Study On System Calibration And Error Compensation Of Flexible Arm Measuring Machines

Traditional orthogonal coordinate measuring machines(CMMs) is called "measurementcenter" with its high precision and powerful function, and is widely used in manufacture andscientific research. However, with the development of science, technology and manufacture,the application of traditional orthogonal CMMs is being restricted in more and moreconditions, such as field measurements, large-size measurement, what’s more it’s measuringblind field is too much. Flexible arm CMMs is based on non-orthogonal coordinate system,which combine robot with measuring technology. Compared with the traditional orthogonalCMMs it have advantages of small size, light weight, low cost, good flexibility, easyoperation, portability, large-size measurement, almost no measuring blind field, easy fieldmeasurements and so on, the applications and demand of flexible arm CMMs is growingincreasely. But compared with the traditional orthogonal CMMs, the wide application offlexible arm CMMs is mainly restricted because of relatively low measurement accuracy. Thestudy of this paper is focused on the system of flexible arm measuring machine and precisiontheory. Including mechanical structure, kinematic modeling, error modeling, calibrationtechniques, error compensation and so on.Based on the mechanical structure, a kinematics model of flexible arm CMMs wasestablished by D-H method, and verified the correctness of the model by the graphical method.By analysis error sources of the flexible arm CMMs, a total differential error model andanalytic error model was established. Large number of simulation analysis about the influenceof different levels of joint angle and joint torsion angle error on measurement precision wascarried on. These simulation results give futher theoretical guidances for design, manufacture,assembly and other technical aspects strictly controlled in order to further improve themeasurement accuracy of flexible arm CMMs in the future.Analysis of off-center installation error of circle grating of the flexible arm CMMs,thermal deformation error caused by temperature change and bending strain deformation errorcaused by mechanics, then explore compensation method to reduce or eliminate the errorabove. Modular design was adopt so as to set up a simple experimental platform, the mainlymodules consist of mechanical systems, computer measurement and control system, softwaresystem based on the virtual instrument of LabVIEW, error composition system concerningdynamic strain and temperature changes. Verify angle measurement principle of the flexiblearm CMMs by the simple experimental platform, monitor thermal deformation andmechanical strain deformation by placed the smart sensor on the measuring arm, and realizereal-time error compensation of thermal deformation and mechanical strain deformation to improve the measurement accuracy and stability.This paper focuses on the key technologies of the flexible arm CMMs, the issuescomprise mechanical structural analysis, kinematics modeling, error modeling, parametercalibration, error compensation and so on, deeply discusses these issues through theory andtechnology levels. In addition, set up a simple experimental platform, through the platformexperimental study of the flexible arm CMMs was carried out. Finally, conclusions weresummarized and the studies need to strengthen and improve in the future were pointed out.