JPH0943522A - Optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of jitter affecting an image even when a rotating polygon mirror is eccentric. SOLUTION: A second light beam from a second light source part 20 is reflected/deflected by a rotating polygon mirror 15, detected by an optical sensor of a synchronizing light detecting part 21, an electric signal at this time is confirmed by a control part not shown in the figure, the surface of the second light source part 20 is put out and a first light source part 13 for forming an image blinks according to the exposure distribution of an image formed on a line to be scanned after a prescribed time from the electric signal. By arranging the second light source part 20 and the synchronizing light detecting part 21 so that the rotating angle error of the rotating polygon mirror 15 caused at the time of detecting the synchronous light beam is located in the middle between the rotating angle errors generated at a scanning starting end and a scanning finishing end by the first light beam, thus, a jitter amount in the formed image is reduced to a half.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used in a laser beam printer or the like.

[0002]

2. Description of the Related Art FIG. 8 is a block diagram of a conventional optical scanning device, in which a cylindrical lens 4 and a polygon mirror are provided on an optical path in front of a laser light source section 3 including a semiconductor laser element 1 and a collimator lens 2. The rotary polygon mirrors 5 are arranged, and the rotary polygon mirror 5 has a plurality of reflecting surfaces equidistant from the rotation center O, and is rotated in the direction of arrow A at a constant speed by a drive motor (not shown).

A scanning lens 6 and a photosensitive drum 7 are arranged in the reflecting direction of the rotary polygonal mirror 5, and a scanning start light beam reflected by the rotary polygonal mirror 5 is condensed near the scanning lens 6. An image lens 8 and an optical sensor 9 that receives this light flux are arranged, and a synchronous light detector 10 that generates a synchronous signal in the scanning direction is formed by these.

Semiconductor laser device 1 of laser light source unit 3
The laser light from is converted into parallel light by the collimator lens 2 and is applied to the reflecting surface of the rotary polygon mirror 5 via the cylindrical lens 4. The laser light is reflected and deflected by the rotary polygon mirror 5, and is imaged in a spot shape on the photosensitive drum 7, which is the surface to be scanned, by the scanning lens 6 and is scanned at a constant speed.

If the light beam from the laser light source section 3 is not a parallel light but a convergent light, the optical path from the rotary polygon mirror 5 to the scanning surface can be shortened and the refracting power of the scanning lens 6 can be reduced. As a result, a compact optical scanning device can be formed, and by making the shape of the scanning lens 6 thin, the tact time and the birefringence can be reduced when the lens is made of plastic.
Furthermore, if the laser light source unit 3 does not have a lens and the divergent light from the semiconductor laser element 1 is used as a light beam as it is, the number of parts can be reduced and an inexpensive and simple device can be obtained.

The scanning start light beam deflected by the rotary polygon mirror 5 enters the synchronous light detector 10 as synchronous light, is received by the optical sensor 9 via the imaging lens 8, and is output from this optical sensor 9. The synchronization signal is used to synchronize the writing of the image signal in each scan. Then, the control unit (not shown) performs scanning by causing the laser light source to blink according to the image signal after a predetermined time delay from the synchronization signal in each scan. As a result, even if the scanning cycle fluctuates due to an angle division error of each surface of the rotary polygonal mirror 5, unevenness of the rotation speed of the drive motor, etc., the signal writing position on the scanned line for each scanning is controlled to be substantially constant. be able to.

[0007]

However, in the above-mentioned conventional example, when the light flux incident on the rotary polygon mirror 5 is convergent light or divergent light, the eccentricity of the rotary polygon mirror 5 causes the light from the center of rotation to each reflecting surface. If the distance fluctuates, a jitter error occurs in which the printing position at the end of printing changes for each scan.

In FIG. 9, the center of rotation of the rotary polygon mirror 5 is O, the reflecting surface of the rotary polygon mirror 5 in the regular position is M, the reflection points and image formation points of the reflecting surface M are P and I, and the distance d. If the reflecting surface of the eccentric rotating polygonal mirror 5 is M ′, and the reflection points and image forming points by the reflecting surface M ′ are P ′ and I ′, when the incident light flux B to the rotating polygonal mirror 5 is convergent light, The light flux is reflected at a reflection point P, which is an intersection with the reflection surface M, and then the distance is changed.
An image is formed at an image forming point I located at the position of L1. On the other hand, the incident light flux B
Is a divergent light, the reflected light flux forms a virtual image in front of the reflecting surface M, and the distance is smaller than L1.

