Alken Inc.

Robert F Higgins

Henry E Himberg

Allan G Rodgers, Jr

Herbert R Jones

Allan G Rodgers

Keith M Hanf

Suzanne T Gagnon

James C Farr

An apparatus and method for determining position and orientation (PnO) of an object within an environment using an electromagnetic tracking system. An adaptive filter is used to strike a tradeoff between low jitter and low latency. When the object is slow moving or stationary, the adaptive filter is set to filter out jitter from the electromagnetic tracking system. When the object is in motion, the adaptive filter is set to reduce latency of the electromagnetic tracking system. An amount of motion of the object is monitored using a non-magnetic tracking device, whereby the setting of the adaptive filter is controlled based on the monitored motion using signals from the non-magnetic tracking device.

Low latency adaptive filter

A system and method for collecting distortion compensation data to continually update and improve a distortion compensation algorithm for correcting position and orientation (PnO) information regarding an object tracked. The method may be performed while the object is freely in motion. Collection of the distortion compensation data is based on a first PnO solution based on the first PnO measurement data and irrespective of the second PnO measurement data, and a second PnO solution based on a correction algorithm that includes the first PnO measurement data, the second PnO measurement data, and PnO correction data. The first and second PnO solutions may be added to the PnO correction data to continually update and improve the distortion compensation algorithm.

Electromagnetic tracking with self learning

An apparatus and method for implementing a technique for performing calibration of an electromagnetic tracking apparatus on-the-fly while operating the apparatus. The apparatus and method uses a non-magnetic tracking device to determine position and orientation of a tracked object that is not subject to magnetic distortion or interference, and store calibration data for future measurements by the electromagnetic tracking apparatus based on the measurements made by the non-magnetic tracking device.

Hybrid tracking with auto-correction

An apparatus and method for determining position and orientation (PnO) of an object within an environment and for automatically determining a hemisphere of the object relative to a source location using an electromagnetic tracking system and a non-magnetic tracking device. The method involves seeding two candidate PnO solutions, one in each hemisphere, based on initial data from the magnetic tracker. Then, as the sensor moves within the tracking volume, both the magnetic tracker and the non-magnetic tracking device are used to track changes in each of the candidate PnO solutions and to determine a correct one of the candidate PnO solutions.

Auto-hemisphere detection in a magnetic tracker

A system and method for implementing a technique for dynamically switching between or mixing position and orientation determinations in a hybrid tracking system using both electromagnetic and non-electromagnetic tracking, and having a transmitter coil array for generating a magnetic field, a receiver circuit for sensing the magnetic field, and at least one non-magnetic sensor.

Dynamic mixing of and switching between sensor measurements in hybrid trackers using electromagnetic tracking

An apparatus and method for implementing a technique for adaptively assigning weighting factors to position and orientation determinations in an electromagnetic or hybrid tracking system having multiple transmitters or multiple receivers. The apparatus may reduce the impact of eddy current distortion to the position and orientation determinations.

Adaptive weighting of multiple sources in a magnetic or hybrid tracking system

An apparatus and method for implementing a reversible connector for receiving coil-based sensor signals in an electromagnetic or hybrid tracking system. The apparatus is designed to reduce the number of connector pins assigned to the coil-based sensor signals while maintaining signal quality.

Reversible connector orientation detection in an electromagnetic tracking system

A method for calibrating a magnetic source of an electromagnetic tracking system for tracking a position and orientation of an object using an inertial motion unit (IMU) mounted to the magnetic source and aligned with the coil array of magnetic source. Pitch and rolls angles of the coil array are calibrated using the IMU.

Self-leveling magnetic source

A method and system for magnetic locating resolves phase ambiguity. The system uses time-division multiplexed magnetic fields emitted from plural transmit coils. The magnetic fields are alternating fields at a carrier frequency, and the fields emitted from different coils in different transmit intervals have known phase relationship with one another as, for example where the alternating fields are coherent with one another. A receiver uses a plurality of sensor coils and derives plural components using the common phase reference or plural phase reference times having a known relationship. If the determinant of a matrix of the components has a first value, the phase information in the components is correct, and position and orientation are derived from the components. If the determinant has a second value, the phase information in the components is incorrect. In this case, corrected components are formed by shifting the phases of the components &#x3c0; radians; the position and orientation are derived from the corrected components.

AC magnetic tracking with phase disambiguation

Plural transmitter coils of a magnetic locating system are driven with widely-separated main frequencies. One of the transmitter coils is also driven with a marker frequency close to the main frequency applied to that coil. The receiver determines a phase relationship with the transmitter based on the main and marker frequencies, so that the receiver does not suffer from phase ambiguity. The main and marker frequencies may interfere with one another, and the receiver may correct for such interference based on known characteristics of the signals at the main and marker frequencies.

AC magnetic tracking system with phase locking

In an AC magnetic tracker one or more multi-axis field sources, each operating at a different frequency, or frequency set, are detected and tracked in three-dimensional space, even when wireless or otherwise not physically connected to the tracking system. Multiple sources can be tracked simultaneously as they each operate with their own unique detectable set of parameters. The invention not only provides the ability to uniquely identify one or more sources by their frequencies, but also to synchronize with these frequencies in order to measure signals that then allow tracking the position and orientation (P&O) of the source(s). Further, these sources need not be present at the time of system start-up but can come and go while being detected, discriminated and tracked. It also should be noted that application of such systems in multiples with more sensors not synchronized to a source or sources also could be employed to give the reverse appearance of a known source phase and incoherency with the sensors.

AC magnetic tracking system with non-coherency between sources and sensors

A magnetic tracker system for use on an operator's head makes 'mouse'/cursor movements on a screen similar to that of the classic computer 'mouse'/track ball/touchpad/joystick. Only head movements are used as opposed to lifting a hand from the keyboard for making such moves. The new &#x201c;mouse&#x201d; avoids interrupting the hands from their position on the keyboard and has no moving mechanical parts that become clogged and that need a special surface (mouse pad) or special surface measurements (optical mouse).

Head-mounted pointing and control device

Techniques for removing distortion in an AC magnetic tracker identify a characteristic frequency in the distortion environment which is then utilized to extract distortion components from the tracker receiver signals so that the corrected position and orientation can be calculated. A multiplicity of alternative techniques for determining this characteristic frequency are disclosed, several of which can be done during operation without interrupting system operation while others can be done off-line. The invention also allows the use of a tuned tracker transmitter since it does not need to operate at multiple frequencies. The invention differs from the prior art by treating an extended conductor characteristic as just another unknown. The position and orientation algorithm solves the 6 unknown coordinates of position and orientation plus the one more unknown&#x2014;the extended conductor characteristic frequency. This enables the tracker to operate full time in one mode of operation without ever suspending normal operation and without additional hardware capabilities.

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South Burlington, VT, United States of America

Robert F Higgins