摘要
光电编码器是一种角位移测量装置,它利用光电转换原理,将光信号转换成相应的电脉冲或数字量,从而定量输出角度值,具有体积小,精度高,工作可靠等优点。由于我国载人航天事业的发展,对轻型编码器的需求量不断增加,编码器向高精度、超小体积和智能化方向发展。但是,受传统编码器码盘刻划工艺和编码方法的限制,编码器的超小体积和高分辨力是一对不可调和的矛盾,而现有的超小型编码器都是通过在一定程度上降低编码器的精度来实现的。针对目前这种情况,提出了一种新型编码器——超小型绝对式矩阵编码器。
本文首先对绝对式光电编码器的编码原理进行了分析,采用格雷码的编码机制,提出了一种新型的矩阵编码方式,即通过刻划两圈矩阵码道进行12位矩阵编码,实现了编码器体积的超小化,其体积约为Φ30mm×15mm;并提出了增加光电读数头,以提高光学信号利用率的方法,实现了从循环二进制码到自然二进制码的转换。
其次,对超小型矩阵编码器的精码校正方法、细分方法和辨向方法进行了分析,提出了可行性方案,并在仿真电路中得以验证。
然后,对基于FPGA的数字译码系统进行了设计,通过器件选型和外围扩展电路设计,构建起基于FPGA的信号处理系统。通过FPGA的内部模块设计,实现了数字译码、FIFO (First Input First Output)和串口输出等功能。
最后,对编码器的测量误差进行了分析,并进行了实验,实验表明编码器分辨率达到了22位,精度达到了0.8”,实验数据与理论分析计算相符,达到了设计要求。该编码器突破了传统格雷码道的局限性,实现了矩阵编码器的超小化和高精密度测量,满足了航空航天、军事和纳米技术等特种行业对超小型编码器的需求。
Optical encoder is a kind of device used to measure the angular displacement; it converted the optical signal into electric pulse or digital quantity to achieve the angle output quantificationally. The encoder offered significant advantages over small cubage, high precision and reliable operation. Due to the requirement of light-duty encoder in manned space flight, the trend requires that encoder satisfies high-precision, super mini cubage and intelligentizing characteristic. However, the super mini cubage and high-precision is a pair of irreconcilable conflict under traditional reticle craftwork and encoding method. Therefore, current super miniaturization encoder was achieved by reducing the precision of encoder. To solve this problem, a new-style absolute matrix encoder was presented in the paper.
First of all, the encoding principle of absolute optical encoder was analyzed, and the Gray code was adopted for encoding. A new-style matrix encoder was presented which carried out 12-bit matrix encoding by reticling two circles, so the cubage is super-small and it can reachΦ30mm×15mm. The decoding method was achieved by increasing the number of photodiode and improving the utilization factor of optical signal.
Secondly, the issues about correction method of precise code、subdivision method and direction identification were analyzed, and a feasible scheme was produced, eventually it was validated in the simulation circuit.
Then the digital decoding system based on FPGA was designed, the signal processing system was constructed by selecting the chip and designing the exterior circuit. The inner module of PFGA actualized digital decode, first input first output, serial port output and etc.
Eventually, the measuring error of encoder was analyzed, the experiment showed that the resolution can reach 22-bit, and measuring precision can reach 0.8", the experiment data accords with theoretical calculation, it can satisfy the design requirement. The encoder breaks through the limitations of traditional gray code, and accomplishes the super miniaturization and high-precision, so it can satisfy the demands of manned space flight、military and nano technology to super miniaturization encoder.
引文
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