Closed-loop Control Experiments Research Articles

Active structural vibration control via sliding modes: Links to Lyapunov design

A nonlinear active vibration control design method is developed based upon an extension of variable structure control (VSC) techniques, in particular sliding mode control, to distributed parameter systems. The temporal compensator design utilizes a generalized wave equation representation of the plant. The control is implemented via a series of decentralized single-input/single-output (SISO) local loops around collocated transducers. No apriori knowledge of the temporal plant model is assumed, hence the resulting designs are insensitive to variations in the plant modal frequencies. The equivalent control reduces to output velocity feedback, a known stabilizing control. Active damping performance is enhanced through the introduction of an additive nonlinear term which selectively increases the velocity feedback control with a constrained nonlinear gain profile away from the zero-velocity phase plane origin. Stability constraints are discussed. For simple structural components such as beams and plates, the design method yields controllers identical to those derived using Lyapunov’s direct method, which extremize total system energy. Example controllers for beams and plates are presented. In order to demonstrate the application of the nonlinear control, closed-loop vibration control experiments on a 56- ×59-in. nine-bay aluminum grillage are summarized.

Active vibration control using a modal-domain fiber optic sensor

A closed-loop control experiment is described in which vibrations of a cantilevered beam are suppressed using measurements from a modal-domain fiber optic sensor. Modal-domain sensors use interference between the modes of a few-mode optical waveguide to detect strain. The fiber is bonded along the length of the beam and provides a measurement related to the strain distribution on the surface of the beam. A model for the fiber optic sensor is derived, and this model is integrated with the dynamic model of the beam. A piezoelectric actuator is also bonded to the beam and used to provide control forces. Control forces are obtained through dynamic compensation ofthe signal from the fiber optic sensor. The compensator is implemented with a real-time digital controller. Analytical models are verified by comparing simulations to experimental results for both open-loop and closed-loop configurations.

Development and implementation of a high speed open loop control technique for micro-positioning of mechanical structures

A method has been developed for dynamic open loop control of a structure modelled as a single degree of freedom system with damping. The technique predicts the required input signal to the system such that a specified output motion is produced with minimal overshoot and ringing. Micropositioning implementation to a mechanical system consisting of a flexible beam driven by a piezoelectric crystal has shown promising results for controlled step and pulse outputs. Significant improvement in both rise time and dynamic control of the beam for a step output was demonstrated with respect to a previous closed loop control experiment on the same structure.