When the distance between the center of rotation O and the reflecting surface M deviates by d due to the eccentricity of the rotary polygon mirror 5, the reflecting point P moves to P'and the image forming point I moves to I'by a distance S. Therefore,
When the optical scanning device has the scanning lens 6, the spot image on the scanning line formed by the scanning lens 6 is a re-imaging of the image forming point I by the reflected light flux of the rotating polygon mirror 5. The movement of the image forming point I of the reflected light flux appears as the movement of the spot image on the scanning line obtained by applying a predetermined image forming magnification.

Assuming that the incident angle of the rotary polygonal mirror 5 on the reflecting surface M is θ, the lateral displacement S of the reflected light flux is given by the following equation due to the normal direction displacement d of the reflecting surface M of the rotary polygonal mirror 5. Become. S = 2 ・ d ・ sin θ ・ ・ ・ (1)

In order to prevent the deviation S of the image formation point I from occurring even if the deviation d of the reflection point P occurs, the reflected light beam is rotated by a slight amount by the rotation of the rotary polygon mirror 5, and the image formation point I and I'should be superposed. The required rotation angle φ of the reflected light flux at that time is called a rotation angle error due to the eccentricity of the rotary polygon mirror 5, and is represented by the following equation. φ ≈ S / L1 [rad] = (2 · d / L1) · sin θ ・ ・ ・ (2)

If the rotation angle error φ is constant over the entire scanning area including the synchronization detection position, it is possible to cancel the positional deviation in the entire scanning area by performing normal synchronization detection. As is clear from the equation (2), since the required rotation angle φ changes with the rotation of the rotary polygon mirror 5, a large scanning position error that is not canceled by the synchronous detection occurs at the scanning end end, and this causes the rotation polygon mirror 5 to rotate. The deviation of the scanning position due to each surface, that is, the jitter appears and the printing quality is degraded.

In order to suppress this jitter to a small extent, it is necessary to suppress eccentricity by improving the processing accuracy of the rotary polygon mirror 5, improve the method for holding the rotary polygon mirror 5, and take measures to raise the temperature. Will cause up.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide an optical scanning device capable of reducing the influence of jitter on an image even if the rotary polygon mirror is decentered.

[0015]

An optical scanning device according to the present invention for achieving the above object comprises a first light source section which emits a non-parallel first light beam, and deflectively scans the first light beam. In a scanning optical device having a rotating polygonal mirror, which image-scans the first light flux deflected and scanned by the rotating polygonal mirror on a predetermined scanning surface, a second optical element that is non-parallel to the rotating polygonal mirror. A second light source unit that emits a light beam and a synchronous light detection unit that receives the reflected light of the second light beam and outputs a synchronization signal in the scanning direction when the rotary polygon mirror is at a predetermined rotation angle are provided. Is characterized by.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a block diagram of the optical scanning device of the first embodiment. In front of a first light source unit 13 including a semiconductor laser element 11 that emits a non-parallel first light beam and a collimator lens 12, a paper surface is shown. A cylindrical lens 14 having a power only in the vertical direction and a rotary polygon mirror 15 are arranged, and the rotary polygon mirror 15 is rotated at a constant angular velocity in the direction of arrow A by a drive unit. In the reflection direction of the rotary polygon mirror 15, a scanning lens 16 which is an anamorphic lens having different imaging characteristics in the scanning plane and in the sub-scanning section, and a scanned surface 17 such as a photoconductor are arranged.

In the vicinity of the first light source section 13, a second light source section 20 composed of an LED element 18 for emitting a second light beam for synchronization detection and a condenser lens 19 is arranged, and the rotary polygon mirror 15 is arranged. The synchronous light detector 21 is provided on the reflected light axis on which the second light flux is reflected when the reflection surface of the second light is at a predetermined angle.

