Prototype Design Of 3D Lidar System Based On MEMS Mirror Scanning

Recent years,with the rapid development of indoor robots and driverless technologies,lidar products have broad applications in the consumer market.However,current mainstream products for consumer-grade 3D lidar are mechanical ones,which are very mature technology but with complicated optical structures.It is very difficult for them to assemble and complete mass production.In addition,to obtain higher density laser point clouds,the number of laser pulse diodes and APD detectors must be increased,which will increase system complexity,making cost reduction difficult.This thesis focuses on the design requirements for a low-cost,miniaturized MEMS 3D lidar system and proposes a lidar prototype based on a two-dimensional MEMS mirror scanner.Firstly,the selection of a pulsed laser diode at the laser-emitting end and the design of its driving circuit are introduced.In the optical design,the optical fiber coupling and collimation schemes are adopted and an optical simulation is conducted,to ensure that the laser beam divergence angle and spot size meet the design specifications.Then,a circuit simulation is conducted to verify the transimpedance amplifying circuit,voltage amplifying circuit,and voltage comparator circuit.The effective reception of the laser pulse sequence information from the laser emitting end reflected by the target is realized.Finally,a twodimensional quasi-static scanning working mode is selected and the theoretical analysis and simulation of the MEMS mirror reflection scanning characteristics are conducted to synchronize the laser pulse sequence emission with the two-dimensional quasi-static scanning of the MEMS mirror.The ranging and display of the MEMS 3D lidar prototype is realized.The experimental results show that the prototype system achieves a 3D imaging effect with a range of 5m,range accuracy of ±3cm,scanning field of 20°×20°,angle resolution of 0.4°×1°,and frame rate of 5Hz.The main research results and innovations of this thesis are summarized as follows:(1)Due to the theoretical modeling of the MEMS mirror's physical model,the scanning characteristics of quasi-static MEMS mirrors are analyzed.Aiming at the chattering phenomenon generated in the input and output process of the traditional sliding mode control algorithm,a novel closed-loop sliding mode control algorithm is proposed and then verified by simulation.The results show that the proposed method may reduce the chattering caused by the traditional sliding mode control algorithm and improve the scanning accuracy of both the output trajectory tracking and the control input in the presence of model uncertainty and external disturbance.(2)Based on the analysis of several common lidar ranging methods,a new pulse Barker coding correlation ranging algorithm is proposed.A bipolar reference sequence is used by the algorithm as it produces lower side lobes after correlation calculation,which may enable better results than traditional unipolar pulse coding techniques.In addition,it is insensitive to changes in surface reflectance of obstacles and has strong anti-interference ability,which are verified through prototype performance tests.(3)Based on lidar design theory,a low-cost,miniaturized MEMS 3D lidar prototype is proposed.This scheme adopts a direct detection ranging system,non-coaxial optical path design,and MEMS mirror to scan the field of view,lowing costs through a reduction in the number of laser pulse diodes,APD detectors,and bandwidth requirements.Also,this scheme reduces the size of the MEMS mirror.Therefore,a miniaturized MEMS 3D lidar prototype is built at an overall size of 14×12×8.3cm,which may be a theoretical basis for the design of MEMS mirror 3D lidar,and may provide practical reference meaning for its industrialization.