Mobile dexterous siren degree of freedom robot arm with real-time control system

• US 5,737,500 A
• Filed: 04/28/1995
• Issued: 04/07/1998
• Est. Priority Date: 03/11/1992
• Status: Expired due to Fees

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Lee, Thomas S., Lim, David, Seraji, Homayoun
• Primary Examiner(s): Hafiz, Tariq R.
• Assistant Examiner(s): Smith, Jeffrey S.
• Application Number:
  US08/431,361
• Time in Patent Office: 1,075 Days
• Field of Search: 901/1, 901/9, 901/15, 318/568.11, 318/568.24, 395/80, 395/86, 395/98, 395/97
• US Class Current: 700/251
• CPC Class Codes: B25J 9/1643 redundant control
• CPC Class Codes: G05B 2219/33169 Name of bus, vme-bus
• CPC Class Codes: G05B 2219/34403 RTI real time, kernel, processing
• CPC Class Codes: G05B 2219/39062 Calculate, jacobian matrix estimator
• CPC Class Codes: G05B 2219/39081 Inexact solution for orientation or other DOF with relation to type of task
• CPC Class Codes: G05B 2219/39082 Collision, real time collision avoidance
• 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 2219/39414 7-DOF
• CPC Class Codes: G05B 2219/39422 7-DOF for arm and 6-DOF for end effector
• 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 2219/40317 For collision avoidance and detection
• CPC Class Codes: G05B 2219/40327 Calculation, inverse kinematics solution using damped least squares method
• CPC Class Codes: G05B 2219/40342 Minimize sum of gravitational torques of some joints
• CPC Class Codes: G05B 2219/40345 Minor measure
• CPC Class Codes: G05B 2219/40362 Elbow high or low, avoid obstacle collision with redundancy control
• CPC Class Codes: G05B 2219/40371 Control trajectory to avoid joint limit as well as obstacle collision
• CPC Class Codes: G05B 2219/40379 : Manipulability

Abstract

The present invention is a mobile redundant dexterous manipulator with a seven-degree-of-freedom robot arm mounted on a 1 degree-of-freedom mobile platform with a six-degree-of freedom end effector including a real-time control system with multiple modes of operation. The manipulator-plus-platform system has two degrees-of-redundancy for the task of hand placement and orientation. The redundancy resolution is achieved by accomplishing two additional tasks using a configuration control technique. This mobile manipulator with control system allows a choice of arm angle control or collision avoidance for the seventh task, and platform placement or elbow angle control for the eighth task. In addition, joint limit avoidance task is automatically invoked when any of the joints approach their limits. The robot is controlled by a processor employing a 6-by-7 Jacobian matrix for defining location and orientation of the end effector.

Claims

1. A method of controlling a robot arm, said robot arm comprising a base with a central axis, n joints, joint angle sensor means connected to each of said joints, joint servo loop means connected to each of said joints, and two ends comprising a mobile platform end having two degrees-of-redundancy and a movable hand end, each of said joints having a joint angle specifying a rotational orientation of said joint, said hand end having m degrees of freedom of movement, wherein m is less than n and said robot arm is characterized by a degree of redundancy, said method comprising:

first defining a first m-by-n matrix for defining location and orientation of said hand end in terms of said rotation angles of said joints;

second defining a second r-by-n matrix for defining r user-specified kinematic functions in terms of said joint angles, wherein r is a positive integer exceeding to the degree of redundancy of said robot arm;

combining said first and second matrices to produce an augmented m+r-by-n matrix;

computing in accordance with forward kinematics from said augmented m+r-by-n matrix and from the joint angles sensed by said joint angle sensor means a set of n desired joint angles and transmitting said set of n desired joint angles to said joint servo loop means to control the robot arm;

defining a translational position of said mobile platform end from said central axis of said base; and

controlling said translational position of said mobile platform end by a platform motion controller.

2. The method of claim 1 wherein each of said kinematic functions defines a constraint in one of (a) location, (b) orientation and (c) configuration of a specified portion of said arm.

3. The method of claim 1 wherein said first m-by-n matrix, second r-by-n matrix and augmented m+r-by-n matrix comprise Jacobian matrices.

4. The method of claim 1 wherein said robot arm has an anthropomorphic structure and one of said joint is an elbow joint, wherein a pair of links of said arm joined together by said elbow joint define an elbow plane of said arm, wherein one of said kinematic functions comprises means for defining an orientation of said elbow plane, and wherein said platform motion controller comprises means for preselecting a wedge angle corresponding to said elbow plane and means for monitoring said orientation of said elbow plane.

