METHODS FOR CONSTRUCTING POSTURE CALIBRATION MATRICES

• US 20110201969A1
• Filed: 02/10/2011
• Published: 08/18/2011
• Est. Priority Date: 02/15/2010
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Chan, Tsz Ping, Hatlestad, John D.
• Granted Patent: US 10,328,267 B2
• Time in Patent Office: Days
• US Class Current: 600/587
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/1116 Determining posture transitions
• CPC Class Codes: A61B 5/1117 Fall detection
• CPC Class Codes: A61B 5/1118 Determining activity level
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

A device can include a multi-dimensional posture sensor that provides an electrical sensor output representative of alignment of first, second, and third non-parallel axes of the device with the gravitational field of the earth, and a processor that includes a calibration circuit and a posture circuit. The calibration circuit measures a first sensor output for the first device axis and a second sensor output for one of a second device axis while the subject is in a first specified posture, measures sensor outputs for the first, second, and third device axes while the subject is in a second specified posture, calculates one or more coordinate transformations, generates transformed sensor outputs using the coordinate transformations, and calibrates the posture sensor by calculating a calibration transformation using the first and second sensor outputs and the transformed sensor outputs. The posture circuit determines a subsequent posture of the subject using the posture sensor.

Claims

1. A device comprising:

a multi-dimensional posture sensor configured to provide an electrical sensor output representative of alignment of respective first, second, and third non-parallel axes of the device with the gravitational field of the earth; and

a processor communicatively coupled to the posture sensor and including;

a calibration circuit configured to;

measure a first sensor output for the first device axis and a second sensor output for one of the second or third device axes while the subject is in a first specified posture;

measure sensor outputs for the first, second, and third device axes while the subject is in a second specified posture;

calculate one or more coordinate transformations using a sensor output from the first specified posture;

transform the sensor outputs for the second posture using the coordinate transformations; and

calibrate the posture sensor by calculating a calibration transformation using the first and second sensor outputs and the transformed sensor outputs; and

a posture circuit configured to determine a subsequent posture of the subject using the posture sensor.

2. The device of claim 1 wherein the calibration circuit is configured to:

calculate, using the first sensor output, a first coordinate transformation associated with a first orientation angle;

calculate, using the first sensor output and the second sensor output, a second coordinate transformation associated with a second orientation angle;

measure third, fourth, and fifth sensor outputs for respective first, second, and third device axes while the subject is in the second specified posture; and

transform the third, fourth, and fifth sensor outputs using the first and second coordinate transformations.

3. The device of claim 2, wherein the calibration circuit is configured to:

calculate elements of a first rotation matrix using the first sensor output;

calculate elements of a second rotation matrix using the first sensor output and the second sensor output; and

multiply the third, fourth, and fifth sensor outputs by the first and second rotation matrices to transform the sensor outputs.

4. The device of claim 1, wherein the calibration circuit is configured to calculate a calibration transformation by calculating elements of a calibration matrix.

5. The device of claim 4, wherein the calibration circuit is configured to:

calculate, using the first sensor output, a first set of matrix components related to a first orientation angle;

calculate, using the first sensor output and one of the second sensor output or the third sensor output, a second set of matrix components related to a second orientation angle;

calculate, using the transformed sensor outputs, a third set of matrix components related to a third orientation angle; and

calculate the elements of the calibration matrix using the first, second, and third sets of matrix components.

6. The device of claim 5, wherein the first orientation angle is associated with a pitch angle, the second orientation angle is associated with a roll angle, and the third orientation angle is associated with a yaw angle.

7. The device of claim 5, wherein the first orientation angle is associated with a pitch angle, the second orientation angle is associated with a yaw angle, and the third orientation angle is associated with a roll angle.

8. The device of claim 1, wherein the posture circuit is configured to:

receive a sensor output for each of the three non-parallel axes of the posture sensor;

transform the sensor outputs using the calibration transformation; and

compare the transformed sensor outputs to specified thresholds to determine posture of the subject.

