Analytical characterization of spatial compliant mechanisms using beam theory. - In: Microactuators, Microsensors and Micromechanisms, (2023), S. 61-76
Due to the advantages of compliant mechanisms, they are widely used in technical fields such as precision engineering, measurement and medical technology. The movement of the mostly monolithically designed mechanisms is primarily achieved by bending the individual structural sections. Due to geometric nonlinearities caused by large deflections, the analytical description of the deformation behavior under the influence of external loads is not trivial. While plane compliant mechanisms can be reliably calculated with different models, the analysis of spatial compliant mechanisms is accordingly more difficult. Due to the complexity of the motion, simplifications are often made in the model assumptions, which have a detrimental effect on the precision of the results. Therefore, this paper presents a method to apply nonlinear beam theory to complex spatial structures that can include both curved sections and sections with non-constant cross-sections. Using selected examples of varying complexity, the model is validated using FEM simulations. In addition, a procedure to characterize branched spatial compliant mechanisms with the proposed analytical model and to calculate their deformation is explained. By efficiently solving the analytical model numerically, the deformed state of the mechanism can be obtained in seconds. Therefore, the model is particularly suitable for early stages of development or iterative synthesis tasks.
https://doi.org/10.1007/978-3-031-20353-4_5
Development of a database to simulate and adapt compliant mechanisms to a given characteristic for improving energy efficiency of a walking robot. - In: Microactuators, Microsensors and Micromechanisms, (2023), S. 46-60
Compliant mechanisms with variable geometric parameters are investigated for the application in a bipedal robot to improve its walking efficiency. These mechanisms have nonlinear torque-angle characteristics and act like torsion springs to change the systems free oscillation frequency. High energy efficiency is achieved if the free oscillation frequency matches the step frequency, meaning the that the robot walks in resonance. For this purpose, the desired characteristic of the optimized elastic coupling is identified via optimization. Then, a database is developed, which consists of boundary conditions and beam elements. In this paper, there are three boundary conditions and three beam elements for demonstration purpose. To simulate a large number of compliant mechanisms with different characteristics, two boundary conditions and a beam element can be combined. The boundary conditions serve as bearing types to connect the beam element to the thighs of a robot. The large deformation behavior is assumed to be simulated by the Euler-Bernoulli beam theory, which is validated by FEM models. Thus, the desired characteristic from the proceeding optimization process is realized by a specific compliant mechanism.
https://doi.org/10.1007/978-3-031-20353-4_4
Microactuators, Microsensors and Micromechanisms : MAMM 2022. - Cham : Springer International Publishing, 2023. - 1 Online-Ressource (xiii, 364 p. 234 illus., 186 illus. in color.). - (Mechanisms and machine science ; volume 126) ISBN 978-3-031-20353-4
This book brings together investigations which combine theoretical and experimental results related to such systems as flexure hinges and compliant mechanisms for precision applications, the non-linear analytical modeling of compliant mechanisms, mechanical systems using compliance as a bipedal robot and reconfigurable tensegrity systems and micro-electro-mechanical systems (MEMS) as energy efficient micro-robots, microscale force compensation, magnetoelectric micro-sensors, acoustical actuators and the wafer bonding as a key technology for the MEMS fabrication. The volume gathers the contributions presented at the 6th Conference on Microactuators, Microsensors and Micromechanisms (MAMM), held in Hyderabad, India in December 2022. The aim of the conference was to provide a special opportunity for a know-how exchange and collaboration in various disciplines concerning systems pertaining to micro-technology. The conference was organized under the patronage of IFToMM (International Federation for the Promotion of Mechanism and Machine Science).
https://doi.org/10.1007/978-3-031-20353-4
Improving energy efficiency of a bipedal walker with optimized nonlinear elastic coupling. - In: Advances in nonlinear dynamics, (2022), S. 253-262
A method to improve the energy efficiency of a bipedal walking robot by means of nonlinear elastic couplings between the robot’s thighs is presented. The robot model consists of five rigid segments which are connected by four actuated revolute joints in the hip and knees. The walking movement is generated and stabilized by a nonlinear controller based on the hybrid zero dynamics approach. The optimum walking gaits and the optimum characteristic of the elastic coupling are identified via numerical optimization whereby the energy consumption of locomotion is minimized. Different walking speeds from 0.2 m/s to 1.4 m/s are considered in the study. According to simulations, the optimal nonlinear elastic coupling reduces the mean energy consumption by 78% over the range of investigated speeds. This is significantly better compared to the coupling with optimal linear torsion spring, which saves 62% energy. The free oscillations frequency of the swing leg under influence of the elastic coupling is derived from a simplified pendulum model. This free oscillations frequency closely matches with the double step frequency of the robot at different walking speeds. The nonlinear elastic coupling gives the robot the capability to walk in resonance at different speeds with a very high energy efficiency.
