JPH04316268A - Scanning beam synchronization controller - Google Patents

Abstract

PURPOSE:To control the timing of a scanning beam with a high precision by a simple and inexpensive constitution. CONSTITUTION:A reference oscillator 100 outputs a reference signal (a) having the same frequency (f) as a timing clock pulse (d) which starts the modulation timing of a laser beam printer or the like, and a reference signal output generating circuit 101 generates a reference signal (b) having the same frequency (f) like a saw tooth wave by the reference signal (a). A photodetector 104 is arranged on the optical path of the laser beam scanned by a rotating polygonal mirror and outputs a synchronizing signal (c) of the scanning timing. A reference signal output holding circuit 102 holds the level of the reference signal (b) from the reference signal output generating circuit 101 by the rise of the synchronizing signal (c), and a comparing circuit 103 compares the level of the reference signal (b) from the reference signal output generating circuit 101 with the level of the reference signal (b) held by the reference signal output holding circuit 102, and a timing clock pulse (d) is outputted in accordance with the level difference.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to laser printers, laser facsimile machines, laser recording devices, laser processing devices, laser information reading devices, etc. The present invention relates to a scanning beam synchronization control device suitable for devices that perform processing, information reading, etc.

0002

2. Description of the Related Art Generally, in a laser beam printer, for example, the modulation timing of a scanning beam must be controlled with extremely high precision for each scan. In this case, it is common to place a photodetector on the optical path of the scanning beam and start modulating the scanning beam in synchronization with the synchronization signal of this photodetector. Since it is not possible to obtain sufficient synchronization accuracy with this method, various proposals have been made.

Conventionally, this type of scanning beam synchronization control device has been disclosed in Japanese Patent Application Laid-open No. 51-46141 and Japanese Patent Application Laid-open No. 51-46141.
As shown in Publication No. 89347, a highly stable reference oscillator such as a crystal oscillator is used, and the oscillation frequency is set to n times the frequency of the timing clock pulse for dot position setting necessary to form the printed dot pattern (n is It is configured to divide the frequency as an integer) in synchronization with the synchronization signal of the photodetector. In this case, the phase difference between the synchronization signal and the timing clock pulse is 1 of the period of the timing clock pulse.
/n or less.

[0004] Another conventional device is the one disclosed in Japanese Patent Application Laid-open No. 5
As shown in Japanese Patent Publication No. 6-126378, Japanese Patent Application Laid-Open No. 61-150567, and Japanese Patent Publication No. 62-26221, a plurality of pulses having the same period and whose phase is slightly shifted from the timing clock pulse are generated by a delay circuit or the like. For example, the synchronization accuracy is improved by selecting the earliest pulse as the timing clock pulse (Japanese Patent Publication No. 62-26221).

[0005]

[Problems to be Solved by the Invention] However, in the conventional devices disclosed in Japanese Patent Application Laid-open No. 51-46141 and Japanese Patent Application Laid-open No. 51-89347, a highly stable reference oscillator such as a crystal oscillator is used. The pulse frequency is 30MHz, and the tolerance for synchronization is 1/16.
(n=16), the reference oscillator is 480MH
There is a problem that a high frequency output of z is required, and therefore the configuration is complicated and expensive.

On the other hand, Japanese Patent Application Laid-open No. 126378/1983,
JP 61-150567, JP 62-262
The conventional device disclosed in Japanese Patent No. 21 does not divide the reference frequency, so the above problem can be solved. However, since synchronization accuracy is determined by the number of pulses used to select timing clock pulses, in order to improve synchronization accuracy, it is necessary to increase the number of delay circuits and improve the synchronization accuracy of the delay circuits. is complicated,
The problem is that it is expensive.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide a scanning beam synchronization control device that can control the timing of a scanning beam with high accuracy using a simple and inexpensive configuration.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the first means is to provide a scanning beam synchronization control device that generates a timing clock pulse for determining the timing of a scanning beam, at the same frequency as the timing clock pulse. a reference oscillator that generates a reference signal; a reference signal generation circuit that uses the reference signal of the reference oscillator to generate a reference signal with the same frequency as the timing clock pulse; and a reference signal generation circuit that detects the scanning beam and outputs a timing synchronization signal of the scanning beam. a holding circuit that holds the level of the reference signal of the reference signal generation circuit with a synchronization signal of the photodetector, a level of the reference signal of the reference signal generation circuit and a level of the reference signal of the holding circuit; and a comparison circuit that outputs a timing clock pulse based on the difference between the two, and the output signal from the comparison circuit is used as the timing clock pulse for setting the dot position of the scanning beam.

The second means is that the oscillation period from the reference oscillator is N times the pixel period (N is an integer of 2 or more), and the output signal from the comparison circuit is used as the timing clock pulse for setting the dot position. It is characterized by using a signal whose frequency is divided by N.

The third means is characterized in that the first and second reference signal generation circuits output sawtooth signals as reference signals.

