Systems and methods for determining linear acceleration

• US 9,921,335 B1
• Filed: 04/07/2015
• Issued: 03/20/2018
• Est. Priority Date: 04/07/2015
• Status: Active Grant

• Current Assignee: Invensense Incorporated (TDK Corporation)
• Original Assignee: Invensense Incorporated (TDK Corporation)
• Inventors: Keal, William Kerry
• Primary Examiner(s): Caputo, Lisa
• Assistant Examiner(s): Hernandez-Prewitt, Roger
• Application Number:
  US14/680,993
• Time in Patent Office: 1,078 Days
• Field of Search: 73382, 73382 G, 702141, 702150
• CPC Class Codes: A61B 5/1117 Fall detection
• CPC Class Codes: G01P 15/00 Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
• CPC Class Codes: G01V 7/02 Details
• CPC Class Codes: G06F 1/1694 the I/O peripheral being a single or a set of motion sensors for pointer control or gesture input obtained by sensing movements of the portable computer
• CPC Class Codes: G06F 3/017 Gesture based interaction, e.g. based on a set of recognized hand gestures interaction based on gestures traced on a digitiser G06F3/04883
• CPC Class Codes: G06F 3/0346 with detection of the device orientation or free movement in a 3D space, e.g. 3D mice, 6-DOF [six degrees of freedom] pointers using gyroscopes, accelerometers or tilt-sensors
• CPC Class Codes: G06F 3/0383 Signal control means within the pointing device

Abstract

Systems and methods are disclosed for deriving linear acceleration using an accelerometer. The orientation of a device may be determined using only accelerometer data. The determined orientation may then be used to determine a gravity vector, such that linear acceleration may be derived by subtracting the gravity vector from accelerometer data.

Claims

1. A method for measuring linear acceleration for a device having an accelerometer comprising:

obtaining a plurality of data samples from the accelerometer;

iteratively determining a plurality of orientations of the device with respect to gravity using only sampled data from the accelerometer;

determining a gravity vector with respect to a first data sample of the plurality of data samples using a determined orientation corresponding to the first data sample; and

subtracting the determined gravity vector from the first sample of data from the accelerometer to derive linear acceleration.

2. The method of claim 1, further comprising applying a gain factor to the plurality of data samples to convert accelerometer data to an angle.

3. The method of claim 2, wherein the gain factor is based on a magnitude of acceleration.

4. The method of claim 2, wherein the gain factor is adjusted dynamically.

5. The method of claim 2, wherein the gain factor is obtained from a look up table.

6. The method of claim 1, wherein each orientation is determined as the sum of previous orientation and a correction rotation comprising terms orthogonal to gravity applied to a previous orientation.

7. The method of claim 6, wherein an orientation of the device corresponding to sample N of the plurality of samples is represented by Q_N and is determined as:

8. The method of claim 1, wherein determining the gravity vector with respect to the first data sample comprises converting a gravity vector in a world frame to a body frame of the device using the determined orientation corresponding to the first data sample.

9. The method of claim 1, further comprising high pass filtering the derived linear acceleration.

10. The method of claim 1, wherein determining the gravity vector further comprises performing a sensor fusion operation with data from a magnetometer of the device.

11. The method of claim 1, wherein determining the gravity vector of the device comprises performing a sensor fusion operation with a previously derived linear acceleration.

12. A device for measuring linear acceleration comprising:

an accelerometer outputting a plurality of data samples;

an orientation module configured to iteratively determine a plurality of orientations of the device with respect to gravity using only sampled data from the accelerometer and to determine a gravity vector with respect to a first data sample of the plurality of data samples using a determined orientation corresponding to the first data sample; and

a linear acceleration module configured to subtract the determined gravity vector from the first sample of data from the accelerometer to derive linear acceleration.

13. The device of claim 12, wherein the orientation module is configured to apply a gain factor to the plurality of data samples to convert accelerometer data to an angle.

14. The device of claim 13, wherein the gain factor is based on a magnitude of acceleration.

15. The device of claim 13, wherein the orientation module is configured to adjust the gain factor dynamically.

16. The device of claim 13, wherein the orientation module is configured to obtain the gain factor from a look up table.

17. The device of claim 12, wherein the orientation module is configured to determine each orientation as the sum of previous orientation and a correction rotation comprising terms orthogonal to gravity applied to a previous orientation.

18. The device of claim 17, wherein an orientation of the device corresponding to sample N of the plurality of samples is represented by Q_N and is determined as:

wherein A_wy is acceleration on a y-axis in a world frame, A_wx is acceleration on an x-axis in the world frame and gain is a factor selected to convert accelerometer data to an angle.

19. The device of claim 12, wherein the orientation module is configured to determine the gravity vector with respect to the first data sample by converting a gravity vector in a world frame to a body frame of the device using the determined orientation corresponding to the first data sample.

20. The device of claim 12, wherein the linear acceleration module is configured to high pass filter the derived linear acceleration.

21. The device of claim 12, further comprising a magnetometer, wherein the orientation module is configured to perform a sensor fusion operation with data from the magnetometer.

22. The device of claim 12, wherein the orientation module is configured to determine the gravity vector by performing a sensor fusion operation with a previously derived linear acceleration.