On some methods to improve kinematic properties of parallel manipulators

This paper is concerned with the design of parallel manipulators with improved kinematic properties, i.e. with good distribution of both linear and rotational velocity of the end effector throughout the workspace. As an example of the solution of such a problem it is presented a new kinematic scheme of POLMAN-3-3 parallel manipulator with planar parallelograms applied as driving systems for transmitting motion from six motors located in the base. Adopted mechanical system is characterized by good kinematic and dynamic properties, i.e. manipulator has good isotropicity of velocity and acceleration distribution, in the workspace. Main advantages of the solution are simplicity and lightness of the construction. Because of that, use of direct drive units can assure short time constant, big acceleration and very small mechanical hysteresis