[0011]

[Operation] In the first means, with the above configuration, a reference signal having the same frequency as the timing clock pulse is generated by the reference oscillator, a reference signal having the same frequency as the timing clock pulse is generated by this reference signal, and the level of this reference signal is A timing clock pulse is generated by the difference in level between the reference signal and the reference signal when the photodetector detects the synchronization signal. Therefore, when improving the synchronization accuracy of the modulation timing of the scanning beam, it is easy and simple because the frequency of the reference oscillator is not divided or multiple pulses are not generated for selecting the timing clock pulse as in the conventional example. The timing of the scanning beam can be controlled with high precision using an inexpensive configuration.

In the second means, a reference signal having a frequency N times the timing clock pulse (N is an integer of 2 or more) is generated by a reference oscillator, a reference signal is generated by this reference signal, and the level of this reference signal is A comparison signal is generated based on the difference in level between the reference signal and the reference signal when the photodetector detects the synchronization signal, and this comparison signal is frequency-divided by 1/N to generate a timing clock pulse. Therefore, since timing clock pulses with the same duty ratio can be generated, it is possible to simplify the configuration of the subsequent control circuit and scanning beam modulation circuit. , the timing of the scanning beam can be controlled with high precision with a simple and inexpensive configuration.

In the third means, since a sawtooth signal is generated as the reference signal, the reference signal generation circuit does not become expensive or complicated.

[0014]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a scanning beam synchronization control device according to the present invention, and FIG. 2 is a timing chart showing main signals of the scanning beam synchronization control device of FIG.

In FIG. 1, a reference oscillator 100 outputs a reference signal a having the same frequency f as a timing clock pulse d for starting the modulation timing of, for example, a laser beam printer, and a reference signal output generation circuit 101 A reference signal b having the same frequency f, such as a sawtooth wave, is generated using the reference signal a. The photodetector 104 is disposed, for example, on the optical path of a laser beam scanned by a rotating polygon mirror, and outputs a scanning timing synchronization signal c. In this case, the timing clock pulse d must be output at the rising edge of the synchronization signal c, for example.

The reference signal output holding circuit 102 holds the level of the reference signal b from the reference signal output generation circuit 101 at the rising edge of the synchronizing signal c, for example, and the comparison circuit 103
The level of the reference signal b from the reference signal output generation circuit 101 and the level of the reference signal b held by the reference signal output holding circuit 102 are compared, and a timing clock pulse d is output based on the level difference.

Next, the detailed operation of the above embodiment will be explained with reference to FIG. The reference oscillator 100 outputs a reference signal a with the same frequency f as the pixel period of a recorded image in, for example, a laser beam printer, and the reference signal output generation circuit 101 uses this reference signal a to generate a reference signal with the same frequency f. Outputs sawtooth signal b.

When the scanning beam passes over the light receiving surface of the photodetector 104, the photodetector 104 outputs a synchronization signal c that becomes high level while the scanning beam passes, and the reference signal output holding circuit 102 outputs a synchronization signal c that becomes high level while the scanning beam passes. The level of the sawtooth signal b from the signal output generation circuit 101 is held at the rising edge of the synchronization signal c. The comparison circuit 103 compares the level of the sawtooth signal b from the reference signal output generation circuit 101 and the level of the sawtooth signal b held by the reference signal output holding circuit 102, and compares the level of the sawtooth signal b from the reference signal output generation circuit 101. A timing clock pulse d is output which remains at a high level while the level of b is high.

Therefore, according to the above embodiment, when improving the synchronization accuracy of the modulation timing of the scanning beam, the frequency f of the reference oscillator 100 is not divided as in the conventional example, and the timing clock pulse d is selected. Since multiple pulses are not generated for this purpose, the modulation timing of the scanning beam can be controlled with high accuracy using a simple and inexpensive configuration. Furthermore, in this embodiment, since a sawtooth signal is output as the reference signal b, the reference signal output generation circuit 101 does not become complicated or expensive.

Next, a second embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a block diagram showing a second embodiment of the scanning beam synchronization control device according to the present invention, and FIG.
3 is a timing chart showing main signals of the scanning beam synchronization control device of FIG. In the above embodiment, since the timing clock pulse d is generated by comparing the level of the sawtooth signal b from the reference signal output generation circuit 101 and the level of the reference signal b held by the reference signal output holding circuit 102, the timing clock pulse d is Although the duty ratio of the pulse d differs for each scan, the present embodiment is configured to generate the timing clock pulse E with the same duty ratio.

In FIG. 3, the reference oscillator 300 has a frequency (N
・Output the reference signal A of f) and use the reference signal output generation circuit 3
01 uses this reference signal A to generate a reference signal B having a frequency (N·f), such as a sawtooth wave. Photodetector 304
is disposed on the optical path of a laser beam scanned by a rotating polygon mirror in, for example, a laser beam printer, and outputs a synchronization signal C for scanning timing. In this case, the timing clock pulse E must be output at the rising edge of the synchronization signal C, for example.

