JPH10288743A - Multi-beam scan method and controller therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-beam scan method and a multi-beam scan controller capable of stabilizing a light quantity of a multi-beam and precisely detecting a laser beam becoming a reference of correction of a write-start position and optical axial deviation. SOLUTION: In a semiconductor laser control circuit deflecting the multi-beam emitted from plural semiconductor lasers 11a, 11b by a polygon mirror 13, converging them to a spot by an fθ lens 14, etc., and scanning it on an image carrier 1, this device is provided with a bias current source subjecting the multi- beam light quantity to sample-and-hold at every one scan line by a sample-and- hold circuit and stabilizing the multi-beam light quantity based on a signal subjected to sample-and-hold, and a synchronous control circuit detecting the surface position of the polygon mirror 13 by making the multi-beam incident on an index sensor 16 and synchronizing the multi-beam, and ends sample processing when the multi-beam L1, L2 arrive at this side of the light receiving part of the index sensor 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam scanning method in which a multi-beam is deflected by a rotary polygon mirror, focused on a spot by an imaging optical system, and simultaneously scanned on an image carrier by a plurality of scanning lines. The present invention relates to a multi-beam scanning control device used.

[0002]

2. Description of the Related Art In order to meet the demand for high-speed recording, a multi-beam emitted from a plurality of semiconductor lasers is deflected by a rotary polygon mirror or the like, focused on a spot by an imaging optical system, and simultaneously formed on an image carrier by a plurality of lines. 2. Description of the Related Art A multi-beam scanning control device that forms a two-dimensional image while scanning and rotating an image carrier in a sub-scanning direction orthogonal to a main scanning direction is known (see Japanese Patent Application Laid-Open No. 2-188713). The multi-beam scanning control device needs to correct a shift amount based on a reference beam and perform synchronous control in order to prevent optical axis deviation of the multi-beam in the main scanning direction and the sub-scanning direction. The multi-beam scanning control device adopting such synchronization control obtains a horizontal synchronization signal by detecting the incident position of the multi-beam in the main scanning direction of the image carrier by an index sensor arranged near the image carrier surface. On the other hand, there is a method of stabilizing the light amount of the semiconductor laser based on a signal sampled and held for each scanning line in order to stabilize the potential of a latent image formed on the image carrier.
Abbreviated.

FIG. 13 is a time chart showing the operation of a conventional non-multi beam scanning control circuit. FIG.
(A) is a time chart showing a sample / hold state, where a high level indicates a sample state and a low level indicates a hold state. FIG. 13B is a time chart showing an input state of image data, and FIG. 13C is a time chart showing a drive current of the semiconductor laser.
FIG. 13D is a time chart showing the reference beam position detection output.

From the time chart shown in FIG. 13, it can be seen that the conventional line APC scanning control circuit for a single beam has obtained a horizontal synchronizing signal with a detection signal from an index sensor at the end of a so-called line APC sampling process. .

[0005]

However, when the multi-beam scanning control is to be performed at the control timing of the line APC in the single beam as described above, the light amount of the multi-beam incident on the index sensor is properly controlled. Therefore, there is a problem that it is difficult to detect a reference laser beam among a plurality of laser beams incident on the index sensor in order to detect the position of the beam. This will be described in detail below.

FIG. 14 is a conceptual diagram showing a scanning state of a multi-beam index sensor.

If there is no optical axis shift in the main scanning direction of each laser beam, as shown in FIG. 14A, a multi-beam is simultaneously inputted to the light receiving portion of the index sensor, and as shown in FIG. As shown in the figure, the amount of light received by the index sensor is larger than that of the index sensor alone. Such a phenomenon causes a malfunction when the shift amount is detected and corrected based on the reference beam and the synchronous control is performed.

If each laser beam has an optical axis shift in the main scanning direction, a reference laser beam is not always input first as shown in FIG. The detection circuit judges the signal input first as a reference, and accordingly, the detection circuit shown in FIG.
As shown in FIG. 4 (c), the reference laser beam cannot be accurately detected, and the deviation amount cannot be accurately detected and corrected.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems, and to accurately detect a laser beam serving as a reference for correction of a writing start position and an optical axis shift in a multi-beam light amount control using a line APC. It is an object of the present invention to provide a multi-beam scanning method and a multi-beam scanning device used therefor.

[0010]

The above object is achieved by the following constitution.

(1) The light quantity of the multi-beam emitted from the semiconductor laser is sampled and held for each scanning line, and the light quantity of the multi-beam is stabilized based on the sampled and held signal. A multi-beam scanning method for detecting the surface position of the rotary polygon mirror and synchronizing the multi-beams by detecting the position of the multi-beams. A multi-beam scanning method characterized by terminating the control of (1).

(2) An automatic light amount control circuit which samples and holds the light amount of the multi-beam emitted from the semiconductor laser for each scanning line by a sample-and-hold circuit and stabilizes the light amount of the multi-beam based on the sample-held signal. A multi-beam scanning control device having a synchronization control circuit for detecting a surface position of the rotating polygon mirror by synchronizing the multi-beam by irradiating a reference beam to the index sensor, and A multi-beam scanning control device, wherein the control of the light quantity is completed by the automatic light quantity control circuit until the light quantity reaches the light receiving portion of the sensor.

