Techniques for determining orientation of a three-axis accelerometer

• US 7,970,573 B2
• Filed: 12/22/2008
• Issued: 06/28/2011
• Est. Priority Date: 12/22/2008
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Huang, Jonathan, Shah, Rahul, Nachman, Lama, Shahabdeen, Junaith Ahemed
• Primary Examiner(s): Khuu; Cindy Hien-Dieu
• Application Number:
  US12/341,055
• Publication Number:
  US 20100161271A1
• Time in Patent Office: 918 Days
• Field of Search: 702/141, 702/151
• US Class Current: 702/141
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/112 Gait analysis
• CPC Class Codes: A61B 5/1123 Discriminating type of movement, e.g. walking or running A61B5/1116, A61B5/112 take precedence

Abstract

A method, apparatus, and article containing computer instructions are described. Embodiments may use accelerometer data regarding forward motion by a wearer of a three-axis on-body accelerometer. Embodiments may further measure an acceleration due to gravity on each axis x, y, z of the accelerometer and use the direction of gravity to associate or align the x axis of the accelerometer with gravity. Embodiments may then use the acceleration not due to gravity to identify the forward motion and associate or align the forward direction with the y axis. The remaining direction may be identified as the sideways direction, which may be associated or aligned with the z axis. Additional activities may then be performed using the now-known orientation of the accelerometer. Other embodiments are described and claimed.

Claims

1. An apparatus comprising:

a memory;

a communications module to receive accelerometer data;

a processor coupled to the memory and the communications module, the processor operative to;

determine an acceleration due to gravity from the received accelerometer data on each axis x, y, z of a three-axis on-body accelerometer regarding forward motion by a wearer of the accelerometer;

associate the x axis with the direction of gravity by rotating the x axis to align with the direction of gravity;

identify the acceleration due to forward motion by rotating the y and z axes about the x axis until a projection of forward motion between y and z is minimized;

associate the y axis with the direction of forward motion by rotating the y axis to align with the direction of forward motion;

identify the sideways direction; and

associate the z axis with the sideways direction.

2. The apparatus of claim 1, wherein the processor is operative to:

select the rotation angles that cause the variance of the y axis to be greater than the variance of the z axis; and

examine time domain characteristics of the cross-correlation of the x and y axes; and

associate the y axis with the direction of forward motion and z axis with the sideways direction by rotating the y axis to align with the direction of forward motion.

3. The apparatus of claim 1, wherein the processor is further operative to perform activity recognition with the associated axes.

4. The apparatus of claim 1, further comprising the three-axis on-body accelerometer.

5. The apparatus of claim 1, wherein the processor is further operative to associate the x axis with the direction of gravity by calculating the angle (a_x) that the x axis makes with the direction of gravity and storing a_x in the memory.

6. The apparatus of claim 5, wherein the processor is further operative to identify the acceleration due to forward motion by:

removing components of the acceleration due to gravity from each axis;

removing the vector projection of the motion in the direction of gravity; and

identifying the axis having the greatest energy as the forward direction.

7. The apparatus of claim 6, wherein the processor is operative to identify the axis having the greatest energy as the forward direction by:

combining axes having a correlation higher than a threshold;

identifying the axis or combined axes having the highest energy as the forward direction; and

examining time domain characteristics of the cross-correlation of the x and y axes; and

associating the y axis with the direction of forward motion by calculating the angle (a_y) that the y axis makes with the direction of forward motion and storing a_y in the memory.

8. The apparatus of claim 7, wherein the processor is operative to:

identify the sideways direction by calculating the cross-product of the forward direction and the downward direction; and

associate the z axis with the sideways direction by calculating the angle (a_z) the z axis makes with the sideways direction and storing a_z in the memory.

9. A method comprising:

receiving accelerometer data regarding forward motion by a wearer of a three-axis on-body accelerometer;

measuring an acceleration due to gravity on each axis x, y, z of the accelerometer;

associating the direction of gravity with the x axis;

rotating the x axis to align with the direction of gravity;

identifying the acceleration due to forward motion;

rotating the y and z axes about the x axis until a projection of forward motion between y and z is minimized;

associating the direction of forward motion with the y axis;

identifying the sideways direction;

associating the sideways direction with the z axis

rotating the y axis to align with the direction of forward motion and the z axis with the sideways direction; and

performing an activity using the associated axes.

10. The method of claim 9, further comprising:

selecting the rotation angles that cause the variance of the y axis to be greater than the variance of the z axis; and

examining time domain characteristics of the cross-correlation of the x and y axes.

11. The method of claim 9, further comprising calculating the angle (a_x) that the x axis makes with the direction of gravity and storing a_x.

12. The method of claim 11, further comprising:

removing components of the acceleration due to gravity from each axis;

removing the vector projection of the motion in the direction of gravity;

identifying the axis having the greatest energy as the forward direction; and

calculating the angle (a_y) that the y axis makes with the direction of forward motion and storing a_y.

13. The method of claim 12, further comprising:

combining axes having a correlation higher than a threshold;

identifying the axis or combined axes having the highest energy as the forward direction; and

examining time domain characteristics of the cross-correlation of the x and y axes; and

calculating the angle (a_y) that the y axis makes with the direction of forward motion and storing a_y.

14. The method of claim 13, further comprising:

calculating the cross-product of the forward direction and the downward direction; and

calculating the angle (a_z) the z axis makes with the sideways direction and storing a_z.

15. An article comprising a non-transitory computer-readable storage medium containing instructions that when executed by a processor enable a system to:

receive accelerometer data regarding forward motion by a wearer of a three-axis on-body accelerometer;

measure an acceleration due to gravity on each axis x, y, z of the accelerometer;

associate the direction of gravity with the x axis;

rotate the x axis to align with the direction of gravity;

identify the acceleration due to forward motion;

rotate the y and z axes about the x axis until a projection of forward motion between y and z is minimized;

associate the direction of forward motion with the y axis;

identify the sideways direction;

associate the sideways direction with the z axis

rotate the y axis to align with the direction of forward motion and the z axis with the sideways direction; and

perform an activity using the associated axes.

16. The article of claim 15, further comprising instructions that when executed enable the system to:

select the rotation angles that cause the variance of the y axis to be greater than the variance of the z axis;

examine the time domain characteristics of the cross-correlation of the x and y axes.

17. The article of claim 15, further comprising instructions that when executed enable the system to:

calculate the angle (a_x) that the x axis makes with the direction of gravity and storing a_x.

18. The article of claim 17, further comprising instructions that when executed enable the system to:

remove components of the acceleration due to gravity from each axis;

remove the vector projection of the motion in the direction of gravity;

identify the axis having the greatest energy as the forward direction.

19. The article of claim 18, further comprising instructions that when executed enable the system to:

combine axes having a correlation higher than a threshold;

identify the axis or combined axes having the highest energy as the forward direction; and

examine the time domain characteristics of the cross-correlation of the x and y axes; and

calculate the angle (a_y) that the y axis makes with the direction of forward motion and storing a_y.

20. The article of claim 18, further comprising instructions that when executed enable the system to:

calculate the cross-product of the forward direction and the downward direction; and

calculate the angle (a_z) the z axis makes with the sideways direction and storing a_z.