The scanning lens 16 has an fθ function for forming a spot on the scanning surface 17 line in proportion to the incident angle of the incident light beam within the scanning surface, and the reflection of the rotary polygon mirror 15 in the sub-scanning direction. It has a surface tilt correction function of forming an image in the vicinity of the surface on the surface to be scanned 17. The non-parallelism of the light flux is the parallelism in the scanning plane and is irrelevant to the convergence of the first light flux in the sub-scanning direction in the surface tilt correction function.

2 to 4 show three types of synchronous light detectors 21, and FIG. 2 is composed of only a photosensor 22 such as a pin photodiode. That is, the light converging property of the second light flux for synchronization detection is used as it is for condensing on the light receiving surface of the optical sensor 22, and the boundary itself of the light receiving surface of the optical sensor 22 is made an opening.

In FIG. 3, the synchronous light detecting section 2 in which an opening 23 and an imaging lens 24 are sequentially arranged in front of the optical sensor 22.
1 is shown. Thus, when there is no imaging lens between the deflecting surface of the rotary polygon mirror 15 and the aperture 23, the rotary polygon mirror 5 is provided on the reflection optical axis when the reflection surface is at a predetermined angle. The distance between the LED element 18 and the condenser lens 19 is adjusted so that the second light flux is image-formed and incident on the opening 23. As a result, the spot image that crosses the aperture 23 is made small, and a large light amount change is caused by a slight position change due to scanning, thereby improving the synchronization detection accuracy.

FIG. 4 shows the synchronous light detecting section 21 in which the aperture 25 and the imaging lens 26 are arranged in front of the optical sensor 22, which allows the total length of the apparatus to be shortened. As described above, when the image forming lens 26 is provided between the deflecting surface of the rotary polygon mirror 15 and the opening 25, the position of the image 25 ′ of the opening 25 formed by the image forming lens 26 is set to the position of the synchronous light detecting section 21. It becomes conjugate with the position of the opening 25.

When operating the optical scanning device, first, the second light source unit 20 is turned on by a control unit (not shown). The second light flux emitted from the second light source unit 20 is reflected and deflected by the rotary polygon mirror 15, but when the second light flux passes through the synchronization detection unit 21, an electric signal is emitted from the optical sensor 22. After confirming this electric signal, the control unit turns off the second light source unit 20, and after a predetermined time from the electric signal, the first light source unit 13 for image formation blinks according to the exposure distribution of the image to be formed on the line to be scanned. Let

The first light flux emitted from the first light source unit 13 is converged by the cylindrical lens 14 in the sub-scanning direction perpendicular to the paper surface, and forms a focal line in the vicinity of the reflecting surface of the rotary polygon mirror 15, The light is reflected and deflected by the rotary polygon mirror 15 and enters the scanning lens 16.

In the optical scanning device for deflecting the parallel light by the rotary polygon mirror 15 at a constant angular velocity and converting it into a spot image that moves at a constant speed on the surface 17 to be scanned, the angle between the optical axis of the scanning lens 16 and the incident light beam. Is θ and the image formation position on the scanned line is y, the following relationship holds. In addition, F is an fθ coefficient and the unit is [mm / rad]. y = F ・ θ (3)

When the reflected light beam from the rotary polygon mirror 15 is parallel light, the fθ coefficient F is equal to the focal length of the scanning lens 16, but when non-parallel reflected light beam is used, f is calculated by the following equation.
The θ coefficient F is obtained. Note that L1 is the distance from the reflection point of the rotary polygon mirror 15 to the image point of the reflected light beam, D is the distance from the reflection point to the front main plane of the scanning lens 16, and f is the focal length of the scanning lens 16. F = (L1 · f) / (L1 + f−D) (4)

Now, L1 = 250 mm, D = 40 mm, f = 3
When set to 00 mm, the fθ coefficient F is F = 147 [mm / ra
d], which means that the incident light flux on the scanning lens 16 is 1 rad.
When rotated, the spot image on the scanned surface 17 is 147 mm
It indicates to move.

