Exploiting the Redundancy of a Hand-Arm Robotic System

In this report, a method for exploiting the redundancy of a hand-arm mechanical system for manipulation tasks is illustrated. The basic idea is to try to exploit the different intrinsic capabilities of the arm and hand subsystems. The Jacobian transpose technique is at the core of the method: different behaviors of the two subsystems are obtained by means of constraints in Null(J) generated by non-orthogonal projectors. Comments about the computation of the constraints are reported in the memo, as well as a description of some preliminary experiments on a robotic system at the A.I. Lab., M.I.T

Contact and grasp robustness measures: analysis and experiments

In this paper we discuss some aspects related to the practical assessment of the quality of a grasp by a robotic hand on objects of unknown shape, based on sensorial feedback from tactile and force sensors on the hand. We briefly discuss the concept of contact and grasp robustness, pointing out that the former is an easily computable but overconservative sufficient condition for the latter. Some experimental results on a simple gripper, the so-called “Instrumented Talon”, are reported as an illustration

Force-Direction Discrimination is Not Influenced by Reference Force Direction (Short Paper)

The authors report an experiment in which twenty-five participants discriminated force vectors presented along five directions (up, left, right, diagonally up left, diagonally up right). The force vectors were presented with a three degree-of-freedom forcefeedback device. A three-interval one-up three-down adaptive procedure was used. The five reference force-direction conditions were presented in randomly interleaved order. The results show an average force-direction discrimination threshold of 33° regardless of the reference-force direction. Position data recorded at a nominal sampling rate of 200 Hz revealed a 10.1 mm average displacement of the fingertip between the start and end positions in a trial. The average maximum deviation from the starting position within a trial was 21.3 mm. We conclude that the resolution with which people can discriminate force direction is not dependent on the direction of the force per se. These results are useful for designers of haptic virtual environments