(3) The multi-beam scanning control apparatus according to (2), wherein the sample-and-hold circuit is held when the multi-beam passes through the index sensor.

(4) The synchronous control circuit detects and corrects positional deviation in the main scanning direction and the sub-scanning direction based on a reference signal obtained when a reference beam is incident on the index sensor. The multi-beam scanning control device according to (2) or (3).

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing a multi-beam scanning method and a multi-beam scanning control device according to this embodiment, a scanning optical system to be controlled will be described with reference to FIGS.

FIG. 1 is a perspective view showing a scanning optical system of a laser printer using a multi-beam output from one semiconductor chip of an array structure in the present embodiment, and FIG. 2 shows a detailed configuration of an index sensor. FIG. Note that the present invention is not limited to a semiconductor laser of one semiconductor chip in an array structure, and is similarly applied to a case where semiconductor lasers of a plurality of semiconductor chips are used.

The scanning optical system 10 oscillates the semiconductor lasers 11a and 11b based on an image signal modulated in accordance with image data to irradiate the multi-beams L1 and L2, and rotates the multi-beams L1 and L2 at a predetermined speed. The multi-beams L1 and L2 are deflected by the polygon mirror 13, focused on a spot equivalent to 600 DPI on the image carrier 1 by the fθ lens 14 or the like, and are scanned in parallel to form two lines of latent images simultaneously. Light source unit 11, collimator lens 12, polygon mirror 13, fθ lens 14
, A reflecting mirror 15 and an index sensor 16.

In this embodiment, the multi-beam L
The scanning direction of L1, L2 is the main scanning direction, and the image carrier 1
Is the sub-scanning direction. The image carrier 1 is driven to rotate in synchronization with the scanning of the multi-beams L1 and L2, so that the multi-beams L1 and L2 and the image carrier 1 relatively move in the sub-scanning direction. Image exposure is performed simultaneously on two lines, and a two-dimensional electrostatic latent image is recorded on the image carrier 1.

The light source unit 11 has two semiconductor laser light emitting portions 11a and 11b arranged in a line, and GaAs is used as a semiconductor material of the semiconductor laser light emitting portions 11a and 11b.
lAs, etc., the maximum output is 10 mW, the light efficiency is 25%, and the spread angle is 8 to 16 in the direction parallel to the bonding surface.
°, and the bonding surface perpendicular direction is 20 to 36 °. With such a configuration, the light source unit 11 emits two divergent lights.

The collimator lens 12 includes the light source unit 1
The two divergent lights emitted from 1 are condensed into multi-beams L1 and L2, which are two parallel light fluxes.

When any one of the multi beams L1 and L2 is indicated, the laser beam L1 or the laser beam L
Two.

The polygon mirror 13 is equivalent to a deflecting optical system. The polygon mirror 13 condenses a beam and reduces a Pepper's sum and an astigmatic difference in order to realize a flat scanning surface. The multi-beams L1 and L2 incident from the lens are deflected and emitted to the fθ lens. By providing a correction optical system (not shown) in the optical path, it is possible to reduce the scanning line pitch unevenness due to the surface tilt error of the polygon mirror 13.

The fθ lens 14 reduces the Pepper's sum and the astigmatic difference in order to realize the flattening of the scanning surface, and removes the field curvature. An imaging optical system for imaging the multi-beams L1 and L2 is provided behind the fθ lens 14.

When the multi-beams L1 and L2 are applied to the tip of the scanning line, the multi-beam L
1 and L2 are led to the index sensor 16.

The index sensor 16 detects the scanning start point of the multi-beams L1 and L2 deflected by the polygon mirror 13, and as shown in FIG. 2, sensors 16A, 16B, 16
C and 16D are arranged integrally in the main scanning direction.

As shown in FIG. 2, the sensor 16A has the long side 16Al of the two sides forming the right angle of the right-angled triangular light receiving section as the edge on the starting end side in the main scanning direction, and the long side 1Al.
6Al are arranged so as to be orthogonal to the main scanning direction (parallel to the sub-scanning direction). As shown in FIG. 2, the sensor 16B has the oblique side 16Bs of the right triangular light receiving portion as an edge on the starting end side in the main scanning direction, and the oblique side 16Bs is oblique in the main scanning direction at an angle formed by the long side and the oblique side. They are arranged to intersect. The sensor 16D is arranged such that when the sub-scanning direction is up and down as shown in FIG. 2, the arrangement of the light receiving sections of the sensor 16A is upside down.

As shown in FIG. 2, the sensor 16C is arranged so that its light receiving portion is axially symmetric with respect to an axis along the sub-scanning direction with the sensor 16A. Such sensors 16A-
Due to the arrangement of 16D, the edge of the sensor 16A on the start side in the main scanning direction and the edge of the sensor 16D on the start side in the main scanning direction are parallel to each other in the sub-scanning direction, and the sensor 16B is on the starting end side in the main scanning direction. The edge and the sensor 16C are not parallel to each other.

