The prototype is a 3 d.o.f parallel manipulator composed of a mobile plate and a fixed base plate, connected by three variable length links which are low-diameter cylindrical bars. The two extremities of each link are articulated respectively with the fixed base plate and with the mobile plate through revolute and respectively ball-and-socket joints. The linear actuator obtained from the combination of an electric motor and a ball-screw system, enables to move the center point of the ball-and-socket joint along a vertical axis. By changing the position of those points, the translational position and the two orientations of the mobile plate can be controlled with respect to the base plate. This closed-loop chain allows to obtain high stiffness of the system and therefore high accuracy for the insertion task. Each link is driven by a 12V DC servo motor giving 0.22[Nm] peak torque through a transmission consisting of a ball screw system. An incremental rotary encoder with a resolution of 8000 ppr is connected directly to each motor to measure the linear displacement of the link. In addition, three similar encoderss are mounted on the gimbal axes at the lower end of the three links in order to provide the necessary data for the forward kinematics solution.
