JP2000314843A - Light beam interval adjusting device and image forming device having light beam interval adjusting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light beam interval adjusting device capable of adjusting the beam interval with excellent precision even if a sensor having low detecting precision is used. SOLUTION: A CCD line sensor 20 is moved in the arraying direction of elements so that the center C1 of the beam spot S1 of a first laser beam is positioned at the central position in the arraying direction of the elements of the specified element (fifth element) of the CCD line sensor 20. And the position where the CCD line sensor 20 is irradiated by the laser beam is displaced so that the center C2 of the beam spot S2 of a second laser beam is positioned at the central position in the arraying direction of the elements of the element (here, tenth element) locating in the position by a prescribed beam interval Bp apart from a specified element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam interval adjusting device for adjusting the beam interval at a target irradiation position of each beam to a predetermined distance by detecting the positions of a plurality of light beams by beam detecting means. The present invention relates to an image forming apparatus using the same.

[0002]

2. Description of the Related Art For example, in the field of image forming apparatuses such as digital copying machines and laser printers, a plurality of laser beams for exposing the surface of an image carrier and the like are emitted in order to cope with high-speed image formation. Various image forming apparatuses using a multi-beam scanning optical system have been developed. In order to obtain an image of good quality using such a multi-beam scanning optical system, an interval (beam) in the sub-scanning direction between a plurality of laser beams when exposing an image carrier or the like to be a target irradiation position. Interval) must be maintained at a predetermined interval.

However, even if the beam interval is once set to a predetermined interval in the manufacturing stage, for example, when the image forming apparatus is used, a laser diode serving as a laser beam generating source or a laser diode disposed in the middle of the optical path of the laser beam is used. The position of a member holding an optical element such as a cylindrical lens is slightly displaced by vibration generated during an image forming operation, or the member or the optical element expands and contracts due to a change in temperature around the member, and the beam interval is reduced. May fluctuate. For this reason, various techniques for adjusting the beam interval to a predetermined interval have been conventionally devised, and an example thereof is disclosed in JP-A-9-1599.
No. 49 discloses this.

FIG. 13A is a diagram showing a schematic configuration of a laser printer disclosed in this publication. As shown in the figure, a laser beam LB0 emitted from a laser diode 901 is split into two laser beams LB1 and LB2 by a multi-beam generating element 902. The split laser beams LB1 and LB2 are supplied to a collimator lens 90.
3. Laser beams LB1, LB2 based on image data
The light reaches a reflection mirror 906 via a modulator 904 and a lens 905 for optically modulating the light, and is reflected there to reach a Dove prism 907. The Dove prism 907 is an optical element that can adjust the interval between the passing laser beams LB1 and LB2 according to the magnitude of the rotation angle in the direction of arrow a. Laser beam LB passing through Dove prism 907
1, LB2 is deflected by a polygon mirror 910 rotating at a high speed via a cylindrical lens 909, and is exposed and scanned in the main scanning direction on the peripheral surface of a photosensitive drum 920 driven to rotate via an optical element group 911 such as an fθ lens. I do.

A CCD line sensor 908 for detecting a beam interval in the sub-scanning direction of the laser beams LB1 and LB2 for exposing and scanning the photosensitive drum 920 is arranged on the exposure scanning start end side on the photosensitive drum 920. Has been established. The CCD line sensor 908 outputs the laser beams LB1 and LB1 before the photosensitive drum 920 is exposed and scanned.
It is scanned by B2. In the CCD line sensor 908, a plurality of photoelectric conversion elements are arranged on a straight line at a predetermined pitch Sp (for example, 10 μm), and the arrangement direction is a direction (sub-scanning direction) orthogonal to the main scanning direction. .

FIG. 13B shows laser beams LB1 and LB.
FIG. 9 is a schematic diagram showing a state in which B2 performs exposure scanning on a CCD line sensor 908. S1 and S2 show beam spots when laser beams LB1 and LB2 are formed on a photosensitive drum 920, respectively. It is. FIG. 13 (c) shows the beam spots S1, S
FIG. 9 is a diagram showing a light intensity distribution when the light source 2 is positioned on the CCD line sensor 908. Here, the laser beam LB
1, LB2 is a Gaussian beam, and its light intensity has a normal distribution characteristic that is maximum at the center of the beam spot and decreases with distance from the center, and as shown in FIG. The light intensity differs depending on the photoelectric conversion element. Since the light intensity is maximized at the position of the center of the beam spot, the center is located at the photoelectric conversion element where the light intensity is maximized (in the figure, the tenth and eighteenth elements). become.).

Therefore, conventionally, which element is the photoelectric conversion element having the maximum light intensity is detected from the output distribution of the CCD line sensor 908, and whether or not the element interval is a predetermined beam interval is determined. If the interval is not the predetermined interval, the Dove prism 907 is rotated by a necessary amount in the direction of the arrow a so that the interval is reached, and the interval between the laser beams LB1 and LB2 is adjusted.

[0008]

However, the prior art described above has a problem that the accuracy of adjusting the beam interval is poor. This is because it is substantially determined that the center position of each of the beam spots S1 and S2 is located in a specific photoelectric conversion element (the tenth and eighteenth elements in the above description) in the element arrangement direction. Because they are not. For example, when the output value of the 10th photoelectric conversion element is maximized, the center may be located at the center position in the 10th element array direction, or the ninth or 11th position may be located from the center position. In some cases, it may be shifted to the element side. Nevertheless, in the conventional method, after detecting the two photoelectric conversion elements having the maximum output value, for example, the center position of these elements is determined in advance as a reference position when adjusting the beam interval. In this case, the position interval is detected and adjusted to a predetermined interval. Therefore, adjustment is performed for both elements in a state that includes an error of one pitch (10 μm) at the maximum, and the adjustment accuracy is deteriorated.

For example, in the case where the beam interval is adjusted to 42 μm in order to print at a resolution of 600 dpi in the sub-scanning direction by the above-described method, even if the Dove prism 90 is used.
7 is rotated at a fine angle, and the beam interval is set to 0.1 μm.
Even if the adjustment can be made in such a small unit, the beam interval varies in the range of 33 to 53 μm due to the above error. In this case, an image formed by exposing and scanning with the laser beams LB1 and LB2 becomes uneven in the sub-scanning direction, and the image quality is significantly deteriorated.

