The Operation and Use of Laser Distance Measurement Sensors
1. Development of time-of-transit laser distance sensors
The application of laser in the detection field is very extensive, the technical content is very rich, and the impact on social production and life is also very obvious. Laser ranging is one of the earliest applications of lasers. This is because the laser has many advantages such as strong directionality, high brightness, and good monochromaticity. Before 1965, the Soviet Union used laser to measure the distance between the earth and the moon (380´103km) with an error of only 250m. In 1969, the Americans landed on the moon with a rear reflector on the moon, and also used lasers to measure the distance between the earth and the moon, with an error of only 15cm. The basic principle of using laser transmission time to measure distance is to determine the target distance by measuring the time required for the laser to go back and forth. . Right now:. Although time-of-transit laser ranging has a simple principle and structure, it was mainly used in military and scientific research in the past, but it is rare in industrial automation. Because the price of the laser ranging sensor is too high, generally several thousand dollars. Virtually all industrial users are looking for a sensor that enables precise distance detection over longer distances. Because in many cases, installing sensors at close range will be limited by physical location and production environment, today's transit time laser distance sensor will solve the problem for engineers in such occasions.
2. Working principle
When the time-of-transit laser sensor works, the laser diode is aimed at the target and emits laser pulses. After being reflected by the target, the laser light scatters in all directions. Part of the scattered light returns to the sensor receiver, where it is captured by the optical system and imaged onto the avalanche photodiode. An avalanche photodiode is an optical sensor with internal amplification so that it can detect extremely faint light signals. The distance to the target can be determined by recording and processing the time elapsed from the time the light pulse is sent until it is received back. Transit Time Laser sensors must determine transit time with extreme precision because the speed of light is so fast. For example, the speed of light is about 3´108m/s, in order to achieve a resolution of 1mm, the electronic circuit of the transit time ranging sensor must be able to distinguish the following extremely short time: 0.001m¸ (3´108m/s) = 3ps To distinguish the time of 3ps, this is an exorbitant requirement for electronic technology, and the cost of implementation is too high. But today's cheap transit-time laser sensors neatly circumvent this obstacle, using a simple statistical principle, the average rule, to achieve a resolution of 1 mm and to guarantee a fast response.
3. Solve problems that cannot be solved by other technologies
Time-of-transit laser distance sensors can be used where other technologies cannot. For example, a common photoelectric sensor that counts the light reflected from a target can also perform a large number of precision position detection tasks when the target is very close. However, when the target is far away or the color of the target changes, it is difficult for ordinary photoelectric sensors to cope. While advanced background noise suppression sensors and triangulation sensors work well when the color of the target changes, their performance becomes less predictable when the target angle is not fixed or the target is too bright. In addition, triangulation sensors generally have a range limited to within 0.5m. Ultrasonic sensors are also often used to detect objects at greater distances though, and because they are not optical, they are not affected by color changes. However, ultrasonic sensors measure distance based on the speed of sound, so they have some inherent disadvantages and cannot be used in the following situations. ①When the target to be measured is not perpendicular to the transducer of the sensor. Because the target of ultrasonic detection must be within an angle of not more than 10° from the vertical azimuth of the sensor. ②When the beam diameter is required to be small. Because the general ultrasonic beam is 0.76cm in diameter when it is 2m away from the sensor. ③Occasions where visible light spots are required for position calibration. ④ windy occasions. ⑤ vacuum occasions. ⑥ Occasions where the temperature gradient is large. Because in this case, the speed of sound will change. ⑦ Occasions that require quick response. The laser distance sensor can solve the detection of all the above occasions.
