JP2002131666A - Multi-beam recorder - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To realize good image writing by detecting a difference in arrival time of a light beam in the main scanning direction of each light beam and eliminating the occurrence of a main scanning position shift. SOLUTION: In a multi-beam recording apparatus which scans a plurality of light beams on a photoconductor at a time and records image data on the photoconductor, a light beam position detecting unit 7 for detecting a scanning position of the plurality of light beams is provided. Detecting the position shift of the light beam in the main scanning direction from the difference in arrival time of each light beam to the light beam position detection unit 7 in accordance with the beam position detection signal output from the light beam position detection unit 7, An image clock start signal generator 8 for generating a pixel clock for generating a corresponding pixel clock, and an image clock generator 9 for generating a pixel clock in accordance with the pixel clock start signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam recording apparatus which is mounted on a laser writing system such as a laser printer or a digital copying machine and scans a plurality of light beams to write an image on a photosensitive member surface.

[0002]

2. Description of the Related Art In a laser optical system mounted on a laser printer or a digital copying machine, to perform high-speed printing output, it is necessary to rotate a polygon mirror for light deflection at a high speed. There is a limit in realizing high-speed rotation because vibration and noise are generated. Therefore, there is known a so-called multi-beam recording apparatus in which a plurality of lines are collectively recorded by one scan using a plurality of light beams without driving the rotation speed of the polygon mirror at high speed. That is, a semiconductor laser array having a plurality of light beams (L
DA) are arranged in the sub-scanning direction, emitted, deflected by a polygon mirror, and scanned on the photosensitive member to collectively record a plurality of lines at a predetermined pitch. In such a multi-beam recording apparatus, it is necessary to accurately detect a beam scanning position.

As a reference technical document relating to such a multi-beam recording apparatus, for example, Japanese Patent Laid-Open No. 6-20634
No. 3, JP-A-9-1856 is disclosed. In Japanese Patent Application Laid-Open No. 6-206343, an optical sensor capable of separating and extracting each peak of a plurality of light beams is used, and a light beam detection signal above a certain threshold level of the output of the light sensor is used. Japanese Patent Application Laid-Open No. 9-1856 uses an optical sensor in which a plurality of light beams are incident simultaneously, and the output voltage of the optical sensor increases as the number of incident light beams increases. Then, a plurality of threshold levels are set, and when a certain threshold level crosses a sensor output signal, the detection signal of the light beam is used.

[0004]

However, in the conventional multi-beam recording apparatus as described above, even if the light source unit is initially adjusted so as to obtain a predetermined sub-scanning pitch, vibrations and vibrations are not caused. A deviation from a predetermined pitch occurs with time due to external factors such as temperature. When the semiconductor laser array (LDA) is tilted to correct this shift, there is a problem in that the beam arrangement, which was originally perpendicular to the main scanning direction, causes a time difference in scanning in the main scanning direction. .

In the apparatus described in Japanese Patent Application Laid-Open No. 6-206343, it becomes difficult to separate the beams when the beams approach in the main scanning direction. Further, the threshold level that can be separated also fluctuates due to the output fluctuation of each beam and the like, so that it is difficult to stably separate at a fixed threshold level. In the apparatus described in Japanese Patent Application Laid-Open No. 9-1856, the threshold level that can be separated also fluctuates due to fluctuations in the output of the light beam and the like, so that stable separation at a fixed threshold level is difficult. Become.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and detects a difference in arrival time of a light beam in the main scanning direction of each light beam, eliminates occurrence of a main scanning position shift, and realizes good image writing. It is an object of the present invention to provide a multi-beam recording apparatus that performs the following.

[0007]

In order to achieve the above object, in the multi-beam recording apparatus according to the first aspect, a plurality of light beams are collectively scanned on a photoconductor, and the light beam is scanned on the photoconductor. In a multi-beam recording apparatus for recording image data, a light beam position detecting means for detecting a scanning position of the plurality of light beams, and each of the light beams according to a beam position detection signal output from the light beam position detecting means. A pixel clock start signal generating means for detecting a position shift of the light beam in the main scanning direction from a time difference of arrival at the light beam position detecting means, and generating a pixel clock for generating a pixel clock corresponding to the beam position shift; And a pixel clock generating means for generating a pixel clock according to the pixel clock start signal.

