JP3468248B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more specifically, to an image forming apparatus which simultaneously scans a recording medium in parallel in the main scanning direction with a plurality of light beams to record a plurality of lines simultaneously. The present invention relates to a technique of detecting a deviation amount of a scanning position between the light beams and correcting image recording based on the detected deviation amount.

[0002]

2. Description of the Related Art Image recording in an image forming apparatus for recording image information by deflecting a laser beam (light beam) modulated on the basis of an image signal by a rotating polygon mirror or the like and scanning the recording medium. It is known that a configuration in which a plurality of laser beams are used to simultaneously record a plurality of lines can be used to increase the speed of the above (see Japanese Patent Laid-Open No. 2-188713).

By the way, as described above, when a plurality of laser beams are simultaneously scanned, if the scanning positions between the plurality of laser beams are deviated in the main scanning direction or the sub-scanning direction, variations in line spacing and writing position may occur. The deviation will impair the fidelity of image formation. Therefore, JP-A-2-188713 and JP-A-57-39
The image forming apparatus disclosed in Japanese Patent No. 669 discloses a configuration in which a deviation amount in the main scanning direction between a plurality of laser beams is detected and a recording start position of each laser beam is determined according to the deviation amount. There is.

[0004]

By the way, in the detection of the scanning position deviation amount between a plurality of laser beams, there are uneven rotations of the motor for rotating the rotary polygon mirror, the accuracy limit of the counter for measuring the deviation amount, and the like. For this reason, there is a drawback that the reproducibility of the deviation amount measurement is low, and due to such low reproducibility, different deviation amounts may be detected for each measurement.

For this reason, if the shift amount of the scanning position is detected for each line and the correction value is determined for each line based on the detection result to perform the correction, the shift amount for each line is measured. There is a possibility that the results may vary, which may cause image recording under different conditions for each line, resulting in poor image quality. Further, due to the low reproducibility, the detection result of the deviation amount differs for each image recording, and there is a possibility that it is not possible to form an image of constant image quality because recording is performed under different conditions for each image recording.

Here, as a means for improving the reproducibility of the deviation amount measurement, it is conceivable to increase the accuracy of the counter used for the deviation amount measurement, and in order to improve the accuracy, it is necessary to increase the frequency of the clock input to the counter. However, there was a limit to the clock frequency, and it was difficult to obtain the desired accuracy. The present invention has been made in view of the above problems, and even if there is unevenness in rotation of a motor that rotates a rotary polygonal mirror, accuracy limit of a counter for measuring a deviation amount, and the like, correction is made for the deviation amount of a scanning position. The present invention aims to improve the image quality in an image forming apparatus that simultaneously scans a plurality of light beams so that the above can be performed stably.

Further, even if there is unevenness in rotation of the motor for rotating the rotary polygon mirror or the accuracy limit of the counter for measuring the deviation amount, the detection accuracy of the deviation amount can be stabilized and the scanning can be performed. It is an object of the present invention to make correction of image recording to cope with positional deviation with high reliability.

[0008]

Therefore, an image forming apparatus according to a first aspect of the present invention is an image forming apparatus which simultaneously scans a recording medium in parallel in the main scanning direction by a plurality of light beams to simultaneously record a plurality of lines. In, before starting scanning in the sub-scanning direction orthogonal to the main scanning direction, the deviation amount of the scanning position between the plurality of light beams is detected in at least one of the main scanning direction and the sub-scanning direction. The correction characteristic determined based on the deviation amount detected before the start of the sub-scanning is fixed during one image recording, and the image recording by the plurality of light beams is corrected according to the deviation amount.

According to a second aspect of the present invention, in the image forming apparatus for simultaneously scanning a recording medium in parallel in the main scanning direction with a plurality of light beams to record a plurality of lines at the same time, the plurality of light beams are provided between the plurality of light beams. The deviation amount of the scanning position is detected a plurality of times in at least one of the main scanning direction and the sub-scanning direction orthogonal to the main scanning direction, and is determined based on a plurality of deviation amount data detected over the plurality of times. Image recording by the plurality of light beams according to a correction characteristic that is set.

Further, in the apparatus according to the invention of claim 3,
The scanning in the main scanning direction by the plurality of light beams is performed by a rotary polygon mirror, and the amount of deviation is detected at least by the number of surfaces of the rotary polygon mirror or more. Further, in the apparatus according to the invention of claim 4, the correction characteristic is determined based on the deviation amount data excluding the maximum value and the minimum value of the plurality of deviation amount data detected over the plurality of times. did.

Further, in the apparatus according to the invention of claim 5,
The displacement amount is detected a plurality of times before the scanning in the sub-scanning direction is started, and the correction characteristic determined based on the plurality of displacement amount data detected before the sub-scanning is started is displayed. One image is fixed during recording, and the image recording by the plurality of light beams is corrected. An image forming apparatus according to a sixth aspect of the present invention is an image forming apparatus that simultaneously scans a recording medium in parallel in a main scanning direction with a plurality of light beams to record a plurality of lines at the same time. In a state in which the speed is compulsorily slowed as compared with the time of image formation, the amount of deviation of the scanning position between the plurality of light beams is at least one of the main scanning direction and the sub scanning direction orthogonal to the main scanning direction. It is configured to detect and correct the image recording by the plurality of light beams based on the detected shift amount.

Further, in the apparatus according to the invention of claim 7,
The detection of the amount of deviation, which is performed by slowing the main scanning speed,
Before the scanning in the sub-scanning direction is started, it is performed a plurality of times,
The correction characteristic determined based on the plurality of displacement amount data obtained by the detection is fixed during one image recording, and the image recording by the plurality of light beams is corrected. Further, in the apparatus according to the invention of claim 8, at least a pair of light beam detection means in which the interval of the timing of detecting the same light beam changes in proportion to the change of the scanning position in the sub-scanning direction is provided in the main scanning direction. Are arranged in parallel to each other, measure the interval of timing detected by the light beam detecting means for each light beam, and shift the scanning position in the sub-scanning direction between a plurality of light beams based on the difference in the measured intervals. It is configured to detect the amount.

