JPH08254405A - Optical displacement sensor - Google Patents

Abstract

PURPOSE: To improve response speed of a drive level control in the case of irradiating a substance of high reflectance. CONSTITUTION: A semiconductor laser 2 is driven by a semiconductor laser drive circuit 1. A light receive signal is received by PSD(a position sensitive device) 6, I/V converted, and added by an adder. The added output is sampled so as to input into a charging circuit 21. When the input signal is changed in the positive direction, the charging circuit 21 which rapidly charges a capacitor rapidly responds to the change in the output of an S/H circuit 10 in the positive direction so as to input it in a differential amplification circuit 22. The response speed of the driven level control signal can be thus improved, when a high reflectance substance is rapidly scanned.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement sensor using a triangulation method.

[0002]

2. Description of the Related Art A conventional optical displacement sensor irradiates light on a measurement area, arranges a position detecting element (PSD) or the like at a predetermined angle with respect to a projected beam, and receives reflected light obtained from an object. . Then, the distance to the object is measured based on the light receiving position of the PSD.

However, in such a conventional optical displacement sensor, if the reflectance of the detected object is different, the received light level fluctuates, and the measurement accuracy is lowered. Therefore, a method of changing the light emission power of the light projecting element according to the reflectance of the measurement object has been considered. FIG. 7 is a block diagram showing the structure of a conventional optical displacement sensor based on the triangulation method. In the figure, a semiconductor laser drive circuit 1 drives a semiconductor laser 2 which is a light projecting element based on a clock signal CL1 supplied from a clock generator 3 to a drive level control signal Vc.
It is driven periodically at the level of. The emission output of the semiconductor laser 2 is applied to the object detection area via the light projecting lens 4. The light receiving lens 5 and the PSD 6 are arranged at a predetermined angle with respect to this projected beam. The PSD 6 obtains a pair of current outputs at both ends according to its light receiving position, and the outputs at both ends are converted into voltage signals by the I / V converters 7 and 8, respectively. The outputs of the I / V converters 7 and 8 are adders 9
Is input to and added. The addition output is input to a sample hold circuit (hereinafter referred to as S / H circuit) 10 and I / O
The output of the V converter 8 is input to the S / H circuit 11. S /
The outputs of the H circuits 10 and 11 sample the input signal based on the clock signal CL3 from the clock generator 3, and the output thereof is given to the divider 12. It is assumed that the clock signal CL2 is synchronized with the clock signal CL1 and its rising time is slightly delayed. Divider 1
2 is for dividing the output of the I / V converter 8 by the output of the adder 9, and outputs a distance signal. This signal is corrected and output as a distance signal via the correction circuit 13. The output of the S / H circuit 10 is input to the differential amplifier circuit 14. The differential amplifier circuit 14 outputs the difference from the reference voltage Vr to the semiconductor laser drive circuit 1 as a drive level control signal Vc.

FIG. 8 is a circuit diagram showing an example of the differential amplifier circuit 14. As shown in the figure, the differential amplifier circuit 14 is
Input resistance Ri to the operational amplifier 15 and the non-inverting input terminal, a feedback resistance Rf, and this feedback resistance Rf
And a reference voltage Vr is input to the non-inverting input terminal of the operational amplifier 14. The capacitor Cf is a capacitor for preventing oscillation.

[0005]

However, in such a conventional optical displacement sensor, in order to receive an object having a low reflectance such as black rubber from an object having a high reflectance such as a white paper at substantially the same level. Needs to control the emission level in a wide range. However, since the reflectivity of the object is large and small, a feedback circuit is provided by providing a differential amplifier circuit in order to keep the received light voltage within an appropriate range so that the divider can correctly calculate. In order to suppress oscillation when feedback is applied, the differential amplifier circuit 14 is provided with the capacitor Cf as described above.
Is added. Although the capacitor Cf does not oscillate, it has a drawback that the overall response speed for controlling the projection power becomes slow. Therefore, when the optical displacement sensor is used for detecting the warp of the lead pin of the IC, for example, the displacement output is appropriate even if the light enters an object having a glossy reflectance of the lead and enters the measurement area. There was a drawback that it took a long time to reach the value. Therefore, there is a drawback that the scanning speed for scanning the IC lead pin is limited.

