Finite Element Modeling of Pneumatic Bending Actuators for Inflated-Beam Robots

Inflated-beam soft robots, such as tip-everting vine robots, can control curvature by contracting one beam side via pneumatic actuation. This work develops a general finite element modeling approach to characterize their bending. The model is validated across four pneumatic actuator types (series, compression, embedded, and fabric pneumatic artificial muscles), and can be extended to other designs. These actuators employ two bending mechanisms: geometry-based contraction and material-based contraction. The model accounts for intricate nonlinear effects of buckling and anisotropy. Experimental validation includes three working pressures (10, 20, and 30 kPa) for each actuator type. Geometry-based contraction yields significant deformation (92.1% accuracy) once the buckling pattern forms, reducing slightly to 80.7% accuracy at lower pressures due to stress singularities during buckling. Material-based contraction achieves smaller bending angles but remains at least 96.7% accurate. The open source models available at http://www.vinerobots.org support designing inflated-beam robots like tip-everting vine robots, contributing to waste reduction by optimizing designs based on material properties and stress distribution for effective bending and stress management

A Comparison of Pneumatic Actuators for Soft Growing Vine Robots

Soft pneumatic actuators are used to steer soft growing "vine" robots while being flexible enough to undergo the tip eversion required for growth. In this study, we compared the performance of three types of pneumatic actuators in terms of their ability to perform eversion, quasi-static bending, dynamic motion, and force output: the pouch motor, the cylindrical pneumatic artificial muscle (cPAM), and the fabric pneumatic artificial muscle (fPAM). The pouch motor is advantageous for prototyping due to its simple manufacturing process. The cPAM exhibits superior bending behavior and produces the highest forces, while the fPAM actuates fastest and everts at the lowest pressure. We evaluated a range of dimensions for each actuator type. Larger actuators can produce more significant deformations and forces, but smaller actuators inflate faster and can evert at a lower pressure. Because vine robots are lightweight, the effect of gravity on the functionality of different actuators is minimal. We developed a new analytical model that predicts the pressure-to-bending behavior of vine robot actuators. Using the actuator results, we designed and demonstrated a 4.8 m long vine robot equipped with highly maneuverable 60x60 mm cPAMs in a three-dimensional obstacle course. The vine robot was able to move around sharp turns, travel through a passage smaller than its diameter, and lift itself against gravity.Comment: 13 pages, 8 figures, 3 table

Design, Optimization, and Verification of Pneumatically Actuated Shape-Morphing Lattices

The concept of shape-morphing is to embed control in a design to broaden its band of functionality. Whether it is for cars, planes, buildings, or personal medicine, the goal is to achieve more with less. That is more efficiency, more functions, more force, and more range with less energy, and less weight. The design of these new types of structures is however complex, as all the variables of a system are intertwined. Existing designs are either simple or small to reduce the number of design variables, although this affects the achievable deformation range of a structure. There is a need for a design method that can handle the complexity of the search space of shape-morphing structures without compromising the breadth of their design space or the accuracy of their deformation. This thesis proposes four design methods, one for compliance-controlled shape-morphing and three for actuator-controlled shape-morphing. First, compliance-control is achieved through optimization of the distribution of materials with varying stiffness in a 2D lattice structure. The method is implemented for geometric and material linearity and nonlinearity to observe how the choice of model affects the accuracy of the deformations. The method is verified by optimizing the material distribution for a 2.5D NACA target shape and replicating the results experimentally using multimaterial 3D printing. Then, the modeling and four fabrication methods for soft pneumatic actuators are compared, as they are necessary to experimentally verify the actuator-controlled shape-morphing methods. The final actuator design is adapted to the constraints of soft lithography, the fabrication method that delivers the most robust and predictable actuators of the four. Actuator-control is achieved by optimizing the actuator layout within a lattice structure with the aim of achieving a target deformation. The three methods show how reducing the search and design space of a structure improves the computational efficiency and accuracy for 2D, 2.5D, and 3D deformation. The first method assumes static and kinematic determinacy and small displacements; the second assumes small displacements in overdeterminate structures; the third can achieve large shape changes in overdeterminate structures. All three methods are verified through finite element analysis and experimentally. Finally the implications of the findings related to the four shape-morphing design methods are discussed. The achievable search and design space of each method are compared. The designer is free to chose the method best adapted to their needs, as each one is a compromise of accuracy, range, and computational efficiency. The methods can be employed for different types of actuation, but their application to industrial fields is hindered by the mechanical properties of the material that can currently be 3D printed. The advent of several new manufacturers of compliant and multimaterial 3D printers promises further industrial developments for the field of shape-morphing

Validation of a nonlinear force method for large deformations in shape-morphing structures