According to the present invention, when the unit for emitting a plurality of light beams is rotated in the direction of the optical axis to adjust the pitch to a predetermined pitch, a time difference occurs between the light beams reaching the light beam position detecting means. Therefore, the pixel clock start signal generation means detects the light beam arrival time difference in the main scanning direction, generates a pixel clock start signal at a timing corresponding to the arrival time difference, and the image clock generation means responds to the arrival time. By generating the pixel clock, the displacement in the main scanning direction is eliminated.

According to a second aspect of the present invention, in the multi-beam recording apparatus, the light beam position detecting means includes a first optical sensor provided perpendicularly to a main scanning direction;
A second optical sensor disposed in parallel with the optical sensor at a predetermined distance from the optical sensor, and a time difference is to be measured based on a light beam that has reached the first optical sensor in one scan first. The arrival time difference is measured by the time when the light beam reaches the second optical sensor.

According to the present invention, the first optical sensor and the second optical sensor arranged at a predetermined interval are arranged, and after the light beam reaches the first optical sensor, the first optical sensor and the second optical sensor are transmitted to the second optical sensor. By measuring the arrival time difference, it becomes possible to accurately synchronize the pixel clocks.

Further, in the multi-beam recording apparatus according to claim 3, the pixel clock start signal generating means includes a beam position detection signal output from the first optical sensor and a pixel position detection signal output from the second optical sensor. A light beam arrival time measuring unit having a capacitor that is charged and discharged at an input timing of the output beam position detection signal, and the light beam arrives at the first optical sensor for the first time in one scan. The capacitor starts charging, stops charging when the light beam whose time difference is to be measured reaches the second optical sensor, holds the charged voltage, and sets the first light when the pixel clock start signal is generated. When the light beam reaches the sensor for the first time in one scan, charging of the capacitor is started, and pixel charging is performed at a timing when the charged voltage matches the held voltage. Tsu is intended to generate a click start signal.

According to this invention, when the light beam first reaches the first optical sensor in one scan, charging of the capacitor is started, and the light beam whose time difference is to be measured is arranged at a predetermined distance. When the light beam reaches the first light sensor when the pixel reaches the second light sensor, the charging of the capacitor is stopped and the charged voltage is held. By starting the charging of the capacitor and generating the pixel clock start signal at the timing when the charged voltage matches the held voltage, the pixel clock start signal can be generated with a simple configuration and control.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a multi-beam recording apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. The present invention is not limited to this embodiment.

According to the present invention, a plurality of light beams of a semiconductor laser array are arranged and emitted in the sub-scanning direction, are deflected by a polygon mirror, and are scanned on a photoreceptor to collectively record a plurality of lines at a predetermined pitch. A multi-beam recording apparatus capable of accurately detecting a time difference between scanning of a light beam in a main scanning direction and controlling a pixel clock start signal to obtain a good written image without occurrence of a main scanning position shift. It is. Hereinafter, the configuration and operation will be described.

FIG. 1 is an explanatory diagram showing a configuration of a multi-beam recording apparatus according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a light source unit on which a semiconductor laser array (LDA) for emitting four light beams (LD1 to LD4) is mounted, reference numeral 2 denotes a cylinder lens, and reference numeral 3 denotes a reflection mirror surface on a side surface of a regular polygon. A polygon mirror that rotates at a predetermined number of rotations, reference numeral 4 denotes an fθ lens that optically corrects a light beam at an equal angular pitch so as to be irradiated on the photosensitive drum 5 at an equal linear pitch, and reference numeral 5 denotes an electrostatic A photosensitive drum on which a latent image is formed, reference numeral 6 denotes a toroidal lens.

Reference numeral 7 denotes a light beam position detector for detecting the positions of a plurality of beams, reference numeral 71 denotes a mirror provided outside the recording area, and reference numeral 8 denotes a beam position detection signal from the light beam position detector 7. An image clock start signal for detecting a position shift of the beam in the main scanning direction based on a difference in arrival time of each beam to the light beam position detection unit 7 and generating a pixel clock start signal for generating a pixel clock corresponding to the beam position shift. A generation unit 9 is an image clock generation unit that generates a pixel clock according to an image clock start signal. A code 10 modulates image data to be written with a pixel clock corresponding to each light beam and inputs the data to the light source unit 1. An image data processing unit.

