Soft robotic compliant two-finger gripper mechanism for adaptive and gentle food handling. - In: 2021 IEEE 4th International Conference on Soft Robotics (RoboSoft), (2021), S. 163-168
In the field of soft robotics there is still a great need for a versatile, simple, and affordable gripper with a high level of adaptability to unknown objects of different sizes, shapes, and stiffness. Most of the existing soft robotic grippers are complex solutions realized with fluid-mechanically driven actuators, active smart materials, cable-driven actuation, and different form-closure principles. However, soft grippers based on compliant mechanisms are rarely introduced and explored so far. Therefore, we present a novel compliant two-finger gripper mechanism for adaptive and gentle gripping, especially of soft and easily squeezable objects like fruits, vegetables, sweets, and sushi. The structurally inherent adaptability is achieved using an optimally synthesized compliant mechanism in combination with a conventional linear actuator. Furthermore, the two-finger gripper passively realizes pinch (parallel) or/and encompass (power) grasping. It is shown by FEM simulations and confirmed by prototype tests that the developed gripper realizes both pinch and encompass grasping with high adaptability. A special advantage of the gripper is the possibility to achieve gentle food-handling of objects with comparable weight independent of the object shape, size, and position without the need for sensors. Moreover, the precise, safe, and fast manipulation of very delicate objects is exemplarily demonstrated for different sushi pieces using the gripper mechanism with an industrial robotic arm.
https://doi.org/10.1109/RoboSoft51838.2021.9479337
Worm-like mobile robot based on a tensegrity structure. - In: 2021 IEEE 4th International Conference on Soft Robotics (RoboSoft), (2021), S. 358-363
This work presents a novel concept to develop mobile robots enabling crawling locomotion in tubular environment. Chain-like systems are designed by serial cascading a uniform tensegrity module. Inspired by the movement of worms in nature, an undulating shape change of the system is targeted to generate locomotion. The shape changeability of an exemplary tensegrity module due to internal actuation is examined in simulations and experiments. A prototype consisting of these tensegrity modules is manufactured and the locomotion principle is verified in experiments. Comparing to existing prototypes this approach enables an enhanced compliance due to the modular assembly of tensegrity structures.
https://doi.org/10.1109/RoboSoft51838.2021.9479193
High-precision and large-stroke XY micropositioning stage based on serially arranged compliant mechanisms with flexure hinges. - In: Precision engineering, Bd. 72 (2021), S. 469-479
Compliant mechanisms are state of the art in micropositioning stages due to their many beneficial features. However, their design usually compromises between motion range, motion accuracy and design space, while mechanisms with distributed compliance are mostly applied. The further use of flexure hinges with common notch shapes strongly limits the stroke in existing high-precision motion systems. Therefore, this paper presents a high-precision compliant XY micropositioning stage with flexure hinges capable of realizing a motion range of ± 10 mm along both axes. The stage is based on a novel plane-guidance mechanism, which is optimized to realize a precise rectilinear motion of the coupler link while keeping the rotation angles of all hinges below 5˚. The XY motion is then achieved by coupling two of these mechanisms in a serial arrangement. Next, the synthesis of the monolithic XY stage is realized by replacing all revolute joints of the rigid-body model with flexure hinges using optimized power function notch shapes. Emphasis is also placed on the embodiment design of the stage and the actuator integration to minimize possible error sources. Finally, the quasi-static behavior of the compliant stage is characterized by a simulation with a 3D FEM model and by an experimental investigation of a prototype. According to the results, the developed compliant XY micropositioning stage achieves a maximum positioning deviation of less than 10 [my]m in both axes and a yaw error of less than 100 [my]rad over a working range of 20 mm × 20 mm with a comparably compact design of the compliant mechanism of 224 mm × 254 mm.
https://doi.org/10.1016/j.precisioneng.2021.02.001
Analysis of planar compliant mechanisms based on non-linear analytical modeling including shear and lateral contraction. - In: Mechanism and machine theory, Bd. 164 (2021), 104397, insges. 23 S.
