JPH09159948A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the deviation of the interval of a light beam in a subscanning direction with simple constitution and to keep exact interval by controlling the positional interval of the center of gravity to the desired interval in accordance with the position of the center of gravity detected by irradiating a photodetector in order with plural light beams one by one. SOLUTION: In the case laser beams from laser units LD1 and LD2 pass through adjusting prisms 1A and 1B, their optical paths are deflected and they irradiate a polygon mirror 3 nearly in parallel by a translucent prism 2. The laser beam emitted from the prism 2 is branched and made incident on a PSD 7. The photodetector of the PSD 7 takes out output voltage in accordance with the position of the center of gravity in the energy distribution of the light beam from the output. A differential amplifier 8 inputs reference voltage and the output voltage in accordance with the position of the center of gravity obtained by successively switching and making two laser beams incident on the PSD 7, and position correcting elements 9A and 9B for LDs 1 and 2 respectively turn the prisms 1A and 1B according to the output voltage.

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 particularly 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 at the same time, and more particularly, The present invention relates to a technique for detecting optical axis shifts of a plurality of light beams.

[0002]

2. Description of the Related Art 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 it on a recording medium. To increase the speed of
It is known that a configuration may be used in which a plurality of dot rows are simultaneously recorded using a plurality of laser beams.

However, as described above, when a plurality of laser beams are simultaneously scanned, the optical axes of the laser beams are deviated, and the respective scanning positions are deviated in the main scanning direction or the sub-scanning direction, resulting in faithfulness. The image formation may be affected.

In view of this, Japanese Patent Laid-Open No. 60-166916 discloses a light receiving device divided into four (107 in FIG. 7) for the purpose of obtaining an optical scanning device which can obtain a good scanning result even when a plurality of light sources are used. And 41) to 44) in FIG. 8), a servo is applied so that the differential output of the light receiving element becomes 0, and the positional relationship of the light spot on the scanning surface is maintained. There is.

In the technique described in the above publication, the positional relationship of the light spots can be accurately maintained if the light receiving element receives only the ideally shaped light spots, but the image forming apparatus deteriorates with time. When the light spot collapses under the influence of vibration applied to the image forming apparatus, the environment, or the like, it is difficult to maintain an accurate positional relationship of the light spot because the center of gravity of the energy distribution of the light spot is not measured. As a result, even if an accurate positional relationship of the light spots is maintained by using not only the four-division type light receiving element but also the division type light receiving element, the respective scanning positions of the center of gravity of the plurality of light beams gradually become in the main scanning direction or the sub-scanning direction. The image quality has deteriorated due to misalignment.

Further, when the split type light receiving element is used, the control is executed depending on the distance d between the light receiving portions as described in the above publication, so that the distance between the light receiving elements expands due to the fluctuation of the ambient temperature. If it fluctuates due to contraction, it is difficult to maintain an accurate positional relationship.

In addition, since it is affected by variations in the characteristics of the four light receiving elements 41 to 44 and variations in the intervals between the light receiving elements, it is expected that fine adjustment will be required for each image forming apparatus, which is troublesome.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in an image forming apparatus configured to perform image recording using a plurality of light beams, in particular, a light beam in the sub-scanning direction. It is possible to detect and adjust the optical axis deviation of the optical axis with a simple configuration, and the detection of the optical axis deviation in the sub-scanning direction and the detection of the optical axis deviation in the main scanning direction may cause a collapse of the light spot or an environmental change. It is also possible, the center of gravity of the light beam keeps a predetermined interval of multiple lines,
An object of the present invention is to provide an image forming apparatus capable of forming a good image.

[0009]

The above object is achieved by the following means. That is, the image forming apparatus of the present invention is an image forming apparatus which scans a photoconductor in parallel in the main scanning direction with a plurality of light beams to record a plurality of lines at the same time. Center of gravity detection means using a light receiving element for detecting the position of, and incident position adjusting means for adjusting the optical element in the optical path of the plurality of light beams to adjust the incident position of each light beam to the light receiving element. Control means for controlling the distance between the positions of the centers of gravity by the incident position adjusting means according to the positions of the respective centers of gravity detected by sequentially irradiating the light receiving elements with the plurality of light beams one by one. It is characterized by having.