Further, in the apparatus according to the invention of claim 9,
At least a pair of light beam detection means are arranged in parallel in the main scanning direction, and each light beam detection means measures an interval between timings at which the same light beam is detected, while each light beam detection means detects a different light beam. The interval of the timing is measured, and the deviation of the scanning position in the main scanning direction between the plurality of light beams is detected based on the difference between the measured intervals.

Further, in the apparatus according to the invention of claim 10,
When the shift amount in the main scanning direction is detected, the start position of image recording by each light beam is corrected based on the shift amount in the main scanning direction, and when the shift amount in the sub scanning direction is detected. By adjusting the scanning position of the light beam in the sub-scanning direction based on the shift amount in the sub-scanning direction, the deviation of the scanning position between the plurality of light beams is corrected to perform image recording.

[0015]

According to the image forming apparatus of the first aspect of the present invention, the deviation amount of the scanning position between the plurality of light beams in the main scanning direction or the sub scanning direction is detected before the start of the sub scanning. Then, the correction characteristic is determined based on the deviation amount, and during the recording of the one image, the correction characteristic based on the deviation amount detected before the start of the sub-scan is used as it is to correct the image recording.

In other words, when the reproducibility of the deviation amount detection is low, if the deviation amount is calculated for each line, a different detection result for each line will occur even though the deviation amount does not actually change. As a result, there is a possibility that a different characteristic will be corrected for each line. Therefore, a correction characteristic at the time of recording the image is determined based on the shift amount obtained before the start of the sub-scanning, and the determined correction characteristic is continuously used until the image recording is completed, and image recording is continuously performed. When one image is recorded, the correction corresponding to the deviation amount is performed with a constant correction characteristic.

On the other hand, according to the image forming apparatus of the second aspect of the present invention, the deviation amount of the scanning position between the plurality of light beams in the main scanning direction or the sub-scanning direction is not limited to one time, but is more than once. A correction characteristic for detecting the correction amount and corresponding to the deviation amount is determined based on the detection result of the plurality of times. If the reproducibility of the deviation amount detection is low, a different deviation amount may be detected for each detection even if the deviation amount does not actually change. Therefore, by detecting the deviation amount over a plurality of times, the value estimated to be the closest to the actual deviation amount in the deviation of the deviation amount detection value is selected, for example, by averaging processing or selection of high-frequency data. And the median value can be selected.

In the apparatus according to the third aspect of the present invention, in the structure in which the main scanning is performed by the deflection of the rotary polygon mirror, the detection of the shift amount over the plurality of times is performed by the number of surfaces of the rotary polygon mirror or more. It is configured to be performed only for the number of times so that it is possible to detect the characteristic change of the scanning position shift due to the variation of each surface of the rotary polygon mirror. Further, in the apparatus according to the invention of claim 4, the correction characteristic is determined based on the remaining displacement amount data excluding the maximum value and the minimum value among the plurality of displacement amount data obtained by the plurality of detections. It was configured to let. As a result, even if a value that is extremely different from the actual value is detected in the deviation amount detection, it is possible to prevent the correction characteristic from being affected based on the detection result.

Further, in the apparatus according to the invention of claim 5,
The displacement amount is detected a plurality of times before the sub-scanning is started, and the correction characteristic determined based on the plurality of displacement amount data obtained before the sub-scanning is fixed during one image recording,
The correction corresponding to the shift amount is made constant for each image recording to avoid image recording under different conditions for each line.

On the other hand, in the image forming apparatus according to the sixth aspect of the present invention, the amount of deviation is detected while the main scanning speed is forcibly slowed down, so that the main scanning is performed at a normal scanning speed. It is possible to improve the accuracy of measuring the scanning time in the main scanning direction, and thus the accuracy of detecting the deviation amount. Here, in the apparatus according to the invention of claim 7, the deviation amount detection in the state where the main scanning speed is forcibly slowed down is performed a plurality of times before the sub-scanning is started, and based on the plurality of detection results. An image is recorded by using the determined correction characteristic as an assessment during recording of one image. According to such a configuration, the main scanning speed is slowed down before the sub-scanning is started to ensure high measurement accuracy, and the variation of each surface of the rotary polygon mirror can be detected by a plurality of detections. The correction characteristics do not change during this and the image quality does not deteriorate.

Further, in the apparatus according to the invention of claim 8,
For example, the light beam detection may be performed so that the interval between the timings at which the same light beam is detected by the light beam detection means arranged in parallel in the main scanning direction changes proportionally due to the deviation of the scanning position in the sub scanning direction. The detection areas of the means are configured to be non-parallel to each other. According to this structure, the interval in the sub-scanning direction between the plurality of light beams is proportional to the deviation of the timing intervals at which the respective light beams are detected, and thus the deviation amount in the sub-scanning direction is detected. It will be.

According to the ninth aspect of the invention,
The time corresponding to the interval of the light beam detecting means is obtained by measuring the time interval at which the same light beam is detected by the light beam detecting means arranged in parallel in the main scanning direction. To measure the interval of the timing when different light beams are detected. And
Based on the deviation between the detection intervals when the same light beam is detected and the detection intervals when different light beams are detected, only the deviation amount of each light beam in the main scanning direction is detected.

Further, in the apparatus according to the invention of claim 10,
When the shift amount in the main scanning direction is detected, the start position of image recording by each light beam is corrected based on the shift amount in the main scanning direction, so that the scan position in the main scanning direction is shifted. Also, the image recording is started from the same position for each light beam, and when the shift amount in the sub-scanning direction is detected, the scanning position of the light beam is adjusted in the sub-scanning direction based on the shift amount. The mechanical adjustment is performed to correct the scanning position in the sub-scanning direction to the desired position.

[0024]

EXAMPLES Examples of the present invention will be described below. Figure 1
FIG. 1 is a diagram showing an image exposure system of a laser printer as an example of an image forming apparatus according to the present invention. The laser printer of this example has two laser beams (light beams) L1 internally modulated according to image data. , L2 are scanned in parallel to the main scanning direction, and two lines are simultaneously recorded.

