JPH07104202A - Light beam scanner - Google Patents

Abstract

PURPOSE:To obtain a stable synchronizing signal having desired pulse width in a light beam scanner utilized in a laser beam printer, etc. CONSTITUTION:As to the light beam scanner a synchronizing signal generating circuit is constituted of a comparator 10 provided with a strobing terminal 13, and a pulse width control circuit 4 constituted of a time constant circuit 5 and a bias circuit 6. The output of a photodetector 1 is inputted to the inverted terminal 12 of the comparator 10, and a reference voltage 17 is inputted to a noninverted terminal 11. The pulse width of the synchronizing signal 19 can be made constant by inputting the output of the photodetector 1 to the strobing terminal 13 through the pulse width control circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device used in an image forming apparatus such as a copying machine, a facsimile, and a laser beam printer for forming an image by an electrophotographic method.

[0002]

2. Description of the Related Art In recent years, a light beam scanning device using a semiconductor laser as a light source has been widely used in the field of electrophotography.

A schematic structure of a conventional light beam scanning device will be described below with reference to the drawings. FIG. 4 shows a conventional light beam scanning device. In the figure, 21
Is a semiconductor laser, and the light beam emitted from the semiconductor laser is a first imaging optical system 22 composed of a double-sided aspherical single lens.
The beam is shaped by the aperture 23 having a slit, and then reaches the rotary polygon mirror 24. The rotary polygon mirror 24 is made of a thin plate-shaped regular hexahedron, and its outer peripheral surface is a mirror surface, and is configured to reflect an incident light beam. The reflected light beam is scanned from left to right by the rotation of the rotary polygon mirror 24, passes through the second imaging optical system 25 composed of a long lens, and forms an image on the scanned object 26. Is configured to.

Next, 28 is an imaging lens provided in the optical path of the light beam reflected from the rotary polygon mirror 24, which is provided near the scanning start position of the reflected light beam and has an aperture having a slit. The light beam shaped via 29 enters the photodetector 1.

The operation of the light beam scanning device constructed as described above will be described below.

The light beam emitted from the semiconductor laser 21 reaches the rotary polygon mirror 24 via the first imaging optical system 22 and the aperture 23, and the rotation of the rotary polygon mirror 24 makes the light beam scanable. There is. A part of the scanning beam is incident on the photodetector 1 via the imaging lens 28 and the aperture 29, and the remaining scanning beam is rotated via the second imaging optical system 25 for each scanning 26. Image on top.

Here, the scanned object 26 must be rotated in conjunction with the rotation of the rotary polygon mirror 24.
Each time the scanning beam is scanned by one, the rotary polygon mirror 24 and the scan target 2 are arranged so that the scan target 26 rotates by one scan.
6 is synchronized.

The method is, for example, to generate a photodetection signal 31 each time a part of the scanning beam is incident on the photodetector 1.
By passing through a voltage comparison type comparator (not shown), it is intended to obtain a pulse-shaped synchronizing signal having a waveform shaped.

Further, the photodetector 1 outputs a photodetection signal 31.
When the position where the rotary polygon mirror 24 is rotated by the angle θ and the print start position are made to coincide with each other after the occurrence of, the reference clock of the image forming apparatus is generated, and the video signal is generated after the angle θ. Since the synchronization signal described above can be used as the video clock signal after delaying the synchronization signal for a specific time, the circuit configuration of the image forming apparatus can be simplified.

[0010]

However, in the above-mentioned conventional configuration, in order to use the synchronizing signal generated from the light detection signal 31 as the video clock signal, the pulse width of the synchronizing signal is always kept constant. It is necessary to obtain a stable video clock signal, and for that reason, it is essential to always keep the pulse width of the light detection signal 31 constant.

However, in the conventional configuration, the light detection signal 31
The slit provided in the aperture 29 was used as a configuration for keeping the pulse width of the slit constant. However, burrs are generated at the ends of the slit, although there is a difference in size, and this slit width must be kept strictly constant. Therefore, keeping the pulse width constant has a manufacturing limit.

