Banner Sensor - The working principle and selection of laser distance sensors

How laser sensors work

In the industrial field, the most common laser sensor is the laser displacement sensor, also known as the laser distance sensor, which can accurately measure the position, displacement and other changes of the measured object without contact, and is mainly used to detect the displacement, thickness, vibration, distance, diameter and other geometric quantities of the object.

According to the measurement principle, the principle of laser displacement sensor is divided into laser triangulation and laser echo analysis, laser triangulation is generally suitable for high-precision, short-distance measurement, and laser echo analysis is used for long-distance measurement.

01. Triangulation

The laser emitter shoots the visible red laser to the surface of the measured object through the lens, and the laser scattered by the surface of the object passes through the receiver lens and is received by the internal CCD linear camera, which can "see" this light point at different angles according to different distances. Based on this angle and the known distance between the laser and the camera, the DSP calculates the distance between the sensor and the object being measured.

At the same time, the beam is processed by analog and digital circuits at the position of the receiving element, analyzed by a microprocessor, the corresponding output value is calculated, and the standard data signal is output proportionally within the analog window set by the user. If a switching output is used, it is turned on within the set window and cut off outside the window. In addition, the analog and switching outputs can be set independently of the detection window.

The maximum linearity of the laser displacement sensor using the triangulation method can reach 1um, and the resolution can reach the level of 0.1um.

02. Wave analysis

Laser displacement sensors use the principle of echo analysis to measure distances to achieve a certain degree of accuracy. The inside of the sensor is composed of a processor unit, an echo processing unit, a laser transmitter, a laser receiver and other parts. The laser displacement sensor emits one million laser pulses per second through the laser emitter to the detected object and returns to the receiver, and the processor calculates the time it takes for the laser pulse to meet the detected object and return to the receiver to calculate the distance value, which is the average output of thousands of measurements. This is measured by the so-called pulse-time method. The laser echo analysis method is suitable for long-distance detection, but the measurement accuracy is lower than that of the laser triangulation method, and the maximum detection distance can reach 250m.

How to choose a laser sensor

It is recommended that you pay attention to the following three points:

01. Pay attention to the structure and material of the object to be measured

Typically, laser displacement sensor measurements require a complete triangular optical path. If the object to be measured has deep grooves or complex surfaces, the triangular optical path may be obscured and cannot be measured. There are also light-absorbing materials, such as black rubber, where most of the light intensity will be absorbed, and the exposure time needs to be adjusted reasonably to obtain sufficient measurement signal. In addition, strong reflections, or specular reflections of the measured object, may cause the light to return vertically without forming a diffuse reflection, which will also lead to poor measurement. Therefore, when using a laser displacement sensor, you must first fully communicate with the manufacturer, and don't take it for granted that it can be measured, but the result is not good.

02. Select the applicable parameter indicators according to your needs

The indicators commonly used to select laser displacement sensors include the accuracy of the sensor, or linearity, absolute error, etc., which refers to the degree of deviation of the measured value of the sensor from the theoretical true value, and this parameter directly reflects whether the measurement is accurate or not. The second is resolution, which refers to the minimum displacement change required by the sensor to change the number of displays, and usually the resolution parameter value is less than the accuracy. The third is the measurement velocity, which directly determines whether the measurement can keep up with the change speed of the measured object, and whether it can fully reflect the whole process of displacement change. Vibration measurements are common in applications where high measurement speed is required. Of course, there are many parameters that can determine the performance of the sensor, including the ambient temperature index, the vibration and shock index that it can withstand, etc.

03. Brand selection

There are many manufacturers of laser displacement sensors at home and abroad, and the product quality, accuracy and resolution are also very different. The quality of well-known foreign brands is good but the price is also very high, while the price of small domestic factories is not high but the stability cannot be guaranteed. Therefore, choosing a well-known brand among domestic manufacturers is the best choice, which can not only achieve localized substitution, but also ensure the reliability, stability, accuracy and other key quality indicators of the product.

Banner Sensor - The working principle and selection of laser distance sensors

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