A snake robot can form various shapes by fitting to an arbitrary continuous curve thanks to its numerous degrees of freedom. When traversing an unknown complex environment, a snake robot may need to perform local shape transformation to avoid obstacles or perform specific tasks. In this study, we present a local shape transformation control method for expanding the mobility of a snake robot. The proposed control method lifts a local part of the robot away from the target continuous curve while the leading part and the trailing part shift accordingly to remain fitted to the continuous curve without twisting. The proposed local shape transformation is realized by changing the approximation range on the continuous curve without changing the shape of the continuous curve. Simulations were conducted to evaluate the effectiveness of the local hump-shaped transformation control on various types of continuous curves. We also evaluated the proposed control method by comparing it with other local shape transformation control methods through simulations. Additionally, we propose two examples of applications which are the recovery from a stuck state and recovery from joint failure. Experiments were conducted to verify the effectiveness of the proposed control method.

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