https://doi.org/10.1007/978-3-030-81166-2_23
Thermosensitive elastomers for shape adaption of soft robotic systems. - In: ACTUATOR 2022: International Conference and Exhibition on New Actuator Systems and Applications, (2022), S. 290-293
Recent advances in soft robotics demonstrate robust and versatile performance for dexterous grasping and manipulation. Due to their intrinsically mechanical compliance, soft robots passively adapt their shape to an object during contact. This results in large contact patches and damping of contact dynamics, which compensates for uncertainties in sensing, modeling, and actuation. Therefore, the behavior of soft robots is also determined by contact-based deformations. Building these kinds of compliant structures by using thermosensitive hybrid materials of polydimethylsiloxane and different thermoplastic filler particles as thermosensitive elastomers (TSE) the design could receive a higher versatility and extra functionality. Thermosensitive elastomers (TSE) consist of an addition curing RTV-2 silicone in which different thermoplastic filler particles are embedded. These thermoplastic particles are polycaprolactone (PCL), polyamide-6 (PA6) and polymethylmethacrylat (PMMA) with melting temperatures in the range of 58deg C to 215deg C. In certain examinations, soft magnetic carbonyl iron particles (CIP) are also included to prove the compatibility of the two particle types within the polydimethylsiloxane (PDMS) matrix and to utilize a possible symbiotic effect of the particle mixtures. By means of mechanical tests, the thermosensitive hybrid materials enable shape changes by applying both external heat and stress/force. With a low melting point in the range of 58 deg C to 60 deg C, PCL offers good application potential compared to the other thermoplastic filler particles. One of PCL most important and application-oriented phenomena is the shape memory effect, which results from internal stresses between elastomer molecular chains and PCL particles. Whereby the external shape arises from the equilibrium of all internal forces. Consequently, the material composites can be referred to as both TSE and shape memory polymers (SMP). By adding soft magnetic particles, an accelerated heat distribution within the samples was detected, which results in a faster occurrence of the corresponding effects. Micro computed tomography (mu-CT) and scanning electron microscopy (SEM) examinations indicate that a homogeneous distribution of PCL and CIP within the thermosensitive elastomer prevails. Moreover, the TSE additionally contain CIP can combine the benefits of temperature and magnetic field effects. Due to the material's ability to imprint or adapt to any shape, thermosensitive elastomers as shape memory polymers represent a potential opportunity to modify pre-existing robotic components. Depending on the initial design and force application, the modified systems could adapt to almost any shape under the influence of temperature. This leads to their use in a variety of applications in adaptive sensors, smart actuators, and gripping elements in soft robotics.
https://ieeexplore.ieee.org/document/9899226
A method for optimising compliant mechanisms :
Eine Methode zur Optimierung nachgiebiger Mechanismen. - In: Getriebetagung 2022, (2022), S. 133-142
In diesem Beitrag wird eine Methode vorgestellt, mit deren Hilfe nachgiebige Mechanismen bezüglich ihres Verformungsverhaltens optimiert werden können. Berechnungsgrundlage der Methode ist die Theorie großer Verformungen stabförmiger Strukturen. Die Berechnung erfolgt mit numerischen Lösungsverfahren in Python. Für die Optimierung werden Festkörpergelenke entlang einer vorgegebenen Balkenachse verschoben. Durch Parameterstudien dreier Mechanismen wird zunächst die Auswirkung der Gelenkposition auf das Verformungsverhalten herausgestellt. Abschließend wird die Berechnungsmethode mit Hilfe von den aus den Parameterstudien resultierenden Ergebnissen erfolgreich verifiziert.