9. The device of claim 1, wherein the second posture is a posture non-orthogonal to the first posture.

10. The device of claim 9, wherein the first posture is an upright posture, and the second posture is more supine than the first posture and less than fully supine.

11. The device of claim 9, wherein the first posture is a supine posture, and the second posture is more upright than the first posture and less than fully upright.

12. A method comprising:

determining a calibration transformation for a multi-dimensional posture sensor by a process including;

measuring a first sensor output for the first device axis and a second sensor output for one of the second or third device axes while the subject is in a first specified posture;

measuring sensor outputs for the first, second and third device axes while the subject is in a second specified posture;

calculating one or more coordinate transformations using a sensor output from the first specified posture;

transforming the sensor outputs for the second specified posture using the coordinate transformations; and

calibrating the posture sensor by calculating a calibration transformation using the first and second sensor outputs and the transformed sensor outputs; and

using the calibration to determine subsequent subject posture from subsequent sensor output.

13. The method of claim 12, wherein calculating one or more coordinate transformations using a sensor output from the first specified posture includes:

calculating, using the first sensor output, a first coordinate transformation associated with a first orientation angle;

calculating, using the first sensor output and the second sensor output, a second coordinate transformation associated with a second orientation angle; and

wherein measuring sensor outputs for the first, second and third device axes includes measuring third, fourth, and fifth sensor outputs for respective first, second and third device axes while the subject is in the second specified posture; and

wherein transforming outputs includes transforming the third, fourth, and fifth sensor outputs using the first and second coordinate transformations.

14. The method of claim 13, wherein calculating the first coordinate transformation includes calculating elements of a first rotation matrix using the first sensor output,

wherein calculating the second coordinate transformation includes calculating elements of a second rotation matrix using the first sensor output and the second sensor output;

and

wherein transforming the third, fourth, and fifth sensor outputs includes multiplying the third, fourth, and fifth sensor outputs by the first and second rotation matrices to transform the sensor outputs.

15. The method of claim 12, wherein calculating a calibration transformation includes calculating elements of a calibration matrix, and wherein using the calibration to determine subsequent subject posture includes using the calibration matrix to determine subsequent subject posture from subsequent sensor output.

16. The method of claim 15, wherein calculating elements of a matrix to calibrate the posture sensor using the sensor outputs includes:

calculating a first set of matrix components related to a first orientation angle using the first sensor output;

calculating a second set of matrix components related to a second orientation angle using the first sensor output and the second sensor output;

calculating a third set of matrix components related to a third orientation angle using the transformed sensor outputs; and

calculating the elements of the calibration matrix using the first, second, and third sets of matrix components.

17. The method of claim 16,

wherein calculating a first set of matrix components related to a first orientation angle includes calculating a first set of matrix components associated with a pitch angle,

wherein calculating a second set of matrix components related to a second orientation angle includes calculating a second set of matrix components associated with a roll angle, and

wherein calculating a third set of matrix components related to a third orientation angle includes calculating a second set of matrix components associated with a yaw angle.

18. The method of claim 16,

wherein calculating a first set of matrix components related to a first orientation angle includes calculating a first set of matrix components associated with a pitch angle,

wherein calculating a second set of matrix components related to a second orientation angle includes calculating a second set of matrix components associated with a yaw angle, and

wherein calculating a third set of matrix components related to a third orientation angle includes calculating a second set of matrix components associated with a roll angle.

19. The method of claim 12, wherein measuring while the subject is in a second specified posture, includes measuring while the subject is in a second specified posture that is non-orthogonal to the first specified posture.

20. The method of claim 12, wherein using the calibration to determine subsequent subject posture includes:

receiving a sensor output for each of three orthogonal axes of the multi-dimensional sensor;

transforming the sensor outputs to body coordinate values using the calibration transformation; and

comparing the sensor outputs to specified thresholds to determine the posture.