The pulse width of the photodetection signal 31 varies depending on the relative mounting positions of the imaging lens 28, the aperture 29 and the photodetector 1, and the beam diameter near the photodetector 1 is about 20 × 40 μm. Since it is narrowed down to, the pulse width varies depending on the position change of the light beam due to the mirror tilt of the rotary polygon mirror 24, and the pulse width of each reflecting surface of the rotary polygon mirror also due to the adhesion of foreign matter such as dust. There is a possibility that it may fluctuate, and there was a limit to making the pulse width constant due to machine precision.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a light beam scanning device capable of obtaining a stable synchronizing signal having a desired pulse width.

[0014]

In order to achieve the above object, the light beam scanning device of the present invention generates a synchronizing signal for obtaining rotational synchronization between a rotating body and a scanned body based on an output signal of a light detecting means. The synchronizing signal generating means comprises a comparing means for comparing the output signal of the light detecting means with a reference signal, and a pulse width control circuit consisting of a time constant circuit and a bias circuit, and the comparing means generates an input signal and a strobe. By providing a strobe terminal whose output is controlled by comparison with the level, and by inputting a part of the output signal of the photodetection means to the strobe terminal via the pulse width control means, It is arranged to obtain the synchronization signal independent of the output signal.

[0015]

By using the time constant circuit, the light beam scanning device of the present invention can make the pulse width of the synchronizing signal constant regardless of the fluctuation of the pulse width of the light detection signal.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a synchronizing signal generating circuit of a light beam scanning device of the present invention, and FIG. 2 is a diagram showing an output waveform in each circuit. The horizontal axis of FIG. 2 indicates the passage of time, and the vertical axis indicates the voltage. It should be noted that in FIG. 1, the process until the photodetector 1 generates the photodetection signal 31 is the same as that in FIG.

In FIG. 1, reference numeral 1 is a photodetector, in which a light receiving element 2 is provided. This light receiving element 2
Receives the light of the semiconductor laser, photoelectrically converts the light into a pulsed light detection signal 3 as shown in FIG.
1 is generated. The light detection signal 31 is amplified by the amplifier 3 and becomes an amplified signal 16 as shown in FIG.

The amplified signal 16 is then input to the inverting terminal 12 of the comparator 10, while the reference voltage 17 set by the resistors 14 and 15 is input to the non-inverting terminal 11 of the comparator 10. The voltage comparison type comparator 10 operates at a high speed because it follows a light beam scanning device that requires high-speed processing. When the amplified signal 16 is a reference voltage 17 or higher, LOW is output, and the amplified signal is output. When 16 is less than the reference voltage 17, HIGH is output, and an output waveform as shown in FIG. 2C is obtained.

Next, the amplified signal 16 is input not only to the inverting terminal 12 of the comparator 10 but also to the pulse width control circuit 4 at the same time. The pulse width control circuit 4 comprises a time constant circuit 5 and a bias circuit 6 and is connected to a strobe terminal 13. The time constant circuit 5 is a capacitor 7
And the resistor 8 and the bias circuit 6 is constituted by the resistor 9.

Amplified signal 1 input to the pulse width control circuit 4
6 is differentiated by the time constant circuit 5, and the differentiated signal becomes a waveform that rises steeply and attenuates based on a constant time constant determined by the capacitor 7 and the resistor 8, as shown in FIG. . This differential signal is input to the strobe terminal 13 of the comparator 10 as the pulse width control signal 18 via the bias circuit 6. This bias circuit 6
Is for adjusting the pulse width of the output signal of the comparator 10 by matching the pulse width control signal 18 with the strobe level.

Here, while the pulse width control signal 18 input to the strobe terminal 13 is at a voltage equal to or higher than the strobe level, the output signal of the comparator 10 operates and the synchronizing signal as shown in FIG. 19 is output, and conversely, while the pulse width control signal 18 is below the strobe level,
The output signal 19 of the comparator 10 stops.