In order to solve such a problem, it is conceivable to increase the detection accuracy by using a high-density CCD line sensor having a device arrangement pitch of about 1 μm, which has been put into practical use in recent years, but this is extremely expensive. Because of this, the cost is greatly increased, which is not preferable. Also, the above problem,
Other than the field of the image forming apparatus, a plurality of light beams may be spaced at a predetermined interval, and may also occur in the field of an apparatus that needs to irradiate an object, such as a laser trimming apparatus. is there.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has an optical beam interval adjusting apparatus and an optical beam interval adjusting apparatus capable of adjusting the beam interval with high accuracy even if a sensor having low detection accuracy is used. It is an object of the present invention to provide a method and an image forming apparatus using the light beam interval adjusting device.

[0012]

In order to achieve the above object, according to the present invention, the positions of the first and second light beams are formed by arranging a plurality of photoelectric conversion elements on a straight line at an equal pitch. A light beam interval adjusting device that adjusts a beam interval at a target irradiation position of both beams so as to be a predetermined distance by detecting the beam by a beam detecting unit;
First moving means for relatively moving the first light beam and the beam detecting means so that the light beam moves in the arrangement direction of the photoelectric conversion elements; and A second moving means for moving in the arrangement direction; and a first light beam formed on the beam detecting means based on the output distribution of each photoelectric conversion element detected by the beam detecting means. The center of the first beam spot to be detected is located at the center position in the arrangement direction on the detection surface of one specific photoelectric conversion element or at an intermediate position between two specific adjacent photoelectric conversion elements. A first control means for controlling the first moving means;
The center of a second beam spot formed by irradiating the second light beam on the beam detecting means is based on the output distribution of each photoelectric conversion element detected by the beam detecting means, When the beam interval at the target irradiation position is a predetermined distance from the center position of the first beam spot, the detection surface of the photoelectric conversion element is separated by the inter-beam distance at the light beam detection position in the arrangement direction. A second control unit for controlling the second moving unit so as to be located at a center position or an intermediate position between two adjacent photoelectric conversion elements.

[0013] The first and second control means may include:
In each of the output distributions, when the output of one photoelectric conversion element is the maximum and the outputs of the photoelectric conversion elements before and after the output decrease substantially symmetrically, the center of the corresponding beam spot is It is determined that one photoelectric conversion element is located at the center in the arrangement direction, and the outputs of certain two photoelectric conversion elements are equal at the maximum, and the outputs of the photoelectric conversion elements before and after the two photoelectric conversion elements are substantially symmetrically reduced. A determination unit that determines that the center of the corresponding beam spot is located in the middle of the two photoelectric conversion elements, and uses the determination result of the determination unit to determine whether the center of the corresponding beam spot is the first or the second. The second moving means is controlled respectively.

When the distance between beams at the light beam detection position when the beam interval is a predetermined distance is L, and the arrangement pitch of the photoelectric conversion elements is D,
Optics for changing the optical distance between the light sources of the first and second light beams and the beam detecting means so that the relational expression of L = (nD / 2) (n is a natural number) is satisfied. A moving element for moving the beam detecting means along an optical path between a light source of the first and second light beams and the beam detecting means, and wherein the beam detecting means comprises the first and second light beams. At least one of tilting means for tilting the beam detecting means so as to tilt with respect to the traveling direction or the scanning direction of the second light beam is provided.

An image forming apparatus of a multi-beam exposure scanning system for forming an image on an image carrier by scanning a plurality of light beams at predetermined intervals in a sub-scanning direction. As an adjusting device, any one of the above-described light beam interval adjusting devices is used. Further, a first light beam and a second light beam are radiated to a beam detecting means configured by arranging a plurality of photoelectric conversion elements on a straight line at an equal pitch, and the beam is irradiated at an irradiation position on the beam detecting means. A light beam interval adjusting method for adjusting an interval between beams to a predetermined interval, wherein the first light beam is detected by the beam detection unit based on an output distribution of each photoelectric conversion element detected by the beam detection unit. The center of the first beam spot formed by irradiation on the means is located at the center position in the arrangement direction of the photoelectric conversion elements on the detection surface of the specific one photoelectric conversion element, or the specific adjacent two spots. A first step of relatively moving the first light beam and the beam detection means in the arrangement direction so as to be at an intermediate position between the photoelectric conversion elements;
The center of a second beam spot formed by irradiating the second light beam on the beam detecting means is based on the output distribution of each photoelectric conversion element detected by the beam detecting means, From the center of the first beam spot so as to be located at the center position in the arrangement direction of the detection surface of the photoelectric conversion element separated by the predetermined interval or at an intermediate position between two adjacent photoelectric conversion elements. Second
And a second step of moving the beam in the arrangement direction.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a beam interval adjusting apparatus and an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a perspective view illustrating an overall configuration of a scanning optical system in an image forming apparatus according to an embodiment of the present invention.

As shown in FIG. 1, the scanning optical system according to the present embodiment is a multi-beam scanning optical system using laser beams L1 and L2 emitted from laser diodes LD1 and LD2, respectively.
1, a light source unit 1 having an LD 2, a polygon mirror 3 rotating in the direction of arrow C, a scanning lens group 4 such as an fθ lens, and a CCD line sensor 20 for detecting laser beams L1 and L2.

Laser diodes LD1, LD of light source unit 1
Laser beams L1 and L2 respectively emitted from
The light beams are incident on a beam combiner 11 composed of a beam splitter in which two polished prisms are bonded to each other at an angle of about 90 °. Here, the laser beam L <b> 1 is deflected by 90 ° by the beam combiner 11 and travels toward the collimator lens 13. One laser beam L <b> 2 passes through the beam combiner 11 as it is and goes to the collimator lens 13. The laser beam L2 is transmitted to the beam combiner 11
Before the light beam reaches the beam position adjusting device 12. The beam position adjusting device 12 is used for displacing the position of the laser beam L2 in the sub-scanning direction in a beam interval adjusting process described later. The configuration of the beam position adjusting device 12 will be described later.

