Hybrid control of flexible multi-body systems

In constrained systems of rigid and flexible bodies, the gross rigid body motion and elastic deformation cannot be controlled independently because of the coupling between these two motions. A hybrid control method for suppressing the vibration of a geometrically nonlinear flexible multi-body system is proposed in this paper. This method utilizes both the passive and active control concepts. In the passive control strategy, flexible components in the system are manufactured from fiber-reinforced composite laminates which have high strength-to-weight and stiffness-to-weight ratios. On the other hand, the active control scheme used in this paper utilizes measurable velocity and acceleration signals to produce the command signals required to activate the actuator forces. A small number of sensors and controllers with constant gain factors are used in order to obtain a low-cost and simple control system. The generalized active control forces associated with the system generalized coordinates are developed using the virtual work and are written in terms of the coupled set of reference and elastic coordinates. The system differential equations of motion are developed using Lagrange's equation and the Jacobian matrix of the nonlinear algebraic constraint equations describing mechanical joints in the system is used to identify a set of independent generalized coordinates. The associated independent differential equations are identified and are written in the state space formulation. The characteristics of the proposed hybrid control are evaluated through computer simulations of a seven-body flexible vehicle. The performance characteristics of the hybrid control are also compared to the performance characteristics of the passive and active controls.