First, the development of transmission time laser distance sensor

The application of laser in the field of detection is very extensive, and 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 directivity, high brightness, and good monochromaticity. Before 1965, the Soviet Union used laser to measure the distance between the Earth and the Moon (380103km) with an error of only 250m. In 1969, when the Americans landed on the moon, they placed mirrors on the lunar surface. They also used lasers to measure the distance between the earth and the moon. The error was only 15 cm.

The basic principle of using laser transmission time to measure distance is to determine the target distance by measuring the time it takes for the laser to travel to and from the target.

Transmission time Laser ranging is simple in principle and simple in structure, but it was mainly used in military and scientific research, but it is rare in industrial automation. Because laser ranging sensors are too expensive, typically in the thousands of dollars, high prices have been the main reason hindering their widespread use. Recently, however, laser ranging sensors have made significant advances in technology, causing their prices to drop to a few hundred dollars, making it the most cost-effective means of detection for many long-range inspections in the future.

The main reason for such a large price cut is the sharp increase in the two recent consumer products.
One is a cellular phone. Since the emergence of cellular mobile communications in the 1970s, the development has been extremely rapid, and users have almost doubled every year, especially in recent years. The development of cellular phones has prompted the telecommunications industry to provide low performance noise amplifiers with excellent performance. The core component of this amplifier is the transmission time timer.

The second is the DVD player. The development of DVD players has driven the development of low-cost visible light diode lasers. The laser from this diode laser has better focusing characteristics for ultra-high-density digital storage. Compared to infrared laser diodes developed for CD players just a few years ago, their focusing characteristics are many times better.

It is the emergence of these new devices, coupled with surface-mount circuit board technology and clean and inexpensive power supplies, which have made the development of transmission time laser distance sensors to a new level.

In fact, all industrial users are looking for a sensor that enables precise distance detection over long distances. Because in many cases the proximity of the sensor will be limited by the physical location and production environment, today's transmission time laser ranging sensor will solve the problem for engineers in such situations.

Second, the working principle

When the transmission time laser sensor is working, the laser diode is first directed to the target to emit a laser pulse. The laser scatters in all directions after being reflected by the target. Part of the scattered light is returned to the sensor receiver, which is received by the optical system and imaged onto the avalanche photodiode. The avalanche photodiode is an optical sensor with an internal amplification function, so it can detect extremely weak optical signals. The target distance can be determined by recording and processing the time elapsed from the time the light pulse is emitted until the return is received. The transmission time laser sensor must measure the transmission time extremely accurately because the speed of light is too fast.

For example, the speed of light is about 3108 m / s, in order to achieve a resolution of 1 mm, the electronic circuit of the transmission time ranging sensor must be able to distinguish the following very short time:
0.001m (3108m / s) = 3ps

To distinguish the time of 3ps, this is an excessive demand for electronic technology, and the cost is too high. But today's inexpensive transmission-time laser sensors cleverly avoid this obstacle, using a simple statistical principle, that is, the averaging rule achieves a resolution of 1 mm and guarantees response speed.
Third, solve problems that other technologies cannot solve
The transmission time laser distance sensor can be used in applications where other technologies are not available. For example, when the target is very close, the calculation of a common photoelectric sensor from the target reflected light can also perform a large number of precise position detection tasks. However, when the target distance is far or the target color changes, the ordinary photoelectric sensor is difficult to cope with.

Although the advanced background noise suppression sensor and the triangulation sensor work well in the case of a target color change, the predictability of performance is deteriorated when the target angle is not fixed or the target is too bright. In addition, the triangulation sensor is generally limited to within 0.5m.

Ultrasonic sensors are also often used to detect objects that are far apart, and because they are not optical devices, they are not affected by color changes. However, the ultrasonic sensor measures the distance based on the speed of sound, so there are some inherent disadvantages that cannot be used in the following cases.

1 When the target to be tested is not perpendicular to the transducer of the sensor. Because the target of ultrasonic testing must be within an angle of no more than 10¡ã from the vertical azimuth of the sensor.

2 Where the beam diameter is small. Because the general ultrasonic beam is 0.76 cm in diameter when it is 2 m away from the sensor.

3 Where the visible spot is required for position calibration.

4 windy occasions.

5 vacuum occasions.

6 Where the temperature gradient is large. Because this situation will cause a change in the speed of sound.

7 need to respond quickly.
The laser distance sensor can solve the above detection in all cases.

Fourth, a wide range of uses in the field of automation
Nowadays, in addition to ultrasonic sensors and ordinary photoelectric sensors, the automatic detection and control method has added a new method that can solve long-distance measurement and inspection - transmission time laser distance sensor. It provides application flexibility for a variety of different situations, which can include the following:

1 device positioning.

2 Measure the level of the material package.

3 Measure the distance of the object on the conveyor belt and the height of the object.

4 Measure the diameter of the logs.

5 Protect the overhead crane from collision.

6 no error check occasions.

Five, several application examples

1.Measure the width of the box on the conveyor belt
Two divergent transmission time laser sensors are used to face each other on both sides of the conveyor. Because the size of the box on the conveyor belt is not fixed, so each sensor measures its distance from the box, set a distance L1, the other is L2. This information is sent to the PLC, which subtracts L1 and L2 from the total distance between the two sensors to calculate the width W of the box.

2.protect the hydraulic forming die
The robot puts a preformed tube into the lower die of the hydroforming machine, and the operator must ensure that the position is accurate for each release. Before the upper die falls, a divergent sensor measures the distance from the critical section of the pipe, which ensures that the die is in the correct position before closing.

3.two-axis crane positioning

The reflector is mounted with two reflective sensors mounted on the two mobile units of the overhead crane. One unit moves back and forth and the other moves left and right. When the crane drives the plate roller, the two sensors monitor the distance to the reflector and the PLC can continuously track the exact position of the crane.
With this new low-cost transmission time laser ranging sensor, reflective or multi-color target long-range position detection is no problem even when the angle of detection is changed.