged by the θ lens 40, the light passes through the dustproof glass 70 to form a spot at the writing start point P1 on the photosensitive drum 50. The formed spot moves in the main scanning direction y with the rotation of the polygon mirror 30, and reaches the writing end position P2 when the polygon mirror 30 rotates to the position shown in FIG. In the writing range W, the beam reflected by the second area 31b in the reflection surface 31 of the polygon mirror 30 is used, and thus the photosensitive drum 5
At 0, a beam of relatively weak intensity is incident.

In the above embodiment, it is assumed that the beam intensity required for the synchronizing signal detection sensor 61 is larger than the beam intensity required for the photosensitive drum 50. However, these relationships are reversed. Specifications can also be assumed.
In such a case, contrary to the above embodiment, if the reflectance of the first region 31a is set lower than the reflectance of the second region 31b, a beam having an intensity suitable for each of the sensor and the drum can be obtained. Can be incident.

When it is desired to perform more detailed intensity adjustment in accordance with the sensitivity of the photosensitive drum or the like, the semiconductor laser 21 and the polygon mirror 3 are added to the configuration of the above embodiment.
An ND filter may be provided in the optical path between zero and zero. In this case, the intensity of the beam reaching the synchronization signal detection sensor 61 is determined by the transmittance of the ND filter and the polygon mirror 30.
The intensity of the beam reaching the photosensitive drum 50 is determined by the reflectance of the ND filter and the reflectance of the second area 31b of the reflection surface 31 of the polygon mirror 30. Is determined by Therefore, the intensity of the beam reaching the photosensitive drum can be finely adjusted by adjusting the transmittance of the ND filter while maintaining the intensity of the beam reaching the synchronization signal detecting sensor 61 higher than the intensity of the beam reaching the photosensitive drum 50. It becomes possible.

[0029]

As described above, according to the rotary polygon mirror of the first aspect, the first area and the second area having different reflectivities are formed on each reflecting surface.
If the beam reflected in the second area is used for detecting a synchronization signal and the beam reflected in the second area is guided to the exposure target surface, the reflectance of the first and second areas is required. By setting in accordance with the beam intensity, it is possible to cope with a case where the required beam intensity differs between the synchronization signal detection sensor and the exposure target surface. Thereby, the same effect can be obtained at lower cost as compared with the case where the ND coating is applied to the dustproof glass.

According to the second aspect of the present invention, the first region is a high reflectance region disposed on the front side in the rotation direction in each reflecting surface, and the second region is a low reflectance region. As a result, a high intensity beam is obtained in the first part of the scanning range of the beam reflected by the rotary polygon mirror, and a low intensity beam is obtained in the subsequent range. Therefore, it is effective to apply this method when the beam intensity required for the synchronization signal detection sensor arranged at the first part of the scanning range is high and the beam intensity required on the surface to be scanned is low.

According to the scanning optical device of the third aspect, by using the rotary polygon mirror in which the first area and the second area having different reflectivities are formed on each reflecting surface, the first surface of each reflecting surface is formed. The beam reflected in the first area is guided to the synchronization signal detection sensor, and the beam reflected in the second area reaches the exposure target surface. Therefore, by setting the reflectivity of the first and second regions in accordance with the required beam intensity,
It is possible to cope with the case where the required beam intensity is different between the synchronization signal detection sensor and the exposure target surface.

Further, according to the configuration of the fourth aspect, by setting the reflectance of the first area higher than the reflectance of the second area, the beam intensity required for the synchronization signal detecting sensor is high, This can be effectively applied when the beam intensity required on the surface to be scanned is low.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a scanning optical device according to an embodiment in a main scanning direction.

FIG. 2 is a perspective view of a polygon mirror used in the scanning optical device of FIG. 1;

FIG. 3 is an explanatory diagram showing an optical path when a beam enters a synchronization signal detection sensor in the scanning optical device of FIG. 1;

FIG. 4 is an explanatory diagram showing an optical path when a beam reaches a start point of a writing range in the scanning optical device of FIG. 1;

FIG. 5 is an explanatory diagram showing an optical path when a beam reaches an end point of a writing range in the scanning optical device of FIG. 1;

FIG. 6 is an explanatory diagram of a conventional scanning optical device in a main scanning direction.

[Explanation of symbols]

 Reference Signs List 21 semiconductor laser 30 polygon mirror 31 reflecting surface 31a first area 31b second area 40 fθ lens 50 photosensitive drum 61 sensor for detecting synchronization signal 70 dust-proof glass

Claims (8)

[Claims] 1. A rotating polygon mirror having a plurality of reflecting surfaces formed on an outer periphery thereof, wherein each of the reflecting surfaces has a first area having a predetermined reflectance and a first area having a reflectance. Different second
Wherein the distribution ratio of the first and second regions on each reflecting surface is the same for the total reflecting surface. 2. The first area is a high-reflectance area disposed on the front side in the rotation direction in each of the reflecting surfaces, and the second area is more rotated in the rotation direction than the first area. 2. The rotating polygon mirror according to claim 1, wherein the rotating polygon mirror is a low-reflectance area disposed on a rear side. 3. The rotating polygon mirror according to claim 2, wherein the first region is provided with an enhanced reflection coating. 4. The method according to claim 1, wherein the distribution ratio of the first region on each reflection surface is relatively small, and the distribution ratio of the second region is relatively large. The rotating polygon mirror described. 5. A light source, a rotary polygon mirror for reflecting and deflecting a beam emitted from the light source, and an imaging optical system for forming a spot by converging the beam reflected by the rotary polygon mirror on a surface to be scanned. A synchronous signal detecting sensor that receives a beam emitted from the imaging optical system in a region before the spot enters a writing range on the scanning target surface and outputs a synchronous signal, and the rotating polygon mirror includes: Each of the reflecting surfaces is a first area for reflecting a beam from the light source when the beam is incident on the synchronization signal detecting sensor, and a first area from the light source when the beam reaches a writing range on the scanning target surface. A second area for reflecting the light beam, and wherein the reflectances of the first and second areas are set to be different from each other. 6. The scanning optical device according to claim 5, wherein the reflectance of the first area is higher than the reflectance of the second area. 7. The scanning optical device according to claim 6, wherein the first region is provided with an enhanced reflection coating. 8. The method according to claim 5, wherein the distribution ratio of the first region on each reflection surface is relatively small, and the distribution ratio of the second region is relatively large. The scanning optical device according to claim 1.