Electromagnetic position measurement system with sensor parasitic loop compensation

Inventors

Ashe, Westley S. • Brunner, Georg

Assignees

Northern Digital Inc

Abstract

A magnetic tracking device includes a sensor configured to generate a sensor electromotive force (EMF). The device includes a mechanism configured to select between a first operating mode in which the sensor generates the sensor EMF when receiving the magnetic field and a second operating mode in which the sensor generates a reduced amount of the sensor EMF when receiving the magnetic field. An interconnecting circuit generates a parasitic EMF in each of the first operating mode and the second operating mode. The interconnecting circuit connects to a processing device which receives a first measurement for the first operating mode, the first measurement representing the sensor EMF and the parasitic EMF, receives a second measurement for the second operating mode, the second measurement representing the parasitic EMF, compares the first measurement and the second measurement, and determines an approximate value of the sensor EMF.

Core Innovation

The document describes an electromagnetic position measurement system including a magnetic tracking device in which a magnetic sensor generates a sensor electromotive force (EMF) measuring a magnetic field generated by a magnetic field transmitter. Spurious electromagnetic fields from sensor interconnects, connector structures, and printed circuit board (PCB) trace loops corrupt an ideal sensor coil signal, and parasitic EMFs produced in the interconnecting circuit interfere with accurate position and orientation determination based on the sensor coil signal.

To address the corruption, the system selects between a first operating mode and a second operating mode that cause the sensor to generate a sensor EMF in the first operating mode and a reduced sensor EMF in the second operating mode. In both operating modes, the interconnecting circuit is configured to generate a parasitic EMF when receiving the magnetic field, and the processing device receives a first measurement representing the sensor EMF and the parasitic EMF, receives a second measurement representing the parasitic EMF and the reduced sensor EMF, compares the first and second measurements, and determines an approximate value of the sensor EMF based on the comparison.

The document further explains that the parasitic EMF arises as induced EMF values generated in loop types including an interconnect loop, a connector loop, and a trace loop. It also describes a diode in parallel with the sensor that is reverse biased in the first operating mode and forward biased in the second operating mode, and an alternative sensitivity-adjustment method in which the mechanism adjusts sensor sensitivity between higher and lower EMF states, with measurement subtraction via comparisons to remove interconnect parasitics.

Claims Coverage

The provided independent claims are clm-00001, clm-00008, and clm-00013. Across these claims, the main inventive features total five core mechanisms: mode switching between a sensor EMF and a reduced sensor EMF, parasitic EMF generation in both modes, comparison-based determination of an approximate sensor EMF, a diode in parallel with the sensor with mode-dependent bias, and sensitivity adjustment between higher and lower EMF states.

The claim set covers magnetic tracking devices and systems that change the sensor EMF contribution between two modes or sensitivity states while generating parasitic EMF in both, and then use comparison of two measurements that include parasitic EMF to determine an approximate sensor EMF; the mode selection is implemented with a diode in parallel with the sensor that is reverse biased and forward biased in respective operating modes.

Stated Advantages

Documented Applications