Penumbra, Inc.

Cameron J Mahon

Alejandro Santiago Diaz

Oded Y Zur

Michael D Collins

Ron Barak

Amir Rubin

Ran Bar-On

Branislav Vasilijevic

A method and apparatus for reducing magnetic tracking error in the position and orientation determined in a magnetic tracking system having a magnetic field generator. In some embodiments, the measured position and orientation of a sensor is compared to an expected theoretical position and orientation. Any error is assumed to be from 'floor distortion,' i.e., eddy currents in the floor caused by the magnetic field generated by the magnetic field transmitter. The floor distortion is modeled as being caused by eddy currents caused by a second magnetic field transmitter that is a reflection of the actual transmitter. An algorithm iteratively searches over a parameter space to minimize the difference between the measured position and orientation and the theoretical position and orientation, and applies a correction to the measured position and orientation. The measurements and corrections of the position and orientation run in real-time with no additional hardware or calibration required.

Method and apparatus for reducing magnetic tracking error due to floor distortion

A system and method that can automatically select a frequency of a magnetic field in a magnetic tracking system. A magnetic tracking system emits an alternating magnetic field using a set of three frequencies. In the present approach, a transmitter is capable of generating multiple sets of three frequencies. A processor selects a first set of frequencies to use and causes the receiver to measure the amplitude of the magnetic field at those frequencies. In one embodiment, the frequency set having the lowest energy is selected. The processor then compares an estimated jitter at those frequencies to the actual jitter experienced using the frequencies. If the actual jitter exceeds the estimated jitter by a predetermined amount, the processor switches to a different set of frequencies and causes the receiver to measure the magnetic field at the new set of frequencies. The process may repeat using the additional sets of frequencies.

Method and apparatus for automatic frequency selection in magnetic tracking systems

A measurement device and methods for detecting distortion or interference in an environment are described herein. The measurement device comprises a transmitter and a receiver attached to a rigid body such that a position and orientation (P&O) of the receiver with respect to the transmitter is fixed. When measuring distortion, the transmitter transmits electromagnetic waves over one or more frequency channels and measures electromagnetic waves over the channel(s) and a P&O of the receiver relative to the transmitter may be computed. Based on the computed P&O and the known P&O of the receiver with respect to the transmitter, the system determines a level of distortion that would cause the change in position and orientation. When measuring interference, the transmitter does not transmit electromagnetic waves and the receiver measures the electromagnetic waves in the environment. The measurement device is moved to identify locations where the measurements of distortion and/or interference are below a threshold value.

Distortion/interference measurement device for virtual reality environments

A system and method for performing synchronization of a magnetic field transmitter and receiver to resolve received signal phase ambiguity based upon the phases of the magnetic fields. Three orthogonal field frequencies are selected. A Fourier transform extracts the sine and cosine of the received signal, which provides the received signal phases and results in a complex signal matrix ('Sigmat'). A search is made for a phase rotation of the frequencies to achieve convergence of the Sigmat at a point it is real-valued; the search may be limited by aligning the Sigmat such that the major element becomes real-valued and rotating the other two frequencies. The correct phase is the one in which the Sigmat has a positive determinant and minimizes any remaining imaginary portion. A transmitter and receiver may be calibrated to account for any analog phase shift. Distortion of the magnetic field may also be detected and corrected.

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Guelph, Canada

Cameron J Mahon