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The objective of this work is to reveal the relationship between the molecular structure and shape-memory property of a hydro-epoxy resin system. The system is prepared using hydro-epoxy, menthane diamine (MDA), and poly(propylene glycol) diglycidyl ether (PPGDGE) with different molecular weights. By keeping the PPGDGE content constant, the crosslink density of the shape-memory hydro-epoxy resin system can be changed by varying the molecular weight of PPGDGE. The results indicate that the glass transition temperature (Tg) and rubber modulus (Er) decrease as the crosslink density decreases. The crosslink density has little influence on shape recovery ratio (Rr). Full recovery can be observed after only several minutes when the temperature is equal to or above Tg. However, the crosslink density has a profound effect on the shape fixity ratio (Rf). If the crosslink density is too low, the shape fixity ratio of shape-memory hydro-epoxy resin would not reach 100%.
This paper presents a seven-link dynamic walking model that is more close to human beings than other passivity-based dynamic walking models. We add hip actuation, upper body, flat feet, and ankle joints with torsional springs to the model. Walking sequence of flat-feet walkers has several substreams, which forms bipedal walking with dynamic series of phases. We investigate the effects of ankle stiffness on gait selection and evaluate different gaits in walking velocity, efficiency, and stability. Experimental results indicate that ankle stiffness plays different roles in different gaits and the gaits, which are more close to human walking with moderate speed, achieve better motion characteristics.
A novel ostraciiform swimming, vision-based autonomous robotic fish is developed in this paper. Its feasibility and capability are shown by implementing a dynamic target following task in a swimming pool. Inspired by boxfish that is highly stable and fairly maneuverable, the robotic fish is designed and constructed by locating multiple propulsors peripherally around a rigid body. Swimming locomotion of the robotic fish is achieved through harmonic oscillations of the tail and pectoral fins. The forces and moments acting on the fins and body are analyzed and the governing motion equations are derived. Through coordinating the movements of the propulsors, several typical swimming patters are empirical designed and realized. A digital camera is integrated in the robotic fish, and the visual information is processed with the embedded microcontroller. To treat the degradation of underwater image, a continuously adaptive mean shift (Camshift) algorithm is modified to keep visual lock on the moving target. A fuzzy logic controller is designed for motion regulation of a hybrid swimming pattern, which employs synchronized pectoral fins for thrust generation and tail fin for steering. A simple target following task is designed via an autonomous robotic fish swimming after a manually controlled robotic fish with fixed distance. The swimming performance of the robotic fish is tested and the effectiveness of the proposed target following method is verified experimentally.
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