Research On Probe Contact Force Of Articulated Arm Coordinate Measuring Machine

Articulated Arm Coordinate Measuring Machine(AACMM)has the advantages of large measuring space,good flexibility and convenient on-site measurement.It is widely used in reverse engineering,car body design and on-site part inspection.However,due to the series mechanical structure characteristics of the AACMM,the errors on each joint will be accumulated and expanded step by step,which eventually leads to the poor accuracy of the measuring machine.Summarizing the current research situation at home and abroad,it can be seen that the current measures to improve the accuracy of AACMM are focused on improving the structural accuracy requirements of the machine or adopting more effective calibration methods.However,an important feature of AACMM applications is manual operation.While manual operation provides good measurement flexibility,it also requires a high level of operator skill,with different personnel applying different forces to the probe when completing measurement operations,which introduces an unpredictable source of error in contact force.This paper therefore designs a contact force detection device for AACMMs and integrates a probe force-deflection model into the AACMM kinematic model to calibrate probe deflection parameters and compensate of measurement error caused by contact force(the same concept involved in the rest of this article,all referred to as contact force error),further improving the accuracy of the measuring machine.The main research work carried out in the thesis includes.(1)Error source analysis and mathematical model establishment of AACMM.Combined with the structural characteristics,the main error sources of the AACMM are systematically analyzed,and the kinematics model,error model and calibration model of the AACMM are constructed in turn.(2)Analysis of the forces on the probe of the measuring machine and design of the measuring force detection device for the AACMM.A local compression model of the measuring machine contact ball and a deformation model of the measuring rod deflection are established based on the Hertz equation and the basic principles of the cantilever beam.Analysis of the influence of the measuring force on the accuracy of the AACMM,a method and device for detecting the measuring force for the AACMM,and the simultaneous acquisition of the measuring force signal and the coordinate point signal data of the AACMM.(3)Research on the self-calibration method of the AACMM based on the F-DH model.The kinematic model and error model of the AACMM with integrated measuring force are established,and the probe deformation compensation model is integrated into the kinematic model to open up a new way to improve the accuracy of the measuring machine.The Jacobi matrix condition number is introduced as an evaluation index for the calibration effect,and the influence of the number of measurement postures and measurement points on the self-calibration results is simulated and analyzed.(4)Experimental study of the contact force error compensation method.Design the contact force error compensation experiment scheme,carry out the comparison experiment of the self-calibration method of the articulated coordinate measuring machine based on the DH model and the F-DH model,and verify the feasibility and effectiveness of the method proposed in this paper.