Polhemus, Inc.

Penumbra, Inc.

Sixense Entertainment, Inc.

Igor Khalfin

Amir Rubin

Herbert R Jones

Oded Y Zur

Herbert S Jones, Jr

A method and apparatus is disclosed for allowing a magnetic tracking system to detect, and operate in close proximity in the same physical environment with, additional magnetic tracking systems. The first user's magnetic tracking system that becomes active in the physical space becomes the master system, and assigns time slots for its own transmitting antennas to generate the magnetic field which is used to determine the position and orientation of the user's limbs relative to the user's head. The master system also determines when other magnetic tracking systems become active in the physical space and assigns to those systems identification codes and time slots for their transmitting antennas to generate a magnetic field so that the position and orientation of the user's hands relative to the user's head for each of those systems may be determined. By requiring each magnetic tracking system to operate in different time slots, there is no interference between the systems.

Method and apparatus for synchronizing multiple magnetic tracking systems

An alternating current (AC) electromagnetic tracker system with increased operational range and an ability to compensate for electromagnetic distortion in the local operating environment. The system uses multiple 'N' sources/transmitters located at known positions in a common reference frame. A sensor receives the generated signal of each of the sources and a processor computes a position and orientation of the sensor from each. The processor further uses the known relative position and orientation between the N sources to compensate for distortion in the operating environment.

Electromagnetic tracker (AC) with extended range and distortion compensation capabilities employing multiple transmitters

A bounding box or volume of interest is flooded with a modulated AC electromagnetic signal from a source. Different types of modulated signals may be used, including single-tone AM and FM. One or more sensors disposed on an object or body within the volume are then used to detect the signal, and a digital and/or analog spectral and phase analysis is performed on the received signal in hardware or software. The processing distinguishes between the direct source to sensor response and the response due to eddy currents. By removing the response due to the distorters, the effects of the electromagnetic distortion can be removed through a more conventional &ldquo;free-space&rdquo; solution. The invention finds applicability in a wide variety of environments, including head tracking systems and helmet-mounted displays for fighter aircraft; head trackers for armored vehicles; medical-guided surgery and biopsy; remote sensing, among other potential uses.

Method and apparatus for electromagnetic position and orientation tracking with distortion compensation employing a modulated signal

A modulated signal (e.g., single tone FM or AM) and DSP spectral and phase analysis is used to enhance the performance of an AC magnetic tracker. The algorithm allows distinguishing between the direct source&mdash;sensor response and the response due to eddy currents, thus allowing elimination of effects of the electromagnetic distortion. This, in turn, eliminates the need for a calibration/mapping, which has proven to be the main obstacle for the wide application of AC electromagnetic tracking systems. The new method and system disclosed do not require witness sensors (but may be used in a combination with them), works in a narrow frequency band that ensures noise stability, may have high operation frequencies (e.g., about 50 kHz) that gives high quality of the signal and increased operation range, as well as high solution update rate, performs real time (each frame) distortion compensation without any prior knowledge about physical properties of distorters. At the same time the new system preserves all known advantages of the AC trackers. The approach finds applicability in head tracking systems and helmet-mounted displays for fighter aircraft, head trackers for armored vehicles, medical-guided surgery and biopsy. The same technology is applicable for remote sensing.

Method and apparatus for electromagnetic position and orientation tracking with distortion compensation employing modulated signal

Methods and apparatus for position/orientation tracking within a bounded volume employ at least one stationary sensor, called a &ldquo;witness sensor,&rdquo; having a fixed position and orientation near or within the volume to account for electromagnetic distortion. One or more probe sensors are placed on an object to be tracked within the volume, and the output of each witness sensor is used to compute the parameters of a non-real effective electromagnetic source. The parameters of the effective source are used as inputs to the computation of position and orientation as measured by each probe sensor, as if the object were in the non-distorted electromagnetic field produced by the effective source or sources. In addition to trackers for helmet-mounted displays in aircraft, tank, and armored-vehicle applications, the invention finds utility in any electromagnetic tracking system which might be subject to electromagnetic distortion or interference. Such application areas include electromagnetic motion capture systems, and medical systems and instruments, among others.

Methods and apparatus for electromagnetic position and orientation tracking with distortion compensation

Electromagnetic field mapping is accelerated by acquiring data from the surface bounding a volume of interest and solving the boundary value problem (BVP) using Green's function in a preferred embodiment. Instead of measuring electromagnetic field components on a step-by-step basis at each point within a region of interest, only a component of the field, preferably the normal component, is measured on the surface bounding the volume. The use of surface data acquisition, a solution to the BVP using Green's function, and optional error correction based on the treatment of errors as virtual sources, combine to produce a process of defining of the electromagnetic field within the volume that reduces to a few minutes what presently takes days or longer, and sometimes impossible. Data acquisition may be carried out either by moving sensors along the surface or, preferably, by fixing the position of several single axis or one-directional sensors on the surface bounding the volume without the necessity of moving parts. All geometry-dependent parameters, as determined by the shape and size of the volume of interest, may be pre-computed or computed independently on measurements. In addition to electromagnetic tracking systems, including LOS tracking, the methodology is directly applicable to electromagnetic motion capture systems, tomographic systems and devices (including optical, X-ray, magnetic), non-destructive electromagnetic measurements, and remote sensing.

Method and apparatus for determining electromagnetic field characteristics within a volume

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&deg; 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.

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South Burlington, VT, United States of America

Igor Khalfin