Bill Goodwine

Toward a Science of Cyber–Physical System Integration

System integration is the elephant in the china store of large-scale cyber-physical system (CPS) design. It would be hard to find any other technology that is more undervalued scientifically and at the same time has bigger impact on the presence and future of engineered systems. The unique challenges in CPS integration emerge from the heterogeneity of components and interactions. This heterogeneity drives the need for modeling and analyzing cross-domain interactions among physical and computational/networking domains and demands deep understanding of the effects of heterogeneous abstraction layers in the design flow. To address the challenges of CPS integration, significant progress needs to be made toward a new science and technology foundation that is model based, precise, and predictable. This paper presents a theory of composition for heterogeneous systems focusing on stability. Specifically, the paper presents a passivity-based design approach that decouples stability from timing uncertainties caused by networking and computation. In addition, the paper describes cross-domain abstractions that provide effective solution for model-based fully automated software synthesis and high-fidelity performance analysis. The design objectives demonstrated using the techniques presented in the paper are group coordination for networked unmanned air vehicles (UAVs) and high-confidence embedded control software design for a quadrotor UAV. Open problems in the area are also discussed, including the extension of the theory of compositional design to guarantee properties beyond stability, such as safety and performance.

MICAbot: a robotic platform for large-scale distributed robotics

This paper presents a novel robotic platform for experimental research in large-scale distributed robotics and mobile sensor networks. The MICAbot is both inexpensive and flexible making it useful for a wide range of experimental goals. In this paper, we provide a description of the MICAbot design. Furthermore, we also discuss general design considerations involved in designing large-scale distributed robots focusing on cost, size, and functionality.

Controllability of kinematic control systems on stratified configuration spaces

This paper considers nonlinear kinematic controllability of a class of systems called stratified. Roughly speaking, such stratified systems have a configuration space which can be decomposed into sub-manifolds upon which the system has different sets of equations of motion. For such systems, considering the controllability is difficult because of the discontinuous form of the equations of motion. The main result in this paper is a controllability test, analogous to Chows theorem, is based upon a construction involving distributions, and the extension thereof to robotic gaits.

Control of cyberphysical systems using passivity and dissipativity based methods

Abstract In cyberphysical systems, where compositionality of design is an important requirement, passivity and dissipativity based design methods have shown a lot of promise. Although these concepts are classical, their application to cyberphysical systems poses new and interesting challenges. The aim of this paper is to summarize some of the on-going work in this area by the authors.

Controlling Unstable Rolling Phenomena

The paper addresses dynamic and control issues related to a dynamical model called the classi cal shimmying wheel. The classical shimmying wheel models the rolling dynamics of many physical rolling systems such as aircraft nose wheels, motorcycles, automotive systems, and tractor-trailer systems. Such a system can exhibit undesirable unstable rolling motion, that is, shimmying, which can often lead to disastrous results. Prior work with this particular model has focused on the stability of the system as well as an analysis of the qualitative nature of its dynamics, including numerical observation of possible chaotic behavior. Such behavior is observed when the rolling element is allowed to slip under certain conditions, which is intended to realistically model real physical rolling systems. In cases where the rolling dynamics of the system arc un stable, the dynamics are characterized by the presence of an attractor wherein the system repeatedly switches back and forth between rolling and slipping. We present a slightly different, but more realistic, condition for the rolling element to switch from pure rolling to a slipping state and observe similar behavior. Additionally, we present a controller for the system designed using the method of feedback linearization. This controller stabilizes the purely rolling system but fails to always stabilize the system that is allowed to slip. We in vestigate the conditions under which the controller stabilizes the slipping system and propose an effective alternative control strategy for the slipping system for the case when the original controller fails to stabilize the system and where the uncontrolled rolling system is unstable. Finally, we investigate the stability of the system about operating points that are not equilibrium points, which models a physical system executing a turn.

Gait controllability for legged robots

We present a general method for determining controllability of a class of kinematic legged robots. The method is general in that it is independent of the robots morphology; in particular, it does not depend upon the number of legs. Our method is based on an extension of a nonlinear controllability test for smooth systems to the legged case, where the relevant mechanics are not smooth. Our extension is based on the realization that legged robot configuration spaces are stratified. The result is illustrated with a simple example.

