Since the very successful application of parallel robots in material handling, many projects attempted to implement the Gough platforms as milling machine manipulators with limited success mainly achieving roughing. The displacement of the milling tool should meet surface finish requirements. Users also wish to increase tool feedrate in order to improve productivity thereby reaching high speed milling levels. Even a constant high speed feedrate brings important challenges since they mean higher actuator accelerations even on straight lines. This work introduces geometric formalization of surface finish which is more realistic then classic error calculations. This research work proposes an off-line simulation tool analysing the milling task feasibility using a robot constituted by a general hexapod parallel manipulator, namely the Gough Platform, often refered as the Stewart Platform. Moreover, in order to meet the machine-tool standards, the parallel robot will be controlled by a typical CNC controller implementing classic position based algorithms adapted to the parallel robots with any kind of actuator polynomial interpolation. Control sampling rates are studied and their impact evaluated. High and very high speed milling simulation results show the implementation of linear and third order interpolation between the actuator set-points calculated from the CAD/CAM computed end-effector or tool set-points points. The results show that linear interpolation are not sufficient for high speed milling and then third order interpolation reach the required surface finish at fast and feasible CNC sampling rates.
|Media of output
|Memorial University of Newfoundland
|Unpublished - 2014