Then, the time when the pulse width control signal 18 as shown in FIG. 2 (d) becomes larger than the strobe level, that is, the comparator 10 as shown in FIG. 2 (e).
Of the time constant circuit 5 and the reference voltage 17 such that the output signal 19 of FIG. 2 becomes shorter than the pulse width generated by the comparison between the amplified signal 16 and the reference voltage 17 as shown in FIG. When the pulse width control signal 18 is properly determined, the pulse width of the synchronization signal 19 is determined by the pulse width control signal 18 that attenuates based on a constant time constant.

At the strobe terminal 13 provided in the comparator 10, the output signal of the comparator 10 operates when a voltage higher than the strobe level is applied, and when the voltage lower than the strobe level is applied. Has a function of stopping the output signal of the comparator 10, and the operating speed of the input of the strobe terminal 13 can follow the processing speed of the light beam scanning device, but the high speed operation of the comparator 10 It has the characteristic of being slower than the speed.

Conventionally, a voltage higher than the strobe level is always applied to the strobe terminal 13 of this type, and the comparator 10
When the output of the semiconductor laser drops, a voltage lower than the strobe level is applied to stop the output signal of the comparator 10. In this embodiment, the reliability of the semiconductor laser is improved and it is no longer necessary to use the strobe terminal 13 in the conventional role. Therefore, the strobe terminal 13 is used to obtain a synchronization signal having a stable pulse width.

As is clear from the above description, the pulse width of the sync signal 19 becomes constant regardless of the fluctuation of the pulse width of the photodetection signal 31, a stable sync signal can be obtained, and the time constant circuit 5 has the same structure. By properly setting the time constant, a synchronization signal having a desired pulse width can be obtained.

Although the differential signal from the time constant circuit 5 is input to the strobe terminal 13 in this embodiment, the differential signal from the time constant circuit 5 is directly input to the inverting terminal of the voltage comparison type comparator. Let's compare it with the case.

FIG. 5 is a block diagram of a comparator having a hysteresis characteristic in a comparative example of one embodiment of the present invention.
In FIG. 5, the photodetection signal 31 from the photodetector is differentiated through a time constant circuit composed of the capacitor 7 and the resistor 8, and the differentiated signal is inverted by the inverting terminal 1 of the voltage comparison type comparator 10.
Enter 2.

Further, the reference voltage 17 is input to the non-inverting terminal 11 of the comparator 10, and although not shown in FIG. 5, a voltage above the strobe level is always applied to the strobe terminal so that the output signal of the comparator 10 is Always working.

The comparator 10 outputs LOW when the voltage of the differential signal is equal to or higher than the reference voltage 17, and outputs HIGH when the voltage of the differential signal is less than the reference voltage 17. However, in the output waveform of the comparator 10, chattering (a phenomenon in which the output fluctuates) as shown in the upper diagram of FIG. 6 occurs, and immediately after outputting one pulse corresponding to one differential signal, the pulse width is very short. It was found that it cannot be used as a synchronization signal because it outputs multiple pulses.

As shown in FIG. 6, as a cause of chattering, a small ripple is observed in the gently attenuated waveform portion of the waveform of the differential signal input to the inverting terminal 12 of the comparator 10, but this waveform operates. High speed comparator 1
When 0 is used and compared with the reference voltage 17, a small ripple of the differential signal is picked up and chattering occurs in the synchronization signal as shown in the figure.

Therefore, chattering can be prevented by inserting a low-resistance resistor 32 as shown in FIG. 5 and providing positive feedback from the output to give a hysteresis characteristic. However, by providing the hysteresis characteristic, once the output of the comparator 10 becomes LOW,
If the input voltage does not become sufficiently lower than the threshold voltage (threshold value) of the comparator 10, the output of the comparator 10 becomes HIG.
Not H. Therefore, the response time of the comparator 10 is remarkably slow, and the circuit shown in FIG. 5 is not practical.

