JPH08201711A - Scanning pitch control method for laser scanning device - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a scanning pitch control method for a laser scanning device, and an object of the present invention is to provide a laser scanning device using a multi-beam, which can provide print quality without uneven scanning pitch. In order to obtain it, it automatically adjusts the scanning pitch and is excellent in terms of adjustment efficiency, and even if the adjustment is misaligned due to environmental changes or vibration after adjustment,
Since the adjustment of the scanning pitch is automatic adjustment as described above, a scanning pitch control method with high adjustment efficiency is provided also in this respect. A scanning pitch of a plurality of multi-beams generated from a multi-beam optical scanning device is detected, a rotation amount of the beam is obtained from the detection output, and the plurality of beams are rotated based on the rotation amount to scan the multi-beam. Automatically control the pitch.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning pitch control method for a laser scanning device, and more specifically, it controls a scanning pitch of a multi-beam optical scanning device used in a laser beam printer or the like to a predetermined value. Eliminates uneven printing pitch,
The present invention relates to a scanning pitch control method for a laser scanning device.

[0002]

2. Description of the Related Art In a laser scanning device such as a laser beam printer, a multi-beam optical scanning device has been required in accordance with high speed and high definition. Multi-beam optical scanning means that when there is one light source, the light is divided into two or more by some method, and when there are two or more light sources, each light is imaged on the photoconductor. Scanning is performed, and thereby, two or more scannings can be performed by one scanning, and high speed and high dot density can be realized without increasing the rotation speed of the rotary polygon mirror.

A conventional multi-beam optical scanning device will be described with reference to FIG. 1 (a diagram for explaining the present invention). Conventionally, the sensor 13 shown in FIG. 1 is a beam detect sensor (hereinafter abbreviated as BD sensor) and detects only the print start position. In addition, the computer 14 and the automatic rotation mechanism 17
Instead, only a rotation adjuster was placed. The light emitted from the light source 1 is split into two or more beams by a multi-beam generating element 2 such as a grating, and is focused by an acousto-optic modulator 4 (hereinafter abbreviated as AOM) by a lens 3. After that, the light is collimated by the lens 5, reflected by the mirror 6, passed through the Dove prism 7, passed through the cylindrical lens 8, scanned by the rotary polygon mirror 9, and the Fθ lens 10 scans two or more beams on the photoreceptor 11. Is image-scanned.

The number of beams is 2 and the interval between the two beams is 2 m
Suppose it was m. The actually required scanning pitch is, for example, about 0.106 mm when the printing density is 240 dpi. Although FIG. 13 shows four beams instead of two beams, if each beam is obliquely arranged and scanning is performed as shown in FIG. 13, scanning can be performed with a value smaller than the beam interval. . That is, even if the beam interval is 2 mm, a scanning pitch of 0.106 mm can be realized by obliquely arranging the beams. The component for adjusting the rotation at an angle is the Dove prism 7 in FIG.

[0005]

When the beam scanning pitch and the printing pitch are different during printing, printing pitch unevenness occurs and the printing quality is seriously affected. In order to eliminate this pitch unevenness, conventionally, a light source for generating a multi-beam is rotated, or a plurality of light beams are rotated by a Dove prism or the like so that the scanning pitch is adjusted to be uniform. Up to now, the above adjustment was visually performed while making a test print. Therefore, since it takes time and cost, the adjustment efficiency is poor, and even if the adjustment is misaligned due to environmental changes or vibrations after the adjustment, the adjustment of the scanning pitch is performed visually while performing the test printing as described above. Therefore, the adjustment efficiency was also poor in this respect.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to automatically adjust the scanning pitch in a laser scanning apparatus using a multi-beam so as to obtain print quality without unevenness in the scanning pitch. Excellent in efficiency,
Even if the adjustment is changed due to environmental changes or vibration after adjustment, the adjustment of the scanning pitch is as described above.
Since automatic adjustment is performed, it is another object of the present invention to provide a scanning pitch control method with good adjustment efficiency.

[0007]

The above object is to detect the scanning pitches of a plurality of multi-beams generated from a multi-beam optical scanning device, obtain the amount of rotation of the beam from the detection output, and to detect a plurality of beams based on this amount of rotation. This is achieved by rotating the beam and automatically controlling the scanning pitch of the multi-beam.

[0008]

According to the present invention, when the scanning pitches of a plurality of multi-beams generated from the multi-beam optical scanning device are detected, the rotation amount of the beam is obtained from the detection output, and the plurality of beams are detected based on this rotation amount. Is rotated to automatically control the scanning pitch of the multi-beam, and by doing so, the occurrence of beam pitch unevenness can be eliminated.

