JPH02226114A - Optical scanner - Google Patents

Abstract

PURPOSE:To control the light emission of a laser diode by electric processing and to simplify the scanner by providing two comparators which compare the driving waveform generated by a scanner driving circuit with two different reference voltages. CONSTITUTION:A resonant scanner 4 equipped with a mirror 3 which reflect the luminous flux from the laser diode 1 is provided and a laser turn-off timing generating means 13 equipped with the two comparators 14 and 15 which compare the driving waveform by the scanner driving circuit 12 driving the resonance scanner 4 with the two different reference voltages is provided. This laser turn-off timing generating means 13 is connected to a laser diode driving circuit 19. A signal for stopping the driving of the laser diode 1 can, therefore, be generated by the laser turn-off timing generating means 13 equipped with the comparators 14 and 15. Consequently, the device is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical scanning device in which a resonant scanner is used as a beam deflection means.

2. Description of the Related Art Conventionally, some bar code reading devices and the like use resonant scanners as beam deflection means. A conventional example will be explained based on FIGS. 4 to 7.

First, what is shown in FIG. 4 is a schematic diagram of a laser scanning type barcode scanner, in which a resonant scanner 4 equipped with a mirror 3 that reflects a laser beam 2 generated by a laser diode 1 is provided. This resonant scanner 4 has a pair of drive coils 7 fixed to a support member 6 erected from a fixed base 5, and the mirror 3 fixed to the free end of a leaf spring 8 fixed to the support member 6. It is formed by The laser beam 2 reflected by this mirror 3 is scanned in one direction to form a beam scanning line 9, and this beam scanning line 9 intersects with the barcode 11 printed on the barcode label 10. Barcode label 1
The reflected light reflected from 0 is received by a light receiving element (not shown) to obtain a read signal.

By energizing the drive coil 7, the mirror 3 swings back and forth as shown in FIG. 5, and a beam scanning line 9 is formed between X and X with X as the center.

Problem to be Solved by the Invention Beam scanning line 9 formed by resonant scanner 4
Figure 6 shows the change over time. This resonant scanner 4
Let f be the operating frequency (resonant frequency) of , and let A be the distance between X, t (or between x, l It is expressed as In the part marked ■ in the figure, the velocity change is small and can be considered to be almost constant, but in the part marked ■ the velocity change is large, and the change in the position of the beam with respect to time cannot be considered linear.

Therefore, reading at both ends of the beam scanning line 9 is impossible, or there is a high risk of misreading. The boundary between linearity and nonlinearity varies depending on the performance of the decoding algorithm for decoding the signal, but generally about 10% of both sides of the beam scanning line 9 are considered to be the nonlinear portion.

On the other hand, as a barcode scanner, it is desirable to make it small, and depending on the usage environment, it is also necessary to have a sealed structure. However, in this case, heat dissipation may not be sufficient and the temperature of the entire device including the laser diode 1 may rise. FIG. 7 shows an example of the temperature characteristics of the laser diode 1. In order to obtain a constant optical output P, the driving current Ip must be increased as the temperature rises. However, the drive current IP
When the amount of heat is increased, the amount of heat generated further increases and the temperature rises, which repeats the vicious cycle. As a result, the laser diode 1 may be destroyed, or the drive circuit may no longer be able to supply current, resulting in a decrease in output.

For this reason, there is an idea to stop driving the laser diode 1 in the nonlinear portion shown in FIG. 6 to suppress the heat generation. For this purpose, a means is required to turn on and off the driving of the laser diode 1, but in conventional systems, means such as providing a detector for the beam scanning line 9 and specifying the range thereof are adopted. This is accompanied by a complicated mechanical structure and a complicated control means.

Means for Solving the Problem A resonant scanner equipped with a mirror that reflects the light beam from a laser diode is provided, and the drive waveforms of a scanner drive circuit that drives this resonant scanner are compared with two different reference voltages. A laser extinguishing timing generating means including a comparator was provided, and this laser extinguishing timing generating means was connected to a laser diode drive circuit.

A signal to stop driving the laser diode can be generated by the laser turn-off timing generating means, which is equipped with two comparators that compare the drive waveform of the scanner drive circuit with two different reference voltages. Since the light emission of the laser diode can be controlled by electrical processing, the device is simple and can be controlled reliably.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 3. The same parts as those described in the conventional example are designated by the same reference numerals, and the description thereof will be omitted. First, resonant scanner 4
is connected to the scanner drive circuit 12. That is, the drive coil 7 of the resonant scanner 4 is connected to the scanner drive circuit 12.

