JP3184583B2 - Synchronous signal generator, synchronous clock signal generator, and image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates, <br/> scanning with a laser beam line of the Hare image forming apparatus suitably used in such an image forming apparatus, the synchronization signal generator and its generating a main scanning synchronization signal The present invention relates to a synchronous clock signal generator for generating an image clock synchronized with a main scanning synchronous signal.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a laser beam printer, a photodetector is provided near a position where a laser beam starts scanning, and an output waveform of the photodetector when the laser beam crosses the photodetector is shaped. That is, the detector output is a square pulse signal, and the time width (pulse width) is widened to be a main scanning synchronization signal that defines the start of laser beam modulation by an image signal for each main scanning.

When an image signal is transmitted, an image clock signal synchronized with the leading edge of the main scanning synchronization signal is generated. The pixel signal stored in the image memory is transmitted to the semiconductor laser one bit at a time by the image clock signal, and the laser is turned on / off according to the pixel signal. In this way, an electrostatic latent image is formed on the photosensitive drum,
An image is formed by an electrophotographic method.

Further, in order to generate an image clock signal synchronized with the main scanning synchronization signal, first generate oscillation clock frequency of 8 times from 4 times of the image clock signal, the image clock this by dividing Signal. A frequency division counter used for frequency division is reset by the main scanning synchronization signal. That is, if the count is always started from a constant count value after the reset (the frequency division operation is started by the main scanning synchronization signal), the countdown output of 1/4 to 1/8 cycle of the original oscillation is reduced with respect to the main scanning synchronization signal. The image clock signal always has a fixed phase relationship. In this way, the image quality is improved by setting the dot shift for each line to be less than 1/4 to less than 1/8 dot.

On the other hand, the response of the photodetector is faster as the area of the light receiving section is smaller. However, if the area of the photodetector is reduced, the output pulse width becomes extremely narrow.
In order to prevent such a loss during transmission of the pulse, a main scanning synchronization signal in which the pulse width of the photodetector output is increased is output. Usually, the pulse width can be widened only in the trailing edge direction, so that only the leading edge of the main scanning synchronization signal is synchronized with the photodetector output. Further, when the semiconductor laser oscillates in multi-mode, the laser beam becomes not a simple Gaussian distribution shape but a double peak shape or a triple peak shape.
When a laser beam having such a distribution is scanned on the photodetector, the output waveform of the detector has some peaks and valleys.

As a countermeasure in such a case, for example, a timer is started at the first peak, the timer is counted until the beam completely passes through the detector, and the pulse width is maintained by maintaining the level of the main scanning synchronization signal during that time. May be used to spread the word. Such only Lee Digg edge of the main scanning synchronization signal is also in the process holds the information of the correct beam scanning start timing.

Therefore , the frequency division is started in synchronization with the leading edge of the photodetector output and the image clock is
Must be generated, but for this purpose, a synchronization pulse synchronized with the leading edge of the photodetector output must first be generated . Therefore, a pulse synchronizer operating with the original oscillation clock is used to generate a synchronization pulse for one cycle of the original oscillation clock. The counter that divides the frequency of the original oscillation clock is reset by the synchronization pulse.

[0008]

SUMMARY OF THE INVENTION However, the above-mentioned prior art
In the technology, the resolution has recently been improved and the frequency of the clock signal of the image has increased.
There was a problem that the speed could not catch up with the use of TL.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an image forming apparatus, a synchronizing signal generating apparatus, and a synchronizing clock which can achieve high-accuracy synchronization with a simple configuration without increasing the cost. It is to provide a signal generator.

Another object of the present invention is to synchronize the image clock signal with the trailing edge, ie, the trailing edge , of the main scanning synchronization signal, thereby eliminating the need for a pulse synchronizer for synchronization and increasing the speed of the image clock signal. Forming apparatus and synchronizing signal generation device that can easily cope with
And a synchronous clock signal generator .

[0011]

In order to solve the above-mentioned problems, a synchronizing signal generator according to the present invention provides a synchronizing signal generator which scans a photosensitive member with a laser beam modulated by an image signal to form an image. In a synchronization signal generator for periodically generating a synchronization signal for defining the start of modulation of a laser beam by an image signal, detection means for periodically detecting a deflected laser beam at a predetermined scanning position And a timing means for generating a signal defining a leading edge of a synchronous signal synchronized with the subsequent detection of the laser beam by measuring a predetermined time from the detection of the laser beam by the detection means, A synchronizing signal is generated in which a leading edge is defined by a signal defining the leading edge generated from the timing means, and a trailing edge is defined by a detection output of the detecting means. And a period signal generating means. Further, the synchronous clock signal generating device according to the present invention comprises:
In a synchronous clock signal generator for generating an image clock signal synchronized with a synchronous signal, a deflected laser beam
Detecting means for periodically detecting the laser beam at a predetermined scanning position , and measuring a predetermined time from the detection of the laser beam by the detecting means, thereby synchronizing with the subsequent detection of the laser beam.
Clocking means for generating a signal defining a leading edge of the synchronization signal, a leading edge defined by a signal defining the leading edge generated from the timing means, and a trailing edge defined by a detection output of the detecting means. And a synchronizing signal generating means for generating a synchronizing signal, and an image clock signal generating means for outputting an image clock signal synchronized with the trailing edge of the synchronizing signal. Also,
An image forming apparatus according to the present invention is an image forming apparatus that scans a photosensitive member with a laser beam modulated by an image signal to form an image , wherein the detecting unit periodically detects a deflected laser beam at a predetermined scanning position. A timer for generating a signal defining a leading edge of a synchronization signal synchronized with the subsequent detection of the laser beam by measuring a predetermined time from the detection of the laser beam by the detection unit; and A synchronizing signal generating means for generating a synchronizing signal in which a leading edge is defined by a signal defining the leading edge and a trailing edge defined by a detection output of the detecting means; and an image synchronized with the trailing edge of the synchronizing signal. An image clock signal generating means for outputting a clock signal, and a signal modulated based on an image signal synchronized with the image clock signal. It characterized by having a laser beam generating means for generating a Zabimu. Preferably, the detection means has a photodetector and a comparator for slicing the output of the photodetector at a predetermined level.

