Progress in spatial robot juggling

We review our progress to date in eliciting dynamically dexterous behaviors from a three degree of freedom direct drive robot manipulator whose real-time stereo cameras provide 60 Hz sampled images of multiple freely falling bodies in highly structured lighting conditions. At present, the robot is capable of forcing a single ping-pong ball into a specified steady state (near) periodic vertical motion by repeated controlled impacts with a rigid paddle. The robot sustains the steady state behavior over long periods (typically thousands and thousands of impacts) and is capable of recovering from significant unexpected adversarial perturbations of the ball\u27s flight phase. Gain tuning experiments corroborate our contention that the stability mechanism underlying the robot\u27s reliability can be attributed to the same nonlinear dynamics responsible for analogous behavior in a one degree of freedom forebear. We are presently extending an algorithm for simultaneously juggling two bodies developed in that earlier work to the three dimensional case

Further progress in robot juggling: the spatial two-juggle

We report on our recently achieved spatial two-juggle: 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 the previously reported one-juggle, we describe our initial approach to the two-juggle planning and control problem. We have developed a number of important refinements to our initial strategy in the course of getting the system to work, and these are reported in some detail. The paper concludes with a discussion of some data from typical two-juggle runs in the laboratory

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

Sequential Composition of Dynamically Dexterous Robot Behaviors

We report on our efforts to develop a sequential robot controller-composition technique in the context of dexterous “batting” maneuvers. A robot with a flat paddle is required to strike repeatedly at a thrown ball until the ball is brought to rest on the paddle at a specified location. The robot’s reachable workspace is blocked by an obstacle that disconnects the free space formed when the ball and paddle remain in contact, forcing the machine to “let go” for a time to bring the ball to the desired state. The controller compositions we create guarantee that a ball introduced in the “safe workspace” remains there and is ultimately brought to the goal. We report on experimental results from an implementation of these formal composition methods, and present descriptive statistics characterizing the experiments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67990/2/10.1177_02783649922066385.pd

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 manager

On the Control of a One Degree-of-Freedom Juggling Robot

International audienceThis paper is devoted to the feedback control of a one degree-of-freedom (dof) juggling robot, considered as a subclass of mechanical systems subject to a unilateral constraint. The proposed approach takes into account the whole dynamics of the system, and focuses on the design of a force input. It consists of a family of hybrid feedback control laws, that allow to stabilize the object around some desired (periodic or not) trajectory. The closed-loop behavior in presence of various disturbances is studied. Despite good robustness properties, the importance of good knowledge of the system parameters, like the restitution coefficient, is highlighted. Besides its theoretical interest concerning the control of a class of mechanical systems subject to unilateral constraints, this study has potential applications in non-prehensile manipulation, extending pushing robotic tasks to striking-and-pushing tasks

Toward a Dynamical Pick and Place

We report on our initial efforts to build robot feedback controllers that develop increased capability from simpler constituent controllers. Previous work with our three degree of freedom robot has resulted in a machine that exhibits various dynamically dexterous skills of superlative ability but very narrow behavioral scope. We focus here on the development of both a formalism and practice for the composition of constituent controllers. The composite should yield automatically purposive combinations of these skills that reach goals no one of the defining controllers could have achieved in isolation. The specific task we initially target, the dynamical pick and place , requires the robot to acquire balls that have been randomly thrown into its work space and set them safely at rest in a specified location. We present a brief overview of the constituent behaviors and a mechanism for their combination along with documentation of our preliminary empirical successes

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. For more information: Kod*La