JPH09218364A - Multibeam scanning optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the multibeam scanning optical system which enables high-precision recording free of print fluctuations even if a rotary polygon mirror has rotational variation or plural semiconductor lasers have variance in wavelength. SOLUTION: Two optical detectors 10 provided on both the side of a photosensitive drum 9 detect plural scanning laser lights and measures the time intervals between corresponding optical detection signals, and a clock period varying means varies the clock period corresponding to the time intervals; and data are read out of a memory according to clock, so that the data are optically recorded.

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 optical system for scanning a large number of beams emitted from a plurality of semiconductor lasers.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a laser printer using a plurality of semiconductor lasers. A plurality of laser module parts 3 for guiding the light from the semiconductor laser 1 to the single mode optical fiber 4 by the lens 2 are prepared, arranged in a line at the emitting end 5 of the optical fiber, and the lights emitted from the laser module parts 3 are simultaneously produced by the rotating polygon mirror. , Scan on the photosensitive drum to perform optical recording. The light spot array 11 that scans on the photosensitive drum is inclined with respect to the scanning direction. The photodetector 10 detects a light spot array that is obliquely arranged and scanned.

FIG. 2 shows scanning light spots 11-1, 11-2, and 11.
-3, 11-4 and the photodetector 10 are shown in the positional relationship. The signals detected by the photodetector are shown as 12-1, 12-2, 12-3 and 12-4 in FIG. 3, and are collectively referred to as BD signals here. These signals are signals generated by the photodetector detecting the scanning light spots 11-1, 11-2, 11-3, and 11-4, respectively. B
The D signals 12-1, 12-2, 12-3, 12-4 serve as triggers to generate a predetermined number of phase-locked clock signals, and the data signals are read out by these clocks and printed.

Reference numerals 13-1, 13-2, 13-3 and 13-4 in FIG. 3 show the sections in which the above clock is generated.

FIG. 4 shows light spots 11-1, 11-2, 11-3, 11-4.
Are scanned by the rotary polygon mirror in the order shown by No. 1, No. 2, No. 3, and No. 4, and scan lines of a certain length printed from left to right on the paper surface on the photosensitive drum. Shows. Since the scanning start position at the left end on the paper surface is close to the photodetector, the scanning start positions of all the scanning lines accurately match. However, on the scanning end side of the right end, as shown by the curve 14, the print position fluctuates in a sinusoidal manner. This is due to the rotation fluctuation of the rotary polygon mirror. Further, the lengths of the scanning lines also vary among the plurality of scanning lines obtained by one scan. This is a unique phenomenon that occurs when scanning multiple beams. The cause of this is that the wavelength of the semiconductor laser that generates the multi-beam is slightly different, so the refractive index of the glass material that constitutes the optical system also differs, which is also called loose wavelength aberration. Is. To solve this, it is sufficient to use an optical system whose wavelength aberration has been corrected, but the cost increases due to an increase in the number of lenses.

[0006]

However, on the scanning end side at the right end, the print position fluctuates sinusoidally as shown by the curve 14. This is due to the rotation fluctuation of the rotary polygon mirror. Further, the lengths of the scanning lines also vary among the plurality of scanning lines obtained by one scan. This is a unique phenomenon that occurs when scanning multiple beams. The cause of this is that the wavelength of the semiconductor laser that generates the multi-beam is slightly different, so the refractive index of the glass material that constitutes the optical system also differs, which is also called loose wavelength aberration. Is. To solve this, it is sufficient to use an optical system whose wavelength aberration has been corrected, but the cost increases due to an increase in the number of lenses.

Therefore, an object of the present invention is to provide an optical system for performing multi-beam scanning using a plurality of semiconductor lasers, even if there are variations in the rotation of the rotary polygon mirror and variations in the wavelengths of the plurality of semiconductor lasers. An object of the present invention is to provide a multi-beam scanning optical system that enables highly accurate recording without shaking.

[0008]

SUMMARY OF THE INVENTION The above-mentioned object is that laser light from a plurality of semiconductor lasers forms a light spot array on a photosensitive drum, and the arrangement direction of the light spot arrays is oblique to the scanning direction. In a multi-beam scanning optical system that arranges and scans so that each of a plurality of laser beams to be scanned is detected by two photodetectors provided on both sides of the photosensitive drum, and the time interval between the corresponding photodetection signals is detected. Is measured, the clock cycle is changed by the clock cycle changing means corresponding to the time interval, and the data is read from the memory based on this clock.

[0009]

FIG. 5 shows a multi-beam scanning optical system according to the present invention. A laser module section 3 that guides light from the semiconductor laser 1 to a single mode optical fiber 4 through a lens 2.
A plurality of optical fibers are arranged in a line at the emission end 5 of the optical fiber, and the light emitted from this is simultaneously scanned on the photosensitive drum by the rotary polygon mirror to perform optical recording. The light spot array 11 that scans on the photosensitive drum is inclined with respect to the scanning direction. The light spots arrayed obliquely and scanned are the photodetector 10 on the scanning start side and the photodetector 15 on the scanning end side.
It is detected by.

