Electromagnetic position and orientation tracking system with distortion compensation employing wireless sensors

Abstract

A solution to the electromagnetic position/orientation tracking problem is presented in an environment wherein strong electromagnetic distortion may be present includes at least one source of an AC electromagnetic field, at least one witness sensor measuring components of the electromagnetic induction vector at known spatial points close to, or within the volume of interest, at least one wireless probe sensor placed on the object being tracked, and a control and processing unit. The wireless sensor has a known response or distortion to the electromagnetic field generated by the primary source. The control/processing unit uses data from the witness sensor(s) to locate the probe sensor, treating the probe sensor as a secondary source of the AC electromagnetic field; that is, as a transponder with initially known magnetic parameters. This information is utilized by a position and orientation algorithm executed by the control/processing unit to define coordinates and attitude of the secondary source and, in turn, the position and orientation H of the object of interest. In the preferred embodiment, the probe sensor is an LC-contour tuned to the frequency of the tracker source. As such, the signal from the probe sensor is 90° phase shifted with respect to the tracker source signal and other signals in the system, including distortion. This allows the witness sensors and processing unit to separate the environmental distortion signal from the probe sensor signal by distinguishing the phase of the signal from the probe sensor.