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Analysis of Laser Displacement Sensing Technology

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At present, the major industrial powers in the world are upgrading their industries, and the upgrading of modern industries is inseparable from laser technology. In addition to playing a huge role in production and processing, laser technology also has important applications in accurate real-time measurement. It provides accurate measurement for the size of electronic products, curvature of transparent components, vibration spectrum of large three-dimensional objects such as automobiles and aircraft, bearing concentricity, eccentricity and vibration, and greatly improves product output and production efficiency.

In order to realize the specific application of laser real-time measurement in the industrial field, it is necessary to develop and popularize various laser sensors. As we all know, modern manufacturing industry is already a sensor-driven world. In almost all manufacturing processes, accurate real-time measurement relies heavily on sensors. With the introduction of optical technology, sensors are developing in the direction of faster, more accurate and more reliable. Compared with traditional measurement methods, optical measurement sensors, especially laser measurement sensors, are widely used in industry because of their non-contact and fast measurement ability. The most typical application example is the high precision laser displacement sensor.

Laser displacement sensors are commonly used for measuring physical quantities such as length, distance, vibration, speed, and azimuth. They can also be used for flaw detection and monitoring of atmospheric pollutants. Measuring the thickness variation of the foil (thin sheet) by the laser displacement sensor can help to detect wrinkles, small holes or overlap, and avoid machine failure; and the position identification of small parts, the monitoring of the parts on the conveyor belt, and the position of the robot (tool center) The application of position and control can ensure the efficient operation of the equipment and production line. On the filling product line, the expansion program of the laser beam reflecting surface can be used to accurately identify whether the filling of the filling product is qualified. At the same time, it can guarantee the quality of filling. In addition, laser displacement sensors have unparalleled advantages in absolute distance measurement, relative displacement measurement, remote vibration measurement or vibration spectrum measurement, contour detection, thickness measurement, curvature measurement, and thickness measurement of transparent objects.

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 principles 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 sensor, laser triangulation method is suitable for high precision and short distance measurement, while laser echo analysis method is used for long distance measurement. In the current application of industrial robots, triangulation method is usually used. The maximum linearity and resolution of this method can reach 1 um and 0.1 um respectively.

Laser triangulation is a kind of distance measurement which can get single point or multi-dimension from angle calculation. The visible red laser is projected onto the surface of the measured object through the lens. The reflected laser is received by the linear CCD camera inside the receiver lens. According to different distances, the linear CCD camera can "see" the light spot at different angles. Based on 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 measured object.

The echo analysis method is to send a million laser pulses to the detector and return to the receiver through the laser transmitter every second. The processor calculates the time required for the laser pulse to encounter the detector and return to the receiver, so as to calculate the distance value. The output value is the average output of thousands of measurement results, i.e. the so-called pulse time method. The longest detection distance can be achieved. Up to 250m.

In the aspect of accurate vibration measurement, the principle of laser Doppler vibrometer (LDV) is based on optical interference, which is measured by the superposition of two coherent beams I1 and I2. The superimposed intensity is not simply the sum of two beam intensities, but also includes a coherent modulation term. The modulation term is related to the path length between two beams of light.

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.

Optical components are currently bulky and expensive, and require a custom and precise assembly process in connection with other electronic components. The integration of optical components allows them to achieve more complex designs and more functions on a lower cost basis. Integrated optical chips can contain tens to hundreds of optical components, including lasers, modulators, photodetectors and filters, on a single optical substrate, and are now an effective solution for existing and emerging markets. Provide innovative optical modules. As the demand for optical sensor technology continues to grow in modern manufacturing, integrated optical chips simplify system design, allowing sensors to make faster, more accurate measurements at a lower cost.

In the future, the demand for various types of laser sensors represented by laser displacement sensors will maintain a rapid growth trend. With the implementation of various domestic incentive policies, the continuous innovation and progress of laser technology and the performance of laser displacement sensor products continue to improve. The large-scale commercial application of laser displacement sensors will soon become a reality.

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