Design of comprehensive performance testing equipment for laser rangefinder based on AVR

Since the traditional laser rangefinder performance test must be carried out outdoors to test the target and is restricted by weather conditions, the technical survey and daily maintenance are greatly restricted. In order to overcome the above problems, the author designed a laser rangefinder comprehensive performance test device based on AVR microcontroller. With the help of this device, the digital test of ranging accuracy, ranging capability, ranging logic, single pulse energy, etc. of different types of laser rangefinders is completed, which greatly improves the detection efficiency and test accuracy.

1 Design

The basic idea of ​​this scheme is based on the working principle and laser transmission process of the simulated laser rangefinder. When the laser rangefinder is working, it first emits a laser pulse from its transmitting channel, which is transmitted through the atmosphere and irradiated on the measured object, and then diffusely reflected. The receiving channel of the laser rangefinder receives the diffusely reflected laser echo. The laser rangefinder is equipped with a laser pulse transmitting, receiving and timing module. The distance traveled by the laser pulse can be calculated according to the time from the emission to the return, so as to obtain the distance between the measured target and the laser rangefinder. The comprehensive performance detection equipment of this scheme corresponds to the receiving and transmitting channels of the laser rangefinder, and provides the transmitting and receiving channels respectively. The timing module is also set up inside the detection equipment accordingly to realize the dual simulation of the target echo time and energy at a certain distance. The detection equipment can replace the target simulated echo pulse to realize the automatic and digital detection of the ranging performance of the laser rangefinder. The overall structure of the comprehensive performance detection equipment is shown in Figure 1.

2 System Structure Diagram

The circuit principle block diagram of the comprehensive performance testing equipment is shown in Figure 2.

It mainly includes microprocessor system, panel display and button control circuit, precision delay signal generator, narrow pulse power drive and luminous intensity control circuit, precision timer, laser pulse synchronizer, laser pulse energy detector and preamplifier, high-speed data acquisition converter and printer control circuit, etc.

3 Key technologies

3.1 Comprehensive test of laser ranging performance by “dual-frequency dual-optical path coupling” method

The basic idea of ​​this scheme is to simulate the diffusely reflected echo of a distant target by a semiconductor laser. After simulating the spectrum and spatial characteristics of the echo, the logic unit of the laser can be driven to work. The flight time of the laser pulse at the corresponding distance is realized by the precision delay module. In this way, the delay characteristics of the laser pulse in space are converted into time characteristics, thereby bringing the distant target closer to the front end of the instrument under test from a certain distance, replacing the traditional detection method that the performance detection of the laser rangefinder must have an actual cooperative target at a distance. As shown in Figure 3.

3.2 Detection of ranging logic

When the detection equipment receives the "sampling" pulse, it controls the precision delay device to start timing. The AVR single-chip microcomputer controls the precision delay device to send out 1, 2, and 3 analog echo pulse signals respectively. These analog echoes correspond to different target distances in time. In this way, several laser pulses can be received on the receiving channel of the laser rangefinder. By operating the "select" knob of the laser rangefinder and displaying them respectively, it can be judged whether the distance measurement logic and distance selection function of the laser rangefinder are normal. The specific implementation method is shown in Figure 4.

3.3 Ranging capability test

This scheme detects the range of the laser rangefinder. First, the AVR single-chip microcomputer is used to set the delay time of the precision delay device to the laser pulse running time corresponding to the range of the laser rangefinder being measured. When the detection equipment receives the "sampling" pulse, it controls the precision delay device to start timing. After the timing is over, the AVR single-chip microcomputer controls the precision delay device to send out a simulated echo pulse signal. At the same time, the AVR single-chip microcomputer luminous intensity control circuit controls the energy of the laser pulse emitted by the semiconductor laser to make the energy equivalent to the energy of the target echo at the corresponding distance. In this way, the target echo pulse on the range can be corresponded on the receiving channel of the laser rangefinder. According to the display result of the laser rangefinder, it can be judged whether the laser rangefinder can meet the range index requirements under normal optical axis conditions.

3.4 Technology-based precision timing circuit module

This comprehensive performance testing equipment adopts constant ratio timing technology to develop a video separation module, which realizes precise delay and precise simulation of distant target echoes. The principle function block diagram is shown in Figure 5.

3.5 "Two-way adjustment" multi-dimensional adjustment platform with independent intellectual property rights

The comprehensive performance testing equipment adopts a "two-way adjustment" adjustment platform with independent intellectual property rights, which realizes the five-dimensional adjustability and rapid conversion of the laser emission and receiving channels, making the detection interface widely applicable to various types of laser rangefinders. Before this, laser rangefinder performance testing required the development of a dedicated mechanical interface for a certain type of equipment, because the various types of laser rangefinders have great differences in the aperture size, horizontal position, and height position of the emission and receiving channels, and even in the left and right position configuration. This project successfully developed a "two-way adjustment" adjustment platform for the first time, which allows the emission and receiving channels to be adjusted over a large range in height and horizontal directions, and the left and right positions can be interchanged, making this detection equipment widely applicable to various platforms and single laser rangefinder modules.

4 Conclusion

This equipment can change the previous situation that the laser rangefinder performance test must be carried out outdoors to test the target and is restricted by weather conditions. It allows technical surveys and daily maintenance to be easily completed indoors. The test results are displayed digitally, which greatly improves the test efficiency and test accuracy. The test equipment is equipped with a three-dimensional adjustment platform. The positions of the laser emission and receiving devices can be adjusted arbitrarily and interchangeably, making it very convenient to adjust the aiming. It can test different types of laser rangefinders. The test equipment can also detect the laser pulse energy. As a laser energy meter, it can quickly detect the output laser energy of various laser emission equipment. After testing by the Jiangsu Provincial Technical Supervision Laser Parameter Measurement Station, various indicators have reached the leading level among similar instruments in China. It was trial-produced in May 2008. After being used by the Pingdingshan Municipal Technical Supervision Bureau and Henan Geological and Mineral Group Geotechnical Engineering Co., Ltd., it has been shown to have good results.