Study of on-machine error identification and compensation methods for micro machine tools

Abstract

Micro machining plays an important role in the manufacturing of miniature products which are made of various materials with complex 3D shapes and tight machining tolerance. To further improve the accuracy of a micro machining process without increasing the manufacturing cost of a micro machine tool, an effective machining error measurement method and a software-based compensation method are essential. To avoid introducing additional errors caused by the re-installment of the workpiece, the measurement and compensation method should be on-machine conducted. In addition, because the contour of a miniature workpiece machined with a micro machining process is very tiny, the measurement method should be non-contact. By integrating the image re-constructive method, camera pixel correction, coordinate transformation, the error identification algorithm, and trajectory auto-correction method, a vision-based error measurement and compensation method that can on-machine inspect the micro machining errors and automatically generate an error-corrected numerical control (NC) program for error compensation was developed in this study. With the use of the Canny edge detection algorithm and camera pixel calibration, the edges of the contour of a machined workpiece were identified and used to re-construct the actual contour of the work piece. The actual contour was then mapped to the theoretical contour to identify the actual cutting points and compute the machining errors. With the use of a moving matching window and calculation of the similarity between the actual and theoretical contour, the errors between the actual cutting points and theoretical cutting points were calculated and used to correct the NC program. With the use of the error-corrected NC program, the accuracy of a micro machining process can be effectively improved. To prove the feasibility and effectiveness of the proposed methods, micro-milling experiments on a micro machine tool were conducted, and the results have demonstrated the success of the micro-machining accuracy enhancement for micro machine tools.

An overview of techniques for monitoring and compensating tool wear in micro-electrical discharge machining

“…The movement of an electrode and its compensation with the required path also depends upon the data received. This real-time compensation method can eliminate errors produced during the re-instalment of work material and electrodes [ 72 ]. The process is mainly driven by volume removed per discharge (VRD) from tool or work material.…”

An on-machine error compensation method for an ultra-precision turning machine

“…Cho and colleagues 10,11 used an OMM system in a milling machine to compensate for the machining error. Wang and colleagues 12,13 developed a vision-based on-machine measurement and compensation method for volumetric errors of a micro machine tool. Jywe et al 14 developed a three-dimensional dynamic performance measurement and error compensation method for a machine tool.…”

Technological advances in measurements and intelligent instrumentation

“…Simultaneous multiple degrees of freedom (DoF) measurement is realized by developing highly accurate interferometric system based on a modified homodyne Twyman-Green interferometer concept. Wang et al [1] also developed on-machine error identification and compensation methods for micro machine tools while Mildner et al [2] successfully advanced a dual-frequency comb generation with differing GHz repetition rates by parallel Fabry-Perot cavity filtering of a single broadband frequency comb source. Meanwhile, Lu et al [3] proposed a two-degree-of-freedom (2-DOF) displacement measurement system based on double diffraction gratings for precise displacement measurement.…”