Design and Control of a Multiple-Section Continuum Robot With a Hybrid Sensing System
Yihua Fang, Xin Dong, Abdelkhalick Mohammad, Dragoş Axinte
Abstract
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.