Next, the operation of the multi-beam recording apparatus configured as described above will be described. Four light beams emitted from the light source unit 1 on which the semiconductor laser array is mounted pass through the cylinder lens 2 and are
Scanning, and the fθ lens 4 and the toroidal lens 6
As a result, an image is formed on the photosensitive drum 5 and batch writing of four adjacent lines is performed.

In the above-described writing operation, the light beam is turned back by the mirror 71 outside the recording area, and travels on the light beam position detecting section 7 which is located at a position optically equivalent to the image forming position of the photosensitive drum 5. Scan. Four light beams (LD1
... LD4) collectively scans the photosensitive drum 5 and records four lines in one scan.

The distance between the laser diodes (hereinafter, appropriately referred to as LD) in the sub-scanning direction can be adjusted to a predetermined pitch. However, each laser diode (LD) may be changed due to environmental changes such as temperature and vibration. The intervals fluctuate. Therefore, the light source unit 1 is rotated in the optical axis direction and adjusted so as to have a predetermined pitch. At this time, there is a time difference between the light beams reaching the light beam position detection unit 7. For this reason, the pixel clock start signal generator 8 detects the light beam arrival time difference in the main scanning direction, generates a pixel clock start signal at a timing corresponding to the arrival time difference, and the image clock generator 9 generates the pixel clock start signal at the arrival time. A corresponding pixel clock is generated, and image data is modulated by a pixel clock corresponding to each light beam in the image data processing unit 10 and input to the light source unit 1.

Therefore, in a multi-beam recording apparatus for writing an image by emitting a plurality of light beams, as described above, by detecting and controlling the light beam arrival time of each light beam in the main scanning direction, the main scanning is performed. Image writing without displacement is realized.

FIG. 2 is an explanatory diagram showing an example of the configuration of the light beam position detector 7. The light beam position detection unit 7 includes a pair of optical sensors, that is, a first optical sensor 11 and a second optical sensor 11 that are separated from each other by a predetermined distance in a direction perpendicular to the main scanning direction. An optical sensor 12 is provided. With such a configuration, the difference in arrival time at the light beam position detection unit 7 is determined based on the light beam (LD1 in FIG. 2) that first reaches the first optical sensor 11 in one scan. The time difference is measured by the time until the light beam to be measured reaches the second optical sensor 12. Thus, the pixel clock can be accurately synchronized.

Next, an example of a circuit for measuring the light beam arrival time in the pixel clock start signal generator 8 will be described. FIG. 3 is a circuit diagram showing a configuration of the light beam arrival time measurement circuit 13. In the figure, reference numeral 14 is SR-FF
(Flip-flop), reference numeral 15 is an analog switch,
Reference numeral 16 denotes a capacitor, reference numeral 17 denotes an analog switch,
Reference numeral 18 denotes a resistor, reference numeral 20 denotes a beam position detection signal from the first optical sensor 11, and reference numeral 21 denotes a second optical sensor 1.
Reference numeral 22 denotes a reset signal, reference numeral 23 denotes an output from the capacitor 16, and reference numeral 24 denotes an output signal from the SR FF14.

The light beam arrival time measuring circuit 13 configured as described above, when the output of the SR FF 14 becomes “H” by the assertion of the beam position detection signal 20 from the first optical sensor 11, The analog switch 15 is turned on, the electric charge is accumulated in the capacitor 16, and the voltage of the output 23 gradually increases. When the beam position detection signal 21 from the second optical sensor 12 is asserted and the output of the SR FF 14 becomes “L”, the analog switch 15 is turned off.
And the accumulation of electric charge is stopped, and the potential of the output 23 is changed immediately before the beam position detection signal 21 is asserted until the reset signal 22 is asserted, the analog switch 17 is turned on, and the accumulated electric charge is discharged. The potential is maintained.

That is, the light beam arrival time measuring circuit 13
In the setting, when the light beam arrives at the first optical sensor 11 for the first time in one scan, charging of the capacitor 16 is started, and the light beam whose time difference is to be measured is changed to the second optical sensor 1.
When charging reaches 2, charging is stopped and the voltage is maintained. When the pixel clock start signal is generated, the capacitor 16 starts charging when the light beam first reaches the first optical sensor 11 in one scan, and the charged voltage matches the held voltage. At this point, a pixel clock start signal is generated. This makes it possible to generate an accurate pixel clock with a simple configuration.

