Pneumatic driven hollow variable stiffness mechanism aiming non-contact insertion of telescopic guide tubes

Disaster robots that can work safely and quickly in complex and fragile environments are required for collecting information from debris for initial response and recovery work. Various snake-like robots have been proposed that can be inserted into a confined space. However, their propulsion mechanisms, such as the wheel, the continuous track, and the vibrating inclined cilia, must be in physical contact with the environment and may induce secondary disasters like a further break and fall of debris. This paper introduces a snake-like robot with a two radial-layer structure that can be propelled not only on an arbitrary trajectory but also without establishing contact with the environment by sliding its two coaxial tubes alternately and switching their stiffness by internal pressurization. This newly invented variable stiffness mechanism has a hollow structure that allows both simplicity of design and positive pressure activation. A prototype model was developed for proof of principle, and the average pulling forces required to actuate either the inner or the outer tube when the other tube is bent at 1/225 and fixed were measured to be namely 67.6 N and 5.66 N, respectively. This evaluation experiment validated the proposed principle of contactless propulsion mechanism. In the future, it might be possible to verify whether non-contact propulsion can be conducted in the air as well, thereby requiring the verification of a theoretical model.