JPH11277793A - Beam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a beam scanner in which beam pitch can be corrected in the sub-scanning direction of two beams using single optical path correcting means and single sensor. SOLUTION: The beam scanner comprises a beam splitter 5 for aligning the optical axis of beams 21, 22, a sensor section 10 for detecting the output level of the beams 21, 22 arranged on the optical path of two beams 21, 22 emitted from the beam splitter 5, a knife edge 32 for intercepting the two beams 21, 22 directed from the beam splitter 5 toward the sensor section 10 disposed at a position equivalent optically to the deflecting face between the beam splitter 5 and the sensor section 10, and a control means 34 for determining the threshold value of the other beam 22 at a correct beam pitch based on the output level of the beam 21 not subjected to optical path correction by an optical path correcting means 33 and moving a cylindrical lens 6b through the means 33 to equalize the output level of the beam 22 with the threshold value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam scanning apparatus such as an electrophotographic apparatus for forming an image by beam scanning.

[0002]

2. Description of the Related Art Conventionally, a beam scanning optical system has been used for image writing in an electrophotographic process, and is mounted on a laser beam printer, a laser facsimile, etc. which are output devices of a computer or a facsimile. Recently, in order to further increase the speed and the resolution, the demand for a beam scanning device that scans a plurality of beams is increasing.

A conventional beam scanning device for scanning a multi-beam will be described below. As shown in FIG.
And a drive circuit 24 for driving the second light source 1b to irradiate the beam 22 by driving the light source 1a. Then, the beam 21 from the first light source 1a and the second light source 1b
Irradiating the photosensitive drum 18 with a beam 22, an electrostatic latent image is formed on the scanned surface 18 a of the photosensitive drum 18 that is uniformly charged. A collimator lens 2a is arranged corresponding to the first light source 1a, and a collimator lens 2b is arranged corresponding to the second light source 1b. Beams 21 and 22 from each of the light sources 1a and 1b are arranged by these collimator lenses. 2
The light is made parallel by a and 2b.

Prisms 3a and 3b for adjusting the pitch in the sub-scanning direction of the beams 21 and 22 from the light sources 1a and 1b are provided on the optical paths of the beams 21 and 22 having passed through the collimator lenses 2a and 2b. A beam splitter 5 for aligning the optical axes of the beams 21 and 22 emitted from 1a and 1b is provided. Optical path correction means 4a and 4b are provided corresponding to the prisms 3a and 3b, respectively, for rotating the prisms 3a and 3b to adjust the pitch of the beams 21 and 22 in the sub-scanning direction to a predetermined interval. ing.

Further, on the optical path of the beams 21 and 22 from the beam splitter 5 to the photosensitive drum 18, a cylindrical lens 6 and a cylindrical lens 6 for condensing the beams 21 and 22 emitted from the beam splitter 5 in the sub-scanning direction. A deflector 7 having a deflecting surface 25 in the vicinity of the light condensing point and deflecting the two beams 21 and 22 at the same time. The beams 21 and 22 deflected by the deflector 7 are condensed on the surface 18a to be scanned of the photosensitive drum 18. A scanning lens system 8 for scanning and a mirror 19 for guiding the beams 21 and 22 to the surface to be scanned 18a are sequentially arranged.

At positions optically equivalent to the deflecting surface 25 on the optical path of the beams 21 and 22 emitted from the beam splitter 5 in a direction different from the deflecting surface 25, the beams 21 and 22 in the sub-scanning direction are arranged. A sensor unit 10 for detecting a pitch interval is provided. The sensor unit 10 includes a two-divided sensor 11 for matching the beam 21 from the first light source 1a and a two-divided sensor 12 for matching the beam 22 from the second light source 1b. The beams 21 and 22 are respectively applied to the boundaries between the corresponding two-split sensors, that is, between the light receiving surfaces 13 and 14 of the two-split sensor 11 and between the light receiving surfaces 15 and 16 of the two-split sensor 12. Thus, the alignment is performed by the prisms 3a and 3b. Note that the two-divided sensors 11 and 12 are
In FIG. 2, the pixels are fixed to each other in the sub-scanning direction by an amount corresponding to a predetermined pitch.

The beam 21 scanned by the deflector 7
In order to synchronize the main scanning direction 22, a synchronization detector 9 is provided. And, by this synchronization detector 9,
Irradiation of the beams 21 and 22 corresponding to the image data at the timing of a predetermined time is performed by the driving circuit 2 of each of the light sources 1a and 1b.
3, 24. Further, the prism 3a is rotated based on a signal from the sensor unit 10, and the beams 21 and
2 a control circuit 17 for controlling the beam pitch in the sub-scanning direction
Is provided. Members other than the photosensitive drum 18 are accommodated in the housing 20.

The operation of the beam scanning device having the above-described configuration will be described below.

