Abstract
Modern control schemes adopted in multibody systems take advantage of the knowledge of a large set of measurements of the most important state variables to improve system performances. In the case of flexible‐link multibody systems, however, the direct measurement of these state variables is not usually possible or convenient. Hence, it is necessary to estimate them through accurate models and a reduced set of measurements ensuring observability. In order to cope with the large dimension of models adopted for flexible multibody systems, this paper exploits model reduction for synthesizing reduced‐order nonlinear state observers. Model reduction is done through a modified Craig‐Bampton strategy that handles effectively nonlinearities due to large displacements of the mechanism and through a wise selection of the most important coordinates to be retained in the model. Starting from such a reduced nonlinear model, a nonlinear state observer is developed through the extended Kalman filter (EKF). The method is applied to the numerical test case of a six‐bar planar mechanism. The smaller size of the model, compared with the original one, preserves accuracy of the estimates while reducing the computational effort.
Highlights
Flexible-link multibody (FLMB) systems are highly promising from an economical and sustainability point of view because of the use of less material and the need for smaller actuators and less power consumption
Flexibility often results in unwanted vibrations that limit motion accuracy and imposes advanced control schemes accounting for the flexible dynamics
By taking advantage of the idea of using reduced-order nonlinear models in the design of nonlinear observers, this work proposes a novel and comprehensive approach for efficient and accurate state estimation in FLMB systems. e method exploits the modified nonlinear CB reduction suitable for flexible-link mechanisms based on the equivalent rigid-link system (ERLS) and formulated through ordinary differential equations outlined in [25] and a wise selection of the most important coordinates, as proposed in [26]
Summary
Flexible-link multibody (FLMB) systems are highly promising from an economical and sustainability point of view because of the use of less material and the need for smaller actuators and less power consumption. E method exploits the modified nonlinear CB reduction suitable for flexible-link mechanisms based on the equivalent rigid-link system (ERLS) and formulated through ordinary differential equations (and independent coordinates) outlined in [25] and a wise selection of the most important coordinates, as proposed in [26] Such a model, that ensures that the dynamics with the highest observability and controllability are modeled in the system, is used for the synthesis of an extended Kalman filter (EKF) [27] to deliver accurate estimates of both the large motion and of the elastic vibrations of a FLMB system by means of a small set of sensed signals and with a reduced computational effort. E method is validated numerically, by investigating sensitivity to model uncertainty and measurement noise, by means of a planar 6-link FLMB system
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