Han Yaodong, Ni Kai, Li Xinghui, Wu Guanhao, Yu Kangning, Zhou Qian, Wang Xiaohao
Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China.
Department of Precision Instrument, Tsinghua University, Haidian District, Beijing 100084, China.
Sensors (Basel). 2020 Apr 16;20(8):2266. doi: 10.3390/s20082266.
Among various nanometer-level displacement measurement methods, grating interferometry-based linear encoders are widely used due to their high robustness, relatively low cost, and compactness. One trend of grating encoders is multi-axis measurement capability for simultaneous precision positioning and small order error motion measurement. However, due to both lack of suitable hardware data processing platform and of a real-time displacement calculation system, meeting the requirements of real-time data processing while maintaining the nanometer order resolutions on all these axes is a challenge. To solve above-mentioned problem, in this paper we introduce a design and experimental validation of a field programmable gate array (FPGA)-cored real-time data processing platform for grating encoders. This platform includes the following functions. First, a front-end photodetector and I/V conversion analog circuit are used to realize basic analog signal filtering, while an eight-channel parallel, 16-bit precision, 200 kSPS maximum acquisition rate Analog-to-digital (ADC) is used to obtain digital signals that are easy to process. Then, an FPGA-based digital signal processing platform is implemented, which can calculate the displacement values corresponding to the phase subdivision signals in parallel and in real time at high speed. Finally, the displacement result is transferred by USB2.0 to the PC in real time through an Universal Asynchronous Receiver/Transmitter (UART) serial port to form a complete real-time displacement calculation system. The experimental results show that the system achieves real-time data processing and displacement result display while meeting the high accuracy of traditional offline data solution methods, which demonstrates the industrial potential and practicality of our absolute two-dimensional grating scale displacement measurement system.
在各种纳米级位移测量方法中，基于光栅干涉测量的线性编码器因其高稳健性、相对低成本和紧凑性而被广泛使用。光栅编码器的一个发展趋势是具备多轴测量能力，以实现同步精密定位和小阶次误差运动测量。然而，由于缺乏合适的硬件数据处理平台和实时位移计算系统，要在所有这些轴上满足实时数据处理要求并同时保持纳米级分辨率是一项挑战。为了解决上述问题，本文介绍了一种以现场可编程门阵列（FPGA）为核心的光栅编码器实时数据处理平台的设计与实验验证。该平台具备以下功能。首先，使用前端光电探测器和I/V转换模拟电路来实现基本的模拟信号滤波，同时采用一个八通道并行、16位精度、最大采集速率为200 kSPS的模数转换器（ADC）来获取易于处理的数字信号。然后，实现了一个基于FPGA的数字信号处理平台，它能够并行且实时地高速计算与相位细分信号对应的位移值。最后，位移结果通过USB2.0经通用异步收发器（UART）串行端口实时传输到PC，从而形成一个完整的实时位移计算系统。实验结果表明，该系统在满足传统离线数据求解方法高精度要求的同时，实现了实时数据处理和位移结果显示，这证明了我们的绝对二维光栅尺位移测量系统的工业潜力和实用性。
