Non-Linear muscle-like compliant controller

Details Non-Linear muscle-like compliant controller Non-Linear muscle-like compliant controller

1999-03-19

2001-06-05

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

Data processing: generic control systems or specific application

Specific application, apparatus or process

Robot control

C700S245000, C700S251000, C700S260000, C700S261000, C700S248000, C700S259000, C700S045000, C700S263000, C901S009000, C901S015000, C901S018000, C901S045000, C600S341000, C600S407000, C600S410000, C600S526000, C600S587000, C318S568100, C318S568110, C318S568180, C318S561000

Reexamination Certificate

active

06243624

ABSTRACT:

TECHNICAL FIELD
The present invention is directed to a compliant controller and more particularly to a compliant controller that provides simultaneous control of position and force in the same direction and without the use of a force sensor.
BACKGROUND OF THE INVENTION
In order to control multiple joints of an industrial robot, an upper level planning controller provides commands to one or more PID controllers. A PID controller is provided for each joint of the robot and is coupled to an actuator, such as a motor or the like, that controls movement of the joint. The PID controller may not be programmed as a compliant controller that provides both position control and force control in response to commands from the planning controller.
Known compliant controllers provide position control and force control for a joint or actuator by switching between a position control algorithm and a force control algorithm as needed. Heretofore, such complaint controllers have not been able to simultaneously provide position and force control in the same direction. Typically, with these known controllers, if a joint is to move in the X direction and apply a force in the X direction, the position control algorithm would be used to move the joint to a desired or commanded position, at which point the movement of the joint would be stopped after a controlled deceleration and the controller would switch to the force control algorithm. In order to control force, known compliant controllers require force sensors to monitor the forces encountered by the actuator so that the force control can provide the appropriate response. During position control, if an unexpected, i.e., disturbing force is encountered, known position controllers respond by increasing the output torque of the actuator in an attempt to overcome the disturbing force and reach the desired position. This can result in damage to the actuator. In attempting to overcome this problem, complex software programs have been developed to control the switching between the position and force controls and to account for the decelerations, etc., associated with stopping movement in order to switch. Because these controllers are so complex and are not sufficiently adaptable to a wide range of disturbing forces, they have not been widely adopted in industry.
As an alternative to known types of compliant controllers discussed above, research has been conducted to control robot joints based on a biological model such as a primate muscle. This research has also extended into using the biological model of a primate muscle for active suspension control. This research is described in the following articles. Wu, C. H., J. C. Houk, K. Y. Young, and L. E. Miller, “Nonlinear Damping of Limb Motion” book chapter, Multiple Muscle Systems: Biomechanics and Movement Organization edited by J. M. Winters and S. L-Y. Woo, Springer-Verlag New York Publishers, 1990, pp. 214-235. Wu, C. H., K. Y. Young, and J. C. Houk, “A neuromuscular-Like Model for Robotic Compliance Control,”
Proceedings of
1990
IEEE Int. Conference on Robotics and Automation
, Cincinnati, Ohio, May 1990, pp. 1885-1890. Wu, C. H., K. Y. Young, and K. S. Hwang, “Analysis of Voluntary Movements for Robotic Control,” IEEE 1991
International Conference on Robotics and Automation
, Sacramento, Calif., Apr. 1991. Wu, C. H., K. Y. Young, K. S. Hwang, and S. Lehman, “Voluntary Movements for Robotic Control,” IEEE
Control Systems Magazine
, Vol. 2, No. 1, February 1992, pp. 8-14. Wu, C. H. and K. S. Hwang, “Nonlinear Neuromuscular Control for Robotic Compliance Control,”
Proceedings of the
1993
IEEE International Symposium on Intelligent Control
, August 1993, 238-243. Wu, C. H. and S. L. Chang, “Implementation of a Neuromuscular-like Control for Compliance on A PUMA 560 Robot,”
Proceedings of the
34
th
IEEE International Conference on Decision and Control
, New Orleans, La., Dec. 1995, 1597-1602. Wu, C. H., S. L. Chang, and D. T. Lee, “A Study of Neuromuscular-like Control for Rehabilitation Robots,”
Proceedings of the
1996
IEEE International Conference on Robotics and Automation
, Minneapolis, Minn., April 1996. Chang, S.L. and C.H. Wu, “Design of an Active Suspension System Based on a Biological Model,”
Proceedings of
1997
American Control Conference
, Albuquerque, N. Mex., June 1997. Wu, C. H., K. S. Hwang, and S. L. Chang, “Analysis and Implementation of a Neuromuscular-like Control for Robotic Compliance,”
IEEE Transactions on Control Systems Technology
, Vol. 5, No. 6, November 1997, pp. 586-597. However, the implementation of the biological model to form a compliant controller suitable for commercialization has been a complex task.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, the disadvantages of prior compliant controllers have been overcome. The present invention implements a biological model of a primate muscle for a compliant controller so as to provide simultaneous position and force control with nonlinear damping for an actuator. The implementation of the present invention allows the compliant controller to easily adapt its output to an unknown and/or unexpected force, i.e., a disturbing force, that is encountered without requiring the use of a force sensor. The compliant controller of the present invention can adapt to a wide range of disturbing forces varying up to 1000 fold without the need to change the controller's internal gain settings.
More particularly, the compliant controller of the present invention does not require the use of force sensors, but instead uses at least one position sensor. The position sensor detects or senses the output position of the actuator. The actuator may be an electric actuator such as a motor, a hydraulic actuator or a pneumatic actuator, etc., the output force or torque of which is being controlled by the compliant controller. The output of the position sensor is coupled to a processor that operates in accordance with a force determining algorithm to determine an output actuating force for the actuator. The force determining algorithm is a function of an initial actuator position, a subsequently sensed actuator position, a commanded, i.e. desired, actuator position and a position calculated from a nonlinear damping function. The processor compares the difference between an initial actuator position and a subsequently sensed actuator position to a value representing a predetermined amount of actuator movement. If the difference between the initial and subsequently sensed actuator positions is less than the predetermined amount of movement, the processor resets the calculated position to a predetermined value to immediately reduce the actuating force in the presence of a disturbing force. If the difference between the initial and subsequently sensed actuator positions is greater than the predetermined amount of movement, the processor sets the initial actuator position to the value of the subsequently sensed actuator position so that the compliant controller can quickly and precisely enable an actuator to attain a commanded position in the absence or removal of the disturbing force.
Unlike prior controllers, there is no need to program deceleration profiles in order to stop the movement of the actuator to switch between position and force controls because the compliant controller
10
of the present invention simultaneously controls position and force. The force determining algorithm in combination with the setting of the calculated position and the setting of the initial position depending upon the amount of sensed actuator output movement, allows the actuator controlled by the compliant controller to quickly attain and stop at a desired position. It allows the controller to automatically respond to a disturbing force encountered by the actuator output by absorbing the force and quickly reducing the controlled actuator output force. The force determining algorithm maintains at least a small amount of actuator output force in the presence of a disturbing force so that when the disturbing force is removed, the

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