Robot design optimization with haptic interface applications

To meet the high performance demands of modern robot applications, design variables such as materials, geometry, actuators and sensors must be chosen for optimum performance. This thesis presents a new way of choosing design variables to tune the capabilities of a robot to the needs of an application. The associated proposals are demonstrated through the design of a haptic interface. It is argued that isotropy over a given workspace is a good measure of design quality for many high performance applications. A new measure of isotropy, the Global Isotropy Index or GII, is presented which is computed from the singular values of a design matrix. To ensure that the singular values are meaningful, a technique is presented which normalizes and scales the design matrix. The technique removes all physical units from the design matrix and scales it to accommodate an application-dependent performance specification and non-homogeneous actuator capabilities. An algorithm has also been developed that solves for the design parameters that result in the optimum GII. It is so efficient that it can be used to compare the relative isotropies of different robot configurations. Performance specifications for a haptic interface are taken from the literature and are augmented by two biomechanical studies. The values obtained are used by the proposed design procedure to select the best of three robots to be used as a haptic pen. The preferred candidate is a novel hybrid design that uses two 3-DOF pantographs to position the ends of a pen shaped end-effector. A prototype with passive roll about the pen axis is built and controlled to simulate three virtual environments including a virtual pencil, a virtual scalpel and a virtual excavator. Its performance characteristics are measured and are used to draw conclusions about the effectiveness of the design procedure. Finally, a further performance improvement is sought via redundant actuation. It is shown that the motion range and force capabilities of a coarse-stage robot can be combined with the precision and high-acceleration of a fine-stage robot by connecting them in series and joining their end-effectors by a flexible coupling. A coarse-fine system such as this is expected to narrow the gap between achievable and ideal haptic interface performance.