激光跟踪仪是一种用于大尺寸空间精密几何坐标测量的重要光学测量仪器。PSD是激光跟踪仪实现对合作目标精密跟踪的脱靶量传感器件, 其探测精度直接影响跟踪测量性能。首先, 简要介绍了激光跟踪测量系统及基工作原理, 然后根据系统需求提出了脱靶量精密探测方案。重点讨论了I/V变换、信号放大、滤波、参数匹配等硬件设计方法以提高PSD输出微弱电流信号的稳定性, 研究提出了基于FPGA和有限状态机的去极值平均滤波算法和扩展除法运算算法分别用于降低噪声干扰与提高测量精度; 数据表明在4mm×4mm的区域内脱靶量探测稳定度优于±2μm。采用该方法实现激光跟踪仪对合作目标的动态跟踪, 很好地满足了激光跟踪仪的精密快速跟踪需要。

Laser tracker is an important optical instrument for precise geometric coordinate measurement in large scale. Position sensitive detector(PSD) is a core miss-distance detecting sensor in laser tracking system, which achieves precise position tracking of cooperation target. The detecting precision has remarkably direct influence on the performance of tracking and measurement. Firstly, one laser tracking measurement system was presented, and the working principle of the system′s tracking unit based on PSD was introduced. Then the miss-distance detecting module was designed and built based on PSD according to the actual demand. The module′s signal process circuit for weak signal detection was emphatically analysed, which met the requirements of PSD driving, I/V conversion, signal amplification, analogy signal filtering, parameter matching and efficient using of AD resources simultaneously. The output signal of PSD module was acquired by a four-channel and synchronous analogy to digital converter. The signal was processed by FPGA which worked in the form of finite state machine. A composite digital filtering algorithm revised from median and mean filtering method was proposed to reduce noise interfering. Based on FPGA an extended divider was put forward to improve accuracy of measurement. Through omitting the low-order byte of the numerator of coordinate formula, one two-step operation of the divider was used to extract effective decimal places. The experimental result shows that the stability of spot position is better than ±2.0 μm in the square effective area 4 mm×4 mm. The further tracking experiment indicates the miss-distance detection method can well meet the demand of the precise and rapid target tracking.