Methods for robotic self-righting

• US 8,977,485 B2
• Filed: 03/15/2013
• Issued: 03/10/2015
• Est. Priority Date: 07/12/2012
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Kessens, Chad C., Smith, Daniel C.
• Primary Examiner(s): Black, Thomas G
• Assistant Examiner(s): PAIGE, TYLER D
• Application Number:
  US13/835,086
• Publication Number:
  US 20140100768A1
• Time in Patent Office: 725 Days
• Field of Search: 701/124, 180/9.3
• US Class Current: 701/124
• CPC Class Codes: B25J 9/1664 characterised by motion, path, trajectory planning
• CPC Class Codes: G05B 2219/40298 Manipulator on vehicle, wheels, mobile
• CPC Class Codes: G05B 2219/40465 Criteria is lowest cost function, minimum work path
• CPC Class Codes: G05D 1/0891 specially adapted for land vehicles
• CPC Class Codes: G05D 3/00 Control of position or direction G05D1/00 takes precedence; numerical control to execute positioning G05B19/18

Abstract

Embodiments of the present invention are directed to methods of autonomously self-righting a maneuverable robot. In one embodiment, an autonomous method for self-righting a maneuverable robot to affect recovery from an overturned state to its nominal upright configuration may include: defining a convex hull and center of mass of each link of the robot; determining the convex hull and overall robot center of mass for each joint configuration of the robot; analyzing each convex hull face to determine its stability or instability; grouping continuously stable orientations of the robot and joint configurations together defining nodes and transitions there between; assigning a cost to transitions between nodes; computing an overall cost for each potential set of transition costs resulting in achievement of the goal; and determining a sequence of one or more actions to self-right the robot such that the sequence of actions minimizes the overall cost of self-righting the robot.

Claims

1. An autonomous method for self-righting a maneuverable robot to affect recovery from an overturned state to its nominal upright configuration, the method comprising:

defining a convex hull and center of mass of each link of the robot;

determining the convex hull and overall robot center of mass for each joint configuration of the robot;

analyzing each convex hull face to determine its stability or instability;

grouping continuously stable orientations of the robot and joint configurations together defining nodes and transitions there between;

assigning a cost to transitions between nodes;

computing an overall cost for each potential set of transition costs resulting in achievement of the goal; and

determining a sequence of one or more actions to self-right the robot such that the sequence of actions minimizes the overall cost of self-righting the robot.

2. The method of claim 1, wherein defining the convex hull comprises:

determining a minimal convex set of points defining the exterior of the robot, wherein co-planar points of the convex set define convex hull faces of the robot.

3. The method of claim 1, further comprising:

creating a conformation space map including all possible stable orientations and joint configurations for the robot.

4. The method of claim 3, further comprising:

grouping continuously stable conformations of the robot together; and

dividing the conformation space map into nodal states based on continuity.

5. The method of claim 3, further comprising:

defining boundaries on the conformation space map which correspond to limitations of motion of the robot, and determining the directed graph based only on the achievable portions of the conformation space map.

6. The method of claim 1, further comprising:

creating a directed graph based on the ability of the robot to transition from one node to another.

7. The method of claim 1, wherein assigning a cost to transitions between nodes comprises:

assigning a cost to only feasible transitions between nodes.

8. The method of claim 1, further comprising:

creating a cost matrix where rows of the matrix represent the costs of transitioning from a particular node and columns of the matrix represent the costs of transitioning to a particular destination node.

9. The method of claim 1, wherein the cost comprises potential energy, execution time, required energy, or any weighted combination thereof.

10. The method of claim 9, wherein assigning cost is based on the minimal change in potential energy between nodes.

11. The method of claim 1, wherein analyzing the stability for each convex hull face comprises:

determining the center of mass of the robot with respect to the direction of gravity relative to the ground contact of each convex hull face.

12. The method of claim 11, wherein determining the robot'"'"'s orientation comprises analyzing inertial measurement unit (IMU) data from the robot to obtain the direction of gravity.

13. The method of claim 1, further comprising:

maintaining the lowest cost transition as a desired transition point between nodes.

14. The method of claim 1, wherein determining the sequence of one or more actions to self-right the robot comprises:

quantifying rightability based on percentage of states within reach of the goal state.

15. The method of claim 1, wherein link positions are determined using forward kinematics.

16. The method of claim 1, further comprising:

executing the sequence of one or more actions to self-right the robot.

17. The method of claim 1, wherein the steps of determining the convex hull and overall robot center of mass for each joint configuration of the robot and analyzing each convex hull face to determine its stability or instability are performed separately by:

determining the convex hull and center of mass for every possible joint configuration; and

subsequently analyzing stability of all the convex hull faces using said determinations.

18. The method of claim 1, wherein the steps of determining the convex hull and overall robot center of mass for each joint configuration of the robot and analyzing each convex hull face to determine its stability or instability are performed concurrently by:

analyzing the stability of each convex hull face while iteratively determining joint configurations.

19. The method of claim 1, wherein determining a sequence of one or more actions to self-right the robot such that the sequence of actions optimizes or minimizes the overall costs of self-righting the robot comprises:

minimizing the total cost in the route through employing a shortest path algorithm, and/or avoiding the edges with the largest costs entirely.

20. A robotic controller comprising:

a processor programmed with instructions to execute the method of claim 1.

21. A non-transitory computer-readable storage medium having computer-readable instructions, that when executed by a processor, implement the method of claim 1.