JPH0313586B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light amount control device that controls the driving current of a light emitting element, particularly a semiconductor laser, by detecting the optical output of the semiconductor laser.

For example, when a semiconductor laser is used as a light emitting element, the optical output of the semiconductor laser is extremely unstable with respect to temperature, and it is necessary to use some means to stabilize the optical output in an environment where the ambient temperature changes. Conventionally, many circuits have been proposed for stabilizing the optical output of semiconductor lasers used as light sources in optical communication devices and the like. In this type of circuit, since the semiconductor laser is driven by an input signal whose carrier wave is modulated by a digital information signal, it has been effective to provide negative feedback of the average value or maximum value of the optical output. However, in laser beam printers where the semiconductor laser is directly driven by an information signal, average value feedback is not possible because it does not include a carrier wave.
The maximum value feedback type requires a light output detection element with a fast response speed, which is not economical.

In other words, in an analog type light amount control device that detects the light amount of the beam and feeds back the detection output, if the response of the feedback system element that controls the light amount is slow, an overshoot of the beam light amount may occur, causing damage to the semiconductor laser element, etc. There was a risk that this would occur. Moreover, in order to speed up the response of the feedback system element and prevent overshoot of the beam light quantity, expensive elements must be used, which is not economical.

There is also a light intensity control device that temporarily samples and holds a value based on the detected beam intensity and controls the beam intensity based on this sample-held value. The problem has been that the semiconductor laser device is deteriorated because it emits more light than necessary.

Furthermore, since the circuit that samples and holds the light intensity is formed using a capacitor etc., even during actual recording operation, the sample and hold value gradually changes due to the discharge of the capacitor, etc., and the light intensity of the beam during recording also changes accordingly. There was an inconvenience caused by the change.

The present invention has been made in view of the above points, and provides a light amount control device that can extend the life of a semiconductor laser element without using expensive elements, and maintain a stable amount of light even while recording each successive page. It is to provide.

That is, the present invention has a semiconductor laser generating means 1 that emits a laser beam modulated by a recording signal, and after the recording operation for one page is completed by the laser beam, and before the recording operation for the next page is started. A light amount control device that adjusts the amount of emitted light of the laser beam during the inter-page period, the laser beam being generated from the semiconductor laser generating means and not modulated by the recording signal during the inter-page period. Detection means 1 for detecting the amount of emitted light
2, a reference signal generating means 13 for generating a reference signal of a constant level for stabilizing the amount of light, a comparing means 14 for comparing the detection output from the detecting means and the reference signal of the constant level, and oscillation of a constant frequency. Oscillation means 15 for outputting a signal
and inputting an oscillation signal from the oscillation means to the counting means 16 according to the comparison result by the first comparison means; and inputting a predetermined signal derived within the inter-page period in order to start the counting operation by the counting means. input means T1 for converting the counted value by the counting means into an analog quantity; D/A converting means 17 for converting the counted value by the counting means into an analog quantity; and applying a current to the semiconductor laser generating means based on the analog signal output from the D/A converting means. and applying means 18 for applying the oscillation signal, and when the detection output from the detection means has not reached the certain level, the counting means starts counting operation based on the input of the predetermined signal, and the oscillation signal In addition to sequentially counting the
The applying means applies a current corresponding to the count value obtained by the counting to the generating means of the semiconductor laser, and when the detection output from the detecting means reaches the certain level, the counting means stops the counting operation. The present invention provides a light amount control device characterized in that the count value at that time is held.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment in which the light amount control device according to the present invention is applied to a beam recording device, in which the laser beam L generated by the semiconductor laser generator 1 is
is collimated by a collimator lens 2 and is incident on a rotating polygon mirror 3 that rotates at a constant speed in the direction of arrow F.

The laser beam deflected by the rotating polygon mirror 3 constituting the deflector is imaged by the imaging lens 4 onto the photosensitive drum 5 constituting the electrostatic recording device, and this imaging spot is formed by the rotation of the rotary polygon mirror 3. It moves in the direction of arrow P in accordance with .

