Study On Structural Parameters Calibration For Six-axes Hybrid Horizontal Processing Device

The level of the propeller processing has been improved significantly in recentyears, but there are also many disadvantages, such as propeller blade vibration,interference, repeated clamping in the large-scale marine propeller processing. Inorder to overcome these shortcomings, two hybrid mechanisms are symmetricallylaid out on the both sides of the marine propeller to realize twin-tool symmetricalprocessing of the marine propeller. And these can effectively improve theprocessing accuracy and processing efficiency of the marine propeller.The hybrid machine tool in this thesis is composed of a serial mechanism with3degrees of freedom and an improved3-RPS parallel mechanism. Meanwhile, theparallel mechanism is installed on the terminal of the serial mechanism usingcantilever type. The total degrees of the freedom are5of the hybrid machine tool.They are translations on the directions X Y and Z and swings around axesand. In order to realize actual processing of the large-scare marine propeller, astructural parameters calibration method of this hybrid processing device is studiedmainly to improve the processing accuracy, which has great scientific significanceand engineering value.Structural characteristics of the device and degrees of freedom are analyzed.Then, considering the coupling problem of pose parameters of parallel mechanismin the hybrid machine, pose parameters are decoupled based on the advanced spatialmechanism. Accordingly, kinematic inverse solution model and positive solutionmodel of the device are established by using analytical method and improvednumerical iteration method respectively. Moreover, accuracies of the kinematicinverse solution model and positive solution model are verified by kinematicsimulation in the ADAMS.Because of the coupled motion of the hybrid device, the serial and parallelmechanisms are calibrated separately. Errors of the terminal of the serial mechanismcan’t be measured directly, thus the mapping relationship between positions of theterminal and the tool point is built. Furthermore, error model and parametersidentification model of the serial mechanism are established. Then, kinematicmodeling considering the structural parameters error is accomplished and errorcompensation of the serial mechanism is realized. According to the structuralcharacteristics of the parallel mechanism, a calibration method of driving rodsreturn home lengths is researched using standard measuring tools with dial gage.Position errors of hinge points are calibrated by means of two rounds of calibration.Then, positions error model of hinge points is established. After that, parameters identification of positions error of hinge points is performed usingLevenberg-Marquardt optimization algorithm. Hence, errors compensations ofdriving rods return home lengths and hinge points’ positions are realized by meansof establishing the motion control model considering the structural parameterserrors. Finally, correctness and effectiveness of the calibration method are verifiedby means of parametric modeling and simulation in the ADAMS.Based on the calibration method in this thesis, the actual calibration of thehybrid propeller processing prototype is performed. The serial mechanism iscalibrated by measuring standard sample, and vertical errors of moving platformson the directions X Y and Z are eliminated. Position error of the tooltranslation and convergence point error of the tool swing can be measured usingstandard gauge block directly. Thus, positions of hinge points in the parallelmechanism are calibrated using position error and convergence point error. Thereby,positions errors of hinge points are eliminated. Through the actual calibration,processing accuracy of the device is improved effectively. And, correctness of thecalibration method in this thesis is verified.