The present invention has been made in view of the above-mentioned conventional problems, and the problem is solved by increasing the response speed of the displacement output when the object to be measured enters the measurement area. The purpose is to solve.

[0007]

According to the invention of claim 1 of the present application, a light projecting means for driving a light emitting element at a level according to a drive level control signal to irradiate a measuring object with light, and a measuring object Light receiving means for receiving the reflected light and outputting a pair of signals according to the light receiving position, signal processing means for calculating a distance signal to the object according to the light receiving position of the light receiving means, and a pair of light receiving signals of the light receiving means Of the addition means for calculating the addition value of the addition means, the charging circuit for receiving the output of the addition means for charging the capacitor through the diode when the addition output rises, and the difference between the output of the charging circuit and the reference voltage are projected. And a differential amplifier circuit for outputting to the means as a drive level control signal.

In the invention of claim 2 of the present application, the charging circuit is
The differential amplifier circuit includes a diode whose anode is connected to the input terminal, a capacitor which is connected to the cathode side of the diode and the ground terminal, and a first switch which short-circuits the diode. An operational amplifier to which each output of the circuit is input, a feedback capacitor connected between the input and output of the operational amplifier, and a second switch connected in series to the feedback capacitor and changing in conjunction with the first switch. It is characterized by including.

According to the invention of claim 3 of the present application, the light emitting element is driven at a level according to the drive level control signal to emit light to the object to be measured, and reflected light is received from the object to be measured. A light receiving unit that outputs a pair of signals corresponding to the light receiving position, a signal processing unit that calculates a distance signal to the object according to the light receiving position of the light receiving unit, and an added value of the pair of light receiving signals of the light receiving unit. An addition unit, an output of the addition unit is input, and a difference unit that periodically takes a difference from a reference value, and a difference signal is output as a drive level control signal when the output of the difference unit changes in the positive direction, and the difference is output. Control signal output means for outputting an average value of a plurality of past differential signals as a drive level control signal when the output of the means changes in the negative direction.

[0010]

According to the invention of claim 1 of the present application having such a feature, the light emitting element is driven by the light projecting means to irradiate the object to be measured with light, and the oscillated light is received by the light reception output. The pair of light receiving signals of the light receiving means are added by the adding means, and the output of the adding means is charged in the capacitor through the diode. Then, the difference between the output of the charging circuit and the reference value is output to the light projecting means as a drive level control signal. By doing so, the drive level can be changed at high speed when the addition output changes in the positive direction, and the response speed when an object having a sharply high reflectance is scanned is improved. Further, in the invention of claim 2, the high speed response mode and the normal mode are switched by the first and second switches interlocking with each other. Further, in the invention of claim 3, the difference means and the control signal output means are realized by a microcomputer.

[0011]

1 is a block diagram showing the overall construction of an optical displacement sensor according to a first embodiment of the present invention. The same parts as those of the conventional example described above are designated by the same reference numerals and detailed description thereof will be omitted. Also in this embodiment, the semiconductor laser drive circuit 1 drives the semiconductor laser 2 at the level of the control signal input based on the clock signal from the clock generator 3. The semiconductor laser 2 irradiates the object detection area with a projection beam via a projection lens 4. Here, the semiconductor laser driving circuit 1, the semiconductor laser 2 and the light projecting lens constitute a light projecting means for driving the light emitting element at a level according to the drive level control signal and irradiating the object to be measured with light. The light receiving lens 5 and the position detection element (PSD) 6 are arranged at a predetermined angle with respect to the projected beam. The light receiving lens 5 and the position detecting element 6 constitute a light receiving means for outputting a pair of signals corresponding to the light receiving position up to the measurement object. The current output of both ends of PSD6 is I / V
The voltage signals are converted by the converters 7 and 8 and added by the adder 9
Given to. The outputs of the adder 9 and the I / V converter 8 are input to the S / H circuits 10 and 11, respectively. The clock generator 3 outputs the clock signal CL2 to the S / H circuits 10 and 11 at a timing slightly delayed from the clock timing of the projection beam. The S / H circuits 10 and 11 give the output to the divider 12, and further output it as a distance signal via the correction circuit 13. Now, in this embodiment, the S / H circuit 1
The output of 0 is input to the differential amplifier circuit 22 via the charging circuit 21. The charging circuit 21 uses the output of the S / H circuit 10 as a signal source for charging the capacitor.

