Development of a continuum robot with inflatable stiffness-adjustable elements for in-situ repair of aeroengines

• An industrial-use continuum robot with long-reach ability is proposed. • A predictable inflation element with a 10:1 expansion ratio is designed to stiffen the continuum robot, enabling a precision of RSME <1 .17 mm. • Demonstration was done in a Rolls-Royce aeroengine for Thermal Barrier Coating repair, which shows the robot's capability and proves the inflation element's robustness. Continuum robots, with their slender configuration and high redundancy, gain increasing interest in industrial applications such as intervention within confined spaces. However, when the robot end effector is required to travel a long distance, the existing products need a large actuation pack and complicated control strategy for a decent accuracy. This paper presents a continuum robot with a novel stiffness-adjustable mechanism designed to address conditions requiring high tip accuracy in long-reach confined spaces. Key innovations include (1) a section capable of inflating its diameter tenfold for the support of a 6-DoF continuum section, (2) a predictive model for a hybrid stiffening arm, and (3) a manual insertion approach that reduces actuation complexity. The proposed design was validated through a prototype that performed repairs on a thermal barrier coating within an aeroengine. During trials, a 12.6 mm diameter arm was inserted through an access port with a diameter of < 15 mm, inflated to 120 mm to securely lock in place, and enabled precise six degrees of freedom (6-DoF) control. The predictive model achieved a Root Mean Square Error below 1.14 mm under payload, demonstrating enhanced positional accuracy compared to traditional continuum robots. These results mark a significant advancement towards robust, precise operations in restricted industrial environments.