JP2000227562A - Multi-beam scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimally correct an interval between beams and the diameter of the beam on a surface to be scanned as a multi-beam scanning optical device. SOLUTION: This multi-beam scanning optical device is constituted so that the laser beams LBa and LBb radiated from laser diodes 10a and 10b are coupled by a beam splitter 11 condensed by a zoom colimator lens 12, transmitted through a single lens 13 and simultaneously used for scanning a photoreceptor drum (surface to be scanned) 25 based on the rotation of a polygon mirror 16. The condensing state of the beam is corrected by moving the lens 13 on an optical axis based on a detected result by a detector 23. Besides, the interval between the beams is corrected by changing the focal distance of the lens 12 based on a result detected by a detector 20.

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.

On the other hand, in the multi-beam scanning optical device, not only the beam interval fluctuates, but also the beam diameter on the surface to be scanned fluctuates due to changes in environmental conditions and assembly errors. To cope with such a problem, Japanese Patent Laid-Open No.
As described in Japanese Patent No. 235872, a method of correcting a beam waist position by moving a single lens on an optical axis to change an optical magnification has been proposed.

However, in the multi-beam scanning optical device, the magnification of the optical system is changed both when correcting the interval in the sub-scanning direction and when correcting the beam diameter. Therefore, if the optimum magnification is not the same, either one cannot be corrected completely.

An object of the present invention is to provide a multi-beam scanning optical device capable of optimally correcting a beam interval and a beam diameter on a surface to be scanned.

[0006]

In order to achieve the above object, a multi-beam scanning optical device according to the present invention condenses laser beams emitted from a plurality of light sources and sets at least a focal length in a sub-scanning direction. A zoom optical element to change,
A lens movable along the optical axis.

In the present invention, by moving the lens along the optical axis, the magnification of the optical system is changed, and the focusing state of the beam on the surface to be scanned is corrected. Further, even if the magnification changes, the zoom optical element changes its focal length without changing the positional relationship between the object point and the image point, and corrects the beam interval on the surface to be scanned. Therefore, according to the present invention, it is possible to optimally correct the beam interval and the focusing state (beam diameter) on the surface to be scanned. The correction may be performed so as to have a magnification between the correction magnification for the focusing state and the correction magnification for the beam interval.

[0008] In the most preferable form of correction, first, the lens is moved along the optical axis to correct the magnification based on the detection result of the condensing state of the laser beam on the surface to be scanned, and then the beam interval is adjusted. This is to correct the magnification (focal length) of the zoom optical element based on the detection result. That is, when the focusing state (beam diameter) is corrected by moving the lens, the beam interval changes. However, by correcting the focusing state and then correcting the beam interval, the focusing state and the beam interval are optimally corrected. be able to.

[0009]

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.

[0010] A multi-beam scanning optical device 1 according to the present invention.
Are generally laser diodes 10a and 10b, a beam splitter 11, a collimator lens 12, a single lens 13, an aperture stop 14, and a cylindrical lens 15.
, A polygon mirror 16, a scanning lens 17, a beam interval detector 20, and a detector 23 at a focus position (condensed state).

The laser diodes 10a and 10b are provided with laser beams LBa and LBa in the X-axis direction and the Z-axis direction orthogonal to each other.
It is arranged to emit Bb. The beam splitter 11 is formed by joining two prisms via a semi-permeable membrane, and includes a straight beam of a laser beam LBa and a laser beam LB.
The reflected light of b enters the collimator lens 12 at the next stage.
As described above, the laser beams LBa and LBb are combined in the same traveling direction by the beam splitter 11, but the intervals 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 collimator lens 12 is a zoom lens having a variable focal length, and includes laser diodes LBa, LBa.
Bb is condensed into parallel light or convergent light. Laser beams LBa and LBb focused by zoom collimator lens 12
Are transmitted through a single lens 13 for focus adjustment and are partially shielded from light by an aperture stop 14, and are regulated to a predetermined beam diameter. The single lens 13 can be moved along the optical axis by a driving mechanism (not shown), and the distance between the single lens 13 and the collimator lens 12 can be adjusted.

The cylindrical lens 15 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 16 in the main scanning direction Y. The polygon mirror 16 is driven to rotate at a constant angular velocity in the direction of arrow a, and the laser beam LBa. LBb is deflected at a constant angular velocity on each deflecting surface of the polygon mirror 16 based on this rotation, and is passed through the scanning lens 17, the cylindrical lens 18, and the return mirror 19, and the photosensitive drum 25.
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 17 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 18 cooperates with the cylindrical lens 15 to form the polygon mirror 1.
6 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.

