Increasing the Dexterity of Redundant Robots

NASA's Jet Propulsion Laboratory, Pasadena, California

Configuration control is emerging as an effective way to control the motions of a robot that has more degrees of freedom than are necessary to define the trajectory of the end effector and/or of the object to be manipulated. The extra or redundant degrees of freedom can be used to give the robot humanlike dexterity and versatility. In configuration control, the configuration of the robot is represented mathematically by a set of configuration variables, which is a generalized coordinate vector that is more relevant to the overall task than is the vector of joint coordinates that appears in conventional approaches to control. The generalized coordinate vector consists of the coordinates of the end effector in task space, plus a number of kinematic functions that involve the redundant degrees of freedom. The basic task of the control system is to make the coordinates of the end effector follow the desired trajectory. The kinematic functions can be selected to define an additional task Q for example, the avoidance of obstacles or kinematic optimization to enhance manipulability. In effect, the additional task defines the trajectory in the redundant degrees of freedom (see figure). The configuration variables can be used in an adaptive control scheme, which does not require knowledge of the complicated mathematical model of the dynamics of the robot or the parameters of the object to be manipulated. The configuration-control method can be implemented in either a centralized or a decentralized control system. Because configuration control is computationally very fast, it is suitable for the development of algorithms for the real-time con trol of robots.

More details can be found in:

Seraji, H., Long, M., and Lee, T. S.: RMotion control of 7 DOF arms: The configuration control approach,S IEEE Trans. on Robotics and Automation, 1993, 9(2), pp. 125-139.

Point of Contact:
Homayoun Seraji,
Mail Stop 198-219
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
seraji@telerobotics.jpl.nasa.gov

Telerobotics Program page

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Last updated: May 10, 1996