The reference signal output holding circuit 302 holds the level of the reference signal f from the reference signal output generation circuit 301 at the rising edge of the synchronizing signal C, for example, and the comparison circuit 303
The level of the reference signal B from the reference signal output generation circuit 301 and the level of the reference signal B held by the reference signal output holding circuit 302 are compared, and a comparison signal D is output in accordance with the level difference. The N frequency divider 305 divides this comparison signal D by 1/N.
and outputs a timing clock pulse E of frequency f.

Next, the detailed operation of the above embodiment will be explained with reference to FIG. The reference oscillator 300 outputs a reference signal A having a frequency (2·f) twice that of the pixels of a recorded image in, for example, a laser beam printer, and the reference signal output generation circuit 301 uses this reference signal A to generate the same reference signal. A sawtooth signal B of frequency (2·f) is output.

When the scanning beam passes over the light receiving surface of the photodetector 304, the photodetector 304 outputs a synchronization signal C that becomes high level while the scanning beam passes, and the reference signal output holding circuit 302 outputs a synchronization signal C that becomes high level while the scanning beam passes. The level of the sawtooth signal B from the signal output generation circuit 301 is held at the rising edge of the synchronization signal C. The comparison circuit 303 compares the level of the sawtooth signal B from the reference signal output generation circuit 301 and the level of the sawtooth signal B held by the reference signal output holding circuit 102, and compares the level of the sawtooth signal B from the reference signal output generation circuit 301 with A comparison signal D that is at a high level while the level of B is high is output. The N frequency divider 305 divides the frequency (2·f) of this comparison signal D into 1/2 and outputs a timing clock pulse E having a frequency f.

Therefore, according to the above embodiment, the reference oscillator 300 generates the timing clock pulse E (frequency f).
A reference signal A with a frequency (Nf) that is N times higher than that of the reference signal A is output, and the N frequency divider 305 divides the comparison signal D by 1/N, thereby generating a timing clock pulse E with the same duty ratio. Therefore, the configurations of the subsequent control circuit and scanning beam modulation circuit can be simplified. Note that the reference oscillator 300 and N frequency divider 305 of this embodiment are for generating timing clock pulses E with the same duty ratio, and have no relation to synchronization accuracy, so they have a simple and inexpensive configuration. The modulation timing of the scanning beam can be controlled with high precision. Further, in this embodiment as well, since a sawtooth signal is output as the reference signal B, the reference signal output generation circuit 301 does not become complicated or expensive.

[0026]

As described above, according to the invention as set forth in claim 1, the timing of the scanning beam can be controlled with high precision with a simple and inexpensive configuration. According to the second aspect of the invention, timing clock pulses having the same duty ratio can be generated, and therefore, the configurations of the control circuit and the scanning beam modulation circuit in the subsequent stage can be simplified. Further, since the reference oscillator and the frequency divider have no relation to synchronization accuracy, the timing of the scanning beam can be controlled with high precision with a simple and inexpensive configuration. According to the third aspect of the invention, since the reference signal generation circuits of the first and second aspects output sawtooth signals as reference signals, the reference signal generation circuits do not become expensive or complicated.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a scanning beam synchronization control device according to the present invention.

FIG. 2 is a timing chart showing main signals of the scanning beam synchronization control device in FIG. 1;

FIG. 3 is a block diagram showing a second embodiment of a scanning beam synchronization control device according to the present invention.

FIG. 4 is a timing chart showing main signals of the scanning beam synchronization control device of FIG. 3;

[Explanation of symbols]

100, 300 Reference oscillator 101, 301 Reference signal output generation circuit 102, 30
2 Reference signal output holding circuit 103, 303 Comparison circuit 104, 304 Photodetector 305 N frequency divider

Claims (3)

[Claims] 1. A scanning beam synchronization control device that generates a dot position setting timing clock pulse for determining the timing of a scanning beam, comprising: a reference oscillator that generates a reference signal having the same frequency as the timing clock pulse; and the reference oscillator. a reference signal generation circuit that generates a reference signal of the same frequency as the timing clock pulse using a reference signal of the reference signal; a photodetector that detects a scanning beam and outputs a synchronization signal for the timing of the scanning beam; a holding circuit that holds a signal level with a synchronization signal of the photodetector; and a comparison circuit that outputs a timing clock pulse based on the difference between the level of a reference signal of the reference signal generation circuit and the reference signal of the holding circuit. A scanning beam synchronization control device, characterized in that the output signal from the comparison circuit is used as a timing clock pulse for setting a dot position of the scanning beam. 2. The oscillation period from the reference oscillator is N times the pixel period (N is an integer of 2 or more), and the output signal from the comparison circuit is divided by N as the timing clock pulse for setting the dot position. 2. The scanning beam period control device according to claim 1, wherein said signal is used. 3. The scanning beam synchronization control device according to claim 1, wherein the reference signal generation circuit outputs a sawtooth signal as the reference signal.