For example, if the multi-beams L1 and L2 scan in the order of the sensors 16A, 16B, 16D and 16C as shown in FIG. 2, the detection start position of the laser beam L1 by the sensor 16A becomes a1, and the laser by the sensor 16A The detection start end position of the beam L2 is a2. Similarly,
The detection start positions of the multi-beams L1 and L2 by the sensors 16B to 16D are b1, b2, c1, c2, d1, and d2. Thereby, each sensor 16A, 16B, 16
The detection signal rises from C and 16D.

In the present embodiment, the multi-beams L1,
A method of measuring the gap in the sub-scanning direction of L2 will be described.

FIG. 3 is a schematic diagram for explaining the principle for detecting a shift in the sub-scanning direction.

The sensors 16B and 16C are arranged side by side in the main scanning direction such that the edges of the light receiving portions on the starting end side in the main scanning direction are not parallel to each other, as shown in FIG. The distance between the edges changes along the sub-scanning direction orthogonal to the main scanning direction. This is because when only the laser beam L1 is turned on and the sensors 16B and 16C detect it, the time interval T1 from the rising edge (b1) of the beam detection of the sensor 16B to the rising edge (c1) of the beam detection of the sensor 16C is: It means that it changes depending on the scanning position in the sub-scanning direction, and only the laser beam L2 is turned on instead of the laser beam L1. Similarly, when the laser beam L2 scans over the sensors 16A to 16D, the beam detection of the sensor 16B is performed. Rise (b
From 2), the rising of the beam detection of the sensor 16C (c)
The time interval T2 up to 2) also varies depending on the scanning position in the sub-scanning direction. Therefore, when the rise interval times T1 and T2 are measured for the multibeams L1 and L2, respectively, the deviation T3 of the interval time in each of the multibeams L1 and L2 becomes
2 is a value correlated with the interval in the sub-scanning direction, and indicates a change in the interval between laser beams in the sub-scanning direction (hereinafter, this is referred to as a shift of the optical axis in the sub-scanning direction).

Therefore, the reference value of the deviation T3 corresponding to the case where the interval between the multi-beams L1 and L2 in the sub-scanning direction is normal, and the deviation T3 obtained by the above-described measurement.
3 is determined as a value corresponding to the amount of deviation of the interval.

The reference value of the deviation T3 is, for example, when the positions b1 and c1 in the sub-scanning direction where the laser beam L1 is detected by the sensors 16B and 16C are assumed to be the reference positions, the scanning position of the laser beam L2 is in the sub-scanning direction. , The positions b2 and c2 in the sub-scanning direction where the laser beam L2 is detected by the sensors 16B and 16C are different from those of the sensor 16B.
Since the interval between the detection start side edges of B and 16C is configured to spread to both sides in the main scanning direction as going downward, the position b2 is shifted to the scanning start side, and conversely, the position c2 is shifted to the scanning start side. It shifts to the terminal side, so that the time T
2 is longer, and the time T3 is longer than the reference.
Therefore, if the deviation between the time T3 and the reference value is obtained, the shift amount of the interval between the multi-beams L1 and L2 is calculated based on the information on the scanning speed and the angle of the oblique side in the sensors 16B and 16C.

The above is the method of measuring the gap in the sub-scanning direction in the present embodiment.

Incidentally, as described above, the multiple beams L1,
In the case of detecting an interval shift in the sub-scanning direction of L2, the time difference caused by the shift varies depending on the angle at which the oblique sides of the sensors 16B and 16C obliquely intersect the main scanning direction, and the angle B ° becomes as sharp as possible. In other words, it is desirable that the interval between the oblique sides of the detection areas of the sensors 16B and 16C is set to change rapidly along the sub-scanning direction.
Furthermore, the angle B ° may be determined based on the adjustment accuracy of the scanning position and the resolution of time measurement.

Next, the multi-beam L in the present embodiment
A method of measuring the gap in the main scanning direction between L1 and L2 will be described.

FIG. 4 is a schematic diagram for explaining the principle for detecting a shift in the main scanning direction.

For example, in the combination of the sensor 16A and the sensor 16D, the edges of the light receiving section on the starting end side in the main scanning direction are parallel to each other, so that the displacement of the scanning position in the main scanning direction is determined by the sensors 16A and 16D. Since only the positional relationship in the main scanning direction can be extracted without being affected by the time interval at which the laser beams are detected, it is possible to detect a shift in the main scanning direction in the multi-beams L1 and L2.

Specifically, by controlling the turning on and off of each of the multi-beams L1 and L2, only the laser beam L1 is turned on, and when the laser beam L1 is detected by the sensor 16A (a1), If the time interval T5 from the rise (d1) at which the laser beam L1 is detected at 16D is measured, the edges of the light receiving portions of the sensors 16A and 16D on the start side in the main scanning direction are parallel to the sub-scanning direction. The time interval T5 is determined only by the interval between the edges of the sensors 16A and 16D on the starting end side in the main scanning direction and the scanning speed without being affected by the scanning position in the sub-scanning direction.

