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This paper presents a new adaptive controller and proof of its global asymptotic stability with respect to the standard rigid body model of robot arm dynamics. Experimental data from a study of this and other globally asymptotically stable adaptive controllers on two very different robot arms (i) reconciles several previous contrasting empirical studies (ii) demonstrates and compares their superior tracking performance (iii) examines contexts which com promise their advantage.

Assembly problems require that a robot with a few actuated degrees of freedom manipulate an environment with a greater number of unactuated degrees of freedom. Since the dynamical coupling between degrees of freedom in this setting is a function of their relative configuration, the motion of such systems is subject to constraints that preclude smooth feedback stabilization. This paper explores the extent to which assembly planning and control may be effected by recourse to some other methodical means of generating stabilizing feedback controllers. A partial solution is offered for a very simple assembly problem involving an intermittent dynamical environment.

For more information: Kod*Lab

Programming machines to operate flexibly and autonomously in the physical world seems to require a sophisticated representation that encodes simultaneously the nature of a task, the nature of the environment within which the task is to be performed, and the nature of the robot’s capabilities with respect to both. We seek a scientific methodology of robot task encoding that encompasses the desired behavioral goals and environmental conditions as well. The methodology must balance the need for flexible expression of abstract human goals against the necessity of a eliciting a predictable response from the commanded machine. This talk focuses on the problem of motion planning as an example of how we propose to say what we mean to a robot and to know what we have said.

For more information: Kod*Lab

Assembly problems require that a robot with a few actuated degrees of freedom manipulate an environment with a greater number of unactuated degrees of freedom. Since the dynamical coupling between degrees of freedom in this setting is a function of their relative configuration, the motion of such systems is subject to constraints that preclude smooth feedback stabilization. In other words, in contrast to purely geometric motion planning problems, assembly planning cannot be carried out within the limits of traditional control theory. This paper explores the extent to which assembly planning and control may be effected by recourse to some other methodical means of generating stabilizing feedback controllers.

For more information: Kod*Lab

In a continuing program of research in robotic control of intermittent dynamical tasks, we have constructed a three degree of freedom robot capable of “juggling” a ball freely in the earth’s gravitational field. This work is a direct extension of that previously reported in [5, 1, 4, 3, 2, 7].

The system consists of four major sections, all of which have been implemented on a network of twelve transputers.

This paper concerns the construction of a class of scalar valued analytic maps on analytic manifolds with boundary. These maps, which we term navigation functions, are constructed on an arbitrary sphere world—a compact connected subset of Euclidean n-space whose boundary is formed from the disjoint union of a finite number of (n − l)-spheres. We show that this class is invariant under composition with analytic diffeomorphisms: our sphere world construction immediately generates a navigation function on all manifolds into which a sphere world is deformable. On the other hand, certain well known results of S. Smale guarantee the existence of smooth navigation functions on any smooth manifold. This suggests that analytic navigation functions exist, as well, on more general analytic manifolds than the deformed sphere worlds we presently consider.

For more information: Kod*Lab

An advanced robot control system joining a GMF A-500 industrial arm with a network of Inmos Transputers is described in the context of the developing field of robotics. The robot system is used to experimentally compare conventional linear control algorithm performance with both the advanced “computer torque” inverse dynamics control algorithm and a recently developed “adaptive computed torque” algorithm.

A program of research in robotics that seeks to encode abstract tasks in a form that simultaneously affords a control scheme for the torque-actuated dynamical systems, as well as a proof that the resulting closed-loop behavior will correctly achieve the desired goals, is reviewed. Two different behaviors that require dexterity and might plausibly connote ‘intelligence’ – navigating in a cluttered environment and juggling a number of otherwise freely falling objects – are examined with regard to similarities in problem representation, method of solution, and causes of success. The central theme concerns the virtue of global stability mechanisms. At the planning level they lend autonomy, that is, freedom from dependence upon some ‘higher’ intelligence. They encourage the design of canonical procedures for model problems, which may then be instantiated in particular settings by a change of coordinates. The procedures developed result in provably autonomous behavior. Simulation results and physical experimental studies suggest the practicability of these methods.

Assembly problems require that a robotic system with fewer actuated degrees of freedom manipulate an environment with a greater number of unactuated degrees of freedom. This paper explores the possibilities of combining a navigation plan for an “animated” version of the environment with a juggling plan that mediates between the conflicting subgoals of that unconstrained world. The hope is to develop a formalism for constructing globally stabilizing feedback controllers for the nonholonomically constrained dynamical systems that represent the underlying problem.

The performance of real-time distributed control systems is shown to depend critically on both communication and computation costs. A taxonomy for distributed system performance measurement is introduced. A roughly accurate method of performance prediction for simple systems is presented. Experimental results demonstrate the effects of communication protocols on real-world system performance.