A real-time distance measurement data processing platform for multi-axis grating interferometry type optical encoders

Abstract

Among various nano-scale linear displacement sensors, grating scales have been widely used in industrial fields due to their strong anti-interference ability, cost-effectiveness and compactness. The main development directions of the scale are: high precision, large range, high speed, high dimension and absolute type. Our team has completed the optical layout design of the absolute two-dimensional grating rule, which brings new challenges to the design data acquisition and processing hardware system due to the requirements of multiple dimensions and high speeds. There is no real-time data processing system suitable for absolute two-dimensional scales. This paper presents our latest progress in designing and implementing an absolute two-dimensional grating distance measurement real-time data processing platform. Our platform mainly contains four different functional modules. First, the circuit conditioning module performs I-V conversion and signal amplification and filtering on the weak current signal output from the photodiode. Secondly, an 8- channel high-speed data acquisition module with 14-bit resolution and 80 MSPS maximum sampling rate was designed to convert analog laser pulse signals into digital signals. Third, we have established a real-time data processing module that allows 16 bits of data to be entered in the FPGA to calculate the absolute two-dimensional scale distance. Finally, a data transfer module based on 128MB DDR SDRAM and USB 2.0 was added so that we can easily debug the platform on a PC. The performance of our system is evaluated in real time. The test platform consists of a laser, a twodimensional grating optical path, and our data processing system. The absolute two-dimensional scale has a moving speed of 1m/s, a signal frequency of 10MSPS, a laser emitting signal wavelength of 540nm, and a moving distance of 10-15mm. Experimental results show that our system can output at a rate of 2500 points per second. Measurement results, measurement deviation is less than 50nm.