Papers by Alberto Trevisani
Journal of Vibration Engineering & Technologies
Purpose This paper proposes an integrated method for optimizing the response of underactuated lin... more Purpose This paper proposes an integrated method for optimizing the response of underactuated linear vibratory feeders operating in open-loop control, under generic periodic excitations. The goal is ensuring a uniform motion of the tray, despite the presence of less actuators than degrees of freedom and of several specifications of the desired motion. Method To cope with the underactuated nature of these systems and with their non-minimum phase behavior, dynamic structural modification and the inverse dynamics approach are properly integrated by exploiting a common definition of the system internal dynamics. In the inverse dynamics problem, the inverse dynamics is stabilized through output redefinition and the resulting ordinary differential equations are integrated to compute causal actuation forces, ensuring almost-exact tracking for as many coordinates as the number of actuators. The tracking of the remaining coordinates of interest is improved through a proper design of the mech...
The International Journal of Advanced Manufacturing Technology, Nov 21, 2020
Resonant vibration generators, such as vibratory feeders or ultrasonic sonotrodes, are often empl... more Resonant vibration generators, such as vibratory feeders or ultrasonic sonotrodes, are often employed in manufacturing to generate harmonic vibrations with suitable amplitude, spatial shape, and frequency, in order to meet the process requirements. These underactuated systems are usually excited in open loop by few actuators, and therefore, it is not ensured that the desired response is correctly achieved, since the feasible motions should belong to the subset of the allowable motions. To achieve the closest approximation of the desired vibrations, some new solutions are here proposed. The first strategy is the optimal shaping of the harmonic forces exerted by the actuators, by solving an inverse dynamic problem through a coordinate transformation and the projection of the desired response onto the subspace of the allowable motion. By exploiting the formulation of such a subspace, a second approach that involves concurrently both the force shaping and the modification of the inertial and elastic system parameters is proposed. The idea of this approach is to exploit the modification of the elastic and inertial parameters to properly shape the allowable subspace in such a way that it spans the desired response. A solution method is developed, and analytical sensitivity analysis is proposed to choose the design variables. Validation is proposed through a linear vibratory feeder with a long flexible tray, taken from the literature. The results show the effectiveness of the proposed strategies that lead to a very precise approximation of the desired response.
Archives of Computational Methods in Engineering, Apr 28, 2021
Vibration absorption is a core research area in the design and control of structures and machines... more Vibration absorption is a core research area in the design and control of structures and machines, and exploiting antiresonances is an effective approach for systems under harmonic excitation. This paper proposes a comparative study and a review of the main passive techniques to antiresonance assignment proposed in the recent literature, by discussing them through some numerical examples too. The techniques discussed include the well-known Tuned Mass Damper, which has been widely developed in the literature. However, as the title reveals, great attention is paid to the methods inherited from the field of dynamic structural modification that assign antiresonances without modifying the number of degrees of freedom, by exploiting a proper modification of the system inertial and stiffness parameters. Due to higher mathematical complexity, these approaches have been less investigated in the literature although they are an effective and less invasive approach to antiresonance assignment, especially for machines. To puzzle out the complicated subject matter of antiresonances, their background and their key features are also discussed by reviewing the main theoretical results and their relationship with the assignment techniques. The paper is also enriched with several numerical examples to compare different methods and investigate the features of antiresonances. The concluding remarks of the paper bring together some open issues in this field of research and outlines some possible research directions.
