John T. Feddema

Decentralized control of cooperative robotic vehicles: theory and application

Describes how decentralized control theory can be used to analyze the control of multiple cooperative robotic vehicles. Models of cooperation are discussed and related to the input/output reachability, structural observability, and controllability of the entire system. Whereas decentralized control research in the past has concentrated on using decentralized controllers to partition complex physically interconnected systems, this work uses decentralized methods to connect otherwise independent nontouching robotic vehicles so that they behave in a stable, coordinated fashion. A vector Liapunov method is used to prove stability of two examples: the controlled motion of multiple vehicles along a line and the controlled motion of multiple vehicles in formation. Also presented are three applications of this theory: controlling a formation, guarding a perimeter, and surrounding a facility.

Weighted selection of image features for resolved rate visual feedback control

The authors develop methodologies for the automatic selection of image features to be used to visually control the relative position and orientation (pose) between the end-effector of an eye-in-hand robot and a workpiece. A resolved motion rate control scheme is used to update the robots pose based on the position of three features in the cameras image. The selection of these three features depends on a blend of image recognition and control criteria. The image recognition criteria include feature robustness, completeness, cost of feature extraction, and feature uniqueness. The control criteria include system observability, controllability, and sensitivity. A weighted criteria function is used to select the combination of image features that provides the best control of the end-effector of a general six-degrees-of-freedom manipulator. Both computer simulations and laboratory experiments on a PUMA robot arm were conducted to verify the performance of the feature-selection criteria. >

Control for slosh-free motion of an open container

This article describes two methods for controlling the surface of a liquid in an open container as it is being carried by a robot arm. Both methods make use of the fundamental mode of oscillation and damping of the liquid in the container as predicted from a boundary element model of the fluid. The first method uses an infinite impulse response filter to alter the acceleration profile so that the liquid remains level except for a single wave at the beginning and end of the motion. The motion of the liquid is similar to that of a simple pendulum. The second method removes the remaining two surface oscillations by tilting the container parallel to the beginning and ending wave. A double pendulum model is used to determine the trajectory for this motion. Experimental results of a FANUC S-800 robot moving a 230 mm diameter hemispherical container of water are presented.

Experimental verification of a command shaping boom crane control system

Presents experimental results of a command shaping control method for suppressing payload swing caused by operator commanded manoeuvres, in rotary, ship-based, boom cranes. The crane configuration investigated, consists of a payload mass that swings on the end of a spherical pendulum of varying lift-line length (hoisting). The lift-line is attached to a boom capable of elevation (luffing) and rotation about a vertical axis (slewing). Positioning of the payload is accomplished through luff, slew and hoist commands issued in real-time by an operator. The command shaping strategy, consisting of a time-varying filter, reduces payload oscillation by 18 dB in experiments using the 1/16th scale Navy Crane Testbed at Sandia National Laboratories.

Decentralized Control of Cooperative Robotic Vehicles

This paper describes how decentralized control theory can be used to control multiple cooperative robotic vehicles. Models of cooperation are discussed and related to the input/output reachability and structural observability and controllability of the entire system. Whereas decentralized control research in the past has concentrated on using decentralized controllers to partition complex physically interconnected systems, this work uses decentralized methods to connect otherwise independent non-touching robotic vehicles so that they behave in a stable, coordinated fashion. A vector Liapunov method is used to prove stability of a single example: the controlled motion of multiple vehicles along a line. The results of this stability analysis have been implemented on two applications: a robotic perimeter surveillance system and self-healing minefield.

Whole arm obstacle avoidance for teleoperated robots

This paper describes a collision avoidance system using Whole Arm Proximity (WHAP) sensors on a PUMA 560 robot arm. The capacitance-based sensors generate electric fields which can completely encompass the robot arm and detect obstacles as they approach from any direction. The directional obstacle information, gathered by the WHAP sensors together with the sensor geometry and robot configuration is used to scale the commanded joint velocities of the robot. A linearized relationship between the WHAP sensor reading and the distance from the obstacle allows direct transformation of perturbations in WHAP readings to perturbations in joint velocities. The WHAP reading is used to directly reduce the component of the command input velocity along the normal axis of the sensor, allowing graceful reductions in speed as the arm approaches the obstacle. By scaling only the component of the velocity vector in the direction of the nearest obstacles, the control system restricts motion in the direction of obstacles while permitting unconstrained motion in other directions.<<ETX>>

Flexible Robot Dynamics and Controls

Contents. 1. Introduction. 2. Mathematical Preliminaries. 3. Flexible Robot Dynamic Modeling. 4. System Identification. 5. Input Shaping for Path Planning. 6. Linear Feedback Control. 7. Nonlinear Systems and Sliding Mode Control. 8. Adaptive Sliding Mode Control. Appendix A: VF02AD Optimization. Appendix B: MATLAB%% Optimization. Appendix C: Hardware & Software Support.

Cooperative Sentry Vehicles And Differential GPS Leapfrog

As part of a project for the Defense Advanced Research Projects Agency, Sandia National Laboratories’ Intelligent Systems & Robotics Center is developing and testing the feasibility of using a cooperative team of robotic sentry vehicles to guard a perimeter, perform a surround task, and travel extended distances. This paper describes our most recent activities. In particular, this paper highlights the development of a Differential Global Positioning System (DGPS) leapfrog capability that allows two or more vehicles to alternate sending DGPS corrections. Using this leapfrog technique, this paper shows that a group of autonomous vehicles can travel 22.68 kilometers with a root mean square positioning error of only 5 meters.

Visual servoing and CAD-driven microassembly

The authors describe current research and development on a robotic visual servoing system for assembly of LIGA (lithography galvonoforming abforming) parts. The workcell consists of an AMTI robot, precision stage, long working distance microscope, and LIGA fabricated tweezers for picking up the parts. Fourier optics methods are used to generate synthetic microscope images from CAD drawings. These synthetic images are used off-line to test image processing routines under varying magnifications and depths of field. They also provide reference image features which are used to visually servo the part to the desired position. Currently, we can visually servo a 100 micron outside diameter LIGA gear to a desired x,y reference position as determined from a synthetic image of the gear.

CAD-driven microassembly and visual servoing

This paper describes current research and development on a robotic visual servoing system for assembly of LIGA (lithography galvanoforming abforming) parts. The workcell consists of an AMTI robot, precision stage, long working distance microscope, and LIGA fabricated tweezers for picking up the parts. Fourier optics methods are used to generate synthetic microscope images from CAD drawings. These synthetic images are used off-line to test image processing routines under varying magnifications and depths of field. They also provide reference image features which are used to visually servo the part to the desired position.