Next, lighting of each of the multi-beams L1 and L2 is performed.
By performing the light-off control, each of the multi-beams L1 and L2 is set so that only the laser beam L1 is incident on the sensor 16A and only the laser beam L2 is incident on the sensor 16D.
The scanning is performed while performing the mask control described above, and the time interval T6 between the rising edge (a1) when the laser beam L1 is detected by the sensor 16A and the rising edge (d2) when the laser beam L2 is detected by the sensor 16D is measured. 16
Since the edges of the light receiving portions of A and 16D on the starting end side in the main scanning direction are parallel to the sub-scanning direction, if the multi-beams L1 and L2 are scanned without being shifted in the main scanning direction, the time intervals T5 and T6. Should be the same time. For example, when the laser beam L2 is scanned after the laser beam L1 is scanned, the delay is obtained as T6−T5 (= T7).

Therefore, if the writing by the laser beam L2 is delayed by the time T7 with respect to the writing by the laser beam L1, the writing is not shifted in the main scanning direction by the two multi-beams L1 and L2 which are shifted in the main scanning direction. Thus, image recording can be performed.

The shape and combination of the light receiving portions of the sensors 16A to 16D are such that the edges of the light receiving portions on the starting end side in the main scanning direction are not parallel to each other in order to detect a shift in the sub-scanning direction. In order to detect a shift in the main scanning direction, there is a combination of sensors in which the edges of the light receiving portion on the starting end side in the main scanning direction are both orthogonal and parallel to the main scanning direction. In addition, if the edge of the light receiving section on the starting end side in the main scanning direction is defined,
The shape of the light receiving section may be triangular or square.

Next, the semiconductor laser control circuit 100 using the line APC in the present embodiment will be described with reference to FIGS.

FIG. 5 shows a line APC in this embodiment.
And FIG. 6 is a block diagram showing details of the synchronization control circuit.

The semiconductor laser control circuit 100 based on the line APC includes the semiconductor laser 11a or the semiconductor laser 11b.
The drive current and the laser power of the semiconductor laser LD are controlled by connecting the anode of the semiconductor laser LD and the cathode of the monitoring photodiode PD. As shown in FIG. 5, the semiconductor laser control circuit 100 includes a comparator 111, a sample and hold circuit 112, a reference voltage source 120, and a bias current source 130.
, A switching current source 140 and a current switching circuit 150. The multi-beam scanning control circuit has two sets of the semiconductor laser control circuit 100 for the semiconductor laser 11a and the semiconductor laser 11b, and further has a synchronous control circuit as shown in FIG.

The semiconductor laser control circuit 100 has a sink type laser drive current output terminal, and can drive the semiconductor laser with a drive current via this output terminal. The semiconductor laser control circuit 100 is a high-speed sample and hold circuit 11
Self-APC (auto power control) that does not require external laser power control because it has built-in 2
The system has been realized. The configuration and function of each unit will be described below.

The self-APC is realized by a switching current setting resistor RS, a photodiode PD, a load resistor RM for monitoring the photodiode current, a comparator 111 and a sample and hold circuit 112. The amount of light from the beams 11a and 11b is sampled and held by the monitoring photodiode PD and the sample and hold circuit 112, and based on the sampled and held light amount signal, the current conducted to the semiconductor lasers 11a and 11b so that the amount of beam becomes constant. Is controlling. Thereby, the latent image potential can be adjusted.

Semiconductor laser 11a or semiconductor laser 11
The PD current generated by the light emission of b conducts through the resistor RM. As a result, a voltage VM is generated. Comparator 1
11 compares the voltage VM with the voltage applied to the Vr terminal. If the comparison result of the comparator 111 is VM <Vr, the current is sourced from the CH terminal to charge the external capacitance CH, and the sample and hold circuit 112
1 is VM> Vr, the sample and hold circuit 112 sinks the current from the CH terminal and
H is discharged.

The reference voltage source 120 is a circuit that generates a reference voltage, and supplies a reference voltage to the bias current source 130 and the switching current source 140.

The bias current source 130 is connected to the semiconductor laser 1
This circuit generates the bias currents IB of 1a and 11b, and sets the bias current IB by adjusting the bias current setting load RB and the bias current setting voltage VB.

The switching current source 140 is a circuit for generating the switching target current Isw. The switching current source 140 adjusts the switching current setting resistor RS and the photodiode current monitoring load resistor RM in order to perform APC with high accuracy. An initial value of the target current Isw is set. The load resistance RM for monitoring the photodiode current is set such that the terminal voltage of the load resistance RM for monitoring the photodiode current and the reference input voltage Vr are equal when the semiconductor laser is driven at the initial set value of the switching target current Isw. I do.

The current switching circuit 150 has a DATA
Is used to control the drive current of the semiconductor laser. The resistance RO is a load resistance of the driving current, and the power supply VCC.
To reduce the power consumption by flowing a current substantially equal to Isw.

Next, a schematic operation of the semiconductor laser control circuit 100 according to the present embodiment will be described with reference to FIGS.