In a multi-beam beam scanning apparatus, it is a major problem to keep the interval between two beams 21 and 22 scanning simultaneously in the sub-scanning direction at several tens of μm, and the scanning apparatus has a means for achieving this. It is included. This is because even if the two beams 21 and 22 are adjusted so as to have a predetermined beam pitch at the time of assembling the optical system, the beam pitch is easily shifted due to a change with time, deformation or distortion of the unit after the device is mounted. This is because it is necessary to correct the beam pitch after assembly.

The beams 21 and 22 emitted from the first light source 1a and the second light source 1b in FIG.
The beam is adjusted to a parallel beam by the collimator lenses 2a and 2b. Next, the beams 21 and 22 are converted into prisms 3a and 3
The optical path is changed by b, and the pitch in the sub-scanning direction is adjusted to a predetermined interval.

The beams 21 and 22 transmitted through the prisms 3a and 3b have their optical axes aligned by a beam splitter 5, and are condensed by a cylindrical lens 6 in the sub-scanning direction. The light is condensed in this manner because the deflecting surface 25 of the deflector 7 has a slight inclination depending on each surface (hereinafter, referred to as “surface tilt”).
This is for imparting an optical conjugate relationship with 8a to mitigate the effects of surface tilt. Then, the deflection surface 25 and the scanned surface 18
Since a has a conjugate relationship in the sub-scanning direction, the two beam pitches on the deflection surface 25 are projected onto the surface to be scanned 18a at the magnification of the scanning lens system 8 in the sub-scanning direction. Therefore, by controlling the two beam pitches on the deflection surface 25, the beam pitch on the scanned surface 18a can be corrected.

Here, the positioning of the beams 21 and 22 in the sub-scanning direction will be described. As described above, the sensor unit 10 that detects the sub-scanning position of each of the beams 21 and 22 is provided on the deflecting surface 25 on the optical path of the beams 21 and 22 emitted from the beam splitter 5 in a direction different from the direction of the deflecting surface 25. It is provided at a position optically equivalent to. The sensor unit 10
Is composed of a two-divided sensor 11 and a two-divided sensor 12,
Each of the beams 21 and 22 is aligned with the boundary of the corresponding two-part sensor. Further, the two-split sensor 11 and the two-split sensor 12 are fixed to be shifted in the sub-scanning direction.

In order to align the beam 21 from the first light source 1a with the two-divided sensor 11 using such a sensor section 10, first, only the first light source 1a is driven by the drive circuit 23, The beam 21 is applied to the two-divided sensor 11. At this time, the prism 3a is rotated by the signal of the control circuit 17 so that the output for the light amount of the light receiving surface 13 and the output for the light amount of the light receiving surface 14 are at the same level, and the optical path of the beam 21 of the first light source 1a is changed. Change to the sub scanning direction.

FIG. 7 shows the relationship between the beam position and the output of the light receiving surface when the beam position is adjusted using the two-split sensor.

As shown in FIG. 7A, when the beam 21 is on the light receiving surface 13, the output level from the light receiving surface 13 is higher than that on the light receiving surface 14, and the light receiving surface 14 is viewed from the light receiving surface 13. And the output difference is a positive value. On the contrary, as shown in FIG.
Side, the output level of the light receiving surface 14 is
And the output difference from the light receiving surface 14 as viewed from the light receiving surface 13 appears as a negative value. Therefore, the current beam position and beam moving direction can be determined from the difference in output level between the light receiving surfaces 13 and 14, and the prism 3a is rotated while the control circuit 17 controls the optical path correcting means 4a.

The change of the optical path by the prism 3a is performed by changing the position of the beam 21 on the deflection surface 25 in the sub-scanning direction by changing the angle of the prism 3a in the sub-scanning direction. Then, as shown in FIG. 7B, when the output levels of the light receiving surface 13 and the light receiving surface 14 become the same, the prism 3
The rotation of a is stopped. At this time, the center of the beam 21 is aligned with the boundary between the light receiving surfaces 13 and 14. As described above, the position of the beam from the first light source 1a is corrected to a predetermined position by rotating the prism 3a.

The beam 22 from the second light source 1b is also
The same operation as in the optical path correction of the beam 21 of the light source 1a is performed to match the boundary between the light receiving surfaces 15 and 16 of the two-divided sensor 12.

Two-split sensor 1 having light receiving surfaces 13 and 14
1 and the two-divided sensor 12 having the light receiving surfaces 15 and 16 are displaced in the sub-scanning direction by a predetermined amount (the pitch amount on the surface to be scanned 18a).
The two beams 21 and 22 for scanning a have an appropriate interval (see FIG. 8).

Such an optical path correction for adjusting the beam pitch of each of the beams 21 and 22 is performed before the beams 21 and 22 actually scan the scanned surface 18a. For example, when this beam scanning device is used for writing in a laser printer, a printing start signal is input, and the printing is performed within a time period in which the rotation of the deflector 7 is stabilized.

