Multi-Point Orientation Control of Discretely-Magnetized Continuum Manipulators

In the past decade, remote actuation through magnetic fields has been used for position and orientation control of continuum manipulators (CMs) with a single magnet at the distal tip. By leveraging multiple points of actuation along the length of the CM it is possible to achieve increasingly complex shapes, which could be of interest in complex navigation tasks, for example, in minimally invasive surgery. In this study we present an approach for multi-point orientation control of discretely magnetized CMs. The approach is demonstrated with a manipulator that contains two permanent magnets, which are each actuated inside a non-homogeneous magnetic field. We formulate an accurate field model that conforms to Maxwell's equations and apply this to the available actuation system. Furthermore, Cosserat rod theory is used to model the manipulator deformation under external wrenches, and is utilized to numerically compute a Jacobian necessary to calculate the actuation inputs. During experiments, a stereo vision setup is used for manipulator shape feedback. Target orientations are manually provided as input to show independent orientation control of the two permanent magnets. Additionally, simulations with an extended virtual clone of the electromagnetic system are performed to show the capability of achieving more complex manipulator shapes. In both scenarios, it is observed that the algorithm is able to independently control the orientation of two interconnected magnets in a non-uniform magnetic field.

I. Introduction

Continuum manipulators (CMs) are continuously deformable elastic structures. Compared to traditional rigid link robots, CMs have infinite degrees of freedom (DOFs) which allows them to deform at any point along their length. This property makes CMs dexterous, enabling them to navigate through constricted spaces and cluttered environments [1]. The challenge lies in steering and navigation of CMs, as actuation at multiple points along the CM also requires actuators at those points. However, actuators attached to the body of the CM increase its size, which is disadvantageous in confined workspaces [2]. Magnetic actuation provides the potential for miniaturization by moving the actuation system outside the confined environment [3].