1、The Development and Application of a Planar Encoder MeasuringSystem for Performance Tests of CNC Machine ToolsW. JyweDepartment of Automation Engineering, National Huwei Institute of Technology, Huwei, Yunlin, TaiwanIn this paper, a measuring device with a planar encoder is developed to test the per
2、formance of a CNC machine tool. With the assistance of a PC, this system can be employed for both 2D contouring tests and 3D positioning tests for a CNC machine tool. The structure and the principle of the system, the applications for the general 2D contouring test, the drift test, and the specified
3、 geometric part path tests. An actual case study on improving the accuracy of machining a cam aredescribed. Finally, a new 3D positioning method using the optic encoder is demonstrated.Keywords: Ball bar system; CNC machine tool; Geometric part path; Planar encoder; Thermal drift test; Three-dimensi
4、onal positioning; Two-dimensional contouring1. IntroductionMachine tool performance and consistency is the main determinant of the quality of parts machined by it. It is of importance to check the performance of the machine tool systematicallyfor direct quality control purposes or to compensate for
5、this uncertainty. Schlesinger, in 1932 1, first provided a systematic testing method for machine tools. This method was developed as the basis of the ISO standard. Tlusty, in 1959 2, employed an electric level and sensor to test the spindle accuracy. Tlusty and Koenigsberger 3 and Burdekin 4 indicat
6、ed new testing rules for machine tools. Burdekin 5 checked the relation between the motion accuracy of machine tools and the machined part. Tlusty 6 proposed a non-cutting testing method. The tests for machine tool performance were then classified into a direct cutting test and an indirect cutting t
7、est. Ericson 7 first described the work zone of machine tools. Bryan and Pearson 8 explained the definition and the way to measure the pitch, roll and yaw motion and straightness error. After the commercial laser interferometer 9 was available, the analysis of volumetric errors 1013 was described. V
8、outsudopoulos and Burdekin 14 indicated a calibrating model for a coordinate measuring machine. Fan 15 used a laser interferometer and a related device with the assistance of a PC to calibrate different types of NC machine tools. Zhang and Hockey 16 obtained the 21 error components by measuring the
9、position errors. Zhang and Zang 17 designed a 1-D ball array to find the 21 error components, then Zhang 18 described a rapid method to obtain the straightness error. In 2000, Jywe 19 described a method of employing a ball bar system for the verification of the volumetric error of CNC machine tools.
10、 Circular tests were developed to check both geometric errors and contouring errors. Burdekin 20 described cutting tests using circular paths for accuracy assessment. Bryan 21 developed the first ball bar system for the contouring test. However, in this system, the uncertainty is high due to the fri
11、ction between the master balls and the magnetic sockets and no accurate contouring radius was given. Knapps system 22,23 used a circular comparison standard disc mounted on the test table of the machine tool and a 2D-probe. The problems for this system are the existence of friction between the 2D pr
12、obe and the disc, its small bandwidth, which causes the system to be unusable for high-speed contouring tests, and the high cost of the 2D probe. Kakinov 2427 provided a series of methods using a ball bar system to calibrate a coordinate measuring machine and CNC machine tools. Knapp 28,29 described
13、 a rule to reduce the errors due to stickslip etc. Burdekin and Park 30 modified the original ball bar system by employing a four-rod linkage. Burdekin and Jywe 31 provided a method to diagnose the contouring error and to adjust the parameters of the CNC controller to optimise the performance of the
14、 tested CNC machine tool. Ziegert and Mize 32 described a laser ball bar system. All these ball bar systems, including the lateral Renishaw system 33 provide only the radius error during the contouring test. This limits the analysis of contouring error since no individual error in each axis is avail
15、able. Jywe 34 used two position silicon detectors (PSD) for a contouring test to obtain the contouring error in each axis. One laser source emits a laser beam and the laser beam is split into two vertical lines and projected onto two positioning silicon detectors, which are set vertically to each ot
16、her on the test machine table. The Heidenhein 35 grid encoder also provides a 2D contouring test, but at very high cost. A planar encoder system was developed 36 for applications such as semiconductor and electronics manufacturing equipment. The system, which has a good dynamic response, can provide up to a 0.1 m resolution in positioning, and it is of importance that it is of low cost. However, the original planar enc
