Accuracy prediction of workpieces considering machine errors of multi-axis machine tools and its identification

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In this research work, the influence of machine errors such as the pitch error of worm-gears and the servo-error of NC controller for five-axis machining centers, which are a typical multi-axis machine tool, is investigated by the computer simulation and experiment. Firstly, the effectiveness of the testing method defined by the clause K6 of ISO 10791-6, which is specified for the five-axis machining centers with a double pivot spindle head, is investigated. It is pointed out from our results that the specified testing method in the ISO standard does not give any useful data. An alternative testing method is proposed, and its method gives us some useful information relating to the geometric accuracy. Then, an alternative measuring instrument of the motion trajectory of five-axis machining centers with a tilting rotary table is also developed. The developed instrument is very simple.A new testing method for checking the synchronous accuracy of a linear axis and a rotary axis is proposed. In the proposed method, a linear axis is simultaneously controlled with a rotary axis, and a circular path is described by the two axes. It is found that the proposed method is useful to check the servo-delay of each axis. Finally, the behavior of the simultaneous five-axis motion is investigated, considering the pitch error of the work gear and servo-delay as well as the geometric deviations. It is pointed out that the inclination angle and the center offset of the three dimensional circular path governs the dynamic behavior of the five controlled axes. In addition, it is found that the backlash and pitch error of the worm gear largely affect to the finishing accuracy of the workpiece of which shape is cone frustum.