[0009]

1 shows a multi-beam optical scanning device. The light emitted from the laser light source 1 passes through a multi-beam generating element 2 such as a grating or a Wollaston prism and is split into multi-beams. After that, each light is focused by the lens 3 and passes through each AOM 4. This AOM
At 4, the light is on / off controlled according to the print data signal,
It is returned to a parallel beam through the lens 5, folded back by the mirror 6, and then passes through the Dove prism 7 for rotation adjustment. The dove prism 7 is provided with a rotation adjusting mechanism 17 such as a stepping motor that moves based on a signal from a beam pitch sensor 13 described later.
Then, the light passing through the rotation adjusting mechanism 17 passes through the cylinder lens 8 having a curvature only in the scanning vertical direction, and is narrowed down in the rotating polygon mirror 9 only in the scanning vertical direction. The light reflected from the rotary polygon mirror 9 passes through the Fθ lens 10 and is converted from equiangular scanning to uniform scanning, and thereafter, the light is narrowed down on the photoconductor 11.

On the other hand, the light 15 passing through the scanning start end of the Fθ lens 10 is reflected by the mirror 12 and strikes the sensor 13 at the same distance as the photoconductor 11. The sensor 13 detects the print start position and the beam pitch. Sensor 1
In 3, the BD sensor is removed and a new beam pitch sensor (hereinafter abbreviated as BP sensor) is attached, and the BD sensor and the BP sensor both have the roles of the BD sensor and the BP sensor. There is. Further, if the scanning pitch is adjusted when printing is not performed, the scanning light detected by the BP sensor 13 may be any light during scanning regardless of the light at the scanning end. For example, as shown in FIG. 2, printing is not performed using the tiltable mirror 16 that does not block the scanning light during printing and stands up only when adjusting the scanning pitch, and reflects the light to the sensor 13. Sometimes, the light at the central scanning portion may be detected and adjusted. This adjustment may be carried out all the time, but it is not necessary to carry out the adjustment unless there is an abnormality, and it is sufficient to carry out the adjustment regularly, for example, once an hour or once a day.

Next, details of the rotating mechanism of the Dove prism and the multi-beam light source will be described. FIG. 3 and FIG. 4 show an example thereof. Holder 20 of Dove prism 7
Alternatively, the gear 21 is arranged around the holder of the rotatable light source, and the gear 21 is rotated by the worm gear 23 attached to the stepping motor 22. Stepping motor 22
A signal after the signal from the BP sensor 13 is calculated by the computer 14 is sent to the, and the Dove prism 7 or the light source is rotated in accordance with the signal to set the scanning pitch to a predetermined size and prevent printing pitch unevenness.

Next, the first method for detecting the scanning pitch of the multi-beam will be described. The sensor is as shown in FIG. 5, and is divided into four light receiving elements 30, 31, 32, and 33. The arrow 34 indicates the scanning direction. The distance X between the boundary between the light receiving elements 30 and 31 and the boundary between the light receiving elements 32 and 33 is set as in the following equation (1) X = P * (M-1) ... (1). However, P indicates a scanning pitch, and M indicates the number of multi-beams.

The purpose of this sensor is to detect the positions of both ends of the multi-beam light. First, only the top beam is illuminated. At this time, by comparing the outputs of the sensors 30, 31, 32, and 33, it is possible to know at which position the upper beam is located. Similarly, when only the bottom beam is illuminated, the beam position can be known from the outputs of the sensors 30, 31, 32, 33. Based on this data, the sensors 30, 3
The calculator 14 calculates whether the difference between 1 and the difference between the sensors 32 and 33 becomes 0 and the beam comes to a predetermined position. Also, if the light from the upper end and the light from the lower end are turned on at the same time and the time sequence of the signals entering the sensors 30 and 31 and the signals entering the sensors 32 and 33 is detected, the vertical relationship of each beam can be known. If this result is transmitted to the stepping motor 22 attached to the dove prism 7 and the rotation mechanism of the light source, the scanning pitch can be correctly set to a predetermined size. Adjustment at the time of the first assembling is done by turning on both ends of the multi-beam and scanning the sensor 3
It is only necessary to adjust so that the difference between the sum of outputs of 0 and 31 and the sum of outputs of sensors 32 and 33 becomes zero. By doing so, as described above, it is possible to automatically adjust to a predetermined scanning pitch. If the pitch unevenness occurs due to some other reason, the output values of the sensors 30, 31, 32, 33 may be corrected so that the pitch unevenness does not occur.