When the optical path correction of the two beams 21 and 22 is completed and the beam pitch becomes a predetermined interval, the beam irradiation corresponding to the image data is performed on the scanned surface 18a. As described above, after the printing start signal is input, the driving of the deflector 7 is stabilized, and after the conditions of other units related to image formation (OPC unit, developing unit, fixing unit, etc.) are set, such a condition is satisfied. Beam irradiation on the scanned surface 18a starts.

The two beams 21 and 22 scanned by the deflector 7 are synchronized in the main scanning direction by a synchronization detector 9 provided at a position before scanning the image area.
Light irradiation corresponding to the image data is performed by the drive circuits 23 and 24 of the light sources 1a and 1b at a predetermined time. Since the scanned surface 18a moves in the sub-scanning direction, a two-dimensional image is formed on the scanned surface 18a by light irradiation with the two beams 21 and 22. Since the beam pitch is at an appropriate interval, a uniform image can be obtained as shown in FIG. As a comparative example, an image when the beam pitch is shifted is shown in FIG.
Shown in

As described above, according to the multi-beam scanning optical system, the surface 18 to be scanned is
Since an image is formed on a, high-speed or high-resolution beam scanning can be performed as compared with one beam scanning.

[0023]

However, in the conventional configuration as described above, it is necessary to provide optical path correction means 4a and 4b in the optical paths of the beams 21 and 22 in order to adjust the two beam pitches. As a result, the cost of the apparatus increases.

Further, since a space for mounting the optical path correcting means 4a and 4b is required, the degree of freedom in designing the layout of the optical system is limited.

Further, since a large number of sensors are required to adjust the two beam pitches, the cost of the apparatus also increases in this respect.

Accordingly, it is an object of the present invention to provide a beam scanning device capable of performing beam pitch correction of two beams in the sub-scanning direction with a single optical path correcting means using a single sensor. .

[0027]

In order to solve this problem, a beam scanning apparatus according to the present invention comprises two light sources for irradiating a beam, and two driving circuits for independently driving the light sources to irradiate the beam. Are installed corresponding to the respective beams emitted from the light source, are provided with two collimator lenses for converting these beams into parallel light, and are installed corresponding to the respective beams emitted from the collimator lens. Two cylindrical lenses that converge in the scanning direction, an optical path correcting unit that moves one of the cylindrical lenses in the sub-scanning direction to correct the optical path of the beam passing through the cylindrical lens, and light emitted from the cylindrical lens. A beam splitter that matches the optical axes of two beams, and a cylinder of two beams emitted from the beam splitter A deflector having a deflecting surface near the focal point of the cull lens and deflecting these beams, a scanning lens system for scanning the two beams deflected by the deflector on the surface to be scanned, and main scanning of the two beams A synchronization detector that detects synchronization of directions, a sensor unit that is provided on an optical path of two beams emitted from the beam splitter in directions different from the deflection surface, and detects output levels of these beams, and a beam splitter. A knife edge that is installed at a position optically equivalent to the deflecting surface between the sensor unit and shields two beams from the beam splitter toward the sensor unit, and the output level of the beam that is not optical path corrected by the optical path correction unit. A threshold value of the other beam at an appropriate beam pitch is obtained based on the calculated value, and the threshold value is set via the optical path correcting means so that the output level of the other beam becomes equal to the obtained threshold value. It is obtained by a control means for moving the command helical lens.

This makes it possible to correct the beam pitch of the two beams in the sub-scanning direction with a single optical path correcting means using a single sensor.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, two light sources for irradiating a beam, two driving circuits for independently driving the light sources to irradiate a beam, and a light source for irradiating a beam are provided. Two collimator lenses are installed corresponding to the respective beams and collimate these beams, and are installed corresponding to the respective beams emitted from the collimator lenses, and collect these beams in the sub-scanning direction. Two cylindrical lenses, an optical path correcting means for moving one of the cylindrical lenses in the sub-scanning direction to correct the optical path of a beam passing through the cylindrical lens, and an optical axis of the two beams emitted from the cylindrical lens And a beam splitter for matching the two beams emitted from the beam splitter near the focal point of the cylindrical lens. A deflector for deflecting these beams, a scanning lens system for scanning the two beams deflected by the deflector on the surface to be scanned, and a synchronous detection for detecting the synchronization of the two beams in the main scanning direction A beam splitter, a sensor section provided on an optical path of two beams emitted in directions different from the deflection surface from the beam splitter, and detecting an output level of these beams; and a deflection surface between the beam splitter and the sensor section. And a knife edge for blocking two beams from the beam splitter toward the sensor unit, and a beam pitch at an appropriate beam pitch based on the output level of the beam that is not optical path corrected by the optical path correction unit. The threshold value of the other beam is obtained, and the cylindrical lens is moved via the optical path correction means so that the output level of the other beam becomes equal to the obtained threshold value. A beam scanning device provided with a control unit, wherein only one of the beams is movable in the sub-scanning direction by an optical path correcting unit, and an output level of the beam that cannot be moved in the sub-scanning direction is detected by a sensor unit. Since the output level is adjusted by correcting the optical path of the beam movable in the sub-scanning direction to the threshold at the appropriate beam pitch determined from the level, the beam pitch correction of the two beams in the sub-scanning direction can be performed in a single unit. This has the effect that the optical path correction means can be performed using a single sensor.