Incidentally, in the multi-beam scanning optical device 1 having the above configuration, the laser diode 10
The beam diameter and beam interval on the surface to be scanned fluctuate due to errors in the light source positions a and 10b (there are errors during assembly and errors caused by changes in temperature, etc.).

Here, with reference to FIG. 2, correction of the beam condensing state and correction of the beam interval on the surface to be scanned will be described. The relationship between the displacement of the light source and the beam position ΔZ, Z ′ is represented by the following equation (1), and the relationship of the focal length of each lens is represented by the following equation (2).

Z ′ = β _f (f _cy / f _co ′) ΔZ (1) (1 / f _co ′) = (1 / f _{co (Z)} ) + (1 / f _AF ) − (D / f _co・ f _AF )… (2)

As an example of specific numerical values, β _f : −1.
5, f _cy : 120, f _{co (Z)} : 16, f _AF : 100, and the single lens 13 is moved to set the lens interval D to 10-2.
It can be adjusted within the range of 0 mm. In this case, the focal length f _co 'of the collimator lens 12 and the beam displacement Z' on the surface to be scanned are numerical values shown in Table 1 below, and the beam interval can be adjusted within the range of these numerical values.

[0020]

[Table 1]

The beam interval can be corrected by changing the beam position on the surface to be scanned based on the above equation (1), and by changing the lens interval D based on the above equation (2). Can be corrected.

By the way, as is apparent from the above equation (2), when the focus position is corrected by moving the single lens 13, the beam displacement Z 'changes and the beam interval also changes. Therefore, it is preferable to correct the beam interval after correcting the focus position.

Further, the zoom collimator lens 12 may be adjusted so that the magnification is between the correction magnification of the light condensing state and the correction magnification of the beam interval. More specifically, with reference to the numerical examples described in Table 1, the optimal focus position is a lens interval D = 15 mm. Beam spacing is 42μ
Assuming that m is optimal, the optimal lens interval D is 10 mm. Therefore, the zoom collimator lens 12 is moved to set the lens interval D in a range of 10 to 15 mm.

Next, the detector 2 at the focus position (light focusing state)
3 will be described. The detector 23 is formed of a photoelectric conversion element, and as shown in FIG. 3, a mask 22 having a triangular slit 22a is provided on the front surface thereof. As shown in FIG. 4A, the slit 22a has a side 22v perpendicular to the scanning direction Y of the laser beam and an inclined side 22v.
i. The slit needs to have the vertical side 22v and the inclined side 22i, and the slit itself can adopt various shapes.

Assuming that the amplified output of the detector 23 when the laser beam passes through the slit 22a has the waveform shown in FIG. 4B, the differential output is the waveform shown in FIG. is there. The peak voltage V1 of the differential output contains information indicating the beam diameter in the main scanning direction, and the peak voltage V2 is
Information indicating both beam diameters in the sub-scanning direction is included.

That is, as shown in FIG. 5A, when the diameter of the beam spot B in the main scanning direction is large, the rising of the output of the detector 23 becomes smooth as shown in FIG. The differential waveform is as shown in FIG. On the other hand, as shown in FIG. 5D, when the diameter of the beam spot B in the main scanning direction is small, the rising of the output of the detector 23 becomes steep as shown in FIG. This is as shown in FIG. As is clear from the comparison between the waveforms of FIGS. 5C and 5F, the voltage V1 of the small-diameter differential waveform in the main scanning direction of the beam spot B is larger than the voltage V1 of the large-diameter differential waveform. .

Next, as shown in FIG. 6A, when the diameter of the beam spot B in the sub-scanning direction is large, the fall of the output of the detector 23 becomes smooth as shown in FIG. 6B. The differential waveform is as shown in FIG. On the other hand, as shown in FIG. 6D, when the diameter of the beam spot B in the sub-scanning direction is small, the fall of the output of the detector 23 becomes steep as shown in FIG. Is as shown in FIG. As is clear from the comparison of the waveforms of FIGS. 6C and 6F, the voltage V2 of the beam spot B in the sub-scanning direction having a smaller diameter in the sub-scanning direction is larger than the voltage V2 of the differential waveform having a larger diameter. .

The waveform detected by the detector 23 is transmitted to the control circuit 30.
The control circuit 30 calculates the focusing state of the beam, and calculates a correction value converted into the amount of movement of the single lens 13. This correction value is transferred to the drive circuit 32 of the single lens 13 to change the position of the single lens 13 on the optical axis (lens interval D). Thus, the focus position is corrected.

