On-line method and apparatus for coordinated mobility and manipulation of mobile robots

• US 5,550,953 A
• Filed: 04/20/1994
• Issued: 08/27/1996
• Est. Priority Date: 04/20/1994
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Seraji, Homayoun
• Primary Examiner(s): Downs, Robert W.
• Assistant Examiner(s): Hafiz, Tariq R.
• Application Number:
  US08/231,597
• Time in Patent Office: 860 Days
• Field of Search: 364/474.36, 364/167.01, 395/80-98, 901/14, 901/15
• US Class Current: 700/263
• CPC Class Codes: B25J 9/162 Mobile manipulator, movable base with manipulator arm mounted on it
• CPC Class Codes: G05B 2219/39081 Inexact solution for orientation or other DOF with relation to type of task
• CPC Class Codes: G05B 2219/39172 Vehicle, coordination between manipulator arm and its moving vehicle
• CPC Class Codes: G05B 2219/39174 Add DOFs of mobility to DOFs of manipulator to add user defined tasks to motion
• CPC Class Codes: G05B 2219/40252 Robot on track, rail moves only back and forth
• CPC Class Codes: G05B 2219/40293 Gantry, portal
• CPC Class Codes: G05B 2219/40297 Macro manipulator and microhand, distributed positioning
• CPC Class Codes: G05B 2219/40298 Manipulator on vehicle, wheels, mobile
• CPC Class Codes: G05B 2219/40327 Calculation, inverse kinematics solution using damped least squares method
• CPC Class Codes: G05B 2219/40349 Optimize manipulability measure function

Abstract

A simple and computationally efficient approach is disclosed for on-line coordinated control of mobile robots consisting of a manipulator arm mounted on a mobile base. The effect of base mobility on the end-effector manipulability index is discussed. The base mobility and arm manipulation degrees-of-freedom are treated equally as the joints of a kinematically redundant composite robot. The redundancy introduced by the mobile base is exploited to satisfy a set of user-defined additional tasks during the end-effector motion. A simple on-line control scheme is proposed which allows the user to assign weighting factors to individual degrees-of-mobility and degrees-of-manipulation, as well as to each task specification. The computational efficiency of the control algorithm makes it particularly suitable for real-time implementations. Four case studies are discussed in detail to demonstrate the application of the coordinated control scheme to various mobile robots.

Claims

1. A method of controlling a mobile robot, the robot of the type having a mobile base having at least one degree of mobility and a manipulatable arm having at least one degree of manipulation;

the method comprising the steps of;

(a) generating a forward kinematic model that relates arm and base joint coordinates to end-effector coordinates;

(b) generating a differential kinematic model that relates end-effector velocity to arm and base joint velocities including Jacobian matrices of the arm and base, respectively;

(c) augmenting by column the arm Jacobian matrix with the base Jacobian matrix to obtain an overall end-effector Jacobian matrix where the availability of base mobility appears as extra columns in the end-effector Jacobian matrix because of effectively increasing the dimension of the joint space;

(d) augmenting by row the end-effector Jacobian matrix of step (c) with a constraint Jacobian matrix which relates to a user-defined additional task to be accomplished due to kinematic redundancy where said additional task results in extra rows in the end-effector Jacobian matrix due to an increase of the task space;

(e) selecting end-effector and constraint task weighting factors and arm and base joint velocity weighting factors;

(f) finding the optimal arm and base motions using a closed-loop damped-least-squares approach; and

(g) moving the arm and base of said robot in accordance with the optimal motions resulting from carrying out steps (a) through (f).

2. The method recited in claim 1 wherein said kinematic redundancy recited in step (d) results from a task space which is at least one dimension less than the sum of the revolute joints and prismatic joints of said robot.

3. The method recited in claim 1 wherein said mobile robot is a tracked robot.

4. The method recited in claim 1 wherein said mobile robot is a gantry robot.

5. The method recited in claim 1 wherein said mobile robot is a wheeled robot.

6. The method recited in claim 1 wherein said mobile robot is a compound robot.

7. The method recited in claim 1 wherein the number of degrees-of-freedom of said mobile robot is equal to the sum of the number of degrees-of-manipulation of said arm and the number of degrees-of-mobility of said base.

8. The method recited in claim 1 wherein said end-effector and constraint task weighting factors are selected on-line based on user requirements for real-time implementation of on-line control of said mobile robot.

9. A method for on-line, real-time control of a mobile robot having a mobile base and a manipulatable arm mounted on the base to provide a number of degrees-of-freedom equal to the sum of the number of degrees-of-base-mobility and the number of degrees-of-arm-manipulation, the robot operating in a multi-dimension task space wherein the number of task-space-dimensions is less than the degrees-of-freedom;

the method comprising the steps of;

(a) generating a forward kinematic model that relates arm and base joint coordinates to end-effector coordinates;

(b) generating a differential kinematic model that relates end-effector velocity to arm and base joint velocities including Jacobian matrices of the arm and base, respectively;

(c) augmenting by column the arm Jacobian matrix with the base Jacobian matrix to obtain an overall end-effector Jacobian matrix where the availability of base mobility appears as extra columns in the end-effector Jacobian matrix because of effectively increasing the dimension of the joint space;

(d) augmenting by row the end-effector Jacobian matrix of step (c) with a constraint Jacobian matrix which relates to a user-defined additional task to be accomplished due to kinematic redundancy where said additional task results in extra rows in the end-effector Jacobian matrix due to an increase of the task space;

(e) selecting end-effector and constraint task weighting factors and arm and base joint velocity weighting factors;

(f) finding the optimal arm and base motions using a closed-loop damped-least-squares approach; and

(g) moving the arm and base of said robot in accordance with the optimal motions resulting from carrying out steps (a) through (f).

10. The method recited in claim 9 wherein said kinematic redundancy recited in step (d) results from a task space which is at least one dimension less than the sum of the revolute joints and prismatic joints of said robot.

11. The method recited in claim 9 wherein said mobile robot is a tracked robot.

12. The method recited in claim 9 wherein said mobile robot is a gantry robot.

13. The method recited in claim 9 wherein said mobile robot is a wheeled robot.

14. The method recited in claim 9 wherein said mobile robot is a compound robot.