1,720,985 research outputs found
Flexible-link multibody system eigenvalue analysis parameterized with respect to rigid-body motion
Full text linkThe dynamics of flexible multibody systems (FMBSs) is governed by ordinary differential equations or differential-algebraic equations, depending on the modeling approach chosen. In both the cases, the resulting models are highly nonlinear. Thus, they are not directly suitable for the application of the modal analysis and the development of modal models, which are very useful for several advanced engineering techniques (e.g., motion planning, control, and stability analysis of flexible multibody systems). To define and solve an eigenvalue problem for FMBSs, the system dynamics has to be linearized about a selected configuration. However, as modal parameters vary nonlinearly with the system configuration, they should be recomputed for each change of the operating point. This procedure is computationally demanding. Additionally, it does not provide any numerical or analytical correlation between the eigenpairs computed in the different operating points. This paper discusses a parametric modal analysis approach for FMBSs, which allows to derive an analytical polynomial expression for the eigenpairs as function of the system configuration, by solving a single eigenvalue problem and using only matrix operations. The availability of a similar modal model, which explicitly depends on the system configuration, can be very helpful for, e.g., model-based motion planning and control strategies towards to zero residual vibration employing the system modal characteristics. Moreover, it allows for an easy sensitivity analysis of modal characteristics to parameter uncertainties. After the theoretical development, the method is applied and validated on a flexible multibody system, specifically using the Equivalent Rigid Link System dynamic formulation. Finally, numerical results are presented and discussed
Vibrational behavior of epicyclic gear trains with lumped-parameter models: Analysis and design optimization under uncertainty
No full textVibrational behavior of epicyclic gearing a critical aspect as this can lead to detrimental structural-mechanical effects including fatigue, comfort and acoustics. In order to better understand this behavior, lumped-parameter models are used in early development phases. Here the eigenfrequencies as well as frequency responses are ascertained with and without consideration of uncertainty. Uncertainty is critical in the early design phases and beyond. In such systems, there is variation in parameter values from a variety of sources. Here the uncertain stiffness will be considered. It is also the goal of this work to dimension the epicyclic gear train to optimize performance. The early design phase is plagued by uncertainty and if this is neglected in the design optimization, this can lead to drastically suboptimal designs. In this work, a methodology is introduced to optimally design and dimension epicyclic gear trains under uncertainty. Though specifically aimed at epicyclic gearing, the methods developed here are general enough for further application fields. Mass and inertia terms are chosen as design variables, though others are possible in this framework. The constraints are so formulated so that the eigenfrequencies avoid the harmonics of the mesh frequencies and its side bands. The uncertain parameters are treated as bounded and therefore intervals are used instead of statistical distributions. Statistical information needed for probabilistic methods of the uncertain parameters are assumed here to be unavailable in early development phases
Minimization of the energy consumption in industrial robots through regenerative drives and optimally designed compliant elements
Full text linkThis paper describes a method for reducing the energy consumption of industrial robots and electrically actuated mechanisms performing cyclic tasks. The energy required by the system is reduced by outfitting it with additional devices able to store and recuperate energy, namely, compliant elements coupled in parallel with axles and regenerative motor drives. Starting from the electromechanical model of the modified system moving following a predefined periodic path, the relationship between the electrical energy and the stiffness and preload of the compliant elements is analyzed. The conditions for the compliant elements to be optimal are analytically derived. It is demonstrated that under these conditions the compliant elements are always beneficial for reducing the energy consumption. The effectiveness of the design method is verified by applying it to two test cases: a five-bar mechanism and a SCARA robot. The numerical validations show that the system energy consumption can be reduced up to the 77.8% while performing a high-speed, standard, not-optimized trajectory
An approximation-based design optimization approach to eigenfrequency assignment for flexible multibody systems
Full text linkThe use of flexible multibody simulation has increased significantly over recent years due to the increasingly lightweight nature of mechanical systems. The prominence of lightweight engineering design in mechanical systems is driven by the desire to require less energy in operation and to reach higher speeds. However, flexible lightweight systems are prone to vibration, which can affect reliability and overall system performance. Whether such issues are critical depends largely on the system eigenfrequencies, which should be correctly assigned by the proper choice of the inertial and elastic properties of the system. In this paper, an eigenfrequency assignment method for flexible multibody systems is proposed. This relies on a parametric modal model which is a Taylor expansion approximation of the eigenfrequencies in the neighborhood of a configuration of choice. Eigenfrequency assignment is recast as a quadratic programming problem which can be solved with low computational effort. The method is validated by assigning the lowest eigenfrequency of a two-bar linkage by properly adding point masses. The obtained results indicate that the proposed method can effectively assign the desired eigenfrequency
In-operation structural modification of planetary gear sets using design optimization methods
No full textPlanetary gears are a crucial component in the drives of automation systems and robots. The vibrational behavior of these components can lead to detrimental structural-mechanical effects including fatigue, comfort and acoustics. As the system parameters can change during operation due to wear and damage, configuration changes need to be designed during the operation to avoid vibrational problems. Possible deviation of system parameters is especially true for the stiffness parameters of the gear mesh and bearings. Lumped-parameter models are efficient yet accurate and are used to ascertain eigenfrequencies as well as frequency responses of planetary gear sets. Using these models, the change in system parameters due to damage accumulation is modeled. Thereafter, in operation configuration changes are calculated with numerical optimization methods to reduce undesired vibrational behavior. As exact parameter values are not know, these are considered uncertain using interval methods. These methods will be shown with a generic benchmark example, yet can be used in a wide range of industrial applications
Application of a parametric modal analysis approach to flexible-multibody systems
No full textIt is widely recognized that modal analysis is an effective tool for the study, modeling, design, control and understanding of mechanical systems. However, its applicability is limited to linear or linearized systems. The validity of linearized models is bounded in an infinitesimal neighborhood of the linearization point (operating point). A series of modal analysis is therefore required to calculate the system modal properties if the operating point varies, as in the case of multibody systems, which typically show gross motion. In order to reduce the computational effort required to solve a series of modal analysis, the parametric modal analysis method recently proposed by Wittmuess et al. (2016) has been applied to derive an analytical polynomial expression for the eigenpairs of a flexible multibody system in generalized coordinates. A numerical validation of a planar flexible manipulator is presented. It shows that the method allows for correctly approximating the modal content over a wide range of the generalized coordinates of the system while drastically reducing the computational effort
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
