JPH0139911B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical scanning device, and more particularly to an optical scanning device in which the output of a laser beam is controlled to a constant level using an analog control signal.

For example, in a laser device used in a printer of a data processing device, it is necessary to control the output of laser light to a constant level in order to maintain a constant print density in the printer. For this purpose, conventionally, as shown in FIG. 1, a laser beam (intensity P ₀ ) oscillated from a laser oscillator 1 is modulated by an optical modulation element (AOM) 2, and then transmitted by a rotating mirror 3 to, for example, an electrostatic drum. When the light receiving surface D is irradiated, a part of the reflected light from the rotating mirror 3 is received by the light detection circuit 4 and converted into an analog signal proportional to the intensity of the laser light. This analog signal is sampled and held in a sample and hold section 5, and converted into a digital signal in accordance with the output from the optical modulation element 2 in an analog-to-digital conversion circuit 6. This digital signal is transmitted to the comparator circuit 7 and compared with a reference value R _f , and an up/down counter provided in the comparator circuit 7 is caused to count up or down based on the comparison with the reference value. The digital output signal corresponding to the counter value thus output is converted into an analog signal by the digital-to-analog conversion circuit 8. This analog signal is then input to the light modulation element 2 via the driver circuit 13 and the AOM driver 14, thereby controlling the light modulation element 2 to change its diffraction efficiency η, thereby increasing the intensity of the laser light at the light receiving surface D. It was controlled so that P ₀ ·η was a constant value.

Therefore, since this type of control method uses digital control, the intensity of the laser beam at the light-receiving surface can only be controlled in steps, and even if the intensity in the middle between steps is optimal, it is difficult to However, there are drawbacks such as the fact that the output of the laser beam cannot be obtained, and the digital control output changes immediately when the output of the laser beam changes, which may cause vibrations in the output of the laser beam.

Therefore, in order to improve the above-mentioned drawbacks, the present invention determines whether the laser beam exceeds the upper or lower limit of the range that can be used for printing exposure, controls the terminal voltage of the capacitor accordingly, and It is an object of the present invention to provide an optical scanning device that automatically adjusts the output level of a laser beam by changing the diffraction efficiency of an optical modulation element in an analog manner according to the terminal voltage of a capacitor. To this end, the optical scanning device of the present invention includes a light beam generating means, a modulating means for modulating the light beam, a scanning means for scanning the modulated light beam on a scanning surface, and a light beam receiving means. , a light beam detection means for converting into an electrical signal; a determination means for receiving the output of the light beam detection means and determining whether the light beam exceeds a usable level; a capacitor that is sufficiently larger than the period of one scan by the means; a charging/discharging control circuit that charges or discharges the capacitor according to the determination result of the determining means; and controlling the modulating means according to the electronic voltage of the capacitor. It is characterized by comprising means for adjusting the output level of the light beam.

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

FIG. 2 shows the configuration of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of its operation.

In the figure, the same reference numerals as in other figures indicate the same parts, 9 is a lower limit comparator circuit, 10 is an upper limit comparator circuit, 11 and 12 are latch driver circuits, 13 is a driver circuit, 14 is an AOM driver, Q _A , Q _B is a transistor, and C _A is a capacitor.

The lower limit comparator circuit 9 is a circuit that generates an output when the intensity of the laser beam detected by the photodetector circuit 4 does not reach the lower limit value _L shown in FIG.
A lower limit reference voltage E ₁ is applied for comparison to determine whether this lower limit value L _l has been reached. When the laser light does not reach the lower limit value L _l , the lower limit comparator circuit 9 detects this and produces an output, and the latch driver circuit 11 at the subsequent stage is operated by the transistor Q _A until the next light level signal comes from the light detection circuit 4. Turn on.

The upper limit comparator circuit 10 sets the intensity of the laser beam detected by the light detection circuit 4 to the upper limit value shown in FIG.
This is a circuit that generates an output when L _U is exceeded.
An upper limit reference voltage E ₂ is applied for comparing whether or not this upper limit value L _U has been reached. When the intensity of the laser beam exceeds the upper limit value L _U , the upper limit comparator circuit 10 detects this and produces an output, and the latch driver circuit 12 in the subsequent stage turns on the transistor Q _B until the next light level signal arrives. Make it.

The latch driver circuits 11 and 12 are controlled by a lower limit comparator circuit 9 and an upper limit comparator circuit 10, and respectively control on/off of transistors Q _A and Q _B.
It consists of a latch and a driver. The driver circuit 13 generates a signal corresponding to the terminal voltage V _A of the capacitor C _A.

The AOM driver 14 generates a control signal to control the diffraction efficiency of the optical modulation element 2, and responds to the terminal voltage of the capacitor C _A transmitted from the driver circuit 13 when a printing dot signal is applied. It generates control signals.

Capacitor C _A is charged by voltage V _CC via resistor R _A when transistor Q _A is on, and discharged via resistor R _B when transistor Q _B is on. The resistors R _{A and} R _B are set so that the time constant for charging and discharging the capacitor C _A is sufficiently larger than one scan period of the print dot signal.
and select the value of capacitor C _A appropriately.

