JP2000227564A - Multi-beam scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct an interval between beams on a surface to be scanned by using a zoom collimator lens and to eliminate the fluctuation of a beam diameter or light quantity on the surface to be scanned occurring in accordance with the above correction as a multi-beam scanning optical device. SOLUTION: This multi-beam scanning optical device is constituted so that the laser beams radiated from two point light sources of a laser diode 10 are condensed by the zoom collimator lens 11, transmitted through an aperture type diaphragm 12 and simultaneously used for scanning a photoreceptor drum (surface to be scanned) 25 based on the rotation of a polygon mirror 14. Then, the interval between the beams is detected by a detector 20 and the focal distance of the lens 11 is changed based on the detected value of the detector 20 so as to correct the interval between the beams. The beam diameter is regulated to be constant by the diaphragm 12 and the emitted light quantity of the diode 10 is also corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam scanning optical apparatus, and more particularly, to a multi-beam scanning optical apparatus which scans laser beams emitted from a plurality of light sources at a predetermined interval in a sub-scanning direction on a surface to be scanned simultaneously. The present invention relates to a scanning optical device.

[0002]

2. Description of the Related Art In general, in a multi-beam scanning optical apparatus for recording an image on a photoreceptor, a plurality of laser beams are sub-scanned due to a change in environmental conditions such as a temperature or an assembly error. The spacing in the direction fluctuates. As a countermeasure against this, Japanese Patent Laid-Open Publication No. Hei 8-234126,
No. 0917 proposes a method of detecting a change in beam interval and changing the focal length of the zoom collimator lens to correct the beam interval on the surface to be scanned while keeping the optical path length constant.

The use of a zoom collimator lens has the advantage that the beam interval can be corrected while keeping the optical path length constant. However, in order to change the focal length, that is, the magnification of the entire optical system is reduced. Due to the change, the beam diameter on the surface to be scanned fluctuates, or the amount of light fluctuates.

Accordingly, an object of the present invention is to provide a multi-purpose optical system in which the beam diameter or light amount on the surface to be scanned does not fluctuate even though the beam interval on the surface to be scanned is corrected using a zoom collimator lens. It is to provide a beam scanning optical device.

[0005]

In order to achieve the above objects, a multi-beam scanning optical device according to the present invention converges laser beams emitted from a plurality of light sources to collect light in a main scanning direction or a sub-scanning direction. A zoom optical element for changing at least one of the focal lengths, and a diaphragm means arranged at a downstream side of the zoom optical element for blocking a part of the laser beam.

Further, the multi-beam scanning optical device according to the present invention includes the zoom optical element, light amount correcting means for correcting light amounts of a plurality of light sources, and light amount correcting means in response to a change in the focal length of the zoom optical element. Control means for controlling.

In the present invention, the distance between a plurality of laser beams on the surface to be scanned is corrected by changing the focal length of the zoom optical element. The correction is performed based on the detected value by detecting the interval between the laser beams. Therefore, if the detection means and the feedback control means are provided, the detection /
Correction can be performed. In the present invention, the beam diameter on the surface to be scanned is kept constant by the aperture means provided downstream of the zoom optical element even if the focal length changes for the purpose of correcting the distance. In addition, by correcting the light amount of the light source according to the change in the focal length, usually, the light amount is maintained constant by increasing the light amount as the focal length becomes longer.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a multi-beam scanning optical device according to the present invention will be described below with reference to the accompanying drawings.

(First Embodiment, See FIGS. 1 to 6) A multi-beam scanning optical device 1 according to a first embodiment generally includes a laser diode 10, a collimator lens 11, an aperture stop 12, and a cylindrical lens. 13, a polygon mirror 14, a scanning lens 15, and a detector 20 for detecting a beam interval on the image plane.

The laser diode 10 has two point light sources, and emits laser beams LBa and LB at predetermined intervals in the Z-axis direction.
emit b. The collimator lens 11 is a zoom lens having a variable focal length, and includes a laser diode LBa,
The LBb is converged into parallel light or convergent light. The laser beams LBa and LBb condensed by the collimator lens 11 are partially shielded by the aperture stop 12, and are regulated to a predetermined beam diameter. The intervals between the laser beams LBa and LBb in the sub-scanning direction Z are set to have an interval on the order of several tens of μm on the image plane. For example, if the printing density is 400
In the case of dpi, the interval on the image plane is 63.5 μm, 60
In the case of 0 dpi, it is 42.3 μm, and in the case of 800 dpi, it is 31.8 μm.

The cylindrical lens 13 has power only in the sub-scanning direction Z, and condenses the laser beams LBa and LBb linearly on the deflection surface of the polygon mirror 14 in the main scanning direction Y. The polygon mirror 14 is driven to rotate at a constant angular velocity in the direction of the arrow a, and the laser beams LBa and LBb are deflected at the same angular velocity on each of the deflecting surfaces of the polygon mirror 14 based on this rotation. Photoreceptor drum 25 via mirror 17
At the same time, the image is formed, and the scanning is performed in the main scanning direction Y. That is,
In the optical device 1, two lines are simultaneously written on the photosensitive drum 25 by one scanning.

