Dynamic motion compensation for orientation instrumentation

• US 7,844,415 B1
• Filed: 01/21/2008
• Issued: 11/30/2010
• Est. Priority Date: 08/20/2007
• Status: Expired due to Fees

• Current Assignee: PNI Corporation (PNI Digital Media)
• Original Assignee: PNI Corporation (PNI Digital Media)
• Inventors: Bryant, Tyler M., Taylor, Andrew T., Figaro, Davy J.
• Primary Examiner(s): Wachsman; Hal D
• Application Number:
  US12/017,161
• Time in Patent Office: 1,044 Days
• Field of Search: 702/151, 702/141, 702/150, 702/153
• US Class Current: 702/151
• CPC Class Codes: G01C 17/02 Magnetic compasses
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices

Abstract

The instant invention discloses a method for an orientation measuring instrument to isolate and separate gravitational and non-gravitational components of acceleration from accelerometer measurements by using an ambient magnetic field, typically the earth'"'"'s magnetic field, as a fixed rotation reference. Using magnetic field measurements, one can track changes in orientation of a device and use that information to determine the gravitation direction, during periods when acceleration measurements include non-gravitational acceleration combined with gravitational acceleration components. In addition to determining orientation, a method and associated instrument provide a non-gravity acceleration vector of the device.

Claims

1. A method for an orientation measuring instrument to transform magnetic and acceleration data in an ambient magnetic field into the vector acceleration of gravity, G, comprising the steps:

acquiring a first sequence of data in time, Bmeas, from two or more magnetometers sensing the ambient magnetic field and a second sequence of data in time, Gmeas, from two or more accelerometers sensing local accelerations wherein the two or more accelerometers are operable with the two or more magnetometers;

processing changes in orientation from Bmeas wherein the ambient magnetic field is used as a rotation reference; and

processing the changes in orientation with Gmeas wherein a rotation matrix is determined from Bmeas and applied to Gmeas such that the result is the vector acceleration of gravity, G.

2. The method of claim 1 further comprising the step:

processing said first sequence of data in time, Bmeas and said vector acceleration of gravity, G, such that the result is an orientation Heading, Pitch and Roll.

3. The method of claim 1 further comprising the step:

processing said second sequence of data in time, Gmeas, and said vector acceleration of gravity, G such that the result is the non-gravitational components, NGA, of said sensed accelerations.

4. The method of claim 3 further comprising the step:

processing said non-gravitational components, NGA, of said acceleration vector, G, in time such that the result is a velocity of said orientation measuring instrument.

5. The method of claim 4 further comprising the step:

processing the velocity in time such that a position of said orientation measuring instrument is determined.

6. The method of claim 1 further comprising the step:

interpolating the first and second sequences of data in time such that the interpolated data of the first and second sequences of data in time correspond to first and second sequences of synchronized measurements;

wherein the interpolating is done after the acquiring of Bmeas and Gmeas and before the processing of changes in orientation from Bmeas and the processing of changes in orientation with Gmeas.

7. The method of claim 1 further comprising the steps:

processing said first sequence of data in time such that the magnitude of said Bmeas is determined; and

determining the presence of magnetic distortions based upon changes in magnitude of said first sequence of data, Bmeas.

8. A method for an orientation measuring instrument to transform acquired data into the vector acceleration of gravity, G, and a substantially undistorted magnetic field, B, in an ambient magnetic field comprising the steps:

acquiring a first sequence of data in time, Bmeas, from two or more magnetometers sensing the ambient magnetic field and acquiring a second sequence of data in time, Gmeas, from two or more accelerometers, sensing local accelerations wherein the two or more accelerometers are operable with the two or more magnetometers;

first processing changes in orientation using Bmeas as a rotation reference;

second processing the changes in orientation with Gmeas to determine G;

third processing changes in orientation using G as a rotation reference; and

fourth processing the changes in orientation with Bmeas to determine B.

9. The method of claim 8 further comprising the step:

processing the vector difference of said B and said Bmeas such that magnetic distortions, Bdist, is determined.

10. The method of claim 9, further comprising the steps:

determining when said magnetic distortions, Bdist, exceeds a predetermined distortion flag; and

generating a signal when Bdist, exceeds the distortion flag.

11. The method of claim 10 further comprising the step:

processing said B and said G such that an orientation Heading, Pitch and Roll of said orientation measuring instrument is determined.

12. The method of claim 8 further comprising the step:

processing said sensed local accelerations based on said second sequence of data from two or more accelerometers, Gmeas, and said vector acceleration of gravity, G, such that non-gravitational components, NGA, are determined.

13. The method of claim 12 further comprising the step:

processing said non-gravitational components, NGA, of said acceleration vector of gravity, G, in time such that a velocity of said orientation measuring instrument is determined.

14. The method of claim 13 further comprising the step:

processing said velocity in time such that a position of said orientation measuring instrument is determined.

15. The method of claim 8 further comprising the step:

interpolating said first and second sequences of data in time such that interpolated data correspond to first and second sequences of synchronized measurements;

wherein the interpolating is done after said acquiring and before said first processing.

16. An instrument for processing data acquired in an ambient magnetic field such that a vector acceleration of gravity, G, is determined comprising:

two or more magnetometers sensing the ambient magnetic field;

two or more accelerometers sensing local accelerations wherein the two or more accelerometers are operable with the two or more magnetometers;

means for processing sequences of data and vectors and matrices as are acquired in an ambient magnetic field and by an accelerometer such that the vector acceleration of gravity, G, may be determined;

means for acquiring and storing a first sequence of data in time, Bmeas, from the two or more magnetometers, and a second sequence of data in time, Gmeas, from the two or more accelerometers; and

wherein the means for processing comprises means for signal conditioning, constraint setting and matrix calculation;

such that the means for processing is operative to determine the vector acceleration of gravity, G based upon a rotation matrix determined from Bmeas and applied to Gmeas.

17. The instrument of claim 16 wherein the means for processing is operative to determine an orientation Heading, Pitch and Roll of the instrument by transforming said vector acceleration of gravity, G, and said Bmeas.