This paper addresses the conceptual design of direct-drive manipulators which have good promise for high speed, high precision manipulation. In the design methodology presented, the procedure begins by considering the kinematic aspects and ends by configuring manipulator structures with promising kinematic and dynamic characteristics. Based on the conceptual design considerations, a novel 3 DOF (RRR) direct-drive manipulator is proposed and analyzed. The manipulator structure has only five links and a compact configuration. Manipulator kinematics and dynamics are analyzed. Design guidelines are derived for static balancing of the manipulator and for minimizing the inertias driven by the motors. Operational configurations that either improve or worsen the kinematic and dynamic behaviour or characteristics of the manipulator are identified. The proposed design has an advantage over many currently known direct-drive manipulators for achieving two desirable mechanical features, namely: static balancing and compactness (smaller driven inertias).

A new design philosophy for the transmission of robot manipulators is proposed and an example of a practical implementation is presented. The philosophy combines the advantages of conventional geared robots in terms of relocating the actuators away from the joints and the alternative direct-drive approach. The gimbal drive is an example of a non-linear transmission where there is negligible friction, no backlash or compliance and which provides a varying reduction ratio for gravity compensation and for some dynamic decoupling. The gimbal drive is implemented on the three degrees of freedom SPRINTA prototype. Static repeatability, as well as tracking error and dynamic repeatability for the industrial goalpost test are measured. The performance demonstrates the potential of such a type of robot.