Robotics has undergone a profound revolution in the past 50 years, moving from the laboratory and research institute to the factory and home. Kinematics and dynamics theories have been developed as ...the foundation for robot design and control, based on the conventional definition of robots: a kinematic chain of rigid links.
This paper presents a compact and efficient 88-line MATLAB code for the parameterized level set method based topology optimization using radial basis functions (RBFs), which is applied to minimize ...the compliance of a two-dimensional linear elastic structure. This parameterized level set method using radial basis functions can maintain a relatively smooth level set function with an approximate re-initialization scheme during the optimization process. It also has less dependency on initial designs due to its capability in nucleation of new holes inside the material domain. The MATLAB code and simple modifications are explained in detail with numerical examples. The 88-line code included in the
appendix
is intended for educational purposes.
A novel layer jamming variable stiffness technique for soft robotics is proposed in this paper, which we call electrostatic layer jamming (ELJ). The basic principle of the ELJ is using electrostatic ...attraction to squeeze material layers to generate friction and then engage jamming. Based on this technique, several specimens used in two common application scenarios including variable tensile stiffness and variable bending stiffness are fabricated, and their stiffness adjustment characteristics are investigated experimentally. Surprisingly, the test data are much larger than the theoretical prediction, which we think is because of the formation of local low air pressure regions between the contact surfaces. Also, the experimental results show that the ELJ technique possesses a large capability of stiffness changing and is space saving. The potential values of the ELJ have been shown by performing with a soft linear actuator for three representative practical applications in the soft robotic field. Finally, the existing problems and advantages of the ELJ technique are discussed, and we believe that this technique will inspire new ways and new opportunities for the soft robotic community.
Abstract
The rapid growth in the miniaturized mechanical and electronic devices industry has created the need for temporary attachment systems that can carry out pick‐and‐place and transfer printing ...tasks for fragile and tiny parts. Current systems are limited by a fundamental trade‐off between adhesive strength and state‐changing trigger force, which causes the need for a rapidly switchable adhesive. In this study, an elastomeric microstructure is presented combining a trapezoidal‐prism‐shaped (TPS) and a mushroom‐shaped microstructure, which overcomes the trade‐off with the help of the TPS structure. The optimal design exhibits a strong adhesive strength of 87.8 kPa and a negligible detachment strength of <0.07 kPa with a low trigger shear stress of 10.7 kPa on smooth glass surfaces. The large tip‐to‐stem ratio (50 to 20 µm) enhances the suction effect, allowing the microstructure to maintain its adhesive performance even in wet conditions. Pick‐and‐place manipulation tasks of a single and an array of ultralight parts from micrometer to millimeter scales are performed to demonstrate the capability of handling fragile and tiny parts. Moreover, it demonstrates the ability to transfer parts across water and air interfaces. This proposed microstructure offers a facile solution for manipulating microscale fragile parts in dry and wet conditions.
This paper proposes a structure-material integrated design method in the framework of level sets. A two-scale optimization is performed, where not only is the structural configuration optimized, but ...the effective properties of the constituent material are also designed by optimizing the configuration of the periodically-arranged microstructures. In this way, the approach can simultaneously generate optimized material distribution patterns as well as optimized materials. Due to the fact that the level set method produces material-void solutions only, the obtained material is uniformly distributed over the material regions of the structure in a strict sense. Three numerical examples are presented to validate the proposed method. The obtained optimal solutions illustrate that whether to design material cells or to optimize structural configurations to achieve the best structural performance would be problem dependent, and thus further demonstrate the necessity and validity of the integrated design scheme.
Designing metallic cellular structures with triply periodic minimal surface (TPMS) sheet cores is a novel approach for lightweight and multi-functional structural applications. Different from current ...honeycombs and lattices, TPMS sheet structures are composed of continuous and smooth shells, allowing for large surface areas and continuous internal channels. In this paper, we investigate the mechanical properties and energy absorption abilities of three types of TPMS sheet structures (Primitive, Diamond, and Gyroid) fabricated by selective laser melting (SLM) with 316 L stainless steel under compression loading and classify their failure mechanisms and printing accuracy with the help of numerical analysis. Experimental results reveal the superior stiffness, plateau stress and energy absorption ability of TPMS sheet structures compared to body-centred cubic lattices, with Diamond-type sheet structures performing best. Nonlinear finite element simulation results also show that Diamond and Gyroid sheet structures display relatively uniform stress distributions across all lattice cells under compression, leading to stable collapse mechanisms and desired energy absorption performance. In contrast, Primitive-type structures display rapid diagonal shear band development followed by localized wall buckling. Lastly, an energy absorption diagram is developed to facilitate a systematic way to select optimal densities of TPMS structures for energy absorbing applications.