Next, a second method for detecting the scanning pitch of the multi-beam will be described. The sensor is as shown in FIG. 6 or 7. FIG. 6 shows a one-dimensional sensor, and FIG. 7 shows a CCD. In either case, a device having fine elements that can detect the positional accuracy of 1/10 or less of the scanning pitch of the multi-beam is used. This is the scanning light 3
Place 4 vertically across. The purpose of this sensor is to detect the distance in the scanning vertical direction between both ends of the multi-beam light being scanned, and to determine the printing start position. First, scanning is performed by shining only the uppermost beam of the multi-beam. The state of this scanning is detected by the one-dimensional sensor in FIG. 6 or the CCD in FIG. 7, and the position is detected. Next, only the beam at the lower end is illuminated, and this position is similarly detected. Next, the beam at the upper end and the beam at the lower end are made to illuminate at the same time, and their time sequence is detected. From these values,
It is possible to obtain the distance in the scanning vertical direction between both beams and the time order of the upper and lower beams. Based on these values, how much the Dove prism 7 and the light source should be rotated can be calculated by the computer 1
If the signal is transmitted to the stepping motor 22 attached to the rotating mechanism, the scanning pitch can be correctly set to a predetermined size. Further, it may be data for simultaneously capturing the respective multi-beam signals and determining the print / write start position. However, one-dimensional sensor or C
If there is any inconvenience, such as when the CD starts up slowly,
Another element may be attached for the BD sensor.

Next, a third method for detecting the scanning pitch of the multi-beam will be described. The sensor is as shown in FIG. 8 or 9. This sensor is composed of a combination of two light receiving elements 35, 36 or 37, 38, 35 and 37 are so-called BD sensors for detecting scanning timing, and 36 and 38 detect scanning pitch together with the BD sensor. It is a BP sensor. These are arranged at the place where the scanning light comes, but they may be arranged at the same place or at different places.

First, the beams at the upper and lower ends of the multi-beam are simultaneously illuminated and scanned. At this time, the sensor 35 or 37 detects the time difference t1 between the two beams.
In addition, the sensor 36 or 38 tilted at an angle θ
Detects the time difference t2 between the two beams. The shape of the sensor 36 may be a triangle like the sensor 38 of FIG. These t1 and t2 can be illustrated as in FIG. 40 is a signal when the sensors 35 and 37 receive the signal from the upper beam, and 41 is a signal from the lower beam.
7 is the signal when received. Reference numeral 42 denotes a signal received by the sensors 36 and 38 from the light from the upper end beam. Reference numeral 43 denotes a signal when the sensors 36 and 38 receive the light of the lower end beam. When the moving speed of the light scanned by the lens system is V, the moving distance X1 during the time t1 is V × t1, and the time t2.
The moving distance X2 between can be calculated as V × t2. Therefore, the distance X in the scanning vertical direction of the upper and lower ends of the beam is obtained from the following equation (2) X = (X1−X2) tan θ.

Further, by using an element having a good rise and fall, it is possible to accurately detect even one triangular element such as the sensor 38 of FIG. The signal in this case is as shown in FIG. 44 is the signal of the upper beam, 45
Is the signal of the bottom beam. Times t1 and t2 in FIG.
Is calculated, the distance in the scanning vertical direction between the two beams can be calculated from Equation 2 as described above.

Next, a fourth method for detecting the scanning pitch of the multi-beam will be described. The sensor is as shown in FIG. The sensor is arranged so that the scanning light passes therethrough. The sensor 50 is called a position sensor, and the resistance value of the sensor changes according to the distances 53 and 54 between the light-transmitting portions 51 and 52 and the reference point 55. First, only the upper beam 51 of the multi-beam scanning light is turned on and scanning is performed. Sensor 50 at this time
The resistance value R1 is detected. Next, the light 5 at the lower end of the scanning light
Only 2 is turned on and scanning is performed. The resistance value R2 of the sensor 50 at this time is detected. Assuming that the resistance per unit length of the sensor 50 is k, the distance X of the two lights in the scanning vertical direction can be obtained by the following equation (3) X = (R1-R2) / k ... (3) .
However, in the case of this method, since it is necessary to detect the beam positions individually, a BD sensor is required in addition to the sensor 50 as in the conventional case.

Up to now, the laser light source 1 and the AOM
4 and the dove prism 7 have been described, when the multi-beam LD 29 and the dove prism 7 are used as shown in FIG. 14, the dove prism 7 is provided with a rotation mechanism and the multi-beam LD 29 is provided as shown in FIG. If only the multi-beam LD 29 is equipped with a rotating mechanism, it is the same.