PSD is a Position Sensitive Device in the field of electronic industry.
That is, when a light spot is incident on the light receiving surface on which semiconductors are laminated, a voltage is generated at each terminal provided on the semiconductor according to the incident position.

[0011]

Embodiments of the present invention will be described below.

FIG. 1 is a diagram showing an image exposure system of a digital copying machine as an example of an image forming apparatus according to the present invention. The digital copying machine of the present embodiment has a built-in scanner (not shown). This is a type in which two laser beams (light beams) L1 and L2 internally modulated according to the read image data are scanned in parallel on the image carrier in the main scanning direction and two lines are simultaneously recorded.

In FIG. 1, laser units LD1 and LD2, which are the light sources of the two laser beams, respectively turn on / off a semiconductor laser element corresponding to image data and divergent light from the semiconductor laser element into parallel light. Collimator lens for converting into laser beams L1 and L2 and an automatic output controller (A for maintaining the laser output at a set value)
PC) is integrated together. Laser unit L
D1 and LD2 are arranged so that the optical axes of the laser beams L1 and L2 are substantially orthogonal to each other.

The laser beams L1 and L2 are deflected in their optical paths when passing through the adjusting prisms 1A and 1B according to the optical element of the present invention, and are further irradiated onto the polygon mirror 3 by the semitransparent prism 2 substantially in parallel. Adjustment prism 1A,
1B is rotatable, and the direction of the optical axes of the laser beams L1 and L2 after transmission can be changed by the rotation. Then, the laser beams L1 and L2 are deflected in the main scanning direction by the polygon mirror 3 and are scanned on the photosensitive drum (recording medium) 6 through the reflecting mirror 4 in parallel to the main scanning direction.

The photosensitive drum 6 has a laser beam L
The laser beams L1 and L2 and the photoconductor drum 6 are relatively moved in the sub-scanning direction (direction orthogonal to the main scanning direction) and are two-dimensionally driven by being rotationally driven in synchronization with the main scanning of Image recording is performed.

As described above, the exposure corresponding to the image data is simultaneously performed for two lines, and an electrostatic latent image is formed on the photosensitive drum 6.
(Recording medium). Then, a toner charged to the opposite polarity is attached to the electrostatic latent image, and development is performed. Thereafter, the recording paper is superimposed on the toner image, and a corona charger reverses the polarity of the corona charging polarity from the back side of the recording paper. The toner image is transferred to the recording paper by applying a polar charge to the recording paper.

The scanning start point of the laser beams L1 and L2 deflected by the polygon mirror 3 is detected by an index sensor 5 arranged on the tip side of the scanning area.

The reflecting mirror 4 receives the laser beams L1 and L2 when the tip of the scanning line is irradiated with the laser beams L1 and L2.
It also serves to guide 1 and L2 to the index sensor 6.

The laser beams L1 and L2 emitted from the semitransparent prism 2 are branched and incident not only on the polygon mirror 3 but also on the PSD 7 arranged in a direction orthogonal to the optical path to the polygon mirror 3. The PSD 7 has a light receiving element for detecting the position of the center of gravity of the present invention, and can output an output voltage corresponding to the position of the center of gravity of the energy distribution of the light beam from the output of the light receiving element. Is. The operation amplification unit 8 has a laser beam L1,
The output voltage corresponding to the position of the center of gravity and the reference value voltage obtained by sequentially switching the L2 to the PSD 7 and inputting the same are input, and the output voltage of the operation amplifying unit 8 is used to correct the position of the LD1 according to the incident position adjusting means of the present invention. The adjustment prism 1A is rotated by the element 9A, and both or one of the adjustment prism 1B is rotated by the LD2 position correction element 9B. In the digital copying machine of this embodiment, the adjustment prisms 1A and 1B are rotated to adjust the distance between the light spots in the sub-scanning direction.
Adjustment prisms 1A and 1B so as to maintain the intervals after adjustment
Is fixed and the image for one page is output.

