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Issues in the haptic display of tool use

Our group is interested in using haptic display for training tool use. Applications include training doctors to use tools during surgery, and training astronauts to use tools during EVA. This paper describes some of the challenges of creating realistic haptic perceptions of tool use. Many of these challenges stem from the importance of unilateral constraints during tool use. Unilateral constraints occur whenever rigid bodies collide, resisting the interpenetration of the bodies, but not holding the bodies together. To identify unilateral constraints, a tool/environment simulation must perform collision detection. To respond properly to a collision, the simulation must estimate the forces that ensue, and integrate the equations of motion. All of these computations must occur in real time, and the simulation as a whole must be stable (to ensure the user's safety). Approaches to these problems are described.