Development of super-accurate angular encoder system with multi-detecting heads using VEDA method

Abstract

In response to the demand for high accuracy and high resolution of angular positioning and movement of CNC machine tools, the demand for rotary encoder systems has also increased for the detection of ultra- precise angular position and movement. Authors had developed a new principle of self-calibration with multiple detecting head which enables detection of the error components of higher order with the less number of detecting heads. The system developed for this paper consists of a rotary scale with grating, sensor head unit with build-in 6 pieces of sensor heads and data processing box containing a circuit to process analog signals from the sensor head unit and output angular data applied calibration value in real time. This paper evaluates the performance of this system. In addition, the angular accuracy of the rotary encoder for servo control inside a machine tool was examined with reference to the self-calibration of the rotary encoder using the proposed method. Measured data of the accuracy of that were also utilized to generate the calibration data of the rotary encoder, and the rotary encoder was calibrated with the calibration data. The measured accuracy showed a resolution of 1/2³⁶ . It was confirmed that the angular positioning accuracy was improved because of the calibration.