FIG. 4 is a circuit diagram in which the light beam arrival time measuring circuit shown in FIG. 3 is arranged corresponding to each laser diode (LD). That is, the light source unit (LDA) 1
Are arranged in correspondence with the four laser diodes (LDs), so that the input of the beam position detection signals 20 and 21 and the reset signal 22 can be selected.
Further, one more light beam arrival time measuring circuit shown in FIG. 3 described above is arranged to generate an image clock start signal. That is, the light beam arrival time measuring circuits 131 to 131
135 are arranged. Also, the output of the light beam arrival time measurement circuit 135 and the light beam arrival time measurement circuits 131-1
The comparators 191 to 194 are connected to compare the output of the laser diode with the output of the respective laser diodes and use the output as a pixel clock start signal of each laser diode.

It should be noted that reference numerals 251, 252,
Reference numerals 253 and 254 are provided for the laser diodes, respectively, and are switch signals for switching the input of the beam position detection signal 20 of the first optical sensor 11, and reference numeral 26.
Reference numerals 1, 262, 263, and 264 are provided for the respective laser diodes, and are switch signals for switching the input of the beam position detection signal 21 of the second optical sensor 12.
Reference numerals 271, 272, 273, and 274 denote reset signals 2
2 is a switch signal for switching input,
Reference numerals 81, 282, 283, 284, 285 denote output signals of the light beam arrival time measuring circuits 131 to 135, respectively, and reference numerals 291, 292, 293, 294 denote comparators 191.
To 194 are pixel clock start signals.

In FIG. 4, an output signal 285 from the light beam arrival time measurement circuit 135 and output signals 281, 282, and 2 from the light beam arrival time measurement circuits 131 to 134 are shown.
83, 284 are compared by comparators 191 to 194, respectively, and the output signals 291, 292, 293, 294 are output.
Is a pixel clock start signal of each laser diode.

FIG. 5 is an explanatory diagram showing a method of measuring the beam arrival time of the LD1, and FIG. 6 is a timing chart of the beam arrival time measurement in FIG. First, LD1
Reaches the first optical sensor 11 (state of FIG. 5A), the beam position detection signal 1 is asserted. At this time, the output signal 24 of the SRFF 24 becomes “H”, and the electric charge is accumulated in the capacitor 16. Next, when the light reaches the second optical sensor 12 (the state shown in FIG. 5B), the beam position detection signal 2 is asserted. At this time, SR
The output signal 24 of the FF 24 becomes “L” and the capacitor 16
Is stopped, and the circuit output potential is held until reset is asserted.

FIG. 7 is an explanatory diagram showing a method of measuring the beam arrival time of the LD 2, and FIG. 7 is a timing chart of the beam arrival time measurement in FIG. This behavior is
This is performed in the same manner as in LD1 described above. That is, first, L
When D2 reaches the first optical sensor 11 (FIG. 7)
(State (a)), the beam position detection signal 1 is asserted. At this time, the output signal 24 of the SRFF 24 becomes “H”, and the electric charge is accumulated in the capacitor 16. Next, when the light reaches the second optical sensor 12 (the state shown in FIG. 7B), the beam position detection signal 2 is asserted. At this time, the output signal 24 of the SRFF 24 becomes "L", the charge accumulation in the capacitor 16 is stopped, and the circuit output potential is held until reset is asserted.

FIG. 9 is a timing chart showing the output operation of the image clock start signal. When the LD 1 reaches the first optical sensor 11, the beam position detection signal 1 is asserted. At this time, the light beam arrival time measurement circuit 1
The output signal 24 of the SR FF 24 in 35 becomes "H", and charging of the capacitor 16 is started. The output signal 285 of the light beam arrival time measuring circuit 135 is compared with a voltage value corresponding to the beam arrival time of each LD, and at a timing when the voltage value (V ₁ , V ₂ , V ₃ , V ₄ ) matches.
The pixel clock start signal of the LD corresponding to the voltage value is asserted, and the pixel clock generator 9 generates a pixel clock synchronized with the pixel clock start signal.

