In the Journal of Microelectromechanical Systems, vol. 11, pp. 574-583, Oct. 2002, we presented an actuation scheme for toggling a bistable MEMS, a buckled beam, from one stable state to the other using radiation pressure of light. The experiments revealed some anomalous behavior of the beam. While long duration laser pulses at a power level slightly above the toggle threshold reliably toggled the beam every time, short duration pulses of the same power toggled the beam only about two-thirds of the time. In addition, when excessively high power levels (far above the toggle threshold) were used, the beam would not reliably toggle regardless of the pulse duration. This paper resolves the anomaly. It presents a nonlinear dynamical analysis of the bistable beam device which explains the anomaly as follows: a slightly higher than threshold force, applied for sufficient time, toggles the beam. If the force duration is longer than the time of decay of the oscillation of the beam about the toggled state, then the beam remains in that state after the force is removed. Otherwise, the beam may return to the original state. On the other hand, if the beam is toggled by a force far above the threshold, then after removal of the force, the beam may oscillate spanning both the states until the motion decays and the beam settles down to one of the states, not necessarily the toggled state, which may appear to be an anomalous behavior. The theoretical model is validated by a series of toggling experiments. [1035]

This paper describes a general technique for fitting a spatial kinematic model to an in-vivo anatomical joint under typical physiological loading conditions. The method employs a nonlinear least squares algorithm to minimize the aggregate deviation between postulated model motion and experimentally measured anatomical joint motion over multiple joint positions. Estimation of the parameters of a universal joint with skew-oblique revolutes to best reproduce wrist motion was used as an example. Experimental motion data from the right wrists of five subjects were analyzed. The technique performed very well and produced repeatable results consistent with previous biomechanical wrist findings.

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