Research On Laser Ranging For No-cooperative Target Based On ApFFT

High-precision laser rangefinder has been occupied by foreign products for many years, and the related technologies have not been known for public because of its involving military security. Currently, our products of laser ranging is far away from the foreign products because of its low-precision and unstable performance. This paper is based on school-enterprise cooperation platform, and a high-precision phase-shift laser rangefinder is designed.The main contents are as follows:1. Several common laser ranging technologies is introduced. The key technologies of phase-shift laser ranging are focused, such as the multi-ruler measuring techniques, phase measurement techniques, and the difference-frequency technology for phase measurement. Then overall system structure is designed and the system errors have been analyzed.2. The signal source circuit is designed based on DDS technology. Laser modulation circuit is well designed, and the modulation depth is more than 95% at 100 MHz frequency, which helps to improve the SNR of the system. APD bias voltage circuit is designed with auto temperature compensation based on TPS40210. For the difference-frequency signal extraction, the traditional method and the APD heterodyne mixing method are both introduced, focusing on the technology of APD as an optoelectronic mixer. Advantages and disadvantages of the two methods are analyzed; then we choose the traditional method based on the actual situation of the project, and finish the relevant circuits design.3. Three algorithms of digital phase-detection are introduced. We select the ap FFT algorithm for phase-detection based on the simulation analysis. The ap FFT algorithm is realized on FPGA, and the simulation for the riming time of algorithm is finished. The software scheme of system is designed base on ARM and FPGA. ARM is in charge of the HCI and the control of FPGA. FPGA is mainly responsible for the algorithm of phase-detection and the initialization or configuration of related hardware circuits.4. The PCB design and prototype production of laser rangefinder have been completed. A series of experiments have been done for the modules testing and the whole prototype testing. The effects of noise on ranging accuracy have been analyzed. Experimental results show that the designed laser rangefinder realized the measurement standard deviation better than 5mm in the range of 0.5~7m without cooperative target, and a single measurement time is less than 2.2ms.