arXiv subjects

Alexander Hasse

Publications and source records attributed to Alexander Hasse.

5 recordsLinked to original sources

arXiv2024

Nonlinear synthesis of compliant mechanisms with selective compliance

The synthesis of compliant mechanisms (CMs) is frequently achieved through topology optimization. Many synthesis approaches simplify implementation by assuming small distortions, but this limits their practical application since CMs typically undergo large deformations that include geometric and material nonlinearities. CMs designed to generate a desired deformation path at the output points under specific loads are known as path-generating CMs. However, these CMs face significant challenges in topology optimization, resulting in the development of only a few optimization methods. Existing approaches often include only certain load cases in the optimization process. Consequently, if a CM designed this way encounters different load cases in practice, its path-generating behavior cannot be guaranteed. The authors have previously contributed to the development of an approach suitable for synthesizing load case insensitive CMs. This paper extends that approach to account for nonlinearities, enabling the synthesis of path-generating CMs. The effectiveness of this extended approach is demonstrated through appropriate design examples. Additionally, the paper presents, for the first time, a shape-adaptive path-generating CM.

math.OC↗

arXiv2021

Topology-optimization based design of multi-degree-of-freedom compliant mechanisms (mechanisms with multiple pseudo-mobility)

Unlike conventional mechanisms, compliant mechanisms produce the desired deformations by exploiting elastic strain and do not need, therefore, moving parts. The number of degrees of freedom of a conventional mechanism, also called mobility, is the number of independent coordinates needed to define a configuration of the mechanism. Due to the different operating principle, such definition of degree of freedom or mobility cannot be directly applied to compliant mechanisms. While those terms are not able to denote a property of a given compliant mechanism, they are meaningful when applied to the design of a compliant mechanism. Compliant mechanisms are, however, mostly seen as elastic structures, for which the term degree of freedom is used in a different meaning. In order to avoid ambiguities, the term pseudo-mobility (already introduced in previous published work) will be used to denote the number of scalar parameters needed to identify one single desired deformation, i.e. one single deformation for which the compliant mechanism is designed. Many synthesis approaches exist for compliant mechanisms with single pseudo-mobility (commonly referred to as "single degree of freedom mechanisms"). In the case of compliant mechanisms with multiple pseudo-mobility (multiple-degree of freedom mechanisms), only synthesis approaches for relatively simple mechanisms exist so far, while systems for more complex tasks like shape adaptation are not covered. In addition, only certain cases of transverse loads are included in the synthesis with these approaches. In this paper, a novel optimization algorithm is presented that addresses these two shortcomings. The algorithm is tested on a simple mechanism with one translation and one rotation kinematic degree of freedom, a compliant parallel mechanism for pure translation and a shape-adaptive structure.

cs.RO↗

arXiv2021

Accuracy and precision: a new view on kinematic assessment of solid-state hinges and compliant mechanisms

Compliant mechanisms are alternatives to conventional mechanisms which exploit elastic strain to produce desired deformations instead of using moveable parts. They are designed for a kinematic task (providing desired deformations) but do not possess a kinematics in the strict sense. This leads to difficulties while assessing the quality of a compliant mechanism's design. The kinematics of a compliant mechanism can be seen as a fuzzy property. There is no unique kinematics, since every deformation need a particular force system to act; however, certain deformations are easier to obtain than others. A parallel can be made with measurement theory: the measured value of a quantity is not unique, but exists as statistic distribution of measures. A representative measure of this distribution can be chosen to evaluate how far the measures divert from a reference value. Based on this analogy, the concept of accuracy and precision of compliant systems are introduced and discussed in this paper. A quantitative determination of these qualities based on the eigenvalue analysis of the hinge's stiffness is proposed. This new approach is capable of removing most of the ambiguities included in the state-of-the-art assessment criteria (usually based on the concepts of path deviation and parasitic motion).

cs.RO↗

arXiv2020

Vibration Reduction by Stiffness Modulation -- a Theoretical Study

Semi-active vibration reduction techniques are defined as techniques in which controlled actions do not operate directly on the system's degrees of freedom (as in the case of active vibration control) but on the system's parameters, i.e., mass, damping, or stiffness. Cyclic variations in the stiffness of a structural system have been addressed in several previous studies as an effective semi-active vibration reduction method. The proposed applications of this idea, denoted here as stiffness modulation, range from stepwise stiffness variations on a simple spring-mass system to continuous stiffness changes on rotor blades under aerodynamic loads. Semi-active systems are generally claimed to be energetically passive. However, changes in stiffness directly affect the elastic potential energy of the system and require external work under given conditions. In most cases, such injection or extraction of energy (performed by the device in charge of the stiffness variation and denoted as the pseudo-active effect) usually coexists with the semi-active effect, which operates by redistributing the potential energy within the system in such a way that it can be dissipated more efficiently. This work focuses on the discrimination between these two effects, which is absent in previous literature. A first study on their dependence on the process parameters of stiffness modulation is presented here, with emphasis on the spatial distribution of the stiffness changes. It is shown that localized changes tend to result in a larger semi-active share of vibration attenuation, whereas a spatially homogeneous stiffness modulation only generates a pseudo-active effect.

math.DS↗

arXiv2020

An AI-Assisted Design Method for Topology Optimization Without Pre-Optimized Training Data

Topology optimization is widely used by engineers during the initial product development process to get a first possible geometry design. The state-of-the-art is the iterative calculation, which requires both time and computational power. Some newly developed methods use artificial intelligence to accelerate the topology optimization. These require conventionally pre-optimized data and therefore are dependent on the quality and number of available data. This paper proposes an AI-assisted design method for topology optimization, which does not require pre-optimized data. The designs are provided by an artificial neural network, the predictor, on the basis of boundary conditions and degree of filling (the volume percentage filled by material) as input data. In the training phase, geometries generated on the basis of random input data are evaluated with respect to given criteria. The results of those evaluations flow into an objective function which is minimized by adapting the predictor's parameters. After the training is completed, the presented AI-assisted design procedure supplies geometries which are similar to the ones generated by conventional topology optimizers, but requires a small fraction of the computational effort required by those algorithms. We anticipate our paper to be a starting point for AI-based methods that requires data, that is hard to compute or not available.

cs.LG↗