METHODS FOR PROCESSING MEASUREMENTS FROM AN ACCELEROMETER

• US 20110172951A1
• Filed: 09/18/2009
• Published: 07/14/2011
• Est. Priority Date: 09/23/2008
• Status: Abandoned Application

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Schlumbohm, Stephan
• Application Number:
  US13/063,938
• Publication Number:
  US 20110172951A1
• Time in Patent Office: Days
• US Class Current: 702/141
• CPC Class Codes: A61B 5/1116 Determining posture transitions
• CPC Class Codes: G01C 9/00 Measuring inclination, e.g. by clinometers, by levels

Abstract

There is provided a method for estimating the orientation of an accelerometer relative to a fixed reference frame, the method comprising obtaining signals from the accelerometer, the signals indicating the components of the acceleration acting on the accelerometer along three orthogonal axes; identifying the axis with the highest component of acceleration; and determining the orientation of the accelerometer by determining the angle between the acceleration acting on the accelerometer and the axis with the highest component of acceleration. There is further provided a method for estimating the vertical acceleration in the fixed reference frame using the estimated orientation.

Claims

1. A method for estimating the orientation of an accelerometer relative to a fixed reference frame, the method comprising:

obtaining signals from the accelerometer, the signals indicating the components of the acceleration acting on the accelerometer along three orthogonal axes;

identifying the axis with the highest component of acceleration; and

determining the orientation of the accelerometer by determining the angle between the acceleration acting on the accelerometer and the axis with the highest component of acceleration.

2. A method as claimed in claim 1, wherein the angle, θ

, between the acceleration acting on the accelerometer and the axis with the highest component of acceleration is determined from

3. A method as claimed in claim 1, further comprising checking for local instability in an orientation determined in a particular sampling instant, i, by:

obtaining a set of signals from the accelerometer for a plurality of sampling instants around the particular sampling instant; and

computing the variance of the norm of the components of the acceleration acting on the accelerometer along the three orthogonal axes for each of the set of signals.

4. A method as claimed in claim 3, wherein the step of computing the variance of the norm comprises calculating:

5. A method as claimed in claim 4, wherein α

is a value selected from the range 15 m/s² to 20 m/s².

6. A method as claimed in claim 1, wherein acceleration due to gravity is acting on the accelerometer.

7. A method as claimed in claim 6, wherein gravity acts in a known direction in the fixed reference frame, and the angle between the acceleration acting on the accelerometer and the axis with the highest component of acceleration provides an estimate of the orientation of the accelerometer relative to the known direction.

8. A method for estimating the acceleration in a particular direction relative to a fixed reference frame from measurements of acceleration acting on an accelerometer, the accelerometer having an arbitrary orientation relative to the fixed reference frame, the method comprising:

estimating the orientation of the accelerometer relative to the fixed reference frame as claimed in claim 1;

using the estimated orientation of the accelerometer to determine the acceleration in the particular direction from the measurements of acceleration.

9. A method for estimating the acceleration in a vertical direction relative to a fixed reference frame from measurements of acceleration acting on an accelerometer, the accelerometer having an arbitrary orientation relative to the fixed reference frame, the method comprising:

estimating the orientation of the accelerometer relative to the fixed reference frame as claimed in claim 7;

using the estimated orientation of the accelerometer to determine the acceleration in the vertical direction from the measurements of acceleration.

10. A method as claimed in claim 9, wherein the step of using the estimated orientation comprises evaluating:

acc_—

vert=(A_z−

g cos θ

)cos θ

+g, if θ

>

0 or there is local instability

acc_—

vert=(g cos θ

−

A_z)cos θ

+g, if θ

<

0 or there is no local instability

where g is the magnitude of the acceleration due to gravity in the vertical direction.

11. An apparatus for estimating the orientation of an accelerometer relative to a fixed reference frame, the apparatus comprising:

processing means adapted to perform the steps in the method of claim 1.

12. An apparatus for estimating the acceleration in a vertical direction relative to a fixed reference frame from measurements of acceleration acting on an accelerometer, the accelerometer having an arbitrary orientation relative to the fixed reference frame, the apparatus comprising:

processing means adapted to perform the steps in the method of claim 9.

13. A computer program product comprising computer executable code that, when executed on a suitable computer or processor, is adapted to perform the steps in the methods of claim 1.