FIG. 2 is a circuit diagram showing an example of the charging circuit 21 and the differential amplifier circuit 22. The charging circuit 21 is S / H
The circuit 10 has a diode D1, whose anode end is connected to the input end, and a capacitor C1 connected between its cathode and the ground end, and the cathode end of the diode D1 is connected to the non-inverting input terminal of the operational amplifier 23. To be done. The inverting input terminal of the operational amplifier 23 is connected to the output terminal to form a voltage follower. The charging circuit 21 charges the capacitor C1 in a short time by the rising output of the S / H circuit 10 to improve the response speed to an object which becomes sharply bright. Since the capacitor C1 does not discharge rapidly with respect to an object that becomes abruptly dark, the response speed decreases. On the other hand, the configuration of the differential amplifier circuit 22 is almost the same as that of the conventional example shown in FIG.
By adding the charging circuit 21, the value of the feedback capacitor Cf0 of the differential amplifier circuit 22 is made sufficiently smaller than Cf, for example, about 1/10 to 1/100.

Next, the operation of the first embodiment will be described.
FIG. 3A shows a usage example of this optical displacement sensor, which is used for detecting the warp of the IC pin by scanning the IC pin parallel to the IC in a direction indicated by an arrow A. This is the case. In this case, the clock pulse is generated from the clock generator 3 at a speed sufficiently higher than the scanning of the pins of the IC, and the semiconductor laser 2 is pulse-driven. Then, the reflected light is received and the I / V conversion value of the PSD 6 is added. By sampling the added value for each clock, the output voltage of the S / H circuit 10 becomes that shown in FIG. 3 (b). In this case, the light reception output is obtained every time when the IC pin is scanned, but the response speed becomes slower because the capacitor C1 of the charging circuit 21 needs to be charged at the rising edge of scanning the first pin, but it stabilizes immediately. In the pin-to-pin gap, the light receiving level gradually decreases.
In this case, the capacitor C1 has no discharge path, and thus discharge is delayed. In this way, an overshoot occurs only when the reflected light that enters the first pin rises, but after that, the received light signal level can be set to a substantially constant level. FIG. 3C is a diagram showing an output waveform of the S / H circuit 10 of the conventional optical displacement sensor having no charging circuit as compared with this. If the charging circuit is not provided as shown in the figure, the output is not stable because an overshoot occurs at each rising edge. In the present embodiment, the feedback capacitor Cf of the differential amplifier circuit can be made small, and the oscillation of the feedback system can be prevented so that the response speed can be increased.

