COMPLEX PISTON CONTOUR MACHINING USING A DIGITAL CAM SYSTEM

A Digital Cam system has been developed for complex piston contour machining. The Digital Cam is driven by an electro-hydraulic servovalve and is controlled by computer programs. Different piston contours can be flexibly machined by just changing computer-stored profiles instead of using many dedicated and expensive master cams. The system bandwidth of the Digital Cam is larger than 90 Hz which is at least two times larger than the system bandwidth of traditional cam and cam-follower mechanisms. Therefore, the Digital Cam system can machine more complicated and complex piston contours of modern advanced piston designs.;Additionally, the influence of the nonlinear behavior of the Digital Cam becomes significant when a Digital Cam system with a system bandwidth larger than 120 Hz is desired. Based on nonlinear Autoregressive Moving Average Vector (NLARMAV) system models, a nonlinear minimum-variance (NLMINIVAR) control algorithm was developed to take into account the inherent nonlinear behavior of the Digital Cam system. Computer simulations show that the NLMINIVAR control algorithm effectively compensate for undesired cam motion deviations caused by the nonlinear behavior of the Digital Cam. The NLMINIVAR control algorithm also produces a 15% improvement in the output accuracy of the Digital Cam.;The ARMAV bivariate time series modelling technique and a minimum-variance control algorithm are used to design an effective linear minimum-variance (MINIVAR) controller to control the cam motion of the Digital Cam. Using computer simulations, the performance of the MINIVAR control algorithm was first studied, and it showed a good input-tracking ability and adaptability. The implementation of the Digital Cam on an existing CNC lathe was controlled by a Motorola VMC 68/2 microcomputer. Experimental results showed that the Digital Cam system has a system bandwidth of at least 90 Hz and can precisely machine piston profiles with a profile error less than (+OR-)20 (mu)m.