Magnetometerless detection of incorrect attachment and calibration of motion tracking system

Abstract

A method for adjusting operation of a motion tracking system comprising a computing apparatus and a plurality of sensors, each sensor comprising a gyroscope and an accelerometer, the method comprising: aligning the plurality of sensors; providing, each sensor of the plurality of sensors to the computing apparatus, a first orientation when the sensors are aligned, the first orientation comprising a first heading; placing the plurality of sensors on a person; providing, each sensor of the plurality of sensors to the computing apparatus, a second orientation when the sensors are placed on the person, the second orientation comprising a second heading; digitally determining, the computing apparatus, whether the plurality of sensors is placed on the person according to a predetermined sensor arrangement based on both the first and second headings of each sensor of the plurality of sensors; and adjusting, the computing apparatus, the operation of the motion tracking system based on the determination. Also, a system for tracking motion of a person.

1 . A method for adjusting operation of a motion tracking system comprising a computing apparatus and a plurality of sensors, each sensor comprising a gyroscope and an accelerometer, the method including the following steps:
 aligning the plurality of sensors;   providing, each sensor of the plurality of sensors to the computing apparatus, a first orientation when the sensors are aligned, the first orientation comprising a first heading;   placing the plurality of sensors on a person;   providing, each sensor of the plurality of sensors to the computing apparatus, a second orientation when the sensors are placed on the person, the second orientation comprising a second heading;   digitally determining, the computing apparatus, whether the plurality of sensors is placed on the person according to a predetermined sensor arrangement based on both the first and second headings of each sensor of the plurality of sensors; and   adjusting, the computing apparatus, the operation of the motion tracking system based on the determination.   
     
     
         2 . The method of  claim 1 , wherein the step of digitally determining whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement comprises includes the following steps:
 digitally computing, the computing apparatus, a transformation for each sensor of the plurality of sensors that aligns the first heading thereof with a predetermined heading, and digitally processing, the computing apparatus, a third heading of each sensor of the plurality of sensors in order to compute heading differences from all pairs of the third headings and determine whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement, each of the third headings being the second heading of the corresponding sensor with the corresponding transformation applied thereto; or   digitally processing, the computing apparatus, the second heading of each sensor of the plurality of sensors in order to compute heading differences from all pairs of the second headings and determine whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement, wherein the first heading of each sensor is processed such that the first heading adjusts the corresponding heading differences computed or heading differences according to the predetermined sensor arrangement.   
     
     
         3 . The method of  claim 2 , wherein the transformations are first transformations, the predetermined heading is a first predetermined heading, and the step of adjusting the operation of the motion tracking system comprises includes at least one of the following steps:
 digitally computing, the computing apparatus, a second transformation for each sensor of the plurality of sensors that aligns the third heading thereof with a second predetermined heading for the corresponding sensor according to the predetermined sensor arrangement, and digitally applying, the computing apparatus, the second transformations or both the first and second transformations computed to each orientation provided by each sensor of the plurality of sensors to the computing apparatus while motion of the person is tracked with the motion tracking system, or to an algorithm of the computing apparatus for processing the motion of the person tracked with the motion tracking system; and   providing at least one user perceptible signal indicative of the computing apparatus having determined that at least one sensor of the plurality of sensors is not placed on the person according to the predetermined sensor arrangement.   
     
     
         4 . The method of  claim 2 , wherein the step of adjusting the operation of the motion tracking system includes at least one of the following steps:
 digitally computing, the computing apparatus, a first transformation for each sensor of the plurality of sensors that aligns the second heading thereof with the first predetermined heading for the corresponding sensor according to both the predetermined sensor arrangement and the first heading, and digitally applying, the computing apparatus, the first transformations computed to each orientation provided by each sensor of the plurality of sensors to the computing apparatus while motion of the person is tracked with the motion tracking system, or to an algorithm of the computing apparatus for processing the motion of the person tracked with the motion tracking system; and   providing at least one user perceptible signal indicative of the computing apparatus having determined that at least one sensor of the plurality of sensors is not placed on the person according to the predetermined sensor arrangement.   
     
     
         5 . The method of  claim 1 , wherein the second orientations are provided by the plurality of sensors while the person has a predetermined posture. 
     