[0031]

As described above, according to the multi-beam recording apparatus of the present invention (claim 1), the unit for emitting a plurality of light beams is rotated in the direction of the optical axis so as to have a predetermined pitch. When the light beam arrives at the light beam position detecting means, a time difference occurs.Therefore, the pixel clock start signal generating means detects the light beam reaching time difference in the main scanning direction, and the pixel clock starts at a timing according to the reaching time difference. A clock start signal is generated, and a pixel clock corresponding to the arrival time is generated by an image clock generating unit, thereby eliminating a position shift in the main scanning direction.
It is possible to provide a multi-beam recording device that realizes good image writing on a photoconductor.

Further, according to the multi-beam recording apparatus according to the present invention (claim 2), in claim 1, the first optical sensor and the second optical sensor arranged at a predetermined interval are arranged. Based on the arrival of the light beam at one optical sensor as a reference, the time difference at which the light beam arrives at the next second optical sensor is measured, so that the pixel clocks can be accurately synchronized.

Further, according to the multi-beam recording apparatus according to the present invention (claim 3), in claim 2, when the light beam first reaches the first optical sensor in one scan, charging of the capacitor is started. When the light beam whose time difference is to be measured reaches the second optical sensor arranged at a predetermined distance, the charging of the capacitor is stopped, the charged voltage is held, and the pixel clock start signal is generated. Sometimes, when the light beam arrives at the first optical sensor for the first time in one scan, charging of the capacitor starts, and the pixel clock start signal is generated at the timing when the charged voltage matches the held voltage. A highly accurate pixel clock start signal can be generated with a simple device configuration and control.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a multi-beam recording apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a configuration example of a light beam position detection unit.

FIG. 3 is a circuit diagram showing a configuration of a light beam arrival time measurement circuit.

FIG. 4 is a circuit diagram in which the light beam arrival time measuring circuit shown in FIG. 3 is arranged corresponding to each laser diode (LD).

FIG. 5 is an explanatory diagram showing a method of measuring a beam arrival time of the LD1.

FIG. 6 is a timing chart of the beam arrival time measurement in FIG.

FIG. 7 is an explanatory diagram showing a method for measuring a beam arrival time of the LD2.

8 is a timing chart of the beam arrival time measurement in FIG.

FIG. 9 is a timing chart showing an output operation of an image clock start signal.

[Explanation of symbols]

 Reference Signs List 1 light source unit 5 photosensitive drum 7 light beam position detecting unit 8 image clock start signal generating unit 9 image clock generating unit 10 image data processing unit 11 first optical sensor 12 second optical sensor 13 light beam arrival time measuring circuit 14 SR-FF 16 capacitor

Claims (3)

[Claims] 1. A multi-beam recording apparatus which scans a plurality of light beams on a photoconductor at a time and records image data on the photoconductor, wherein a light beam position detecting device detects a scanning position of the plurality of light beams. Means for detecting a position shift of the light beam in the main scanning direction from a difference in arrival time of each light beam to the light beam position detection means in accordance with a beam position detection signal output from the light beam position detection means; Pixel clock start signal generating means for generating a pixel clock for generating a pixel clock corresponding to the shift; and pixel clock generating means for generating a pixel clock according to the pixel clock start signal. Multi-beam recording device. 2. A light beam position detecting means, comprising: a first optical sensor provided perpendicularly to a main scanning direction; and a second optical sensor arranged in parallel with a predetermined distance from the first optical sensor. An optical sensor, wherein a light beam whose time difference is to be measured is based on a light beam that first reaches the first optical sensor in one scan, and
2. The multi-beam recording apparatus according to claim 1, wherein the arrival time difference is measured based on the arrival time at the optical sensor. 3. The pixel clock start signal generating means according to claim 1, wherein said charge / discharge is performed at an input timing of a beam position detection signal output from said first optical sensor and a beam position detection signal output from said second optical sensor. A light beam having a light beam arrival time measuring means having a capacitor to be performed, the light beam to start charging the capacitor when the light beam first reaches the first optical sensor in one scan, and to measure a time difference Stops charging when the second light sensor is reached, holds the charged voltage, and when the light beam first reaches the first light sensor in one scan when the pixel clock start signal is generated, 3. The method according to claim 2, wherein charging of the capacitor is started, and a pixel clock start signal is generated at a timing when the charged voltage matches the held voltage. Multi-beam recording device.