FIGS. 7 to 9 are time charts showing the operation of the multi-beam scanning control circuit according to the present embodiment.
FIGS. 7 and 8 each specifically show a signal that is a feature of the present invention, and corresponds to the first half of FIG. In FIG. 7, before two beams output from one semiconductor chip of the array structure reach the light receiving portion of the index sensor, the light amounts of the two beams are alternately controlled by a set of semiconductor laser control circuits. . In FIG. 8, before the two beams output from the two semiconductor chips reach the light receiving portion of the index sensor, the light amounts of the two beams are simultaneously controlled by two sets of semiconductor laser control circuits.

FIGS. 7, 8 and 9 are time charts showing the power-on state. A reset circuit for preventing an excessive current from flowing through the semiconductor lasers 11a and 11b when the power is turned on is built in, and a bias current source 13 is provided in a range of VCC <3.5V.
0 and the switching current source 140 is turned off,
The CH terminal is forcibly fixed to the “L” level.

(B1), (b2) and (b) are time charts showing the state of the / ENB input. The control of the drive current by the DATA input shown in (d) controls the drive current to the semiconductor lasers 11a and 11b while the current source is on, whereas the control by the / ENB input controls the operation of the switching current source 140. Turn on / off. In particular,/
When ENB = “L”, the bias current source 130 and the switching current source 140 are turned on, and when / ENB = “H”, the bias current source 130 and the switching current source 140 are turned off.
When / ENB = “H”, the CH terminal is forced to “L”
At this level, the external capacitor CH is forcibly discharged.

FIG. 7C is a time chart showing the sample / hold state S / H of the laser beam serving as a reference among the multi-beams. S / H input = “H”, DATA =
The signal is sampled when the signal is "H", and when the S / H input is "L", the CH terminal is in a high impedance state (hold) regardless of the input state of VM, Vr and DATA.

FIG. 9D is a time chart showing the input state of the image data (DATA) of the laser beam serving as a reference among the multiple beams. DATA shown in (d) =
When “H”, the drive current is Isw + IB, and DATA
= "L", the drive current is IB. (E) is a time chart showing the drive current of the semiconductor laser that outputs the reference laser beam.

FIG. 9F is a time chart showing the position detection output of the laser beam serving as a reference among the multiple beams. In FIGS. 7 and 8, APC indicates a period during which the light intensity of the semiconductor laser beam is controlled by the line APC.

(G) is a time chart showing a sample / hold state of a laser beam which is not a reference among the multi-beams.
Hold state at low level. (H) is a time chart showing an input state of image data of a laser beam that does not become a reference of the multi-beam, and (i) is a driving current of a semiconductor laser of a laser beam that does not become a reference of the multi-beam. It is a time chart shown.

After the power is turned on, the polygon mirror 13 that scans the multi-beams is not rotated or is rotated stably. After the output of the index sensor 16 is masked for a certain period, all the sample and hold circuits 112 are set to the sample state, The output voltage from the voltage source 120 is increased to near the reference operating voltage. In the present embodiment, when the sample-and-hold circuit 112 is in the sample state, the modulation signal is set to be always on.

Before the end of the mask period, all the sample and hold circuits 112 are set to the hold state, and the modulation signal is turned off.

By turning on the modulation signal of the reference laser beam among the multi-beams L1 and L2,
Keep the semiconductor laser on. Thus, the index sensor 16 is controlled by the reference laser beam of the multi-beams L1 and L2 while the semiconductor laser 11 is turned on outside the image forming area of the image carrier 1 based on the index signal from the index sensor 16. Before scanning, the sample and hold circuit 112 is switched to the sample state. After the sample, switch to the hold state, turn on the modulation signal, scan the index sensor 16,
A reference index signal is generated.

Based on the index signal obtained from the reference laser beam of the multi-beams L 1 and L 2, the remaining laser beams are sampled / held at the same timing as the reference laser beam to be in the hold state, and the modulation signal Is turned off to prevent other beams from being input to the index sensor.

The sample / hold timing of the other beam in the two beams output from the two semiconductor chips may or may not be the same as the reference beam. That is, if the sample timing is such that the laser beam is not input to the index sensor outside the image area of the image carrier 1, the laser beam may be set uniquely for each laser beam based on the reference index signal. On the other hand, when two beams are output from one semiconductor chip, since there is only one monitoring photodiode PD inside, the sample / hold timing of the other beams must always be different from the reference beam. is there.

As described above, the multi-beam line APC
By obtaining the horizontal synchronization signal without inputting the sample lighting to the index sensor, that is, by performing the multi-beam light amount control before the multi-beam reaches the light receiving section of the index sensor, the light amount of the multi-beam is stabilized. In addition, a laser beam serving as a reference for correction of a writing start position and optical axis shift can be accurately detected.

Next, the detailed configuration of the synchronization control circuit will be described with reference to FIG.

The synchronization control circuit detects the surface position of the polygon mirror 13 rotating at a predetermined speed by causing the multi-beams L1 and L2 to enter the index sensor 16 via the mirror 15 from the deflection optical system shown in FIG. , And a circuit for synchronizing in the main scanning direction.
2 has a function of detecting shifts in the main scanning and sub-scanning directions, and as shown in FIG. 6, the time interval measuring unit 171, the shift calculating unit 172 in the main scanning direction, and the shift calculating unit 1 in the sub-scanning direction
73.

