Now showing 1 - 4 of 4
  • Publication
    Wave-based control of under-actuated flexible structures with strong external disturbing forces
    (Institute of Engineering and Computational Mechanics, 2012-05) ;
    Wave-based control (WBC) of underactuated, flexible systems considers actuator motion as launching a mechanical wave into the flexible system which it then absorbs on its return to the actuator. The launching and absorbing proceed simultaneously. This simple, intuitive idea leads to robust, generic, highly efficient, precise, adaptable controllers, allowing rapid and almost vibrationless re-positioning of the system, using only sensors colocated at the actuator-system interface. These wave-based ideas have already been shown to work on simple systems such as mass-spring strings, systems of Euler-Bernoulli beams, and flexible space structures undergoing slewing motion (rotation with lateral translation). The current work extends this strategy to systems experiencing external disturbing forces, whether body forces which endure over time, such as gravitational effects which change with system orientation, or transient forces such as from impacts or external viscous damping. The revised strategy additionally provides robustness to some sensor errors.  The strategy has the controller learn about the disturbances and compensate for them, yet without needing new sensors or measurements beyond those of standard WBC.
      394
  • Publication
    Multibody domain decomposition for parallel processing: a wave-based approach to handling interface dynamics
    For many good reasons there is growing interest in ways to allow parallel processing of multibody dynamics problems. Some recent approaches include “Domain Decomposition” and “Divide and Conquer”. This paper explores a new approach, reported as work in progress, with initial, promising results. The strategy is an extension of work done on wave analysis of lumped systems in another context. In the approach, a larger system is subdivided into smaller subsystems, which are solved in parallel. Interconnection points are boundaries for each. Dynamic coupling across boundaries is handled in terms of transmitted and reflected motion components (or "waves"), in both directions, across the boundaries.
      219
  • Publication
    Boundary-controlled travelling and standing waves in cascaded lumped systems
    (Elsevier, 2012-05) ;
    This paper shows how pure travelling waves in cascaded, lumped, uniform, mass-spring systems can be defined, established, and maintained, by controlling two boundary actuators, one at each end. In most cases the control system for each actuator requires identifying and measuring the notional component waves propagating in opposite directions at the actuator-system interfaces. These measured component waves are then used to form the control inputs to the actuators. The paper also shows how the boundaries can be actively controlled to establish and maintain standing waves of arbitrary standing wave ratio, including those corresponding to the classical modes of vibration of such systems with textbook boundary conditions. These vibration modes are achieved and maintained by controlled reflection of the pure travelling wave components. The proposed control systems are also robust to system disturbances: they react to overcome external disturbances quickly and so to re-establish the desired steady motion.
      541
  • Publication
    Travelling waves in boundary-controlled, non-uniform, cascaded lumped systems
    (Elsevier, 2012-05) ;
    A companion paper considers travelling and standing waves in cascaded, lumped, mass-spring systems, controlled by two boundary actuators, one at each end, when the system is uniform. It first proposes definitions of waves in finite lumped systems. It then shows how to control the actuators to establish desired waves from rest, and to maintain them despite disturbances. The present paper extends this work to the more general, non-uniform case, when mass and spring values can be arbitrary. A special ¿bi-uniform¿ case is first studied, consisting of two different uniform cascaded systems in series, with an obvious, uncontrolled, impedance mismatch where they meet. The paper shows how boundary actuator control systems can be designed to establish, and robustly maintain, apparently pure travelling waves of constant amplitude in either the first or the second uniform section, in each case with an appropriate, partial, standing wave pattern in the other section. Then a more general non-uniform case is studied. A definition of a ¿pure travelling wave¿ in non-uniform systems is proposed. Curiously, it does not imply constant amplitude motion. It does however yield maximum power transfer between boundary actuators. The definition, and its implementation in a control system, involves extending the notions of ¿pure¿ travelling waves, of standing waves, and of input and output impedances of sources and loads, when applied to non-uniform lumped systems. Practical, robust control strategies are presented for all cases.
      459