Mode selection for reduced order modeling of mechanical systems excited at resonance
International Journal of Mechanical Sciences, Aug 1, 2016
Abstract Welding, food cutting, atomizing, cleaning and deagglomerating are just a few common use... more Abstract Welding, food cutting, atomizing, cleaning and deagglomerating are just a few common uses for ultrasonic resonators, which are carefully designed to operate excited in resonance. Finite element analysis is nearly always adopted for predicting and improving resonator performances. Large number of small elements are usually needed to guarantee accuracy. As a consequence, models have typically very large dimensions, and hence considerable computational and ill conditioning problems arise. Model reduction techniques can be extremely useful to keep model dimensions to a minimum. In this paper a new ranking method, called Interior Mode Ranking (IMR), is introduced for the selection of the interior normal modes in the Craig Bampton reduction technique, which is one of the most popular model reduction methods, often available in commercial finite element software packages. The IMR method allows ranking the interior modes analytically by comparing the contributions provided by the interior modes of the subsystem with constrained boundary conditions to the dynamics of interest of the complete system (with actual boundary conditions). The method is general and can be applied to any resonator in the reduction at the system level. Here it is employed to obtain an accurate reduced-order model of an ultrasonic welding bar horn. The results achieved by the method are compared with those yielded by other ranking techniques. The comparison shows that the IMR method outperforms the other ranking techniques and leads to accurate representations of the excited modes.
Performances of flexible link multibody systems, in terms of accuracy and repeatability, can be n... more Performances of flexible link multibody systems, in terms of accuracy and repeatability, can be negatively affected by link flexibility that causes unwanted vibration. Therefore, advanced controllers are necessary for vibration suppression. The synthesis of such controllers typically relies on the knowledge of all the system state variables, whose direct measurement is complicated, or at least of a meaningful set of the most relevant ones. For such a reason, these state variables should be estimated through state observers. In particular, state observers based on reduced-order dynamic models should be employed, to reduce the computational effort. This paper shows some preliminary results on state estimation in flexible-link multibody systems based on nonlinear, reduced-order dynamic model formulated through independent coordinates. Reduction is performed through a modified Craig-Bampton strategy. Numerical simulations of a six-bar planar mechanism show that the proposed observer delivers accurate estimates of both the rigid and elastic variables.
Model reduction through enhanced Craig-Bampton transformation and interior mode selection
A reduction strategy at system level for flexible link multibody systems
Machines, Jun 8, 2022
This paper proposes the preliminary results on a novel control architecture based on model predic... more This paper proposes the preliminary results on a novel control architecture based on model predictive control (MPC) for cable-driven parallel robots (CDPRs) and applies them to a three degrees of freedom (3-DOF) robot with a suspended configuration, leading to a cable-suspended parallel robot (CSPR). The goal of the control scheme is ensuring accurate path tracking of the reference end-effector path, while imposing a priori positive cable tensions. To handle the nonlinearities characterizing the dynamic model that governs this kind of multibody system and to keep the computational effort low, a position-dependent MPC algorithm with an embedded integrator is designed to compute the optimal cable tensions required to track the end-effector commanded path. Such tensions must belong to the feasible domain defined through a lower bound, which is slightly greater than zero, to ensure that cables pull the end-effector, and an upper bound, to represent the maximum stress that cables can withstand without breaking. The resulting controller is nonlinear, although it performs a local linearization in the prediction at each time step to reduce the computational effort. The optimal tensions are then transformed into the commanded motor torques through the inverse dynamic model of the servomotors driving the winches, since no force measurement is adopted in the controller implementation. The control architecture is designed and numerically validated through a spatial CSPR with lumped end-effector, and driven by three cables (i.e., with a non-redundant configuration). Four different paths are assumed to highlight various features of the proposed controller.
Journal of physics, Sep 1, 2016
The dynamic response of flexible-link multibody systems (FLMSs) can be predicted through nonlinea... more The dynamic response of flexible-link multibody systems (FLMSs) can be predicted through nonlinear models based on finite elements, to describe the coupling between rigidbody and elastic behaviour. Their accuracy should be as high as possible to synthesize controllers and observers. Model updating based on experimental measurements is hence necessary. By taking advantage of the experimental modal analysis, this work proposes a model updating procedure for FLMSs and applies it experimentally to a planar robot. Indeed, several peculiarities of the model of FLMS should be carefully tackled. On the one hand, nonlinear models of a FLMS should be linearized about static equilibrium configurations. On the other, the experimental mode shapes should be corrected to be consistent with the elastic displacements represented in the model, which are defined with respect to a fictitious moving reference (the equivalent rigid link system). Then, since rotational degrees of freedom are also represented in the model, interpolation of the experimental data should be performed to match the model displacement vector. Model updating has been finally cast as an optimization problem in the presence of bounds on the feasible values, by also adopting methods to improve the numerical conditioning and to compute meaningful updated inertial and elastic parameters.
