A modified Stewart platform manipulator with improved dexterity

A design for a six-degree-of-freedom (6-DOF) parallel manipulator is presented. The design is a modification of the Stewart platform that places the legs of the manipulator on two concentric circles both at the base and at the end effector. The legs can therefore cross over one another in space without interference, which allows them to move closer to the horizontal. This brings the force/torque and velocity capacities in different directions more into balance. The degree of improvement attainable is quantified by defining a measure of dexterity as the average condition number of the Jacobian matrix over a centralized subregion of the workspace, and optimizing the manipulator design with respect to a weighted sum of dexterity and workspace volume. This measure of dexterity is compared with other measures on the basis of the singular values of the Jacobian. It is shown that the new design offers significantly improved dexterity over the traditional Stewart platform design