The length of the scanned surface 17 of the optical scanning device is 210.
The angle between the first light flux incident on the rotating polygon mirror 15 and the optical axis of the scanning lens 16 or the normal to the surface 17 to be scanned is 70 degrees with the counterclockwise direction being positive. Scanned surface 17 length 2
The reflection angle of the first light flux at both ends y = ± 105 mm of 10 mm is ± 105/147 = ± 0.7143 from the equation (3).
[Rad] = ± 40.93 °, from which the reflection angle of the rotary polygon mirror 15 at the scanning start end and the scanning end is θs = (70−40.93) /2=14.53 at the start end.
°, at the end, θe = (70 + 40.93) / 2
= 55.47 °.

Next, as shown in FIG. 9, the rotary polygon mirror 1 is used.
Considering the case where 5 is eccentric and the position of the reflecting surface is displaced by the distance d with respect to the surface normal direction of the reflecting surface of the rotary polygonal mirror 15, the distance d of the reflecting surface is changed by the equation (1). The movement S of the image point of the reflected light flux and the corresponding correction rotation angle φ
From Equations (1) and (2), at the starting end, Ss = 2 · d · sin (14.57 °) = 0.503 · d φs = Ss / L1 = 0.00201 · d · [rad ] At the end end, Se = 2 · d · sin (55.47 °) = 1.648 · d φe = Se / L1 = 0.00659 · d [rad].

If the rotation angle error at the synchronization detection position is approximately the same as the value at the image printing start end when the synchronization is detected, the uncorrected portion at the end end is (0.00659-
0.00201) · d = 0.00458 · d [mm]. When this is converted into the positional deviation ΔS on the surface to be scanned 17, it is multiplied by the fθ coefficient F to obtain ΔS = 147 × 0.0045.
8 · d≈0.673 · d, and for example, a positional variation of the reflecting surface of d = 20 μm causes a jitter of 13.5 μm.

In order to reduce the absolute value and improve the quality of the image by distributing this position variation not only to the scanning end edge but also to the scanning start edge, the second light source section is provided. 20 and the synchronous light detector 21 are arranged so that the rotation angle error caused by the synchronization detection is in the middle of the rotation angle error generated at the scanning start end and the scanning end end.

The opening 23 of the synchronous light detector 21 in FIG.
From the reflection point of the rotary polygon mirror 15 to L2,
The second light flux emitted from the light source unit 20 of the rotary polygon mirror 1
Assuming that the incident angle when passing through the aperture 23 after being deflected by the reflecting surface of No. 5 is θb, the rotation angle error φb generated at this time is φb = (d / L2) · si
Since nφb, φs <φb <φe may be satisfied, that is, the common term d may be omitted so that the following relationship is established. (sinθs) / L1 <(sinθb) / L2 <(sinθe) / L1 (5)

For example, θb is 10 °, φb = (φs + φ
e) / 2, the distance L2 is 40 mm.

In this way, due to the eccentricity of the rotary polygon mirror 15, the jitter that appears only at the scanning end end in the related art is distributed to the scanning start end, and the amount of jitter in the image formed as a result can be suppressed to half that of the prior art. You can

FIG. 5 shows a block diagram of the second embodiment.
1 is the same as that of FIG. 1 except the light source unit 30 and the synchronous light detection unit 31, and the same reference numerals represent the same members. The second light source unit 30 that emits the second light flux for synchronization detection includes the LED element 3
2 and the opening 33, the angle of incidence of the second light flux on the reflecting surface of the rotary polygon mirror 15 is set to be opposite to the angle of incidence of the first light flux. In addition, the synchronous light detector 3
1 is an optical sensor 34 such as a pin photodiode, and an opening 3
5 and the imaging lens 36.

FIG. 6 shows the relationship between the reflecting surface of the rotary polygon mirror 15 and the position of the image 35 'of the aperture 35 of the synchronous light detector 31.
The position of the image 35 ′ of the aperture 35 is determined by the imaging lens 36.
It is formed in a direction opposite to the light beam traveling direction from the reflecting surface of the rotary polygon mirror 15.

In equation (5), the distance L1 and the reflection angles θs and θ
When e is positive and the reflection angle θb is negative, the distance L2 is also small. This is because the light beam for detecting the synchronization signal is reflected in the direction opposite to the first light beam, and the opening 35 is located upstream of the reflecting surface of the rotary polygon mirror 15 in the traveling direction of the reflected light.