Reducing energy and material consumption is a priority for the construction, aerospace, and automotive industries. Shape morphing addresses these concerns by broadening the band of functionality of a structure by adapting its shape to an external stimulus, such as pressure, or an internal stimulus, such as embedded actuation. This work outlines the development of an actuator placement optimization method for overdeterminate lattice structures with the objective of achieving predetermined large shape changes accurately. The deformation is modeled with both a linear and a nonlinear force method to determine their validity for large-shape change and their usefulness for the field of shape morphing. The linear and nonlinear methods are compared in four benchmark problems and two case studies relevant to the field of shape morphing. The nonlinear method is shown to achieve a level of accuracy 102 to 104 higher compared to FEM simulation, while using 23% fewer actuators and up to 77.3% less elongation of actuators, which makes it more favorable for shape-morphing applications. Two case studies for applications in aerospace and construction show that the nonlinear force method is better equipped for large shape change in overdeterminate meshed freeform target shapes and doubly curved surfaces with a high variable density. However, the nonlinear force method is less computationally efficient than the linear force method, as expected. A judicious choice of constraints can help reduce the run time.ISSN:1615-147XISSN:1615-148

A nonlinear optimization method for large shape morphing in 3D printed pneumatic lattice structures

Shape morphing has been increasingly investigated as a solution to increase the functionality and efficiency of structures. The main criteria to assess the quality of a shape morphing structure in this paper are: accuracy of deformation and range and number of achievable target shapes. The lightweight lattice structures used in this work inherently address the first criteria. The focus of this work is to address accuracy and range by developing a nonlinear optimization method that can handle large shape changes and a variety of target shapes for 2D and 3D overdeterminate lattice structures. The accuracy and deformation range of the method are verified numerically using Finite Element Analysis (FEA) and experimentally through a modular, 3D printed pneumatic lattice toolkit. The method is shown to replicate desired target shapes with a minimum accuracy of 80.4% for case studies in 2D and 69.1% in 3D. The simulation and the experimental results replicate results from the actuator placement optimization with a minimum accuracy of 92.3% and 76.2% respectively in 2D, and 88.2% and 69.6% in 3D. The impact of varying the size and degree of static overdeterminacy of a structure on its deformation range is evaluated. The proposed optimization method provides designers with more design freedom in terms of the structure type, target shape, and deformation range than shown in similar publications.ISSN:1361-665XISSN:0964-172

Actuator placement optimization in an active lattice structure using Generalized Pattern Search and verification

Shape morphing structures are actively used in the aerospace and automotive industry. By adapting their shape to a stimulus such as heat, light, or pressure, a design can be optimized to achieve a broader band of functionality over its lifetime. The quality of a structure with respect to shape-morphing can be assessed using five criteria: weight, load-carrying capacity, energy consumption, accuracy of the controlled deformation, and the range and number of achievable target shapes. This work focuses on the use of lightweight and stiff active lattice structures, where the layout of actuators within the structure determines the final deformation. It uses a statically and kinematically determinate Kagome lattice pattern that has been shown to deform the most accurately with the least energy. The use of a determinate structure justifies the implementation of a simplified deformation model. The deformation resulting from a given actuator layout can be expressed as a linear combination of the deformation of individual actuators, which are all computed in a pre-processing step and expressed with an influence matrix. The actuator layout is thus optimized for several target shapes. The linear combination model is shown to replicate FEM simulations with an average of 94.8% accuracy for all target shapes. The actuator layouts in one-level lattices are tested using a novel design for a 3D printed modular Kagome pneumatic lattice structure. The experimental results replicate the target shapes with an average accuracy of 79.9%. The resulting actuator layouts are shown to form more target shapes with a similar deformation range as similar publications.ISSN:1361-665XISSN:0964-172

Systematic Design, Control and Parametric Testing of an Automated Resuscitator Bag Mechanical Ventilator

The COVID-19 crisis has revealed and exacerbated a shortage of mechanical ventilators in hospitals around the world, regardless of their government’s resources. Where some countries can respond to the situation by ordering more high-end ventilators, the price is often too high for low- and middle-income countries (LMICs) and securing them can be difficult. The goal of this work is to design, prototype, and test a low-cost ventilator, called ETH breathe, based on the automated compression of a resuscitator bag. A holistic and systematic design approach is taken to create a compact and adaptable device that can safely meet the current requirements. This is achieved by using 72% standard parts out of 33 (72%) and prioritizing compactness in the mechanical design. The control system is developed to provide both continuous mandatory ventilation (CMV) and spontaneous breathing support or assist control (AC), which significantly extends the potential use cases beyond patient sedation. The prototype is tested for accuracy, modularity, and oxygen response using a full physiological artificial lung. The results show for the first time in literature that the design operates within the defined requirements, based on emergency government regulations, and can be used with different sizes of resuscitator bags and different positions of the flow sensor. This provides a sound basis for further development of a low-cost, portable mechanical ventilator for potential use in LMICs.ISSN:1050-0472ISSN:1528-900

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field