The traditional numerical control machine is designed according to the Cartesian coordinate system, and is a cantilever structure that is connected in series and cascaded and nested. The error between the drive chains is cumulative. Virtual axis CNC machine tools (also called parallel machine tools, six-legged machine tools, virtual axis machine tools or new agile manufacturing and machining centers) are new members of the machine tool family. They have abandoned the traditional fixed rail tool guidance method and used six degrees of freedom in parallel. The mechanism (Stewart platform) is its structural body, so it is theoretically possible to machine arbitrarily complex surface parts (such as impellers, molds, etc.). In addition, the coupling of the movement effects of the telescoping poles of this new machine tool has the potential for high accuracy. Machine tool accuracy tests usually include geometric accuracy, position accuracy, and job accuracy tests. At present, no standard has been seen in ISO organization or a country for the accuracy testing of virtual axis CNC machine tools. This article refers to the content of the traditional numerical control machine tool precision test, and combines the characteristics of the virtual axis CNC machine tool, draws up its work accuracy inspection program. 1 Inspection of the Working Accuracy of Traditional CNC Machine Tools As regards the inspection of the working accuracy of traditional CNC machine tools, the United States NAS979 (National Aerospace Standards) has formulated the “Circular-Rhombus-Square†test piece cutting standard (referred to as the trial cutting method) standard, and similar in China. The standard. Table 1 is the method of testing the accuracy of CNC universal tool milling machine with test cutting method. From Table 1, we can see that the test cut method verifies the straightness of the machine tool along the X coordinate in four ways: the perpendicularity of the X, Y, and Z coordinates with each other: the straightness, roundness of the NC interpolation, and the hole in the XY plane. Position accuracy and other items. In addition, this method determines the corresponding size of the cutting test piece according to the stroke range of each coordinate of the CNC machine tool. This rule is due to the linear mapping between the error and stroke of each coordinate of the traditional machine tool. Therefore, it is reasonable to use a small-sized test piece to inspect the working accuracy of a large stroke. The test cutting method is used to test the working accuracy of the machine tool, which requires high test conditions for the accuracy of the test piece, long experimental period, and because most of the cutting motion is performed along the XY plane, the precision of the XZ and YZ planes is not evaluated, so that the traditional numerical control cannot be evaluated. All the properties of the machine. The latest international machine tool inspection standards recommend replacing the NAS 979 test method with the ball bar test method to perform rapid and effective inspection of the machine tool's working accuracy. 2 Development of Verification Test Plan for Virtual Axis CNC Machine Tools
Machine tool model diagram