     
         6 . The method of  claim 1 , wherein:
 each sensor of the plurality of sensors further comprises a magnetometer; and   the method further includes, prior to the step of placing the plurality of sensors on the person, the following step:
 not processing measurements of the magnetometers in a sensor fusion algorithm of each sensor of the plurality of sensors; or 
 reducing a weight of the measurements of the magnetometers in the sensor fusion algorithm of each sensor of the plurality of sensors. 
   
     
     
         7 . The method of  claim 1 , further includes the following steps:
 digitally computing, the computing apparatus, heading differences from all pairs of first headings; and   digitally processing, the computing apparatus, the computed heading differences of the first headings in order to determine if one or more sensors of the plurality of sensors are aligned such that they have a 180° heading rotation with respect to the corresponding other sensor of the plurality of sensors; and   wherein the computing apparatus both digitally determines whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement and adjusts the operation of the motion tracking system if each computed heading difference of the first headings fulfills the following:   a modulus of the heading difference is less than or equal to a predetermined threshold; or   a modulus of 180° minus the heading difference is less than or equal to the predetermined threshold.   
     
     
         8 . The method of  claim 1 , wherein the step of aligning the plurality of sensors includes the following steps:
 providing a first device comprising at least one cavity adapted for introduction of one or more sensors of the plurality of sensors; and   introducing each sensor of the plurality of sensors into the first device.   
     
     
         9 . A system for tracking motion of a person, the system comprising:
 a plurality of sensors, each sensor comprising a gyroscope and an accelerometer; and   a computing apparatus comprising at least one processor, at least one memory and means for transmitting and receiving data;   each sensor of the plurality of sensors being configured to provide, to the computing apparatus, a first orientation when the sensors are aligned, and a second orientation when the sensors are placed on the person, the first and second orientations comprising first and second headings, respectively; and   the computing apparatus being programmed to:
 digitally determine whether the plurality of sensors is placed on the person according to a predetermined sensor arrangement based on both the first and second headings of each sensor of the plurality of sensors; and 
 adjust an operation of the system based on the determination. 
   
     
     
         10 . The system of  claim 9 , wherein the computing apparatus is programmed to digitally determine whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement by:
 digitally computing a transformation for each sensor of the plurality of sensors that aligns the first heading thereof with a predetermined heading, and digitally processing a third heading of each sensor of the plurality of sensors in order to determine whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement, each third heading being the second heading of the corresponding sensor with the corresponding transformation applied thereto; or   digitally processing the second heading of each sensor of the plurality of sensors in order to compute heading differences from all pairs of second headings and determine whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement, wherein the first heading of each sensor is processed such that it adjusts the corresponding heading differences computed or heading differences according to the predetermined sensor arrangement.   
     
     
         11 . The system of  claim 10 , wherein the transformations are first transformations, the predetermined heading is a first predetermined heading, and the computing apparatus is programmed to adjust the operation of the system by at least one of the following steps:
 digitally computing a second transformation for each sensor of the plurality of sensors that aligns the third heading thereof with a second predetermined heading for the corresponding sensor according to the predetermined sensor arrangement, and digitally applying the first and second transformations computed to each orientation provided by each sensor of the plurality of sensors to the computing apparatus; and   providing at least one user perceptible signal indicative of the computing apparatus having determined that at least one sensor of the plurality of sensors is not placed on the person according to the predetermined sensor arrangement, the system comprising at least one means for providing the at least one user perceptible signal.   
     
     
         12 . The system of  claim 10 , wherein the computing apparatus is programmed to adjust the operation of the system by at least one of the following steps:
 digitally computing a first transformation for each sensor of the plurality of sensors that aligns the second heading thereof with a first predetermined heading for the corresponding sensor according to both the predetermined sensor arrangement and the first heading, and digitally applying the first transformations computed to each orientation provided by each sensor of the plurality of sensors to the computing apparatus; and   providing at least one user perceptible signal indicative of the computing apparatus having determined that at least one sensor of the plurality of sensors is not placed on the person according to the predetermined sensor arrangement, the system comprising at least one means for providing the at least one user perceptible signal.   
     