Vibrissa-inspired tactile sensing : object shape detection under frictional influences. - Ilmenau, 2022. - x, 154 Seiten
Technische Universität Ilmenau, Dissertation 2022
Die taktile Sensorik birgt große Potenziale für die Weiterentwicklung von technischen Geräten und deren Einsatz in unstrukturierten Umgebungen. Häufig sind taktile Sensorkonzepte von der Natur inspiriert, z.B. durch die mystazialen Vibrissen der Ratte. Diese speziellen Tasthaare dienen als multimodale Sensoren, die Ratten u.a. zur Objektformkennung befähigen. Die vorliegende Arbeit verfolgt einen biomimetischen Ansatz mit dem Ziel der Weiterentwicklung vibrissen-inspirierter Sensoren für die 3D-Objektformerkennung unter Reibungseinflüssen. Das biologische Vorbild Vibrisse besteht im Wesentlichen aus einem hochflexiblen, nicht-sensorischen Haarschaft, welcher in seinen eigenen Follikel-Sinus-Komplex eingebettet ist, der sensorische Komponenten enthält. Diese Struktur wird abstrahiert und auf ein technisches Sensorkonzept übertragen. Zur Realisierung der Objektabtastung wird ein schlanker, einseitig eingespannter, hochflexibler Taster durch lineare Verschiebung der Einspannung entlang des Zielobjekts gestrichen. Die resultierenden Lagerreaktionen dienen als einzige Observablen für die Rekonstruktion von Kontaktpunktfolgen zwischen Taster und Objekt, die schließlich auf die Form des letzteren schließen lassen. Zu diesem Zweck wird das Sensorkonzept mechanisch modelliert und mithilfe von Modellgleichungen beschrieben. Aufbauend auf der Analyse der 2D-Objektabtastung und -Rekonstruktion unter Reibungseinflüssen wird das Modell auf den allgemeinen 3D Fall erweitert. In Simulationen und Experimenten wird die allgemeine Umsetzbarkeit der Objektformerkennung demonstriert. Simulationsbasierte Parameterstudien verdeutlichen zudem den Einfluss der (Coulomb) Reibung auf die Lagerreaktionen und die Rekonstruktionsergebnisse. Während die Lagerreaktionen signifikant von Reibungseffekten beeinflusst werden, ist der Fehler der rekonstruierten Kontaktpunkte reibungsinvariant (unbeeinflusst durch den Reibungskoeffizienten). Diese Erkenntnisse werden im Zusammenhang mit den experimentellen Ergebnissen diskutiert. Darüber hinaus wird für den Fall der 2D-Objektabtastung ein Ansatz zur Rekonstruktion von Reibungsparametern vorgestellt, für den ein erster experimenteller Konzeptnachweis erbracht wird. Schließlich wird das Sensormodell mit Blick auf das biologische Vorbild durch Implementierung einer elastischen Lagerung und einer rotatorischen Abtastkinematik angepasst.
Shape-programmable cantilever made of a magnetoactive elastomer of mixed content. - In: Smart materials and structures, ISSN 1361-665X, Bd. 31 (2022), 10, 105021, S. 1-14
This work presents an approach to the macroscopic field-controlled mechanics of magnetoactive elastomers of mixed content, which are a special type of smart materials made of an elastic composite and a combination of two essentially different ferromagnetic fillers. High-coercive particles of NdFeB-alloy powder for the magnetically hard (MH) filler and carbonyl iron powder particles with nearly zero coercivity for the magnetically soft (MS) filler are usually used. The MH particles are tens-of-micron in size and impart to the elastomer a remanent magnetisation, whereas due to the MS particles of several microns in size, the elastomer acquires a high magnetic susceptibility. Since large MH particles once magnetised in a strong field possess their own fields to which the MS particles are susceptible, the overall elastomer magnetisation as well as its mechanical response greatly depends on the relative concentration of both fillers. This work particularly studies the bending deformation of horizontally fixed magnetoactive cantilevers with the permanent magnetisation along the length axis under the action of gravity and a vertically applied uniform magnetic field. The cantilevers of the same geometry and fixed NdFeB content but different carbonyl iron concentration are considered. The magnetomechanical model is developed based on the finite-strain theory assuming the plane-stress approximation of the two-dimensional cantilever of infinite width. The magnetic energy comprises two magnetic terms, one of which is qualitatively linear and the other one is quadratic in the applied field strength. The numerically calculated field-programmed equilibrium bending shapes of the cantilevers are compared with the experimentally observed shapes. The model provides good agreement with the experiment up to moderate concentrations of the MS filler, when the coefficients of customary interpolation formulas for the concentration dependencies of elastic modulus and magnetic susceptibility are properly adjusted.