In FIG. 2, a laser beam modulated by a light modulation element 2 is reflected by a rotating mirror 3 and is detected by a light detection circuit 4 before scanning a light receiving surface D such as an electrostatic drum. At this time, the light detection circuit 4
T ₀ to _{T 1} in Figure 3 while detecting the laser beam
As shown in the figure, a light level signal corresponding to the intensity of this laser light is output. This optical level signal is then output to the lower limit comparator circuit 9 and the upper limit comparator circuit 10. At this time, if the intensity of the laser beam detected by the light detection circuit 4 is lower than its lower limit value _Ll , this light level signal is lower than the lower limit reference voltage _E1 , so the lower limit comparator circuit 9
The latch driver circuit 11 generates an output "1" at time _T1 . This turns on transistor Q _A , which turns on the capacitor
C _A is charged by voltage V _CC through resistor R _A .
As a result, the terminal voltage V _A of capacitor C _A is
It gradually rises as shown in the figure. This terminal voltage V _A
Due to the rise in , the output signal of the driver circuit 13 also gradually rises, and the control signal of the AOM driver 14 changes accordingly, increasing the diffraction efficiency η of the light modulation element 2.
control is performed so that the output P ₀ ·η of the laser beam at the light-receiving surface D becomes stronger. In this way, the intensity of the laser beam on the light receiving surface D is increased.

Then, before the next scan on the light receiving surface D, as shown at times T ₂ to _{T 3} , if the intensity of the laser light detected by the photodetection circuit 4 is still lower than the lower limit L _l , the lower limit is The comparator circuit 9 produces an output again, the latch driver circuit 11 continues to produce an output "1", and the transistor Q _A remains on. In this way, the terminal voltage V _A of the capacitor C _A increases, and the control signal of the AOM driver 14 changes accordingly, further changing the diffraction efficiency η of the light modulation element 2 and increasing the amount of laser light irradiated onto the light receiving surface D. Make the strength even stronger.

Thus, prior to the next scan, time T ₄ ~
As shown at T ₅ , when the intensity of the laser beam detected by the photodetector circuit 4 is greater than its upper limit value L _U , an output is generated from the upper limit comparator circuit 10 and the latch/driver circuit 12 outputs "1". Of course, at this time, since the intensity of the laser beam is greater than its lower limit value _Ll , no output is generated from the lower limit comparator circuit 9. Therefore, as described above, the output "1" of the latch driver circuit 12 turns on the transistor Q _B , and the capacitor C _A
will be discharged through the resistor _RB . As a result, the terminal voltage V _A of the capacitor C _A gradually decreases, and accordingly, the intensity of the laser light irradiated onto the light receiving surface D also gradually decreases.

However, when the light detection circuit 4 detects the intensity of the laser beam at time T ₆ to _{T 7} , the intensity of the laser beam is greater than its upper limit value L _U , so an output is generated from the upper limit comparator circuit 10 and the latch driver circuit 12 continues to output "1". Therefore, the transistor Q _B remains on, the capacitor C _A continues to be discharged, the terminal voltage V _A continues to gradually decrease, and the intensity of the laser beam at the light receiving surface D decreases accordingly. If the intensity of the laser beam detected by the photodetector circuit 4 at time _T8 to _T9 is lower than the lower limit value _Ll , the latch is activated.
Since the driver circuit 12 does not output "1" and the latch driver circuit 11 outputs "1", the transistor Q _A is turned on again and the capacitor C _A is charged again. By repeating the above operations, the terminal voltage V _A of the capacitor C _A reaches a certain optimum value, and the intensity of the laser light detected by the photodetector circuit 4 reaches its upper limit value L _U at times T ₁₀ to _{T 11} . and the lower limit value L _l , both the lower limit comparator circuit 9 and the upper limit comparator circuit 10 produce no output, and the latch driver circuit 11,
Since neither transistor 12 outputs "1", transistors Q _A and Q _B are each turned off.

As a result, the capacitor C _A is neither charged nor discharged, so the terminal voltage V _A of the capacitor C _A is held at a constant value, and the diffraction efficiency η of the light modulation element 2 is also kept constant accordingly. Become. In this way, the intensity P ₀ ·η of the laser beam at the light receiving surface D can be maintained at a constant value.

Therefore, according to the present invention, the terminal voltage is changed by charging and discharging the capacitor, and the diffraction efficiency of the light modulation element is changed accordingly in an analog manner. Compare the light level with the standard value and increase /
Compared to a method in which a down counter is counted up or down and the light modulation element is digitally controlled based on the counter value, control can be performed more stably and precisely. Furthermore, temperature changes and changes over time in the laser output change over a long period of time, but when digitally controlled, the laser output is controlled for each scan. However, in the present invention, by setting the time constant for charging and discharging the capacitor to be sufficiently larger than the period of one scan, it is possible to perform control that matches laser output fluctuations well, resulting in a more stable control system. can do.

[Brief explanation of drawings]

FIG. 1 shows a conventional automatic light level control system, FIG. 2 shows a modified embodiment of the present invention, and FIG. 3 is an explanatory diagram of its operation. In the figure, 1 is a laser oscillator, 2 is a light modulation element, and 3 is a laser oscillator.
is a rotating mirror, 4 is a light detection circuit, 9 is a lower limit comparator circuit, 10 is an upper limit comparator circuit, 1
1 and 12 are latch driver circuits, 13 is a driver circuit, and 14 is an AOM driver, respectively.

Claims (1)

[Claims] 1. A light beam generating means, a modulating means for modulating the light beam, a scanning means for scanning the modulated light beam on a scanning surface, and a means for receiving the light beam and converting it into an electrical signal. a light beam detection means for determining whether the light beam has exceeded a usable level based on the output of the light beam detection means; and a determination means for determining whether or not the light beam exceeds a usable level;
a capacitor that is sufficiently larger than the scanning period; a charging/discharging control circuit that charges or discharges the capacitor according to the determination result of the determining means; and means that controls the modulating means according to the terminal voltage of the capacitor. An optical scanning device, comprising: adjusting an output level of the light beam.