Compliant mechanisms are commonly used in precision engineering while analyzing their deflection is particularly challenging. Often, FEM simulations are chosen in an iterative process. Analytical approaches that consider pure bending, shear or other effects are usually limited to the mechanism as a system. However, certain configurations comprise compliant elements with different aspect ratios. The aim of this paper is to integrate the theories of shear and lateral contraction into a unified form with the existing theory of bending for large deflections and make them applicable individually for specific sections of continuous compliant mechanisms. Recommendations are made as to when which theory should be used. Building on that, a comprehensive tool for analyzing compliant mechanisms developed in Python is introduced. The tool offers the possibility to create arbitrary compliant mechanisms including branched links and various boundary conditions. A tool for parametric studies allows to optimize the given geometry for realizing a specific motion task. Further, FEM and measurement results correlate well with the application results. The presented user interface can be beneficial for the accelerated analysis and synthesis of compliant mechanisms.
https://doi.org/10.1016/j.mechmachtheory.2021.104397
Theoretical and experimental investigations of magnetic hybrid materials and their application in soft gripping. - Ilmenau, 2021. - xix, 193 Seiten
Technische Universität Ilmenau, Dissertation 2021
Soft Robotics ist ein aktuelles Forschungsfeld. Die Anwendung mechanisch nachgiebiger Materialien in technischen Applikationen wird aktuell intensiv vorangetrieben. Intelligente nachgiebige Materialien, beispielsweise Materialien, die ihre mechanischen Eigenschaften reversibel ändern können, werden in immer mehr technischen Anwendungen eingesetzt. Vordergründig geschieht dies mit den Zielen der Funktionserweiterung und der individuellen reversiblen Anpassbarkeit an veränderte Umgebungsbedingungen. Magnetorheologische Elastomere sind intelligente nachgiebige Hybridmaterialien, bestehend aus einer Elastomermatrix, die mit ferromagnetischen Partikeln gefüllt ist. In Abhängigkeit von der beabsichtigten Verwendung dieser Hybridmaterialien werden weich- oder hartmagnetische Partikel eingesetzt. Diese Materialien besitzen die besondere Fähigkeit, ihre mechanischen Eigenschaften zu ändern, wenn auf sie Magnetfelder einwirken. Diese vorteilhaft nutzbare Eigenschaft macht ihren Einsatz in zahlreichen technischen Anwendungen dort effizient, in welchen Strukturen mit reversibel veränderbarer mechanischer Nachgiebigkeit eingesetzt werden sollen. Bedingt durch ihre vorteilhaften Eigenschaften werden diese Materialien aktuell intensiv erforscht. Im Fokus der meisten Forschungsarbeiten auf diesem Gebiet stehen dabei die mechanische und magnetische Charakterisierung der Materialeigenschaften, sowie die Erarbeitung von Materialmodellen, die eine Beschreibung des magneto-mechanischen Verhaltens dieser Materialien mit hoher Genauigkeit erlauben. Viele Effekte im Verhalten dieser Materialien sind aktuell noch nicht tiefgründig untersucht bzw. verstanden worden. In dieser Arbeit werden diese Hybridmaterialien aus ingenieurtechnischer Sicht betrachtet. Die Untersuchungen an diesen Materialien werden auf potentielle technische Applikationen fokussiert. Dabei wird der Schwerpunkt auf den magnetfeldinduzierten elasto-plastischen Effekt dieser Materialien, sowie auf die Nutzung dieses Effektes in einer exemplarischen technischen Anwendung, in End-Effektoren für die Greifertechnik, gelegt. In der Arbeit werden magnetorheologische Elastomere untersucht, die weichmagnetische Partikel in verschiedenen Volumenkonzentrationen enthalten. Im ersten Teil der Arbeit werden schwerpunktmäßig experimentelle Untersuchungen durchgeführt, um geeignete Material- und Zusammensetzungsdesigns für das Hybridmaterial im Hinblick auf die gewünschte Anwendung definieren zu können. Mit Hilfe der anschließenden theoretischen Untersuchungen wird die Quantifizierung der magnetischen und mechanischen Eigenschaften dieser Materialien auf der Makro-Skala erreicht. Aufbauend auf diese Untersuchungen wird eine Methodik erarbeitet, die die Beschreibung des magneto-mechanischen Verhaltens dieser Materialien mittels Anwendung der Finite-Elemente-Methode ermöglicht. Die exemplarische Verwendung dieser Materialien als End-Effektor beim Greifen von empfindlichen Objekten impliziert die formschlüssige Umhüllung der zu greifenden Gegenstände. Mit Magnetfeldern werden die Effekte der Nachgiebigkeitsänderung und der magnetfeldinduzierten Plastizität in diesen Hybridmaterialien stimuliert. Dadurch wird eine Formanpassung und damit formschlüssiges Greifen ermöglicht. In der Arbeit wird ein End-Effektor-Prototyp hergestellt und getestet, um die vorteilhafte Anwendbarkeit magnetorheologischer Elastomere in der Soft Robotics aufzuzeigen.
