Exploratory Research on Controlled Passive Haptic Displays

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Robotic devices move autonomously, apply forces to objects in their environment, react to forces applied to them to achieve desired velocities, positions or impedances. Conventional robots use motors (active power transduction devices) to achieve these ends. This research examines a passive alternative to provide forces to resist motion initiated by a human or other active agent for the purpose of haptic display of remote or virtual environments or for guidance of the agent's motion. Ultimate applications are for virtual reality displays, for teleoperation, for surgical assistance, for exercise and for rehabilitation. The advantages of a passive approach include the elimination of inherent dangers of an active device and the reduction of cost and complexity when a power supply must be provided. This research will utilize a recently constructed prototype passive arm known as PTER (Passive Trajectory Enhancing Robot) as a test case. PTER has two degrees of freedom, coupled via electromagnetic brakes so that energy can be diverted in a controlled manner from one axis to the other. The research will explore the theoretical and practical aspects of the control algorithms to accomplish this coupling for purposes of haptic display such as PTER. The limitations of the passive actuators provide the uniqueness and challenge of the control. The control algorithm will be tested to determine effectiveness of the controlled passive device against two alternatives: (1) a direct physical display (not programmable) and (2) an electrically powered virtual display on an available kinematically identical robot. The measures of performance be both quantitative and subjective. The accuracy of the trajectory followed and the accuracy of representation of an environment's impedance (force-velocity relationship) can be quantitatively evaluated. Human operators will be employed to provide a more subjective evaluation on the effectiveness of the passive display. Example task s will be to follow a virtual maze as guided by the feel imparted by the device.