Gain-scheduling control of a cable-driven MRI-compatible robotic platform for intracardiac interventions

In this paper, we design and implement a gain-scheduling controller for a parallel structure robotic platform (that we name ROBOCATH) developed to be used in intracardiac interventions under beating-heart conditions. The primary mission for this manipulator is to safely steer the cardiac catheters inside the left ventricle to reach any desired target points under magnetic resonance imaging (MRI) guidance. In this paper, we first derive a reduced-order dynamic model of the robot based on the Lagrange method to capture the nonlinear dynamics of the platform. The model is then used for the design of a state feedback linear parameter varying (LPV) controller to command the robot to position the catheter in any desired state. During the controller design process, appropriate selection of scheduling parameters not only helps hide the nonlinearities of the system dynamics but also leads to a set of decoupled models for the structure, where each degree of freedom could be treated separately. The performance of the controller is compared with a variable-gain proportional-derivative-integral (PID) controller designed in our earlier work. The experimental results show that the proposed control scheme has significant advantages in terms of implementation, set point tracking and actuator saturation over the baseline PID controller.