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Robotic prostheses have both emerging in the engineering literature recently. Such prostheses have the ability to better reproduce the variety of behaviors exhibited by the healthy limb during locomotion j_5, relative to passive prostheses. Powered prostheses require a controller to coordinate the movement of the prosthesis with that of the user; accordingly, various control approaches have been recently described 6_12. Such controllers should provide to the user safe, intuitive, and well-coordinated interaction with the prosthesis. This article presents and compares two different control systems for a powered knee and ankle prosthesis for transfemoral amputees that were constructed to provide such functionality (Le., to enable power delivery from the prosthesis in a manner that is safe, natural, and coordinated with the motion of the user). The first controller utilizes only impedance-like behaviors, while the second utilizes bcth impedance4keand admittance-like behaviors in ohyt-i C p. proach. The controllers were implemented. or a powered knee and ankle prosthas and tested in walking trials by a transfemoral amputee. Data from these trials irdcates that bath controllers achieve ~tig. rable performance with respect to ~dthy subject data, despite some substantial structural differences between the two.
A PIECEWISE PASSIVE IMPEDANCE CONTROL FRAMEWORK
A control structure for providing local passivity
Prosthesis motion can be decomposed into two components: movement associated with the internal configuration of the prosthesis, and movement of the prosthesis through space. The former can be described by the prosthesis joint angles, and the latter by joint angles combined with a set of generalized coordinates locating the center of mass and principal axes of the prosthesis relative to an inertial reference frame. For the control problem considered here, the control of movement of the prosthesis through space is assumed to be primarily governed by the user, in the same manner that a user would control movement of a passive prosthesis. As such, the control framework described here considers only the dynamics associated with the internal configuration of the prosthesis, hereafter referred to as the prosthesis dynamics (i.e., the dynamics described by the set of generalized coordinates consisting of prosthesis joint angles).
Two distinct sources of power can impart energy to the prosthesis: the amputee and the prosthesis actuators. The generalized forces associated with the user,/u,...