Ph.D. Thesis Defense by Davin K. Swanson
Wednesday, April 2, 2003

(Dr. Wayne Book, advisor)

"Implementation of Arbitrary Path Constraints using Dissipative Passive Haptic Displays"

Abstract

This research addresses the problem of providing arbitrary path constraints with a dissipative passive haptic display. Haptic displays are physical man-machine interfaces which interact with the user through the sense of touch. A dissipative passive display is one which uses actuators which may only dissipate energy; the user of such a device must initially provide all of the system's kinetic energy.

In some applications of haptic displays, it is necessary to constrain the user to a predefined path or surface in the workspace. This is referred to as a path constraint. Ideally, the user should be allowed to control the motion of the device along the defined path while the device prevents orthogonal motion. Restrictions in control effort due to the actuators used in passive displays make for a challenging control problem which is not easily solved through conventional methods.

Three control concepts are introduced. Two of the concepts allow the incorporation of coupling actuators, which allow the transfer of energy between links of the device. A set of human subject tests is used to fully evaluate these controllers with humans-in-the-loop using an existing two degree-of-freedom passive display with dissipative and coupling actuators. Physical performance metrics for path-following tasks are devised and used in the evaluation of the controllers. Also, physical metrics which may be used to predict or measure users' perceived levels of workload and smoothness are proposed, and data from the human subject tests is used to prove a correlation between the physical metrics and survey data.