The time interval measuring section 171 is a circuit for measuring the time intervals T1, T2, T5, and T6 shown in FIGS. 3 and 4, and includes a selector 171a and a phase detector 17a.
1b, 171c, delay line 171d, selector 1
71e, phase difference calculating section 171f, flip-flop 1
71g, counter 171h, latches 171i, 171
j, one-shot circuit 171k.

The selector 171a outputs a combination of any two of the detection signals fsa, fsb, fsc and fsd of the sensors 16A, 16B, 16C and 16D according to each correction mode and the like. In this embodiment, the sensor 16B and the sensor 16C are used for measuring the gap in the sub-scanning direction as described with reference to FIG. 3, and the main scanning direction is used as described with reference to FIG. The description will be made assuming that the sensor 16A and the sensor 16D are used for measuring the gap.

The phase detectors 171b and 171c
Is a pulse generation circuit that outputs an analog signal input from the selector 171a as a pulse signal. The pulse signal pd1 output from the phase detector 171b
Are input to the selector 171e, the phase difference calculator 171f, and the selector 172a, and are input to the phase detector 171c.
The pulse signal pd2 output from the
f and the input of the selector 172a.

The delay line 171d receives the reference clock c.
lk as input and clocks dl0 to dl1 having a phase difference
5 is output to the selector 171e and the selector 172h.

If the selector 171e is in the measurement mode of the gap in the sub-scanning direction, the phase detectors 171b and 171c use the phase detectors 171b and 171c to output the delay clocks dl0 to dl15 synchronized with the rising edges of the detection signals pd1 and pd2 of the sensors 16B and 16C. Each of them is detected, and the delay clock selc is output from the Philip flop 17
1g and a circuit for outputting to the counter 171h.

If the phase difference calculating section 171f is in the measurement mode of the interval shift in the sub-scanning direction, the sensor 16
A clock synchronized with the detection timing B (b1 or b2) and the detection timing (c1 or c2) of the sensor 16C
Phase difference (1/16 cycle unit), that is, a fraction of the detection interval of the sensors 16B and 16C within the clock cycle is obtained, and the result is generated by the one-shot circuit 171k from the detection signal of the sensor 16C. The one-shot pulse is sent to the latch 171j.

If the counter 171h is in the measurement mode of the interval deviation in the sub-scanning direction, the selector 171h
rising edge b1 of the outputs of the sensors 16B and 16C, using the delay clock selc input from e as a count.
(B2), c1 (c2) interval time T1, T2 is measured,
Assuming that the mode is the measurement mode of the gap in the main scanning direction, the rises a1, d1 (d
The interval times T5 and T6 in 2) are measured. Counter 171
Assuming that the counting section of h is the measurement mode of the interval shift in the sub-scanning direction, the count section is controlled by the flip-flop 171g to which the outputs of the sensors 16B and 16C are input. The counter 171h latches the count value in the latch 171i with a one-shot pulse generated from the detection signal of the sensor 16C.

As described above, the time interval measuring section 171 measures the times T1 and T5, which are the detection intervals of the sensors 16B and 16C when only the laser beam L1 is turned on, and stores the measured times in the latch 171i. Similarly, the times T2 and T6 when only the laser beam L2 is turned on.
Is measured and stored in the latch 171j. As a result, the time intervals T5 and T6 at the time of detection by the sensors B and C are obtained and latched as the phase difference between the clock count value and the clock.

The main scanning direction shift calculating section 172 compares the count value obtained as described above with the phase difference to determine the shift time interval T5 of the multi-beams L1 and L2 in the main scanning direction as a clock count. The operation is divided into the value and the clock phase difference, and the operation result is latched by the latches 172e and 172.
Latch to 2f. The shift calculator 172 in the main scanning direction includes:
If the scanning mode of the multi-beams L1 and L2 is determined from the calculation result of the shift time to determine the interval shift mode in the sub-scanning direction, the sensors 16B and 16C
Is determined as the index signal, and the result of the determination is latched.

The shift calculator 172 in the main scanning direction controls the phase of the print clock and the image forming timing, and gives a shift within one cycle of the print clock, which is indicated as a phase difference between the print clocks, to the selector 172h. The print clock DCLK1 corresponding to the laser beam L1 and the print clock DCLK2 corresponding to the laser beam L2 are selectively output from the print clocks dl0 to dl15 so as to have a phase difference corresponding to the shift. , Selector 172a, latch 172b, and selector 17
2c, the shift calculator 172d, and the latches 172e and 172f.
And a phase difference calculator 172g and a selector 172h.

The selector 172a receives the detection outputs pd1 and pd2 from the phase detectors 171b and 171c as inputs, and outputs one of the detection results pd1 and pd2 according to the selection result of the index signal to the phase difference calculator 172g.
To send to.

The selector 172c outputs the data of the shift time T5 and the selection result of the index signal to the trigger signal ZH generated when only one laser beam is turned on immediately before the power is turned on or image formation is performed to calculate the time Tφ. It latches on the basis of.

The shift calculator 172d outputs the shift indicated as the phase difference of the print clock to the phase difference calculator 172g via the latch 172f.

