Development of an Abb? error compensator for 3-axis NC machine tools
Date Issued
2012
Date
2012
Author(s)
Wang, Chih-Hsiung
Abstract
The position feedback control of current NC machine tool controllers all adopt displacement sensor (optical scale or encoder) as a single sensor system. This displacement sensor is, however, never in line with the motion axis of the cutter. It is known that each axis motion has inherent six degrees of geometrical errors, namely three linear and three angular errors, among which the angular errors being enlarged to cause the positioning error of the axis motion due to the well known Abbé principle.
In the measurement system, the micro autocollimator is developed for the detection of pitch and yaw angular errors. Moreover, a sensor that can measure the roll angular error is fabricated by use of two collimated laser and two quadrant detectors. Finally, the micro autocollimator and the roll sensor are integrated into three angle measurement system, which can measure pitch、yaw and roll angular errors.
This research aims at the development of three angular sensors and in corporation with the current NC control to develop an Abbé error compensation system, being an innovative multi-sensor feed-back compensation system. This system allows the machine tool to detect the angular error of each axis in real-time and the corresponding Abbé offsets so as to dynamically compensate for the Abbé error. Based on the 3-axis vertical machining center and position feedback type (light scale), the volumetric error for Abbé error is derived. In addition, the Abbé compensator for PC-based controller is also developed. This developed Abbé error compensation system is to be built in the NC controller to enhance the machine tool accuracy.
Experiments show that the positioning error of an investigated NC machine tool is mainly affected by Abbé error. With the proposed Abbé error compensation system, the positioning accuracy can be significantly improved to more than 80%
Subjects
Abb?error
volumetric error
three angle sensor
3 DOF measuring system
Abb?error compensator
Type
thesis
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