5. The method of claim 4, further comprising, by said platform motion controller, the steps of:

(a) defining an initial hand end position, x_hi, of said robot arm;

(b) defining an initial orientation of said elbow plane, φ

_i ;

(c) defining lengths l₁ and l₂, respectively, of said pair of links; and

(e) commanding said mobile platform to move -Δ

_X.sbsb.h if said elbow plane does not equal said preselected wedge angle so that said elbow plane orientation returns to said preselected wedge angle and said hand position remains constant, wherein;

##EQU27##

6. The method of claim 1 wherein at least one of said kinematic functions constrains location of said arm.

7. The method of claim 1 wherein at least one of said kinematic functions minimizes a sum of selected mechanical parameters of at least some of said joints.

8. The method of claim 7 wherein said parameters comprising different weighting coefficients for different ones of said joints.

9. The method of claim 8 further changing said weighting coefficients during movement of said arm.

10. The method of claim 7 wherein said one of mechanical parameters comprises velocity errors of said joints with respect to desired velocities.

11. The method of claim 7 wherein one of said mechanical parameters comprises joint angle errors with respect to desired joint angles.

12. The method of claim 9 wherein at least one of said user-specified functions corresponds to one of:

i. joint limit avoidance;

ii. trajectory generation;

iii. arm simulation.

13. The method of claim 12 wherein said joint limit avoidance comprises the steps of:

(a) initiating said platform motion controller if each of said joints are near their respective positional limits; and

(b) relaxing movement of said joints based on respective weighting coefficients of said joints when one of said joints are near their respective positional limits so that each joint is not at a maximum positional limit.

14. The method of claim 12 wherein said trajectory generation comprises two independent trajectory generators, the first trajectory generator producing smooth continuous cycloidal functions so that transition from an initial value to a final value is made in a specified time, and a second trajectory generator specifying a plurality of via-points so that a smooth trajectory between points is generated and velocities between said via-points are smoothly blended.

15. The method of claim 5 wherein said arm simulation exactly duplicates said actual arm movements.

26. The method of claim 1 further comprising the step of performing said defining, combining, computing, and controlling steps continuously and in real-time, wherein said robot arm operates and performs said steps simultaneously.

16. A method of controlling a robot arm, said robot arm comprising a base with a central axis, n joints, a joint angle sensor device connected to each of said joints, a joint servo loop device connected to each of said joints, and two ends comprising a mobile platform end and a movable hand end, each of said joints having a joint angle specifying a rotational orientation of said joint, said hand end having m degrees of freedom of movement, wherein m is less than n and said robot arm is characterized by a degree of redundancy, n-m, said method comprising:

first defining a first m-by-n matrix for defining location and orientation of said hand end in terms of said rotation angles of said joints;

second defining a second r-by-n matrix for defining r user specified kinematic functions in terms of said joint angles, wherein r is a positive integer exceeding the degree of redundancy of said robot arm, and wherein at least one of said kinematic functions minimizes a sum of selected mechanical parameters of at least some of said joints and said selected mechanical parameters include different weighting coefficients for different ones of said joints, said weighting coefficients being able to be changed during movement of said arm;

combining said first and second matrices to produce an augmented m+r-by-n matrix;

computing in accordance with forward kinematics from said augmented m+r-by-n matrix and from the joint angles sensed by said joint angle sensor device a set of n desired joint angles and transmitting said set of n desired joint angles to said joint servo loop device to control the robot arm;

defining a translational position of said mobile platform end from said central axis of said base; and

controlling said translational position of said mobile platform end by a platform motion controller.

17. The method of claim 16 wherein said robot arm has an anthropomorphic structure and one of said joint is an elbow joint, wherein a pair of links of said arm joined together by said elbow joint define an elbow plane of said arm, wherein one of said kinematic functions comprises means for defining an orientation of said elbow plane, and wherein said platform motion controller comprises means for preselecting a wedge angle corresponding to said elbow plane and means for monitoring said orientation of said elbow plane.

18. The method of claim 17, further comprising, by said platform motion controller, the steps of:

(a) defining an initial hand end position, x_hi, of said robot arm;

(b) defining an initial orientation of said elbow plane, φ

_i ;

(c) defining lengths l₁ and l₂, respectively, of said pair of links; and

(e) commanding said mobile platform to move -Δ

_X.sbsb.h if said elbow plane does not equal said preselected wedge angle so that said elbow plane orientation returns to said preselected wedge angle and said hand position remains constant, wherein;

##EQU28##

19. The method of claim 16 wherein at least one of said kinematic functions constrains location of said arm.

27. The method of claim 16 further comprising the step of performing said defining, combining, computing, and controlling steps continuously and in real-time, wherein said robot arm operates and performs said steps simultaneously.