The phase difference calculating section 172g includes a selector 172
A delay clock having a phase difference corresponding to the deviation is calculated with respect to the delay clock input from a, and the calculation result is output to the selector 172h.

The selector 172h receives the information of the phase difference based on the deviation correction, the delay clocks dl0 to dl15 from the delay line 171d, and the detection signals from the sensors 16B and 16C selected by the selector 172c. Multi-beam L1, L2
And outputs the print clocks DCLK1 and DCLK2 corresponding to.

The shift calculator 173 in the sub-scanning direction includes a time difference calculator 173a, a latch 173b, and a shift calculator 173d.

The shift detector 173 in the sub-scanning direction calculates the clock count number and the clock phase difference as the times T1 and T2.
Is obtained, the time difference calculation unit 173a calculates the times T1 and T2
Are individually calculated using the count number and the clock phase difference, and the result is temporarily stored in the latch 173b. The shift calculator 173d compares the reference value given via the operation unit with the data stored in the latch 173b,
The shift (the amount of change in the interval) of the multi-beams L1 and L2 in the sub-scanning direction is calculated and provided to an adjustment mechanism to correct the shift in the sub-scanning direction. Here, for example,
In the case where a mechanism capable of adjusting the scanning position in the sub-scanning direction is provided as disclosed in Japanese Patent No. 50809, the multi-beams L1, L
By adjusting the scanning position in the sub-scanning direction 2, it is possible to correct the interval between the multi-beams L1 and L2 in the sub-scanning direction to a specified value.

Next, the operation of the synchronization control circuit 170 will be described with reference to FIGS.
This will be described with reference to FIG.

FIG. 10 is a time chart showing the correction of deviation within one cycle of the print clock in the main scanning direction.

For example, the laser beam L1 is at the head in the scanning direction, and the multi-beams L1,
If the laser beam L1 is incident on the sensor 16B when L2 is selectively incident, the multi-beam L
It is assumed that the shift in the main scanning direction of 1 and L2 is 2 counts in the print clock and 2 steps (2/16 cycle) in phase difference. In this case, while the detection signal of the sensor 16B is output as an index signal, a delay clock synchronized with the index signal is output as a print clock DCLK1 corresponding to the laser beam L1, and the print clock DCLK1 for the beam L1 is 2/2. A delay clock having a phase difference of 16 periods is output as a print clock DCLK2 for the laser beam L2. By outputting the print clocks DCLK1 and DCLK2 having different phases in correspondence with the multi-beams L1 and L2, a shift within one cycle of the print clock is compensated as a phase difference of the print clock.

A shift of an integral multiple of the cycle of the print clock is caused by the selector 172h for setting the image forming timing of each of the multi-beams L1 and L2 based on the count of the print clock.
Is reflected in Thus, the multi-beams L1,
If the correction for compensating for the deviation of the L2 in the main scanning direction is performed separately for the phase of the print clock and the image forming timing, the circuit load is reduced as compared with the case where only the image forming timing is corrected for the deviation. It can cope with the occurrence of a large deviation.

If it is determined from the calculation result of the shift time that the laser beam L2 is the first in the main scanning direction, the image of the laser beam L1 that is scanned after the detection of the laser beam L2 by the sensor 16C is delayed. The formation timing and the phase of the print clock may be corrected as described above.

FIG. 11 is a time chart showing correction of a deviation of an integral multiple of the print clock in the main scanning direction.

For example, the write start position of the head laser beam L1 is determined by the print clock DCK1 from the index signal.
If the count number of the print clock DCLK2 from the index signal is N
If the count value reaches the value corresponding to the + shift, it means that a shift of an integral multiple of the cycle of the print clock DCLK has been compensated.

Further, the shift within one cycle of the print clock DCLK is corrected by the phase difference between the print clocks DCLK1 and DCLK2 corresponding to the respective multi-beams L1 and L2, as described above. By correcting the deviation in the main scanning direction obtained as the phase difference of the multi-beams L1, L2, a more faithful image can be recorded.

The HV signal (horizontal and vertical synchronizing signals) for controlling the image forming start timing is indicated by the count value of the print clock for each of the multi-beams L1 and L2 with respect to the deviation obtained as the clock count value. The deviation is corrected by controlling the effective image area according to the count of the print clock based on the common index signal.

FIG. 12 is a time chart for detecting a shift in the sub-scanning direction.

FIG. 12 shows a case where the time difference (time between a1 and d1) when the laser beam L1 is detected by the sensors 16A and 16D is measured.

In FIG. 12, the reference clock clk is set to 1
The 16 types of delay clocks dl0 (reference clocks) to dl15 are generated from the digital delay line while being sequentially delayed by / 16 cycle. In FIG. 12, clocks clk, dl1, dl2, dl8, dl12, d
11 is shown, and other delay clocks are not shown. For example, if the clock synchronized with the rise a1 of the detection signal of the sensor 16A (the clock that rises first immediately after the rise of the detection signal) is the clock dl8, the rise at the time of synchronization is set as the first count, and then the clock dl8 Are sequentially counted.

