1,721,021 research outputs found
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
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
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
Energy saving in mechatronic systems through optimal point-to-point trajectory generation via standard primitives
No full textSensitivity Analysis of Flexible Multibody Dynamics with Generalized- α Time Integration and Baumgarte Stabilization: A Study on Numerical Stability
No full textOptimal In-Operation Redesign of Mechanical Systems Considering Vibrations-A New Methodology Based on Frequency-Band Constraint Formulation and Efficient Sensitivity Analysis
No full textThe vibrational behavior of components in mechanical systems like drives and robots can become critical under changes in the system properties or loading in operation. Such undesired vibration can lead to detrimental conditions including excess wear, fatigue, discomfort, and acoustic emissions. Systems are designed to avoid certain frequencies to avoid such problems, but system parameters can change during operation due damage, wear, or change in loading. An example is the change in system properties or operation state that then activates resonance frequencies in our system. Therefore, this work has the goal of modifying the modal behavior of a system to avoid vibrational problems. Methods of design optimization are applied to find a new optimum design for this altered condition. Here, this is limited to the addition of mass in order to move the resonance frequency out of critical ranges. This though requires a new formulation of the optimization problem. We propose a new constraint formulation to avoid frequency ranges. To increase efficiency, a reduced analytical sensitivity analysis is introduced. This methodology is demonstrated on two test cases: a two-mass oscillator followed by a test case of higher complexity which is a gear housing considering over 15,000 design variables. The results show that the optimization solution gives the position and amount of mass added, which is a discrete solution that is practically implementable
ANALYTICAL SENSITIVITY ANALYSIS OF FLEXIBLE MULTIBODY DYNAMICS WITH INDEX-1 DIFFERENTIAL-ALGEBRAIC EQUATIONS AND BAUMGARTE STABILIZATION
No full textApplication 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
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