FIG. 2 is a control block diagram of the digital copying machine of this embodiment.

The CPU 10 relates to the control means of the present invention,
Position correction element 9A for D1 and position correction element 9B for LD2
Are sequentially driven to control the distance between the positions of the center of gravity to a desired distance. That is, the CPU 10 causes the laser units LD1 and LD2 to sequentially emit light according to a switching signal (not shown).
Laser unit LD1 emits light and laser unit LD
Since the laser beam L1 is incident on the PSD 7 when 2 is stopped, the PSD 7 causes the laser beam L1 to enter.
The position of the center of gravity of the light spot by 1 is detected. Therefore, the CPU 10 sends the PSD 7 by the PSD output switching signal.
The output is switched to the operational amplifier 8A. To the other input terminal of the operational amplifier 8A, the reference value voltage obtained by analog-converting the data of the reference value 1 generated by the CPU 10 by the D / A converter 11A is input, and the output voltage is input to the LD1 position correction element 9A. To be done. CPU1
0 outputs the correction signal 1 to the LD1 position correction element 9A when the LD1 starts to emit light, and the LD1 position correction element 9A becomes active only when the correction signal 1 is input and is output from the operation amplifier 8A. The adjustment prism 1A is rotated according to the voltage.

Since the CPU 10 can also adjust the center of gravity of the light spot for the laser beam L2, the image forming apparatus can control the distance between the center of gravity of the light spots of the laser beams L1 and L2 to a desired distance. It will be possible.

A piezoelectric element, a stepping motor or the like may be used as the LD1 position correction element 9A to deflect the adjustment prism 1A.

Next, the operation of the image forming apparatus will be described with reference to the timing chart of FIG.

The CPU 10 starts the emission of light by the laser unit LD1 after a lapse of a predetermined time t0 from the end of the image formation for one page based on the image data of the nth page (t10) (t11). Further, when a predetermined time t1 has elapsed from the start of light emission (t11), the correction signal 1 is output (t
12) Activate the position correction element 9A for LD1.
The LD1 position correction element 9A is active for a predetermined time T1, and receives the output voltage of the operation amplifier 8A to adjust the center of gravity of the light spot of the laser beam L1 on the photosensitive drum 6 by the adjustment prism 1A. Make adjustments.

When the predetermined time T1 has elapsed, the output of the correction signal 1 is stopped (t13), and the LD1 position correction element 9A ends the adjustment. Subsequently, the emission of the light beam LD1 is also terminated (t14), the CPU 10 outputs a PSD output switching signal (t15), and the output of PSD7 is switched to the system for detecting the barycentric position of LD2.

When the system is switched to a system for detecting the position of the center of gravity of LD2, the procedure similar to the adjustment of the position of the center of gravity of LD1 is performed by LD2.
Is repeated. That is, the laser unit LD2
The emission of light is started (t16), and when a predetermined time t2 elapses, the correction signal 2 is output (t17) to activate the LD2 position correction element 9B. The LD2 position correction element 9B is active for a predetermined time T2, and adjustment by the adjustment prism 1B is performed so that the center of gravity of the light spot of the laser beam LD2 on the photosensitive drum 6 is at an appropriate position. The center of gravity of the optical spot of LD2 is adjusted so as to have an appropriate distance from the center of gravity of LD1.

When the predetermined time T2 has passed, the output of the correction signal 2 is stopped (t18), and the LD2 position correction element 9B ends the adjustment. Subsequently, the emission of the light beam LD2 is also terminated (t19), the CPU 10 stops the PSD output switching signal (t20), and the output of PSD7 returns to the system for detecting the position of the center of gravity of LD1.

As described above, since the barycentric positions of LD1 and LD2 have been adjusted to proper intervals, the image forming apparatus starts the image formation of the (n + 1) th page.

