The postural stiffness of the human arm has previously been estimated by displacing the hand from a series of equilibrium positions and correlating the resultant displacements and restoring forces. We extend this experimental methodology to include measurement of dynamic components of impedance. The stiffness-damping-mass characteristics are represented numerically as matrices and graphically as ellipses characterized by size, shape, and orientation. The latter depict the predominant nonrotational component of the impedance force fields. The results suggest: (1) joint damping is related to both joint stiffness and joint inertia; and (2) two-joint impedances, i.e., impedances associated with muscles connected across both the elbow and shoulder joints, play a relatively smaller role in damping than in stiffness. The ability to modulate stiffness in the face of initial static bias forces, i.e., "loading", is also examined. We observe regular shifts in the human arm endpoint's "spring center" corresponding to the bias force directions and magnitudes.>

The authors describe the design and implementation of a motor drive control system for an omnidirectional wheelbase, the Ilonator platform, developed at the Robotics Institute at Carnegie Mellon University. The experimental mobile platform is mounted on four omnidirectional wheels which permit a full three degrees of freedom (3 DOF) in the plane. The distributed servo-control system is coordinated by onboard computer which converts 3-DOF acceleration commands into individual velocity commands for the four wheels. Four HCTL-1000 motor control chips close the velocity-control feedback loops for the wheels. Details of the platform kinematics and motion command structure, servo hardware design and implementation, software for command and joystick control, and the experimental tuning of the controller parameters are presented.>

This paper describes the analysis and implementation of a motor drive control system for an intelligent wheelchair being developed at the Robotics Institute at Carnegie-Mellon University. The experimental mobile platform is mounted on four so-called Ilonators which permit motion in any direction without conventional steering of the wheel axes. The kinematics of the platform were determined analytically and a simulation program was developed to generate reference wheel velocity trajectories corresponding to several basic platform trajectories. These reference trajectories were used to drive the platform under open-loop control. The paper includes a description of the motor-drive hardware implementation, and experimental results. The results of this work provide the foundation for the implementation of feedback control of the wheels and higher-level supervisory control.

When a person walks the head undergoes horizontal and vertical rotations, and also horizontal and vertical translations. To visually fixate on an object while walking, compensatory horizontal and vertical eye movements must be made. The model for this gaze (head plus eye) control system includes three types of eye movements: smooth pursuit, saccadic, and vestibulo-ocular. The smooth pursuit system uses a target-selective adaptive controller that compensates for the large inherent time delay and produces zero-latency tracking of predictable targets. Target movements were selected to minimize the role of the saccadic control system. Typical tracking is shown while seated with the head restrained, standing with unrestrained head, performing voluntary head rotations, and walking. Each additional degree of freedom produced additional head movements that were compensated by additional eye movements. It is shown that while a human walks the effects of head rotations (yaw) cancel the effects of head translations, thus minimizing the resulting horizontal eye rotations necessary to maintain fixation.