According to a second aspect of the present invention, in the first aspect, the control means selects a beam pitch selected from a plurality of thresholds set corresponding to the plurality of beam pitches. This is a beam scanning device that moves a cylindrical lens via an optical path correction unit so that the output level of the other beam becomes the threshold value corresponding to the threshold value, and the selection of the threshold value without adding a new sensor or manufacturing a new sensor. This has the effect that the beam pitch can be set to an arbitrary distance by just using this.

According to a third aspect of the present invention, there are provided two light sources for irradiating a beam, two driving circuits for independently driving the light sources to irradiate the beam, and Two collimator lenses that are installed correspondingly to make these beams parallel, and are installed corresponding to each beam emitted from the collimator lens,
Two cylindrical lenses for condensing these beams in the sub-scanning direction, and optical path correction means for moving one of the cylindrical lenses in the sub-scanning direction and correcting the optical path of the beam passing through the cylindrical lens, A beam splitter for matching the optical axes of the two beams emitted from the cylindrical lens, a deflector having a deflection surface near the converging point of the cylindrical lens for the two beams emitted from the beam splitter, and deflecting these beams; A scanning lens system that scans the two beams deflected by the deflector on the surface to be scanned, a synchronization detector that detects synchronization of the two beams in the main scanning direction, and a beam at a position optically equivalent to the deflection surface. Two beams emitted from the beam splitter in a direction different from the deflecting surface. A linear position sensor that detects the output level of the other beam and the cylindrical lens are moved via the optical path correction means, and the other beam is adjusted so that an appropriate beam pitch is set between the beam on the side not optical path corrected by the optical path correction means. Control means for correcting the optical path of the beam, detects the absolute position of the beam that cannot be moved in the sub-scanning direction with high resolution, and moves the other beam position in the sub-scanning direction with respect to this detected position. Since the beam pitch is adjusted in such a manner, the beam pitch of the two beams in the sub-scanning direction can be corrected by a single optical path correction unit using a single sensor.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In these drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted.

FIG. 1 is an explanatory view showing a beam scanning device according to an embodiment of the present invention, FIG. 2 is a plan view showing the structure of an optical path correcting means in the beam scanning device shown in FIG. 1, and FIG. FIG. 4 is an explanatory diagram showing an example of a sensor output level depending on the position of the sensor, FIG. 4 is an explanatory diagram showing a plurality of threshold values and corresponding beam positions, and FIG. 5 is an explanatory diagram showing an attached state of a position sensor according to an embodiment of the present invention. It is.

As shown in FIG. 1, the scanning device according to the present embodiment includes a driving circuit 23 for driving the first light source 1a to irradiate the beam 21, and a driving circuit 23 for driving the second light source 1b. Are provided, respectively. Then, the beam 2 from the first light source 1a
Irradiated with the beam 22 from the first and second light sources 1b, the scanned surface 1 of the uniformly charged photosensitive drum 18
An electrostatic latent image is formed on 8a. A collimator lens 2a is arranged corresponding to the first light source 1a, and a collimator lens 2b is arranged corresponding to the second light source 1b.
The beams 21 and 22 from the respective light sources 1a and 1b are collimated by the collimator lenses 2a and 2b.

On the optical path of the beams 21 and 22 having passed through the collimator lenses 2a and 2b, a cylindrical lens 6 for condensing the beams 21 and 22 in the sub-scanning direction, and the beams 21 and 22 emitted from the respective light sources 1a and 1b. Is provided. Also,
The second light source 1 is moved by moving the cylindrical lens 6b in the sub-scanning direction in accordance with the cylindrical lens 6b.
An optical path correction unit 33 that corrects the beam 22 emitted from b in the sub-scanning direction is provided.

Further, on the optical path of the beams 21 and 22 from the beam splitter 5 to the photosensitive drum 18, a deflection surface 2 is provided.
5 that deflects the two beams 21 and 22 at the same time, and the beams 21 and 22 deflected by the deflector 7
A scanning lens system 8 for condensing the light on a scanned surface 18a of the photosensitive drum 18 and scanning the same, and a mirror 19 for guiding the beams 21 and 22 to the scanned surface 18a are sequentially arranged.

On the optical path of the beams 21 and 22 emitted from the beam splitter 5 in a direction different from that of the deflection surface 25, a sensor unit 10 for detecting a pitch interval between the beams 21 and 22 in the sub-scanning direction is arranged. ing. This sensor unit 10
It comprises a photo sensor 31 for detecting the positions of the beams 21 and 22. Beam splitter 5 and sensor unit 1
At a position optically equivalent to the deflection surface 25 between 0 and 0, a knife edge 32 that shields the beams 21 and 22 at predetermined positions from the beam splitter 5 toward the sensor unit 10 is disposed.