Next, a second embodiment of the present invention will be described. Since the charging circuit is always connected in the above-described first embodiment, the response speed becomes extremely slow for an object that becomes dark rapidly due to a decrease in the output of the S / H circuit 10. Therefore, the displacement cannot be measured stably depending on the object to be measured. Second
In the embodiment, in consideration of such a case, the connection of the first embodiment and the connection of the conventional example are switched by a switch. FIG. 4 is a circuit diagram of the charging circuit 31 and the differential amplifier circuit 32 according to the second embodiment of the present invention. In this figure, the configuration other than the charging circuit 31 and the differential amplifier circuit 32 is the same as that of the first embodiment. In this embodiment, as shown in the figure, the S / H circuit 10
Is input to the analog switch 33. The analog switch 33 uses the clock signal CL3 from the clock generator 3.
, And its output is connected to the capacitor C1 via the diode D1. This clock signal CL3 is supplied during the period when the output of the S / H circuit 10 is stable,
For example, it is assumed that the timing is set to an intermediate timing of the clock CL2. The other structure is almost the same as that of the charging circuit 21 of the first embodiment described above, and the operational amplifier 34 for the voltage follower is connected to the cathode of the diode D1. A switch 35 that short-circuits both ends of the diode D1 is provided. The differential amplifier circuit 32 has substantially the same configuration as the differential amplifier circuit 14 shown in the conventional example, and the reference voltage Vr is input to the non-inverting input terminal of the operational amplifier 36. The input resistor Ri is connected between the inverting input terminal and the output end of the charging circuit 31, and the feedback resistor Rf is connected between the inverting input terminal and the output end.
And capacitors Cf1 and Cf2 are connected in parallel. A switch 37 is connected in series to the capacitor Cf2. The switches 35 and 37 are interlocking switches as shown in the figure, and are configured so that the switches 35 and 37 are simultaneously opened or closed. The feedback capacitor Cf2 has the same capacitance as the capacitor Cf of the differential amplifier circuit shown in the conventional example, and Cf1 has a smaller value, that is, a value of 1/10 to 1/100 as described above. To do.

In this way, if the switches 35 and 37 are operated to open these switches, the above-mentioned charging circuit 31 operates and the feedback resistance connected to the differential amplifier circuit 32 at that time is only Cf1. Become. In this case, the operation mode is the same as that of the first embodiment in which the response speed at the time of incident light is improved. At this time, the clock CL of the S / H circuits 10 and 11
Analog switch 33 with timing CL3 different from 2
And the charging circuit 31 operates at this timing.
On the other hand, when the switches 35 and 37 are closed, the diode D1 is short-circuited, so that the diode does not work and the charging circuit 3
1 is simply a sample and hold circuit. The sampling timing of this sample hold circuit is held during the period when the output of the S / H circuit 10 is stable. In this case, since the capacitor Cf2 is also connected to the feedback circuit of the differential amplifier circuit 32, the capacitors Cf1 and Cf2 are connected to the differential amplifier circuit. In this case, a normal operation mode similar to the conventional example is entered, and the capacitance of the capacitor can be increased to prevent oscillation.

FIG. 5 is a block diagram showing the structure of an optical displacement sensor according to the third embodiment of the present invention. In the figure, the output of the S / H circuit 10 is input to the A / D converter 41. The A / D converter 41 converts an input signal into a digital signal at each clock timing of light projection, and its output is input to the CPU 42. As will be described later, the CPU 42 has a function of a difference means for calculating a difference between the addition output and the reference value, and a control signal output means for outputting a control signal based on the change in the positive and negative directions. The output is output to the above-mentioned semiconductor laser drive circuit 1 via the D / A converter 43. Other configurations are the same as in the first embodiment.

Next, the flow chart of the CPU 42 will be described with reference to FIG. When the operation is started, first, in step 51, initial setting is performed. In this initial setting, all the input buffers F (1), F (2) ... F (n) are set to 0. Here, n is an arbitrary integer, for example, 10. Next, in step 52, the output A + B of the A / D converter 41 is read. Here, A and B are I /
These are the outputs of the V converters 7 and 8. Then, in step 53, the reference value R is subtracted from the input value (A + B) to obtain F (0).
And Next, in step 54, the data is updated, and the value of F (i) is assigned to F (i) +1 for all F (i) (i = 0 to 9). Then, in step 54, F (1) and F (2) are compared. If F (1) is larger, the received light level has increased, so steps 56, 5
In step 7, the value of F (1) is set as the output value F, and the value of F is output. This value is converted into an analog signal by the D / A converter 43 as described above. On the other hand, if the value of F (2) is large in step 55, the light receiving level has decreased, so the routine proceeds to step 58, where the average value of the values of F (1) to F (n) is set as the output value F. Then, the routine proceeds to step 57, where this value is output and the processing ends. In this flowchart, in steps 52 and 53, the output of the adding means is input,
A difference means for calculating the difference from the reference value is configured. Steps 54 to 57 output a difference signal as a control signal when the output of the difference means changes in the positive direction, and the output of the difference means changes in the negative direction. At this time, the function of the control signal output means for outputting the average value of the difference means as the control signal is achieved.
By doing so, the same effect as that of the first embodiment can be realized by the CPU. In addition to this, the functions of the divider 12 and the correction circuit 13 for object detection may be realized by the CPU.

