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Vibration modes obtained from a modal analysis can be better explained from a screw theoretical standpoint. A vibration mode can be geometrically interpreted as a pure rotation about the vibration center in a plane and as a twisting motion on a screw in a three dimensional space. This paper presents a method to diagonalize a spatial stiffness matrix by use of a parallel axis congruence transformation when the stiffness matrix satisfies some conditions. It also describes that the diagonalized stiffness matrix can have the planes of symmetry depending on the location of the center of elasticity. For a system with the planes of symmetry, the vibration modes can be expressed by the axes of vibration. Analytical solutions for the axes of vibration have been derived. A numerical example of an application to the vibration analysis of an optical disc drive has been presented.

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In this paper, we introduce the 2-DOF robotic exoskeleton system for upper limb rehabilitation after stroke. We focused on the 2-DOF powered exoskeleton which consists of a cable-driven mechanism actuated by two motors. Strain gages measured torques which loaded elbow flexion/extension and wrist pronation/supination axes. sEMG(Electromyography) was used to detect the intentional movements of subjects to begin each training trials.

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