| Lidar is a radar system that emits laser beams to detect characteristic quantities such as the position and speed of targets.It has the advantages of high resolution,good concealment,and strong anti-interference ability.At present,it has been widely used and developed in the fields of laser guidance,laser mapping,unmanned driving and laser 3D imaging.MEMS lidar is attracting more and more attention due to its technical advantages such as low cost,high reliability and long life.However,such as large-angle and high-filling ratio scanning,wide-field high-concentration ratio broadband detection,etc.,there are several scientific problems and technical difficulties that need to be broken through.To this end,this paper has carried out researches on the theoretical estimation of lidar transmitting and receiving parameters,multi-beam MEMS large-angle scanning,non-imaging array laser echo detection,and overall performance testing and evaluation.The main research contents are as follows:(1)Theoretical estimation method of transmitting and receiving parameters of pulsed lidar.Based on the lidar distance equation,the theoretical estimation methods of lidar scanning transmitting and receiving optical structure parameters,minimum detectable power and maximum detection range are studied.For the theoretical estimation of the optical parameters,the emission light source and the collimation system are selected,and the optimal matching relationship between the emission beam spot and the MEMS scale is determined.For the theoretical estimation of the receiving optical parameters,the etendue is calculated by using the radiation angle coefficient to evaluate the lightgathering ability of the receiving optical system.By analyzing the relationship between the size of the detector surface element,the structural parameters of the receiving lens and the field of view,the optimal position of the detector is optimized to maximize the receiving field of view.For the calculation of the main performance parameters of lidar,based on the overall technical index requirements of detection probability and false alarm rate,parameters such as detection distance and ranging accuracy,field of view and angular resolution,and divergence angle are calculated.(2)MEMS scanning technology with large angle and high filling ratio.A large-angle scanning technology for multi-beam MEMS micromirrors is proposed.The optical scanning angle of an electrostatically driven MEMS micromirror with a diameter of 2.4mm under quasi-static conditions is about 16°.Using a folded optical path scanning optical system design,the six collimated beams are distributed according to 2×3 and converge on a single MEMS micromirror at different spatial angles.The designed spatial scanning angle is better than 48°×26°.Due to the deviation of different beam angles,the scanning trajectory is distorted,resulting in a large gap between the scanning beams.Two sets of 3-beam single MEMS micromirrors are used to overcome the distortion and fill the scanning gap.The multi-beam MEMS micromirror variable angle and high filling ratio scanning technology is proposed,and the farthest detection distance is divided into three distance gates: near,middle and far.By controlling the bias voltage of the MEMS micromirror,the short-range scanning angle is up to 48°×26°,followed by the medium range,and the long range is the smallest.The relationship between the spatial angular resolution of the scanning beam,the divergence angle and the beam filling ratio of the target area is established,and the optimal spatial angular resolution and beam divergence angle parameter values are determined so that the scanning beams between angular intervals do not overlap.(3)Large field of view and high concentration broadband response laser echo detection technology.A large-panel broadband four-quadrant In Ga As-APD detector structure is designed.The 2×2 four-quadrant constitutes a large-panel to increase the field of view and light-gathering capability,a single small-panel increases the detector response bandwidth,and a low-noise broadband preamplifier reduces electronic noise.At the same time,a four-quadrant detector bandwidth test system is established.The optical structure design of aspherical lens with high light-gathering ratio is proposed,and the etendue of aspherical lens is calculated by using the radiation angle coefficient,so as to evaluate the light-gathering ability of aspherical lens.Under the condition that the receiving field of view of the single lens is as large as possible,Zemax software is used for ray tracing to optimize the optical structure parameters such as the focal length and effective aperture of the lens.A combined design of an array optical receiving system with a large field of view is proposed,using a 2×3 aspheric lens array combination,the total receiving field of view is better than 48°(horizontal)× 26°(vertical).(4)Lidar imaging experiment and main performance test evaluation.Using the designed and developed multi-beam MEMS wide-angle scanning system and nonimaging wide-field wide-band receiving system,combined with the existing highprecision and high-data rate laser ranging signal processing system,a multi-beam MEMS lidar imaging experimental system is built.The overall performance of the prototype is evaluated by establishing a test target for the main performance parameters of the lidar,and conducting imaging experiments and tests on detection distance,ranging accuracy,field of view,angular resolution,and beam divergence angles at different scanning angles.Using the different retroreflectivity of different targets,the intensity information of the echo signal of the laser beam is extracted,and the ability of point cloud images to identify targets with similar characteristics is studied. |
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