A Wireless 6-DoF Pose Tracking System Using a Triaxially Anisotropic Soft Magnet

Magnetic tracking, as a noncontacting and occlusion-free pose tracking method, has been increasingly employed to track various intracorporeal medical devices such as endoscopes and medical robots for monitoring, guidance, and automation of the medical procedure. Existing electromagnet-based tracking systems cannot achieve wireless tracking while permanent magnet-based systems are prone to magnetic disturbances and is only able to estimate 5-Degrees of Freedom (DoF) pose (3-DoF position and 2-DoF orientation). In this article, a new wireless 6-DoF magnetic pose tracking system is proposed using a stationary electromagnet as the primary magnetic source and a high-magnetic-permeability soft magnet as the sensitive element attached to the moving target. The soft magnet experiences a pose-dependent magnetization by the local field from the electromagnet, and its magnetic field is then measured by stationary sensors for pose estimation. The geometry of the soft magnet is designed with triaxially unequal dimensions (e.g., triaxial ellipsoids) to enable anisotropic magnetization and thereby 3-DoF orientation tracking. The magnetic response to the 6-DoF motion of the soft magnet is analytically modeled and experimentally validated. An artificial neural network is trained to inverse the nonlinear measurement model and directly estimate the pose from magnetic measurements. Pose tracking experiments are conducted with simultaneous translation and rotation of the soft magnet, which shows that the position error is below 5 mm and the orientation error is below 4°.