Proceedings of the 10th ECCOMAS Thematic Conference on MULTIBODY DYNAMICS, 2021
Cable-driven parallel robots are light-weight parallel robots where cables replace rigid actuator... more Cable-driven parallel robots are light-weight parallel robots where cables replace rigid actuators to move an end-effector. As a consequence, they can be characterized by very large workspaces, high-dynamic handlings, ease of reconfigurability and/or low-cost architecture. Since the driving links are flexible, the state variables of the robot cannot be always directly measured, thus the development of state observers is essential. In this work a general approach to develop a nonlinear state observer based on an Extended Kalman Filter is proposed and validated numerically by referring to a cable-suspended parallel robot. The state observer is based on a system model obtained converting a set of Differential Algebraic Equations into Ordinary Differential Equations through two different methods: the penalty formulation and the Udwadia-Kalaba formulation.
Wave Based Control (WBC) has been proven to be very effective in combining position and oscillati... more Wave Based Control (WBC) has been proven to be very effective in combining position and oscillation control of underactuated flexible multibody systems [1]. This paper proposes an extension of the method aimed at ensuring accurate path tracking of a load suspended by a planar Cartesian crane, even in the presence of non ideal actuators and sensors. The basic configuration of WBC [1] uses the measured mechanical wave coming back from the flexible system to the actuator, the so called returning wave, to accomplish both position control and active swing damping. In Cartesian cranes, two independent controllers for the X and Y axis set the trolley position references, q T , to be the sum of two components (q denotes both the X and Y motion). The first component is set to half the load displacement reference, q L , and is the launch wave. The second component is the measured returning wave, denoted bq . The addition of this second component performs active vibration damping while moving ...
Performances of flexible link multibody systems, in terms of accuracy and repeatability, can be n... more Performances of flexible link multibody systems, in terms of accuracy and repeatability, can be negatively affected by link flexibility that causes unwanted vibration. Therefore, advanced controllers are necessary for vibration suppression. The synthesis of such controllers typically relies on the knowledge of all the system state variables, whose direct measurement is complicated, or at least of a meaningful set of the most relevant ones. For such a reason, these state variables should be estimated through state observers. In particular, state observers based on reduced-order dynamic models should be employed, to reduce the computational effort. This paper shows some preliminary results on state estimation in flexible-link multibody systems based on nonlinear, reduced-order dynamic model formulated through independent coordinates. Reduction is performed through a modified Craig-Bampton strategy. Numerical simulations of a six-bar planar mechanism show that the proposed observer del...
Preliminary in Vitro Biocompatibility Test on a New Wearable/Portable Device for Extracorporeal Blood Ultrafiltration
Man-machine interaction by haptic systems
Development and Performance Assessment of a Laser Triangulation Scanner for Digitizing Shoe Lasts
AMST’02 Advanced Manufacturing Systems and Technology, 2002
This paper presents a non-contact laser triangulation 3D digitizer which offers a good combinatio... more This paper presents a non-contact laser triangulation 3D digitizer which offers a good combination of accuracy, efficiency, robustness and portability. The key component of the digitizer is an accurate laser triangulation rangefinder which moves on a vertical plane and continuously measures the distance of a last attached to a rotating shaft. A PD control action keeps the distance between the sensor and the last surface within the sensor measuring range, and close to the reference distance which minimizes measurement errors. One linear encoder, measuring the sensor horizontal displacements, and a shaft-position encoder, measuring the last angular displacements, provide the additional data needed for cross section reconstruction. The problem of digitizing a cross section which does not contain the center of rotation is faced using a photoelectric sensor detecting the cross section dimensions before the last reaches the rangefinder. The experimental results prove the effectiveness of the proposed system.
