Slip avoidance

• US 9,387,896 B1
• Filed: 08/25/2014
• Issued: 07/12/2016
• Est. Priority Date: 08/25/2014
• Status: Active Grant

• Current Assignee: Boston Dynamics, Inc. (SoftBank Group Corp.)
• Original Assignee: Google Inc. (Alphabet Inc.)
• Inventors: Blankespoor, Kevin, Perkins, Alex, da Silva, Marco
• Primary Examiner(s): Marc, McDieunel
• Application Number:
  US14/468,031
• Time in Patent Office: 687 Days
• Field of Search: 700/245, 623/24, 623/47, 623/50, 623/53
• US Class Current: 1/1
• CPC Class Codes: B25J 9/1615 characterised by special kind of manipulator, e.g. planar, scara, gantry, cantilever, space, closed chain, passive/active joints and tendon driven manipulators
• CPC Class Codes: B25J 9/162 Mobile manipulator, movable base with manipulator arm mounted on it
• CPC Class Codes: B62D 57/032 with alternately or sequentially lifted supporting base and legs; with alternately or sequentially lifted feet or skid B62D57/024 takes precedence
• CPC Class Codes: G05B 2219/40065 Approach, touch and then push object
• CPC Class Codes: Y10S 901/01 Mobile robot
• CPC Class Codes: Y10S 901/46 Sensing device

Abstract

An example method may include i) determining, by a robot having at least one foot, a representation of a coefficient of friction between the foot and a ground surface; ii) determining, by the robot, a representation of a gradient of the ground surface; iii) based on the determined representations of the coefficient of friction and the gradient, determining a threshold orientation for a target ground reaction force on the foot of the robot during a step; iv) determining the target ground reaction force, where the target ground reaction force comprises a magnitude and an orientation; v) determining an adjusted ground reaction force by adjusting the orientation of the target ground reaction force to be within the determined threshold orientation; and vi) causing the foot of the robot to apply a force on the ground surface equal to and opposing the adjusted ground reaction force during the step.

Claims

1. A method comprising:

determining, by a robot having at least one foot, a representation of a coefficient of friction between the foot and a ground surface;

determining, by the robot, a representation of a gradient of the ground surface;

based on the determined representations of the coefficient of friction and the gradient, determining, by the robot, a threshold orientation for a target ground reaction force on the foot of the robot during a footstep of the robot;

determining, by the robot, the target ground reaction force, wherein the target ground reaction force comprises a magnitude and an orientation;

determining, by the robot, an adjusted ground reaction force by adjusting the orientation of the target ground reaction force to be within the determined threshold orientation; and

causing the foot of the robot to apply a force on the ground surface approximately equal to and opposing the adjusted ground reaction force during the footstep.

2. The method of claim 1, wherein the adjusted ground reaction force is the target ground reaction force.

3. The method of claim 1, wherein the representation of the coefficient of friction between the foot and the ground surface is a first representation, wherein the threshold orientation is a first threshold orientation, wherein the target ground reaction force is a first target ground reaction force, wherein the force applied by the foot is a first force, and wherein the adjusted ground reaction force is a first adjusted ground reaction force, the method further comprising:

determining, by the robot, a second representation of the coefficient of friction between the foot and the ground surface, wherein the second representation is greater than the first representation;

based on the determined second representation of the coefficient of friction and the determined representation of the gradient, determining, by the robot, a second threshold orientation for a second target ground reaction force on the foot of the robot during the footstep;

determining, by the robot, the second target ground reaction force, wherein the second target ground reaction force comprises a magnitude and an orientation;

determining, by the robot, a second adjusted ground reaction force by adjusting the orientation of the second target ground reaction force to be within the determined second threshold orientation; and

after causing the foot of the robot to apply the first force on the ground surface approximately equal to and opposing the first adjusted ground reaction force during the footstep, causing the foot of the robot to apply a second force on the ground surface approximately equal to and opposing the second adjusted ground reaction force during the footstep.

4. The method of claim 3, wherein causing the foot of the robot to apply the second force on the ground surface approximately equal to and opposing the second adjusted ground reaction force during the footstep comprises adjusting the orientation of the first force applied by the foot during the footstep.