During the counting, the detection signal of the sensor 16D rises, and the rise of this detection signal (d1)
Assuming that the clock synchronized with the clock dl12 is the clock dl12, the clock is calculated by subtracting 1 from the counted number of rising edges of the clock dl8 (including the rising edge of the clock dl8 synchronized with the detection signal (a1) of the sensor 16A). The phase difference between the clock dl8 and the clock dl12 is obtained by multiplying the period by the period (4/16 period, which can be expressed as delay clock number = dl4).
Is the output time difference between the detection signals of the sensors 16A and 16D (the interval between a1 and d1).

In detecting a shift in the sub-scanning direction, the 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 counted by the clock count. Number and delay clock number.
In the calculation of the time difference, the count number and the delay clock number may be calculated respectively.

In this case, the information on the deviation in the sub-scanning direction is output to the adjustment mechanism (for example, a stepping motor) as the clock count number and the delay clock number.

As described above, the multi-beam scanning control circuit according to the present embodiment delays the generation of the horizontal synchronization signal corresponding to laser beam L2 by the time T7 with respect to the generation of the horizontal synchronization signal corresponding to laser beam L1. In particular, the writing position is controlled.

When the times T5 and T6 are obtained as the count number of the delay clock and the clock phase difference, the horizontal synchronizing signal is adjusted based on the count number of the clock, and the deviation obtained as the clock phase difference is ,
The adjustment may be made by selecting a print clock corresponding to each of the multiple beams L1 and L2 from the delay clocks dl0 to dl15.

Accordingly, the semiconductor laser control circuit 100 according to the present embodiment can accurately detect the optical axis shift in the main scanning direction and the sub-scanning direction by having the above configuration. A stable image can be recorded by setting the axis to a normal position and performing writing control in accordance with the positional relationship of the laser beam in the main scanning direction.

[0104]

According to the first to sixth aspects of the present invention, by stabilizing the light amount of the multi-beam until the multi-beam reaches the light receiving portion of the index sensor, the writing position and the optical axis deviation can be improved. The position of the laser beam serving as a reference can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a scanning optical system of a laser printer according to an embodiment.

FIG. 2 is a schematic diagram showing a detailed configuration of an index sensor.

FIG. 3 is a schematic diagram illustrating a principle for detecting a shift in the sub-scanning direction.

FIG. 4 is a schematic diagram illustrating a principle for detecting a shift in the main scanning direction.

FIG. 5 is a block diagram illustrating a multi-beam scanning control circuit according to the present embodiment.

FIG. 6 is a block diagram illustrating details of a synchronization control circuit.

FIG. 7 is a time chart illustrating an operation of the multi-beam scanning control circuit according to the present embodiment.

8 is a time chart showing an operation of the multi-beam scanning control circuit shown in FIG.

FIG. 9 is a time chart illustrating an operation of a multi-beam scanning control circuit according to another embodiment.

FIG. 10 is a time chart showing correction of deviation within one cycle of a print clock in the main scanning direction.

FIG. 11 is a time chart showing correction of a deviation of an integral multiple of a print clock in the main scanning direction.

FIG. 12 is a time chart for detecting a shift in the sub-scanning direction.

FIG. 13 is a time chart showing an operation of a conventional non-multi scan control circuit.

FIG. 14 is a conceptual diagram showing a scanning state of a multi-beam index sensor.

[Explanation of symbols]

 11a, 11b Semiconductor laser 16 Index sensor 16A, 16B, 16C, 16D Sensor 112 Sample hold circuit 170 Synchronous control circuit 171 Time interval measuring section 172 Shift calculating section in main scanning direction 173 Shift calculating section in sub-scanning direction CH External capacitor

Claims (6)

[Claims] 1. A light quantity of a multi-beam emitted from a semiconductor laser is sampled and held for each scanning line, a light quantity of the multi-beam is stabilized based on the sampled and held signal, and a reference beam is sent to an index sensor. By being incident, the surface position of the rotating polygon mirror is detected, and in the multi-beam scanning method for synchronizing the multi-beam, the light amount of the multi-beam is controlled until the multi-beam reaches the light receiving portion of the index sensor. A multi-beam scanning method characterized by terminating. 2. An automatic light quantity control circuit which samples and holds the light quantity of a multi-beam emitted from a semiconductor laser for each scanning line by a sample-and-hold circuit, and stabilizes the light quantity of the multi-beam based on the sample-held signal. A multi-beam scanning control device having a synchronization control circuit for detecting a surface position of the rotary polygon mirror by irradiating a reference beam to the index sensor, and synchronizing the multi-beam. A control of the amount of light by the automatic light amount control circuit before the light beam reaches the light receiving section. 3. The multi-beam scanning control device according to claim 2, wherein the sample-and-hold circuit is held when the multi-beam passes through the index sensor. 4. The synchronization control circuit detects and corrects a positional deviation in a main scanning direction and a sub-scanning direction based on a reference signal obtained when a reference beam is incident on the index sensor. The multi-beam scanning control device according to claim 2 or 3, wherein: 5. The multi-beam scanning control device according to claim 2, wherein said semiconductor laser comprises one semiconductor laser. 6. The multi-beam scanning control device according to claim 2, wherein said semiconductor laser comprises a plurality of semiconductor lasers.