Research On Autofocus Laser Triangulation Measuring Instrument

In order to alleviate conflicts between large range and high measurement accuracy of laser triangulation to a certain extent,a laser triangulation system with autofocus feature is proposed in this paper.The measuring system is based on the principle of direct-incident laser triangulation.By adjusting the mirror,the focal plane of the illumination laser can be changed,so the light spot can always focus on the surface of the object.Then the automatic focusing is realized.Firstly,the principle of laser triangulation is introduced.On this basis,a scheme of autofocus measurement system is proposed,and we explain how this system appears to work.After establishing the mathematical model of the electromechanical system,the transfer function of the voice coil motor control system is obtained.Secondly,the optical system is analyzed and the design parameters of it are determined.The design and evaluation of lighting module and imaging module are completed by ZEMAX.Then,the structure design and ANSYS simulation of the flexure hinge supporting the voice coil motor are carried out,and the mechanical structure of the whole system is designed.An all-analog voice coil motor drive circuit,which is based on a constant current source is designed,and analyzed by Multisim circuit simulation software.After that,the software system is developed based on MATLAB.Finally,the voice coil motor drive circuit,the flexure hinge and the positioning system are tested respectively.After calibrating the measurement system,autofocus experiments and a simple measurement experiments are performed.The results show that the linearity of the flexure hinge is 2.98%,and the coefficient of elasticity is 1.990N/mm.The positioning system of voice coil motor has a step response overshoot of about 4%,stability time of 120 ms,positioning noise of ±0.3μm and displacement resolution of 6μm,with load of 17.1Ω and 2.8mH.