Sensor devices and methods for calculating an orientation while accounting for magnetic interference

A sensor device to measure orientation comprising:

• a plurality of sensing devices including a magnetometer and one or more from a group of an accelerometer and a gyroscope, wherein the magnetometer measures a magnetic field and produces a magnetic field reading including at least a magnitude of the magnetic field;
• a processor, wherein the processor is communicatively coupled to the plurality of sensing devices by a communication bus, wherein each sensing device provides a signal over the communication bus to the processor representing a physical orientation of the sensor device;
• and
• a non-transitory computer-readable memory storing instructions that, when executed by the processor, cause the processor to:
• receive a current magnetometer reading including at least a current magnetic field magnitude as detected by the magnetometer;
• detect a presence of the sensor device within an interfering magnetic field based on comparing a difference between the current magnetic field magnitude and a reference magnetic field magnitude
• with a threshold;
• adjust a trust value of the magnetometer such that the trust value is decreased in response to the sensor device being detected within the interfering magnetic field based on the difference between the current magnetic field magnitude and the reference magnetic field magnitude being greater than or equal to the threshold;
• increase the trust value when:
• the sensor device is detected outside the interfering magnetic field based on the difference between the current magnetic field magnitude and the reference magnetic field magnitude being less than the threshold, the trust value is less than a maximum trust value, and following a waiting period beginning when the difference between the current magnetic field magnitude and the reference magnetic field magnitude was last above the threshold, wherein:
• the trust value ranges from a minimum trust value to the maximum trust value,
• the trust value is increased by converging the trust value from the minimum trust value to the maximum trust value over a convergence period so long as the difference between the current magnetic field magnitude and the reference magnetic field magnitude is not greater than the threshold during the convergence period, and
• the convergence period is defined by:
• T<-Tmin+(1−I/Imax)*(Tdefault−Tmin),
• where:
• T is the trust value,
• Tmin is the minimum trust value,
• Tdefault is the maximum trust value,
• Imax is a number of consecutive iterations to return the trust value to the maximum trust value, and
• I is a number of iterations remaining to return the trust value to the maximum trust value;
• switch between the signals of the plurality of sensing devices to compute an orientation of the sensor device based at least on the trust value, wherein the trust value affects a reliance on magnetic field readings in computing the orientation of the sensor device;
• and
• provide an output signal, wherein the output signal indicates the orientation of the sensor device.

A method of computing an orientation of a sensor device comprising a plurality of sensing devices and a processor communicatively coupled to the plurality of sensing devices by a communication bus, wherein the plurality of sensing devices includes a magnetometer and one or more from a group of an accelerometer and a gyroscope with each sensing device providing a signal over the communication bus to the processor representing a physical orientation of the sensor device, the method comprising:

• receiving by the processor a plurality of magnetic field readings from the magnetometer, each magnetic field reading comprising at least a magnetic field magnitude;
• storing by the processor, in a non-transitory computer-readable memory, the plurality of magnetic field readings in a time delay table;
• selecting by the processor, as a current magnetic field reading, an oldest magnetic field reading from the plurality of magnetic field readings stored in the time delay table according to a time delay threshold;
• detecting by the processor a presence of the sensor device within an interfering magnetic field based on comparing a difference between the current magnetic field magnitude and a reference magnetic field magnitude
• with a threshold;
• adjusting by the processor a trust value of the magnetometer such that the trust value is decreased in response to the sensor device being detected within the interfering magnetic field based on the difference between the current magnetic field magnitude and the reference magnetic field magnitude being greater than or equal to the threshold;
• switching between the signals of the plurality of sensing devices for computing an orientation of the sensor device based at least on the trust value, wherein the trust value affects a reliance on magnetic field readings in computing the orientation of the sensor device;
• and
• providing an output signal, wherein the output signal indicates the orientation of the sensor device.