Therefore, while rotating the rotating polygon mirror 3 at high speed,
If the photosensitive drum 5 is rotated in a constant direction at a constant speed, the entire area of the photosensitive drum 5 can be scanned with a laser beam.

Reference numeral 6 indicates a beam detector provided outside the information recording area of the photosensitive drum 5, which detects the arrival of the laser beam to the beam detector 6, forms a synchronization signal, and processes this synchronization signal for information processing. The signal is applied to the circuit 7, and a recording signal is applied to the semiconductor laser generator 1 at a timing controlled by the synchronization signal.

Therefore, a laser beam modulated by a recording signal is emitted from the laser generator 1, but such control is widely known in, for example, Japanese Patent Laid-Open No. 51-89346, so it will not be described here. Detailed explanation will be omitted.

The laser beam modulated by the recording signal is irradiated onto the photosensitive drum 5 in this way, but since the photosensitive drum 5 has been uniformly charged in advance by a charger (not shown), the irradiation with the laser beam An electrostatic latent image is formed according to the irradiation, this electrostatic latent image is visualized by a developing device (not shown), this developed image is transferred to paper etc. by a transfer device (not shown), and the transferred paper is By fixing the image using a fixing device (not shown), it is possible to obtain recording paper on which an image corresponding to the recording signal is recorded.

As mentioned above, the semiconductor laser generator 1 emits the laser beam (front beam) L toward the front and at the same time emits the back beam BB toward the rear.
The BB receives light from the photodetector circuit 11, forms a detection signal according to the beam intensity, and sends this detection signal to the control circuit 1.
2 to control the beam emission intensity of the semiconductor laser generator 1.

FIG. 2 shows the control circuit 12 and the information processing circuit 7.
13 is a circuit diagram illustrating in more detail a light amount control device included in a part of the device, in which 13 is a reference level setting circuit that generates a constant potential reference signal, and 14 is a detection signal from the photodetection circuit 12 and the reference level setting circuit. 1
This is a comparison circuit that compares the magnitude of the reference signal from 3 and stops the counting operation of the counter 16 when the detection signal becomes larger. 15 is an oscillation circuit that oscillates a signal with a constant frequency; 16 is the oscillation circuit 1;
5 and counts the oscillation signal, and starts counting when a timing signal is applied from terminal T1, and when the counting operation does not stop due to the output of the comparator circuit 14 even after counting up to a predetermined value. , an overflow signal is derived, the counter is cleared, and the counting operation is stopped, and the comparison circuit of the comparison circuit 14 is also stopped.

17 is a D/A exchange circuit that exchanges the count value of the counter 16 into an analog quantity; 18 is a current amplification circuit that is connected to the D/A exchange circuit 17 and amplifies the obtained analog signal; 19 is a circuit from terminal T2; This is a switch circuit that operates ON/OFF according to the applied recording signal. When the switch circuit 19 is ON, the current on the signal line SL2 is applied to the semiconductor laser generator 1, and when it is OFF, the current on the signal line SL2 is applied to the semiconductor laser generator 1. This is to control the current on the signal line SL2 so as not to be applied to the semiconductor laser generator 1. Also, this switch circuit 19
When the timing signal from terminal T1 is input,
It becomes ON state regardless of the recording signal of the terminal T2, and then when the output of the comparison circuit 14 described later is input, the ON state due to the timing signal is canceled, and the ON/OFF state occurs again according to the recording signal of the terminal T2.
perform an action.

To further explain the light amount control operation of the beam recording device configured as above, the terminal T1
When a timing signal is applied to the switch circuit 19 (this timing signal is derived during idle time between when the beam recording device finishes recording one page worth of images and starts recording the next page), the switch circuit 19 is held in the ON state, and the counter 16 is cleared to start counting operation.

Therefore, the counter 16 starts counting, but since this count value Na gradually increases, the signal line
The current on SL2 also increases in response.

As a result, the intensity of the emitted beam from the semiconductor laser generator 1 gradually increases, but the counting operation continues until the detection signal becomes larger than the reference signal.

