A Novel Double Ball Bar Based On Indexable Rotary Joint

Geometric error measurement is the key to error compensation of CNC machine tools and improvement of machining accuracy.As a CNC machine tool circular path error detection instrument,Double Ball Bar(DBB)has the advantages of compact structure,simple operation high measurement accuracy,and reliable detection results.It is widely used in error diagnosis and accuracy evaluation of Computer Numerical Control(CNC)machine tools.Due to the limitation of existing DBB structure,the measuring radius is determined by the length of different extension rods equipped.Therefore,the measurement range is limited to several circles with different radii.And the existing DBB cannot achieve full-scale measurement of geometric errors within the working range of the CNC machine tool.The operation of stopping when the extension rod is replaced causes measurement discontinuity,also reduces the detection efficiency of the DBB.Aiming at the above shortcomings,this dissertation proposes a novel double ball bar with based on indexable rotating joints(hereinafter referred to as Indexing Double Ball Bar,IDBB).It can detect the circle path error in any CNC machine tool working plane under the condition of single installation(to avoid repeated installation and positioning).The IDBB is beneficial to expand the error detection range of the DBB,improve the detection efficiency,and provide more selectable detection circle track radius for the geometric error detection in the working area of the CNC machine tool.Through theoretical analysis,simulation analysis and experimental verification,this dissertation focuses on the principle of machine tool error detection based on I-DBB and its its accuracy influencing factors.This dissertation mainly expands from the following aspects:(1)Design the mechanical structure of the I-DBB,and establish the error detection model based on the I-DBB.The error factors that affect the precision of CNC machine tools are analyzed and classified.Based on the error detection model of the I-DBB,the common error sources of CNC machine tools are simulated and analyzed to verify the feasibility of the I-DBB bar error detection principle.(2)The mechanical error model of the I-DBB is established,and numerical simulation is carried out.The influence of structural parameters such as the inclination angle,connecting rod length and indexing angle error on the measuring accuracy of the I-DBB is analyzed.And the reasonable design range of each structural parameter is proposed.(3)An experimental system for verifying the principle of error detection of CNC machine tools based on an I-DBB is established,and an experimental device for the IDBB is designed and processed,and feasibility verification experiments are carried out.The experimental results verify the correctness of the error detection principle of CNC machine tools based on theI-DBB and the feasibility of the experimental system.(4)The error magnification characteristics of the indexing double ball bar are studied,and the resolution of the indexing double ball bar is calculated.A comparative experiment is designed to compare and analyze the error detection effect of the indexing double ball bar and the traditional DBB,so as to verify the error amplification characteristic of the indexing double ball bar.