The Experts below are selected from a list of 582 Experts worldwide ranked by ideXlab platform
Annalisa Fregolent - One of the best experts on this subject based on the ideXlab platform.
-
Substructure decoupling without using Rotational Dofs: Fact or fiction?
Mechanical Systems and Signal Processing, 2015Co-Authors: Walter D׳ambrogio, Annalisa FregolentAbstract:Abstract In the framework of experimental dynamic substructuring, substructure decoupling consists in the identification of the dynamic behaviour of a structural subsystem, starting from the dynamic behaviour of both the assembled system and the residual subsystem (the known portion of the assembled system). On the contrary, substructure coupling identifies an assembled system starting from the component subsystems. The degrees of freedom (Dofs) of the assembled system can be partitioned into internal Dofs (not belonging to the couplings) and coupling Dofs. In substructure coupling, whenever coupling Dofs include Rotational Dofs, the related Rotational FRFs must be obtained experimentally. Does this requirement holds for substructure decoupling too, as it is commonly believed? Decoupling can be ideally accomplished by adding the negative of the residual subsystem to the assembled system (direct decoupling) and by enforcing compatibility and equilibrium at enough interface Dofs. Ideally, every DoF of the residual subsystem belongs to the interface between the assembled system and the residual subsystem. Hopefully, not all the coupling Dofs are necessary to enforce compatibility and equilibrium. This may allow us to skip coupling Dofs and specifically Rotational Dofs. The goal of the paper is indeed to establish if Rotational FRFs at coupling Dofs can be neglected in substructure decoupling. To this aim, after highlighting the possibility of avoiding the use of coupling Dofs from a theoretical standpoint, a test bed coupled through flexural and torsional Dofs is considered. Experimental results are presented and discussed.
-
Ignoring Rotational Dofs in Decoupling Structures Connected Through Flexotorsional Joints
Dynamics of Coupled Structures Volume 4, 2015Co-Authors: Walter D’ambrogio, Annalisa FregolentAbstract:Substructure decoupling consists in the identification of the dynamic behaviour of a structural subsystem, starting from the dynamic behaviour of both the assembled system and the residual subsystem (the known portion of the assembled system). The degrees of freedom (Dofs) of the coupled system can be partitioned into internal Dofs (not belonging to the couplings) and coupling Dofs. In direct decoupling, a fictitious subsystem that is the negative of the residual subsystem is added to the coupled system, and appropriate compatibility and equilibrium conditions are enforced at interface Dofs. Compatibility and equilibrium can be required either at coupling Dofs only (standard interface), or at additional internal Dofs of the residual subsystem (extended interface), or at some coupling Dofs and some internal Dofs of the residual subsystem (mixed interface). In this paper, a test bench is considered made by a cantilever column with two staggered short arms coupled to a horizontal beam. This involves both flexural and torsional Dofs, on which Rotational FRFs are quite difficult to measure. Using a mixed interface, Rotational Dofs are neglected and substituted by internal translational Dofs. Experimental results are presented and discussed.
-
Are Rotational Dofs Essential in Substructure Decoupling
Dynamics of Coupled Structures Volume 1, 2014Co-Authors: Walter D’ambrogio, Annalisa FregolentAbstract:Substructure decoupling consists in the identification of the dynamic behavior of a structural subsystem, starting from the known dynamic behavior of both the coupled system and the remaining part of the structural system (residual subsystem). The degrees of freedom (Dofs) of the coupled system can be partitioned into internal Dofs (not belonging to the couplings) and coupling Dofs. In direct decoupling, a fictitious subsystem that is the negative of the residual subsystem is added to the coupled system, and appropriate compatibility and equilibrium conditions are enforced at interface Dofs. Compatibility and equilibrium can be required either at coupling Dofs only (standard interface), or at additional internal Dofs of the residual subsystem (extended interface), or at some coupling Dofs and/or some internal Dofs of the residual subsystem (mixed interface). Using a mixed interface, Rotational coupling Dofs could be eliminated and substituted by internal translational Dofs. This would avoid difficult measurements of Rotational FRFs. This possibility is verified in this paper using simulated experimental data.
