A laser displacement sensor is a sensor that uses laser technology for measurement. It consists of a laser, a laser detector, and a measurement circuit. The laser sensor is a new type of measurement instrument. It is capable of non-contact measurement of position, displacement, and other object changes. It can measure displacement, thickness, vibration, distance, diameter, and other precise geometric measurements.
Laser has the excellent characteristic of good straightness. Also, the laser displacement sensor has higher accuracy than the ultrasonic sensor we know. However, the laser generation device is relatively complex and large so it will be more demanding for the application range of the laser displacement sensors.
1、Discrimination principle
In practical application, displacement has two directions. After selecting a direction, the displacement has positive and negative, so the displacement direction can not be determined by using a photoelectric element to measure the Mohr stripe signal. To identify the direction, need to have a π/2 phase difference between the two Mohr stripe signals. As in Figure 2, two photoelectric elements are placed at 1/4 stripe spacing apart, and two-phase difference π/2 electrical signals u01 and u02 are obtained. Two square wave signals, u01' and u02', are obtained after shaping. Grating forward movement u01 ahead of u02 90 degrees, reverse movement u02 ahead of u01 90 degrees, so through the circuit to identify the phase can determine the direction of grating movement.
2, subdivision technology
With the increase in measurement accuracy requirements, the unit of grid distance can no longer meet the requirements, and the need to take appropriate measures to subdivide the moiré stripe. The so-called subdivision is in the moiré stripe signal changes in a cycle, issued several pulses to reduce the pulse equivalent. If n pulses are sent out in one cycle, the measurement accuracy can be improved by n, and each pulse is equivalent to 1/n of the original grid distance. n times the frequency of the counted pulses is increased after subdivision, also called n times the frequency.
There are two methods of subdivision commonly used: one: direct subdivision. In the position of the difference of 1/4 Mohr stripe spacing placed on the two photoelectric elements, you can get two phase differences of 90o electrical signals, using the inverter to invert the phase to get four, in turn, 90o difference in the AC signal. Similarly, in the two Mohr stripes placed between the four sequential 1/4 stripe spacing photoelectric elements, you can get four phase difference of 90o AC signal to achieve four times the frequency subdivision. The second: is circuit subdivision.
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