| Summary: | 碩士 === 國立中正大學 === 機械系 === 92 === In recent years, the development of machine tools trends toward high-speed feeding and high accuracy. The accuracy of machine tools is affected greatly by error analysis and compensation techniques. Therefore, it is very important to establish a complete error model. In general, the errors could be categorized into two parts. One is generated during the process of manufacturing and assembly and the other is produced during machining such as feed error, thermal effect, backlash error, vibration and chattering etc. In this thesis, the dynamic formulation of a Novel 3-PRS parallel manipulator with joint clearance is derived from Newton’s 2nd law, and the effects of joint clearance upon the cutting errors and transmitting forces of joints are discussed.
For motion analysis of system, the relation between the feed of ball screw and tool tip profile is first derived by inverse kinematics. Then, we apply the relation in forward kinematics and obtain the ideal tool tip trajectory. Next, the dynamic formulation of system with joint clearance is derived with joint clearance model, and is solved by integration method. The effects of different joint clearance and operation period are also discussed.
According to the numerical results, if there is no clearance in the joints of the mechanism, the desired feeding rate of the tool tip keeps constant under the schemed feeding condition of the ball screws when the tool tip trajectory is a circle. On the same cutting condition, the feeding rate of the tool tip becomes a pseudo-periodic time function if the joint clearances are considered. Besides, the displacement error of tool tip in the vertical direction grows faster than the other directions when joint clearance increases gradually. Besides, the undulation of revolute joint transmitting forces grows faster than that of ball joint transmitting forces. And we also find that the effect of the ball joint clearances upon the system response is greater than that of the revolute joint clearances.
|
|---|
