Slender continuum robots are uniquely placed to address inspection and intervention tasks in difficult-to-access environments. Tasks such as minimally invasive surgery andin situmaintenance of complex machinery require dexterous robots with accurate motion control, and benefit from instruments with small diameters and large internal passages for services. Intrinsic proprioception, or built-in position sensory feedback, has been described in prior work on continuum and soft robots but seldom employed for motion closed-loop control. In this research article, we present a novel tubular resistive stretch sensor with ionic liquid conductors to enable closed-loop position control of low-cost, 3-D printed continuum robots. We describe a methodology for sensor characterization and calibration drawing from a model of their behavior under strain, allowing us to apply four stretch sensors as proprioceptive feedback for motion control of a four-axis slender continuum manipulator. We demonstrate a substantial (approximately 65%) improvement in position control accuracy and repeatability over open-loop methods and show a promising step toward low-cost, scalable position feedback for slender continuum robots.

Automation of inspection and repair tasks on complex installations is gaining attention from industries with high-value assets such as aerospace, nuclear and marine. This paper reports on a five degrees of freedom robotic system capable of performing accurate and repeatable repair procedures through a narrow inspection port, which minimizes the cost and downtime associated with unscheduled maintenance. Careful study of the target working volume and repair process informed the design of a robotic probe capable of replicating the operation. Kinematic analysis of the robot's flexible, prismatic and rotary joints was used to define accurate machining paths in 3D space, and the results were verified using an optical motion capture system (accuracy of 0.25 mm). After comprehensive verifications of the constitutive elements, the robotic system was successfully demonstrated for repair of a high-pressure compressor aerofoil in a gas turbine. The results not only proves the ability of the system to address such difficult repair scenarios but also highlights a domain of opportunities in developing specialist robotics for repair of high-value assets, which is a subject to growing global demand.