METHOD FOR CALIBRATING AN ACCELEROMETER OF AN ELECTRONIC DEVICE, AN ACCELEROMETER, AND AN ELECTRONIC DEVICE HAVING AN ACCELEROMETER WITH IMPROVED CALIBRATION FEATURES

• US 20100192662A1
• Filed: 01/30/2009
• Published: 08/05/2010
• Est. Priority Date: 01/30/2009
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: Blackberry Limited
• Inventors: Yanni, Mamdouh Kamal
• Granted Patent: US 8,459,094 B2
• Time in Patent Office: Days
• US Class Current: 73/1.38
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

An accelerometer with improved calibration features, an electronic device having an accelerometer with improved calibration features, and a method of calibrating an accelerometer of an electronic device are provided. In accordance with one embodiment, there is method of calibrating an accelerometer of an electronic device, the accelerometer having at least a primary sensing axis and a secondary sensing axis, the second sensing axis being oriented parallel to the primary sensing axis and in the opposite direction of the primary sensing axis, the method comprising: measuring acceleration calibration data using the primary sensing axis and the secondary sensing axis of the accelerometer; determining calibration parameters in accordance with measured calibration data from the accelerometer; and storing the calibration parameters in a memory of the electronic device.

Claims

1. A method of calibrating an accelerometer of an electronic device, the accelerometer having at least a primary sensing axis and a secondary sensing axis, the second sensing axis being oriented parallel to the primary sensing axis and in the opposite direction of the primary sensing axis, the method comprising:

measuring acceleration calibration data using the primary sensing axis and the secondary sensing axis of the accelerometer;

determining calibration parameters in accordance with measured calibration data from the accelerometer; and

storing the calibration parameters in a memory of the electronic device.

2. The method of claim 1, wherein the calibration parameters comprise a bias factor of the primary sensing axis, the determining comprising:

determining a bias factor for the primary sensing axis using acceleration calibration data obtained from the primary sensing axis and the secondary sensing axis.

3. The method of claim 2, wherein the bias factor is determined as an average of acceleration calibration data obtained from the primary sensing axis and the accelerometer measurement from the secondary sensing axis when the electronic device is in a first orientation.

4. The method of claim 2, wherein the bias factor is determined as an average of acceleration calibration data obtained from the primary sensing axis and the accelerometer measurement from the secondary sensing axis when the electronic device is in a first and second orientation.

5. The method of claim 1, wherein the calibration parameters comprise a sensitivity of the primary sensing axis, the method comprising aligning the primary and secondary sensing axis with a force of gravity, and determining the sensitivity of the primary sensing axis using acceleration calibration data obtained from the primary sensing axis and the secondary sensing axis.

6. The method of claim 5, wherein the sensitivity is determined using the formula:

$S=\frac{A^{\mathrm{\prime <br><br>}}-A}{2}$

where S is the sensitivity, A′

is acceleration calibration data from the primary sensing axis when the primary sensing axis is aligned with the force of gravity, and A is acceleration calibration data from the secondary sensing axis when the secondary sensing axis is aligned with the force of gravity.

7. The method of claim 1, wherein the calibration parameters comprise a sensitivity of the primary sensing axis, the method comprising determining a sensitivity of the primary sensing axis using acceleration calibration data obtained from the primary sensing axis and the secondary sensing axis using the formula:

$S=\frac{A^{\mathrm{\prime <br><br>}}-A}{2}$

where S is the sensitivity, A′

is acceleration calibration data from the primary sensing axis when the primary sensing axis is aligned with the force of gravity, and A is acceleration calibration data from the secondary sensing axis when the secondary sensing axis is aligned with the force of gravity; and

transposing the sensitivity from a coordinate system in which the primary sensing axis and the secondary sensing axis are not aligned with the force of gravity to a second coordinate system wherein the primary sensing axis and the secondary sensing axis are in parallel alignment with the force of gravity.

8. The method of claim 1, further comprising measuring acceleration measurement data using the accelerometer, and adjusting the measured acceleration in accordance with the calibration parameters stored in the memory.

9. The method of claim 8, further comprising:

measuring a temperature of the accelerometer;

determining a temperature correction factor for the accelerometer measurements in accordance with the measured temperature; and

adjusting the measured acceleration in accordance with the calibration parameters stored in the memory and the temperature correction factor.

10. The method of claim 1, wherein the accelerometer has three pairs of sensing axes, each of the three pairs of sensing axes being mutually orthogonal to the other three pairs of sensing axes, each of the three pairs of sensing axes comprising a primary sensing axis and a secondary sensing axis, the method comprising:

measuring acceleration calibration data using the primary sensing axis and the secondary sensing axis of each pair of sensing axes;

determining calibration parameters of each pair of sensing axes in accordance with measured calibration data from the accelerometer; and

storing the calibration parameters in a memory of the electronic device

11. An accelerometer, comprising a sensing element having a first pair of sensing axes oriented in the opposite directions, the first pair of sensing axes comprising a primary sensing axis and a secondary sensing axis.

12. The accelerometer of claim 11, wherein the sensing element has three pairs of sensing axes, each of the three pairs of sensing axes being mutually orthogonal to the other three pairs of sensing axes, each of the three pairs of sensing axes comprising a primary sensing axis and a secondary sensing axis.

13. The accelerometer of claim 12, wherein the three pairs of sensing axes are formed from a common sensing element.

14. An electronic device, comprising:

an accelerometer comprising a sensing element having a first pair of sensing axes oriented in the opposite directions, the first pair of sensing axes comprising a primary sensing axis and a secondary sensing;

a controller connected to the accelerometer;

a memory connected to the controller for storing the calibration data for the accelerometer;

the controller, in a calibration mode, being configured to determine calibration parameters in accordance with measured calibration data from the accelerometer and store the calibration parameters in the memory;

the controller, in a measuring mode, being configured to measure acceleration using the accelerometer and to adjust the measured acceleration in accordance with the calibration parameters stored in the memory.

15. The electronic device of claim 14, wherein the calibration parameters comprise a bias factor of the primary sensing axis, wherein the controller, in the calibration mode, is configured to determine the bias factor as the average of accelerometer measurements from the primary sensing axis and the accelerometer measurement from the secondary sensing axis.

16. The electronic device of claim 14, wherein the calibration parameters comprise a sensitivity of the primary sensing axis, wherein the controller, in the calibration mode, is configured is configured to determine a sensitivity of the primary sensing axis using accelerometer measurements taken when the primary sensing axis is aligned with a force of gravity.

17. The electronic device of claim 14, further comprising a low pass filter for filtering accelerometer measurements to remove a dynamic component caused by movement of the accelerometer.

18. The electronic device of claim 14, further comprising a low drop out regulator providing power to the accelerometer.

19. The electronic device of claim 14, wherein the accelerometer is a ratiometric accelerometer.

20. The electronic device of claim 14, further comprising a temperature sensor for measuring a temperature of the accelerometer, wherein the memory contains a mapping of temperature to temperature correction factors, the controller in the measured mode being configured to determine a temperature correction factor for the accelerometer measurements in accordance with the measured temperature, and adjust the measured acceleration in accordance with the temperature correction factor.