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Laser displacement sensor introduction


There are many technologies that can achieve accurate optical displacement measurement. Industrialized laser displacement sensors generally use laser triangulation and laser echo analysis. In addition, they can use the principle of color confocal and interferometry to accurately shift. measuring. In addition, laser displacement sensors are also used for non-contact vibration measurements. However, the above methods are defective for specific measurement conditions and measurement requirements.

For laser displacement sensors, laser triangulation is suitable for high-precision, short-distance measurements, and laser echo analysis is used for long-distance measurements. In current industrial robot applications, triangulation is usually used. This method has a maximum linearity of 1 um and a resolution of 0.1 um.

Laser triangulation is a single point or multidimensional distance measurement from angle calculation. The visible red laser is directed through the lens to the surface of the object to be measured. The laser reflected by the object passes through the receiver lens and is received by the internal CCD linear camera. According to different distances, the CCD linear camera can "see" the light at different angles. point. From this angle and the known distance between the laser and the camera, the digital signal processor can calculate the distance between the sensor and the object being measured.

The echo analysis rule is to use a laser transmitter to emit one million laser pulses per second to the detector and return it to the receiver. The processor calculates the time required for the laser pulse to encounter the detector and return to the receiver. The distance value, which is the average output of thousands of measurements, the so-called pulse time method, with a maximum detection distance of up to 250 m.

In terms of accurate vibration measurement, the commonly used laser Doppler vibrometer (LDV) works on the basis of optical interference and is measured by superposition of two coherent beams I1 and I2. The superimposed light intensity is not the sum of the simple two beams of light, and includes a coherent modulation term. The modulation term is related to the path length between the two beams.

Although the laser triangulation measurement is relatively simple and reliable, its disadvantage is that the measurement accuracy decreases as the measurement distance and range increase, so the measurement range is limited. In addition, a certain amount of open space is required to meet the measurement requirements of the triangulation method, so that it cannot be applied in deep trenches or deep holes. The laser echo analysis method is suitable for long-distance detection, but the measurement accuracy is lower than the laser triangulation method. In terms of vibration measurement applications, the detection capabilities (frequency range/vibration range/precision) of the two previous displacement/distance measurement techniques are limited. While LDV can perform very accurate vibration measurement and instantaneous displacement measurement, it lacks the ability to measure absolute displacement or distance, and the cost is also quite high.

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