Kinematics of the wire-driven parallel robot MARIONET using linear actuators

Wire-driven parallel robots are special types of Gough-Stewart platform in which the rigid extensible legs are substituted by extensible wires. Usually wire length change is obtained by coiling the wire on a drum actuated by a rotary motor. We present here a robot using linear actuator and a pulley system allowing a higher modularity of the actuation system. The kinematics of this redundant system (the system has 7 wires), taking into account the elasticity of the wires, is presented. Inverse kinematics may be solved either by first choosing the wire tensions, the control vector being then a linear function of the tensions or by solving directly a system of non linear equations whose unknowns are the components of the control vector. Forward kinematics is a much more complex issue, involving the solving of a large system. We present a solving approach but this problem remains an open issue.