In FIG. 1, the light source unit 1 includes the above-mentioned 2
The two semiconductor lasers 1a and 1b are arranged in one row, and the two divergent lights emitted from the light source unit 1 become two parallel laser beams L1 and L2 by the condenser lens 2. The two laser beams L1 and L2 are applied to a polygon mirror 3, and the polygon mirror (rotating polygon mirror) 3
The two laser beams L1, L2 deflected by
The photosensitive drum (recording medium) 5 is scanned via the fθ lens 4.

The photosensitive drum 5 has a laser beam L1,
The laser beams L1 and L2 and the photosensitive drum 5 are relatively moved in the sub-scanning direction (direction orthogonal to the main scanning direction) by being rotationally driven in synchronization with the main scanning of L2, and two-dimensional image recording is performed. Is done. As described above, the exposure corresponding to the image data is simultaneously performed for two lines to form the electrostatic latent image on the photosensitive drum 5 (recording medium). Then, toner having a reverse polarity is attached to the electrostatic latent image to develop it, and then the recording paper is superposed on the toner image, and the corona charger reverses the polarity of the corona charging from the back side of the recording paper. The toner image is transferred to the recording sheet by applying the polar charge to the recording sheet.

The scanning start point of the laser beams L1 and L2 deflected by the polygon mirror 3 is detected by an index sensor 6 arranged at the tip side of the scanning area. The reflecting mirror 7 has a laser beam L at the tip of the scanning line.
When the laser beams L1 and L2 are emitted,
2 for guiding the index sensor 6 to the index sensor 6.

As shown in FIG. 2, the index sensor 6 is integrally provided with five sensors A to D (A to D: light beam detecting means) which individually output detection signals as one-chip sensors. To be done. The sensors A to D are arranged side by side in the main scanning direction so that the laser beams L1 and L2 are scanned in the order of A → B → D → C. The light beam detection area (light receiving area) of each of the sensors A to D is formed in the shape of a right triangle having a height in the sub-scanning direction (vertical direction in FIG. 2) that includes the scanning lines of the two laser beams L1 and L2 with a margin. ing.

In the sensor A, the long side of the two sides forming the right-angled angle of the detection area of the right-angled triangle is the edge on the starting end side (left side in FIG. 2) in the main scanning direction, and the above-mentioned The long sides are arranged so as to be orthogonal to the main scanning direction (parallel to the sub scanning direction). Further, in the sensor B, the hypotenuse of the detection area of the right-angled triangle serves as the edge on the starting side in the main scanning direction, and the hypotenuse obliquely intersects the main scanning direction at an angle formed by the long side and the hypotenuse. Will be placed.

Further, the sensor D is arranged so that the arrangement state of the detection region of the sensor A is vertically inverted when the sub-scanning direction is vertical. Further, the sensor C is arranged so that its detection area is axially symmetrical with respect to the sensor A with respect to the axis along the sub-scanning direction. The sensors A and C shown in FIG.
Is arranged such that the long side of the two sides forming the right-angled angle is orthogonal to the main scanning direction, but the long side may be arranged to be parallel to the main scanning direction. good.

Due to the arrangement of the sensors A to D, the edges of the sensors A to D on the starting side in the main scanning direction are parallel to each other in the sub scanning direction, and the sensors B and C are parallel to each other.
Are non-parallel to each other, and the inclination directions with respect to the main scanning direction are reversed. That is, in the sensors B and C, the distance between the edges on the starting side in the main scanning direction of the light beam detection region increases as the scanning positions of the laser beams L1 and L2 shift downward in FIG.

In FIG. 2, the detection start end position of the laser beam L1 by the sensor A (the position where the beam detection signal rises) is shown as a1, the detection start end position of the laser beam L2 is shown as a2, and so on. Sensors B to D
The detection start position of the laser beams L1 and L2 by
It is shown as b2, c1, c2, d1, d2. The laser beam detection timing interval by the sensors A to D indicates the interval of the timing at which the laser beam is detected at the detection start end position, in other words, the rising interval of the beam detection signals of the sensors A to D. To do.

The sensors A to D are used to detect the scanning position deviation between the laser beams L1 and L2 in the main scanning direction and the sub scanning direction as follows. First, the detection of the shift amount of the scanning position in the sub-scanning direction will be described with reference to the flowchart of FIG. First, only the laser beam L1 is turned on and the main scanning is performed (S1).

Then, the laser beam L1 is applied to the sensor A.
When scanning up to D, the time (detection timing interval) T1 (detection timing interval) from the rise (b1) of the beam detection signal of the sensor B to the rise (c1) of the beam detection signal of the sensor C is measured (see FIG. 4). (S2). Then
Instead of the laser beam L1, only the laser beam L2 is turned on and main scanning is performed (S3).

Then, similarly, the laser beam L2
Scans the sensors A to D, the time T2 (see FIG. 4) from the rise (b2) of the beam detection signal of the sensor B to the rise (c2) of the beam detection signal of the sensor C is measured (see FIG. 4). S4). When the measurement of the times T1 and T2 is completed, the absolute value T3 of the deviation between the times T1 and T2 is calculated (S5).

Further, a difference between the reference value of the deviation T3 corresponding to the case where the distance between the laser beams L1 and L2 in the sub-scanning direction is normal and the deviation T3 actually obtained by the above processing is calculated. , The difference is converted into a shift amount in the sub-scanning direction (S6). The reference value may be arbitrarily changed and set through the operation unit of the laser printer.

That is, assuming that the positions b1 and c1 in the sub-scanning direction where the laser beam L1 is detected by the sensors B and C are assumed as reference positions, the scanning position of the laser beam L2 is lower in the sub-scanning direction in FIG. Suppose it is shifted to the side. In this case, at the positions b2 and c2 in the sub-scanning direction where the laser beam L2 is detected by the sensors B and C, the distance between the detection start end side edges of the sensors B and C is lower in the main scanning direction in FIG. By being configured to spread at a constant rate on both sides, the interval (time T2) between the positions b2 and c2 is lengthened by a distance corresponding to the amount of deviation in the sub-scanning direction, and thus the deviation of the time T3 from the reference time is deviated. It will correspond to the quantity.

