Degree

Doctor of Philosophy (PhD)

Department

Department of Mechanical & Industrial Engineering

Document Type

Dissertation

Abstract

Continuum robots, due to their compliant structures and ability to navigate through constrained environments, offer significant advantages in applications requiring safe physical interaction and dexterous motion. However, challenges related to limited structural stiffness, payload capacity, and precise control remain open problems in the field. This dissertation presents novel contributions aimed at addressing these limitations through two main actuation units of continuum robots: tendon-driven continuum robots (TDCRs) and concentric tube robots (CTRs). In the first part, we focus on methods to improve the stability and modify the stiffness of the TDCR. A tendon decoupling strategy is introduced for planar TDCRs. The method is mathematically modeled, validated through kinematic simulations, and confirmed via experimental characterization. Additional investigations into alternative tendon routings, including helical and spiral paths, demonstrate improved stiffness profiles. A linearly adjustable nonlinear compliance mechanism, inspired by Hertzian contact theory, is integrated into the stiffening cables to enable continuous output stiffness adjustment without the need for an active control loop. For example, via implementing this methodology on a prototype robot, the stiffening cables and adjustable stiffness mechanism allow for the stiffness to be adjusted between a range of 6x to 11x of the stiffness in the corresponding case of only actuating cables (the most common tendon routing in literature). Inclusion of a stiffening cable of a higher-order mode showed a reduced effect, allowing for stiffnesses in the range of 1.5x to 2.2x of the stiffness in the case of only actuating cables. The stiffening tendon routing approach is further extended to three-dimensional spatial configurations, supported by simulations, the results confirm a strongly decoupled tendon length change for some of the purposed tendon routing. A new structural design in which the central backbone is replaced with a radially offset support to allow uninterrupted tendon routing while maintaining desired strain limits. The second part focuses on the development of a long concentric tube robot for industrial integrity assessments and applications. A grounded robotic platform capable of actuating tubes up to 102 cm in length is designed and tested, incorporating a novel contact-based locomotion strategy to improve navigation in complex environments. Frictional interactions with the environment are characterized qualitatively to determine operational thresholds. Lastly, a hand-held version of the CTR robot with coiled tubing configuration is developed, featuring custom actuation and control units, achieving an insertion length of 85 cm.

Date

7-15-2025

Committee Chair

Gilbert, Hunter B.

DOI

10.31390/gradschool_dissertations.6880

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