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Abstract
The purpose of this paper is to propose a general precision allocation method to improve machining performance of CNC machine tools based on certain design requirements. A comprehensive error model of machine tools is established by using the differential motion relation of coordinate frames. Based on the comprehensive error model, a reliability model is established by updating the primary reliability with an advanced importance sampling method, which is used to predict the machining accuracy reliability of machine tools. Besides, to identify and optimize geometric error parameters which have a great influence on machining accuracy reliability of machine tools, the sensitivity analysis of machining accuracy is carried out by improved first-order second-moment method. Taking a large CNC gantry guide rail grinder as an example, the optimization results show that the method is effective and can realize reliability optimization of machining accuracy.
Highlights
CNC machine tools integrate many technologies, such as accuracy machinery, electronics, electric drag, automatic control, automatic detection, fault diagnosis, and computer
The principle of differential motion between coordinate frames is applied to geometric error modeling of machine tools, and a new precision design method is proposed by combining with reliability theory
When the grinder is seen as one open kinematic chain, the reference coordinate frame is located on the working table, and the geometric errors direction of the part between the bed and the working table are opposite to the direction defined in the measurement, so the differential motion vector of the X-axis is denoted as: ( ) ∆EX
Summary
CNC machine tools integrate many technologies, such as accuracy machinery, electronics, electric drag, automatic control, automatic detection, fault diagnosis, and computer. The improved first-order second-moment method is used to establish a sensitivity analysis model, which can identify and optimize the main geometric error parameters that affect the machining accuracy reliability, so that the machining accuracy reliability of machine tools can meet the design requirements. The principle of differential motion between coordinate frames is applied to geometric error modeling of machine tools, and a new precision design method is proposed by combining with reliability theory. It has important theoretical significance and practical value for further study machining precision reliability of machine tools. Taking a large CNC gantry rail grinder as an example, the geometric error modeling process of this machine tool is presented using differential motion relation of coordinate frames. From equations (3) and (8), the differential motion matrices of each axis of the grinder relative to the tool can be obtained, which are:
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