Therefore, if the deviation between the time T3 and the reference time is obtained, the deviation amount of the distance between the laser beams L1 and L2 in the sub-scanning direction is calculated based on the information on the scanning speed and the angle of the hypotenuse in the sensors B and C. Can be calculated. It should be noted that the above-mentioned detection of the shift amount of the scanning position in the sub-scanning direction can be performed by providing a sensor pair in which the interval of the timing of detecting the same light beam changes in proportion to the change of the scanning position in the sub-scanning direction. Yes, as above,
The timing of the fall of the beam detection signal may be used as the base point of time measurement instead of the interval of the rise of the beam detection signal, and the shape of the detection region of the sensor is not limited.

Further, in the above method, the laser beam L
Although the interval in the sub-scanning direction between 1 and L2 is detected, the absolute sub-scanning position may be displaced.
By comparing the time T1 or the time T2 with the reference time, absolute deviation of the sub-scanning position can be detected, or
For example, a sensor may be separately provided to detect that the laser beam L1 is scanned at the regular sub-scanning position.

Here, for example, with the scanning position of the laser beam L1 in the sub-scanning direction being fixed, Japanese Patent Laid-Open No. 63-50.
When a mechanism capable of adjusting the scanning position in the sub-scanning direction is provided on the laser beam L2 side as disclosed in Japanese Patent No. 809, the laser beam L2 in the sub-scanning direction in the sub-scanning direction is calculated based on the information on the calculated displacement amount. By adjusting the scanning position with the scanning position of the laser beam L1 fixed (see FIG. 8), it becomes possible to correct the interval between the laser beams L1 and L2 in the sub-scanning direction to a desired value.

In the apparatus disclosed in the above-mentioned Japanese Patent Laid-Open No. 63-50809, a holding plate for holding a prism for passing a laser beam is supported rotatably around an axis parallel to the prism surface, and The prism angle is adjusted by advancing and retracting the adjusting screw that comes into contact with the rotating front end portion and determines the angle of the holding plate, thereby adjusting the pitch (interval) in the sub-scanning direction.

Next, the detection of the deviation amount of the scanning position in the main scanning direction will be described with reference to the flowchart of FIG. First, turn on only the laser beam L1 (S1
1) Measure the time difference (detection timing interval) T5 (see FIG. 6) between the rising edge (a1) at which the laser beam L1 is detected by the sensor A and the rising edge (d1) at which the laser beam L1 is detected by the sensor D. (S12).

Since the edges of the light beam detection areas of the sensors A and D on the starting side in the main scanning direction are parallel to the sub scanning direction (orthogonal to the main scanning direction), the time difference T5 is obtained.
Is not affected by the scanning position in the sub-scanning direction and is determined only by the interval between the edges of the sensors A and D on the starting end side in the main scanning direction and the scanning speed. Next, each laser beam L is arranged so that only the laser beam L1 is incident on the sensor A and only the laser beam L2 is incident on the sensor D.
Scan while performing mask control of 1 and L2 (S13),
The time difference T6 (see FIG. 6) between the rising edge (a1) at which the laser beam L1 is detected by the sensor A and the rising edge (d2) at which the laser beam L2 is detected by the sensor D is measured (S14).

The mask control is performed for each laser beam L1,
It may be controlled by turning on / off L2, or the laser beams L1, L2 may be selectively incident on the sensors A, D by using a polarizing element or the like. here,
When the laser beams L1 and L2 are scanned without shifting in the main scanning direction, the time differences T5 and T6 should be the same time. For example, the laser beam L2 scans after the scanning of the laser beam L1. In the case of the above, the delay (shift of the scanning position in the main scanning direction) is the time T
7 (= T6-T5) (S1
5: see FIG. 6).

In the above description, the amounts of deviation of the laser beams L1 and L2 in the main scanning direction are detected using the sensors A and D, but the time T3 corresponding to the interval in the sub scanning direction is obtained in advance. Therefore, it is possible to detect the shift amount in the main scanning direction using the sensors A and C. As described above, when the deviation amount of the scanning position in the main scanning direction between the laser beams L1 and L2 is detected as the time T7, the writing to the laser beam L2 is performed for the writing by the laser beam L1. If it is delayed by just the amount, the image recording can be started without being shifted in the main scanning direction by the two laser beams L1 and L2 that are scanned while being shifted in the main scanning direction.

The laser beam L is used to control the writing position.
The generation of the horizontal synchronization signal corresponding to laser beam L2 may be delayed by the time T7 with respect to the generation of the horizontal synchronization signal corresponding to 1. By the way, the measurement of the detection timing interval of the laser beams L1 and L2 by the sensors A to D is performed in the present embodiment as shown in FIG.

Although FIG. 7 shows the case where the time difference (time between a1 and d1) at which the laser beam L1 is detected by the sensors A and D is measured, the sensors A to D are shown.
The same applies to other combinations. Figure 7
, 16 kinds of delay clocks dl0 (reference clock) by sequentially delaying the reference clock clk by 1/16 cycle
~ Dl15 is generated using a digital delay line.

In FIG. 7, the clocks clk, dl
1, dl2, dl8, dl12, dl15 are shown, and other delay clocks are not shown. If, for example, the clock synchronized with the rising edge a1 of the detection signal of the sensor A (the clock that first rises immediately after the rising edge of the detection signal) is the clock dl8, the rising edge at the time of synchronization is the first count, and then this clock is continued.
The rising edge of dl8 is counted sequentially.

If the detection signal of the sensor D rises during the counting and the clock synchronized with the rise (d1) of this detection signal is the clock dl12, the number of the rising edges of the clock dl8 up to that time (sensor A The value obtained by subtracting 1 from the detection signal (a1) including the rising edge of the clock dl8 multiplied by the clock cycle is the phase difference between the clock dl8 and the clock dl12 (4/16 cycle, which is the delay clock). Number = dl4)) is added, and the output time difference of the detection signals of the sensors A and D (interval between a1 and d1).
become.

For example, in the above-described deviation detection in the sub-scanning direction, the respective times T1 and T2 are obtained as the clock count number and the delay clock number as described above, while the reference time corresponding to the specified value of the interval is also obtained. Since the clock count number and the delay clock number are given, the count number and the delay clock number may be respectively calculated in the calculation of the time difference. In this case, the information about the shift amount in the sub-scanning direction is obtained as the clock count number and the delay clock number, and the shift amount in the main scanning direction is similarly detected as the clock count number and the delay clock number.