The laser beams L1 and L2 incident on the collimator lens 13 are converted into parallel rays here, and then condensed by the cylindrical lens 2 in the sub-scanning direction.
The light is reflected and deflected by the mirror surface of the polygon mirror 3 driven at high speed in the direction of arrow C by a polygon motor (not shown), and is rotated as an image carrier, for example, in the direction D via the scanning lens group 4 and the folding mirror 5. The surface of the photosensitive drum 6 is exposed and scanned in the main scanning direction (arrow Xs direction). In addition,
Since the laser beams L1 and L2 are both Gaussian beams, the beam intensity distribution of the beam spots S1 and S2 formed on the surface of the photosensitive drum 6 has a Gaussian distribution. Here, an image is formed at a resolution of 600 DPI. Therefore, the beam spot S1 by the laser beam L1 and the beam spot S1 by the laser beam L2 are formed.
The interval (hereinafter, this interval is referred to as “beam interval”) in the sub-scanning direction (the direction of the arrow Ys) between the center position (the position where the beam intensity is maximized) with respect to 2 is adjusted in the beam interval adjusting process. Is set to 42 μm.

At the exposure scanning start end of the photosensitive drum 6, at a position optically equivalent to the surface of the photosensitive drum 6,
A CCD line sensor 20 in which a plurality of photoelectric conversion elements are arranged in a sub-scanning direction in a state of being adjacent on a straight line is provided. The CCD line sensor 20 is used for detecting a beam interval between the laser beams L1 and L2 in the sub-scanning direction in the beam interval adjusting process.

In the beam interval adjusting process, the CCD line sensor 20 is adjusted by moving the CCD line sensor 20 in a direction parallel to the sub-scanning direction (the direction of arrow E). While being slidably held so as to be able to move smoothly without rattling on the sensor holding member 23 via the rail,
One end is a linear stepping actuator 2
It is connected to one shaft 22.

The linear stepping actuator 21 is provided with a motor driving section 55 of the control section 50 (see FIG. 5).
When the screw-shaped shaft 22 is rotated in response to a drive pulse output from the controller, the head position of the shaft 22 is configured to be able to advance and retreat in a linear direction (direction of arrow E) parallel to the axial direction. Is a known actuator. In the present embodiment, the amount of movement in the axial direction in one step is 10
μm, but 1/32 of 1 step angle
The CCD line sensor 20 is moved at a pitch of 0.31 μm by performing a known fine step drive capable of rotating the shaft 22 with an accuracy of (1). In addition,
The CCD line sensor 20 has a linear stepping
When the actuator 21 is not driven, a tension spring (not shown) for preventing the shaft 22 from rattling is engaged.

The photosensitive drum 6 is uniformly charged by removing the residual toner on the surface thereof before the above-mentioned exposure scanning, and is driven to rotate in the direction of arrow D in the uniformly charged state. When the exposure is performed, an electrostatic latent image is formed on the surface. The formed electrostatic latent image is developed and visualized as a toner image, for example, and the toner image is
After being transferred onto the conveyed recording sheet, the recording sheet is pressed and heated to be fixed. The recording sheet on which the toner image is fixed is discharged out of the apparatus, and the image forming operation ends.

The image forming apparatus according to the present embodiment is connected to an external computer (not shown), and a control unit 50, which will be described later, receives an image signal sent from the external computer, and The image data is generated by performing various processes, and a signal corresponding to the image data is output to the laser diodes LD1 and LD2 to emit the laser beams L1 and L2.

FIG. 2 is a diagram showing the configuration of the beam position adjusting device 12. This beam position adjusting device 12
The position of the laser beam L2 is displaced by utilizing refraction generated when the laser beam passes through a parallel plate made of optical glass. In the beam interval adjusting process, the position of the laser beam L2 is displaced using the beam position adjusting device 12 to adjust the beam interval. Hereinafter, the configuration of the beam position adjusting device 12 will be described.

The beam position adjusting device 12 comprises a parallel flat plate 121 and an adjusting plate holder 122 for holding the parallel flat plate 121 so as to be rotatable in the direction of arrow A or B about a rotary shaft 123.
And a swing arm 124 attached to the rotating shaft 123, and a linear stepping actuator 126 for swinging the swing arm 124. FIG.
FIG. 4 is a perspective view showing a part of an adjustment plate holder 122 and a swing arm 124 extracted therefrom.

As shown in both figures, a tension spring 125 is hung on one end of the swing arm 124.
The other end of the tension spring 125 is connected to the frame 128. The other end of the swing arm 124 is provided with a linear stepping actuator 12.
6 is in contact with the shaft 127 and moves forward and backward in the direction of arrow G, whereby the swing arm 124
It swings around 23.

This linear stepping actuator 126 is, like the linear stepping actuator 21 described above, an axis 1 corresponding to the drive pulse.
27 is moved forward and backward linearly. Therefore, for example, when the shaft 127 is advanced, the parallel flat plate 121 is tilted in the direction of arrow A via the swing arm 124. Conversely, when the parallel flat plate 121 is retracted, the parallel flat plate 121 tilts in the direction of arrow B.

Here, the movement amount per one step angle is 20 μm.
m by using a motor drive unit 57 (see FIG. 5) described later in fine step drive.
7 are made to advance and retreat at a pitch of 0.625 μm. FIG. 4 is a schematic diagram showing a state where the laser beam L2 is transmitted through the parallel flat plate 121 which is rotated in the direction of arrow B and tilted. The laser beam L2 incident on the inclined parallel plate 121 is refracted according to the angle of incidence and the refractive index of the parallel plate 121 based on Snell's law, and is displaced to a position shown by a broken line L2 '. At this time, the laser beam L2
Is displaced in the direction of arrow F shown in FIG. 1, which is the direction of arrow E on the CCD line sensor 20. On the other hand, when the parallel plate 121 is tilted in the direction of arrow A, the laser beam L2 is displaced in the direction opposite to the direction shown in FIG. As described above, when the parallel flat plate 121 is rotated in the direction of the arrow A or B, L2 formed on the CCD line sensor 20 is
Can be moved in the direction of arrow E. This movement amount is determined by the refractive index of the parallel flat plate 121 and the inclination angle of the parallel flat plate 121. Here, when the shaft 127 moves by one pitch,
The center of the beam spot S2 is configured to move 0.31 μm on the CCD line sensor 20.

