Research On Key Technologies Of MEMS-based Large Scannig Laser 3D Image Sensor

With the development of artificial intelligence,sensor,automation and the interaction between human and nature,it is an urgent need to capture the complex environmental perception technology.Laser 3D image sensor is one of the preferred sensors in the field of unmanned vehicle due to its advantages including high measurement precision,strong directivity,fast response rate and being unaffected by ground clutter.Micro-Electro-Mechanical System(MEMS)scanning laser 3D image sensor has caused great concern becaused of it advantages of light weight,fast speed and low cost,which leads to be one of the most promising technologies to overcome many defects of traditional mechanical rotary laser 3D image sensor,and close to the real practical applications.This paper focuses on the scientific problems and key technologies of MEMS 3D image sensor,such as the kinetic process and tracking control method of MEMS,the large field MEMS scanning technology,high sensitivity laser receiving technology and high precision return pulse timing and measurement technology,the main contents of this research paper are listed as follows:Firstly,the kinetic characteristics of MEMS's electrostatic actuation are theoretically analyzed,and the tracking control method is found.Through establishing the kinetic model of MEMS electrostatic actuation,the dynamic process under the conditions of external excitation function is analyzed,and the periodic motion law of the stability of MEMS is revealed.At the same time,the tracking control method can be carried out according to the control instructions.The relationship between scanning voltage of MEMS and the optical angle of the scanning beam is tested.The scanning voltage and the instruction path function are controlled to perform the high speed and high efficiency scanning of MEMS scanning angle and scanning pattern.Secondly,according to the shortcomings of MEMS's small mechanical angle and large divergence angle of the traditional MEMS-based optical angle extension system,a large field scanning optical system consisted of an f-? lens and an object telescentric lenses group is discussed in order to solve the above disadvantages.The physical model of large field scanning optical system is established,thenafter the the angle extension relationship between focal length of f-? lens and that of object telescentric lens group is analyzed,employing the commonly used optical design software,the structure parameters of optical system based on this method is completed.By ray trace simulation,the laser spotsize at distance of approximately 100 m is evaluated,with result of less than 10 cm,obtaining a large scanning angle about 60?× 60?.This method can also further extend the scannig to a larger view.Thirdly,aiming at the shortage of the traditional receiving optical system constructed of imaging objective lens with field mirror(or optical fiber tap,or immersion lens),the non-imaging objective lens system is investigated to solve the problem of small photosensitive surface in a large receiving field of view.By employing the etendue,the evaluation model of non-imaging optical system is established;Comparing with the optical utilization of the imaging system and the non-imaging system,a three-piece non-imaging optical system is designed and optimized in optical design software,obtaining the receiving field of view greater than 50??50? and no more than 3mm in diameter of the receiving photosentitive surface.Fourthly,based on high speed integrated chip,a time interval measurement module and a constant fraction discrimination module are discussed and designed,respectively,the time measurement accuracy of sub-nanosecond is realized.The pulse time discrimination module work with nanosecond pulse is developed to solve the timing precision of sub-nanosecond;the time-to-digital converter module with data rate in hundreds kHz order of magnitude is developed to realize the communication with upper computer at high data rate;Using the time-to-digital converter chip GP22,the double stop-channels differential time measurement method is opted to realize the accuracy of sub-nanseconds.Fifthly,the optical system,laser,detector,signal processor and mechanical structure modules are optimized;then a set of MEMS scanning laser 3D image sensor principle prototype is integrated,and some imaging experiments are taking in this prototype,in order to verify the rationality of the optimization design and tease out the problem need to improve.As the laser emission receiving system and MEMS scanning system are two independent subsystems,analyzing the the inconsistency problem betwwen the motion law of MEMS scanning track and pulse transmition,solving the alignment problem of the x-y coordinate of MEMS system and the z coordinate obtained from laser transmitting receiving system.Because what the laser range finding measured is actually the radial distance,it needs to study the transformation from cylindrical coordinate system to cartesian coordinate system,in order to solve the problem of the pillow distortion in 3D image.