When the shift amount in the main scanning direction is obtained as the count number of the delay clock and the clock phase difference, the horizontal synchronization signal is adjusted based on the clock count number, and the shift amount obtained as the clock phase difference is calculated. , Each laser beam L1 from the delay clocks dl0 to dl15
The adjustment may be made by selecting the dot clock corresponding to L2.

Here, the deviation amount in the main / sub-scanning direction is detected and the correction (scanning position adjustment,
The execution timing of (setting of synchronization signal characteristics) will be described with reference to the flowchart of FIG. In the flowchart of FIG. 9, first, it is determined whether or not the sub-scanning (image recording) is started (S21).
The shift amount in the sub-scanning direction described in the flowchart of FIG. 7 is detected (S22).

Then, in order to eliminate the detected deviation in the sub-scanning direction, for example, the sub-scanning position of the laser beam L1 is fixed and the sub-scanning position on the laser beam L2 side is adjusted (S23). When the detection of the deviation amount in the sub-scanning direction and the scanning position adjustment based on the detection result are completed, subsequently, the deviation amount in the main scanning direction described in the flowchart of FIG. 5 is detected (S24). Then, the output characteristic (writing position) of the horizontal synchronizing signal is determined for each of the laser beams L1 and L2 based on the shift amount in the main scanning direction (S2).
Five).

When the detection of the deviation amount in the sub-scanning direction and the adjustment of the scanning position and the detection of the deviation amount in the main scanning direction and the setting of the synchronization signal are completed as described above, the sub-scanning (image recording) is started. (S26) Until one image is recorded, the process is not advanced to S22 to S26, and the image is recorded by the sub-scanning position adjusted before the start of the sub-scan and the horizontal synchronizing signal set before the start of the sub-scan. (S27).

As described above, before the sub-scanning is started, the shift amounts in the main and sub-scanning directions are obtained, and the sub-scanning position adjustment and the output characteristic of the horizontal synchronizing signal corresponding to the detected shift amount are calculated. The setting is performed, and the deviation amount is not newly detected during image recording, the correction characteristic corresponding to the deviation amount detected before the sub-scanning is started is fixed as it is, and the image recording is performed to the end. The amount of deviation is detected and the correction characteristic is determined in units of one image recording.

The detection of the scanning position shift amount is influenced by the rotation unevenness of the motor for rotating the polygon mirror (rotary polygon mirror) 3, the measurement accuracy of the detection timing intervals of the sensors A to D, and the reproduction of the measurement result. It is difficult to maintain high sex. For this reason, if the shift amount is obtained for each main scanning (for each line), and the sub-scanning position is adjusted and the writing position is corrected each time based on the detection result,
Although the deviation amount does not actually change, a different deviation amount is detected for each line due to the low reproducibility,
As a result, image recording is performed with different sub-scanning intervals and writing positions for each line, which may deteriorate image quality.

Therefore, in the present embodiment, based on the shift amount obtained before the start of the sub-scan, the correction characteristics at the time of recording the image (the sub-scanning position of the laser beam L2 and the writing positions of the respective beams L1 and L2). Until the recording of the image is finished, the image is recorded by continuously using the determined correction characteristic, and the sub-scanning interval and the writing position are recorded with the correction operation of at least the deviation amount. I tried not to change.

As described above, the shift amount is detected before the sub-scan is started, the correction characteristic corresponding to the shift amount is determined based on the detected shift amount, and once the sub-scan is started, the If the determined correction characteristic is fixed and the image is recorded, it is possible to avoid the deterioration of the image quality due to the variation of the correction characteristic during the image recording. However, since there is a variation in the detection of the deviation amount from the beginning, even if the above-described configuration makes it possible to perform constant correction during one image recording, if there is a large error in the detection result of the deviation amount before the start of sub-scanning, the image quality deteriorates. Resulting in.

Therefore, as shown in the flowchart of FIG. 10, a plurality of deviation amount data are obtained by detecting the deviation amount a plurality of times, and a high reliability is obtained based on these plural deviation amount data. It is desirable to detect the amount. In the flowchart of FIG. 10, first, it is determined whether or not the sub-scanning (image recording) is started (S31). When the sub-scanning is not started, the deviation amount in the sub-scanning direction described in the flowchart of FIG. Detect (S3
2).

When the deviation amount in the sub-scanning direction is detected, it is determined whether or not such detection is performed a predetermined number of times (S33), and the deviation amount detection in S32 is performed until the deviation amount is detected a predetermined number of times. Let it repeat. It is preferable that the predetermined number of times is equal to or larger than the number of surfaces of the polygon mirror (rotary polygon mirror) 3. This is because the deviation amount of the scanning position may change depending on which surface of the polygon mirror 3 is deflected due to the variation of each surface of the polygon mirror 3. If the deviation amount is detected by the number of times equal to or larger than the number of surfaces of the polygon mirror 3, all the deviation amount data when deflected on each surface are obtained, and on which surface the deviation amount is deflected based on the deviation amount data. In this case, it is possible to set a correction characteristic that is substantially satisfactory.

When the deviation amount in the sub-scanning direction is detected a predetermined number of times, the deviation amount for finally adjusting the scanning position is set based on the deviation amount data collected a predetermined number of times. (S34) Then, the sub-scanning position is adjusted based on the finally set displacement amount (S35). To set the final deviation amount data, specifically, the average value of a plurality of deviation amount data is set as the final deviation amount, or the frequency of the deviation amount is obtained, and the most frequent amount is determined as the final deviation amount. The amount of deviation,
Alternatively, the median value between the maximum value and the minimum value in the plurality of shift amount data may be set as the final shift amount.

In detecting the deviation amount over a plurality of times, singular data that is extremely different from other deviation amounts may appear, and if an average value, a maximum frequency value or a median value is obtained including this singular data, , There is a risk of being greatly affected by the singular data and causing an error in the deviation amount. Therefore, based on the remaining deviation amount data excluding the maximum value and the minimum value among a plurality of deviation amount data, the average value and the maximum It is advisable to calculate the frequency value and median value.

