Abstract

Optical encoders are widely used in applications requiring precise displacement measurement and fluent motion control. To reach high positioning accuracy and repeatability, and to create a more stable speed-control loop, essential attention must be directed to the subdivisional error (SDE) of the used encoder. This error influences the interpolation process and restricts the ability to achieve a high resolution. The SDE could be caused by various factors, such as the particular design of the reading head and the optical scanning principle, quality of the measuring scale, any kind of relative orientation changes between the optical components caused by mechanical vibrations or deformations, or scanning speed. If the distorted analog signals are not corrected before interpolation, it is very important to know the limitations of the used encoder. The methodology described in this paper could be used to determine the magnitude of an SDE and its trend. This method is based on a constant-speed test and does not require high-accuracy reference. The performed experimental investigation of the standard optical linear encoder SDE under different scanning speeds revealed the linear relationship between the tested encoder’s traversing velocity and the error value. A more detailed investigation of the obtained results was done on the basis of fast Fourier transformation (FFT) to understand the physical nature of the SDE, and to consider how to improve the performance of the encoder.

Highlights

  • Optical encoders are usually the most reliable devices for precise displacement measurement and motion control

  • Performance of the tested linear encoder was checked under different scanning speeds

  • The maximal traversing velocity specified by a vendor of the encoder was 1 m/s

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Summary

Introduction

Optical encoders are usually the most reliable devices for precise displacement measurement and motion control. Due to their high accuracy, resolution, and repeatability, as well as their ability to work under different environmental conditions and their relatively low price, they are used in a variety of applications. Some examples are manually controlled machine tools and computer-numericalcontrol (CNC) machines [1,2,3,4], robotics [5,6,7,8,9,10], servosystems [11,12,13,14], monitoring and fault diagnosis systems [15,16,17,18], tracking systems [19,20], linear and rotary positioning stages [21,22,23,24], and other precision-positioning applications [25].

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