[0012]

FIG. 1 shows an embodiment of the present invention.

1 is a semiconductor laser, 2 is a collimator lens for collimating a laser beam, and 3 is a rotary polygon mirror, which is driven by a motor that rotates at high speed.

Reference numeral 4 denotes an f-θ lens, and reference numeral 5 denotes a reflection mirror, which is placed at the start end of main scanning by a laser beam. 6 is a condenser lens, 7 is a slit, and 8 is a photodetector.
It should be noted that the broken lines in the figure indicate light paths.

A comparator 9 slices the output waveform of the photodetector 8 with the reference voltage VREF as a threshold level.

An oscillation circuit 10 for the original oscillation clock is a crystal oscillator for generating a clock signal having a frequency four times the required image clock in the embodiment.

Reference numerals 11 and 12 denote D-flip-flops.
A four-frequency divider is configured.

Reference numeral 13 denotes an output terminal for an image clock signal.

FIG. 2 is a time chart showing the operation of the circuit of FIG.

The operation will be described below with reference to FIGS.

The semiconductor laser 1 is forcibly turned on at the start of scanning by a circuit configuration (not shown). This forced lighting means is called forced lighting by an unblanking signal and is conventionally known (for example, Japanese Patent Laid-Open No. 57-23914) and is not shown in the drawing.

The output light of the semiconductor laser 1 is collimated by a collimator lens 2, deflected by a rotating polygon mirror 3, and formed into an image by an f-θ lens 4. A reflection mirror 5 is provided on an optical path near the scanning start position. The laser beam reflected by the reflection mirror 5 before the image forming surface (on a photosensitive drum not shown) is guided to a condenser lens 6. I will

The laser beam that has passed through the condenser lens 6 is restricted in the pass band by the slit 7 placed at the image forming position, and enters the photodetector 8.

The output of the photo detector 8 is shown in FIG. When this output is sliced by the comparator 9, the waveform shown in FIG. This is the main scanning synchronization signal. The original oscillation clock from the original oscillation oscillator 10 is shown in FIG. 2 (c). When the original oscillation clock is frequency-divided by で in the D-flip-flop 11, the output of the waveform shown in FIG. can get. Further, when the output is frequency-divided by the D-flip-flop 12, an output having a waveform shown in FIG. 2E is obtained.

That is, when the D-flip-flops 11 and 12 are reset by the main scanning synchronizing signal (FIG. 2B), first the outputs of the flip-flops 11 and 12 (FIG.
(D) and (e) are both at the “L” level. The output of the flip-flop 11 rises at the rise of the first original oscillation clock (FIG. 2C) after the trailing edge of the main scanning synchronization signal ends, and the output of the flip-flop 12 to which the rise has been inputted also rises.

As described above, the output of the D-flip-flops 11 and 12 rises at the rise of the original oscillation clock immediately after the trailing edge of the main scanning synchronization signal, so that the image clock synchronized with the trailing edge of the main scanning synchronization signal A signal can be obtained at the terminal 13 (FIG. 2 (e)).

In this embodiment, since a detection signal having a wide pulse width is obtained by the condenser lens, it is not necessary to increase the pulse width by signal processing, and the main scanning synchronization signal can be obtained only by slicing the detection signal. it can. In addition, since such a main scanning synchronization signal is synchronized with beam detection at both the leading edge and the trailing edge,
As another embodiment of the present invention, an image clock synchronized with the leading edge may be generated.

[Another Embodiment] FIG. 3 shows a second embodiment.

Here, only the main scanning synchronizing signal generating circuit is shown. That is, in the first embodiment, when the scanning speed of the laser beam is extremely high, the width of the main scanning synchronization signal may be too narrow. An example of a waveform shaping circuit that can be used in such a case will be described.

In FIG. 3, 14 is a timer, 15 is a set / reset flip-flop, and 16 is an output terminal of a main scanning synchronization signal.

FIG. 4 is an operation time chart of each component of FIG.

