Energy-Based Optimal Ranking of the Interior Modes for Reduced-Order Models under Periodic Excitation

This paper introduces a novel method for ranking and selecting the interior modes to be retained in the Craig-Bampton model reduction, in the case of linear vibrating systems under periodic excitation. The aim of the method is to provide an effective ranking of such modes and hence an optimal sequence according to which the interior modes should be progressively included to achieve a desired accuracy of the reduced-order model at the frequencies of interest, while keeping model dimensions to a minimum. An energy-based ranking (EBR) method is proposed, which exploits analytical coefficients to evaluate the contribution of each interior mode to the forced response of the full-order system. The application of the method to two representative systems is discussed: an ultrasonic horn and a vibratory feeder. The results show that the EBR method provides a very effective ranking of the most important interior modes and that it outperforms other state-of-the-art benchmark techniques

Deformation Control in Rest-to-Rest Motion of Mechanisms with Flexible Links

This paper develops and validates experimentally a feedback strategy for the reduction of the link deformations in rest-to-rest motion of mechanisms with flexible links, named Delayed Reference Control (DRC). The technique takes advantage of the inertial coupling between rigid-bodymotion and elasticmotion to control the undesired link deformations by shifting in time the position reference through an action reference parameter. The action reference parameter is computed on the fly based on the sensed strains by solving analytically an optimization problem. An outer control loop is closed to compute the references for the position controllers of each actuator, which can be thought of as the inner control loop. The resulting multiloop architecture of the DRC is a relevant advantage over several traditional feedback controllers: DRC can be implemented by just adding an outer control loop to standard position controllers. A validation of the proposed control strategy is provided by applying the DRC to the real-time control of a four-bar linkage

Robust Assignment of Natural Frequencies and Antiresonances in Vibrating Systems through Dynamic Structural Modification

This paper proposes a novel method for the robust partial assignment of natural frequencies and antiresonances, together with the partial assignment of the related eigenvectors, in lightly damped linear vibrating systems. Dynamic structural modification is exploited to assign the eigenvalues, either of the system or of the adjoint system, together with their sensitivity with respect to some parameters of interest. To handle with constraints on the feasible modifications, the inverse eigenvalue problem is cast as a minimization problem and a solution method is proposed through homotopy optimization. Variables lifting for bilinear and trilinear terms, together with bilinear and double-McCormick's constraints, are exploited to provide a convexification of the problem and to boost the attainment of the global optimum. The effectiveness of the proposed method is assessed through four numerical examples

Modelli e schemi per il controllo del moto di attuatori idraulici

This thesis deals with the modeling and control of electohydraulic systems. On basis on an accurate nonlinear model, an innovative position control scheme is proposed. Such a control scheme is mady by some decoupled actions, each one aimed at achieving a specific target in the dynamic response of the system. Besides that, an original and innovative scheme for the coordinated motion control of multi-dof hydraulic systems is proposed. Such a control scheme, referred to as Delayed Reference Synchronization Control, aims at reducing the synchronization error by delaying the references of the inner position loop of the axis, on basis on an equivalent elastic error. The effectiveness of both control schemes is assessed by numerical simulations by means of an accurate simulator employed in Simulink

A NON-TIME BASED STRATEGY FOR THE COORDINATED MOTION CONTROL OF HYDRAULIC ACTUATORS

Despite the extensive research concerning the motion control of a hydraulic systems, the coordinated motion (synchronized motion) of multi-axis hydraulic systems is still an open and challenging field. In such a frame, this paper presents an innovative non-time based control strategy for the coordinated motion control of multi-axis hydraulic systems. The proposed approach, named DRSC (Delayed Reference Synchronization Control) allows achieving the coordinated motion by delaying the position reference of each actuator on the basis of an action reference parameter, which plays therefore the role of a delayed time. Such a scalar variable is computed on the fly on the basis of a properly defined equivalent elastic error, which is in turn a function of the state of the system and of the position measurements. The theory developed is demonstrated through numerical simulations by applying it to the path tracking control of a two-axis hydraulic system

DESIGN OF DELAYED REFERENCE CONTROLLERS FOR SIMULTANEOUS PATH TRACKING AND ACTIVE VIBRATION DAMPING OF MULTI-DEGREE-OF-FREEDOM LINEAR SYSTEMS

This paper presents an innovative non-time-based control strategy for the simultaneous path tracking and active vibration damping of multi-degree-of-freedom linear systems. The fundamental difference between the proposed scheme, and those that have already appeared in literature, is that it allows keeping the coordinated motion of different actuators. In other words, the use of such a scheme guarantees that a desired path in space is accurately followed while suppressing the undesired vibrational effects. The control strategy consists in actively suppressing the undesired vibrations by suitably changing the path reference for the system. Such a result can be achieved by making the path reference for the system be a function of an action reference parameter rather than just the time. The reference parameter depends on time and on a variable which plays the role of a time delay. The latter is computed on the fly, on the basis of the measured vibration. A cascade control structure is obtained, where no specific position controllers or actuators are to be employed in the inner loop. The theory developed is demonstrated through numerical simulations by applying it to the vibration and path tracking control of a four-degrees-of-freedom two-mass system