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•Two families (P and IWP) of elastically isotropic open-cell uniform thickness shell lattices are developed via shape optimization.•Shell mid-surfaces are represented by a B-spline ...parameterized Monge patch model to maintain cubic symmetry and simplify sensitivity evaluation.•P/IWP family lattices approach 70%/80%, 40%/60%, 40%/60% of Hashin-Shtrikman upper bounds of bulk, Young’s, shear moduli at 10% relative density.•Introduction of Young’s/bulk modulus maximization into the optimization alleviates dependence on initial designs and slightly improves the stiffness by 3–5%.•IWP-family lattices outperform stiffness-optimal truss lattices on bulk, Young’s, shear moduli by 82%, 50%, 45% at 10% relative density.
Shell lattices are composed of smooth, non-intersecting and periodic thin shells. Their open-cell topology facilitates the manufacturing and multifunctional applications. This work proposes a shape optimization framework to obtain uniform thickness shell lattices with superior elastic moduli and isotropic elasticity. A B-spline parameterized Monge patch model is used to represent the mid-surface within the 1/48 unit cell, which maintains the cubic symmetry and simplifies the sensitivity evaluation. Two groups of elastically isotropic shell lattices are obtained, including Primitive (P) and I-graph-wrapped package (IWP). The highest achievable bulk, Young’s, shear moduli of P/IWP family lattices are nearly 70%/80%, 40%/60%, 40%/60% of the Hashin-Shtrikman upper bounds at 10% relative density. Besides, the Young’s/bulk modulus maximization is further introduced into the optimization to seek potential stiffness improvement, yielding similar optimized lattices with close stiffness for arbitrary initial designs. The highest achievable moduli are slightly improved by 3~5% than those without moduli maximization. In general, P-family lattices possess comparable Young’s, shear and higher bulk moduli to the stiffest truss lattices, while IWP-family lattices possess superior stiffness. This work proposes a systematic design approach to obtain elastically isotropic uniform thickness shell lattices, which can be applied to the other lattice families with Monge patch representations.
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•A design and characterisation framework for hierarchical sheet TPMS lattices.•A wide range of geometric and mechanical properties are achieved by hierarchies.•2-order Gyroid lattices ...exhibit stable failure behaviour with a flat stress plateau.•2-order Gyroid lattices outperform single scale under buckling at ultralow densities.•2-order Gyroid lattices exhibit reduced stiffness and strength compared to single scale.
Lattices with hierarchical architectures exhibit unique geometric and mechanical properties compared with single scale ones. While numerous research efforts have focused on hierarchical strut lattices, hierarchical sheet lattices have yet to be studied in detail. This paper proposes a systemic framework including geometric design, finite element modelling, additive manufacturing, and mechanical testing for hierarchical sheet triply periodic minimal surface (TPMS) lattices such that the lattice walls comprise successively smaller scale TPMS architectures. Geometric properties including relative densities and volume-specific surface areas of hierarchical lattices are analytically calculated and verified via numerical calculations. The compressive properties of 2-order sheet Gyroid lattices are investigated with finite element simulations and experimentally validated using micro-selective laser melting fabricated stainless-steel specimens. Geometric analysis shows that hierarchical sheet lattices have great potential to achieve a wide range of controllable geometric properties including hierarchical porosities, ultralow densities, and significantly enlarged surface areas. Simulation results indicate that 2-order lattices have superior buckling strength over single scale lattices at ultralow densities. At moderate densities, 2-order lattices exhibit reduced modulus and strength, but more stable failure behaviour. With these unique combinations of geometric and mechanical properties, hierarchical sheet TPMS designs are shown to be desirable structural configurations for biomedical scaffolds.
This paper presents a simple but effective additive hyperelasticity technique to circumvent numerical difficulties in solving the material density-based topology optimization of elastic structures ...undergoing large displacements. By adding a special hyperelastic material to the design domain, excessive distortion and numerical instability occurred in the low-density or intermediate-density elements are thus effectively alleviated during the optimization process. The properties of the additional hyperelastic material are established based on a new interpolation scheme, which allows the nonlinear mechanical behaviour of the remodelled structure to achieve an acceptable approximation to the original structure. In conjunction with the adjoint variable scheme for sensitivity analysis, the topology optimization problem is solved by a gradient-based mathematical programming algorithm. Numerical examples are given to demonstrate the effectiveness of the proposed method.
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