The operation will be described below with reference to FIGS.

The output of the comparator 9 is shown in FIG. This is the same as FIG. This comparator output is input to the timer 14, and the timer 14 measures the period T to generate a pulse shown in FIG. This period T is one of the main scanning of the laser beam.
It is set slightly shorter than the cycle.

The output of the timer 14 is the flip-flop 1
5, and the output of the comparator 9 is input to the reset input terminal R of the flip-flop 15. This flip-flop 15 by a pulse width is spread, output Toreri Nguejji is synchronized with the leading edge of the input signal is obtained. This output (FIG. 4 (h)) is led out to the main scanning synchronization signal output terminal 16. This signal is input to, for example, the clear terminals CLR of the synchronous circuit flip-flops 11 and 12 in FIG. 1 and used for synchronizing the image clock signal.

As described above, according to each embodiment of the present invention, a main scanning synchronization signal and a high-frequency image clock signal synchronized with the main scanning synchronization signal can be obtained at a low cost with a simple configuration.

In the present invention, the image clock is obtained by resetting the frequency dividing counter with the main scanning synchronizing signal. For example, Japanese Patent Application Laid-Open Nos.
Alternatively, it may be obtained by using the circuit disclosed in JP-A-220588. In this case, the data may be taken in the flip-flop or the latch circuit in synchronization with the leading edge or trailing edge of the main scanning synchronization signal.

[0037]

As described above , according to the present invention ,
Without using a pulse synchronizer, it is possible to obtain an image clock signal synchronized with simply by accurate resetting for example, divide counter.

Further , according to the present invention, since the circuit configuration is simplified, it is possible to easily cope with an increase in the speed of the image clock signal. For example, even in a circuit using a normal TTL, a highly accurate synchronous clock signal can be obtained. Can occur.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the configuration of FIG. 1;

FIG. 3 is a block diagram showing a main configuration of another embodiment of the present invention.

FIG. 4 is a timing chart for explaining the operation of the configuration of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 6 Condensing lens 8 Photodetector 9 Comparator 11, 12 D-flip-flop

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-162973 (JP, A) JP-A-3-143645 (JP, A) JP-A-1-218840 (JP, A) JP-A-1- 128033 (JP, A) JP-A-1-115269 (JP, A) JP-A-63-163872 (JP, A) JP-A-62-226166 (JP, A) (58) Fields studied (Int. ⁷ , DB name) G02B 26/10 B41J 2/44 H04N 1/113 H04N 1/23 103

Claims (6)

(57) [Claims] 1. A synchronizing signal for periodically generating a synchronizing signal for defining a start of modulation of a laser beam by an image signal when an image is formed by scanning a photosensitive member with a laser beam modulated by an image signal. in generator, detection means for periodically detect <br/> the deflected laser beam at a predetermined scanning position, by measuring a predetermined time from the detection of the laser beam by said detecting means, then the laser beam Same as detection
Clocking means for generating a signal defining the leading edge of the expected synchronization signal; a leading edge is defined by a signal defining the leading edge generated from the timing means, and a trailing edge is determined by a detection output of the detecting means. A synchronizing signal generating means for generating a specified synchronizing signal. 2. The method according to claim 1, wherein the detecting unit includes: a photodetector;
2. A comparator for slicing the output of the photodetector at a predetermined level.
3. The synchronization signal generator according to item 1. 3. A synchronous clock signal generator for generating an image clock signal synchronized with a synchronous signal, comprising: detecting means for periodically detecting a deflected laser beam at a predetermined scanning position; By measuring a predetermined time from the detection of the laser beam by the means , the same
Clocking means for generating a signal defining the leading edge of the expected synchronization signal; a leading edge is defined by a signal defining the leading edge generated from the timing means, and a trailing edge is determined by a detection output of the detecting means. A synchronous clock signal generating device comprising: a synchronous signal generating means for generating a prescribed synchronous signal; and an image clock signal generating means for outputting an image clock signal synchronized with a trailing edge of the synchronous signal. 4. The detecting means includes: a photodetector;
4. A comparator for slicing the output of the photodetector at a predetermined level.
3. The synchronous clock signal generator according to claim 1. 5. An image forming apparatus for forming an image by scanning a photosensitive member with a laser beam modulated by an image signal, wherein a deflected laser beam is periodically detected at a predetermined scanning position. means, by measuring a predetermined time from the detection of the laser beam by said detecting means, the the subsequent detection of the laser beam
Clocking means for generating a signal defining the leading edge of the expected synchronization signal; a leading edge is defined by a signal defining the leading edge generated from the timing means, and a trailing edge is determined by a detection output of the detecting means. Synchronizing signal generating means for generating a specified synchronizing signal; image clock signal generating means for outputting an image clock signal synchronized with the trailing edge of the synchronizing signal; modulation based on the image signal synchronized with the image clock signal An image forming apparatus comprising: a laser beam generating unit that generates a laser beam. 6. The photodetector includes a photodetector,
6. A comparator for slicing the output of the photodetector at a predetermined level.
An image forming apparatus according to claim 1.