As described above, if the deviation amount in the sub-scanning direction is obtained a plurality of times and the average value of the deviation amount is set as the final deviation amount, the reproducibility of the deviation amount measurement is improved. Even if a small deviation amount is detected for each measurement, it is possible to detect the variation range and set a value close to the true deviation amount, and thus the sub-scanning position can be corrected more accurately. .

The shift amount in the main scanning direction is also detected a plurality of times (preferably more than the number of faces of the polygon mirror 3) as in the sub-scanning direction (S36, S37), and the detected shift amount data is obtained. Is set as the final shift amount in the main scanning direction (S38), and the horizontal synchronizing signal for each of the beams L1 and L2 is set based on the set shift amount (S39).

When the detection of the deviation amount in the sub-scanning direction and the adjustment of the scanning position and the detection of the deviation amount in the main scanning direction and the setting of the synchronization signal are completed as described above, the sub-scanning (image recording) is started. (S40) Until one image is recorded, the process is not advanced to S32 to S39, and the image is recorded by the sub-scanning position adjusted before the start of the sub-scan and the horizontal synchronizing signal set before the start of the sub-scan. (S41).

Incidentally, in the configuration in which the deviation amount of the scanning position is detected a plurality of times and the final deviation amount is set from the plural deviation amount data obtained by the detection, the influence of the deviation of the deviation amount measurement is sufficient. Since it is possible to reduce the amount of deviation, it is possible to perform the deviation amount for each main scanning instead of the configuration in which the deviation amount is detected only before starting the sub-scanning as described above, and the detection timing of the deviation amount is limited before starting the sub-scanning. Not a thing.

However, since it takes time to detect the amount of deviation over a plurality of times, as described above, before the sub-scanning (every one image recording).
It is preferable that it is configured to be performed when the power is turned on or when the power is turned on. By the way, the deviation in the measurement of the deviation amount occurs due to the unevenness in the rotation of the motor and the unevenness of each surface of the polygon mirror, and also due to the accuracy of time measurement. Therefore, by increasing the accuracy of the time measurement, it is possible to suppress the variation in the measurement of the deviation amount and to perform the correction with high accuracy.

Here, according to the flowchart of FIG.
An embodiment will be described in which the accuracy of time measurement for detecting the deviation amount is increased with a simple configuration to correct the scanning position deviation. In the flowchart of FIG. 11, first, it is determined whether or not the sub-scanning (image recording) is started (S5).
1). When the sub-scanning is not yet started, the deviation amounts of the beams L1 and L2 in the main and sub-scanning directions are detected.
Before the deviation amount is detected, the main scanning speed, that is, the rotation speed of the polygon mirror 3 is set to be forcibly slower than that during normal image recording (S52).

In this embodiment, as described above, the intervals between the timings at which the sensors A to D detect the beams L1 and L2 in accordance with the main scanning are measured to determine the scanning positions in the main scanning and sub-scanning directions. Since the deviation is detected, it is possible to increase the accuracy of the deviation amount measurement by seemingly increasing the clock frequency by slowing the main scanning speed and increasing the number of clocks generated during the measurement time.

Therefore, while the deviation amount is being detected (S53-S
60) is designed to maintain a predetermined main scanning speed (rotational speed of the polygon mirror 3) which is slower than that during normal image recording. When the main scanning speed is set to be slow, the amount of deviation in the sub-scanning direction shown in the flowchart of FIG. 3 is detected a predetermined number of times (preferably more than the number of polygon mirror 3 surfaces).
(S53, S54), the average deviation amount, which finally becomes the adjustment data of the sub-scanning position, is averaged based on a plurality of deviation amount data obtained by the predetermined number of detections, and the maximum frequency It is set by selecting data, selecting the median value, etc. (S55).

Here, since the speed of the main scanning is slowed down, the resolution of time T1, T2 and time T3 becomes high,
The time corresponding to the shift amount in the sub-scanning direction can be measured with high accuracy. Of course, since the deviation amount is detected a plurality of times, it is possible to specify the deviation range of the deviation amount measurement due to factors other than the accuracy of time measurement (non-uniform rotation of the motor, dispersion of each surface of the polygon mirror 3). Therefore, the shift amount in the sub-scanning direction can be obtained with high accuracy.

When the deviation amount in the sub-scanning direction is finally obtained, the sub-scanning position is adjusted based on the deviation amount data (S56). Similarly, the shift amount in the main scanning direction shown in the flowchart of FIG. 5 is detected (S57-59), and the horizontal synchronizing signals of the laser beams L1 and L2 are generated based on the shift amount in the main scanning direction. The characteristic (writing position of each beam) is determined (S60).

In this way, when the detection of the shift amount in the main scanning direction and the sub scanning direction, the adjustment of the sub scanning position based on the detection result, and the setting of the output characteristic of the horizontal synchronizing signal are completed, the actual image recording is performed. Therefore, the main scanning speed (rotational speed of the polygon mirror 3) is set back to the speed during normal image recording (S61). Then, the sub-scanning (image recording) is started (S62), and the sub-scanning position adjusted and the set horizontal synchronization signal based on the detection result before the sub-scanning is started without newly detecting the deviation amount during the image recording. The image is recorded as it is (S63).

Since the accuracy of time measurement can be improved by reducing the main scanning speed, it is not essential to detect the deviation amount for a plurality of times. Although the detection timing of the deviation amount is not limited to before the start of the sub-scanning, since the main scanning speed needs to be changed, the deviation amount is detected every one main scanning (one line). As described above, it is preferable to perform the configuration before the sub-scanning (every one image is recorded), or when the power is turned on.

By the way, the shapes and combinations of the detection areas of the sensors A to D used for detecting the deviation in the sub-scanning direction and the main scanning direction are not limited to those shown in FIG. For example, the configurations of the sensors A to D as shown in FIGS. That is, in order to detect the deviation in the sub-scanning direction, the same laser beam L
It is sufficient to arrange at least a pair of sensors in parallel with each other in the main scanning direction in which the interval between the timings of detecting 1 and L2 changes in proportion to the change in the scanning position in the sub scanning direction. It suffices to provide at least a pair of sensors that change the detection timing interval only at the main scanning timing without being affected by the change in the scanning position in the sub-scanning direction. When the rise is used as the base point of time measurement, if the edge of the light beam detection area on the starting side in the main scanning direction is specified,
The shape of the detection area may be triangular or square.