FIG. 5 is a block diagram showing the configuration of the control unit 50. As shown in FIG.
1. Image data receiving unit 52, image memory 53, laser diode driving unit 54, motor driving units 55 and 57, CCD
It comprises a drive unit 56, a ROM 58, and a RAM 59.
The image data receiving unit 52 performs various image correction processes such as an edge enhancement process on the image data sent from the external computer, and then outputs the image data to the image memory 53 to store the image data.

The laser diode driving section 54 includes a CPU 5
In response to the instruction from the controller 1, the corrected image data is read from the image memory 53, and the laser diodes LD1 and LD2 are driven based on the image data to emit laser beams L1 and L2. The motor drive unit 55 generates a drive pulse for fine-step driving the linear stepping actuator 21. Since the generation of the driving pulse is a known technique, the description is omitted here.

The CCD driving section 56 outputs a driving pulse signal for driving the CCD line sensor 20. The motor driving unit 57 generates a driving pulse for causing the linear stepping actuator 126 to perform fine step driving. The ROM 58 stores a control program related to an image forming operation, a control program related to a beam interval adjusting process, and the like.

The CPU 51 reads out necessary programs from the ROM 58, performs data processing in the image data receiving unit 52, and controls the laser diode driving unit 54 to drive the laser diodes LD1 and LD2 to perform a smooth image forming operation. At the same time, a beam interval adjustment process is executed. In the beam interval adjusting process, the output signals of the respective photoelectric conversion elements sequentially sent from the CCD line sensor 20 are A / D converted to obtain the output values of the respective photoelectric conversion elements. In the management table.

The RAM 59 stores the output value data of each photoelectric conversion element sent from the CPU 51 in an internal management table. Next, the concept and method of adjusting the beam interval in the present embodiment will be described. FIG.
The laser beams L1 and L2 simultaneously emit the CCD line sensor 2
It is a schematic diagram which shows a mode when exposing and scanning on 0. Here, beam spots S1 and S2 in the figure show spot images in a range where the beam intensity is equal to or higher than a certain intensity on the CCD line sensor 20, respectively.
Reference numerals 1 and C2 denote the positions of the centers of the beam spots S1 and S2 (positions at which the beam intensity is maximized), and these intervals are the beam intervals Bp in the sub-scanning direction (rightward in the drawing). FIG. 3 shows a state where the beam interval Bp is adjusted to a predetermined interval (42 μm).

In the present embodiment, as one of the techniques for adjusting the beam interval, the photoelectric conversion elements (hereinafter simply referred to as “elements”) of the CCD line sensor 20 have a constant pitch (hereinafter referred to as “array pitch”). Utilizing the features arranged in Sp, the arrangement pitch Sp and the beam interval Bp (42 μm) to be adjusted are Bp = n · Sp (n
Is a natural number) (in this case, the relational expression is satisfied by using the CCD line sensor 20 having the arrangement pitch Sp of 8.4 μm). By setting the positions of the centers C1 and C2 to the center position in the sub-scanning direction of two elements (fifth and tenth elements in the figure) at positions separated by 5 pitches, respectively, The beam interval Bp is adjusted to a predetermined interval (hereinafter, the center position in the sub-scanning direction is simply referred to as “center position”). Therefore, in this method, the positions of the centers C1 and C2 are determined by using specific elements (fifth and first).
It is necessary to position the element at the center of the (0th element) with high precision.

Here, a method for positioning the centers C1 and C2 at the center of the element will be described. FIG. 7 is a schematic diagram showing a state where only the beam spot S1 is formed on the CCD line sensor 20 when the laser beam L1 is exposed and scanned on the CCD line sensor 20. The output distribution of the line sensor 20 is also shown. At this time, the output distribution of the CCD line sensor 20 is such that the fifth element is the largest, and the fourth, sixth, third and seventh outputs decrease symmetrically. This is because the laser beam L1 is a Gaussian beam, and the beam intensity of the beam spot S1 has a Gaussian distribution. Therefore, when the center C1 is located at the center of the fifth element, the beam spot S1
This is because the intensity distribution in the sub-scanning direction is symmetric with respect to the center position of the fifth element.

Therefore, for example, when the center C1 is shifted from the center position of the fifth element to a position close to the position adjacent to the adjacent fourth element, the output distribution does not become as shown in FIG. The fourth output is maximal, the fourth output is larger than the sixth output, and is no longer symmetric. That is,
When an output distribution is obtained such that the output of a specific element is maximized and the outputs of elements before and after the element are symmetrically reduced (hereinafter, such a distribution is referred to as a “symmetric distribution”). However, it can be said that the center C1 of the beam spot S1 is located at the center position of the specific element.
Therefore, if the output value of each element is obtained and the CCD line sensor 20 is moved in a direction parallel to the sub-scanning direction so that the output distribution becomes a symmetrical distribution, C1 can be set to exactly the fifth element. This means that it is located at the center position.

In such a method, it is desirable to use an actuator that can move the CCD line sensor 20 in as small a unit as possible. This is because the output distribution changes according to the amount of movement of the CCD line sensor 20. In the present embodiment, 0.31 μm
A linear stepping actuator 21 capable of moving the CCD line sensor 20 in units of m is used, which corresponds to about one-eighth of the width of one element (8.4 μm).

However, even when the output distribution is not completely symmetrical as shown in the figure, it is assumed that the center C1 is located almost at the center of the fifth element by making it the state closest to the symmetrical distribution. Can also be considered. Here, the case where the distribution is not completely symmetric means that the CCD line sensor 20 is used to make the fourth and sixth output values the same.
Is moved back and forth in units of 0.31 μm, but the output value is alternately large and small. Center C
In the case where 1 is located within a range of 0.31 μm before and after in the sub-scanning direction from the center position of the fifth element, the CCD
Even if the line sensor 20 is moved in units of 0.31 μm,
This is because the center C1 cannot be located exactly at the center of the fifth element. However, even in such a state, the center C1 is 0.31 μm from the center position.
Since the distance is within the range of m, considering that the width of one element is 8.4 μm, it is considered that the position may be substantially regarded as a substantially central position. Further, since the intensity distribution of the beam spot S1 is a Gaussian distribution, even if the center C1 is at a position slightly shifted from the CCD line sensor 20 in a direction parallel to the main scanning direction (vertical direction in the figure), for example. If the output distribution becomes symmetrical, it can be said that the center C1 is located at the center of the fifth element in the sub-scanning direction.

