Closed-loop Position Tracking Control of a Continuum Robot Using Magnetic Localization

Continuum robots with continuous bending capability have been widely applied in manufacturing, equipment inspection, and minimally invasive surgeries for their inherent compliance, easy access to confined spaces, and large workspace. However, there exist significant errors when continuum robots are controlled in an open-loop manner by directly inverting the kinematic model, because kinematic models cannot accurately cover nonlinearities in actuation mechanisms and compliant bodies as well as unknown external interaction forces. In this paper, a closed-loop control method using magnetic localization as feedback is proposed to achieve accurate position tracking control of a dual-section cable-driven continuum robot. In the proposed wireless magnetic localization system, only a passive permanent magnet is installed on the robot tip, and its magnetic field is measured by a nearby magnetic sensor array for position estimation using an extended Kalman filter. A proportional-integral controller is designed to generate the cable control input using magnetic localization information and differential inverse kinematics of the continuum robot. Experimental results demonstrate that the proposed closed-loop control method achieves a high position control accuracy of around 5 mm on rectangular and pentagram trajectories. The magnetic localization system is also validated to have a small position error of around 3 mm. Therefore, the proposed closed-loop control method using permanent-magnet-based localization can enable real-time and accurate position estimation and tracking control of continuum robots, with no need for installation of wired sensors or powered electronics on the robot.