This paper concentrates on size-dependent dynamic pull-in instability of micro-bridge gyroscopes under the combined effects of instantaneous DC voltage and the Casimir attraction. Hamilton’s principle is employed to derive the governing equations of motion based on the modified couple stress theory. Galerkin’s reduced order model is then utilized to obtain the ordinary differential equations of motion. In order to solve the reduced equations, fourth order Runge-Kutta method is used. The accuracy of the present model is validated through comparison with available results in the literature. Afterward effects of system parameters on the dynamic pull-in behavior of the system are investigated. It is found that neglecting the Casimir effect can lead to false results especially for systems with small initial gaps.

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