FIG. 8 is a schematic diagram showing a state where only the beam spot S2 is imaged on the CCD line sensor 20 when the laser beam L2 is exposed and scanned on the CCD line sensor 20. The output distribution of the CCD line sensor 20 at this time is also shown. The center C2 of the beam spot S2 can be located at the center of the tenth element by the same method as the center C1. That is, the output value of each element is acquired, and the linear stepping actuator 126 is used to adjust the parallel plate 12 so that the output distribution becomes a symmetric distribution state.
By rotating the laser beam 1 and moving the position of the laser beam L2 in parallel in the sub-scanning direction, the center C2 is positioned exactly at the center of the tenth element. In this embodiment, the position of the laser beam L2 can be moved in the CCD line sensor 20 in units of 0.31 μm using the above-described beam position adjusting device.

FIG. 9 is a flowchart showing the beam interval adjustment processing. In the present embodiment, this processing is executed at a predetermined timing, for example, when the power is turned on to the apparatus, or every time the image forming operation is performed a predetermined number of times, for example, 1000 times. First, CPU
51 rotates the polygon mirror 3 to drive the laser diode LD1 to light up (step S1). Then, the output signals of the respective elements when the laser beam L1 irradiates the CCD line sensor 20 are received, and the signals are transmitted to A / A.
D-convert to obtain the output value of each element (step S2),
These data are stored in a management table in the RAM 59. Then, referring to the management table, it is determined whether or not the output value of the specific element is the maximum and the output values of the elements before and after the specific element are the same (step S3).
That is, the output distribution becomes the symmetric distribution shown in FIG. 7 (the output value of the fifth element becomes maximum, the fourth and sixth output values become the same, and the output values of the third and seventh elements become the same. Is determined).

If it is not in this state (step S
3 to “N”), and supplies one drive pulse to the linear stepping actuator 21 so that the CCD line sensor 2
0 is moved by 0.31 μm (step S4). For example, if the output value of the fifth element is the largest and the output value of the sixth element is larger than the output value of the fourth element, the center C1 is within the fifth element. Is located at a position deviated from the central position by the sixth element, so that it is in the sub-scanning direction.

Steps S2 to S4 are repeated until the output distribution becomes a symmetric distribution. At this time, the contents of the management table in the RAM 59 are updated by overwriting the newly obtained output value data of each element with the previous data. When it is determined that the output distribution has become symmetrical ("Y" in step S3), the driving of the laser diode LD1 is stopped (step S5). By the above processing, the center C1 is located at the center of the fifth element.

Next, the CPU 51 sets the laser diode L
D2 is driven to light (step S6). Then, the output signals of the respective elements when the laser beam L2 irradiates the CCD line sensor 20 are received, and the signals are A / D converted to obtain the output values of the respective elements (step S7). Is stored in the management table in the RAM 59.

Then, with reference to the management table, the output value of the element (the tenth element) located at a position apart from the specific element (the fifth element) by the beam interval Bp becomes maximum, It is determined whether the output values are the same (step S8). That is, the output distribution is the symmetric distribution shown in FIG. 8 (the output value of the tenth element is the maximum, the ninth and eleventh output values are the same, and the output values of the eighth and twelfth elements are the same. State) is determined.

If it is not in this state (step S
At step S8, one drive pulse is supplied to the linear stepping actuator 126 (step S9) to rotate the parallel flat plate 121. For example, if the output value of the eleventh element is the maximum, it is necessary to move the laser beam L2 in a direction approaching the laser beam L1. It becomes the B direction.

The processes in steps S7 to S9 are repeated until the output distribution becomes a symmetric distribution. When it is determined that the output distribution becomes a symmetric distribution ("Y" in step S8), the rotation of the polygon mirror 3 is stopped, and the laser The driving of the diode LD2 is stopped (step S10), and the process ends. By the processing of steps S6 to S10, the center C2 is located at the center position of the tenth element, whereby the beam interval is adjusted to a predetermined interval (42 μm).

As described above, the output distribution of each element of the CCD line sensor 20 is such that the output value of a specific element is maximized, and the output values of the elements before and after that are reduced almost symmetrically. By adjusting the positions of the CCD line sensor 20 and the parallel plate 121 so as to obtain a distribution, the centers C1 and C2 are respectively located at the center positions of specific elements. The problem that caused an adjustment error because the element with the maximum was the element with the center of the beam spot could not be practically determined as to where the center of the element was located, The beam interval can be adjusted with extremely high accuracy.

In the above description, the beam interval B to be adjusted is
The case where p and the arrangement pitch Sp satisfy the relational expression of Bp = n · Sp (n is an integer) has been described. However, the book that specifies the center position of the beam spot by making the output distribution symmetrical. Using the idea of the invention, FIG.
As shown in FIG. 0, the center of the beam spot may be located at an adjacent position between two adjacent elements.

FIG. 9 shows the center C2 of the beam spot S2.
FIG. 9 is a diagram showing a state when the ninth and tenth elements are located adjacent to each other and an output distribution of each element at that time. When the center C2 is located adjacent to the ninth and tenth elements, the beam intensity distribution in the element arrangement direction of the beam spot S2 becomes symmetrical just at the adjacent position. The output value of the ninth element becomes maximum and equal, and the output values of the elements before and after the element are substantially symmetrically reduced (this can also be said to be a symmetrical distribution based on the ninth and tenth elements).

Therefore, if the position of the parallel plate 121 is adjusted so that the output distribution becomes the distribution shown in FIG.
Should be located at the adjacent position. In this case, since the center C1 is located at the center of the fifth element, the beam interval Bp is equal to 4.5 pitches.
In other words, by adjusting the center of the beam spot at an adjacent position of an adjacent element, it is possible to adjust even a unit of 1/2 pitch. Also, if this method is used, the center C1 can of course be located, for example, at a position adjacent to the fourth and fifth elements (in this case, the beam interval is the same as the above for five pitches). Thus, it can be adjusted to a predetermined 42 μm.)