The scanning lens 15 is a well-known one, and has a function of correcting the main scanning speed on the image plane at a constant speed and a function of correcting curvature of field. The cylindrical lens 16 cooperates with the cylindrical lens 13 to form the polygon mirror 1.
4 has a function of correcting the tilt error.

The photosensitive drum 25 is driven to rotate at a constant speed in the direction of arrow b, and the sub-scanning and the laser beams LBa, LBa are performed.
The photosensitive drum 25 is moved by the main scanning of Bb (in the direction of arrow Y).
A two-dimensional image (electrostatic latent image) is written thereon.

In the multi-beam scanning optical apparatus 1 having the above-described configuration, the beam on the surface to be scanned is changed due to an error in the position of the point light source of the laser diode 10 and a change in the focal length of the optical element due to a change in temperature. The intervals fluctuate.

Here, referring to FIG. 2, the displacement (ΔY ′, ΔZ ′) of the laser beam on the surface to be scanned when the light source is displaced (ΔY, ΔZ) in the main scanning direction or the sub-scanning direction. explain.

FIG. 2A shows a case where the light source is displaced by .DELTA.Y, and the displacements .DELTA.Y 'and .DELTA.X' of the beam on the surface to be scanned are represented by the following equations (1) and (2). ΔY ′ = β _m · ΔY (1) ΔX ′ = β _m ² · ΔX (2) where β _m = f _f / f _co

FIG. 2B shows a case where the light source is displaced by .DELTA.Z, and the displacements .DELTA.Z 'and .DELTA.X' of the beam on the surface to be scanned are represented by the following equations (3) and (4). _{ΔZ '= β s · ΔZ ...} (3) ΔX' = β s 2 · ΔX ... (4) _{However, β s = (f cy /} f co) · β f

That is, as is apparent from the above equations (1) to (4), beam displacements ΔZ ′ and ΔX ′ on the surface to be scanned are:
The correction can be made by adjusting the focal length f _co of the collimator lens 11. Therefore, in the first embodiment,
The collimator lens 11 is a zoom lens, and the focal length of the collimator lens 11 is adjusted based on a beam interval error detected by a beam interval detector 20 described below.

FIG. 3 shows a mechanism for detecting displacement amounts .DELTA.Y 'and .DELTA.Z' of laser beams LBa and LBb at positions equivalent to the surface to be scanned after deflection. The detector 20 includes optical sensors 21, 22, 23, and 24 having triangular detection surfaces for receiving a reflected beam from a mirror 26 arranged in the main scanning direction. In FIG. 3 shows a scanning locus of a laser beam. The displacement amount ΔY ′ in the main scanning direction is determined by detecting the detection time t1 of the optical sensors 21 and 23 with the laser beams LBa and LBa.
It is measured for each Bb and calculated based on the difference between the two measured values. The displacement amount ΔZ ′ in the sub-scanning direction is
Is calculated based on the detection time t2 of the laser beam LBa and the detection time t3 of the laser beam LBb.

Further, in order to determine the scanning position in the sub-scanning direction, another optical sensor 25 is turned on by the laser beam LBa.
On the scanning locus, and detects that the laser beam LBa is being scanned at a predetermined position.

The detected times t1, t2, and t3 are input to a control circuit 27, which calculates a displacement amount and also calculates a correction value. This correction value is transferred to the zoom drive circuit 28 of the collimator lens 11, and changes the focal length of the collimator lens 11.

As described above, by changing the focal length of the collimator lens 11, the beam position on the surface to be scanned can be corrected. However, since the beam diameter and the light amount on the surface to be scanned change with the change of the focal length, it is practically necessary to compensate for at least one of them.

With respect to the beam diameter D _m on the surface to be scanned,
It is represented by the following equation (5) (see FIG. 4). _{D m = k 1 λ (f} f / D o) = k 2 λF NO ... (5) k 1, k 2: proportional constant lambda: wavelength D _o: the incident beam diameter f _f to fθ lens focal the fθ lens distance F _NO: of fθ lens F _NO

[0024] As apparent from Equation (5), also vary the focal length f _co of the collimator lens 11, if the beam diameter D _o which is incident on the scanning lens 15 is constant, on the surface to be scanned beam diameter D _m is not changed. Therefore, in the first embodiment, the aperture stop 1 is located downstream of the collimator lens 11.
2, the beam diameter _Do was _kept constant.
Note that various types of apertures can be employed as the aperture means.

On the other hand, since the beam divergence angle θ from the light source changes with the change in the focal length f _co , it is necessary to correct the light amount according to the change. FIG. 5 shows the relationship between the focal length of the collimator lens 11 and the light amount utilization rate. That is, when the focal length f _co increases, the light amount utilization rate decreases. Therefore, the amount of decrease is compensated for by increasing the drive current of the laser diode 10.

