GYRO ZERO TURN RATE OFFSET CORRECTION OVER TEMPERATURE IN A PERSONAL MOBILE DEVICE

• US 20110301900A1
• Filed: 06/04/2010
• Published: 12/08/2011
• Est. Priority Date: 06/04/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Patel, Parin
• Granted Patent: US 8,577,633 B2
• Time in Patent Office: Days
• US Class Current: 702/104
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38

Abstract

A personal mobile device housing contains a display screen, a wireless telephony communications transceiver, and a battery charger interface. A temperature sensor and a gyro sensor whose zero turn rate output contains an offset are also included. A lookup table has gyro zero turn rate offset correction values associated with different temperature values. A programmed processor accesses the lookup table to correct the output of the gyro sensor for zero turn rate offset. It is automatically determined, during in-the-field use, when the device is in a motionless state, and the output of the temperature and gyro sensors are read. The read gyro output is written to the lookup table as part of a pair of associated temperature and zero turn rate offset correction values. Other embodiments are also described and claimed.

Claims

1. A personal mobile device comprising:

a multi-function handheld portable device housing in which are integrated a display screen;

a wireless communications transceiver;

a battery charger interface;

a temperature sensor;

a gyro sensor whose zero turn rate output contains an offset;

storage in which a look-up table is stored, the look-up table having a plurality gyro zero turn rate offset correction values associated with a plurality of different temperature values, respectively; and

a programmed processor to access the look-up table to correct an output value of the gyro sensor for zero turn rate offset, wherein the programmed processor is to

(a) automatically determine, during in-the-field use of the personal mobile device, when the device is in a motionless state, (b) read output of the temperature sensor, c) read output of the gyro sensor, and (d) write the read gyro output to the lookup table as a part of a pair of associated temperature and zero turn rate offset correction values.

2. The mobile device of claim 1 wherein the programmed processor is to repeatedly perform (a)-(d), during in-the-field use of the device, as the device encounters a range of different temperatures.

3. The mobile device of claim 1 wherein the temperature sensor and the gyro sensor are integrated in the same integrated circuit package.

4. The mobile device of claim 2 further comprising:

a movement sensor that detects linear movement of the device,

wherein the programmed processor is to (a) read output of the movement sensor, and (b) when the read output remains within a predetermined zero threshold range for a predetermined time interval determine that the device is in the motionless state.

5. The mobile device of claim 4 wherein the programmed processor is to, prior to writing the read gyro output to the lookup table, determine if the read gyro output is within an expected range for ZRO, wherein the expected ZRO range is computed based on one or more pre-existing pairs of associated temperature and zero rate offset correction values in the look-up table.

6. The mobile device of claim 4 wherein the programmed processor is to, prior to writing the read gyro output to the lookup table, estimate a zero rate offset correction value associated with the read output of the temperature sensor, based on pre-existing data stored in the device that describes variation of the gyro sensor'"'"'s zero rate offset over temperature, and then compares the read gyro output to the estimated zero rate offset correction value.

7. A personal mobile device comprising:

a gyro sensor whose zero turn rate output contains an offset;

storage in which a look-up table is stored, the look-up table having a few initial entries that were written to the storage during manufacturing test of the device, wherein each entry includes a different temperature value and a respective gyro zero turn rate offset correction value; and

a programmed processor to access the look-up table to correct an output of the gyro sensor for zero turn rate offset, wherein the programmed processor is to add many new entries to the look-up table during in-the-field use of the device, wherein for each new entry the programmed processor is to (a) automatically determine that the device is in a motionless state, (b) read an output of the gyro sensor and determine an associated temperature of the gyro sensor, and (c) write the read gyro output to the lookup table as part of a pair of associated temperature and zero turn rate offset correction values included in the new entry.

8. The mobile device of claim 7 further comprising:

an accelerometer that detects linear acceleration of the device,

wherein the programmed processor is to (a) read an output of the accelerometer, and (b) when the read accelerometer output remains within a predetermined zero threshold range for a predetermined time interval, decide that the device is in the motionless state.

9. The mobile device of claim 8 wherein the programmed processor is to verify the read gyro output before writing to the lookup table, by comparing the read gyro output to a pre-existing offset correction value in the table.

10. The mobile device of claim 8 wherein the programmed processor is to, before writing the read gyro output to the lookup table, compare the read gyro output to a pre-existing offset correction value in the table.

11. The mobile device of claim 8 wherein the programmed processor is to compute an estimated offset correction value that is associated with the temperature of the gyro sensor, based on previously stored data in the device that describes variation of the gyro sensor'"'"'s zero rate offset over temperature,

and wherein the programmed processor is to, before writing the read gyro output to the lookup table, compare the read gyro output to the estimated offset correction value.

12. A method for operating a personal mobile device having a gyro sensor, comprising:

correcting an output of a gyro sensor in the device by accessing a look-up table stored in the device, wherein the table has a plurality of entries that were written during manufacturing test of the device, wherein each entry includes a different temperature value and a respective gyro zero turn rate offset correction value; and

adding a plurality of new entries to the look-up table during in-the-field use of the device, by, for each new entry,

determining that the device is in a motionless state and, while in that state, reading the gyro sensor and determining a temperature of the gyro sensor for the reading, and

writing the read gyro value to the lookup table as part of a pair of associated temperature and zero turn rate offset correction values included in the new entry.

13. The method of claim 12 further comprising:

before writing the read gyro value to the lookup table, comparing the read gyro value to one or more offset correction values stored in the table.

14. The method of claim 12 further comprising:

before writing the read gyro value to the lookup table, comparing the read gyro value to an estimated offset correction value that is associated with the determined temperature of the gyro sensor.

15. The method of claim 14 further comprising:

computing the estimated offset correction value based on previously stored data in the device that describes variation of the gyro sensor'"'"'s zero rate offset over temperature.