Study On Accuracy Analysis And Calibration Of Parallel Double-Joint Cmm

Parallel Double-Joint CMM(Coordinate Measuring Machine)is a type of non-orthogonal coordinate measuring equipment which has the advantages of low cost,flexible movement,wide measurement space and suitable for field measurement. Therefore, the measuring system has been developed rapidly in recent years. Parallel Double-Joint CMM based on non-orthogonal coordinate measuring system,which has an angle scale and two precision joints for measurement of X-Y plane,linear displacement guide and ruler for Z axis. As we know, comparing with orthogonal coordinate system,non-orthogonal coordinate system has lower accuracy and more complex relationship of coordinates conversion. In order to improve the accuracy of non-orthogonal coordinate system,error compensation is essential.The major work of this paper includes the following aspects:The characteristics of the measuring machine has been analyzed,using the improved D-H model of the five parameters to export mathematical models of error compensation. In theory, the system error of Parallel Double-Joint CMM is 12um after compensated.Meanwhile, this paper has analyzed error sources of the machine and calculated the influence to measurement structure caused by random error such as grating sensor accuracy, shaft runout, jumping straight joints, torque deformation and operating force. Measures have been taken to control the accuracy of devices which cause the random error, to improve the structural design, to analyze the influence to the accuracy of the machine caused by bending deformation of system weight and reading error of eccentric circular grating. Then the rationality of existing mechanical parameters has been stduied.Using the basic idea of parameter determination and inversion method, the program of calibration has been designed and the error introduced by calibration has been calculated.The programs which are detected for linear joint position error, straightness error, error of grating back to zero and temperature deformation error have been designed to check the size of errors and find the way for compensation.Finite element analysis software ANSYS10.0 has been used to take simulation for gravity deformation and torque deformation model. The total limit of error has been acquired, based on the accuracy of random error and calibration above. Finally,the improvement and measures to impoved the accuracy of the machine have been proposed.