Alfred A. Rizzi

Comparative experiments with a new adaptive controller for robot arms

A model-based adaptive controller and proof of its global asymptotic stability with respect to the standard rigid-body model of robot-arm dynamics are presented. Experimental data from a study of one new and several established globally asymptotically stable adaptive controllers on two very different robot arms: (1) demonstrate the superior tracking performance afforded by the model-based algorithms over conventional PD control; (2) demonstrate and compare the superior performance of adaptive model-based algorithms over their nonadaptive counterparts; (3) reconcile several previous contrasting empirical studies; and (4) examine contexts that compromise their advantage. >

Further progress in robot juggling: the spatial two-juggle

A spatial two-juggle is discussed. The device has the ability to bat two freely falling balls into stable periodic vertical trajectories with a single three degree-of-freedom robot arm using a real-time stereo camera system for sensory input. After a brief review of a previously-reported one-juggle, the authors initial approach to the two-juggle planning and control problem is described. A number of important refinements to their initial strategy are given. Data from typical two-juggle runs in the laboratory are given.<<ETX>>

An active visual estimator for dexterous manipulation

We present a working implementation of a dynamics based architecture for visual sensing. This architecture provides field rate estimates of the positions and velocities of two independent falling balls in the face of repeated visual occlusions and departures from the field of view. The practical success of this system can be attributed to the interconnection of two strongly nonlinear dynamical systems: a novel triangulating state estimator; and an image plane window controller. We detail the architecture of this active sensor, provide data documenting its performance, and offer an analysis of its soundness in the form of a convergence proof for the estimator and a boundedness proof for the controller.

Distributed real-time control of a spatial robot juggler

The Yale spatial juggler and an emerging set of working principles for the design and implementation of embedded real-time distributed controllers are described. The robot uses a distributed network of transputers to process stereo camera data and control the torque of a three-degree-of-freedom arm to juggle a ball. The juggling algorithm is a direct extension of a novel class of nonlinear feedback controllers, called mirror laws. The algorithm takes the form of a mathematical expression that specifies robot position as a function of the balls position and velocity. The programming approach, called geometric programming, substitutes event-driven dynamical processes and geometrical transformations for a more syntactically oriented if-then-else approach.<<ETX>>

Further progress in robot juggling: solvable mirror laws

In previous papers we have reported successful laboratory implementations of a family of juggling algorithms. In all but the one degree of freedom case, these empirically successful algorithms have so far resisted our analytical efforts to explain why they work. This is in large measure a consequence of our inability to write down using elementary functions an expression for the closed loop dynamics they induce. We discuss in this paper a modified juggling algorithm whose resulting closed loop dynamics can be written down directly. We offer data establishing the empirical success of the new algorithm. Theoretical analysis of the closed loop dynamics is presently in progress.<<ETX>>

A "robust" convergent visual servoing system

This paper describes a simple visual servoing control algorithm capable of robustly positioning a three degree of freedom end effector based only on information from a stereo vision system. The proposed control algorithm does not require estimates of the grippers spatial position, a significant source of calibration sensitivity. The controller is completely immune to positional camera calibration errors, and we demonstrate robustness to orientation miscalibration through a series of simulations and experiments.

Preliminary Experiments in Spatial Robot Juggling

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 falling freely in the earths gravitational field. This work is a direct extension of that previously reported in [7, 3, 5, 4]. The present paper offers a comprehensive description of the new experimental apparatus and a brief account of the more general kinematic, dynamical, and computational understanding of the previous work that underlie the operation of this new machine.

A Dynamical Sensor for Robot Juggling

We discuss the sensory management strategy that has evolved over the course of our efforts to build a three degree of freedom robot capable of juggling two balls at once . A field rate stereo camera system passes estimates of the balls’ positions to a juggling algorithm that drives the robot’s joint actuators. In order to meet the stringent real-time constraints imposed by such a visual servoing task, we have found it necessary to pay increasingly careful attention to our strategy for controlling the dynamics of the camera window management system. The paper concludes with an initial attempt to formalize this control problem. For more information: Kod*Lab Disciplines Electrical and Computer Engineering | Engineering | Systems Engineering Comments Electronic version of an article published as [World Scientific Series in Robotics and Intelligent Systems, Volume 7, 1993, 229-256] [DOI: 10.1142/9789814503709_0008]

Toward the control of attention in a dynamically dexterous robot

In the recent successful effort to achieve the spatial two-juggle - batting two freely falling balls into independent stable periodic vertical orbits by repeated impacts with a three degree of freedom robot arm, the authors have found it necessary to introduce a dynamical window manager into their real-time stereo vision. This paper describes these necessary enhancements to the original vision system and then proposes a more formal account of how such a feedback based sensor might be understood to work. Further experimentation will be required to determine the extent to which the analytical model explains (and might thus be used as a tool to improve) the performance of the system presently working in the laboratory.

Toward Obstacle Avoidance in Intermittent Dynamical Environments

In this paper we discuss a robotic task requiring dynamical safety in the face of an intermittent environment. We define and offer examples of this notion. We then construct a dynamically safe composite controller from dynamically safe constituents, and present empirical evidence of its effectiveness.