Further, in the above description, the four sensors A to D are constituted by the sensor pair used for detecting the deviation in the sub scanning direction and the sensor pair used for detecting the deviation in the main scanning direction.
It is possible to perform a similar function with the three sensors A to C, as shown in FIG. That is, in the configuration shown in FIG. 16, the two sensors A and B formed in the square light beam detection area are provided.
Is arranged so that the edge of the detection area on the starting side in the main scanning direction is orthogonal to the main scanning direction, while the sensor C in which the light beam detection area is formed in a triangle has a hypotenuse on the starting side in the main scanning direction. It is arranged so as to obliquely intersect with the main scanning direction.

When the shift amount in the sub-scanning direction is detected with the sensor structure shown in FIG. 16, a combination of the sensor B (or sensor A) and the sensor C is used (see FIG. 17). Here, although the edge of the detection area of the sensor B on the starting end side in the main scanning direction is orthogonal to the main scanning direction,
Since the end edge of the detection area on the starting side in the main scanning direction obliquely intersects the main scanning direction, the interval between the timings at which the sensors B and C detect the same beam is proportional to the change in the scanning position in the sub scanning direction. Change.

Therefore, if a shift in the sub-scanning direction occurs, it will appear as a change in the time difference detected by each of the sensors B and C, so that the shift amount in the sub-scanning direction can be detected (FIG. 17). reference). Further, when detecting the deviation in the main scanning direction by the sensors A to C as shown in FIG. 16, it is possible to detect the deviation in the same manner as described above by using the combination of the sensors A and B as shown in FIG.

That is, the three sensors A to A as shown in FIG.
Even when configured by C, if there is a sensor pair having a detection area edge parallel to the sub-scanning direction and one sensor having a detection area edge diagonally intersecting in the main scanning direction. It is possible to detect both the amount of deviation in the sub-scanning direction and the amount of deviation in the main scanning direction. Therefore, the combination of the three sensors A to C is not limited to the configuration of FIG. 16, and various modes such as those shown in FIGS. 19 to 22 can be easily assumed.

Further, in the present embodiment, the structure in which the two laser beams L1 and L2 are simultaneously scanned to record two lines at the same time has been described. However, the structure in which three or more beams are simultaneously scanned is also the same. It is possible to obtain the shift amount by using the above, and the number of beams is not limited. Further, in this embodiment, the amount of deviation of the scanning position in the main scanning direction,
Although both the amount of deviation of the scanning position in the sub-scanning direction is detected, only one of them may be detected.

[0081]

As described above, according to the image forming apparatus of the first aspect of the present invention, the correction amount of the image recording is determined by detecting the deviation amount of the scanning position before the start of the sub-scanning, and the image is corrected. Since the determined correction characteristics are continuously used until the image recording is completed, the image recording is performed.
The correction characteristic is not changed during the image recording due to the variation in the deviation amount detection, and the image recording can be performed with the constant correction characteristic, and the image quality is ensured.

On the other hand, in the apparatus according to the invention of claim 2,
Since the configuration is such that the final deviation amount data for determining the correction characteristics is set based on the data of a plurality of deviation amounts detected over a plurality of times, knowing the deviation characteristics of the deviation amount measurement, Higher amounts can be detected. Further, in the apparatus according to the invention of claim 3, in the configuration in which the main scanning is performed by the deflection of the rotary polygonal mirror, the number of times of detecting the deviation amount over the plurality of times is set to be equal to or more than the number of surfaces of the rotary polygonal mirror. Thus, the variation characteristic of each surface of the rotary polygon mirror can be detected, and thus the accuracy of the deviation amount measurement can be improved.

Further, in the apparatus according to the invention of claim 4,
Since the final deviation amount for determining the correction characteristics is specified based on the remaining data excluding the maximum value and the minimum value of the plurality of deviation amount data obtained by the plurality of detections, Even if an extremely different shift amount is detected due to measurement variations, it is possible to avoid the correction characteristics from being affected by the unique data.

Further, in the apparatus according to the invention of claim 5,
Since the displacement amount is detected a plurality of times before the sub-scan is started and the displacement amount is not detected and the correction characteristic is not changed during the image recording, a constant condition is set based on the accurately detected displacement amount. One image can be recorded with. On the other hand, in the apparatus according to the sixth aspect of the present invention, when the deviation amount of the scanning position is detected, the scanning speed of the main scanning is forcibly slowed down, so that the accuracy of time measurement accompanying the main scanning of the light beam is improved. Therefore, the accuracy of the deviation amount detection based on the time measurement can be improved.

Further, in the apparatus according to the invention of claim 7,
The amount of deviation, which is performed at a slower main scanning speed, is detected a plurality of times before the start of sub-scanning, the correction characteristic is determined based on the detection results of the plurality of times, and the determined correction characteristic is calculated. Since it is fixed during the recording of one image, it is possible to accurately detect the deviation of the deviation amount detection based on a plurality of deviation amounts that are detected with high accuracy based on highly accurate time measurement, and to record one image. The correction corresponding to the deviation amount can be performed under a highly accurate constant correction condition.

According to the eighth aspect of the invention,
The shift amount in the sub-scanning direction can be easily detected based on the light beam detecting means arranged in parallel in the main scanning direction and the measurement of the detection timing interval of the light beam by the detecting means. Further, in the apparatus according to the invention of claim 9, the deviation amount in the main scanning direction can be simply calculated based on the light beam detecting means arranged in parallel in the main scanning direction and the measurement of the detection timing interval of the light beam by the detecting means. Can be detected.

