JPH02266964A - Laser-beam output control circuit - Google Patents

Abstract

PURPOSE:To prevent the performance degradation of an apparatus by holding the output signal of an analog-digital converter through a holding circuit by the output signal of a position transducer and by controlling a constant current source so that the output signal of said holding circuit is equal to the reference signal from a reference signal apparatus. CONSTITUTION:A laser-beam emitting means 11 is supplied with current by a constant current source 16 and the emission output of said laser-beam emitting means 11 is detected by an output detector 17. Also, a laser beam from the laser-beam emitting means 11 is detected at a specified position by a position transducer 15 and a reference signal apparatus 18 generates a reference signal forming a reference. Further, an automatic output stabilizing circuit 19 converts the output signal of said output detector 17 into a digital value by an analog/ digital converter 21, holds the output signal of said analog/digital converter 21 through a holding circuit 22 by the output signal of said position transducer 17, and controls the constant current source 16 so that the output signal of said holding circuit 22 is equal to the reference signal from the reference signal apparatus 18.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser light output control circuit for controlling the light emission output of a laser light emitting means in a laser light scanning device.

[Conventional technology]

2. Description of the Related Art Generally, in an image forming apparatus such as a laser beam scanning printer having a laser beam scanning device, a latent image is formed by irradiating a photoreceptor with a laser beam using the laser beam scanning device. The laser beam scanning device forms a latent image on the photoreceptor by scanning the laser beam from the laser beam emitting means with the scanning means and turning the laser beam on and off using information using the modulation means. The light emitting output of the light emitting means is controlled to be constant by a laser light output control circuit.

In an image forming apparatus such as a laser beam scanning printer, as shown in FIG. 5, the period during which the photoreceptor is irradiated with laser light includes a period during which the laser light is turned on and off to form an arbitrary latent image on the photoreceptor. During this period (3), the light emission output of the laser light emitting means cannot be controlled. Therefore, it is necessary to control the light emission output of the laser light emitting means during periods other than period (2), and the result of controlling the light emission output of the laser light emitting means must not be changed during period (2). Conventionally, in a laser beam output control circuit, after the period (■) ends, the laser beam from the laser beam emitting means is turned on and the amount of light is detected by an output detector, and the output signal of the output detector is detected from the turning on of the laser beam. After the period until stabilization has elapsed, the light emission output of the laser beam emitting means is controlled to be constant based on the output signal of the output detector in period (3).

The current of the laser light emitting means is maintained so as not to change during the period (3) from the end of the light emission output control of the laser light emitting means to the start of the next light emission output control of the laser light emitting means. Such a laser light output control circuit is known from, for example, Japanese Unexamined Patent Publication No. 134668/1983.

In addition, as shown in FIG. 6, another laser light output control circuit is such that the laser light from the laser light emitting means is kept on during the period (2) when no latent image is formed on the photoreceptor, and the laser light emitting means is turned on during this period. JP-A-58-21 discloses a device that controls the light emission output and maintains the IT flow of the laser beam emitting means so as not to change during a long period (■) including the period (■) of forming a latent image on the photoreceptor.
This is known from Publication No. 2256 and the like.

[1M to be solved by the invention] In the above laser light output control circuit, in the former case, the period ■,
There is a drawback that careful design is required for the settings of (2), the stability of period (2), temperature, changes over time, etc. In addition, in the latter case, the period of
Setting (2) becomes unnecessary, but since the period (2) is long, a digital holding circuit is required to hold the current of the laser beam emitting means, which becomes expensive, and there is no difference between the start and end of latent image formation. There is a drawback that fluctuations occur in the light emission output of the laser light emitting means, resulting in deterioration of performance.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a laser light output control circuit that does not cause performance deterioration, is simple in design, and is inexpensive.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a laser beam scanning device having a laser beam emitting means for generating a laser beam and a scanning means for scanning the laser beam from the laser beam emitting means. a constant current source that supplies a current; an output detector that detects the light emission output of the laser light emitting means; a position detector that detects the laser light from the laser light emitting means at a predetermined position; and a reference that serves as a reference. The automatic output includes a reference signal device that generates a signal, and an automatic output stabilization circuit that controls the constant current source so that the output signal of the output detector and the reference signal from the reference signal device are equal. The stabilizing circuit includes an analog/digital converter that converts the output signal of the output detector into a digital value, and a holding circuit that holds the output signal of the analog/digital converter based on the output signal of the position detector. The constant current source is controlled so that the output signal of the holding circuit and the reference signal from the reference signal device are equal.