The operation of the image forming apparatus described above will be described with reference to the flowchart of FIG.

The laser unit LD1 starts to emit light based on the light emission command from the CPU 10 (S1), and subsequently the correction signal 1 is turned on (S2) to deflect the adjusting prism 1A and start adjusting the position of the center of gravity of the LD1. To do. When the predetermined time T1 (see FIG. 3) has elapsed, the correction signal 1 is turned off (S3), and the adjustment of the position of the center of gravity of the LD1 is completed. Subsequently, the emission of the light beam LD1 is also terminated (S4), and the CPU
10 outputs a PSD output switching signal (S5), PSD7
Is switched to a system for detecting the position of the center of gravity of LD2.

When the system is switched to a system for detecting the position of the center of gravity of the LD2, the laser unit LD2 starts emitting light (S6), and subsequently the correction signal 2 is turned on (S6).
7) The adjustment prism 1B is deflected to start adjusting the position of the center of gravity of the LD 2. In S7, the L imaged on the photosensitive drum 6 is formed.
The adjustment of the adjustment prism 1B by the LD2 position correction element 9B is performed so that the positions of the centers of gravity of the light spots of D1 and LD2 are at proper intervals. Predetermined time T2 (see FIG. 3)
When is passed, the correction signal 2 is turned off (S8) LD2
The adjustment of the center of gravity position of is completed. Continued light beam LD
The emission of light 2 is also terminated (S9), the CPU 10 outputs a PSD output switching signal (S10), and the interval adjustment of the barycentric position of each light spot is terminated, while the image forming apparatus starts image formation.

According to the image forming apparatus having the above-described structure, the plurality of light beams are sequentially emitted to the center of gravity detecting means, so that the position of the center of gravity of each light beam can be detected. Further, since the incident position adjusting means can adjust the incident positions to have a desired interval, the incident position can be adjusted according to the position of the center of gravity of each light beam. As a result, it becomes possible to accurately control the interval between the plurality of lines of the plurality of light beams in the sub-scanning direction according to the center of gravity.

FIG. 5 is a flow chart for explaining the control of the second embodiment in which the image forming apparatus of the present invention is combined with a technique for detecting the optical axis deviation by another method.

FIG. 6 is a plan view of the sensor used in the second embodiment.

As shown in FIG. 6, the index sensor 5 is integrally provided with four sensors A to D that individually output detection signals, and the sensors A to D are arranged side by side in the main scanning direction. 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 a right triangle. Then, the sensor A forms a right angle included in the detection area of the right triangle 2
The long side of the sides is the edge on the starting end side in the main scanning direction, and the long side is arranged so as to be orthogonal to the main scanning direction (parallel to the sub-scanning direction). Further, the sensor B is configured such that the hypotenuse of the detection area of the right-angled triangle is the edge on the starting end side in the main scanning direction, and that the hypotenuse obliquely intersects the main scanning direction at an angle formed by the long side and the hypotenuse. Be placed. Further, the sensor D is arranged such that the arrangement state of the detection area of the sensor A is upside down when the sub-scanning direction is up and down.
Further, the sensor C is disposed such that its detection area is axially symmetric with respect to the axis along the sub-scanning direction with respect to the sensor A.

The sensors A and C shown in FIG. 6 are arranged so that the long side of the two sides forming the right angle is perpendicular to the main scanning direction. It may be arranged so as to be parallel to.

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 directions of inclination with respect to the main scanning direction are reversed.

In FIG. 6, the detection start 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 position of the laser beam L2 is shown as a2, and so on. Sensors B to D
Start detection positions of the laser beams L1 and L2 by b1,
b2, c1, c2, d1, and d2.

In this embodiment, the sensors A to A having the above-mentioned configuration are used.
Using D, the deviation of the distance between the laser beams L1 and L2 in the sub-scanning direction is measured as shown in the flowchart of FIG.

The program shown in the flow chart of FIG. 5 is executed every time the digital copying machine is powered on. First, as described in the first embodiment, the PSD is used in the sub-scanning direction. The intervals between the plurality of lines (hereinafter, also referred to as sub-pitch) are adjusted (S21).

