A hybrid force-magnetic control scheme for flexible medical device steering

Magnetically-actuated flexible surgical robot has promising applications for ultra-narrow and tortuous orifices, however, how to minimize the energy consumption, physical interaction between the external electromagnet (EEM) and the human body, and the bulky size of the magnetic actuation system remains a major challenge. This work presents a hybrid force-magnetic control scheme that can magnetically steer catheters with the least distance in order to reduce energy consumption and the size of the magnet. In addition, the use of force feedback control allows the motion of magnet adapts to the movement of patient's body, ensuring safety during the operation. The scheme is composed of two parts: a Jacobian-based inverse kinematic model that enables 3D position control of the catheter's distal tip through the EEM, and a force control algorithm based on admittance control that converts external forces applied to the magnet into position errors, making the system compliant that allows for safe contact with the human body. Experiment was conducted to validate the feasibility and accuracy of the proposed control scheme. The results show that the catheter's distal tip can be controlled to follow desired trajectories with a minimum Root Mean Square (RMS) error of 0.43 +/- 0.22 mm, and the hybrid control scheme can reduce electrical power consumption effectively while achieving similar performance with an RMS error of 0.52 +/- 0.41 mm. It is also able to maintain contact forces within a safe range (<15 N) during actuation.