Stabilization of Inverted Coupled Pendula Using Parametric Excitation

Parametric stabilization of a single inverted pendulum has been extensively studied using the Mathieu equation and its corresponding stability diagram. The inverted single pendulum may be stabilized using parametric excitation at a specified frequency and amplitude given by a narrow stable region in the Mathieu diagram. Coupled pendula with parametric excitation or corresponding resonant systems have been studied from mathematical view point (Cesari, 1959; Gambill, 1955; Richards, 1983), from electrical view point (Sato, 1962a; Sato, 1962b; Sato, 1971; Sato, 1975) and from mechanical view point (Sato, 1995). Coupled pendula with parametric excitation have been studied within a limited region by some researchers, including the authors. A study of inverted coupled pendula with parametric excitation has not been performed as far as the authors know. Usually it is assumed that inverted coupled pendula are unstable in the absence of any other stabilizing mechanism such as feedback. One question is whether the inverted coupled pendula could be stabilized only by parametric excitation? The present paper gives an affirmative answer to this question in a limited and finite region. The stability is also examined using the differential equations and other methods.