Sensor-based orientation system

• US 7,533,569 B2
• Filed: 03/15/2007
• Issued: 05/19/2009
• Est. Priority Date: 03/15/2006
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Sheynblat, Len
• Primary Examiner(s): Williams; Hezron
• Assistant Examiner(s): Shah; Samir M
• Application Number:
  US11/686,945
• Publication Number:
  US 20070214886A1
• Time in Patent Office: 796 Days
• Field of Search: 735/09, 735/10
• US Class Current: 73/510
• CPC Class Codes: G01C 21/166 Mechanical, construction or arrangement details of inertial navigation systems
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

A method for measuring positional changes of an object, including rotation about any or all of three axes, using linear accelerometers. There is disclosed a method of using a linear accelerometer to integrate two other 3D linear accelerometers in order to measure and supply for further use six-dimensional information, that is, translation in three dimensions and rotation about three axes. Two linear accelerometer sensors are used to determine all but one of the variables in the six degrees of freedom. Output from a third accelerometer generates the data need to determine a sixth, rotational, degree of freedom. The need for a gyroscope for detecting changes in heading (i.e., yaw of azimuth) may therefore be avoided.

Claims

1. A method for determining changes in orientation of an object in six degrees of freedom, comprising:

providing first and second linear accelerometers disposed on an imaginary axis relative to the object;

providing a third linear accelerometer disposed off the imaginary axis relative to the object;

measuring, with the first linear accelerometer, a first linear movement of the object in relation to an x-y-z coordinate system;

measuring, with the second linear accelerometer, a second linear movement of the object in relation to the x-y-z coordinate system;

measuring, with the third linear accelerometer, a third linear movement of the object in relation to the x-y-z coordinate system;

determining, with measurements from the first, second and third linear accelerometers, a change in position of the object; and

determining, with measurements from the first, second and third linear accelerometers, a change in orientation of the object.

2. The method of claim 1, wherein the act of determining the change in orientation comprises comparing respective outputs of the first and second linear accelerometers relative to an accelerometer axis of sensitivity.

3. The method of claim 1, wherein the act of determining the change in orientation comprises comparing the respective outputs of the first and second linear accelerometers relative to each accelerometer axis of sensitivity.

4. The method of claim 1, comprising the further act of calculating a tilt acceleration relative to an axis of sensitivity of at least one of the accelerometers.

5. The method of claim 1, comprising the further act of detecting an imbalance in respective magnitudes of acceleration of the first and second linear accelerometers along an axis of the x-y-z coordinate system.

6. The method of claim 1, further comprising:

assigning initial coordinates (X₀, Y₀, Z₀), in the x-y-z coordinate system, to each of the accelerometers at a first time; and

computing changes from the initial coordinates for each of the accelerometers between the first time and a second time.

7. The method of claim 6, wherein the act of computing changes from the initial coordinates for each of the accelerometers comprises:

receiving data from each of the accelerometers; and

inputting the data from each of the accelerometers into the equation

(X₁, Y₁, Z₁)=(X₀, Y₀, Z₀)+∫

∫

(ax, ay, az)(t−

t₀)

wherein a is acceleration relative to an axis, X₀ is the x-coordinate of the accelerometer at the first time, Y₀ is the y coordinate of the accelerometer at the first time, Z₀ is the z-coordinate of the accelerometer at the first time, and (X₁, Y₁, Z₁) defines the position of the accelerometer in the x-y-z coordinate system at the second time.

8. An apparatus for determining changes in orientation of an object in six degrees of freedom, comprising:

a first linear accelerometer;

a second linear accelerometer positioned with respect to the first linear accelerometer to define an imaginary axis;

a third linear accelerometer disposed off the imaginary axis;

means for measuring, with the first and second linear accelerometers, the linear movement of the object in relation to an x-y-z coordinate system;

means for measuring, with the third linear accelerometer, the linear movement of the object in relation to the x-y-z coordinate system; and

a processing unit to determine, from the measurements from the first, second and third linear accelerometers, a change in a position and an orientation of the apparatus.

9. The apparatus of claim 8, wherein the means for measuring, with the first and second linear accelerometers, the linear movement of the object comprises means for comparing respective outputs of the first and second linear accelerometers relative to an accelerometer axis of sensitivity.

10. The apparatus of claim 8, wherein the processing unit calculates at least one tilt acceleration relative to at least one axis of sensitivity of the accelerometers.

11. The apparatus of claim 10, wherein the processor further detects an imbalance in respective magnitudes of acceleration of the first and the second linear accelerometers along an axis of the x-y-z coordinate system.

12. The apparatus of claim 11, wherein the processor assigns initial coordinates, in the x-y-z coordinate system, to each of the accelerometers at a first time, and computes changes in coordinates of each accelerometer between the first time and a second time.

13. The apparatus of claim 12, wherein the processor receives data from each of the accelerometers, and calculates with a double integral equation the positions of the accelerometers in the x-y-z coordinate system at the second time.

14. A computer program product for enabling a computer to determine changes in orientation of an object in six degrees of freedom comprising:

software instructions for enabling the computer to perform predetermined operations; and

a computer readable storage medium bearing the software instructions;

the predetermined operations including;

providing first and second linear accelerometers disposed on an imaginary axis relative to the object;

providing a third linear accelerometer disposed off the imaginary axis relative to the object;

measuring, with the first linear accelerometer, a first linear movement of the object in relation to an x-y-z coordinate system;

measuring, with the second linear accelerometer, a second linear movement of the object in relation to the x-y-z coordinate system;

measuring with the first and second linear accelerometers the annular rotation of the object in relation to two axes of rotation; and

measuring with the third linear accelerometer, a third linear movement of the object in relation to the x-y-z coordinate system;

determining, with measurements from the first, second and third linear accelerometers, a change in positon of the object; and

determining, with measurements from the first, second and third linear accelerometers, a change in orientation of the object,

wherein the computer determines changes in orientation of the object in six degrees of freedom.