Research On Parallel Laser Range Measurement Technique Used In 3-D Measurement

Three-Dimensional (3-D) measurement technique is an important research subject of modern industry measurement domain, it has the widespread application in many social domains like reverse-engineering, national defense, medicine, cultural relic preservation. 3-D measuring technique are multifarious and various now. But no method can satisfy large-scale measurement, high-precision and high speed measurement. The laser parallel range measurement technique this thesis proposed namely belongs to the time-of-flight method. The system can measure multi-spots simultaneously each time so that the measurement speed is greatly raised. It also can guarantee the range finder precision in a millimeter level. Cooperating with the scanning movement of the machine, the system can complete high-speed, high-accuracy and large-scale 3-D measurement. What's more, it also has merits such as non-contact measurement, small influence of being sheltered, and so on .So the technique a very good application prospect.The 3-D measurement system of laser ranging type get 3-D coordinates of each spot via fast range measuring and goniometric point by point, its main components are goniometric, range finder as well as scanning control system. The thesis conducts the key research aiming at parallel range measurement sensor system of its key components, and designed laser parallel range measuring system based on sine-wave modulation. The design mentality is as follows: Produce multi-channel modulation signals whose frequency difference is Af (several kHz )using DDS technology, these modulation signals drive corresponding laser diode(LD), the multi-channel modulation laser which has been collimated and adjusted irradiate at object surface , the returns light arrive at the identical APD receiver. Then the tiny current signal converts to corresponding voltage signal. Afterwards, measurement signal of high-frequency becomes low-frequency and easier measurement signal. Next, collect reference signal and measurement signal through high speed A/D component under DSP's control, the sampled data send in DSP and carry on phase demodulation operation, work out phase difference of each modulation signal after round-trip on measured distance, what's more, aiming at the reduction of precision of the phase demodulation because of inevitable factors such as noise, disturbance between signals , all-phase FFT spectral emendation is adopted and precision of the phase demodulation is highly raised. Afterwards, the round-trip time can be set out through the phase difference, and then each distance can be calculated farther. This method of parallel phase demodulation and range measurement make full use of the frequency band and the high speed and powerful digit phase demodulation function of DSP, may realize multi-channel laser parallel range measurement, and improve the speed and efficiency of range measurement.The preliminary experiment and simulation result indicated that the system's technical approach is feasible and achieved the expectation effect, which establish the technology foundation of 3-D measurement system that has practical application function.