-
Decoupling procedures in the general framework of Frequency Based Substructuring
Society for Experimental Mechanics, 2009Co-Authors: W. D'ambrogio, Annalisa FregolentAbstract:The decoupling problem, i.e. the identification of the dynamic behaviour of a structural subsystem, starting from the known dynamic behaviour of the complete system, and from information about a second component subsystem, is revisited in the general framework of Frequency Based Substructuring. Several approaches have been proposed in the literature to tackle the decoupling problem. However, all of them present some pitfalls that have been also highlighted, such as modal truncation, lack of information on coupling Dofs (Rotational Dofs), ill-conditioning in the neighbourhood of particular frequencies. It has been shown that the last problem can be circumvented by including internal Dofs in the measured dataset, of course together with coupling (or interface) Dofs. In previous papers, two frequency based approaches were considered: an impedance based approach and a mobility based approach. In both approaches, the FRF matrix of the coupled system is assumed to be known at the coupling Dofs, and eventually at some internal Dofs of one subsystem. In this paper, an approach derived through the dual formulation, within the general framework of frequency based substructuring, is developed and discussed. Possible difficulties in the use of additional internal Dofs are envisaged and investigated. © 2009 Society for Experimental Mechanics Inc
Clement Gosselin - One of the best experts on this subject based on the ideXlab platform.
-
singularity analysis of 3t2r parallel mechanisms using grassmann cayley algebra and grassmann geometry
Mechanism and Machine Theory, 2012Co-Authors: Semaan Amine, Mehdi Tale Masouleh, Stephane Caro, Philippe Wenger, Clement GosselinAbstract:Abstract This paper deals with the singular configurations of symmetric 5-DOF parallel mechanisms performing three translational and two independent Rotational Dofs. The screw theory approach is adopted in order to obtain the Jacobian matrices. The regularity of these matrices is examined using Grassmann–Cayley algebra and Grassmann geometry. More emphasis is placed on the geometric investigation of singular configurations by means of Grassmann–Cayley algebra for a class of simplified designs whereas Grassmann geometry is used for a matter of comparison. The results provide algebraic expressions for the singularity conditions, in terms of some bracket monomials obtained from the superbracket decomposition. Accordingly, all the singularity conditions can be enumerated.
-
workspace analysis and optimal design of a 3 leg 6 dof parallel platform mechanism
International Conference on Robotics and Automation, 2003Co-Authors: Bruno Monsarrat, Clement GosselinAbstract:A new class of six-degree-of-freedom (Dofs) spatial parallel platform mechanism is considered in this paper. The architecture consists of a mobile platform connected to the base by three identical kinematic chains using five-bar linkages. Recent investigations showed that parallel mechanisms with such a topology for the legs can be efficiently statically balanced using only light elastic elements. This paper follows up with a workspace analysis and optimization of the design of that parallel mechanism. More specifically, considering a possible industrial application of the architecture as a positioning and orienting device of heavy loads, an optimization procedure for the maximization of the volume of the three-dimensional (3-D) constant-orientation workspace of the mechanism is first presented. As the mechanism could also have great potential as a motion base for flight simulators, we develop here a discretization method for the computation and graphical representation of a new workspace with coupled translational and Rotational Dofs. This workspace can be defined as the 3-D space which can be obtained when generalized coordinates x,y and torsion angle /spl psi/ in the tilt-and-torsion angles parametrization are constant. A second procedure is then presented for the maximization of the volume of this second subset of the complete workspace. For both approaches, our purpose is to attempt an optimal design of the mechanism by maximizing the volume of the associated 3-D Cartesian region that is free of critical singularity loci.
Walter D׳ambrogio - One of the best experts on this subject based on the ideXlab platform.