[For production]

A current is supplied to the laser light emitting means by a constant current source, and the light emission output of the laser light emitting means is detected by an output detector. Further, the laser beam from the laser beam emitting means is detected by a position detector at a predetermined position, and the reference signal device generates a reference signal that serves as a reference.

The automatic output stabilization circuit converts the output signal of the output detector into a digital value using an analog/digital converter, and holds the output signal of the analog/digital converter in a holding circuit using the output signal of the position detector. The constant current source is controlled so that the output signal from the reference signal generator becomes equal to the reference signal from the reference signal generator.

〔Example〕

FIG. 2 shows a laser beam scanning device in an example of a laser beam scanning printer to which the present invention is applied.

The laser light emitted from the laser light emitting means 11 is scanned by the scanning means 12 made of a polygon mirror and irradiated onto the photoreceptor 14 via the fθ lens 13, and the laser light from the laser light emitting means 11 is modulated (not shown). The zero position detector 15 is modulated by information to form a latent image on the photoreceptor 14, and is installed at a predetermined position that does not block the laser beam irradiated onto the photoreceptor 14.
Detects the laser beam that enters the laser beam through the fO lens 13. For example, a semiconductor laser is used as the laser light emitting means 11, and a current is supplied from a constant current source 16. The output detector 17 detects how the laser beam emitting means 11 emits light, and the reference signal device 18 generates a reference signal that serves as a reference. An automatic output stabilization (APC) circuit 19 outputs the output signal of the output detector 17 and the reference signal from the reference signal device 18 during a predetermined period during which a latent image is not formed on the photoreceptor 14 based on the output signal of the position detector 15. The current of the constant current source 16 is controlled so that the values are equal to each other, and the current of the constant current source 16 is maintained except for the above-mentioned predetermined period.

FIG. 1 specifically shows the configuration of the APC circuit 19, and FIG. 3 is its timing chart.

The signal from the position detector 15 is delayed by a time delay circuit 20 as shown in FIG. The output signal of 17 is converted into a digital value by an analog/digital (A/D) converter 21. The data holding circuit 22 is connected to the A/D converter 2 when the position detector 15 detects the laser beam based on the signal from the position detector 15.
Capture and hold the output signal of 1. Since this data holding circuit 22 holds digital values, it can be constructed of, for example, a standard TTL 74LS373. The output data of the data holding circuit 22 is transferred to the reference signal generator 18 by the comparator 23.
compared to a reference signal from Like the data holding circuit 22, this comparator 23 can also be constructed of standard TTL. The comparator 23 controls the counter circuit 24 according to the comparison result,
When the output data of the data holding circuit 22 is smaller than the reference signal from the reference signal generator 18, a count up command is issued to the counter circuit 24 to increase the current of the constant current source 16. This count-up command causes the re-counter circuit 2 to
4 counts up the clock, and the count value of the counter circuit 24 is converted into an analog quantity by the digital/analog converter 25 and applied to the constant current source 16 as a control signal. Therefore, when the count value of the counter circuit 24 increases, the current of the constant current source 16 increases. The laser light emitting means 11 has a constant current! The amount of light emitted increases in proportion to the current supplied from 16.

Furthermore, when the output data of the data holding circuit 22 is larger than the reference signal from the reference signal device 18, the comparator 23 issues a countdown command to the counter circuit 24 to decrease the current of the constant current source 16. The counter circuit 24 counts down the clock according to this countdown command,
The current of the constant current source 16 decreases, and the light emission power of the laser beam emitting means 11 decreases. Comparator 23 is data holding circuit 22
When the error data is equal to the reference signal from the reference signal device 18, a count stop signal is given to the counter circuit 24 to maintain the current state, and thereby the light emission output of the laser beam emitting means 11 maintains the current state.

As shown in FIG. 3, the data input to the comparator 23 from the data holding circuit 22 is determined by the signal from the position detector 15, so the settling time until the comparator 23 outputs the comparison result is determined by the time delay circuit. The counter circuit 24 is operable when the output signal of the time delay circuit 20 is input, and becomes inoperable when the output signal of the time delay circuit 20 is not input, and the counter circuit 24 is not operable and does not calculate the count value. Hold. Therefore, in reality, the laser light emitting means 1
The APC period ■ which controls the light emission output of the output detector 17.1 is almost instantaneous. The settling time of the A/D converter 21 is (laser light detection period of the position detector 15 - Td).

These times are generally several tens of microseconds to several hundred microseconds, which is sufficient for ordinary TTL and A/D converters.

