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This work investigates the usage of compliant universal grippers as a novel foot design for legged locomotion. The method of jamming of granular media in the universal grippers is characterized by having two distinct states: a soft, fluid-like state which in locomotion can be used to damp impact forces and enable passive shape adaptation especially on rough terrain, and a hard, solid-like state that is more suited to transmit propulsion forces. We propose a system that actively uses and switches between both states of a foot design based on granular jamming and detail the implementation on a quadruped robotic platform. The mechanism is inspired by the stiffness varying function of the tarsal bones in a human foot, and our aim is to understand how the change of foot stiffness can be used to improve the locomotion performance of legged robots. Using the same open loop trot gait in all experiments, it is shown that a fast state transition enables the robot to profit from both states, leading to more uniform foot placement patterns also on rough terrain compared to other tested feet. This results in overall faster gaits and even enables the robot to climb steeper inclined surfaces.
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Auke Ijspeert, Mahdi Khoramshahi, Metin Sitti
impact damping'' and
propulsion force transmission'', and we show how this regularizes step sizes on rough terrain. We then present one mode-switch method in control, a force feedback strategy named tegotae''. This switches the functionality of leg movement between
displacing the leg'' and displacing the body'', and we show how this informs the controller about which legs are bearing less weight and thus are more suited to be moved. We suggest that these methods can be applied to any legged structure and use modular robots to demonstrate these concepts. In parallel, we also improved our previously developed self-reconfigurable modular robot platform
Roombots'' such that they perform a variety of tasks centered around adaptive and assistive furniture with up to 12 modules. This includes demonstrations of self-reconfiguration, mobile furniture, object manipulation, interaction capabilities and the development of a user interface. With these improvements, this platform can in the future also be used for further locomotion research where the shape-shifting ability could be of major importance.Peter Eckert, Simon Lukas Hauser, Auke Ijspeert, Alexandre Tuleu