- 170 - ICORR ’99: International Conference on Rehabilitation Robotics, Stanford, CA MODELLING HUMAN DYNAMICS IN-SITU FOR REHABILITATION AND THERAPY ROBOTS William Harwin and Steven Wall Department of Cybernetics, University of Reading, England Abstract This paper outlines some rehabilitation applications of manipulators and identifies that new approaches demand that the robot make an intimate contact with the user. Design of new generations of manipulators with programmable compliance along with higher level controllers that can set the compliance appropriately for the task, are both feasible propositions. We must thus gain a greater insight into the way in which a person interacts with a machine, particularly given that the interaction may be non-passive. We are primarily interested in the change in wrist and arm dynamics as the person co-contracts his/her muscles. It is observed that this leads to a change in stiffness that can push an actuated interface into a limit cycle. We use both experimental results gathered from a PHANToM haptic interface and a mathematical model to observe this effect. Results are relevant to the fields of rehabilitation and therapy robots, haptic interfaces, and telerobotics. Background There are several application areas where machines make an intimate contact with the user and in these situations it is important to gain a good understanding of human neuro- musculo-skeletal dynamics. Several areas in the field of rehabilitation robotics require this type of close contact with a person and in these situations it is possible that some useful information can be gained from that contact. Close contact robots in rehabilitation include power-assisted orthotic mechanisms [1], robots in physical therapy[2,3], and EPP based telerobotics[4]. In non-rehabilitation applications, close contact robots are common in haptic interfaces and telerobotics. To aid the design of close contact machines requires good knowledge of the human under conditions similar to those that will be experienced in practice. Although it is attractive to develop linear approximations of human dynamics as this allows for easier stability analysis, human arm dynamics are inherently non-linear and time dependent and include factors such as fatigue, posture, and movement history. In rehabilitation the clinical condition gives a further complication adding additional factors to the equation such as tremor, muscle atrophy, and limb flaccidity. We use a two level approach to understanding human neuro-musculo- skeletal dynamics and investigate co- contraction in the process. An