The beam 21 scanned by the deflector 7
In order to synchronize the main scanning direction 22, a synchronization detector 9 is provided. And, by this synchronization detector 9,
Irradiation of the beams 21 and 22 corresponding to the image data is performed at a timing of a predetermined time. The sensor unit 10
The optical path correction means 33 is driven based on the signal from
An optical path correction means control circuit (control means) 34 for controlling the sub-scanning direction is provided. And the photosensitive drum 1
The members other than 8 are accommodated in the housing 20.

As shown in FIG. 2, the optical path correction means 33 for correcting the beam 22 in the sub-scanning direction by moving the cylindrical lens 6b in the sub-scanning direction has a lens holder 56 to which the cylindrical lens 6b is fixed. ing. A shaft 55 and a guide shaft 58, which extend over the base 52 and extend in the sub-scanning direction,
Is penetrating. The lens holder 56 is slidably mounted on the shaft 55 and the guide shaft 58.

The shaft 55 is rotatably attached to the base 52. A screw portion 59 is formed on the shaft 55 over a predetermined length.
9 is fitted with a screw portion formed at a position where the lens holder 56 passes through the shaft.

The base 52 has a stepping motor 51,
A worm gear 53 attached to the shaft of the stepping motor 51 and a worm wheel 54 meshing with the worm gear 53 are provided, and the worm wheel 54 meshes with a shaft 55. Therefore, when the stepping motor 51 rotates, the shaft 55 is rotated by the worm wheel 54. Then, by the rotation of the shaft 55, the lens holder 56 holding the cylindrical lens 6b moves in the sub-scanning direction along the guide shaft 58.

The operation of the beam scanning device configured as described above will be described below.

The beams 21 and 22 emitted from the first light source 1a and the second light source 1b, respectively, are adjusted to parallel beams by the collimator lenses 2a and 2b. Next, the beams 21 and 22 are transmitted to the cylindrical lenses 6a and 6
The light is focused in the sub-scanning direction by b. At this time, the pitch of the beam 22 in the sub-scanning direction is adjusted by the optical path correction unit 33, and the details will be described later.

After the beams 21 and 22 transmitted through the cylindrical lenses 6a and 6b have their optical axes aligned by the beam splitter 5, they are synchronized by the synchronization detector 9 in the main scanning direction. Thus, the light irradiation corresponding to the image data is performed at the timing of the predetermined time by each of the light sources 1a and 1a.
b is performed by the drive circuits 23 and 24 of the scanning surface 18.
A two-dimensional image is formed on beam a by beams 21 and 22.

Next, the pitch adjustment of the beams 21 and 22 in the sub-scanning direction will be described. Two beams 21,
The pitch of 22 is adjusted by adjusting the pitch of the beams 21 and 22 on the deflection surface 25 to an appropriate interval. The optical path of the beam 22 in the sub-scanning direction is changed by moving the cylindrical lens 6b for compensating the surface tilt of the deflecting surface in the sub-scanning direction by the optical path correcting means 3.

First, the position of the fixed beam 21 which is not subjected to optical path correction as a reference is detected. That is, when the beam 21 of the first light source 1a is emitted by the drive circuit 23 of the first light source 1a, the beam 21 passes through the collimator lens 2a, the cylindrical lens 6a, and the beam splitter 5, and is directed toward the deflection surface 25. And sensor part 1
It is separated into a component going to zero. The beam 21 directed to the deflecting surface 25 is used for irradiating the scanned surface 18a with light, and the beam 21 directed to the sensor unit 10 is guided to the photosensor 31 in order to detect the beam position from each of the light sources 1a and 1b. A knife edge 32 is provided between the photosensor 31 and the beam splitter 5 as a reference for beam alignment. When part or all of the beam 21 from the first light source 1a is blocked by the knife edge 32, the amount of light reaching the photo sensor 31 changes depending on the amount of light blocking.

Here, as shown in FIG. 3, the sensor output is low at the beam position (a) where the entire beam 21 is shielded by the knife edge 32. Further, at a beam position (b) where the center of the beam 21 is shielded about half of the edge of the knife edge 32, the sensor output is about half of the maximum output. At the beam position (c) where the beam 21 is not shielded by the knife edge 32, the sensor output indicates the maximum. Thus, the knife edge 32
When the center of the beam 21 approaches the vicinity, the sensor output sharply changes. Therefore, in the vicinity of the knife edge 32, the relationship between the knife edge 32 and the beam 21 can be detected with high accuracy. Therefore, if the light amount based on the positional relationship between the knife edge 32 and the beam 21 is obtained in advance as the back data, the position of the beam 21 can be detected from the data. In this way,
From the sensor output of the photo sensor 31, the beam position of the fixed beam 21 emitted from the first light source 1a with respect to the knife edge 32 is obtained.

From the obtained beam position of the beam 21, the position of the beam 22 of the second light source 1b with respect to the knife edge 32, that is, an appropriate beam pitch is calculated.
The light quantity (threshold) at the position of the beam 22 is determined. This processing may be performed by software based on the back data relating to the position, or may be performed by hardware. However, in the present invention, the beam 2 shielded by the knife edge 32 is used.
Since the beam position is determined based on the amount of light in the photosensors 31 and 22, the beam output power for adjusting the beam pitch must be kept constant.

Next, when the threshold value of the beam 22 for correcting the optical path in the sensor unit 10 is determined, the emission of the beam from the first light source 1a is stopped, and the emission of the beam 22 from the second light source 1b is performed. Let it. Beam 22 from second light source 1b
Is obtained by moving the cylindrical lens 6b in the sub-scanning direction by the optical path correcting means 33 in accordance with a signal from the optical path correcting means control circuit 34 so that the beam position becomes the threshold determined from the position of the beam 21 of the first light source 1a. To adjust.

Here, the optical path correcting means 33 decelerates the beam 22 in the sub-scanning direction in one step by the stepping motor 51 so that the moving amount in the sub-scanning direction becomes about 1 μm. The stepping motor 51 is connected to the optical path correction means control circuit 3.
4 is driven by the signal from. Also, the optical path correction means 3
Reference numeral 3 denotes a worm gear 53 and a worm wheel 5 which have a large reduction ratio of the stepping motor 51 so that the step size of the optical path correction becomes small.
4 is employed. Thus, when the stepping motor 51 rotates, the worm wheel 54 rotates the shaft 55. Then, the shaft 55
The lens holder 56 which holds the cylindrical lens 6b by fitting with the screw moves in the sub-scanning direction along the guide shaft 58. The parallel light incident on the cylindrical lens 6b focuses the beam on the optical axis in the sub-scanning direction of the cylindrical lens 6b. Therefore, when the cylindrical lens 6b is moved in the sub-scanning direction, the position of the beam 22 is moved along the sub-scanning direction. Move in the direction. Since the deflecting surface 25 and the scanned surface 18a are optically conjugate with each other in the sub-scanning direction, if the beam pitch on the deflecting surface 25 is adjusted to a predetermined interval, the scanned surface 18a
The beam pitch at is adjusted. For example,
The magnification in the sub-scanning direction is -0.5, and the stepping motor 5
The step angle of 1 is 18a degrees, the reduction ratio is 1/25, and the pitch between the screw portion 59 and the screw on the lens holder 56 side is 0.5 mm.
Then, in one step in the stepping 51, the step amount ΔP of the beam movement on the scanned surface 18a is ΔP = | 0.5 / (25 × 20) × (−0.5) | =
0.5 μm.

Next, the beam correction control in the optical path correction means 33 will be described. As an example of the correction control, there is binary control in which the H level is set when the sensor output is higher than a set threshold value of the beam for which the optical path correction is performed, and the L level is set when the sensor output is lower than the set threshold value.

In the beam correction control, the optical path correction means 33
, The beam 22 is moved in the direction in which the sensor output level changes. Then, when the sensor output level changes, the movement of the beam 22 is stopped.

Here, the alignment is performed at a point where the level changes from the H level to the L level due to hysteresis for preventing oscillation of the sensor unit 10 and the optical path correction means control circuit 34, the gear of the optical path correction means 33, and the play of the screw part. There is a positional difference between when the alignment is performed and when the alignment is performed at the point where the level changes from the L level to the H level. In such a case, it is possible to eliminate the positional difference by always fixing the direction in which the level changes. For example, when performing the alignment, it is always performed at the time when the level changes from the H level to the L level. If the sensor output is at the H level, the position is determined at the point where the sensor output changes to the L level. If the sensor output is at the L level, the beam 22 is once moved to the H level position, and then the beam 22 is changed from the H level to the L level. The beam movement is stopped at the changing point. With such control, stable correction of the beam 22 can be always performed.

When the correction of the beam 22 is completed, the power supply to the stepping motor 51 is stopped. This is because if the stepping motor 51 is always energized, heat is generated from the stepping motor 51, and the lens system and components inside the optical system may be thermally damaged and the optical performance may be degraded. is there. If the worm gear 53 and the worm wheel 54 are used as in this embodiment,
Since the stepping motor 51 having the worm gear 53 is hard to rotate, the influence on the optical path accuracy of the beam 22 is small even if the stepping motor 51 is not always pulled up. And by doing this,
The position of the beam 22 can be controlled accurately.

Next, the setting of the beam pitch will be described. 300DP resolution in sub-scanning direction with beam scanning device
When switching between I and 600 DPI, it is necessary to switch the pitch of the two beams 21 and 22.

In a beam scanning device having a fixed beam pitch of 300 DPI, when the beam scanning device is used at 600 DPI, one beam is used to reduce the moving speed of the scanned surface 18 a to １ ／ of the speed at 300 DPI, or The speed per scan of the beam must be quadrupled (deflection speed of the deflector). Therefore, only one of the two beams can be used, and the advantage of the multi-beam optical system cannot be utilized.

On the other hand, in the present beam scanning device, 30
A beam pitch of 0 DPI or 600 DPI can be selected, and by using two beams, the moving speed of the surface 18a to be scanned is reduced to half, or the speed of the beam per scanning is doubled. Scanning can always be performed with two beams, and the advantages of the multi-beam scanning optical system can be utilized. The switching of the beam pitch is performed by providing a plurality of threshold values of the beam 22 for performing the optical path correction and selecting a threshold value corresponding to a predetermined pitch from the threshold values.

Here, as shown in FIG. 4, the sensor output of the beam 21 whose optical path is not corrected is L0. Therefore, the position of the beam 21 whose optical path is not corrected is Pos0.
Becomes

Here, the position of the beam 22 is set to 300 DPI.
In order to make it equal to Pos1, which is P1 away from Pos0. Since the relationship between the beam position and the sensor output is stored in advance as back data, the sensor output corresponding to the threshold value at Pos1 is L1. Therefore, beam 22
Is adjusted to the threshold value A by the optical path correcting means 33. Similarly, when 600 DPI is selected, the beam 22 that performs optical path correction on the beam 21 that has not undergone optical path correction is corrected to the position Pos2 using the threshold value B of the sensor output L2. By setting the threshold value corresponding to the beam pitch in this way, the beam pitch can be freely switched simply by selecting the threshold value corresponding to the desired beam pitch.

Since the beam pitch can be switched simply by selecting the threshold value, it is not necessary to add a new sensor or manufacture a new sensor. In addition, it is not necessary to lengthen the beam in the sensor unit 10 in the main scanning direction and to make a work so that the beam is irradiated to the added sensor.

Here, without using the knife edge 32, a linear position sensor such as a CCD or PSD is attached to the sensor unit 10 at an angle to the sub-scanning direction so that the absolute position of each beam can be directly read. You may.

When the knife edge 32 is used, the positions of the two beams 21 and 22 are detected based on the relative distance from the knife edge 32. On the other hand, if a position sensor is attached, the beam pitch can be corrected by directly detecting two beam positions. A general-purpose CCD
The size or accuracy of one pixel related to the position detection of the PSD or PSD is about 10 μm, and the position detection accuracy is rough if used as it is for the detection of the beam pitch interval. Therefore, if the line-shaped position sensor is installed obliquely with respect to the sub-scanning direction, the size of one pixel in the sub-scanning direction is reduced in a pseudo manner, thereby increasing the accuracy.

As shown in FIG. 5, the linear position sensor 61 has a structure in which a plurality of pixels 62 are arranged in a line. The shape of the beam 63 at the position sensor 61 is a horizontally long linear shape narrowed only in the sub-scanning direction in order to correct the tilt of the deflection surface.

As shown in FIG. 5A, when the line-shaped position sensor 61 is installed in the sub-scanning direction as it is, when the beam diameter in the sub-scanning direction is 100 μm, the position sensor 6
In 1, the beam 63 is received by about ten pixels 62. Then, the position of the beam 63 must be determined from the signals of the ten pixels 62. On the other hand, as shown in FIG. 5B, when the line-shaped position sensor 61 is installed at an angle of, for example, 30 degrees with respect to the sub-scanning direction, about 20 pixels 62 of the position sensor 61 receive the beam 63. become,
The accuracy of detecting the position of the beam 63 can be improved. The beam 63 from the position sensor 61 has a length of about 2 to 5 mm in the main scanning direction.
Can be received in the range of the pitch adjustment even if the angle is greatly inclined.

With this arrangement, the pitch adjustment of the two beams is performed by detecting the absolute position of the beam whose optical path is not to be corrected by the position sensor 61 and adjusting the optical path correcting means 33 so that the beam whose optical path is to be corrected comes to the predetermined absolute position. Can be used for correction. In this case, it is also possible to match the desired beam pitch selected from a plurality of beam pitches.

[0066]

As described above, according to the present invention, only one beam is made movable in the sub-scanning direction by the optical path correcting means, and the output level of the beam that cannot be moved in the sub-scanning direction is detected by the sensor unit. Since the output level is adjusted by correcting the optical path of the beam movable in the sub-scanning direction to the threshold at the appropriate beam pitch determined from this output level, the beam pitch of the two beams in the sub-scanning direction is adjusted. There is an effective effect that the correction can be performed by a single optical path correction unit using a single sensor.

Further, according to the present invention, there is an effective effect that the beam pitch can be set to an arbitrary distance only by selecting the threshold without adding a new sensor or manufacturing a new sensor. can get.

