Design and optimal springs stiffness estimation of a Modular OmniCrawler in-pipe climbing Robot

TL;DR

This paper presents a novel modular OmniCrawler robot for in-pipe inspection, focusing on its design, compliant joints with springs, and optimal stiffness estimation through simulation and real-world validation.

Contribution

It introduces a new compliant in-pipe climbing robot with optimized spring stiffness and modular design, enhancing obstacle negotiation and adaptability in small diameter pipes.

Findings

Optimal spring stiffness values were derived via constraint optimization.

Simulation results in ADAMS MSC matched experimental validation.

Replacing springs with series elastic actuators improved bend negotiation.

Abstract

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 (\text{\O} 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.