5. The method of claim 3, wherein the second adjusted ground reaction force is the second target ground reaction force.

6. The method of claim 3, wherein determining the second threshold orientation for the second target ground reaction force on the foot of the robot during the footstep comprises determining the second threshold orientation for the second target ground reaction force on the foot of the robot during the footstep after a determined time period.

7. The method of claim 6, wherein the footstep of the robot comprises an estimated duration, the method further comprising:

determining, by the robot, the time period to be approximately half of the estimated duration of the footstep.

8. The method of claim 3, the method further comprising:

detecting, by the robot, an indication of an increase of the gradient of the ground surface, wherein determining the second representation of the coefficient of friction is based on the detected indication of the increase of the gradient.

9. The method of claim 1, wherein the threshold orientation is approximated by a cone pointing toward the ground surface, wherein the cone comprises a center axis perpendicular to the ground surface, wherein the target ground reaction force is a first target ground reaction force, wherein the force applied by the foot is a first force, and wherein the adjusted ground reaction force is a first adjusted ground reaction force, the method further comprising:

detecting, by the robot, an indication of an increase of the gradient of the ground surface;

based on the detected indication of an increase of the gradient, determining, by the robot, an adjusted threshold orientation for a second target ground reaction force wherein the center axis of the cone approximating the threshold orientation approaches a gravity vector;

determining, by the robot, the second target ground reaction force, wherein the second target ground reaction force comprises a magnitude and an orientation;

determining, by the robot, a second adjusted ground reaction force by adjusting the orientation of the second target ground reaction force to be within the adjusted threshold orientation; and

after causing the foot of the robot to apply the first force on the ground surface approximately equal to and opposing the first adjusted ground reaction force during the footstep, causing the foot of the robot to apply a second force on the ground surface approximately equal to and opposing the second adjusted ground reaction force during the footstep.

10. The method of claim 1, wherein the representation of the coefficient of friction between the foot and the ground surface is a first representation, wherein the threshold orientation is a first threshold orientation, wherein the target ground reaction force is a first target ground reaction force, wherein the force applied by the foot is a first force, and wherein the adjusted ground reaction force is a first adjusted ground reaction force, the method further comprising:

detecting, by the robot, an indication of a slip of a second foot of the robot;

based on the detected indication of the slip, determining, by the robot, a second representation of a coefficient of friction between the foot and the ground surface, wherein the second representation is less than the first representation;

based on the determined second representation and the determined representation of the gradient, determining, by the robot, a second threshold orientation for a second target ground reaction force for the foot of the robot on the ground surface during the footstep;

determining, by the robot, the second target ground reaction force, wherein the second target ground reaction force comprises a magnitude and an orientation;

determining, by the robot, a second adjusted ground reaction force by adjusting the orientation of the second target ground reaction force to be within the second threshold orientation; and

before causing the foot of the robot to apply the first force on the ground surface approximately equal to and opposing the first adjusted ground reaction force during the footstep, causing the foot of the robot to apply a second force on the ground surface approximately equal to and opposing the second adjusted ground reaction force during the footstep.

11. A robot comprising:

at least one foot;

a processor;

a non-transitory computer readable medium; and

program instructions stored on the non-transitory computer readable medium that, when executed by the processor, cause the robot to perform functions comprising;

determining, by the robot, a representation of a coefficient of friction between the foot and a ground surface;

determining, by the robot, a representation of a gradient of the ground surface;

based on the determined representations of the coefficient of friction and the gradient, determining a threshold orientation for a target ground reaction force on the foot of the robot during a footstep of the robot;

determining the target ground reaction force, wherein the target ground reaction force comprises a magnitude and an orientation;

determining an adjusted ground reaction force by adjusting the orientation of the target ground reaction force to be within the determined threshold orientation; and

causing the foot of the robot to apply a force on the ground surface approximately equal to and opposing the adjusted ground reaction force during the footstep.