[0018]

As described in detail above, according to the present invention, the received light signal is passed through the charging circuit having the diode and the capacitor, so that the response speed at the time of incident light is increased without oscillation due to the feedback system. can do. Therefore, when used for detecting the warp of the pins of the IC, the pins can be scanned at high speed, which is extremely effective. According to the second aspect of the present invention, it is possible to switch between the mode in which the response speed when the reflected light is incident is high and the normal operation mode. Further, according to the invention of claim 3, the same effect can be obtained by performing such processing using a microcomputer.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical displacement sensor according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a charging circuit and a differential amplifier circuit according to a first embodiment of the present invention.

FIG. 3 is a time chart showing the operation of this embodiment.

FIG. 4 is a circuit diagram showing a charging circuit and a differential amplifier circuit according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of an optical displacement sensor according to a third embodiment of the present invention.

FIG. 6 is a flowchart showing the operation of the third embodiment of the present invention.

FIG. 7 is a block diagram showing an example of a conventional optical displacement sensor.

FIG. 8 is a circuit diagram showing an example of a conventional differential amplifier circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 semiconductor laser drive circuit 2 semiconductor laser 6 position detection element 7,8 I / V converter 9 adder 10,11 S / H circuit 12 divider 13 correction circuit 14,22,32 differential amplification circuit 15,23, 34,36 Operational amplifier 21,31 Charging circuit 33 Analog switch 35,37 Switch 41 A / D converter 42 CPU 43 D / A converter

Claims (3)

[Claims] 1. A light projecting unit that drives a light-emitting element at a level according to a drive level control signal to irradiate a measurement target with light, and a pair of units that receives reflected light from the measurement target and that receives light. A light receiving unit that outputs a signal, a signal processing unit that calculates a distance signal to an object according to a light receiving position of the light receiving unit, an adding unit that calculates an added value of a pair of light receiving signals of the light receiving unit, The output of the adding means is input, and the charging circuit that charges the capacitor via the diode when the addition output rises, and the difference between the output of the charging circuit and the reference voltage is output to the light projecting means as a drive level control signal. An optical displacement sensor comprising: 2. The charging circuit includes a diode having an anode connected to an input terminal, a capacitor connected to a cathode side of the diode and a ground terminal, and a first switch short-circuiting the diode. The differential amplifier circuit includes an operational amplifier to which the reference voltage and the output of the charging circuit are respectively input, a feedback capacitor connected between the input and output of the operational amplifier, and the first switch connected in series to the feedback capacitor. The optical displacement sensor according to claim 1, further comprising a second switch that changes in conjunction with the second switch. 3. A light projecting means for driving a light emitting element at a level according to a drive level control signal to irradiate a measuring object with light, and a pair of receiving means for receiving reflected light from the measuring object and corresponding to the light receiving position. A light receiving unit that outputs a signal, a signal processing unit that calculates a distance signal to an object according to a light receiving position of the light receiving unit, an adding unit that calculates an added value of a pair of light receiving signals of the light receiving unit, An output of the adding means is input, and a difference means that periodically takes a difference from a reference value, and a difference signal is output as a drive level control signal when the output of the difference means changes in the positive direction. An optical displacement sensor, comprising: a control signal output unit that outputs an average value of a plurality of past differential signals as a drive level control signal when the output changes in the negative direction.