Structural and Multidisciplinary Optimization, 2020
The paper proposes a multi-domain approach to the optimization of the dynamic response of an unde... more The paper proposes a multi-domain approach to the optimization of the dynamic response of an underactuated vibrating linear system through eigenstructure assignment, by exploiting the concurrent design of the mechanical properties, the regulator and state observers. The approach relies on handling simultaneously mechanical design and controller synthesis in order to enlarge the set of the achievable performances. The underlying novel idea is that structural properties of controlled mechanical systems should be designed considering the presence of the controller through a concurrent approach: this can considerably improve the optimization possibilities. The method is, first, developed theoretically. Starting from the definition of the set of feasible system responses, defined through the feasible mode shapes, an original formulation of the optimality criterion is proposed to properly shape the allowable subspace through the optimal modification of the design variables. A proper choic...
The International Journal of Advanced Manufacturing Technology, 2020
Resonant vibration generators, such as vibratory feeders or ultrasonic sonotrodes, are often empl... more Resonant vibration generators, such as vibratory feeders or ultrasonic sonotrodes, are often employed in manufacturing to generate harmonic vibrations with suitable amplitude, spatial shape, and frequency, in order to meet the process requirements. These underactuated systems are usually excited in open loop by few actuators, and therefore, it is not ensured that the desired response is correctly achieved, since the feasible motions should belong to the subset of the allowable motions. To achieve the closest approximation of the desired vibrations, some new solutions are here proposed. The first strategy is the optimal shaping of the harmonic forces exerted by the actuators, by solving an inverse dynamic problem through a coordinate transformation and the projection of the desired response onto the subspace of the allowable motion. By exploiting the formulation of such a subspace, a second approach that involves concurrently both the force shaping and the modification of the inertia...
Applied Sciences, 2020
This paper proposes a novel method for pole placement in linear vibrating systems through state f... more This paper proposes a novel method for pole placement in linear vibrating systems through state feedback and rank-one control. Rather than assigning all the poles to the desired locations of the complex plane, the proposed method exactly assigns just the dominant poles, while the remaining ones are free to assume arbitrary positions within a pre-specified region in the complex plane. Therefore, the method can be referred to as “regional pole placement”. A two-stage approach is proposed to accomplish both the tasks. In the first stage, the subset of dominant poles is assigned to exact locations by exploiting the receptance method, formulated for either symmetric or asymmetric systems. Then, in the second stage, a first-order model formulated with a reduced state, together with the theory of Linear Matrix Inequalities, are exploited to cluster the subset of the unassigned poles into some stable regions of the complex plane while keeping unchanged the poles assigned in the first stage....
Estimation of the digging and payload forces in excavators by means of state observers
Mechanical Systems and Signal Processing, 2019
Abstract A state estimation-based approach is proposed to determine both the forces exchanged bet... more Abstract A state estimation-based approach is proposed to determine both the forces exchanged between the soil and the bucket of a hydraulic excavator during digging tasks and the load of the soil accumulated in the bucket. The suggested approach ensures real-time force estimates, which constitutes a necessary preliminary requirement to address the open issue of unmanned earthmoving machine development. The estimates are carried out employing a two-stage estimation approach. It requires the implementation of two observers partially coupled based on kinematic and dynamic excavator models, and measurements which can be collected easily and by inexpensive sensors. An estimation regularization is introduced, which allows to get accurate estimates also in the presence of ill-conditioned system models. The approach is validated by applying it to a very accurate numerical simulator. The sensitivity analysis carried out at varying level of modeling errors highlights that digging and payload forces can be estimated efficiently and effectively in the presence of both relevant model and measurement errors.
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Papers by Alberto Trevisani