12. The robot of claim 11, wherein the adjusted ground reaction force is the target ground reaction force.

13. The robot of claim 11, wherein the representation of the coefficient of friction between the foot and the ground surface is a first representation, wherein the threshold orientation is a first threshold orientation, wherein the target ground reaction force is a first target ground reaction force, wherein the force applied by the foot is a first force and wherein the adjusted ground reaction force is a first adjusted ground reaction force, and wherein the program instructions, when executed by the processor, further cause the robot to perform functions comprising:

determining a second representation of the coefficient of friction between the foot and the ground surface, wherein the second representation is greater than the first representation;

based on the determined second representation of the coefficient of friction and the determined representation of the gradient, determining a second threshold orientation for a second target ground reaction force on the foot of the robot during the footstep;

determining the second target ground reaction force, wherein the second target ground reaction force comprises a magnitude and an orientation;

determining a second adjusted ground reaction force by adjusting the orientation of the second target ground reaction force to be within the determined second threshold orientation; and

after causing the foot of the robot to apply the first force on the ground surface approximately equal to and opposing the first adjusted ground reaction force during the footstep, causing the foot of the robot to apply a second force on the ground surface approximately equal to and opposing the second adjusted ground reaction force during the footstep.

14. The robot of claim 13, wherein the program instructions for causing the foot of the robot to apply the second force on the ground surface approximately equal to and opposing the second adjusted ground reaction force during the footstep comprise program instructions for adjusting the orientation of the first force applied by the foot during the footstep.

15. The robot of claim 13, wherein the second adjusted ground reaction force is the second target ground reaction force.

16. The robot of claim 13, wherein the program instructions for causing the foot of the robot to apply a second force on the ground surface approximately equal to and opposing the second adjusted ground reaction force during the footstep comprise program instructions for causing the foot of the robot to apply a second force on the ground surface approximately equal to and opposing the second adjusted ground reaction force after a determined time period.

17. The robot of claim 16, wherein the footstep of the robot comprises an estimated duration, and wherein the program instructions, when executed by the processor, further cause the robot to perform functions comprising:

determining the time period to be half of the estimated duration of the footstep.

18. The robot of claim 13, wherein the program instructions, when executed by the processor, further cause the robot to perform functions comprising:

detecting an indication of an increase of the gradient of the ground surface, wherein determining the second representation of the coefficient of friction is based on the detected indication of the increase of the gradient.

19. The robot of claim 11, wherein the threshold orientation is approximated by a cone pointing toward the ground surface, wherein the cone comprises a center axis perpendicular to the ground surface, wherein the target ground reaction force is a first target ground reaction force, wherein the adjusted ground reaction force is a first adjusted ground reaction force, wherein the force applied by the foot is a first force, and wherein the program instructions, when executed by the processor, further cause the robot to perform functions comprising:

detecting an indication of an increase of the gradient of the ground surface;

based on the detected indication of an increase of the gradient, determining an adjusted threshold orientation for a second target ground reaction force wherein the center axis of the cone approximating the threshold orientation approaches a gravity vector;

determining the second target ground reaction force, wherein the second target ground reaction force comprises a magnitude and an orientation;

determining a second adjusted ground reaction force by adjusting the orientation of the second target ground reaction force to be within the adjusted threshold orientation; and

after causing the foot of the robot to apply the first force on the ground surface approximately equal to and opposing the first adjusted ground reaction force during the footstep, causing the foot of the robot to apply a second force on the ground surface approximately equal to and opposing the second adjusted ground reaction force during the footstep.

20. The robot of claim 11, wherein the representation of the coefficient of friction between the foot and the ground surface is a first representation, wherein the threshold orientation is a first threshold orientation, wherein the target ground reaction force is a first target ground reaction force, wherein the adjusted ground reaction force is a first adjusted ground reaction force, wherein the force applied by the foot is a first force, and wherein the program instructions, when executed by the processor, further cause the robot to perform functions comprising:

detecting, by the robot, an indication of a slip of a second foot of the robot;

based on the detected indication of the slip, determining, by the robot, a second representation of a coefficient of friction between the foot and the ground surface, wherein the second representation is less than the first representation;

based on the determined second representation and the determined representation of the gradient, determining a second threshold orientation for a second target ground reaction force on the foot of the robot on the ground surface during the footstep;

determining the second target ground reaction force, wherein the second target ground reaction force comprises a magnitude and an orientation;

determining a second adjusted ground reaction force by adjusting the orientation of the second target ground reaction force to be within the second threshold orientation; and

before causing the foot of the robot to apply the first force on the ground surface approximately equal to and opposing the first adjusted ground reaction force during the footstep, causing the foot of the robot to apply a second force on the ground surface approximately equal to and opposing the second adjusted ground reaction force during the footstep.