This scanner drive circuit 12 is connected to a laser extinguishing timing generating means 13.

This laser extinguishing timing generating means 13 generates two different reference voltages, namely, Vref and Vref.
is connected to the input sides of two comparators 14 and 15, with voltage applied to one side. Here, the relationship between the two types of reference voltages is
V ref, ) V refz. The output sides of these comparators 14 and 15 are connected to a NOR circuit 16.

Then, an AND circuit 17 is provided, and this AND circuit 1
An external control terminal 18 and an output section of the laser extinguishing timing generating means 13 are connected to the input side of 7. This AND circuit 17 is connected to a laser diode drive circuit 19 that drives the laser diode 1.

Therefore, the laser diode drive circuit 19 has Vr
ef, A and P to which the reference power source 20 is connected.

C circuit (Automatic Power Control)
A control transistor 22 is connected to the output side of the A, P, C circuit 21, and the laser diode 1 is connected between the control transistor 22 and the ground.
A resistor 23 R1 is connected between the control transistor 22 and a potential portion -■. Further, connected to the input side of the A, P, C circuit 21 are a monitoring PD 24 that receives the light from the laser diode 1 and monitors its light emission state, and a variable resistor 25 indicated as R2. The function of the monitor PD 24 is that when the system is stable and the optical output of the laser diode 1 is constant, when the output of the laser diode 1 increases for some reason, the output VDP of the monitor PD 24 also increases, and Vref,
This decreases the difference between the two, lowering the driving current of the laser diode 1, and reducing the optical output.

Further, a switch 26 is connected in parallel with the monitoring PD 24, and this switch 26 is turned ON-OFF by a level conversion means 27 connected to the AND circuit 17.

In such a configuration, the drive waveform generated from the scanner drive circuit 12 varies so as to cross two types of reference voltage Vref and reference voltage Vref, as shown in FIG. 3(a). Therefore, in the comparator 14, an output is generated at a portion higher than the reference voltage Vref, and in the other comparator 15, an output is generated at a portion lower than the reference voltage Vref. The outputs of such comparators 14 and 15 are combined in a NOR circuit 16 and sent to a scanner drive circuit 12.
In the nonlinear portion of the drive waveform, a signal to turn off the laser diode 1 is generated. That is, in the nonlinear portion, the switch 26 is turned on via the level conversion means 27.

This state is similar to the state in which the output DP of the monitor PD 24 is at its maximum, and the laser diode 1 is turned off via the A, P, and C circuits 21. That is, the change in the drive waveform is shown in FIG. 3(a), and the output of the laser extinguishing timing generating means 13 alternately repeats H level and L level as shown in FIG. 3(b). As a result, the laser diode 1 repeatedly turns on and off as shown in FIG. 3(c).

Effects of the Invention As described above, the present invention provides a resonant scanner equipped with a mirror that reflects the light beam from the laser diode, and compares the drive waveforms of the scanner drive circuit that drives the resonant scanner with two different reference voltages. A laser extinguishing timing generating means equipped with two comparators is provided, and is connected to the laser diode drive circuit which is the laser extinguishing timing generating means, so that the driving waveforms generated by the scanner driving circuit are compared with two different reference voltages. The laser extinguishing timing generating means equipped with two comparators can generate a signal to stop driving the laser diode, and thereby the light emission of the laser diode can be controlled by electrical processing. The device is simple and can be controlled reliably.This also makes it possible to suppress the heat generation of the laser diode with a simple structure, prevent temperature rise, and ensure stable drive with low current. It has the effect of being able to do the following.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing an example of a laser diode drive circuit, Fig. 3 is a waveform diagram showing the driving state of each part, and Fig. 4 is a barcode scanner. FIG. 5 is a plan view of a part thereof, FIG. 6 is a waveform diagram showing changes in beam scanning lines, and FIG. 7 is a characteristic diagram of a laser diode. 1...Laser diode, 3...Mirror 4...
Resonant scanner, 12... Scanner drive circuit, 1
3... Laser extinguishing timing generation means, 14.15.
...Comparator, 19...Laser diode drive circuit - trillion watts'' 7 Figure 11 Self-tuning 911: (,nA)

Claims (1)

[Claims] Comparing a laser diode, a resonant scanner equipped with a mirror that reflects the light beam from the laser diode, a scanner drive circuit that drives the resonant scanner, and the drive waveforms of the scanner drive circuit with two different reference voltages. 1. An optical scanning device comprising: a laser extinguishing timing generating means provided with two comparators; and a laser diode drive circuit connected to the laser extinguishing timing generating means.