Design and optimal springs stiffness estimation of a Modular OmniCrawler in-pipe climbing Robot
This addresses the problem of in-pipe inspection and maintenance in industrial settings, though it is incremental as it builds on existing modular and compliant robot concepts.
The paper tackled the design of a compliant modular robot for climbing small pipes, achieving a solution with optimized spring stiffness for a 75mm diameter pipe and later modifying it with series elastic actuators to handle bends and friction variations.
This paper discusses the design of a novel compliant in-pipe climbing modular robot for small diameter pipes. The robot consists of a kinematic chain of 3 OmniCrawler modules with a link connected in between 2 adjacent modules via compliant joints. While the tank-like crawler mechanism provides good traction on low friction surfaces, its circular cross-section makes it holonomic. The holonomic motion assists it to re-align in a direction to avoid obstacles during motion as well as overcome turns with a minimal energy posture. Additionally, the modularity enables it to negotiate T-junction without motion singularity. The compliance is realized using 4 torsion springs incorporated in joints joining 3 modules with 2 links. For a desirable pipe diameter (\textØ 75mm), the springs' stiffness values are obtained by formulating a constraint optimization problem which has been simulated in ADAMS MSC and further validated on a real robot prototype. In order to negotiate smooth vertical bends and friction coefficient variations in pipes, the design was later modified by replacing springs with series elastic actuators (SEA) at 2 of the 4 joints.