Design and implementation of wormlike creeping mobile robot for EAST remote maintenance system

Highlights: • Wormlike creeping robot walking on the V-shaped circular slot in EAST fusion vessel. • Mobile platform to carry equipments or assist manipulators for maintenance tasks. • Chain structure design with n(n ≥ 2) creeping units each of which has three segments. • Creeping gait planning to construct a multi-axis coordinating control scheme. • Evaluation and verification of basic motion performance and mechanical properties. - Abstract: Maintenance for nuclear fusion vessel is crucial, yet it faces great difficulty due to the complex internal physical and geometric conditions. Since the limitation on inherent strength, load, size, etc, a manipulator robot can only complete very limited tasks. Robotic arm systems for remote operation such as JET and MPD can carry certain tools to complete a variety of operating tasks, but it is difficult to achieve the system which is very complex. Therefore, if the inherent idea of using a single robot to complete the specified functions can change, it is possible to make the problems simpler and easier to solve by adding auxiliary robots working together with the robotic arm systems to complete the assigned tasks. Under the above background, based on the deeply analyzing and refining the functional requirements of the vessel operation robot, proceeding from the perspective of ability to move and carry a certain operating device, this paper presents a wormlike creeping mobile robot walking on the V-shaped circular slot inside a nuclear fusion vessel such as EAST (Experimental Advanced Superconducting Tokamak). We have designed and implemented the principle prototype of the robot which has chain structure with n (n ≥2) creeping units. Each creeping unit is of three-part structure, which consists of fore segment, mid segment and back segment connected by bidirectional universal joint. The fore and back segments stretch the paws to contact the surface of V-shaped slot, while the mid segment realizes the overall movement of robot. In order to evaluate the design and implementation of the mobile robot platform, functional analysis is devoted to modules of robot. Especially for the requirements of walking stability on the V-shaped slot, creeping gait planning is analyzed to construct a multi-axis coordinating movement control scheme for creeping motion. Finally, by using the simulated EAST nuclear fusion vessel, the principle prototype is tested, and the preliminary evaluation of its functional index and related technical parameters is carried out. The experimental results show that the principle prototype of the robot can achieve stable walking on the V-shaped circular slot at the bottom of the nuclear fusion vessel, and it has a certain ability to carry equipments.