MOBILE ROBOT HAVING FRICTION COEFFICIENT ESTIMATION FUNCTION AND FRICTION COEFFICIENT ESTIMATION METHOD

• US 20150019103A1
• Filed: 02/24/2014
• Published: 01/15/2015
• Est. Priority Date: 07/09/2013
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: CHOI, Hyun Do, YOON, Suk June
• Granted Patent: US 9,283,966 B2
• Time in Patent Office: Days
• US Class Current: 701/82
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 8/172 Determining control parameters used in the regulation, e.g. by calculations involving measured or detected parameters B60T8/17551 takes precedence
• CPC Class Codes: B60T 8/1763 responsive to the coefficient of friction between the wheels and the ground surface B60T8/1764 takes precedence
• CPC Class Codes: B60W 2552/40 Coefficient of friction
• CPC Class Codes: B60W 40/068 Road friction coefficient
• CPC Class Codes: G05D 1/027 comprising intertial navigation means, e.g. azimuth detector inertial navigation G01C21/16; inertial navigation combined with non-inertial navigation instruments G01C21/165
• CPC Class Codes: G05D 1/0272 comprising means for registering the travel distance, e.g. revolutions of wheels measuring distance traversed on the ground by vehicles, e.g. using odometers G01C22/00
• CPC Class Codes: Y10S 901/01 Mobile robot

Abstract

A mobile robot configured to move on a ground. The mobile robot including a contact angle estimation unit estimating contact angles between wheels of the mobile robot and the ground and uncertainties associated with the contact angles, a traction force estimation unit estimating traction forces applied to the wheels and traction force uncertainties, a normal force estimation unit estimating normal forces applied to the wheels and normal force uncertainties, a friction coefficient estimation unit estimating friction coefficients between the wheels and the ground, a friction coefficient uncertainty estimation unit estimating friction coefficient uncertainties, and a controller determining the maximum friction coefficient from among the friction coefficients such that the maximum friction coefficient has an uncertainty less than a threshold and at a point of time when the torque applied to each of the wheels changes from an increasing state to a decreasing state, among the estimated friction coefficients.

Claims

1. A mobile robot configured to move on a ground, the mobile robot comprising:

a contact angle estimation unit configured to estimate contact angles between wheels of the mobile robot and the ground and uncertainties associated with the contact angles;

a traction force estimation unit configured to estimate traction forces applied to the wheels and uncertainties associated with the traction forces using state variables of the wheels;

a normal force estimation unit configured to estimate normal forces applied to the wheels and uncertainties associated with the normal forces using the contact angles, the contact angle uncertainties, the traction forces, and joint pose information;

a friction coefficient estimation unit configured to estimate friction coefficients between the wheels and the ground using the traction forces and the normal forces;

a friction coefficient uncertainty estimation unit configured to estimate uncertainties of the friction coefficients using the traction forces, the traction force uncertainties, the normal forces, the normal force uncertainties, and the friction coefficients; and

a controller configured to determine a maximum friction coefficient from among the friction coefficients such that the maximum friction coefficient has an associated one of the friction coefficient uncertainties that is less than a threshold and at a point of time when the torque applied to the wheels changes from an increasing state to a decreasing state.

2. The mobile robot according to claim 1, further comprising:

joint pose detection units configured to detect the joint pose information; and

wheel state variable detection units configured to detect the state information of the wheels.

3. The mobile robot according to claim 2, wherein the joint pose detection units are inclinometers or inertial measurement units (IMU).

4. The mobile robot according to claim 2, wherein the wheel state variable detection units include encoders.

5. The mobile robot according to claim 1, wherein the joint pose information includes joint angles and joint angular velocities.

6. The mobile robot according to claim 1, wherein the state information of the wheels includes the torques applied to the wheels, angular velocities, radiuses and inertia moments of the wheels.

7. The mobile robot according to claim 1, wherein the traction force estimation unit is configured to estimate the traction forces by applying the detected wheel state variables to a model of the wheels.

