Tripod robot with cylindrically actuated limbs: Structure and kinematics

The kinematic analysis of a novel tripod with six degrees of freedom is presented. The kinematic chains of the mechanism have an RCS structure. Two elements of each cylindrical pair C of the chain constitute a crank-type limb that carries out two controlled motions––rotation around and translation along the limb axis. The limb is connected passively to the fixed base and to the movable platform by rotational and spherical hinges, respectively. The structure, kinematics, working space and singular positions of the tripod are examined. Since three of the six active tripod motions are rotations, the inverse kinematics solution is non-unique; this, in turn, necessitates the choice of one of eight variants for the initial positions of the limbs and one of two directions for limb rotations.