20. A method of controlling a robot arm said robot arm comprising a base with a central axis, n joints, joint angle sensor means connected to each of said joints, joint servo loop means connected to each of said joints, and two ends comprising a fixed pedestal end and a movable hand end, each of said joints having a joint angle specifying a rotational orientation of said joint, said hand end having m degrees of freedom of movement, wherein m is less than n and said robot arm is characterized by a degree of redundancy, n-m, said method comprising:

first defining a first m-by-n matrix for defining location and orientation of said hand end in terms of said rotation angles of said joints;

second defining a second r-by-n matrix for defining r user specified kinematic functions in terms of said joint angles, wherein r is a positive integer exceeding the degree of redundancy of said robot arm, and wherein at least one of said kinematic functions corresponds to one of,

i. minimizing a sum of gravitational torques on at least some of said joints,

ii. minimizing a sum of selected mechanical parameters of at least some of said joints, said parameters comprising velocity errors of said joints with respect to desired velocities, and

iii. minimizing a sum of selected mechanical parameters of at least some of said joints, said parameters comprising joint angle errors with respect to desired joint angles;

combining said first and second matrices to produce an augmented m+r-by-n matrix;

computing in accordance with forward kinematics from said augmented m+r-by-n matrix and from the joint angles sensed by said joint angle sensor means a set of n desired joint angles and transmitting said set of n desired joint angles to said joint servo loop means to control the robot arm;

defining a translational position of said mobile platform end from said central axis of said base; and

controlling said translational position of said mobile platform end by a platform motion controller.

21. The method of claim 20 wherein said computing operates in successive iterations, said joint angles sensed by said joint angle sensor means correspond to a current one of said iterations and said set of n desired joint angles correspond to a next one of said iterations.

22. The method of claim 21 wherein said first m-by-n matrix, second r-by-n matrix and augmented m+r-by-n matrix comprise Jacobian matrices.

23. The method of claim 21 wherein said selected mechanical parameters further include different weighting coefficients for different ones of said joints.

24. The method of claim 23 further changing said weighting coefficients during movement of said arm.

25. The method of claim 20 further comprising the steps of:

(a) operating said arm with a teleoperated commands;

(b) providing automated commands issued by a trajectory generator; and

(c) combining said teleoperated commands with said automated commands so said arm can be collectively operated by said teleoperated commands and said automated commands.

28. The method of claim 20 further comprising the step of performing said defining, combining, computing, and controlling steps continuously and in real-time, wherein said robot arm operates and performs said steps simultaneously.

29. A method of controlling a robot arm in real-time, said robot arm comprising a base with a central axis, n joints, joint angle sensor means connected to each of said joints, joint servo loop means connected to each of said joints, and two ends comprising a mobile platform end and a movable hand end, each of said joints having a joint angle specifying a rotational orientation of said joint, said hand end having m degrees of freedom of movement, wherein m is less than n and said robot arm is characterized by a degree of redundancy, said method comprising:

first defining a first m-by-n matrix for defining location and orientation of said hand end in terms of said rotation angles of said joints;

second defining a second r-by-n matrix for defining r user-specified kinematic functions in terms of said joint angles, wherein r is a positive integer exceeding to the degree of redundancy of said robot arm;

combining said first and second matrices to produce an augmented m+r-by-n matrix;

computing in accordance with forward kinematics from said augmented m+r-by-n matrix and from the joint angles sensed by said joint angle sensor means a set of n desired joint angles and transmitting said set of n desired joint angles to said joint servo loop means to control the robot arm; and

performing said defining, combining, and computing steps continuously and in real-time, wherein said robot arm operates and performs said steps simultaneously.

30. A robot arm for operating in a work envelope and performing tasks, comprising:

a base with a central axis and n joints;

a joint angle sensor device connected to each of said joints;

joint servo loop means connected to each of said joints;

two ends comprising a mobile platform end and a movable hand end;

wherein each of said joints has a joint angle specifying a rotational orientation of said joint, wherein said hand end has m degrees of freedom of movement, wherein m is less than n, and wherein said robot arm is characterized by a degree of redundancy;

means for defining a first m-by-n matrix for defining location and orientation of said hand end in terms of said rotation angles of said joints;

means for defining a second r-by-n matrix for defining r user-specified kinematic functions in terms of said joint angles, wherein r is a positive integer exceeding to the degree of redundancy of said robot arm;

means for combining said first and second matrices to produce an augmented m+r-by-n matrix; and

means for computing in accordance with forward kinematics from said augmented m+r-by-n matrix and from the joint angles sensed by said joint angle sensor device a set of n desired joint angles and transmitting said set of n desired joint angles to said joint servo loop means to control the robot arm.

31. The method of claim 30, wherein said robot arm is controlled continuously and in real-time so that said robot arm operates and performs tasks simultaneously.