Research On Error Measuring Instrument For Circular Interpolation Of NC Machine Tools

Accompany with the development of modern manufacturing industry, the precise and ultra-precise machining technique has become increasingly important. As the widely used equipments in the manufacturing industry, the CNC machine tools are facing new challenges and opportunities for the new age. Improving CNC machine tools accuracy is the key to improve the quality of CNC machine products and strengthen the market competitiveness in the world while the error of CNC machine tools is the main obstacle. The technology of measurement is the precondition to reduce or compensate the error of CNC machine products. Circular test is one of the most important means for machine tools measuring. Accuracy information of the machines could be acquired and the error sources of machines could be identified by measuring the circular track, which can provide support for machine design and error compensation.Based on circular test principle, an error measuring instrument for circular interpolation of NC machine tool—Circular Test Instrument (CTI) is developed. A series of work is accomplished including mechanical structure design and manufacture, data acquisition system development and PC application programming.Machine tool errors and their measurements are presented in the paper. Existing integrated measurement and equipments for NC machines are summarized and their pros and cons are analyzed.Based on the analysis of circular test, the mechanical structure of CTI is designed and manufactured. A specific method to install the basement on the table is adopted to solve the unparallel problem between the bar and measurement plane. The errors generated during manufacture and measurements are analyzed. To ensure the measurement accuracy, a calibration procedure is adopted to compensate the errors in the radius direction of the circular track.A data acquisition system for CTI is developed, based on the USB communication protocol. The technique of USB is summarized. The communication printed circuit board is designed, of which the latest series single-chip PIC18F4550 of Microchip is the key component. A PC data acquisition application is developed. The application framework is planned. Based on the multimedia timer and explicit linking the Dynamic Linking Library, the real time reading and saving of error data is realized. The measurement circular contouring is dynamically displayed through Windows GDI.It is verified though experiments that the CTI achives the design accuracy and meets the measurement requirements.