Abstract: Embodiments of an AC magnetic tracker include frequency-based compensation for metal distortion. The tracker measures the position and orientation of the receiver relative to the transmitter in up to six dimensions, position (x, y, z) and orientation (azimuth, elevation, roll). In some embodiments, magnetic fields are transmitted at selected frequencies and the received magnetic fields are measured in-phase with the transmitted magnetic field. In other embodiments, magnetic fields are transmitted at selected frequencies and the received magnetic fields are measured both in-phase and in-quadrature with the transmitted magnetic field. In yet other embodiments, a transition signal is transmitted and the received decaying signal is measured. Other embodiments disclose some combination of these features. The metal's inductive limit, decay time constant and polarity sign are calculated from the received signals.

Abstract: In a sourceless orientation sensor, the sensor measures the three orientation angles azimuth, elevation and roll in a fixed reference three-dimensional coordinate frame. The sensor utilizes a three-axis magnetic sensor to measure changes in the Earth's magnetic field in order to determine the azimuth and roll (or elevation) angles after the elevation (or roll) angle has been determined by other means. A first embodiment utilizes a separate sensor to measure the elevation (or roll) angle in a fixed reference three-dimensional coordinate frame while a three axis magnetic sensor is used to measure the Earth's magnetic field. The azimuth and the roll (or elevation) angles are then determined from these measurements. A second embodiment utilizes a combination of a three-axis accelerometer to sense the Earth's gravity to measure the absolute elevation and roll angles for slow motions and a two-axis rate sensor to measure the azimuth and elevation velocities in the sensor frame.

Abstract: A hybrid motion tracker captures the motion of a person. Magnetic field sensors and optical sources are placed on a person, each located on different limbs. A fixed transmitter emits electromagnetic energy and infrared light is transmitted from the optical light sources to the fixed optical sensors. The magnetic field sensors sense the magnetic field and a computer calculates each sensor's position and orientation relative to the fixed transmitter. The optical system's Position Sensing Detectors measure the transmitted infrared light and the computer calculates the position and orientation of each optical light source. The position and orientation of each sensor is used to reconstruct the person's motion in real time, which is sent to a host computer. The computer utilizes the optical system which is more precise than the magnetic field system to compensate for the magnetic field system and thereby achieve higher accuracies. The system is a hybrid system using both magnetic fields and infrared light.

Abstract: The position and orientation of remote sensors is determined using pulsed magnetic fields generated from a fixed location. Pulsed magnetic fields are sequentially generated from a plurality of spatially independent components defining a source coordinate frame. The pulsed magnetic fields are sensed by a remote sensor having a plurality of passive field sensing elements. Eddy current distortions are sensed separately and subtracted by the system. The system measures the effect of metallic objects present in the environment and dynamically adjusts the measured values accordingly. The sensed magnetic fields, free of eddy current distortion, are used in order to calculate the position and orientation of the remote object. The system shortens the duration of pulsed magnetic fields and operates correctly at much further distances for the same energy output as compared to known systems.

Abstract: The motion of a person is measured in real time using magnetic fields. A magnetic transmitter and a number of magnetic receivers are placed at different points on the person. The transmitter transmits magnetic fields sequentially from three orthogonal coils. The magnetic field is received at each receiver, which consists of three orthogonal coils. The computer resolves the sequential position and orientation coordinates from each receiver into the person's movement, relative to the transmitter, from knowledge of where each receiver is placed on the person. Other embodiments measure the transmitter's position and orientation relative to a fixed location outside of the person. The computer then resolves the position and orientation data into the person's motion relative to the fixed location outside of the person.

Abstract: A system for the determination of the distance and orientation of an object carrying at least three light sensors from a fixed reference point when the object is irradiated by two modulated scanning beams of known angular orientation and rotational frequency. Timing circuitry located in the control processor determines the time interval .DELTA.t, between successive interceptions of the object by each of the beams. Knowledge of this time interval and the scanning beams' relative positions and angular orientations permits calculation of the object's spatial coordinates. The optical beams utilized are fan-shaped in cross-section. The method of operation is also disclosed.