A pneumatic muscle~PM! system was studied to determine whether a three-element model could describe its dynamics. As far as the authors are aware, this model has not been used to describe the dynamics of PM. A new phenomeno-logical model consists of a contractile ~force-generating! ele-ment, spring element, and damping element in parallel. The PM
system was investigated using an apparatus that allowed precise and accurate actuation pressure (P) control by a linear servo-valve. Length change of the PM was measured by a linear potentiometer. Spring and damping element functions of P were determined by a static perturbation method at several constant Pvalues. These results indicate that at constant P,
PM behaves as a spring and damper in parallel. The contractile element function ofPwas determined by the response to a step
input in P, using values of spring and damping elements from
the perturbation study. The study showed that the resulting
coefficient functions of the three-element model describe the
dynamic response to the step input ofPaccurately, indicating
that the static perturbation results can be applied to the dy-namic case. This model is further validated by accurately pre-dicting the contraction response to a triangular Pwaveform.
All three elements have pressure-dependent coefficients for
pressure Pin the range 207