     
         13 . The system of  claim 9 , wherein:
 each sensor of the plurality of sensors further comprises a magnetometer;   the computing apparatus is further programmed to command each sensor of the plurality of sensors to configure a sensor fusion algorithm thereof such that the sensor fusion algorithm:
 does not process measurements of the magnetometer; or 
 reduces a weight of the measurements of the magnetometer; and 
   the computing apparatus is further programmed to command each sensor of the plurality of sensors to provide the second orientation or both the first and second orientations after configuring the sensor fusion algorithm thereof.   
     
     
         14 . The system of  claim 9 , further comprising a device, the device comprising at least one cavity adapted for introduction of one or more sensors of the plurality of sensors. 
     
     
         15 . A computer-readable storage medium having stored therein a computer program that has instructions which, when executed by a computing device, cause the computing device to perform the following steps:
 receiving first orientations from a plurality of sensors of a motion tracking system when they are aligned, each first orientation comprising a first heading;   receiving second orientations from the plurality of sensors when they are placed on a person, each second orientation comprising a second heading;   digitally determining whether the plurality of sensors is placed on the person according to a predetermined sensor arrangement based on both the first and second headings of each sensor of the plurality of sensors; and   adjusting operation of the motion tracking system based on the determination.   
     
     
         16 . The computer-readable storage medium of  claim 15 , wherein digitally determining whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement comprises:
 digitally computing a first transformation for each sensor of the plurality of sensors that aligns the first heading thereof with a first predetermined heading, and digitally processing a third heading of each sensor of the plurality of sensors in order to compute heading differences from all pairs of third headings and determine whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement, each third heading being the second heading of the corresponding sensor with the corresponding first transformation applied thereto; or   digitally processing the second heading of each sensor of the plurality of sensors in order to compute heading differences from all pairs of second headings and determine whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement, wherein the first heading of each sensor is processed such that it adjusts the corresponding heading differences computed or heading differences according to the predetermined sensor arrangement.   
     
     
         17 . (canceled) 
     
     
         18 . (canceled) 
     
     
         19 . The computer-readable storage medium of  claim 16 , wherein adjusting the operation of the motion tracking system comprises at least one of:
 digitally computing a second transformation for each sensor of the plurality of sensors that aligns the third heading thereof with a second predetermined heading for the corresponding sensor according to the predetermined sensor arrangement, and digitally applying the second transformations or both the first and second transformations computed to each orientation received from each sensor of the plurality of sensors while motion of the person is tracked with the motion tracking system, or to an algorithm for processing the motion of the person tracked with the motion tracking system; and   providing at least one user perceptible signal indicative of having determined that at least one sensor of the plurality of sensors is not placed on the person according to the predetermined sensor arrangement.   
     
     
         20 . The computer-readable storage medium of  claim 15 , wherein adjusting the operation of the motion tracking system comprises at least one of:
 digitally computing a first transformation for each sensor of the plurality of sensors that aligns the second heading thereof with the first predetermined heading for the corresponding sensor according to both the predetermined sensor arrangement and the first heading, and digitally applying, the computing apparatus, the first transformations computed to each orientation received from each sensor of the plurality of sensors while motion of the person is tracked with the motion tracking system, or to an algorithm of the computing apparatus for processing the motion of the person tracked with the motion tracking system; and   providing at least one user perceptible signal indicative of having determined that at least one sensor of the plurality of sensors is not placed on the person according to the predetermined sensor arrangement.   
     
     
         21 . The computer-readable storage medium of  claim 15 , wherein the instructions further cause the computing device to perform the step of commanding each sensor of the plurality of sensors to configure a sensor fusion algorithm thereof such that the sensor fusion algorithm: does not process measurements of a magnetometer of the respective sensor; or reduces a weight of the measurements of the magnetometer of the respective sensor. 
     
     
         22 . The computer-readable storage medium of  claim 15 , wherein the instructions further cause the computing device to perform the following steps:
 digitally computing heading differences from all pairs of first headings; and   digitally processing the computed heading differences of the first headings in order to determine if one or more sensors of the plurality of sensors are aligned such that they have a 180° heading rotation with respect to the corresponding other sensor of the plurality of sensors; and   wherein the computing device both digitally determines whether the plurality of sensors is placed on the person according to the predetermined sensor arrangement and adjusts the operation of the motion tracking system if each computed heading difference of the first headings fulfills the following:   a modulus of the heading difference is less than or equal to a predetermined threshold; or   a modulus of 180° minus the heading difference is less than or equal to the predetermined threshold.