When the counter 16 obtains the count value Na in this way, if it becomes larger than the detection signal, the counting operation is stopped by the output of the comparison circuit 14, and the counter 16 continues counting until the next timing signal is applied. Holds the number Na. In addition, when the counting operation stops, the ON state of the switch circuit 19 caused by the timing signal of the terminal T1 is cleared, and the switch circuit 19 responds to the recording signal of the terminal T2 until the next timing signal is applied.
Performs ON/OFF operation.

Therefore, a current Ia corresponding to this count value Na is derived on the signal line SL2, and when a recording signal is applied to the terminal T2, the semiconductor laser generator 1 is driven according to this current Ia. .

Even if the counter 16 reaches the preset count value N2 due to a failure in the photodetector circuit 12, etc., the comparator circuit 14
If the counter stop signal is not derived from the signal line SL1, an overflow signal is derived from the comparison circuit 14.
The operation of the switch circuit 19 is stopped, and the operation of the switch circuit 19 is stopped.
The ON state is cleared, and the counter 16 is cleared to be in the initial state.

Therefore, when the current on the signal line SL2 increases and the semiconductor laser generator 1 is about to be damaged, the drive current is reduced to prevent damage to the semiconductor laser generator.

In the embodiment shown in FIG. 2, the timing signal is derived before the recording of a page on the photosensitive drum 5 by the laser beam L is completed and the recording of the next page is started, and after the completion of the light amount adjustment. Recording of the next page is started.

Furthermore, in the above embodiment, the back beam of the semiconductor laser generator was used as the incident light for the photodetection circuit.
It is also possible to use an optical system to guide the front beam to the photodetection circuit only during a part of the front beam or during the light amount control period.

Furthermore, in the above embodiment, the dynamic range of the system can be expanded by biasing the current amplifier circuit 18 and causing an initial value current to flow through the switch circuit 19.

As described in detail above, according to the present invention, overshoot in the amount of beam light is prevented, so that the lifetime of the semiconductor laser element can be increased. In addition, after the laser beam completes the recording operation for one page and before the start of the recording operation for the next page, the amount of light emitted by the laser beam is adjusted, so a photodetector element with a fast response speed is not required, which is economical. An excellent light amount control device can be provided. Furthermore, when the amount of light emitted by the laser beam reaches a predetermined value, the counting operation of the counting means is stopped and the counted value is held, so that a stable amount of light can be obtained even while recording each page. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a beam recording device to which the present invention is applied, and FIG. 2 is a circuit diagram showing a light amount control device according to the present invention. Here, 1 is a semiconductor laser generator, 12 is a photodetector circuit, 13 is a reference level circuit, 14 is a comparison circuit,
19 is a switch circuit.

Claims (1)

[Scope of Claims] 1. A semiconductor laser generating means for emitting a laser beam modulated by a recording signal, and after the recording operation for one page is completed by the laser beam, the recording operation for the next page is started. A light amount control device that adjusts the amount of emitted light of the laser beam during the previous inter-page period, the laser beam being generated from the semiconductor laser generating means and not modulated by the recording signal during the inter-page period. a detection means for detecting the amount of light emitted by the detector; a reference signal generating means for generating a reference signal at a constant level for stabilizing the amount of light; and a comparison means for comparing the detection output from the detecting means with the reference signal at the constant level. , oscillation means for outputting an oscillation signal of a constant frequency;
A counting means for counting oscillation signals from the oscillating means according to the comparison result by the first period comparing means; and inputting a predetermined signal derived within the inter-page period in order to start the counting operation by the counting means. input means; D/A conversion means for converting the counted value by the counting means into an analog quantity; and application means for applying current to the semiconductor laser generation means based on the analog signal output from the D/A conversion means. and when the detection output from the detection means has not reached the certain level, the counting means starts a counting operation based on the input of the predetermined signal, and sequentially counts the oscillation signals. With,
The applying means applies a current corresponding to the count value obtained by the counting to the semiconductor laser generating means, and when the detection output from the detecting means reaches the certain level, the counting means stops counting operation, A light amount control device characterized in that a count value at that time is held.