This paper focuses on the problem of force-feedback for the human-operator hand when manipulating virtual objects. We propose a method for the computation of feedback-forces that have to be applied on each individual phalanx and jinger of the human hand in order to display pertinent, kinesthetic information about static or dynamic chamcteristics of objects present in the virtual scene. External forces and moments of the manipulated virtual objects have to be mapped on the contact-forces space of the virtual grasp. The method is based on the solution of a nonlinear programming problem, formu-lated by performing a static analysis of a general, multiple contact points virtual grasp. A methodology for modelling interactions within a virtual environment, and performing realistic grasping and manipu-lation, is also presented.

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The Powered Gait Orthosis (PGO) is a powered exoskeleton developed as an experimental device to provide bipedal locomotion to individuals with physical impairment. The current prototype consists of a single degree of freedom (DOF) system for each leg, providing power and proper displacement required for bipedal locomotion . It is the goal of this research to obtain the forces that are present in the device while it is in normal operation . In addition, the time ratio of the hip function generator has been varied to determine the effect that different time ratios have on system forces and required user energy. The time ratio is the relationship between the time period that the thigh is in swing phase and when it is in support phase. Knowing the forces in the system and the optimal time ratio will allow for the design and construction of a feasible device for the rehabilitation and assistance of individuals who have lost the ability to walk.

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