JPH0434503Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention is based on the beam scanning position of a laser optical system that deflects and scans a laser beam emitted from a laser light source such as a semiconductor laser using a rotating reflector (polygon mirror). Regarding a detection device.

(Prior art and its problems) When the laser beam emitted from the laser light source is deflected by a polygon mirror to scan the rotating drum in the main scanning direction (the direction of the drum's rotation axis), the writing timing of the rotating drum is controlled. Therefore, it is necessary to accurately detect the point in time when the laser beam passes through a predetermined scanning position.

Conventionally, as a device for detecting this scanning position,
There is one constructed as shown in Figure 5. That is, the photodiode 10 is installed directly at a predetermined scanning position on the scanning path of the laser beam, or is installed on the optical path of the laser beam that is deflected through a reflecting mirror installed at the position, and the photodiode 10 is The output V1 obtained when the laser beam scans the diode 10 is compared with the set voltage V2 by the comparator 20, and the reference position of the laser beam is determined based on the output change of the comparator 20 that occurs when V2<V1. It is configured to detect passage.

However, with the configuration as described above, when the amount of light of the laser beam emitted from the laser light source changes, the time T at which the output of the comparator 20 changes changes to T1, as shown in Figure 6. Therefore, there is a problem in that the detection reference position shifts before and after the beam light amount changes.

(Purpose of the invention) In view of the above-mentioned circumstances, an object of the present invention is to provide a laser beam scanning position detection device that can avoid changes in the detection reference position due to changes in the amount of beam light.

(Structure of the invention) Therefore, the laser beam scanning position detection device according to the invention uses a delay circuit to detect the output of the photo sensor installed at a predetermined scanning position on the laser beam scanning path or a position corresponding to the scanning position. At the same time, the output of the delay circuit and the output of the photo sensor are compared by a comparator, and the beam scanning position is detected based on the comparison result of the comparator.

(Embodiment of the invention) The first illustrated scanning position detection device has a photodiode 10 installed at a predetermined position on the scanning path of a laser beam, a power supply 11, and a resistor R connected in series. The photo sensor 1 is configured to output a voltage V1 to a pair of output lines 12 and 13, respectively, when the laser beam scans the photo sensor 1.

One output line 12 is connected to a buffer 14 and a resistor R1.
The output side is connected to the non-inverting side input terminal of the comparator 20 which is pulled up via the input terminal, and the output terminal of the comparator 20 and this non-inverting side input terminal are connected via a feedback resistor R2. . That is, a predetermined voltage level is always input to the non-inverting input terminal of the comparator 20 from the output terminal, and when the laser beam scans the photodiode 10, the output V1 from the photo sensor 1 also remains unchanged. It is configured to be input.

Further, the other output line 13 is connected to the analog delay circuit 1
5, and the output line 16 of the analog delay circuit 15 is connected to the inverting input terminal of the comparator 20 via an amplifier 17 with adjustable gain as a level adjustment circuit. That is, only when the laser beam scans the photodiode 10, the output V1 from the photo sensor 1 reaches the analog delay circuit 1.
5, the voltage level that dropped when passing through the analog delay circuit 15 is returned to the same level as the output level from the buffer 14 by the amplifier 17 with the adjusted gain, and then the comparator 20 It is configured to be input to the inverting side input terminal of.

In this configuration, the comparator 2 is connected before and after the laser beam scans the photodiode 10.
The input waveform W1 of the non-inverting side input terminal and the input waveform W2 of the inverting side input terminal of 0 are as shown in FIG. 2, respectively. That is, when the laser beam is not scanning over the photodiode 10, the comparator 20
A predetermined level of input is applied only to the non-inverting input terminal of the photodiode 10, but when the laser beam scans the photodiode 10, a waveform W1 is first generated at the non-inverting input terminal, and then a waveform W1 is generated at the inverting input terminal.
2 occurs, and an output fall T from the comparator 20 occurs at the intersection of both input waveforms W1 and W2. This output fall T corresponds to the laser beam passing through the predetermined scanning position described above.

In the detection position configured in this way, for example, the third
As shown in FIG. Even if the amount of incident light changes, the intersection position of both waveforms will not change at all as shown in FIG. Therefore, even if the amount of laser beam scanning the photodiode 10 changes, both waveforms W1 and W
There is no influence on the position T where 2 intersects and the output of the comparator 20 falls, and beam scanning position detection is always performed at a constant reference position.

In the above embodiment, if the resistance value of the resistor R of the photo sensor 1 is increased, the amplifier 17 can be used as a simple buffer, and the buffer 14 can be used as an amplifier with adjustable gain (in this case, amplification means attenuation).
It is also possible to configure it as

(Effect of the invention) According to the laser beam scanning position detection device according to the invention, two input waveforms are formed with a predetermined timing shift from the output of one photo sensor and compared by a comparator, and the two input waveforms intersect. Since the beam scanning position is configured to be detected based on changes in the output of the comparator that occur during the process, it is possible to avoid changes in the detection position due to changes in the beam light intensity, and the beam scanning position can always be detected at a constant position. It has become possible to do so.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the laser beam scanning position detection device according to the present invention, and FIG. 2 is a correspondence diagram of the comparator input waveform and output change in the first illustrated embodiment.
3 and 4 are explanatory diagrams showing the logical correspondence between the input waveform and output change of the comparator, FIG. 5 is a circuit diagram showing a conventional device, and FIG. 6 is a comparator input in the embodiment shown in FIG. FIG. 3 is a correspondence diagram between waveforms and output changes. 1... Photo sensor, 10... Photo diode, 12, 13... Division output line, 15... Delay circuit, 16... Delay circuit output line, 20... Comparator,
T...Comparator output change position.

Claims (1)

[Claims for Utility Model Registration] (1) Delaying the output of a photo sensor installed at a predetermined scanning position on the scanning path of a laser beam or a position corresponding thereto using a delay circuit;
A laser beam scanning position detection device, characterized in that the output of the delay circuit and the output of the photo sensor are compared by a comparator, and the beam scanning position is detected based on the comparison result of the comparator. (2) The laser beam scanning position detection device according to claim (1), further comprising a level adjustment circuit that equalizes the output level of the output of the delay circuit and the output of the photo sensor.