FIG. 6 shows scanning light spots 11-1, 11-2, 11
-3, 11-4 and the photodetectors 10 and 15 are shown in the positional relationship. BD signals detected by the photodetector 10 on the scanning start side are indicated by 12-1, 12-2, 12-3, and 12-4 in FIG. These signals correspond to the signals generated by the scanning light spots 11-1, 11-2, 11-3 and 11-4, respectively. On the other hand, the BD signal detected by the photodetector 15 on the scanning end side is 15-1, 15-2, 15-3, 15
It is represented by -4. Time interval of each BD signal 16-
1, 16-2, 16-3, 16-4 are measured with the measurement clock.

FIG. 8 shows a circuit configuration for outputting print data for one semiconductor laser. The pair of BD signals generated by the two photodetectors when the semiconductor laser of interest is optically scanned are designated as 12-1 and 15-1. The measurement clock is BD
The phase is synchronized with the signal 12-1 and input to the counter. The counter measures time interval 16-1 by counting the number of measurement clocks between BD signals 12-1 and 15-1. The clock selection circuit generates an optimum print clock according to the number counted by the counter. That is, if the number of counts between BD signals exceeds a predetermined value, it means that the rotation speed of the rotary polygon mirror is slow, or the scanning width or printing width is shortened due to wavelength aberration. Therefore, the cycle of the print clock is lengthened so that it becomes a predetermined value in the next scan. It is assumed that the print clock generated by the above circuit is further phase-locked with the BD signal 12-1 by the phase-locking circuit.
Based on the phase-synchronized print clock, the contents of the data temporarily stored in the FiFo memory are read out and sent to the printer.

FIGS. 9 and 10 show a clock selection circuit 2
The composition of the species is shown. In FIG. 9, clocks are prepared in advance from fc1 to fc4, and the output of the counter selects and outputs the optimum clock by the determination circuit.
In FIG. 10, the output of the counter is converted into the magnitude of the voltage by the D / A converter, and the print clock is generated by the VCO (voltage controlled oscillator) whose clock cycle changes depending on the magnitude of the voltage.

[0013]

According to the present invention, in an optical system for performing multi-beam scanning using a plurality of semiconductor lasers, printing is performed even if there are fluctuations in the rotation of the rotary polygon mirror and variations in the wavelengths of the plurality of semiconductor lasers. It is possible to provide a multi-beam scanning optical system that enables highly accurate recording without shaking.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a conventional technique.

FIG. 2 is an explanatory view showing a positional relationship between optical scanning and a photodetector using a conventional oblique light spot array.

FIG. 3 is an explanatory diagram showing a relationship between a conventional photodetector output and printing time.

FIG. 4 is an explanatory diagram of print fluctuation caused by multi-beam scanning.

FIG. 5 is a configuration diagram of a multi-beam scanning optical system of the present invention.

FIG. 6 is an explanatory view showing a positional relationship between optical scanning by an oblique light spot array and optical detectors arranged on a scanning start side and a scanning end side in the optical system of the present invention.

FIG. 7 is an explanatory diagram showing the relationship between the light detection output and the time interval between the paired light detection outputs in the optical system of the present invention.

FIG. 8 is a configuration diagram of a control circuit used in the optical system of the present invention.

FIG. 9 is a configuration diagram of a clock selection circuit used in the optical system of the present invention.

FIG. 10 is a configuration diagram of a clock selection circuit used in the optical system of the present invention.

[Explanation of symbols]

1 is a semiconductor laser, 2 is a lens, 3 is a semiconductor laser module part, 5 is an optical fiber array part, 7 is a rotary polygon mirror, 10 is a photodetector, 11 is a light spot array, and 9 is a photosensitive drum.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoji Hirose 1060 Takeda, Hitachinaka-shi, Ibaraki Prefecture Within Hitachi Koki Co., Ltd.

Claims (3)

[Claims] 1. A multi-scan system in which laser light from a plurality of semiconductor lasers forms a light spot array on a photosensitive drum and is arranged such that the array direction of the light spot arrays is oblique to the scanning direction. In the beam scanning optical system, each of a plurality of laser beams to be scanned is detected by two photodetectors provided on both sides of the photosensitive drum, and the time interval between the corresponding photodetection signals is measured, and the corresponding time interval is measured. A multi-beam scanning optical system for optical recording by changing the clock cycle by the clock cycle changing means and reading data from the memory based on this clock. 2. The multi-beam scanning optical system according to claim 1, wherein the clock cycle changing means selects from a clock generating circuit having a plurality of clock cycles by a switch circuit. 3. The multi-beam scanning optical system according to claim 1, wherein a voltage control type oscillator is used as the clock cycle changing means.