Further, in the apparatus according to the invention of claim 10,
Based on the detection result of the amount of deviation in the sub-scanning direction, adjustment is performed so that scanning is performed at the regular sub-scanning position, and simultaneous recording of a plurality of lines can be performed at fixed sub-scanning intervals. By correcting the writing position of image recording based on the detection result of the deviation amount in the main scanning direction, even if the scanning position is deviated in the main scanning direction, the writing positions by the respective light beams can be aligned. Become.

[Brief description of drawings]

FIG. 1 is a perspective view showing an image exposure system according to an embodiment of the present invention.

FIG. 2 is a diagram showing details of an index sensor.

FIG. 3 is a flowchart showing detection of a scanning position shift amount in the sub-scanning direction.

FIG. 4 is a diagram showing detection characteristics of a scanning position shift amount in the sub-scanning direction.

FIG. 5 is a flowchart showing detection of a scanning position shift amount in the main scanning direction.

FIG. 6 is a diagram showing detection characteristics of a scanning position shift amount in the main scanning direction.

FIG. 7 is a time chart for explaining time measurement using a clock.

FIG. 8 is a block diagram showing a configuration of scanning position adjustment based on a scanning position shift amount in the sub-scanning direction.

FIG. 9 is a flowchart showing a first embodiment of image recording accompanied by detection and correction of a scanning position shift amount.

FIG. 10 is a flowchart showing a second embodiment of image recording accompanied by detection and correction of a scanning position shift amount.

FIG. 11 is a flowchart showing a third embodiment of image recording accompanied by detection and correction of a scanning position shift amount.

FIG. 12 is a diagram showing another example of the sensor configuration.

FIG. 13 is a diagram showing another example of the sensor configuration.

FIG. 14 is a diagram showing another example of the sensor configuration.

FIG. 15 is a diagram showing another example of the sensor configuration.

FIG. 16 is a diagram showing a configuration of a sensor including three sensors.

FIG. 17 is a diagram showing characteristics of displacement amount detection in the sub-scanning direction by three sensors.

FIG. 18 is a diagram showing characteristics of displacement amount detection in the main scanning direction by three sensors.

FIG. 19 is a diagram showing another example of the sensor configuration.

FIG. 20 is a diagram showing another example of the sensor configuration.

FIG. 21 is a diagram showing another example of the sensor configuration.

FIG. 22 is a diagram showing another example of the sensor configuration.

[Explanation of symbols]

1 Light source unit 1a, 1b Semiconductor laser 2 condenser lens 3 polygon mirror 4 fθ lens 5 photosensitive drum 6 Index sensor 7 Reflector A to D sensor

Claims (10)

(57) [Claims] 1. An image forming apparatus for simultaneously scanning a recording medium in parallel with a main scanning direction by a plurality of light beams to simultaneously record a plurality of lines, wherein scanning in a sub-scanning direction orthogonal to the main scanning direction is started. Previously, the deviation amount of the scanning position between the plurality of light beams is detected in at least one of the main scanning direction and the sub-scanning direction, and is determined based on the deviation amount detected before the start of the sub-scanning. An image forming apparatus configured to correct the image recording by the plurality of light beams according to the shift amount while fixing the correction characteristic during one image recording. 2. An image forming apparatus that simultaneously scans a recording medium in parallel in a main scanning direction with a plurality of light beams to record a plurality of lines at the same time. The plurality of detections are performed in at least one of the main scanning direction and the sub-scanning direction orthogonal to the main scanning direction, and the plurality of the plurality of detections are performed according to the correction characteristics determined based on the plurality of deviation amount data detected over the plurality of times. An image forming apparatus configured to correct image recording by a light beam. 3. A structure in which scanning in the main scanning direction by the plurality of light beams is performed by a rotary polygon mirror, and the amount of deviation is detected at least a number of times equal to or greater than the number of surfaces of the rotary polygon mirror. The image forming apparatus according to claim 2, which is characterized in that. 4. The correction characteristic is determined on the basis of deviation amount data excluding a maximum value and a minimum value of a plurality of deviation amount data detected over a plurality of times. The image forming apparatus according to any one of 3 above. 5. A plurality of times of detecting the deviation amount is performed before starting the scanning in the sub-scanning direction, and is determined based on a plurality of deviation amount data detected before the start of the sub-scanning. 5. The image forming apparatus according to claim 2, wherein the correction characteristic thus set is fixed during one image recording, and the image recording by the plurality of light beams is corrected. 6. An image forming apparatus for simultaneously scanning a recording medium with a plurality of light beams in parallel in a main scanning direction to record a plurality of lines at the same time. Then, the amount of deviation of the scanning position between the plurality of light beams is detected in at least one of the main scanning direction and the sub-scanning direction orthogonal to the main scanning direction, and the detected amount is detected. An image forming apparatus configured to correct image recording by the plurality of light beams based on a shift amount. 7. A displacement amount detection performed at a slower main scanning speed is performed a plurality of times before starting scanning in the sub-scanning direction, and based on a plurality of displacement amount data obtained by the detection. 7. The image forming apparatus according to claim 6, wherein the correction characteristic determined by the above is fixed during one image recording to correct the image recording by the plurality of light beams. 8. At least a pair of light beam detection means whose timing intervals for detecting the same light beam change in proportion to the change of the scanning position in the sub-scanning direction are arranged in parallel in the main scanning direction. An interval between the timings detected by the light beam detecting means is measured for each beam, and a deviation amount of the scanning position in the sub-scanning direction between the plurality of light beams is detected based on the difference between the measured intervals. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6 or 7. 9. At least a pair of light beam detecting means are arranged in parallel in the main scanning direction, and each light beam detecting means measures an interval between timings at which the same light beam is detected, while each light beam detecting means respectively. The distance between the timings at which different light beams are detected is measured, and the shift of the scanning position in the main scanning direction between the plurality of light beams is detected based on the difference between the measured distances.
The image forming apparatus according to any one of 2, 3, 4, 5, 6 and 7. 10. When the deviation amount in the main scanning direction is detected, the start position of image recording by each light beam is corrected based on the deviation amount in the main scanning direction, and the deviation amount in the sub scanning direction is determined. If detected, the scanning position of the light beam in the sub-scanning direction is adjusted based on the displacement amount in the sub-scanning direction to correct the displacement of the scanning position between the plurality of light beams to perform image recording. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9.