Control-Integrated Design by Theoretical Simulation for a Torque-Actuated 6-SBU Stewart Platform
AMAE Int. J. on Manufacturing and Material Science, (2012)Abstract
A design algorithm has been proposed for a Stewart platform with six legs, each having a ball-screw at the middle and powered by a torque motor at the bottom. When a motor shaft rotates, the leg extends or collapses and the axis could rotate about a spherical joint supporting the motor. Consequent actuation from all the legs through a universal joint at the top of each causes the platform to change its pose. The joints at each end lie on the intersection of a pitch circle and a semi-regular hexagon. An inverse model that neglects friction and leg inertia has been employed in a step-by-step simultaneous search to determine the platform height at the neutral and the radius of the bottom pitch circle within the constraint of permissible joint angle and motor specifications. The proposed control for a basic pose demand involves a feedforward estimation of motor torque variation, a proportional-derivative feedback and appropriate compensating demand for minimizing unwanted coupled motion. The forward modeling of the pose dynamics and its Simulink implementation have established the control as satisfactory.