[0020]

According to the present invention, in a laser scanning device using a multi-beam, the scanning pitch is automatically adjusted so as to obtain a print quality without unevenness in the scanning pitch, which is excellent in the adjustment efficiency. Even if the adjustment is misaligned due to environmental changes or vibrations after the adjustment, the scan pitch adjustment is automatic adjustment as described above. Can be provided.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a first embodiment of the present invention,
It is a figure when using a gas laser, AOM, and a Dove prism.

FIG. 2 is a diagram illustrating a second embodiment of the present invention,
It is a figure like the case of FIG. 1 at the time of using a gas laser, AOM, and a dove prism.

FIG. 3 is a diagram showing a specific example of a rotation mechanism used in the present invention as viewed from the optical axis direction.

FIG. 4 is a diagram showing another specific example of the rotating mechanism used in the present invention as seen from the optical axis direction.

FIG. 5 is a diagram showing a first beam pitch sensor used in the present invention.

FIG. 6 is a diagram showing a one-dimensional sensor which is one of second beam pitch sensors used in the present invention.

FIG. 7 is a diagram showing a CCD which is one of the second beam pitch sensors used in the present invention.

FIG. 8 is a diagram showing a specific example of a third beam pitch sensor used in the present invention.

FIG. 9 is a diagram showing another specific example of the third beam pitch sensor used in the present invention.

FIG. 10 shows the output from FIG.

FIG. 11 is a diagram showing the output from FIG. 9.

FIG. 12 is a diagram showing a fourth beam pitch sensor used in the present invention.

FIG. 13 is a diagram showing how four beams are scanned as a multi-beam.

FIG. 14 is a diagram for explaining the third embodiment of the present invention, and is a diagram for the case where a multi-beam LD and a Dove prism are used.

FIG. 15 is a diagram for explaining the fourth embodiment of the present invention, and is a diagram when only a multi-beam LD is used.

[Explanation of symbols]

1 ... Laser light source, 2 ... Multi-beam generating element, 3 ... Lens, 4 ... Acousto-optic modulator, 5 ... Lens, 6 ... Mirror, 7
... Dove prism, 8 ... Cylindrical lens, 9 ... Rotating polygon mirror, 10 ... Fθ lens, 11 ... Photoconductor, 12 ... Mirror, 13 ... Beam pitch sensor, 14 ... Calculator, 15 ...
Rays at the printing start end, 16 ... Retractable mirror, 17 ... Automatic rotation adjusting mechanism, 18 ... Semiconductor laser light source, 19 ... Lens,
20 ... Dove prism holder, 21 ... Gear, 22 ... Stepping motor, 23 ... Worm gear, 28 ... Semiconductor laser holder, 29 ... Multi-beam semiconductor laser, 30, 3
1, 32, 33 ... Light receiving element, 34 ... Beam scanning direction, 3
5, 36, 37, 38 ... Light receiving element, 40 ... Signal from upper beam receiving element 35 or 37, 41 ... Signal from lower beam receiving element 35 or 37, 42 ... From upper beam receiving element 36 or 38 Signal, 43 ...
Signal from the light receiving element 36 or 38 of the lower end beam, 4
4 ... Signal from light receiving element 38 for upper end beam, 45 ... Signal from light receiving element 38 for lower end beam, 50 ... Position sensor, 51 ... Scanning state of upper end beam, 52 ... Scanning state of lower end beam, 53 ... Upper end Distance between beam and reference, 5
4 ... Distance between bottom beam and reference, 55 ... Reference position.

Claims (5)

[Claims] 1. A multi-beam optical scanning device detects a scanning pitch of a plurality of multi-beams, obtains a rotation amount of the beam from the detection output, and rotates the plurality of beams based on the rotation amount to rotate the multi-beam. Pitch control method for a laser scanning device, characterized in that the scan pitch of the laser is automatically controlled. 2. A means for detecting the scanning pitch according to claim 1, which has a photodetecting section divided into four in the scanning vertical direction, and obtains the scanning pitch from the output difference of these four detecting sections when scanning light. A method for controlling a scanning pitch of a laser scanning device, comprising: 3. The one-dimensional sensor or CCD in which a large number of elements are arranged in the vertical scanning direction is used as the means for detecting the scanning pitch in claim 1, and the scanning pitch is obtained from this output when light is scanned. And a method for controlling a scanning pitch of a laser scanning device. 4. A means for detecting the scanning pitch according to claim 1, wherein a photodetector having an oblique straight line portion with respect to the scanning direction is used, and the scanning pitch is obtained from a time difference of light detection when scanning light. A method for controlling a scanning pitch of a laser scanning device. 5. A scanning pitch control method for a laser scanning device, wherein a position sensor is used as the means for detecting the scanning pitch according to claim 1, and the scanning pitch is obtained from the difference in resistance value when light is scanned.