Shi, Hongshen
(2025)
An approach on haptics and control of continuum robots.
PhD thesis, University of Nottingham.
Abstract
This thesis investigates solutions in the areas of force sensing, force/position control, and haptic control for continuum robots. To navigate narrow and constrained environments, continuum robots possess unique characteristics distinct from traditional rigid robots, including high flexibility, a small diameter-to-length ratio, and low stiffness. These structural and operational features introduce significant challenges in modelling, sensing, and control.
A comprehensive literature review is presented, covering the primary methods and notable examples in continuum robot modelling, shape/force sensing, and position/force control. The overarching research goal is to develop a widely applicable haptic sensing and control system for continuum robots. Key technical challenges—such as interaction force measurement, hybrid force/position control, and haptic feedback control—are thoroughly explored and experimentally validated in this thesis.
To address the challenge of interaction force measurement, two novel approaches are proposed. The first is an indirect force sensing method that estimates machining forces (e.g., milling or grinding) by analysing acoustic features from the machining process. This method is applied for the first time to a semi-continuum robot and utilizes a remote microphone to capture machining sounds. Experiments were conducted using two types of tools and three types of materials to evaluate the method’s robustness under various conditions. The second approach involves the development of a novel strain gauge–based triaxial force sensor, capable of measuring forces up to 20 N with an error margin of only 0.25% in the radial direction. Both force sensing methods require minimal to no modifications to the robot, and their effectiveness has been experimentally validated.
For position and force control of multi-section continuum robots, a hybrid force/position control strategy based on direct force sensing is developed. A kinematic model employing the piecewise constant curvature (PCC) assumption is used for efficient robot control. Position tracking is achieved through a vision-based tracking system, while external forces are directly measured using the previously introduced sensor. Both position and force acquisition methods are demonstrated to be accurate and stable. A hybrid controller is then implemented to achieve simultaneous closed-loop control of position and force. Compared to other controllers that rely on indirect sensing, this approach offers higher accuracy and reduced computational complexity by leveraging direct sensing and control.
Regarding haptic feedback and control, a system is proposed to enable manual operation of continuum robots in scenarios where conventional force sensors cannot be used. This system includes components for force acquisition, teleoperation, and haptic feedback. To demonstrate its general applicability, a haptic control experiment involving machining tasks is conducted, verifying the feasibility and effectiveness of the proposed method across various use cases.
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