Simultaneous control of longitudinal and transverse vibrations of an axially moving string with velocity tracking

In this paper, an active control scheme for an axially moving string system that suppresses both longitudinal and transverse vibrations and regulates the transport velocity of the string to track a desired moving velocity profile is investigated. The control scheme utilizes three inputs: one control force at the right boundary, which is exerted by a hydraulic actuator equipped with a damper, and two control torques applied at the left and right rollers. The equations of motion are derived by using Hamilton's principle. Two nonlinear partial differential equations govern the longitudinal and transverse motions, where the variation of the tension of the string due to the transverse and longitudinal vibrations is considered. Among four boundary conditions, two describe the rotational dynamics of the left and right rollers; one determines the dynamics of the hydraulic actuator at the right boundary, and the last one denotes that the left boundary is fixed. The Lyapunov method is employed to generate control laws. Asymptotic stability of the transverse and longitudinal dynamics and the velocity tracking error is achieved. The effectiveness of the proposed control scheme is illustrated via numerical simulations. (c) 2012 Elsevier Ltd. All rights reserved.