Current research into soft robots not only needs to improve their compliance, but also requires consideration of the real-time controllability of rigidity and flexibility. By combining the advantages of Pneu-Net structure and the driven jamming mechanism, we developed a soft actuator model for a soft robot with real-time variable stiffness. Firstly, the model of the soft actuator coupled with pneumatic structure and jamming mechanism was built. Secondly, we analyzed the pneumatically-driven structure by using the finite element method and researched the influences of pressure in cavities as well as shape and size of cavities on the performance of bending motion. On this basis, the pneumatically-driven structure was optimized. Finally, a prototype of the soft robot arm with variable stiffness was designed to carry out the experiment for verifying the variable stiffness of the soft actuator. Theoretical analysis and experimental results demonstrate that the soft robot can withstand a variable stiffness of between 0.025-0.138N/mm. In addition, the maximum elongation of the designed coupling mechanism can reach 25mm.INDEX TERMS Soft actuator, robot with variable stiffness, particle jamming, three-dimensional printing.
Soft robots have wide potential applications prospects in unstructured environments owing to their being able to imitate forms of motion of creatures in climbing and creeping through small spaces. By utilising the high flexibility of soft materials, a pneumatic soft climbing robot was designed. At first, a model for soft climbing robots with a stiffness gradient was designed according to the drive mode of pneumatic networks in soft robots. Afterwards, the visco-mechanical properties of robots at the contact surface were analysed and also the deformation characteristics of cavities were discussed by using the method of minimum potential energy. Subsequently, through simulation and use of the finite element method, the optimal number of cavities in an actuator required by a climbing robot was calculated and also the climbing behaviours of the robot were analysed. Finally, by employing 3D printing and layer-by-layer casting, a prototype soft climbing robot was prepared to perform climbing experiments. The research is expected to provide a new method for monitoring complex unstructured environments.
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