Abstract
This study proposes using the iterative learning control method to adjust the volumetric error-compensated tool path, where the working volume motion accuracy of three-axis computerized numerical control (CNC) milling machine tools is increased by segmented modification of the part program. As the three-axis CNC milling machine tools generally have volumetric error of working volume, this study refers to the measured and established table of volumetric errors and uses the method of the modifying part program for volumetric error compensation of machine tools. This study proposes using part-program single-block positioning segmented for volumetric error compensation, as the generated compensated part program with multiple compensated blocks can effectively compensate the volumetric error of working volume in the tool moving process. In terms of the compensated tool path computing method, this study uses the iterative learning control (ILC) method and refers to compensated tool path and volumetric errors along the compensated tool path for iterative computation. Finally, a part program with multiple blocks is modified by the converged optimal compensated tool path, in order that the modified part program has higher-precision volumetric error compensation effect. The simulation result shows that the rate of improvement of error of the volumetric error compensation method proposed in this study is 70%. The result of cutting tests shows that the average rate of improvement of the straightness error of the test workpiece is 60%, while the average rate of improvement of height error is 80%. Therefore, the results of simulation and cutting tests can prove the feasibility of using the ILC method for segmented modification of the volumetric error-compensated part programs proposed in this study.
Highlights
Manufacturing mechanical parts with higher accuracy has been the machining target of various computerized numerical control (CNC) machine tools through the ages, as the conventional pitch error measurement and compensation methods cannot meet the requirement
Existing part-programRWamtiethoodIfLiifimCcpcaortoimovnpeemmnesenattthi(oo%nd)s only c08o.03n0.6s2i29der t0h8.00e.02c31o7mpe08.n01s0.8a37t5ion of the position of a single block of a part program but neglect the movement bias induced by volumetric error in the
This study used the iterative learning control (ILC) concept and referred to the present compensated tool path and volumetric error induced by the compensated tool path to calculate the compensated tool path
Summary
Manufacturing mechanical parts with higher accuracy has been the machining target of various computerized numerical control (CNC) machine tools through the ages, as the conventional pitch error measurement and compensation methods cannot meet the requirement. As induced by the kinematic and geometric errors of a CNC machine tool, usually corrupts the dimensional accuracy of the machined mechanical parts; based on the developed error estimation model, Vahebi Nojedeh et al [26] developed NC program editor software to modify and generate the errors the compensated NC program by recursively computing the compensated positions along the modified tool path. This study refers to the measured and established table of volumetric errors, as based on the part-program modification method, to segment the tool moving path, and uses the concept of ILC (iterative learning control) adjustment to design a segmented compensation method for the volumetric error of the part program, meaning the part program can be modified to have volumetric error compensation effect with higher tool moving accuracy.
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