Next, the beam interval detector 20 will be described. The detector 20 is composed of a two-dimensional CCD, and receives the reflected light of the laser beam LBa from the beam splitter 11 and the transmitted light of the laser beam LBb through the condensing lens 26 to detect the displacement of each beam. I do. The detection data is input to the control circuit 30. The control circuit 30 calculates the amount of displacement of the beam and the correction value of the focal length of the collimator lens 12 corresponding thereto, and transfers the correction value to the zoom drive circuit 31.

On the other hand, the focal length f of the collimator lens 12
_Since the beam divergence angle θ from the light source changes with the change of _co , it is necessary to correct the light amount according to the change. FIG. 7 shows the relationship between the focal length of the collimator lens 12 and the light amount utilization rate. That is, when the focal length f _co increases, the light amount utilization rate decreases. Therefore, the light amount is compensated for by increasing the drive voltage of the laser diodes 10a and 10b.

When the light energy I on the surface to be scanned has a Gaussian distribution shown in FIG. 8, the light energy I is represented by the following equation (3), and the control circuit 30 uses the equation (3) to calculate the energy. The correction value for the loss is calculated and transferred to the light amount correction circuit 33. The light quantity correction circuit 33 controls the drive voltage of the light source and corrects the light quantity.

[0032]

(Equation 1)

FIG. 9 is a flowchart summarizing the control procedure of the above-described image adjustment. First, step S
In step 1, the focus position of the laser beam is detected using the detector 23, and a correction value for correcting the focus position is calculated. Next, in step S2, the focus position is corrected by moving the single lens 13 based on the correction value. Further, in step S3, the beam interval is detected using the detector 20, and a zoom correction value is calculated. Next, in step S4, it is determined whether the interval is larger than the reference value,
If it is larger, in step S5, the focal length of the collimator lens 12 is changed to be shorter based on the correction value, and the beam interval is corrected. Next, in step S6, the light amount of the light source is corrected, and the light amount on the surface to be scanned is maintained constant.

On the other hand, when the beam interval is smaller than the reference value (NO in step S4, YES in step S7)
In step S8, based on the correction value, the collimator lens 12
Is changed so as to increase the focal length, and the beam interval is corrected. Next, in step S9, the light amount of the light source is corrected, and the light amount on the surface to be scanned is kept constant.

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 and the means for detecting the condensed state. The arrangement relationship of the laser diodes is also arbitrary, and a laser diode having a plurality of light-emitting sources built in one element can be used. 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.

[Brief description of the drawings]

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

FIG. 2 is an optical path diagram showing displacement of a laser beam in a sub-scanning direction.

FIG. 3 is a perspective view showing the detector in a beam focusing state.

FIG. 4 is a chart showing an output waveform of the detector.

FIG. 5 is a chart illustrating detection of a beam diameter (main scanning direction) by the detector.

FIG. 6 is a chart illustrating detection of a beam diameter (sub-scanning direction) by the detector.

FIG. 7 is a graph showing a light amount utilization ratio with respect to a focal length of a collimator lens.

FIG. 8 is a graph showing a distribution of light energy.

FIG. 9 is a flowchart showing an outline of a control procedure of image formation adjustment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Multi-beam scanning optical device 10a, 10b ... Laser diode 12 ... Zoom collimator lens 13 ... Single lens 20 ... Beam interval detector 23 ... Condensing state detector 30 ... Control 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 2-13-3, Machi-cho Osaka International Building Minolta Co., Ltd. F-term (reference) 2H045 AA01 BA22 BA32 CA03 CA88 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 multi-beam scanning optical device comprising: a zoom optical element that emits light and changes at least a focal length in a sub-scanning direction; and a lens that can move along an optical axis. 2. A multi-beam scanning optical device 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. An interval detecting means for detecting an interval; a first optical magnification changing means; a condensing state detecting means for detecting a condensing state of at least one of the plurality of laser beams on a surface to be scanned; Optical magnification changing means, and after correcting the optical magnification using the second optical magnification changing means based on the detection result of the light-condensing state detecting means, collecting the beam based on the detection result of the interval detecting means. A control means for correcting the optical magnification using the first optical magnification changing means without changing the light state. 3. 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 predetermined intervals in a sub-scanning direction at a constant speed. Interval detecting means for detecting an interval; condensing state detecting means for detecting a condensing state of at least one of the plurality of laser beams on the surface to be scanned; optical magnification changing means; A correction magnification based on the detection result of the means,
Control means for controlling the optical magnification changing means so as to have a magnification between the correction magnification based on the detection result of the interval detecting means, and a multi-beam scanning optical apparatus.