-
Substructure decoupling without using Rotational Dofs: Fact or fiction?
Mechanical Systems and Signal Processing, 2015Co-Authors: Walter D׳ambrogio, Annalisa FregolentAbstract:Abstract In the framework of experimental dynamic substructuring, substructure decoupling consists in the identification of the dynamic behaviour of a structural subsystem, starting from the dynamic behaviour of both the assembled system and the residual subsystem (the known portion of the assembled system). On the contrary, substructure coupling identifies an assembled system starting from the component subsystems. The degrees of freedom (Dofs) of the assembled system can be partitioned into internal Dofs (not belonging to the couplings) and coupling Dofs. In substructure coupling, whenever coupling Dofs include Rotational Dofs, the related Rotational FRFs must be obtained experimentally. Does this requirement holds for substructure decoupling too, as it is commonly believed? Decoupling can be ideally accomplished by adding the negative of the residual subsystem to the assembled system (direct decoupling) and by enforcing compatibility and equilibrium at enough interface Dofs. Ideally, every DoF of the residual subsystem belongs to the interface between the assembled system and the residual subsystem. Hopefully, not all the coupling Dofs are necessary to enforce compatibility and equilibrium. This may allow us to skip coupling Dofs and specifically Rotational Dofs. The goal of the paper is indeed to establish if Rotational FRFs at coupling Dofs can be neglected in substructure decoupling. To this aim, after highlighting the possibility of avoiding the use of coupling Dofs from a theoretical standpoint, a test bed coupled through flexural and torsional Dofs is considered. Experimental results are presented and discussed.
Metin Sitti - One of the best experts on this subject based on the ideXlab platform.
-
simultaneous six degree of freedom control of a single body magnetic microrobot
International Conference on Robotics and Automation, 2019Co-Authors: Joshua Giltinan, Metin SittiAbstract:As precise motion-controlled applications of mobile untethered devices emerge into real-world scenarios, full manipulator dexterity will be required. In rigid bodies without joints, one such requirement will be the ability to control all six-degrees-of-freedom (DOF). Magnetic fields and their spatial gradients are ideal for micromanipulation due to their long-range strong forces and torques, but the 6-DOF closed-loop control of such devices is a current challenge. Here we present a single-body microrobot that simultaneously demonstrates all 6-DOF. We accomplish this through the magnetic shape anisotropy of the microrobot design, yielding magnetization components, which are used to generate a torque about the 6 $^\text {th}$ DOF. We show that, under our design conditions, we can independently control the magnetic field as well as the magnetic force and torque. This allows for the open-loop control of the other Rotational Dofs, assuming the microrobot net magnetization vector will align with the magnetic field. We also describe a method that enables posing the 6 $^\text {th}$ DOF without feedback. These methods will enable the development of mobile submillimeter magnetic structures capable of full 6-DOF control for bioengineering, lab-on-a-chip, and desktop micromanufacturing applications.
John Ocallahan - One of the best experts on this subject based on the ideXlab platform.
-
frequency response function expansion for unmeasured translation and rotation Dofs for impedance modelling applications
Mechanical Systems and Signal Processing, 2003Co-Authors: Peter Avitabile, John OcallahanAbstract:Inclusion of Rotational effects is critical for the accuracy of the predicted system characteristics, in almost all system modelling studies. However, experimentally derived information for the description of one or more of the components for the system will generally not have any Rotational effects included in the description of the component. The lack of Rotational effects has long affected the results from any system model development whether using a modal-based approach or an impedance-based approach. Several new expansion processes are described herein for the development of FRFs needed for impedance-based system models. These techniques expand experimentally derived mode shapes, residual modes from the modal parameter estimation process and FRFs directly to allow for the inclusion of the necessary Rotational dof. The FRFs involving translational to Rotational Dofs are developed as well as the Rotational to Rotational dof. Examples are provided to show the use of these techniques.
