Apparatus and method for correcting bias of gyroscope mounted on mobile robot

• US 20080022790A1
• Filed: 07/05/2007
• Published: 01/31/2008
• Est. Priority Date: 07/05/2006
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Choi, Ki-wan, Lee, Hyoung-ki, Bang, Seok-won, Kim, Dong-yoon
• Granted Patent: US 7,840,369 B2
• Time in Patent Office: Days
• US Class Current: 74/5.4
• CPC Class Codes: G01C 19/42 for indicating rate of turn; for integrating rate of turn
• CPC Class Codes: Y10T 74/1229 Gyroscope control

Abstract

An apparatus correcting a bias of a gyroscope that is mounted on a mobile robot and that measures an angular velocity of the mobile robot. The apparatus includes: at least one encoder respectively measuring a traveling velocity of a respective at least one wheel of the mobile robot; a modeling unit calculating an angular velocity of the mobile robot by using the measured traveling velocity; a bias presuming unit determining a confidence range by using difference values between the calculated angular velocity and the measured angular velocity, and calculating a presumed bias by using a value in a confidence range among the difference values; and a bias removing unit removing the presumed bias from the measured angular velocity.

Claims

1. An apparatus correcting a bias of a gyroscope that is mounted on a mobile robot and that measures an angular velocity of the mobile robot, the apparatus comprising:

at least one encoder respectively measuring a traveling velocity of a respective at least one wheel of the mobile robot;

a modeling unit calculating an angular velocity of the mobile robot by using the measured traveling velocity;

a bias presuming unit determining a confidence range by using difference values between the calculated angular velocity and the measured angular velocity, and calculating a presumed bias by using a value in a confidence range among the difference values; and

a bias removing unit removing the presumed bias from the measured angular velocity.

2. The apparatus of claim 1, further comprising a rotation angle compensating unit interpolating the calculated presumed bias so as to remove an accumulated error of a rotation angle occurring in a range excluding the confidence range.

3. The apparatus of claim 1, wherein the at least one wheel is at least two wheels, and wherein the modeling unit divides a difference value between the traveling velocities of the wheels by a distance between the wheels so as to calculate the angular velocity of the mobile robot.

4. The apparatus of claim 1, wherein the bias presuming part comprises a subtracter that calculates a difference value between the calculated angular velocity and the measured angular velocity, and a bias calculating part that divides an observation time into a plurality of time ranges, respectively compares a representative value of the difference value calculated in each respective time range with a predetermined threshold so as to determine a confidence range in the plurality of time ranges, and calculates a presumed bias by using the representative value in the determined time range.

5. The apparatus of claim 4, wherein the representative value is an average, intermediate value, or mode.

6. The apparatus of claim 4, wherein the observation time is a time when the mobile robot is stopped and moved.

7. The apparatus of claim 4, wherein, when a peak value of the calculated difference value is larger than another threshold in the determined confidence range, the bias calculating part excludes a corresponding confidence range from the final confidence range.

8. The apparatus of claim 4, wherein the bias presuming unit comprises a threshold setting part that sets the threshold by using a distribution of an output value of the gyroscope when the mobile robot is stopped.

9. The apparatus of claim 8, wherein the threshold setting part calculates an Allan variance function by using the output value of the gyroscope, and sets the threshold by using a value that is obtained by inputting a width of the determined confidence range into the Allan variance function.

10. The apparatus of claim 9, wherein the threshold setting part multiplies the value obtained from the Allan variance function by a predetermined constant so as to set the threshold.

11. The apparatus of claim 9, wherein the bias presuming unit further comprises a bias updating part that updates a present presumed bias by calculating a weighted sum of the calculated presumed bias and a past presumed bias.

12. The apparatus of claim 1, wherein the bias removing unit comprises a subtracter calculating a difference value between the calculated presumed bias and the output value of the gyroscope, and a multiplier multiplying the difference value by a predetermined scale factor.

13. A method of correcting a bias of a gyroscope that is mounted on a mobile robot and that measures an angular velocity of the mobile robot, the method comprising:

measuring a traveling velocity of at least one respective wheel of the mobile robot;

calculating an angular velocity of the mobile robot by using the measured at least one traveling velocity;

determining a confidence range by using difference values between the calculated angular velocity and the measured angular velocity;

calculating a presumed bias by using a value in a confidence range among the difference values; and

removing the presumed bias from the measured angular velocity.

