单圈绝对式编码器相比于增量式编码器及传统的绝对式编码器有独特的优势, 其关键技术在于译码系统的设计及译码算法的研究。为了提高单圈绝对式编码器集成度、响应速度及精度, 设计了译码系统, 该系统采用线阵CCD作为码盘图像光电转换装置, 并利用FPGA实现电路控制及译码算法。同时提出了新的译码算法, 该算法一方面将CCD输出信号二值化后的电平信号高电平计数, 判断组合得到粗码信息; 另一方面应用质心法进行细分定位, 通过计算条纹质心与虚拟中心的偏差得到细分角度值。最后, 通过两者结合得到角度信息。基于该系统研制的经纬仪样机精度达到2″。

In comparison with incremental and traditional absolute encoder, the single-ring absolute encoder processes more advantage. And the research of decoding system and algorithm are essential to the single-ring absolute encoder. In order to improve single-ring absolute photoelectric encoder′s circuit integration, response speed and accuracy, a decoding system was designed in this paper. Linear CCD was used in this system as the disc image receiving and photoelectric conversion device which also provided the basement of subdivision algorithm. And FPGA was used to achieve circuit control and decoding algorithm. A new decoding algorithm was also proposed in this paper. On the one hand, the coding information was achieved by counting high electrical level of the binaryzation signal of CCD′s output. Coding information was obtained by recognition of the disc image and combination of 12-bits coding number. On the other hand, precise value was obtained by calculating the shifting between the centroid of image and virtual center. The centroid of stripe was calculated based on CCD centroid location algorithm. Finally, the value of angle was precisely received from combination of these two values. A prototype of theodolite was developed based on this single-ring absolute encoder decoding system and can reach the accuracy of 2".