In this embodiment, the differential signal from the time constant circuit 5 is input to the strobe terminal 13 through the bias circuit 6, but as described above, the operating speed of the input to the strobe terminal 13 is the processing speed of the light beam scanning device. Although it can follow, it is slower than the high-speed operation speed of the comparator 10, so the output signal of the comparator 10 is stopped without picking up a small ripple of the differential signal, and a stable synchronization signal with a pulse width is obtained. be able to.

When the pulse width of the synchronizing signal 19 is controlled by utilizing the time constant circuit as in this embodiment, the time constant circuit is vulnerable to temperature changes. Therefore, the temperature dependence of the time constant circuit in this embodiment will be described below. A brief description of the measures against

The pulse width of the synchronizing signal 19 is generally ± 7.
Accuracy of about% is required. FIG. 3 is an actual measurement value of the temperature dependence of the pulse width of the synchronizing signal 19 in the circuit of FIG. 1, in which the horizontal axis represents the ambient temperature change and the vertical axis represents the amount of change in the pulse width of the synchronizing signal 19.

In FIG. 3, (a) uses a ceramic capacitor having a capacitance tolerance of ± 20% as the capacitor 7, and (a) uses a ceramic capacitor having a capacitance tolerance of ± 10% as the capacitor 7. In this case, (c) shows the temperature dependence of the pulse width of the synchronizing signal 19 when a film capacitor having a capacitance tolerance of ± 5% is used as the capacitor 7.

When the ambient temperature changes from -20 ° C to + 60 ° C, (a) is ± 10 with respect to room temperature (20 ° C).
%, (A) is ± 5%, and (c) is about ± 2.5%. Therefore, in the circuit of FIG. 1, by using a film capacitor having a capacitance tolerance of ± 5% or a ceramic capacitor having a capacitance tolerance of ± 10% as the capacitor 7, it is possible to control the pulse width of the synchronization signal 19 with high precision. Is possible.

[0037]

As described above, according to the present invention, a synchronizing signal having a stable pulse width can be obtained regardless of fluctuations in the pulse width of the photodetection signal generated by the photodetector, and the time constant of the time constant circuit can be obtained. Since it is possible to obtain a synchronization signal with a desired pulse width by appropriately setting,
A highly accurate light beam scanning device can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of a synchronization signal generation circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing an output waveform in each circuit according to an embodiment of the present invention.

FIG. 3 is a diagram showing the ambient temperature dependence of the pulse width of the synchronization signal in the embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional light beam scanning device.

FIG. 5 is a block diagram of a comparator having a hysteresis characteristic in a comparative example of one embodiment of the present invention.

FIG. 6 is a diagram showing a waveform of a synchronization signal obtained by the circuit of FIG.

[Explanation of symbols]

 1 Photodetector 2 Light receiving element 3 Amplifier 4 Pulse width control circuit 5 Time constant circuit 6 Bias circuit 7 Capacitors 8, 9, 14, 15 Resistor 10 Comparator 11 Non-inverting terminal 12 Inversion terminal 13 Strobe terminal 17 Reference voltage 18 Pulse Width control signal 19 Synchronization signal 31 Optical detection signal

Claims (1)

[Claims] 1. A light beam generating means for generating a light beam, and a scanning line is formed by reflecting a light beam emitted from the light beam generating means on a mirror surface provided on a peripheral surface of a rotating body. A light beam scanning means; a light detecting means provided in the optical path of the light beam scanned by the light beam scanning means; and a light beam rotatably provided by the light beam scanning means for forming an image forming optical beam. A scanning object imaged via a system, and a synchronization signal generating means for generating a synchronization signal for obtaining rotational synchronization of the scanning object from the output signal of the light detecting means, The synchronizing signal generating means is composed of a comparing means for comparing the output signal of the light detecting means and a reference signal, and a pulse width control circuit consisting of a time constant circuit and a bias circuit, and the comparing means is an input signal. By having a strobe terminal whose output is controlled by comparison with a strobe level, and by inputting a part of the output signal of the photodetection means to the strobe terminal via the pulse width control means,
A light beam scanning device, wherein the synchronizing signal is obtained which is not influenced by an output signal of the light detecting means.