The reference signal device 18 is composed of dip switches 26 to 31 and pull-up resistors 32 to 37, as shown in FIG. Can be set. When it is desired to adjust the light emitting output of the laser light emitting means 11 due to variations in the photoreceptor 14, etc., the reference signal is varied using the dip switches 26 to 31.
What is necessary is to adjust the light emission output of 1.

The counter circuit 24 receives an overflow (carry) signal,
Underflow (borrow) signals are output when the light emission output of the laser light emitting means 11 exceeds the adjustment range of the APC circuit 19, making it possible to detect an abnormality in the circuit.

The counter circuit 24 is reset to 0 by an external reset signal, whereby the current of the laser beam emitting means 11 becomes the initial value (minimum value) and the light emission output of the laser beam emitting means 11 becomes the initial value. Therefore, for example, the soft start necessary for the laser beam emitting means 11 when the power is turned on can be made possible by resetting the counter circuit 24 when the power is turned on, and also, in the event of an abnormality, the counter circuit 24 can be reset to start the laser beam emitting means 11. damage can be minimized.

The count stop signal from the comparator 23 is output when the APC circuit 19 is in a stable (locked) state, but this count stop signal is output as a lock signal to the outside through the gate circuit 39, and when the lock mask signal is turned on. Sometimes the count stop signal is blocked by the gate circuit 39.

By outputting a lock signal to the outside when the APC circuit 19 is in a stable state, it becomes possible to detect the startup timing of the entire system, and by making this lock signal maskable, there is no possibility of irregularities in the startup timing of the entire system. It becomes possible to prevent necessary detection from being performed.

The above-described laser light output control circuit includes a reference signal device 18, a time delay circuit 20. Data holding circuit 22. Since the comparator 23 and the counter circuit 24 can all be constructed of inexpensive standard TTL, one circuit can be made inexpensive, and performance does not deteriorate due to temperature or aging. Further, since it is possible to easily form a gate array into an ASIC, it is possible to create a circuit with a lower layer, smaller size, and lower cost. Furthermore, constant current source 16. Output detector 17. Recently, the analog ICs of the A/D converter 21 and the digital/analog converter 25 can be made into ASICs, so all the circuits can be housed on one chip, improving reliability and reducing the number of layers. Cost reduction can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, in a laser beam scanning device having a laser beam emitting means for generating a laser beam and a scanning means for scanning the laser beam from the second laser beam emitting means, the laser beam emitting means is a constant current source that supplies current;
an output detector that detects the light emission output of the laser light emitting means, a position detector that detects the laser light from the laser light emitting means at a predetermined position, and a reference signal device that generates a reference signal as a reference; an automatic output stabilizing circuit that controls the constant current source so that the output signal of the output detector and the reference signal from the reference signal device are equal, and the automatic output stabilizing circuit controls the output of the output detector. It includes an A/D converter that converts a signal into a digital value, and a holding circuit that holds the output signal of the A/D converter according to the output signal of the position detector, and the output signal of the holding circuit and the reference. Since the constant current source is controlled so that the reference signal from the signal device is equal to the reference signal, the design is simple and inexpensive.

No performance deterioration occurs.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a schematic diagram showing a laser beam scanning device in an example of a laser beam scanning printer to which the present invention is applied, FIG. 3 is a timing chart of the above embodiment, and FIG. 4 is a reference signal device of the above embodiment. The circuit diagrams, FIGS. 5 and 6, are timing charts of each conventional laser light output control circuit. 1. Laser light emitting means, 15. Position detector,
16... Constant current source, 17... Output detector, 18...
・Reference signal device, 19... Automatic output stabilization circuit, 21...
- A/D converter, 22... data holding circuit.

Claims (1)

[Claims] A laser beam scanning device comprising a laser beam emitting means for generating a laser beam and a scanning means for scanning the laser beam from the laser beam emitting means, a constant current source supplying a current to the laser beam emitting means; an output detector that detects the light emission output of the laser light emitting means, a position detector that detects the laser light from the laser light emitting means at a predetermined position, a reference signal device that generates a reference signal as a reference; an automatic output stabilizing circuit that controls the constant current source so that the output signal of the output detector and the reference signal from the reference signal device are equal, and the automatic output stabilizing circuit controls the output signal of the output detector and the reference signal from the reference signal device. an analog/digital converter that converts the output signal into a digital value, and a holding circuit that holds the output signal of the analog/digital converter according to the output signal of the position detector, and the output signal of the holding circuit and the reference signal. A laser light output control circuit characterized in that the constant current source is controlled so that the constant current source is equal to a reference signal from a laser light source.