Design and Control of a Multiple-Section Continuum Robot With a Hybrid Sensing System

After decades of development, the technology of continuum robots continues to mature gradually and is used for various applications, e.g., inspection and repair in high-value-added industries, such as aerospace and nuclear. However, such robots are invariably designed with a hyper-redundant structure which causes condition-dependent uncertainties and errors in practical operations. In this article, a hybrid sensing solution—consisting of a dual displacement sensor system (linear and rotary encoders) and a self-carried visual tracking system—is presented to improve the control performance of a multisection cable-driven continuum robot. The dual displacement sensor system works to measure the cable-displacement error at the proximal end of the arm and predicts the cable elongation in the arm to eliminate the control error of the robot in joint-space via a new two-stage cable-displacement control approach. Simultaneously, the self-carried visual system provides real-time section-by-section tip tracking to improve the controllability of the arm in the task space. This feedback is then integrated with a two-level closed-loop controller to achieve accurate tip-positioning control. A series of validation experiments are carried out to validate the approach. Compared with an off-the-shelf position tracking system, the measurement error of the proposed self-carried visual tracking system is smaller than 2 mm, with a mean error of 0.67 mm, within the workspace of a single-section continuum robot. The distal-tip control accuracy of a two-section robot can achieve 1.72 mm under the closed-loop controller supported by the hybrid sensing system.