https://doi.org/10.1088/1361-665X/ac8f79
Modellbasierte Entwicklung von Methoden, Algorithmen und Werkzeugen zur Analyse und Synthese nachgiebiger Mechanismen. - Ilmenau : Universitätsverlag Ilmenau, 2022. - 1 Online-Ressource (XXI, 184 Seiten, Seite XXIII-LV). - (Berichte der Ilmenauer Mechanismentechnik (BIMT) ; Band 7)
Technische Universität Ilmenau, Dissertation 2022
Nachgiebige Mechanismen sind in technischen Anwendungen weit verbreitet, insbesondere in der Robotik, Präzisions-, Mess- und Medizintechnik. Ihr Verformungsverhalten wird maßgeblich durch die Gestaltung ausgewählter nachgiebiger Strukturabschnitte, beispielsweise durch die gezielte Reduktion der Querschnittsabmessungen, beeinflusst. Die Bewegung des Mechanismus erfolgt vorwiegend durch Biegung dieser Abschnitte. Die Berechnung des Verformungsverhaltens unter dem Einfluss äußerer Belastungen stellt aufgrund von geometrischer Nichtlinearität eine anspruchsvolle Aufgabe bei der Analyse und Synthese nachgiebiger Mechanismen dar. Daher wird in dieser Arbeit ein Beitrag zur analytischen Modellbildung und damit zum Analyse- und Syntheseprozess geleistet. Die Modellgleichungen werden für ebene und räumliche Anwendungsfälle gegeben. Mit Hilfe dieser können nachgiebige Mechanismen mit variierenden Querschnitten, Krümmungen, Werkstoffen und Verzweigungen charakterisiert werden. Für die Betrachtung beliebiger Mechanismen werden die Gleichungen in einer rekursiven Form gegeben. Aufgrund von Strukturabschnitten unterschiedlicher Querschnitte werden, über reine Biegung hinaus, auch Querkraftschub und Querkontraktion im Modell berücksichtigt. Es werden Untersuchungen durchgeführt um zu definieren, wann diese Effekte, in Abhängigkeit der Geometrie, zu berücksichtigen sind. Auf Basis dieser Untersuchungen werden Empfehlungen für die zu verwendende Theorie gegeben. Durch die Formulierung der Gleichungen in einer einheitlichen Form wird ermöglicht, die Theorie für einzelne Abschnitte eines nachgiebigen Mechanismus individuell anzupassen. Weiterhin wird das Modell durch Beispielmechanismen für zwei- und dreidimensionale Anwendungsfälle mit Hilfe der Finiten-Elemente-Methode und experimentellen Untersuchungen validiert. Dabei werden die Empfehlungen der einzusetzenden Theorie angewendet. Daraufhin werden Algorithmen zur Dimensionierung einzelner Festkörpergelenke und nachgiebiger Mechanismen gegeben. Dadurch kann deren Bewegungsverhalten im Hinblick auf konkrete Zielkriterien verbessert werden. Abschließend werden die Methoden in drei eigenständig ausführbare Softwarewerkzeuge implementiert, die frei zur Verfügung gestellt sind. Durch deren Entwicklung wird ein Beitrag zum Entwurf sowie zur Analyse und Synthese von Festkörpergelenken und nachgiebigen Mechanismen geleistet.
https://doi.org/10.22032/dbt.53126
Actuators based on a controlled particle-matrix interaction in magnetic hybrid materials for applications in locomotion and manipulation systems. - In: Magnetic hybrid-materials, (2022), S. 653-680
The paper deals with the investigation of magneto-sensitive elastomers (MSE) and their application in technical actuator systems. MSE consist of an elastic matrix containing suspended magnetically soft and/or hard particles. Additionally, they can also contain silicone oil, graphite particles, thermoplastic components, etc., in various concentrations in order to tune specific properties such as viscosity, conductivity and thermoelasticity, respectively. The focuses of investigations are the beneficial properties of MSE in prototypes for locomotion and manipulation purposes that possess an integrated sensor function. The research follows the principle of a model-based design, i.e. the working steps are ideation, mathematical modelling, material characterization as well as building first functional models (prototypes). The developed apedal (without legs) and non-wheeled locomotion systems use the interplay between material deformations and the mechanical motion in connection with the issues of control and stability. Non-linear friction phenomena lead to a monotonous forward motion of the systems. The aim of this study is the design of such mechanical structures, which reduce the control costs. The investigations deal with the movement and control of 'intelligent' mechanisms, for which the magnetically field-controlled particle-matrix interactions provide an appropriate approach. The presented grippers enclose partially gripped objects, which is an advantage for handling sensitive objects. Form-fit grippers with adaptable contour at the contact area enable a uniform pressure distribution on the surface of gripped objects. Furthermore, with the possibility of active shape adaptation, objects with significantly differing geometries can be gripped. To realise the desired active shape adaptation, the effect of field-induced plasticity of MSE is used. The first developed prototypes mainly confirm the functional principles as such without direct application. For this, besides the ability of locomotion and manipulation itself, further technological possibilities have to be added to the systems.