Then, the laser unit LD1 is turned on (S22), and scanning is performed with only one line. When the laser beam L1 scans the sensors A to D, the time (detection time difference) T1 from the rise of the beam detection of the sensor B (b1) to the rise of the beam detection of the sensor C (c1) is measured ( S23).

Next, instead of the laser beam L1, only the laser beam L2 is turned on and scanning is performed with only one line (S24).

Then, similarly, the laser beam L2
Scans the sensors A to D, the time T2 from the rise of the beam detection of the sensor B (b2) to the rise of the beam detection of the sensor C (c2) is measured (S25).

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.

Further, the 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-mentioned processing is calculated as above. The value is obtained as a value corresponding to the gap amount of the interval, and it is determined whether the sub-pitch of the plurality of lines is an appropriate interval. (S26).

The reference value may be arbitrarily changed and set through the operation unit of the digital copying machine.

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, for example, the scanning position of the laser beam L2 is downward in the sub-scanning direction in FIG. Suppose it is shifted to the side. In this case, the positions b2 and c2 in the sub-scanning direction where the laser beam L2 is detected by the sensors B and C are in the main scanning direction as the distance between the detection start end edges of the sensors B and C goes downward in FIG. By being configured to spread on both sides, the position b2 is shifted to the scanning start end, and conversely, the position c2
2 is shifted to the end of the scan, so that the time T2
Becomes longer, and the time T3 becomes longer than the reference.

Therefore, if the deviation between the time T3 and the reference value is obtained, the deviation amount of the interval between the laser beams L1 and L2 can be calculated based on the information on the scanning speed and the angle of the hypotenuse in the sensors B and C. Is something that can be done.

Here, in the case where a mechanism capable of adjusting the scanning position in the sub-scanning direction is provided as disclosed in, for example, Japanese Patent Laid-Open No. 63-50809, the laser is calculated based on the information on the calculated shift amount. By adjusting the scanning positions of the beams L1 and L2 in the sub-scanning direction, the laser beam L
It is possible to correct the distance between 1 and L2 in the sub-scanning direction to a specified value.

That is, when it is determined in S26 that the sub-pitch is not appropriate, the index sensor 5 adjusts the sub-pitch again. That is, similarly to S22 to S25, the laser unit LD1 is turned on (S27), and the sensors A to D are scanned to start the beam detection of the sensor B (b1) to the start of the beam detection of the sensor C (c1). The time T1 is measured (S28). Next, the laser unit LD1 is turned on (S29), and the time T2 from the rise of the beam detection of the sensor B (b2) to the rise of the beam detection of the sensor C (c2) is measured (S30). Subsequently, the deviation T3 is calculated again and the sub-pitch is adjusted based on the difference from the specified value (S31). After that, the sub-pitch is measured by using the PSD in the procedure of FIG. 4, and the data of the reference values 1 and 2 are switched and updated in the state where the adjustment is completed in S31. By comparing the PSD output with the updated reference values 1 and 2, the rotation of the adjustment prism 1A and the adjustment prism 1B by the LD1 position correction element 9A and the LD2 position correction element 9B is always based on optimum information. It becomes possible to execute.

The laser beam L1,
When detecting the gap deviation of L2 in the sub-scanning direction, the time difference caused by the deviation varies depending on the angle at which the hypotenuses of the sensors B and C obliquely intersect the main scanning direction, and the angle b ° shown in FIG. Is set to an acute angle as much as possible, in other words, it is desirable that the interval between the hypotenuses of the detection areas of the sensors B and C changes rapidly along the sub-scanning direction.
The angle b ° may be determined according to the adjustment accuracy of the scanning position and the resolution of time measurement.

Further, the measurement results of the times T1 and T2,
Information such as the finally calculated deviation amount may be displayed on the display unit provided in the digital copying machine.

