| Compared with other ordinary optical surfaces,optical complex surface has excellent optical properties which are widely applied in high-tech areas including astronomy,aerospace and so on.But its geometrical characteristics which cannot be described with mathematical model and its intractable material property bring severe challenges to the processing of optical complex surface.In order to improve the processing quality and efficiency of optical complex surface,the laboratory developed a five-axis ultrasonic polishing experiment platform.During the processing of NC machine tools,the geometrical errors of machine tools affect the posture and position of tools as well as the machining precision.To further improve the machining precision of the five-axis ultrasonic polishing experiment platform,this paper establishes the kinematics model of experimental platform by using screw theory and establishes the geometric error model of experimental platform by using multi-body system theory and puts forward an effective geometric error compensation method.On the basis of analyzing kinematic form and kinematic chain of common five-axis machine tools,with the screw theory as the mathematical theory,based on global coordinate system,the Kinematics Positive&Reverse Solution model commonly used by five-axis machine tools is established.Take five-axis ultrasonic polishing experiment platform as an example,kinematic chain analysis of ultrasonic polishing experiment platform is conducted and its Kinematics Positive&Reverse Solution model is established.With the multi-body system theory as the theoretical basis,various moving parts of ultrasonic polishing experimental platform are abstracted into the adjacent typical body and geometric errors of various moving parts are analyzed.Taking errors as a movement,the paper considers the relative rest and relative motion among bodies in the ideal and actual situation.Actual kinematic model of tools towards work-piece coordinate system in the actual situation is established and the geometric error model of ultrasonic polishing machine tool in work-piece coordinate system is established through combining the kinematics model of Chapter Two.Based on the kinematics model and the geometric error model of five-axis ultrasonic polishing experiment platform,the paper proposes a compensation method.Geometric error compensation is firstly conducted on rotation axis and then on translational axis.Dealing with rotation axis error will change the tool's position which results in new problems of position error.A geometric error compensation calculation program has been developed.With the strong data processing ability of MATLAB software,reducing the calculations of ultrasonic polishing experiment platform's geometric error and compensation can effectively calculate the geometric error and generate the data files of tools' position as well as the error curve image before and after the geometric error compensation.Compensation effect can be expressed visually through the image.Finally,on the basis of the ultrasonic polishing experiment platform's actual size,experimental platform's 3D model is established in Solidworks software.Optical parts are designed in Pro/E software,and processed tool position data files are generated after simulation processing.The established 3D model of ultrasonic polishing experiment platform,the stock piece to be processed,and the related fixture are put into the Vericut software environment.The related motion parameters are set and tool position data files of two work-pieces(one work-piece exists geometric errors and the other has gone through error compensation)are added to conduct the numerical control simulation processing.In Vericut software environment,by utilizing the model contrasting function of the software,over-cutting and residual condition in two processing states are analyzed and the effectiveness of the compensation method is verified. |
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