As described above, in the method of locating the centers C1 and C2 at the center of a specific element or at the position adjacent to an adjacent element, Bp = (n / 2) .Sp (n
Is a natural number). This is because if the beam interval Bp is not an integral multiple of two times the element arrangement pitch, there is no point in adjusting to the center position or the adjacent position.

If only the CCD line sensor 20 having an arrangement pitch that does not satisfy the above relational expression can be used, for example, the beam interval adjusting process can be performed by using means as shown in FIG. FIG. 11 is a diagram showing an example of means for satisfying the above relational expression. FIG. 11A shows laser diodes LD1, LD
FIG. 3 is a diagram showing a case where an optical element for changing an optical distance between laser beams L1 and L2, for example, a cylindrical lens 7, is provided in the optical path between the CCD 2 and the CCD line sensor 20.

Here, Bp is a beam interval to be originally adjusted (a beam interval on the photosensitive drum 6), and does not satisfy the above relational expression. The cylindrical lens 7 is disposed at a position where the laser beams L1 and L2 pass only when entering the CCD line sensor 20. Here, when the laser beams L1 and L2 pass through the cylindrical lens 7, their optical distances are changed, and the beam interval Bp 'on the CCD line sensor 20 becomes an integer equal to a half of the array pitch Sp. I try to double. Then, the beam intervals Bp and C to be adjusted
Bp 'on the CD line sensor 20 is associated with the center C1, C2 of the beam spots S1, S2 on the CCD line sensor 20 in the beam interval adjustment processing.
By adjusting the interval to Bp ', the beam interval Bp to be essentially adjusted is adjusted.

FIG. 11B shows laser beams L1 and L2.
An example in which the above relational expression is satisfied by moving the position of the CCD line sensor 20 along the optical path of FIG. Bp and Bp ′ shown here correspond to those in FIG.
It is the same as (a). Since the CCD line sensor 20 is moved along the optical path, it is suitable when the incident angles of the laser beams L1 and L2 on the CCD line sensor 20 are different. Further, instead of moving the CCD line sensor 20 along the optical path, the CCD line sensor 20 may be inclined with respect to the optical path.

FIG. 11C shows the CCD line sensor 20.
Is tilted with respect to the scanning direction of the laser beams L1 and L2. Here, the scanning direction is the left direction in FIG. By tilting the CCD line sensor 20 in this manner, the arrangement pitch Sp becomes as if Sp ′ (= S
p · cos θ).
Can be changed to satisfy the above relational expression.

The means shown in FIGS. 11 (a) to 11 (c) are not limited to being used only for satisfying the above-mentioned relational expressions. For example, resolution conversion (for example, from 600 dpi to 4
(Conversion to 00 dpi). When changing the beam interval Bp by resolution conversion, for example, 4
Only when the resolution is 00 dpi, the cylindrical lens 7 is interposed in the optical path using a moving mechanism,
Moving the CCD line sensor 20 along the optical path,
Alternatively, the CCD line sensor 20 is set to the laser beam L1,
By tilting with respect to the traveling direction or scanning direction of L2, the beam interval B corresponding to each resolution is obtained.
The relationship between p and the arrangement pitch Sp can be the above relationship.

It is needless to say that the present invention is not limited to the above embodiment, and the following modified examples can be considered. (1) In the above embodiment, two laser beams L1,
Although the scanning optical system for exposing and scanning L2 has been described, the present invention can be applied even when three or more laser beams are used.
For example, in the case of three laser beams, the distance between the first and second laser beams may be adjusted, and then the distance between the first and third laser beams may be adjusted in the same manner.

(2) In the above embodiment, the CCD line sensor 20 is moved by the linear stepping actuator 21 so that the center C1 of the beam spot S1 is located at the center of a specific element. Instead of using an actuator, a device capable of linearly moving the CCD line sensor 20 at a fine pitch, for example, a linear motor may be used.

Further, since it is sufficient if the irradiation position of the laser beam L1 on the CCD line sensor 20 in the sub-scanning direction can be moved, for example, the CCD
The line sensor 20 may be fixed, and the same one as the beam position adjusting device 12 may be arranged in the optical path between the laser diode LD1 and the CCD line sensor 20.

In the beam position adjusting device 12,
The laser beam L2 is a parallel flat plate 121 made of optical glass.
Although the position of the laser beam L2 is displaced by using refraction when transmitting the laser beam, the method of displacing the position is not limited to this. For example, by moving the laser diode LD2 itself in fine units, the position irradiated on the CCD line sensor 20 can be changed as shown in FIG.
Or the Dove prism used in the above-described conventional technique may be provided in place of the beam position adjusting device 12. Further, a new collimator lens may be disposed between the laser diode LD2 and the beam combiner 11, and the collimator lens may be moved. Conversely, the beam synthesizer 11 can be moved to displace the position of the laser beam L1.

In short, in the beam position adjustment processing,
It is sufficient that the irradiation position of each laser beam on the CCD line sensor 20 can be finely adjusted in the sub-scanning direction for each laser beam. (3) The beam interval adjustment processing may be executed forcibly at a time other than the determined timing, for example, at the time of manufacturing an apparatus. Further, it may be appropriately performed according to the amount of change in temperature around the scanning optical system.
Since a temperature detecting means such as a thermistor is provided in the scanning optical system, the detection signal is continuously obtained by the control unit 50, and when the temperature change exceeds a predetermined change amount, the beam interval adjustment processing is executed. is there. In this way, even if the holding member of the laser diode LD1 expands and contracts due to a temperature change, the beam interval is reliably adjusted to the predetermined interval. Further, a sensor capable of detecting a change in humidity may be arranged together.

(4) In the above-described embodiment, the CCD line sensor 20 is provided at a position close to the exposure start end of the photosensitive drum 6, but is not limited to this position. For example, the CCD line sensor 20 may be disposed at a position directly below the beam combiner 11 shown in FIG. 1 and the element arrangement direction is parallel to the optical path of the laser beam L2. In this case, when the laser beams L1 and L2 pass through the beam combiner 11, a part of the light is separated from the light directed to the photoconductor drum 6 so as to travel below the beam combiner 11. And this light is C
Detection is performed by the CD line sensor 20. And
If the CCD line sensor 20 is configured to be able to move in the element array direction as described above, the beam interval can be adjusted by the same processing as described above.