The installation position of the PSD 7 is not limited to that of the first and second embodiments, but the PSD 7 can be inserted in the optical path between the semi-transparent prism 2 and the polygon mirror 3, or can be placed in the vicinity of the index sensor 5. It can also be arranged so that the light beam deflected by the mirror 3 is incident. PS
When D7 is arranged so that it can be inserted into the optical path between the semitransparent prism 2 and the polygon mirror 3, it is necessary to wait for the completion of the movement of the PSD 7 for each dot spacing adjustment operation. Also PSD7
When the installation position is such that the light beam deflected by the polygon mirror 3 is incident near the index sensor 5, the polygon mirror 3 is adjusted for each dot interval adjustment operation.
Must be stopped until the adjustment is completed so that the light beam is incident on one point of the PSD 7.

However, in the first and second embodiments, the adjusting prisms 1A and 1A according to the optical element of the present invention are used.
A plurality of light beams incident on B are branched by a semitransparent prism 2 which is a branching means of the optical path. Therefore, even if the laser units LD1 and LD2 are continuously turned on, the PSD
Since the light spot does not move on 7, the adjustment is possible based on the center of gravity of the energy distribution of the light beam, the control is simple, and no extra stop time is required, so that the image productivity is excellent, which is the most preferable.

The three laser beams L1, L2, L
In a configuration in which three lines are simultaneously recorded by using 3,
For example, the shift in the sub-scanning direction is detected for the two laser beams L1 and L2 in the same manner as described above using a pair of sensors, and further, the shift is detected for the two laser beams L1 and L3. Since the deviation of each of the laser beams L2 and L3 in the sub-scanning direction based on the position can be detected, the configuration is not limited to the configuration using the two laser beams L1 and L2.

[0058]

As described above, according to the image forming apparatus of the present invention, the deviation of the interval between the light beams in the sub-scanning direction (deviation of the optical axis) can be detected with a simple structure. Even if the light spot collapses or the environment fluctuates, it is possible to accurately maintain the intervals between the plurality of lines and form a good image.

[Brief description of the drawings]

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

FIG. 2 is a block diagram for explaining control of interval adjustment.

FIG. 3 is a timing chart for explaining control of interval adjustment.

FIG. 4 is a flowchart for explaining control of interval adjustment.

FIG. 5 is a flowchart for explaining control according to the second embodiment.

FIG. 6 is a plan view of an index sensor used in the second embodiment.

FIG. 7 is a conceptual diagram showing an image exposure system of a conventional interval adjustment technique.

FIG. 8 is a plan view showing a split type sensor of a conventional gap adjusting technique.

[Explanation of symbols]

 LD1, LD2 Laser unit 1A, 1B Adjusting prism 2 Semi-transparent prism 3 Polygon mirror 4 Reflecting mirror 5 Index sensor 6 Photosensitive drum 7 PSD 8 Differential control unit 81, 8B Differential amplifier 9A, 9B LD1 position correction element 10 CPU 11A, 11B D / A converter

Claims (4)

[Claims] 1. An image forming apparatus for simultaneously scanning a plurality of lines by scanning a photosensitive member in parallel with a main scanning direction by a plurality of light beams, wherein the position of the center of gravity of the energy distribution of the light beams is received. A barycenter detecting means using a light receiving element for detecting; an incident position adjusting means for adjusting an optical element in an optical path of the plurality of light beams to adjust an incident position of each light beam to the light receiving element; The light receiving element is sequentially irradiated to the light receiving elements one by one, and the incident position adjusting means controls the distance between the positions of the centers of gravity to be a desired interval according to the positions of the respective centers of gravity detected. An image forming apparatus characterized by. 2. A branching means for branching a light beam emitted from the optical element into a light path incident on the center of gravity detection means and a light path incident on a rotary polygon mirror for performing the scanning. The image forming apparatus described. 3. The image forming apparatus according to claim 1, wherein the distance between the positions of the centers of gravity is the distance between the plurality of lines in the sub-scanning direction. 4. The image forming apparatus according to claim 1, wherein the center of gravity detecting means is a PSD.