8. The mobile robot according to claim 1, wherein the normal force estimation unit is configured to estimate the normal forces by,

forming a quasi-static equilibrium equation using the traction forces, the contact angles, the joint angles, the angular velocities, and a mobile robot model;

and

calculating a least-squares solution of the formed quasi-static equilibrium equation.

9. The mobile robot according to claim 1, wherein the contact angle estimation unit is configured to estimate the contact angles and the contact angle uncertainties using images acquired through cameras mounted on the wheels.

10. The mobile robot according to claim 1, wherein the contact angle estimation unit is configured to estimate the contact angles and the contact angle uncertainties using force information detected through force sensors mounted on the wheels.

11. A friction coefficient estimation method comprising:

estimating contact angles between wheels of a mobile robot and a ground and uncertainties associated with the contact angles;

detecting joint poses of the mobile robot and state variables of the wheels;

estimating traction forces applied to the wheels using the state variables of the wheels;

estimating uncertainties associated with the traction forces;

estimating normal forces applied to the wheels using the contact angles, the contact angle uncertainties, the joint poses, the traction forces, and the traction force uncertainties;

estimating uncertainties associated with the normal forces;

estimating friction coefficients between the wheels and the ground using the traction forces and the normal forces;

estimating uncertainties associated with the friction coefficients using the traction forces, the traction force uncertainties, the normal forces, the normal force uncertainties, and the friction coefficients; and

determining a maximum friction coefficient from among the friction coefficients such that the maximum friction coefficient has an associated one of the friction coefficient uncertainties that is less than a threshold and at a point of time when the torque applied to the wheels changes from an increasing state to a decreasing state.

12. The friction coefficient estimation method according to claim 11, wherein the estimating contact angles and the contact angle uncertainties is performed using images acquired through cameras mounted on the wheels.

13. The friction coefficient estimation method according to claim 11, wherein the estimating contact angles and the contact angle uncertainties is performed using force information detected through force sensors mounted on the wheels.

14. The friction coefficient estimation method according to claim 11, wherein the estimating traction forces is performed by applying the state variables of the wheels to a model of the wheels.

15. The friction coefficient estimation method according to claim 11, wherein the estimating normal forces is performed by,

forming a quasi-static equilibrium equation using the traction forces, the contact angles, the joint angles, the angular velocities, and a mobile robot model;

and

calculating a least-squares solution of the formed quasi-static equilibrium equation.

16. A mobile robot configured to move on a ground, the mobile robot comprising:

a moving unit configured to move the mobile robot with respect to the ground; and

a controller configured to control a rate of acceleration and deceleration of the moving of the mobile robot based on a friction coefficient between the moving unit and the ground.

17. The mobile robot of claim 16, wherein the friction coefficient is a maximum friction coefficient and controller is configured to estimate the maximum friction coefficient between the moving unit and the ground by,

estimating friction coefficients and uncertainties associated therewith;

selecting a plurality of the estimated friction coefficients whose corresponding uncertainties are less than a threshold; and

selecting as the maximum friction coefficient the estimated friction coefficient that corresponds to a time when a torque applied to the moving unit changes from an increasing state to a decreasing state.

18. The mobile robot of claim 17, wherein the moving unit includes wheels that are configured to transport the mobile robot through rotation of the wheels, and controller is configured to estimate the friction coefficients by,

estimating contact angles between the wheels and the ground and uncertainties associated with the contact angles;

estimating traction forces applied to the wheels and uncertainties associated with the traction forces using state variables of the wheels;

estimating normal forces applied to the wheels and uncertainties associated with the normal forces using the contact angles, the contact angle uncertainties, the traction forces, and joint pose information; and

estimating the friction coefficients between the wheels and the ground using the traction forces and the normal forces.

19. The mobile robot of claim 18, wherein the controller is configured to,

estimate the contact angles using one of images acquired through cameras and force information detected by force sensors, and

estimate the traction forces by applying the state variables of the wheels to a model of the wheels.

20. The mobile robot of claim 19, wherein the state variables indicate at least an inertia, moment, torque, radius and angular velocity of the wheels.