Self-sensing electroadhesive polymer gripper with magnetically controllable surface geometry. - In: Actuator 2021, (2021), S. 318-320
Jumping locomotion system based on a multistable tensegrity structure. - In: Mechanical systems and signal processing, ISSN 1096-1216, Bd. 152 (2021), 107384
All known locomotion principles are limited respective to environmental conditions. Often, the occurrence of obstacles or gaps means the break-off for the operating motion systems. For such circumstances, a controllable jumping locomotion is required to cross these barriers. However, this locomotion demands sophisticated requirements to the actuation. The abrupt actuation is commonly realized by high dynamic actuators or complex mechanisms. In this work, a simple solution utilizing the multistability of a compliant tensegrity structure is described. Therefore, a two-dimensional tensegrity structure featuring four stable equilibria is considered. Based on bifurcation analyses a feasible actuation to control the current equilibrium configuration is derived. Changing between selected equilibrium states enables a great difference in potential energy, which yields a jumping motion of the structure. Based on numerical simulations a suitable actuation strategy is chosen to overcome obstacle and steps by jumping forward or backward, respectively. The theoretical approach is examined experimentally with a prototype of the multistable tensegrity structure.
https://doi.org/10.1016/j.ymssp.2020.107384
Reconfiguration of planar quadrilateral linkages utilizing the tensegrity principle. - In: Mechanism and machine theory, Bd. 156 (2021), 104172
The development of reconfigurable planar four-bar linkages by applying the tensegrity principle is considered. Conventional quadrilateral linkages enable two operation modes differing in the kinematic behavior. However, a change between these states is not possible due to the geometric constraints. To enable a reconfiguration between the different modes one-sided limited nonholonomic constraints are introduced in this work. This issue is realized by applying ropes that cannot resist compression. However, to guarantee an appropriate load case in operation a prestress within the mechanism is required. Hence, the linkage is extended to a tensegrity-based mechanism. The structural dynamics are derived using the Lagrange formalism and the structural behavior is evaluated using numerical simulations. Furthermore, a prototype of an exemplary tensegrity-based mechanism is manufactured and experiments regarding the mechanical properties, in particular the reconfiguration, are performed. The results suggest the potential benefit of applying the tensegrity principle within conventional planar four-bar linkages.
https://doi.org/10.1016/j.mechmachtheory.2020.104172
A method to approach constant isotropic permeabilities and demagnetization factors of magneto-rheological elastomers. - In: Journal of magnetism and magnetic materials, ISSN 1873-4766, Bd. 527 (2021), 167742
The use of non-conventional materials is nowadays of much interest in scientific community. Magneto-rheological elastomers are hybrid materials, which in presence of magnetic fields state a change in their mechanical properties. They are composed by an elastomeric matrix with embedded magnetic particles. One of the most attractive features of these materials is that as soon as the magnetic field is removed from the material, the original mechanical properties are completely recovered, with negligible differences in comparison to the original state. This paper focuses on the study of magnetic characteristics of these smart materials, such as relative permeability and demagnetizing factors, for samples with different volume concentration of ferromagnetic particles.
https://doi.org/10.1016/j.jmmm.2021.167742
A novel simple, adaptive, and versatile soft-robotic compliant two-finger gripper with an inherently gentle touch. - In: Journal of mechanisms and robotics, ISSN 1942-4310, Bd. 13 (2021), 1, S. 011015-1-11015-14
https://doi.org/10.1115/1.4048752