JP2909565B2 - Laser displacement meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement meter using laser light.

[0002]

2. Description of the Related Art FIG.
FIG. 2 is a block diagram of a laser displacement meter configured to detect the reflected light with a position detecting element and measure a distance to a test object. In such a laser displacement meter, the timing circuit 10
0, the drive unit 101 is activated, and the laser diode L
D is intermittently driven to irradiate the object OB with a laser beam whose intensity is modulated. At that time, the laser beam reflected from the object OB is received by the position detecting element PSD, Position signal I output from position detection element PSD
The calculation unit 106 calculates the displacement amount to the test object by calculating 1, 1 and I2. In such a laser displacement meter, the position detecting element PSD
Since two current values I1 and I2 corresponding to the light receiving spot position of the reflected light from the test object OB appearing above are output,
These outputs I1 and I2 are converted to IV converters 102a and 102b.
, And converts the voltage into a voltage.
AD through sample and hold circuits 104a and 104b
After being input to the converter 105 and converted into a digital signal, the arithmetic unit 106 calculates the following equation to obtain the displacement amount to the object to be measured. In other words, in such a displacement sensor, if the values obtained by converting the signal outputs I1 and I2 from the position detecting element by the AD converter are [V1] and [V2], respectively, the displacement (deviation) from the center of the position detecting element PSD. ) The value of Z is The calculation unit 106 converts the displacement Z into a distance signal, and calculates the displacement L to the test object. Further, in such a displacement sensor, the AD converter 105 obtains an output by converting an analog value into a digital value.
It is determined according to the resolution of the AD converter. Therefore,
Now, assuming that V1 + V2 = Vc, the AD converter 105
If the full-scale value of the output signal is VADF and the resolution of the AD converter 105 is n bits, the resolution of the displacement amount
L is expressed by FR as the displacement when the output of the AD converter 105 changes from 0 to VADF. It is obtained by the formula. Therefore, when the amount of light decreases and the value of V1 + V2 = Vc is halved, the resolution is also halved. To prevent this, it is conceivable to double the gain of both amplifiers. When the gain of the amplifier is doubled, one position signal becomes much larger than the other position signal near the limit of the measurement range, so that the signal level of FIG. As shown by the dashed line in b), the output of the larger one is almost always the AD converter.
In this case, the output of the A / D converter becomes saturated even with a small change in the amount of received light, and the measurement may not be possible.

[0003]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above circumstances, and does not lower the resolution even when the amount of received light decreases, and also provides A for small changes in the amount of light.
A laser that functions without saturating the output of the D converter
Provide the displacement meter.

[0004]

According to the present invention proposed to achieve the above object, a laser beam emitted from a laser light emitting element is reflected by an object to be measured, and the reflected light is received by a position detecting element. , The output from this position detecting element
An improvement of a laser displacement meter which obtains a distance to an object to be measured by performing an arithmetic operation in an arithmetic unit after performing a digital conversion by a converter, wherein two signals output from a position detecting element are independently gain controlled. And a gain control circuit for controlling the gain of these amplifiers in accordance with a control signal from the arithmetic unit. The arithmetic unit converts the signals output from the two amplifiers into digital signals. When the sum of the output signals of the AD converters is determined to be less than half of the full scale value based on the output signal, a control signal is sent to the gain control circuit so that the output level of the AD converter is small. The configuration is such that the gain of the amplifying unit on the side is doubled.

[0005]

According to the present invention, by adopting the above configuration, the apparent resolution is not reduced. Also,
Only when the output sum of the A / D converter becomes less than half of the full scale level, the gain of the amplifying part on the low side of the A / D converter is doubled. Will not be.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. Since the basic configuration is the same as that of the displacement sensor shown in FIG. 2, the same reference numerals as those in FIG. As is clear from FIG. 1, the position detection element PSD 2
Each of the two amplifying units 103a and 103b has an arithmetic unit 106
The difference is that gain control circuits 1 and 2 for gain control are added, and AD converters 3 and 4 are individually provided. Here, when the sum of the levels of the output signals of the AD converters 3 and 4 becomes equal to or less than half of the full scale value, the arithmetic unit 106 determines the gain of the amplifying unit of the two AD converters 3 and 4 with the smaller output level. 2 so that
The gain of the corresponding gain control circuit 1 or 2 of the two gain control circuits 1 and 2 is set to double. According to such a displacement sensor of the present invention, the operation unit 106 calculates the following equation based on the signals V1 and V2 output from each of the AD converters 3 and 4, and obtains the displacement Z. Finally, the displacement L is obtained by using a triangulation method. Therefore, according to such a displacement sensor, for example, when the gain of the amplifying unit is a and b and the output of the AD converter at that time is V1a and V1b, V1a + V1b <
If the condition of 1/2 VADF, V1a> V1b is satisfied, the arithmetic unit 106 keeps the gain of the amplifier 103a of the larger output V1a as it is and doubles the gain of the amplifier 103b of the smaller output V1b. Therefore, a control signal is sent to the gain control circuit 2 to control the gain of the amplifying unit 103b to twice. At this time, if the signal level output from the AD converter 4 corresponding to the amplification unit 103b is V1b ', the calculation unit 106 calculates the shift (displacement) Z , And the displacement L to the test object is converted and measured based on the calculated Z.

[0007]

According to the present invention, as described above, even when the amount of light received by the position detecting element decreases, the displacement can be measured with high accuracy without lowering the resolution.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing an internal configuration of a conventional displacement sensor.

FIG. 3A is a diagram showing the output relationship of V1 and V2 AD converters, and FIG. 3B is a diagram showing V1 and V2 when the gain is increased;
2 is an output relation diagram of the AD converter (a broken line indicates a state where the output of the AD converter is saturated).

[Explanation of symbols]

 LD: Laser light emitting element OB: Object to be detected PSD: Position detecting element I1, I2: Position signal 1, 2, Gain control circuit 3, 4, AD converter 106 ..Calculation units

Continuation of the front page (56) References JP-A-4-158211 (JP, A) JP-A-3-135714 (JP, A) JP-A-2-247504 (JP, A) JP-A-4-62403 (JP) JP-A-61-225606 (JP, A) JP-A-5-52552 (JP, A) JP-A-64-15907 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB G01C 3/00-3/32 G01B 11/00-11/30

Claims (1)

(57) [Claims] 1. A laser light emitted by a laser light emitting element is reflected by an object to be measured, the reflected light is received by a position detecting element, and an output from the position detecting element is converted by an AD converter.
In a laser displacement meter which calculates a displacement distance to an object to be measured by performing an arithmetic operation by an arithmetic unit after digitally converting the two signals, two amplifiers for independently controlling gains of two signals output from the position detecting elements are provided. And a gain control circuit for controlling the gains of these amplifying units in accordance with a control signal from the arithmetic unit.
When it is determined that the sum of the output signals of the converter is less than half of the full scale value, a control signal is sent to the gain control circuit, and the output of the AD converter is set to the lower side of the amplifier. A laser displacement meter configured to double the gain.