By arranging the CCD line sensor 20 at this position, the beam interval adjustment can be performed without scanning the laser beam, so that it is not necessary to rotate the polygon mirror 3 during the adjustment. However, the beam interval adjusted at this position and the photosensitive drum 6
Since the above beam interval is not always the same, it is necessary to make an adjustment after relating them in advance.

(5) In the above embodiment, the CCD line sensor 20 is used as means for detecting the laser beams L1 and L2. However, the detecting means is not limited to this, and an element having a photoelectric conversion function may be used. For example, a two-dimensional CCD
It can also be applied to area sensors and photodiode arrays. Also, without making multiple photodiodes adjacent,
It is also conceivable to arrange them at regular intervals. In this case, the center of the beam spot is located at an intermediate position between the two photodiodes instead of the adjacent position.

Further, the photodiodes may be arranged at a position interval as shown in FIG. In the figure, photodiodes 81 and 82, 83 and 84, 8
5 and 86 are adjacent to each other, but 82 and 83, 8
Nos. 4 and 85 are arranged at intervals of k (k is an integer of 2 or more) times the arrangement pitch Sp. Thus, even if the photodiodes are arranged at intervals, the center of the beam spot can be located, for example, at a position adjacent to 83 and 84. In this case, the output value of 83 and 84 is maximized, and the output value of 82 and 85 is the same, and the output value of 81 and 86 is the same so that the output distribution becomes the same (distribution as shown in FIG. 10). What is necessary is just to adjust the position of a laser beam. Similarly, it can be located at an intermediate position between 82 and 83. That is, when the center of the beam spot is adjusted to an adjacent position or an intermediate position of the photodiode, the photodiode can be arranged in this way, and no photodiode is arranged between 82 and 83 and between 85 and 86. The cost can be reduced by the amount.

(6) In the above embodiment, in the image forming apparatus having the multi-beam scanning optical system, the beam interval between the laser beams L1 and L2 to be exposed and scanned is adjusted. The adjusting device is not limited to the field of the image forming apparatus, and a device that needs to irradiate an object, for example, irradiates a target with an object, for example, a laser beam at intervals of a plurality of light beams. The present invention can also be applied to fields such as a laser etching apparatus and a laser trimming apparatus that perform removal processing. When applied to such an apparatus, depending on the magnitude of the output of the laser beam, beam detection means such as a CCD sensor may be destroyed. Therefore, adjusting the beam interval weakens the output of the laser beam. It is desirable to be performed in the state where it was carried out.

[0068]

As described above, according to the present invention, the center of the first beam spot formed by irradiating the first light beam on the beam detecting means is defined as follows.
The first moving means for controlling the first moving means so as to be located at the center position in the arrangement direction on the detection surface of one specific photoelectric conversion element or at an intermediate position between two specific adjacent photoelectric conversion elements. And a second light beam formed by irradiating the second light beam onto the beam detecting means.
The center of the beam spot of the photoelectric conversion element is separated from the center of the first beam spot by the distance between the beams at the light beam detection position when the beam interval at the target irradiation position is a predetermined distance. And a second control means for controlling the second moving means so as to be located at a center position of the detection surface in the arrangement direction or an intermediate position between two adjacent photoelectric conversion elements. Since the photoelectric conversion element having the maximum output value as described in (1) was merely determined as the element having the center of the beam spot, it was not possible to determine the position of the center of the element. Will not occur,
The distance between beams at the light beam detection position when the beam interval becomes a predetermined distance can be adjusted with extremely high precision in a unit of の of the arrangement pitch of the photoelectric conversion elements.

Further, the first and second control means include:
In each of the output distributions of the photoelectric conversion elements detected by the beam detecting means, the output of a certain photoelectric conversion element is the largest, and the outputs of the photoelectric conversion elements before and after the output decrease substantially symmetrically. In this case, it is determined that the center of the corresponding beam spot is located at the center of the one photoelectric conversion element in the arrangement direction, and the outputs of certain two photoelectric conversion elements are equal at the maximum, And determining means for determining that the center of the corresponding beam spot is located in the middle of the two photoelectric conversion elements when the output of the photoelectric conversion element decreases substantially symmetrically. The first or second moving means is controlled by using the determination result of the above. Therefore, if the light beam is symmetrical when the beam intensity of the beam spot is centered on a certain position, for example, the beam intensity Distribution even be as close to the triangle instead of chevron, that the center of the beam spot is located at the position of the central or intermediate can be accurately determined.

Also, an optical element for changing an optical distance between the light source of the first and second light beams and the beam detecting means, a light source of the first and second light beams and the beam detecting means, Third moving means for moving the beam detecting means along the optical path between
And at least one of the tilting means for tilting the beam detecting means so as to tilt with respect to the traveling direction or the scanning direction of the second light beam, so that the distance between beams at the light beam detecting position is L, When the arrangement pitch of the photoelectric conversion elements is D, L = (n · D / 2) (n
Is a natural number).

Further, the image forming apparatus adopting the multi-beam exposure scanning method uses the light beam interval adjusting device according to the present invention as the device for adjusting the interval between beams to a predetermined interval, so that the beam interval can be adjusted accurately. As a result, scanning pitch unevenness in the sub-scanning direction does not occur, and high-quality image formation can be performed.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an overall configuration of a scanning optical system in an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a beam position adjusting device.

FIG. 3 is a perspective view showing an adjustment plate holder and a swing arm disposed in the beam position adjustment device.

FIG. 4 is a schematic diagram showing a state when a laser beam L2 is transmitted through a parallel flat plate that is rotated in the direction of arrow B and tilted.

FIG. 5 is a block diagram illustrating a configuration of a control unit.

FIG. 6 is a schematic diagram showing a state when laser beams L1 and L2 are simultaneously exposed and scanned on a CCD line sensor.

FIG. 7 is a diagram showing a state where only the beam spot S1 is formed on the CCD line sensor and a state of an output distribution of the CCD line sensor at that time.

