| As an important indicator to describe the comprehensive performance of CNC machine tools,the kinematic accuracy also plays a decisive role in the processing quality of the parts to a great extent.Compared with the specimen cutting method,the instrument detection method can be more efficient and convenient to detect the kinematic accuracy of machine tools,so it is widely used in the acceptance and routine maintenance of CNC machine tools.However,with the popularity of five-axis CNC machine tools,the limitation and tediousness of traditional detection equipment are increasingly apparent.RTCP function is the essential function of high-grade five-axis linkage CNC machine tools,and its main purpose is to improve the efficiency of NC programming and reduce the non-linear kinematic error caused by the rotation axis.With this function,the machine tool tip can be controlled by the post instruction to remain relative stationary in the workpiece coordinate system,while the tool orientation moves along the specified trajectory,so that the translational and rotation axes are involved in the linkage of large motion range.Based on this characteristic,the RTCP error detection method has improved the measurement accuracy due to the narrowing of the range to be measured,and threedimensional kinematic error can be obtained in one-time installation to improve the efficiency.However,this measurement method cannot accurately obtain the location information corresponding to the kinematic error of the axes,which leads it difficult to improve the accuracy of the follow-up error tracing and compensation.To solve this problem,the following research has been conducted in this paper:1.The delay defect of machine tool RTCP error measurement method in the process of simultaneous obtaining kinematic error and axes location information has been analyzed.Combined with the location constraint relationship of machine tool axes when the RTCP function is turned on,a synchronous measurement method is proposed.Supporting synchronous acquisition system solution is presented,and the rationality of system is demonstrated.2.According to functional requirements and technical indicators,the system detailed design and key components selection are completed.On the basis of working principle analysis of the half-bridge inductive probe,the conditioning circuit based on AD698 is designed and debugged,and its static characteristics are further calibrated;frequency multiplier and phase discrimination circuit is designed and debugged,for meanwhile the corresponding CPLD multiplier program is written.Based on the above work,the integration of the hardware parts of the acquisition system is completed.3.Based on the software requirements analysis and overall design,the acquisition application program is finished on the development platform of LabVIEW.Its main functions include equipment commissioning before measurement,multi-channel synchronous acquisition triggered by the machine tool spindle’s start-up,data preprocessing and real-time storage,display results.The final "error-location" curve will provide basis for follow-up error traceability and compensation,and the human-computer interface is simple and friendly.4.To test whether the synchronous measurement system can realize the simultaneous measurement of the tool tip error and the moving posture of the five-axis machine tool,and highlight its advantages over traditional measurements methods,a contrast experiment based on five-axis CNC machine tools has been designed and completed in this paper.Through this experiment,the basic functions of the system,the synchronization and the accuracy of the measurement results has been proved. |
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