A method of fine size measurement for telecentricity-based error compensation

Abstract

Focusing on the stable magnification, near zero distortion, and wide field of depth (DoF), the telecentric optical system is well suited for size measurements with a large range of working distances. However, suffering from the telecentricity-based error (TBE), the size measurement is connected with the working distances and imaging position of the image sensor, even within the DoF. Therefore, a model of TBE compensation is established, inspired by the radial distortion model in the camera calibration. With the correction of radial distortion coefficients for different working distances, the TBE is evidently improved. The feasibility of the proposed method is verified both in the theory and experiment. Our results show that the uncertainty of size measurement at different working distances of the DoF is improved obviously after the TBE compensation, which is attractive for fine size measurements in industry.

A Review: High-Precision Angle Measurement Technologies

“…Optical methods predominantly depend on the disk encoder scheme, commonly denoting the grating encoder arrangement, which employs a grating disk configuration for measurement purposes [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Previous researchers have conducted a lot of research on it, including structural optimization [ 36 ] and algorithm supplementary modifications [ 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ]. The above method mainly relies on the scale of the code disk to measure large angles.…”

Self-Calibration Method for Circular Encoder Based on Two Reading Heads with Adjustable Positions

“…Zhang et al [18] proposed a self-calibration method for circular encoders with multiple reading heads, deduced and analyzed the principle of error suppression of the reading head layout on the calibration results through harmonic analysis of angle measurement errors, and established a nonuniformly distributed layout of the reading heads to eliminate higher-order harmonic errors. Li et al [19] introduced the main sources of error in angle measurements of circular encoders, analyzed the distribution pattern of angle measurement errors, and calibrated the accuracy of angle measurement using higher precision instruments. Additionally, the calibrated error data were fitted into a third-order sine function for error correction, and the effectiveness of the error correction was verified through experiments.…”

Sphericity measurement based on telecentric imaging mechanism with image distortion correction and eccentricity error compensation

“…With this feature, telecentric imaging systems have been widely used to machine vision applications, including form error evaluation, geometry recognition, 3D reconstruction, etc [17,18]. In addition, research has suggested the possibility of applying telecentric imaging techniques to algebraic geometric forms [19]. When it comes to camera selection, line scan cameras offer four main advantages compared to area scan cameras: higher resolution, faster acquisition speed, continuous acquisition and processing, and a simple and reasonable structure.…”