FIG. 8 is a diagram showing a state where only the beam spot S2 is formed on the CCD line sensor and a state of an output distribution of the CCD line sensor at that time.

FIG. 9 is a flowchart illustrating a beam interval adjustment process.

FIG. 10 shows a beam spot S2 at a position different from that of FIG.
FIG. 3 is a diagram showing a state when an image is formed and a state of an output distribution of the CCD line sensor at that time.

FIG. 11A shows two laser diodes and a CCD.
In the optical path between the line sensors, the laser beams L1 and L2
FIG. 4 is a diagram showing an example in which an optical element that changes the optical distance from the optical element is provided. (B) is a diagram showing a state where the position of the CCD line sensor is moved along the optical path of the laser beams L1 and L2. (C) is a diagram showing an example in which the CCD line sensor is tilted with respect to the scanning direction of the laser beams L1 and L2.

FIG. 12 is a diagram showing an example in which photodiodes are arranged in a straight line instead of a CCD line sensor.

FIG. 13A is a diagram illustrating a schematic configuration of a conventional laser printer, and FIG. 13B is a diagram illustrating a state where laser beams LB1 and LB2 are exposed and scanned on a CCD line sensor in the laser printer. FIG.
(C) is a diagram showing a light intensity distribution when the beam spots S1 and S2 are located on the CCD line sensor.

[Explanation of symbols]

 Reference Signs List 6 photosensitive drum 7 cylindrical lens 11 beam combiner 12 beam position adjuster 13 collimator lens 20 CCD line sensor 21, 126 linear stepping actuator 22, 127 axis 23 sensor holding member 50 control unit 51 CPU 52 image data receiving unit 53 image memory 54 Laser diode drive unit 55, 57 Motor drive unit 56 CCD drive unit 58 ROM 59 RAM 81 to 86 Photodiode 121 Parallel plate 122 Adjustment plate holder 123 Rotation axis 124 Swing arm C1, C2 Center position of beam spot L1, L2 Laser beam LD1, LD2 Laser diode S1, S2 Beam spot

Claims (5)

[Claims] 1. A target irradiation of both beams by detecting the positions of the first and second light beams by a beam detecting means configured by arranging a plurality of photoelectric conversion elements on a straight line at an equal pitch. A light beam interval adjusting device that adjusts a beam interval at a position to be a predetermined distance, wherein the first light beam and the first light beam are moved so that the first light beam moves in an array direction of the photoelectric conversion elements. First moving means for relatively moving the beam detecting means;
Second moving means for moving the light beam in the arrangement direction, and the first light beam is irradiated on the beam detecting means based on an output distribution of each photoelectric conversion element detected by the beam detecting means. The center of the first beam spot formed as a result is located at the center position in the arrangement direction on the detection surface of one specific photoelectric conversion element, or at an intermediate position between two specific adjacent photoelectric conversion elements. A first control unit that controls the first moving unit so that the second light beam is located at a position of the second light beam based on an output distribution of each photoelectric conversion element detected by the beam detection unit. The center of the second beam spot formed by irradiating the beam on the beam detecting means is positioned at a distance from the center of the first beam spot to the beam interval at the target irradiation position. At the center of the detection surface of the photoelectric conversion elements separated by the inter-beam distance at the light beam detection position when the light beam is detected, or at an intermediate position between two adjacent photoelectric conversion elements. And a second control means for controlling the second moving means. 2. The first and second control means are arranged such that the output distribution is such that the output of a certain photoelectric conversion element is maximum, and the outputs of photoelectric conversion elements before and after the output distribution are substantially symmetric. When decreasing, it is determined that the center of the corresponding beam spot is located at the center of the one photoelectric conversion element in the arrangement direction, and the outputs of certain two photoelectric conversion elements are equal at the maximum. And determining means for determining that the center of the corresponding beam spot is located in the middle of the two photoelectric conversion elements when the output of the photoelectric conversion element before and after the photoelectric conversion element decreases substantially symmetrically. 2. The light beam interval adjusting device according to claim 1, wherein each of the first and second moving units is controlled using a result of the judgment by the judging unit. 3. When the distance between beams at the light beam detection position when the beam interval is a predetermined distance is L, and the arrangement pitch of the photoelectric conversion elements is D, L =
An optical element for changing an optical distance between a light source of the first and second light beams and a beam detecting means so that a relational expression of (nD / 2) (n is a natural number) is satisfied. A third moving means for moving the beam detecting means along an optical path between a light source of the first and second light beams and the beam detecting means, and wherein the beam detecting means comprises the first and second light beams. 3. The apparatus according to claim 1, further comprising at least one of tilting means for tilting said beam detecting means so as to tilt with respect to a traveling direction or a scanning direction of the light beam.
The light beam interval adjusting device according to claim 1. 4. An image forming apparatus of a multi-beam exposure scanning system for forming an image on an image carrier by scanning a plurality of light beams at predetermined intervals in a sub-scanning direction. An image forming apparatus using the light beam interval adjusting device according to claim 1 as an adjusting device. 5. A first light beam and a second light beam are radiated to a beam detecting means constituted by arranging a plurality of photoelectric conversion elements on a straight line at an equal pitch, and the beam is irradiated on the beam detecting means. A light beam interval adjusting method for adjusting an interval between each beam at an irradiation position to a predetermined interval, wherein the first light beam is adjusted based on an output distribution of each photoelectric conversion element detected by the beam detecting unit. The center of the first beam spot formed by irradiating the beam detecting means is located at the center of the detection surface of one specific photoelectric conversion element in the center of the arrangement direction of the photoelectric conversion elements, or at a specific position. A first moving means for relatively moving the first light beam and the beam detecting means in the arrangement direction so as to be at an intermediate position between two adjacent photoelectric conversion elements;
And a second beam spot formed by irradiating the second light beam onto the beam detection means based on the output distribution of each photoelectric conversion element detected by the beam detection means. The center is located at the center of the detection surface of the photoelectric conversion element separated by the predetermined distance from the center of the first beam spot in the arrangement direction or at an intermediate position between two adjacent photoelectric conversion elements. So that the second
A second step of moving the light beam in the arrangement direction.