Hybrid robot motion task level control system

Details Hybrid robot motion task level control system Hybrid robot motion task level control system

2001-04-20

2002-09-24

Cuchlinski, Jr., William A. (Department: 3661)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Robot control

C700S029000, C700S031000, C700S059000, C700S063000, C700S250000, C700S258000, C700S260000, C700S261000, C700S262000, C700S263000, C700S264000, C318S568170, C318S572000, C318S578000, C901S006000, C901S009000, C901S033000, C901S034000, C901S035000, C901S041000, C701S023000

Reexamination Certificate

active

06456901

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to robot controllers and, more particularly, a hybrid control system for controlling the movement of a robot in the neighbor of and at kinematic singular configurations.
A robot task is usually described in its task space. The direct implementation of a task level controller can provide significant application efficiency and flexibility to a robotic operation. Implementation of the task level controller becomes even more important when robots are working coordinately with humans. The human intuition on a task is always represented in the task space. However, the major problem in the application of the task level controller is the existence of kinematic singularities. While approaching a singular configuration, the task level controller generates high joint torques which result in instability or large errors in task space. The task level controller is not only invalid at the singular configuration, but also unstable in the neighborhood of the singular configuration. Therefore, a myriad of methods have been proposed to solve this problem.
For instance, the Singularity-Robust Inverse (SRI) method was developed to provide an approximate solution to the inverse kinematics problem around singular configurations. Since the Jacobian matrix becomes ill-conditioned around the singular configurations, the inverse or pseudoinverse of the Jacobian matrix results in unreasonable torques being applied by a task level controller. Instead, the SRI method uses a damped least-squares approach (DLS) to provide approximate motion close to the desired Cartesian trajectory path. The basic DLS approach has been refined by varying the damping factors to improve tracking errors from the desired trajectory path. By considering the velocity and acceleration variables, the SRI method can be further improved to reduce the torque applied to individual joints and achieve approximate motion. By allowing an error in the motion, the SRI method allows the robot to pass close to, but not go through a singularity point. It can be shown that such a system is unstable at the singular points. This means that robot movement can not start from or can not actually reach the singularity points. Obviously, this creates difficulties for many robot applications.
In another instance, a path tracking approach augments the joint space by adding virtual joints to the manipulator and allowing self motion. Based on the predictor-corrector method of path following, this approach provides a satisfactory solution to the path tracking problem at singular configurations. Timing is not considered at the time of planning and it is reparameterized in solving the problem. However, when a timing is imposed on the path, it forces the manipulator to slow down in the neighborhood of singular configurations and to stop at the singular configuration.
The normal form approach provides a solution of inverse kinematics in the entire joint space. With appropriately constructed local diffeomorphic coordinate changes around the singularity, the solution of inverse kinematics can be found and then transformed back to the original coordinates. All joint space solutions are obtained by gluing together the regular and the singular piece. The normal form method is heavily computationally involved. In addition, it is experimentally difficult to implement it in real-time.
Finally, a time re-scale transformation method for designing robot controllers also incorporates the dynamic poles of the system. This method achieves slow poles in the vicinity of a singularity configuration and fast poles in the regular area. It can be shown that this method results in similar error dynamics as found in the SRI method.
Therefore, it is desirable to design a hybrid robot motion control system which is stable in the entire robot workspace including at the singularity configurations. Based on the analysis of the singular configurations of nonredundant robot manipulators, the robot workspace is divided into subspaces by the singularity configurations. In different subspaces, different continuous robot controllers could be used. A hybrid system approach is used to integrate different continuous robot controllers and singularity conditions are adopted as switching conditions for discrete control. With the hybrid motion control system, a robot can pass by singular configurations and achieve a stable and continuous motion in the entire workspace.
SUMMARY OF THE INVENTION
In accordance with the present invention, a hybrid control system is provided for controlling the movement of a robot. The hybrid control system includes a singularity detector; a task level controller that receives a motion plan and determines a first set of control commands which are defined in a task space; and a joint level controller that receives the motion plan and determines a second set of control commands which are defined in a joint space. The singularity detector monitors the movement of the robot and detects robot movement in a region about a singularity configuration. When robot movement occurs outside of this region, the task level controller is operable to issue the first set of control commands to the robot. When the robot movement occurs inside of this region, the joint level controller is operable to issue the second set of control commands to the robot. In this way, the hybrid control system of the present invention ensures feasible robot motion in the neighborhood of and at kinematic singularity configuration.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.


REFERENCES:
patent: 36929 (1862-11-01), Workman
patent: 4356440 (1982-10-01), Curtiss et al.
patent: 4621332 (1986-11-01), Sugimoto et al.
patent: 4987356 (1991-01-01), Yamada et al.
patent: 5265295 (1993-11-01), Jinno et al.
patent: 5276390 (1994-01-01), Fisher et al.
patent: 5442269 (1995-08-01), Takayama et al.
patent: 5509847 (1996-04-01), Jinno et al.
patent: 5579442 (1996-11-01), Kimoto et al.
patent: 5590034 (1996-12-01), Snell
patent: 5646493 (1997-07-01), Hara et al.
patent: 5880956 (1999-03-01), Graf
patent: 6039290 (2000-03-01), Wie et al.
patent: 6067862 (2000-05-01), Murray et al.
patent: 6092004 (2000-07-01), Harima
patent: 6181983 (2001-01-01), Schlemmer et al.
patent: 6204620 (2001-03-01), McGee et al.
patent: 6278906 (2001-08-01), Piepmeier et al.
Osumi et al., Cooperative control of two industrial robots with force control devices, 1995, IEEE, pp. 550-555.*
Egeland et al., A note Lyapunov stability for an adaptive robot controller, 1994, IEEE, pp. 1671-1673.*
Fjellstad et al., Singularity-free tracking of unmanned underwater vehicles in 6 DOF, 1994, IEEE, pp. 1128-1133.*
Osumi et al., Cooperative control between multiple manipulators with flexibility, 1993, IEEE, pp. 1935-1940.*
A. K. Bejczy, S. Lee, “Robot Arm Dynamic Model Reduction for Control,” Proceedings of IEEE Conference on Decision and Control, San Antonio, Tex, pp. 1466-1476, 1983.
B. E. Bishop, M. W. Spong, “Control of Redundant Manipulators Using Logic-Based Switching,” Proceedings of IEEE Conference on Decision and Control, Leuven, Belgium, pp2664-2669, May 1998.
M. S. Branicky, “Multiple Lyapunov Functions and Other Analysis Tools for Switched and Hybrid Systems,” IEEE Transactions on Automatic Control, vol. 43, No. 4, 1998, pp. 475-482.
F. Cheng, T. Hour, Y. Sun, T. H. Chen, “Study and Rosolution of Singularities for a 6 DOF PUMA Manipulators,” IEEE Transactions on systems, Man and Cybernetics B: Cybernetics, vol.27, No.2, Apr. 1997, pp. 332-343.
S. Chiaverini, B. Siciliano, O. Egeland, “Review of the Damped Least-Squares Inverse Kinematics with Experiments on an Industrial Robot Manipulator,” IEEE Trans. Control System Technology, vol.2, No.2, Jun. 1994, pp. 123-134.
Fabrizio Caccavale, Setfano Chiaverini, and Bruno Siciliano, “Second-Order Kinematic Control of Robot Manipulators with Jacobian Damped Least-Squares Inverse: Theory and Experiments,” IEEE/ASME Transactions

Affiliated with

Also associated with

Rating

Hybrid robot motion task level control system does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Hybrid robot motion task level control system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hybrid robot motion task level control system will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2905458