Motion Planning for Nonlinear Symmetric Distributed Robotic Formations

This paper develops a motion planning algorithm which exploits symmetries in distributed systems to reduce motion planning computation complexity. Symmetries allow for algebraic manipulations that are computationally costly, which normally must be carried out for each component in a distributed system, to be related among various symmetric components in a distributed system by a simple algebraic relationship. This leads to a large reduction in the complexity of the overall motion planning problem for a group of distributed mobile robotic agents. In particular, due to the manner in which a symmetric system is defined, the structure of the Chen—Fliess—Sussmann differential equations has a simple relationship among various symmetric components of a distributed system. Essentially, symmetries are defined in a manner which preserves the Lie algebraic structure of each component. In a system with distributed computational capability, the motion planning computations may be distributed throughout formation in such a way that the objectives of the formation are satisfied and collision avoidance is guaranteed. The algorithm maintains a rigid body formation at the beginning and end of the trajectory, as well as possibly specified intermediate points. Due to the generally nonholonomic nature of mobile robots, guaranteeing a rigid body formation during the intermediate motion is impossible. However, it is possible to bound the magnitude of the deviation from the rigid body formation at any point along the trajectory. Simulation and experimental results are provided to demonstrate the utility of the algorithm.

Regularizing Shear Layer for Adaptive Optics Control Applications

*** † ‡ § This paper uses a discrete-vortex code to examine a shear layer’s response to forcing at its origin. The code and its thermodynamic overlay have been used in previous studies to predict the optically-aberrating characteristics of relatively-high-Mach-number, subsonic shear layers that can be classified as weakly compressible. The results reported in this study are again directed toward the shear layer’s optical characteristics; however, the intent was to use forcing to create periodic aberrating fields, referred to as “regularized” shear-layer aberrations. The study shows that the use of single-frequency forcing produces a regularized shear layer for distances preceding the point where the unforced shear layer’s natural frequency occurs. In the case of the forced shear layer, a greater thickness is produced closer to its point of origin until collapsing onto the unforced shear layer thickness past the point of regularization. The aberration periodicity is shown to have lower robustness toward the furthest downstream extent of regularization due to uncontrolled pairing. This region is made more regular by applying both fundamental and subharmonic forcing at the shear layer’s origin; however, such subharmonic forcing is sensitive to the phasing of the fundamental to that of the subharmonic.

Vision-Based Control of a Mobile Base and On-Board Arm

In this paper we present a new methodology to achieve vision-based control using a mobile manipulator to reach a required three-dimensional target position and orientation. Examples of mobile manipulators include standard forklifts and backhoes, which have a fixed manipulator mounted on a mobile platform. The overall objective of this methodology is to apply the nonholonomic degrees of freedom represented by two independently driven wheels together with the holonomic dexterity of the on-board arm in order to bring about a desired positioning objective for the arm. Mobile Camera-Space Manipulation and an extended Kalman filter are implemented to use a minimum number of holonomic and nonholonomic degrees of freedom as required for the end member of the on-board arm to achieve a target position and orientation. We present this vision-based method to control mobile manipulators as an alternative to methods such as visual servoing and calibration (i.e., stereo approaches). This new approach only requires a minimum number of holonomic degrees of freedom to achieve the required three-dimensional positioning by taking full advantage of the nonholonomic degrees of freedom. Experimentally, the method shows itself to be robust to errors in the nominal kinematics and the optics models, as demonstrated by the experimental tests.

Numerical simulation of the thermal control of heat exchangers

The temperature control of outlet air by changing the water flow rate in a single-pass waterto-air cross-flow heat exchanger is investigated. The conservation laws are applied to finite control volumes and an implicit formulation is used for transient numerical solutions. Conjugate forced convection heat transfer from the tube is solved to calculate the temperatures of the air and water coming out of the heat exchanger. In the simulations the outlet air temperature is controlled by changing the water flow rate entering the heat exchanger using a proportional-integral (PI) controller. The range of controllability of the heat exchanger was studied first. Then disturbances in the form of step changes in the inlet air temperature, the air flow rate, and the set point temperature were separately introduced. The effects of the limiting-condition constraints and different control parameters on controlling the outlet air temperature are presented. The results show that the control behavior can be simulated numerically and that this control methodology is effective within limits.