14. The method of claim 13, wherein the calculating an angular velocity further comprises calculating the angular velocity of the mobile robot by dividing a difference value between the travel velocities of the wheels by a distance between the wheels.

15. The method of claim 13, wherein:

the determining of the confidence range comprises calculating a difference value between the calculated angular velocity and the measured angular velocity, dividing an observation time into a plurality of time ranges, and respectively comparing a representative value of the difference value calculated in each respective time range with a predetermined threshold so as to determine a confidence range in the plurality of time ranges; and

the calculating a presumed bias comprises calculating a presumed bias by using the representative value in the determined time range.

16. The method of claim 15, wherein the representative value is an average, intermediate value, or mode.

17. The method of claim 15, wherein the observation time is the time when the mobile robot is stopped and moved.

18. The method of claim 15, wherein the determining a confidence range further comprises excluding a corresponding confidence range from the final confidence range when a peak value of the calculated difference value is larger than another threshold in the determined confidence range.

19. The method of claim 15, wherein the determining a confidence range comprises setting the threshold by using the distribution of the output value of the gyroscope measured when the mobile robot is stopped.

20. The method of claim 19, wherein the setting a threshold comprises calculating an Allan variance function by using the output value of the gyroscope, and setting the threshold by using a value that is obtained by inputting a width of the confidence range into the Allan variance function.

21. The method of claim 20, wherein the threshold is set to a value that is obtained by multiplying the value obtained from the Allan variance function by a predetermined constant.

22. The method of claim 15, wherein the calculating a presumed bias further comprises updating a present presumed bias by calculating a weighted sum of the calculated presumed bias and a past presumed bias.

23. The method of claim 13, wherein the removing a presumed bias comprises calculating a difference value between the calculated presumed bias and the output value of the gyroscope, and multiplying the difference value by a predetermined scale factor.

24. An apparatus correcting an offset value of a gyroscope of a mobile robot in real-time during movement of the mobile robot, comprising:

a modeling unit calculating a calculated angular velocity of the mobile robot using a measured traveling velocity of each wheel of the mobile robot;

a bias removing unit correcting for a bias offset in a measured angular velocity of the mobile robot measured by the gyroscope, the bias removing unit generating a corrected measured angular velocity by removing a presumed bias from the measured angular velocity; and

a bias presuming unit calculating the presumed bias value using a confidence range in which a difference between the calculated angular velocity and corrected measured angular velocity is less than a threshold, the confidence range determined using difference values between the calculated angular velocity and the measured angular velocity.

25. The apparatus of claim 24, wherein the modeling unit receives a linear velocity of each wheel and calculates the angular velocity in a rotation angle obtainable by integrating the measured angular velocity.

26. The apparatus of claim 24, wherein the bias presuming unit comprises a bias updating part that calculates the presumed bias value using a past bias value and a new bias value calculated by the bias presuming unit, the presumed bias value calculable by the following expression

G_bias(k)=A·

G<sub>bias—

old</sub>+(1−

A)·

G<sub>bias—

new</sub> and

wherein 0≦

A≦

1, and

wherein G<sub>bias—

old</sub> is the past bias value, G<sub>bias—

new</sub> is a new bias value, and G_bias(k) is the calculated presumed bias value.

27. The apparatus of claim 26, further comprising a rotation angle compensating unit compensating for accumulated error of a rotation angle occurring between updates of the bias value on the basis of the following expression

ψ

_gc(k)=ψ

_g(k)−

(y₁−

y₂)×

n×

T×

0.5,

wherein, ψ

_g(k) is the rotation angle of the mobile robot measured by the gyroscope, ψ

_gc(k) is a compensated rotation angle, n is a number of time ranges between two confidence ranges, and T is a width of a time range.

28. A method of compensating, in real-time, for bias drift of a gyroscope mounted in a mobile robot, during the movement of the mobile robot, the method comprising:

calculating a calculated angular velocity of the mobile robot using a measured traveling velocity of each wheel of the mobile robot;

correcting for a bias offset in a measured angular velocity of the mobile robot measured by the gyroscope, the bias removing unit generating a corrected measured angular velocity by removing a presumed bias from the measured angular velocity; and

calculating the presumed bias value using a confidence range in which a difference between the calculated angular velocity and corrected measured angular velocity is less than a threshold, the confidence range determined using difference values between the calculated angular velocity and the measured angular velocity.