FIG. 7 is a block diagram of the third embodiment, in which the rotating polygon mirror 15 is rotated in the opposite direction to that of the previous embodiment, and the reflection angle of the synchronizing signal detecting light beam is the reflection of the first light beam. Angle θ s,
It is set to be larger than θe, and other than that, the configuration is similar to that of FIG.

Therefore, the distance L2 to the position of the opening 25 of the synchronous light detecting section 21 becomes larger than the distance L1, and providing the actual opening at this position hinders downsizing of the apparatus.
It is preferable to shorten the optical path by using the configuration of the synchronous light detection unit 21 shown in.

[0039]

As described above, in the optical scanning device according to the present invention, the optical scanning device is provided with the second light source for detecting the synchronizing signal, and the opening positions of the second light source and the synchronizing light detecting portion are desired. By setting the above relationship, the jitter that appears largely only at the scanning end end is distributed to the scanning start end, and as a result, the amount of jitter generated due to the eccentricity of the rotary polygon mirror is reduced and the quality of the printed image is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment.

FIG. 2 is a configuration diagram of a synchronous light detector.

FIG. 3 is a configuration diagram of a synchronous light detector.

FIG. 4 is a configuration diagram of a synchronous light detector.

FIG. 5 is a configuration diagram of a second embodiment.

FIG. 6 is a configuration diagram of a synchronous light detector.

FIG. 7 is a configuration diagram of a third embodiment.

FIG. 8 is a configuration diagram of a conventional example.

FIG. 9 is an explanatory diagram of jitter due to eccentricity of a rotating polygon mirror.

[Explanation of symbols]

 13 1st light source part 14 Cylindrical lens 15 Rotating polygonal mirror 16 Scanning lens 20, 30 2nd light source part 21, 31 Synchronous light detection part 22 Optical sensor

Claims (4)

[Claims] 1. A first light source unit that emits a non-parallel first light flux, and a rotary polygon mirror that deflects and scans the first light flux, and the first polygon deflected and scanned by the rotary polygon mirror. In a scanning optical device for image-forming scanning of a light beam of a predetermined scanning surface on a predetermined scanning surface, a second light source unit that emits a second light beam that is non-parallel to the rotary polygonal mirror, and the rotary polygonal mirror at a predetermined rotation angle. An optical scanning device comprising: a synchronous light detector that receives the reflected light of the second light flux at a certain time and outputs a synchronous signal in the scanning direction. 2. The synchronous light detecting section has a light detecting element and an opening for limiting light incident on the light detecting element, and an optical element having power in the scanning direction between the opening and the rotary polygon mirror. There is no member, and the distance from the opening to the reflection point of the second light flux and the distance from the image formed after the first light flux reflects the rotary polygon mirror to the reflection point are different. 1. The optical scanning device according to 1. 3. The synchronous light detection unit includes a light detection element, an opening for limiting light incident on the light detection element, and an optical member having power in the scanning direction between the opening and the rotary polygon mirror. A distance from a real image or a virtual image of the aperture formed by the optical member to a reflection point of the second light flux, and an image formed after the first light flux reflects the rotary polygon mirror to a reflection point. The optical scanning device according to claim 1, wherein the distance is different from the distance. 4. The distance from the image formed after the first light flux is reflected by the rotary polygon mirror to the reflection point is L1, the aperture in the synchronous light detection unit, the virtual image of the aperture, or the real image of the aperture The distance to the reflection point of the second light flux is L2, the incident angle of the first light flux on the reflecting surface of the rotary polygon mirror at the scanning start end is θs, the incident angle at the scanning end end is θe, and the synchronous light detection unit is The incident angle of the second light flux at
And the distance L1 is positive when the first light flux is divergent light and negative when the first light flux is convergent light, and the distance L2 is negative when the aperture has a real image and positive when the aperture does not have a real image. When the angle to the normal line of the reflecting surface of the rotary polygon mirror is expressed with the counterclockwise direction as positive, (sin θs) / L1 <(sin θb) / L2 <(sin
The optical scanning device according to claim 2, wherein the relationship of θe) / L1 is established.