When the light energy I on the surface to be scanned has the Gaussian distribution shown in FIG. 6, the light energy I is represented by the following equation (6), and the control circuit 27 uses the equation (6) to calculate the energy. The correction value for the loss is calculated and transferred to the light amount correction circuit 29. The light quantity correction circuit 29 controls the drive voltage of the light source to correct the light quantity.

[0027]

(Equation 1)

FIG. 7 shows a multi-beam scanning optical device 2 according to a second embodiment.
Means that the two laser diodes 10a and 10b are laser beams LBa and LB in the X-axis direction and the Z-axis direction orthogonal to each other.
b, and the laser beams LBa, LB
b is combined by a beam splitter 18. The interval between the laser beams LBa and LBb is detected by the two-dimensional CCD 19. The same members as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The beam splitter 18 is formed by joining two prisms via a semi-permeable membrane, and the straight light of the laser beam LBa and the reflected light of the laser beam LBb are incident on the next stage of the zoom collimator lens 11. The two-dimensional CCD 19 receives the reflected light of the laser beam LBa from the beam splitter 18 and the transmitted light of the laser beam LBb from the beam splitter 18, and detects the displacement of each beam. The detection data is input to the control circuit 27, which calculates the amount of displacement of the beam and the correction value of the focal length of the collimator lens 11 corresponding thereto, and transfers them to the zoom drive circuit.
Also, with the correction of the focal length, the laser diode 10
The light emission amounts of a and 10b are also corrected.

(Other Embodiments) The multi-beam scanning optical device according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention. In particular, various methods can be adopted for the means for detecting the interval between a plurality of laser beams. In addition, the present invention can be applied to a multi-beam system of not only two beams but also three beams or more. Further, the types and arrangement of the various optical elements constituting the optical path are arbitrary.

In each of the above embodiments, the beam diameter on the surface to be scanned is fixed and the light amount of the light source is corrected in accordance with the change in the focal length of the collimator lens. Practical specifications of drawing an image on the photoreceptor can be satisfied even if only one of them is performed.

In particular, if the image quality of a printer incorporating the multi-beam scanning optical device is taken into consideration,
In order to compensate for the image deterioration due to the correction of the beam position on the photoreceptor, it is also possible to change various parameters of the image forming device such as changing the developing bias voltage of the developing device. Specifically, the developing bias voltage may be set higher to increase the beam diameter, and may be set lower to decrease the beam diameter.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a multi-beam scanning optical device according to a first embodiment of the present invention.

FIG. 2 is an optical path diagram showing displacement of a laser beam on a surface to be scanned.

FIG. 3 is an explanatory diagram showing an example of a method of detecting a beam interval.

FIG. 4 is an optical path diagram for explaining a calculation formula of a beam diameter.

FIG. 5 is a graph showing a light amount utilization ratio with respect to a focal length of a collimator lens.

FIG. 6 is a graph showing light energy distribution.

FIG. 7 is a schematic configuration diagram illustrating a multi-beam scanning optical device according to a second embodiment of the invention.

[Explanation of symbols]

 1, 2, multi-beam scanning optical device 10, 10a, 10b laser diode 11, zoom collimator lens 12, aperture stop 18, beam splitter 19, two-dimensional CCD 20, beam interval detector 27, control means 28, zoom drive Circuit 29: Light amount correction circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hidenari Tatebe 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Inventor Toshikazu Suzuki Azuchi, Chuo-ku, Osaka-shi, Osaka 2-3-1, Machi-cho Osaka International Building Minolta Co., Ltd. F-term (reference) 2H045 AA01 BA22 BA32 CA03 CA88 CB22 DA02

Claims (3)

[Claims] 1. A multi-beam scanning optical apparatus for simultaneously scanning a laser beam emitted from a plurality of light sources on a surface to be scanned at a predetermined interval in a sub-scanning direction at a constant speed, wherein the laser beams emitted from the light sources are collected. A zoom optical element that emits light and changes at least one of a focal length in a main scanning direction and a sub-scanning direction; and a diaphragm unit that is disposed downstream of the zoom optical element in a beam traveling direction and shields a part of a laser beam. A multi-beam scanning optical device, comprising: 2. A multi-beam scanning optical apparatus for simultaneously scanning a laser beam emitted from a plurality of light sources on a surface to be scanned at a predetermined interval in a sub-scanning direction at a constant speed. Correction means, a laser beam emitted from the light source, a zoom optical element for changing the focal length in at least one of the main scanning direction and the sub-scanning direction, and a change in the focal length of the zoom optical element. And a control means for controlling the light quantity correction means in response thereto. A detecting means for detecting a beam interval of at least one of a main scanning direction and a sub-scanning direction of the laser beam; a control means for driving the zoom optical element based on a detection result of the detecting means; The multi-beam scanning optical device according to claim 1 or 2, further comprising: