JP2000180755A - Division optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the level difference of light quantity at a joint, even for the case of division scanning by plural laser beams. SOLUTION: A division optical scanner 10 is equipped with laser beam source parts 12A and 12B, which are respectively connected to a control part 14. The laser beam 16A, emitted from the laser beam source part 12A, is made incident on the reflection surface of a polygon mirror 18 and deflected toward a surface to be scanned 20 by the mirror 18 so as to scan the surface 20 from P0 to P2. The laser beam 16B scans the surface 20 from P1 to P3. The control part 14 measures the light quantity of the laser beam 16A and that of the laser beam 16B at the positions of P1 and P2 which are the boundary of an overlap region, and calculates a cross point where the light quantity of the laser beam 16A and that of the laser beam 16B are coincident within the overlap region, then the calculated cross point is set as a division position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laser printer,
The present invention relates to a divided optical scanning device used in an electrophotographic digital image forming apparatus such as a laser copy machine, and more particularly to a divided optical scanning device that divides an exposure range and scans with a plurality of light beams.

[0002]

2. Description of the Related Art Conventionally, an optical scanning apparatus used in an electrophotographic digital image forming apparatus such as a laser printer or a laser copying machine has a wide scanning range (exposure range) of a light beam and a high scanning speed. Various improvements have been made to realize this.

However, in order to widen the exposure range, it is necessary to increase the size of optical components such as an fθ lens.
For this reason, there is a problem that the optical scanning device becomes large. To increase the scanning speed, the number of rotating polygon mirrors (hereinafter, polygon mirrors) for deflecting a light beam is increased, or the rotation speed of a motor for rotating the polygon mirror is increased. Needed.

When the number of surfaces of the polygon mirror is increased, the size of the polygon mirror is increased in order to maintain the optical characteristics of the optical scanning device. Therefore, the load on the motor for rotating and driving the polygon mirror increases. The generation of windage and vibration is a problem. In addition, when increasing the rotation speed of the motor that rotates the polygon mirror, the increase in the rotation speed causes a problem of vibration, and a motor that can rotate stably even at high speed is required. Will be higher.

In order to solve the above-mentioned problem, a plurality of laser beams are made incident on a polygon mirror at different angles, and the exposure range on the photoreceptor is divided and scanned, thereby increasing the exposure range. An optical scanning device that achieves both high scanning speed and high scanning speed has been proposed (Japanese Patent Laid-Open No. 63-377 / 1988).
No. 18). When such an optical scanning device is used, since the photoconductor is scanned by a plurality of laser beams, the amount of light at the joint between adjacently scanned laser beams may not be equal. For this reason, there is a problem that a streak pattern is generated at a joint and a step of an image is conspicuous, and a high-quality image cannot be obtained, as compared with a case where scanning is performed with a single laser beam in the related art.

In order to solve such a problem, conventionally, the light amount of the laser beam is adjusted at a division position (usually at the center of the scanning range) which is a joint between adjacent laser beams, and a step of the light amount at the joint occurs. I was trying not to.

However, even if the division position is adjusted to the center of the scanning range and the light amount of the laser beam is adjusted in order to eliminate the step of the light amount and to maintain the continuity of the image, the laser beam is actually in the entire scanning range. The light quantity distribution of the beam becomes unbalanced.

For example, as shown in FIG. 13, in the ideal state, scanning is performed from the leftmost scanning position to the central scanning position.
The light quantity distribution of the two laser beams of the st laser beam and the 2nd laser beam that scans from the scanning center position to the scanning right end position is as shown in (1), and the light quantities match at the joint between the scanning center positions. As shown in (2), the overall light quantity is almost the same, but a step in the light quantity occurs at the joint. For this reason, when the light amount is adjusted so as to increase the light amount of the second laser beam, the light amount at the joint is the same as in (3), but the light amount increases as a whole, so that scanning was performed with the first laser beam. A density difference occurs between the image in the range and the image in the range scanned by the second laser beam, and the quality of the image deteriorates. In particular, it is fatal in an image forming apparatus requiring high image quality.

Further, even if the optical scanning device can be designed so as to reduce the difference in the light amount distribution, the SOS (Start Of S) which detects the variation at the time of manufacturing and the scanning start position.
(can) Due to the relationship between the sensors, a change in the writing position of the laser beam causes a step in the amount of light at the division position.

For example, as shown in FIG. 14, in the ideal state, the light amount distribution of the laser beam is as shown in (1), and the light amounts of the first laser beam and the second laser beam coincide at the joint position. Actually, the writing position of the laser beam shifts (shifts to the left in FIG. 14) as shown in (2), so that a step in the amount of light occurs at the joint and the image quality deteriorates. Further, even if the light amount is adjusted in this state, there is a difference in the overall light amount as described above.

In order to solve such a problem, instead of actively adjusting the amount of light at the joint between adjacent laser beams, a scanning range (hereinafter referred to as an overlap area) in which adjacent laser beams can scan each other. In this overlap area, the light amount of one laser beam is gradually reduced, and the light amount of the other laser beam is gradually increased, and the exposure amount in the overlap region is averaged, and the other exposure is performed. A technique has been proposed in which the difference between the range and the light amount is made inconspicuous by eliminating the difference from the range (JP-A-3-98066).

[0012]

However, in the technique described in Japanese Patent Application Laid-Open No. 3-98066, the light quantity in the overlap area is averaged, so that the step of the light quantity is reduced. Since the same image data is written twice, there is a problem that the image in the overlap area is blurred.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem. Even when the laser beam is divided and scanned by a plurality of laser beams, it is possible to eliminate a step in the amount of light at a joint, and to form a streak pattern or an image at the joint. An object of the present invention is to provide a divided optical scanning device capable of preventing occurrence of disturbance or image blur.

[0014]

According to a first aspect of the present invention, there is provided a divided light scanning apparatus, comprising: a plurality of light sources; a light source driving means for driving the plurality of light sources; A scanning area on the surface to be scanned corresponding to a plurality of light beams respectively emitted from the light source is divided so as to partially overlap along the main scanning direction of the light beam, and the partial scanning area is divided into the plurality of light beams. Scanning means for scanning with each beam, in the overlapping area, in the overlapping area,
Setting means for setting, as a division position, a position at which the light amounts of the two light beams that scan the overlapping area substantially coincide with each other, and the plurality of light beams on the surface to be scanned at the division position set by the setting means And control means for performing control so as to perform divided exposure according to (1).

According to the first aspect of the present invention, a plurality of light sources are provided, and the plurality of light sources are driven by light source driving means. The light source driving unit can keep the light amount of the light beam emitted from the light source uniform or adjust the light amount.

[0016] The scanning means is a portion obtained by dividing a scanning area on the surface to be scanned corresponding to the plurality of light beams respectively emitted from the plurality of light sources so as to partially overlap in the scanning direction of the light beam. A scanning region is scanned by each of the plurality of light beams.

[0017] The setting means sets, as a division position, a position in the overlapping area where the light amounts of the two light beams that scan the overlapping area substantially coincide with each other. The control means controls so that the surface to be scanned is dividedly exposed at the division position set by the setting means. For this reason, even when the scanning area is divided and scanning is performed with a plurality of light beams, the division position of the scanning area, that is, the level difference in the amount of light at the joint can be eliminated, and a streak pattern, image disorder or image blur at the joint can be eliminated. Can be prevented from occurring.

According to a second aspect of the present invention, there is provided a split optical scanning apparatus, wherein a plurality of light sources and a plurality of light beams emitted from the plurality of light sources are used to scan a scanning area on a surface to be scanned with the light beams. Scanning means for scanning each of the partial scanning areas divided so as to partially overlap along the main scanning direction of the beam with the plurality of light beams, and scanning the overlapping area at both ends of the overlapping area; Light amount detecting means for respectively detecting the light amounts of the two light beams; and, based on the detection result of the light amount detecting means, whether or not there is a position where the light amounts of the two light beams substantially match in the overlapping area. When the determining means determines that there is a position where the light amounts of the two light beams substantially coincide with each other, the light amounts of the two light beams are determined based on the detection result of the light amount detecting means. When the calculating means for calculating the coincident position and the determining means determine that there is no position where the light amounts of the two light beams substantially match, the position where the light amounts of the two light beams substantially match is determined. Light amount adjusting means for adjusting the light amount of at least one of the two light beams so as to be present; and setting the position at which the light amounts of the two light beams substantially coincide with each other as a division position on the surface to be scanned. And control means for performing control so as to perform divisional exposure with the light beam of the book.

According to a third aspect of the present invention, in the divided optical scanning device according to the second aspect, the data representing the position where the light amounts of the two light beams substantially coincide with each other is determined from the boundary position of the overlapping area. The data is characterized by a distance to a position where the light amounts of a plurality of light beams substantially match and a distance from a scanning start position of the light beam to a boundary position of the overlapping area.

According to the second aspect of the present invention, the scanning means moves the scanning area on the surface to be scanned in the scanning direction of the light beam corresponding to the plurality of light beams respectively emitted from the plurality of light sources. The plurality of light beams scan the partial scanning areas divided so as to partially overlap each other.

The light amount detecting means detects the light amounts of the two light beams for scanning the overlapping area. That is,
The amount of light at two ends on both sides of the overlapping area for one light beam is detected. The determining means determines whether or not there is a position where the light amounts of the two light beams substantially coincide with each other in the overlapping area. This determination can be made by examining the magnitude relationship between the light amounts of the two detected light beams.

When the determining means determines that there is a position where the light amounts of the two light beams substantially match, the calculating means determines that the light amounts of the two light beams substantially match based on the detection result of the light amount detecting means. Calculate the position to perform. In this calculation, for example, for each light beam, a linear equation is calculated from the light amounts at both ends of the detected overlapping area. Then, by finding the intersection of each of the calculated linear formulas, it is possible to specify a position where the light amounts of the two light beams substantially match.

The data representing the position at which the light amounts of the two light beams substantially coincide with each other may be such that the light amounts of the two light beams substantially coincide with each other from the boundary position of the overlapping region. The data may be data represented by a distance to a position to be scanned and a distance from a scanning start position of the light beam to a boundary position of the overlapping area.

The light amount adjusting means determines that there is a position where the light amounts of the two light beams substantially coincide with each other when the determining means determines that there is no position where the light amounts of the two light beams substantially coincide with each other. Then, the light amount of at least one of the two light beams is adjusted. That is, the case where there is no position where the light amounts of the two light beams substantially coincide with each other is the case where the intersection of the calculated linear equation does not exist, so that at least one of the two light beams is generated so that the intersection occurs. The light amount of the light beam is adjusted.

The control means performs control such that a position where the light amounts of the two light beams substantially coincide with each other is set as a division position, and the surface to be scanned is dividedly exposed by the plurality of light beams.

[0026]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, the split optical scanning device 10 according to the present embodiment includes laser light source units 12A and 12B, and is connected to a control unit 14, respectively. Laser beam 16A emitted from laser light source 12A and laser beam 16B emitted from laser light source 12B
Are respectively incident on the reflection surface of the polygon mirror 18. The polygon mirror 18 has, for example, a hexagonal prism shape, and is rotationally driven by a motor (not shown) at a substantially constant angular speed in the direction of arrow Q in the drawing.

The laser beam 16A incident on the reflection surface of the polygon mirror 18 is deflected in the direction of the surface to be scanned 20, and moves from P0 to P2, which is one end of the entire scanning range X of the surface to be scanned, as indicated by arrows in FIG. The scanning is performed on the scanned surface 20 along the direction A (main scanning direction).

On the other hand, the laser beam 16B incident on the reflecting surface of the polygon mirror 18 is deflected in the direction of the surface to be scanned 20, and moves from P1 to the other end P of the entire scanning range X.
The scanning is performed on the surface to be scanned 20 along the direction of arrow A in FIG.

The SOS sensor 22 connected to the control unit 14 and the laser beam emitted from the laser light source unit 12A and deflected by the polygon mirror 18 are located outside the scanning range of the surface 20 to be scanned and on the scanning start side. A reflection mirror 24 that reflects the beam 16B toward the SOS sensor 22 is provided. The SOS sensor 22 outputs a synchronization signal (SOS signal) to the control unit 14 when the laser beam 16B is incident. The control unit 14 controls the laser light source units 12A and 12B.

As shown in FIG. 1, the scanning range of the laser light source unit 12A and the scanning range of the laser light source unit 12B overlap in the range from P1 to P2 (hereinafter, referred to as an overlap area). The image area (exposure area) where the image data is actually written on the scanned surface 20 is from P4 to P4.
The area is up to 5. The control unit 14 controls the light amount of the laser beam 16A and the laser beam 16A in the overlap area.
The laser beam 16A and the laser beam 16B are scanned with the scanning position where the light amount of B coincides with the division position, that is, the division position of the laser beam 16A becomes the image data writing start position (exposure start position). As described above, the laser light source units 12A and 12B are controlled such that the division position of the laser beam 16B is the image data write end position (exposure end position).

Laser light source unit 12A and laser light source unit 12
FIG. 2 shows the scanning timing of B. First, the case where the division position is P6 will be described. As shown in FIG. 2, when the laser beam 16B emitted from the laser light source unit 12B is received by the SOS sensor 22 at time t0, writing of image data is started at time t1 after a lapse of a predetermined time. This corresponds to the position of P4 in FIG. Almost at the same time, the dividing position P6
Exposure of the laser beam 16A emitted from the laser light source unit 12A from the position is started, and writing of image data starts. Next, at time t2, the laser beam 16B
And the laser beam 16A reaches the position P5. Thus, the exposure for one line is completed.

Next, a case where the division position is set to a position other than P6 will be described. For example, if the division position is P1,
The laser beam 16B from the laser light source 12B is exposed from P4 to P1, and the laser beam 16A from the laser light source 12A is exposed from P1 to P5. The exposure time of the laser beam 16B at this time is the time from time t1 to t2 ′, and the exposure time of the laser beam 16A is the time from time t1 ′ to t2.

Further, when the division position is P2,
The laser beam 16B exposes from P4 to P2, and the laser beam 16A exposes from P2 to P5. The exposure time of the laser beam 16B at this time is from time t1 to t2 ″.
The exposure time of the laser beam 16A is the time from the time t1 "to the time t2. In this manner, when the division position is changed to a position other than P6, the exposure end time of the laser beam 16B is changed. The exposure start time of the laser beam 16A changes, and if there is a difference in the amount of light at the division position, the image becomes a streak pattern or the image is disturbed.

FIG. 3 shows a light quantity distribution of the divided optical scanning device 10. The vertical axis indicates the light amount, and the horizontal axis indicates the scanning position. Laser beam 16B (1st laser beam) and laser beam 16A (2nd laser beam)
Is generally gentle mountain-shaped distribution. In the overlap region, there is a point where the light quantity of the laser beam 16B and the light quantity of the laser beam 16A are almost equal. This is the cross point Pc in FIG. If the cross point Pc is set as a division position, the laser beam 16B is scanned from P0 to Pc, and the laser beam 16A is scanned from Pc to P3, no step in the amount of light at the joint position occurs. The cross point Pc is not always located at the same position, and may not exist. Therefore, the control unit 1
In step 4, the presence or absence of a cross point is determined and the position is specified (details will be described later).

FIG. 4 shows a schematic configuration of the control unit 14. The control unit 14 includes a main controller 26 including a CPU, a ROM, a RAM, and input / output ports (not shown), a light amount measurement circuit 28, an image memory 30, and a timing generation circuit 32.

The light quantity measuring circuit 28 is connected to a photodiode (PD) 34 for detecting the light quantity of the laser beam. As the photodiode 34, one photodiode 34 may be used as shown in FIG. 5A, or two or more photodiodes 34A and 34B may be used as shown in FIG. Is also good. When one photodiode is used, the photodiode 34 is connected to P
When two photodiodes are used, the photodiodes 34A and 34B are arranged at positions P1 and P2, respectively. In the present embodiment, the two photodiodes 34A and 34B
Will be described.

The light quantity measuring circuit 28 outputs a monitor signal (described later) to the laser light source sections 12A and 12B based on the monitor start signal output from the main controller 26 and the SOS signal output from the SOS sensor.
A sample signal as shown in (3) of FIG. 5 is generated, and at this timing, the amount of light detected by the photodiodes 34A and 34B is sampled. Thereby, for example, when the light amount distribution in the overlap region is as shown in (4) of FIG. 5, the light amounts at the positions P1 and P2 are sampled as shown in (5) of FIG. You. When using one photodiode,
A portion between the position of P1 and the position of P2 may be masked without generating the sample signal. In this way, it is possible to sample only the light amounts at the positions P1 and P2.

The light quantity data measured by the light quantity measuring circuit 28 is output to the main controller 26. The main controller 26 performs a light amount determination and a cross point calculation as necessary, outputs a count value corresponding to the determined cross point to the timing generation circuit 32, and stores an address value corresponding to the count value in the image memory. Output to 30. In the timing generation circuit 32,
In accordance with the SOS signal and the count value output from the main controller 26, a 1st laser beam (laser beam 16B) line sync enable signal (1st_L / S_E signal) which becomes low level only during an image writing period (exposure period), for example. And outputs a 2nd laser beam (laser beam 16A) line sync enable signal (2nd_L / S_E signal) to the image memory 30.

In the image memory 30, 1st_L / S_E
When the signal and the 2nd_L / S_E signal become low level, reading of image data starts from the address output from the main controller 26 and the light quantity measuring circuit 28
And outputs them as partial image data (1st image data, 2nd image data) to the laser light source unit 12A and the laser light source unit 12B via the. The output of image data is 1
The operation stops when the st_L / S_E signal and the 2nd_L / S_E signal become high level.

As shown in FIG. 4, the laser light source section 12B includes a laser diode driver (LDD) 36B and a laser diode (LD) 38B.
B is modulated and driven in accordance with the first image data output from the image memory 30. Similarly, the laser light source unit 12A also includes a laser diode driver 36A and a laser diode 38A, and the laser diode driver 36A stores the laser diode 38A in the image memory 30.
Modulation drive according to the 2nd image data output from.

Further, the main controller 26 outputs a light amount adjustment signal to the laser diode driver 36A of the laser light source unit 12A as necessary, and adjusts the light amount of the laser beam 16A.

Next, the light quantity measuring circuit 28 will be described with reference to FIG. The light quantity measuring circuit 28 includes a circuit for measuring the light quantity of the first laser beam and a circuit for measuring the light quantity of the second laser beam. Since both have the same configuration, the configuration for measuring the light quantity of the second laser beam is used. A detailed description is omitted.

As shown in FIG. 6, the light quantity measuring circuit 28
Counters 40B and 42B are provided. Counter 40B
When the SOS signal and the monitor start signal are input, the counter 42B counts the scan time corresponding to the scan time from when the predetermined first laser beam reaches the positions P1 and P2, which are the boundaries of the overlap region, from the scan start position. Counting starts at the values CB1 and CB2, respectively.

When the counting is completed, the sample signal is set to O
Output to the R circuit 44B. That is, a sample signal as shown in (3) of FIG. 5 is output when the laser beam 16B reaches the positions of P1 and P2. OR circuit 44B
Then, the input sample signal is sampled and held (S
/ H) circuit 46B, a timing generator (TG) circuit 48B, and a flip-flop (FF) circuit 50B.

The FF circuit 50B outputs a low level by default, but switches the output from a low level to a high level and from a high level to a low level each time a sample signal is input. The FF circuit 50B is connected to the inverter circuit 56B, and the inverter circuit 56B inverts the output from the FF circuit 50B and outputs the inverted signal to one input terminal of the AND circuit 58B. further,
The 1st image data output from the image memory 30 is input to the other input terminal of the AND circuit 58B. Also, A
The output terminal of the ND circuit 58B is connected to the input terminal of the LDD 36B.

That is, the monitor signal is at a low level only while the start of monitoring of the light quantity is instructed by the main controller 26 and the first laser beam scans the overlap area (from P1 to P2), and otherwise is at a high level. Becomes Therefore, the amount of light can be monitored when the monitor signal is at the low level. When writing a normal image, the monitor signal is at a high level, so that the output of the AND circuit 58B outputs the first image data to the LDD 36B as it is.

On the other hand, when the sample signal is input to the S / H circuit 46B, the outputs from the photodiodes 34A and 34B are held, and the A / D conversion circuit 52B
Output to The A / D conversion circuit 52B converts the input light amount into a digital value and outputs the digital value to the latch circuit 54B as light amount data. The TG circuit 48B outputs a timing signal to the latch circuit 54B at a predetermined timing based on the input sample signal. The latch circuit 54B latches the light amount data output from the A / D conversion circuit 52B based on the timing signal output from the TG circuit 48B, and outputs the light amount data to the main controller 26. That is, as shown in FIG. 7, the light amount 1s (st
(art) and the light amount 1e (end) at the position P2 are output to the main controller 26.

Next, as an operation in the present embodiment,
The light amount determination and cross point determination processes performed by the main controller 26 of the control unit 14 will be described with reference to the flowchart shown in FIG. 8 and the timing chart shown in FIG.

First, the main controller 26 sends the monitor start signal to the counters 40A, 40A of the light quantity measuring circuit 28.
B, 42A and 42B (step 100). Then, scanning of the first laser beam from the laser light source unit 12B is started, and the SOS signal is output to the counters 40A and 40A.
When input to B, 42A, and 42B, respectively, the counters 40A, 40B, 42A, and 42B count until they reach predetermined count values CA1, CB1, CA2, and CB2.

The count values CA1, CB1, CA
2, CB2 is a count value corresponding to the scanning time from when the first laser beam reaches the position of P1 from the scanning start position, and CB2, respectively, when the first laser beam is at P
A count value corresponding to the scanning time to reach position 2;
This is a count value corresponding to the scanning time from when the 2nd laser beam reaches the position P1 from the scanning start position to the count value corresponding to the scanning time from when the 2nd laser beam reaches the position P2 from the scanning start position.

On the first laser beam side, a counter 40
When the counting by B or 42B ends, that is, when the laser beam 16B reaches the position of P1 or P2, a pulse signal is output to the OR circuit 44B, respectively.
The OR circuit 44B converts the sample signal shown in FIG. 10 into an S / H circuit 46B, a TG circuit 48B, and an FF circuit 50B.
Output to

When the first sample signal is input, the output of the FF circuit 50B switches from low level to high level, the output is inverted by the inverter circuit 56B, and the low level is output to the AND circuit 58B. . Then, when the second sample signal is input, the output is switched from high level to low level, the output is inverted by the inverter circuit 56B, and the high level is ANDed.
Output to the circuit 58B. That is, it is at a low level only while the first laser beam scans the overlap area. With this monitor signal, the laser diode 3
8B is turned on, and the light amount can be monitored.

On the other hand, in the S / H circuit 46B, when the sample signal is input, the outputs from the photodiodes 34A and 34B are held and output to the A / D conversion circuit 52B. The A / D conversion circuit 52B converts the input light quantity into a digital value, and outputs the digital value to the latch circuit 54B as light quantity data 1s, 1e. The TG circuit 48B outputs a timing signal to the latch circuit 54B at a predetermined timing based on the input sample signal. Latch circuit 54B
Then, based on the timing signal output from the TG circuit 48B, the light amount data 1s and 1e output from the A / D conversion circuit 52B are latched and output to the main controller 26.

On the second laser beam side, the counter 40
When the counting by A or 42A ends, that is, when the laser beam 16A reaches the position of P1 or P2, a pulse signal is output to the OR circuit 44A, respectively.
The OR circuit 44A converts the sample signal shown in FIG. 10 into an S / H circuit 46A, a TG circuit 48A, and an FF circuit 50A.
Output.

When the first sample signal is input, the output of the FF circuit 50A switches from low level to high level, the output is inverted by the inverter circuit 56A, and the low level is output to the AND circuit 58A. . Then, when the second sample signal is input, the output switches from high level to low level, the output is inverted by the inverter circuit 56A, and the high level is ANDed.
Output to circuit 58A. That is, it is at a low level only while the first laser beam scans the overlap area. With this monitor signal, the laser diode 3
8A is turned on, and the light amount can be monitored.

On the other hand, in the S / H circuit 46A, when the sample signal is input, the outputs from the photodiodes 34A and 34B are held and output to the A / D conversion circuit 52A. The A / D conversion circuit 52A converts the input light amount into a digital value and outputs the digital value to the latch circuit 54A as light amount data 2s, 2e. The TG circuit 48A outputs a timing signal to the latch circuit 54A at a predetermined timing based on the input sample signal. Latch circuit 54A
Then, based on the timing signal output from the TG circuit 48A, the light amount data 2s and 2e output from the A / D conversion circuit 52A are latched and output to the main controller 26.

In the main controller 26, the light amount data 1s, 1e, 2s, 2
e (step 102). It is determined whether or not a cross point exists based on the acquired light amount data 1s, 1e, 2s, and 2e. Whether or not a cross point exists is determined by the captured light amount data 1s, 1e, 2s,
The determination can be made based on the magnitude relationship of 2e and the inclination of the amount of light in the overlap area. Assuming that the length of the overlap region in the scanning direction is L, the inclinations of the first laser beam and the second laser beam in the overlap region are (1e-1s) / L and (2e-2s) / L, respectively.
It is represented by

For example, as shown in FIG.
When both the t laser beam and the second laser beam have a normal light amount distribution, 1s> 2s and 2e> 1e,
Further, (1e-1s) / L <0, (2e-2s) / L
> 0, and there is a cross point Pc. However,
If the light amount distribution is as shown in (2) to (6) in FIG. 11 due to manufacturing variations or the like, no cross point occurs, so it is necessary to adjust the light amount of the second laser beam, for example. . For example, in (2) of FIG. 11, the light quantity distribution of the 2nd laser beam is substantially flat and has a downward slope, and when 1s> 2s, the light quantity of the 2nd laser beam is reduced as a whole. It is necessary to make it. Thereby, the cross point can be predicted as the position of 1 s.

FIG. 12 shows the magnitude relationship between the light quantity data 1s, 1e, 2s, and 2e, the relationship between the inclination of the light quantity in the overlap area, and the presence / absence of a cross point. FIG.
2 shows all combinations (16 patterns)
It is shown. Thus, the light amount data 1s, 1e,
The presence or absence of a cross point can be determined by considering the magnitude relationship between 2s and 2e and the inclination of the amount of light in the overlap region.

First, the main controller 26 determines whether or not the light quantity data 1s is larger than the light quantity data 2s and whether the light quantity data 1e is larger than the light quantity data 2e (step 104). Light quantity data 1s is light quantity data 2s
When the light amount data 1e is larger than the light amount data 2e, that is, in the case of the patterns 1 to 4 shown in FIG. 12, the inclination of the first laser beam (1e−
1s) / L is the inclination of the 2nd laser beam (2e-2s)
/ L is determined (step 10
6).

The tilt of the first laser beam (1e-1s)
When / L is larger than the inclination (2e-2s) / L of the 2nd laser beam, that is, in the case of the pattern 1 or 2 shown in FIG. 12, the light amount of the 2nd laser beam needs to be increased, and the cross point Can be predicted as the position of P1, so that the light amount adjustment signal is set to LD so that the light amount of the second laser beam increases by (1s−2s).
Output to D36A (step 108). This allows
The light amount of the first laser beam and the light amount of the second laser beam coincide at the position P1.

The tilt of the first laser beam (1e-1s)
When / L is equal to or smaller than the inclination (2e-2s) / L of the second laser beam, that is, in the case of the pattern 3 or 4 shown in FIG. 12, the light amount of the second laser beam needs to be increased, and the cross point is Since the position of P2 can be predicted, the light amount of the second laser beam is (1e
-2e) the light amount adjustment signal to the LDD 36
A is output to A (step 110). Thereby, 1st
The light amount of the laser beam and the light amount of the second laser beam are P
The two positions coincide.

On the other hand, if the result in step 104 is negative, it is determined whether the light quantity data 1s is smaller than the light quantity data 2s and whether the light quantity data 1e is smaller than the light quantity data 2e (step 112). When the light amount data 1s is smaller than the light amount data 2s and the light amount data 1e is smaller than the light amount data 2e, that is, in the case of the patterns 13 to 16 shown in FIG. 12, the inclination (1e-1s) of the first laser beam. It is determined whether / L is larger than the inclination (2e-2s) / L of the second laser beam (step 114).

The tilt of the first laser beam (1e-1s)
When / L is larger than the inclination (2e-2s) / L of the 2nd laser beam, that is, in the case of the patterns 13, 14, and 16 shown in FIG. 12, it is necessary to reduce the light amount of the 2nd laser beam. Since the cross point can be predicted as the position of P2, a light amount adjustment signal is output to the LDD 36A so that the light amount of the second laser beam is reduced by (2e-1e) (step 116). Thus, the light amount of the first laser beam and the light amount of the second laser beam match at the position P2.

The tilt of the first laser beam (1e-1s)
When / L is equal to or smaller than the inclination (2e-2s) / L of the second laser beam, that is, in the case of the pattern 15 shown in FIG. 12, the light amount of the second laser beam needs to be reduced, and the cross point is P1. Since the position can be predicted, the light amount of the second laser beam is (2s−1).
s) The light amount adjustment signal is output to the LDD 36A so as to decrease by the amount (step 118). Thus, the light amount of the first laser beam and the light amount of the second laser beam match at the position P1.

The light quantity of the second laser beam is adjusted little by little, the light quantity data is fetched each time, and this operation is repeated until the light quantity of the first laser beam and the light quantity of the second laser beam match. You may make it.

As described above, when there is no cross point, the light amount of the second laser beam is adjusted. The amount of change in the light amount is determined by the light amount of the first laser beam and the light amount of the second laser beam within the overlap region. Therefore, the change in the overall amount of light is very small, and is not so large as to cause a deterioration in image quality due to a change in image density or the like.

If the determination in step 112 is negative, that is, in the case of patterns 7 to 10 and 12 shown in FIG.
Since there is a cross point, the position of the cross point is calculated (step 120). The calculation of the cross point will be described with reference to the flowchart shown in FIG.

In step 200 shown in FIG. 9, the light quantity data 1s and 1e taken in
A linear equation in the overlap region of the laser beam is obtained. In the next step 202, a straight line equation in the overlap region of the 2nd laser beam is obtained from the light quantity data 2s and 2e similarly taken in. The approximation is not limited to the linear approximation, and if the optical characteristics of the divided optical scanning device 10 are known in advance, the approximation may be performed using a curve expression based on the optical characteristics.

In step 204, the intersection of the straight line formulas obtained in steps 200 and 202 is calculated. This intersection is a cross point where the light quantity of the first laser beam and the light quantity of the second laser beam match. The cross point is expressed as a width (distance) from the position of P1, but it is desirable to convert the cross point into a numerical value in units of an image clock in consideration of a circuit configuration and a control method. Therefore, in step 206, the data of the cross point is converted into a numerical value in units of the image clock. Thus, the converted data is represented as the number of image clocks from the position of P1.

In the next step 208, the predetermined data from the generation of the SOS signal on the first laser beam side to the position P 1 and the data from the position P 1 to the cross point calculated in step 206 are added. (See FIG. 10). Also, the SO on the second laser beam side
The predetermined specified data from the generation of the S signal to the position P1 and the data from the position P1 to the cross point calculated in step 206 are added (see FIG. 10).
That is, the number of image clocks up to the scanning end position of the first laser beam and the number of image clocks up to the scanning start position of the second laser beam, that is, the respective image clock numbers up to the image division position are calculated.

The cross point is determined as described above. Next, an operation of actually writing image data will be described. First, the 1 calculated by the main controller 26
The number of image clocks up to the scanning end position of the st laser beam and the number of image clocks up to the scanning start position of the second laser beam are used as count values as the timing generation circuit 32
To the image memory 30 as address data.

When the SOS signal is input, the timing generation circuit 32 starts counting, and for 1 second at a predetermined timing (when the first laser beam reaches the position P4).
The t_L / S_E signal is set to low level. This allows
Image data stored at the address output from the main controller 26 is read from the image memory 30 and output to the LDD 36B via the light amount measurement circuit 28. The LDD 36B controls on / off of the LD 38B according to the input image data. Thereby, the surface to be scanned 20 is exposed according to the image data.

Then, the count is counted by the main controller 2.
When the count value reaches the scanning end position of the first laser beam output from 6, that is, when the first laser beam reaches the cross point, the 1st_L / S_E signal is set to a high level. Thus, reading of the image data from the image memory 30 is stopped, and the exposure of the first laser beam is completed.

At the same time as the scanning of the first laser beam is started, the scanning of the second laser beam is also started.
That is, when the SOS signal is input, the timing generation circuit 32 starts counting, and the main controller 26
When the count value reaches the scanning start position of the 2nd laser beam output from, that is, when the 2nd laser beam reaches the cross point, the 2nd_L / S_E signal is set to low level. As a result, the image data stored at the address output from the main controller 26 is read from the image memory 30 and output to the LDD 36A via the light amount measurement circuit 28. In LDD36A,
On / off of the LD 38A is controlled according to the input image data. Thereby, the surface to be scanned 20 is exposed according to the image data.

When the second laser beam reaches the position P5, the 2nd_L / S_E signal is set to a high level. Thereby, reading of the image data from the image memory 30 is stopped, and the exposure of the second laser beam is completed.

As described above, the cross point at which the light amount of the first laser beam and the light amount of the second laser beam coincide with each other in the overlap region is calculated, and the cross point is used as a division position to set the first laser beam and the second laser beam.
Since the scanning is divided by the laser beam, the step of the light quantity at the dividing position, that is, at the joint can be eliminated.
Further, even when the light amount distribution changes and there is no cross point, since the cross point can be generated by adjusting the light amount of the second laser beam, the step of the light amount at the joint can be eliminated. It is possible to prevent streak patterns, image disorder, or image disorder.

In this embodiment, when there is no cross point, only the light quantity of the second laser beam is adjusted. However, the present invention is not limited to this, and only the light quantity of the first laser beam may be adjusted. Alternatively, the light amounts of both the first laser beam and the second laser beam may be adjusted.

In the case where the light amount distribution hardly changes, the division position is changed to various positions so that printing can be performed in advance, and a plurality of types of test images are printed by changing the division position at the shipping stage. May be used to set a division position where the step of the light amount is the smallest. This eliminates the need for a means for detecting the amount of light, a means for determining the amount of light, and a means for calculating the cross point, so that the apparatus can be configured at low cost.

[0081]

As described above, according to the present invention,
A setting unit that sets a position where the light amounts of the two light beams that scan the overlapping area of the partial scanning region substantially coincide with each other as a division position, and performs division exposure on the surface to be scanned at the set division position. Therefore, even when the scanning area is divided and scanning is performed with a plurality of light beams, it is possible to eliminate the division position of the scanning area, that is, to eliminate the step in the amount of light at the joint, and to perform a streak pattern or image disorder at the joint. This has the effect that the occurrence of image blur can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a split optical scanning device.

FIG. 2 is a timing chart for explaining an exposure operation in the divided optical scanning device.

FIG. 3 is a diagram showing a light amount distribution of the divided optical scanning device.

FIG. 4 is a block diagram illustrating a schematic configuration of a control unit.

FIG. 5 is a diagram for explaining the arrangement of the photodiodes and the detection of the amount of light by the photodiodes.

FIG. 6 is a circuit diagram of a light quantity measuring circuit.

FIG. 7 is a diagram for explaining light amount measurement in an overlap area.

FIG. 8 is a flowchart showing a flow of processing of a cross point determination routine.

FIG. 9 is a flowchart showing a flow of processing of a cross point calculation routine.

FIG. 10 is a timing chart for explaining the operation of the light quantity measurement.

FIG. 11 is a diagram showing a light amount distribution in an overlap region.

FIG. 12 is a diagram illustrating a relationship between light amounts in an overlap region.

FIG. 13 is a diagram for explaining a light amount distribution.

FIG. 14 is a diagram for explaining a relationship between a write start position of image data and a light amount distribution.

[Explanation of symbols]

Reference Signs List 10 split optical scanning device 12 laser light source unit 14 control unit (control unit, determination unit, calculation unit, light amount adjustment unit) 16 laser beam 18 polygon mirror 20 scanned surface 22 SOS sensor 24 reflection mirror 34 photodiode (light amount detection unit) 36 LDD 38 LD

Claims (3)

[Claims] A plurality of light sources; a light source driving unit for driving the plurality of light sources; and a scanning area on a surface to be scanned corresponding to a plurality of light beams emitted from the plurality of light sources, respectively. A scanning unit that scans each of the partial scanning regions divided so as to partially overlap along the main scanning direction of the beam with the plurality of light beams; and two scanning units that scan the overlapping region in the overlapping region. Setting means for setting, as a division position, a position at which the light beam amounts substantially coincide with each other; and control for performing divisional exposure on the surface to be scanned by the plurality of light beams at the division position set by the setting means. Means, and a split optical scanning device comprising: 2. A plurality of light sources, and a scanning area on a surface to be scanned corresponding to a plurality of light beams respectively emitted from the plurality of light sources partially overlaps in a main scanning direction of the light beams. Scanning means for scanning each of the divided partial scanning areas with the plurality of light beams, and light quantity detecting means for respectively detecting the light quantities of the two light beams for scanning the overlapping area at both ends of the overlapping area. Determining means for determining, based on the detection result of the light amount detecting means, whether or not there is a position where the light amounts of the two light beams substantially coincide with each other in the overlapping area; Calculating means for calculating a position at which the light amounts of the two light beams substantially match based on a detection result of the light amount detecting means when it is determined that there is a position where the light amounts of the two light beams substantially match; If the determining means determines that there is no position where the light amounts of the two light beams substantially match, the two light beams are positioned so that the position where the light amounts of the two light beams substantially match exists. A light amount adjusting unit that adjusts the light amount of at least one of the light beams; and a position where the light amounts of the two light beams substantially match each other is set as a division position so that the surface to be scanned is divided and exposed by the plurality of light beams. Control means for controlling the light beam splitting device. 3. The data representing a position at which the light amounts of the two light beams substantially coincide with each other includes a distance from a boundary position of the overlapping area to a position at which the light amounts of the two light beams substantially coincide with each other. The split optical scanning device according to claim 2, wherein the data is data represented by a distance from a scanning start position to a boundary position of the overlapping area.