Further, according to the present invention, the absolute position of a beam that cannot be moved in the sub-scanning direction is detected with high resolution, and the other beam position is moved in the sub-scanning direction with respect to this detected position to adjust the beam pitch. Therefore, an effective effect is obtained that the beam pitch correction of the two beams in the sub-scanning direction can be performed by a single optical path correction unit using a single sensor.

According to the present invention, the number of optical path correction means and sensors can be reduced, so that it is possible to obtain a beam scanning device capable of reducing the size of the optical system at low cost. That is, an effective effect is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a beam scanning device according to an embodiment of the present invention;

FIG. 2 is a plan view showing a configuration of an optical path correcting unit in the beam scanning device of FIG.

FIG. 3 is an explanatory diagram showing an example of a sensor output level according to a knife edge and a beam position.

FIG. 4 is an explanatory diagram showing a plurality of thresholds and beam positions corresponding thereto.

FIG. 5 is an explanatory view showing an attached state of the position sensor according to the embodiment of the present invention;

FIG. 6 is an explanatory view showing a conventional beam scanning device.

FIG. 7 is an explanatory diagram showing a relationship between a beam position and a light receiving surface output when a beam position is adjusted using a two-division sensor.

FIG. 8 is an explanatory diagram showing a beam pitch of two beams.

9A is an explanatory diagram showing a printed image when the beam pitch is at an appropriate interval, and FIG. 9B is an explanatory diagram showing a printed image when the beam pitch is shifted.

[Explanation of symbols]

 1a Light source (first light source) 1b Light source (second light source) 2a, 2b Collimator lens 5 Beam splitter 6a, 6b Cylindrical lens 7 Deflector 8 Scanning lens system 9 Synchronous detector 10 Sensor unit 21 Beam 22 Beam 23, 24 Drive circuit 25 Deflection surface 32 Knife edge 33 Optical path correction means 34 Optical path correction means control circuit (control means) 61 Position sensor 63 Beam

Claims (3)

[Claims] 1. Two light sources for irradiating a beam, two driving circuits for independently driving the light source to irradiate a beam, and installed in correspondence with each of the beams emitted from the light source. Two collimator lenses for collimating beams, two cylindrical lenses installed corresponding to the respective beams emitted from the collimator lens, and condensing these beams in the sub-scanning direction; Optical path correction means for moving the cylindrical lens in the sub-scanning direction to correct the optical path of the beam passing through the cylindrical lens; a beam splitter for matching the optical axes of the two beams emitted from the cylindrical lens; A deflecting surface is provided near the converging point of the cylindrical lens of the two beams emitted from the splitter. A deflector that deflects these beams, a scanning lens system that scans the two beams deflected by the deflector on a surface to be scanned, a synchronization detector that detects synchronization of the two beams in the main scanning direction, A sensor unit that is provided on an optical path of two beams emitted from the beam splitter in directions different from the deflection surface, and detects an output level of these beams; and a sensor unit between the beam splitter and the sensor unit. Appropriate based on a knife edge that is installed at a position optically equivalent to the deflecting surface and blocks two beams from the beam splitter toward the sensor unit, and an output level of a beam that is not optical path corrected by the optical path correction unit. A threshold value of the other beam at a proper beam pitch is obtained, and the output level of the other beam is set to the determined threshold value via the optical path correcting means so that the output level of the other beam becomes equal to the threshold value. And a control means for moving the cylindrical lens. 2. The control device according to claim 1, wherein the control unit controls the output level of the other beam so that the output level of the other beam is equal to a threshold value corresponding to the selected beam pitch from a plurality of threshold values set corresponding to the plurality of beam pitches. 2. The beam scanning device according to claim 1, wherein the cylindrical lens is moved via an optical path correcting unit. 3. Two light sources for irradiating a beam, two driving circuits for independently driving the light source to irradiate a beam, and installed in correspondence with each of the beams emitted from the light source. Two collimator lenses for collimating beams, two cylindrical lenses installed corresponding to the respective beams emitted from the collimator lens, and condensing these beams in the sub-scanning direction; Optical path correction means for moving the cylindrical lens in the sub-scanning direction to correct the optical path of the beam passing through the cylindrical lens; a beam splitter for matching the optical axes of two beams emitted from the cylindrical lens; A deflecting surface is provided near the converging point of the cylindrical lens of the two beams emitted from the splitter. A deflector that deflects these beams, a scanning lens system that scans the two beams deflected by the deflector on a surface to be scanned, a synchronization detector that detects synchronization of the two beams in the main scanning direction, A line that is installed at a position optically equivalent to the deflecting surface and is inclined with respect to the sub-scanning direction of the beam, and that detects an output level of two beams emitted from the beam splitter in a direction different from the deflecting surface. Shape sensor, and moving the cylindrical lens via the optical path correcting means, and correcting the optical path of the other beam so that the appropriate beam pitch is formed between the beam on which the optical path correcting means does not correct the optical path. A beam scanning device comprising: