Verification of an Autonomous Reliable Wingman using CCL

We present a system of two aircraft, one human-piloted and one autonomous, that must coordinate to achieve tasks. The vehicles communicate over two data channels, one high rate link for state data transfer and one low rate link for command messages. We analyze the operation of the system when the high rate link fails and the aircraft must use the low rate link to execute a safe "lost wingman" procedure to increase separation and re-acquire contact. In particular, the protocol is encoded in CCL, the Computation and Control Language, and analyzed using temporal logic. A portion of the verified code is then used to command the unmanned aircraft, while on the human-piloted craft the protocol takes the form of detailed flight procedures. An overview of the implementation for a June, 2004 flight test is also presented

Feedback Controlled Software Systems

Software systems generally suffer from a certain fragility in the face of disturbances such as bugs, unforeseen user input, unmodeled interactions with other software components, and so on. A single such disturbance can make the machine on which the software is executing hang or crash. We postulate that what is required to address this fragility is a general means of using feedback to stabilize these systems. In this paper we develop a preliminary dynamical systems model of an arbitrary iterative software process along with the conceptual framework for stabilizing it in the presence of disturbances. To keep the computational requirements of the controllers low, randomization and approximation are used. We describe our initial attempts to apply the model to a faulty list sorter, using feedback to improve its performance. Methods by which software robustness can be enhanced by distributing a task between nodes each of which are capable of selecting the best input to process are also examined, and the particular case of a sorting system consisting of a network of partial sorters, some of which may be buggy or even malicious, is examined

A formalism for the composition of concurrent robot behaviors

We introduce tools which help one to compose concurrent, hybrid control programs for a class of distributed robotic systems, assuming a palette of controllers for individual tasks is already constructed. These tools, which combine the backchaining of continuous robot behaviors with Petri nets, expand on successful work in sequential composition of robot behaviors. We apply these ideas to the design and verification of a robotic bucket brigade and to simple, distributed assembly tasks as found in automated factories

Toward the Regulation and Composition of Cyclic Behaviors

Many tasks in robotics and automation require a cyclic exchange of energy between a machine and its environment. Since most environments are under actuated —that is, there are more objects to be manipulated than actuated degrees of freedom with which to manipulate them—the exchange must be punctuated by intermittent repeated contacts. In this paper, we develop the appropriate theoretical setting for framing these problems and propose a general method for regulating coupled cyclic systems. We prove for the first time the local stability of a (slight variant on a) phase regulation strategy that we have been using with empirical success in the lab for more than a decade. We apply these methods to three examples: juggling two balls, two legged synchronized hopping and two legged running—considering for the first time the analogies between juggling and running formally

Locally Interacting Hybrid Systems with Embedded Graph Grammars

Abstract — In many cooperative control methods, the network topology in¤uences the evolution of its continuous states. In turn, the continuous state may in¤uence the network topology due to local restrictions on connectivity. In this paper we present a grammatical approach to modeling and controlling the switching of a system’s network topology, continuous con-trollers, and discrete modes. The approach is based on embedded graph grammars, which restrict interactions to small subgraphs and include spatial restrictions on connectivity and progress. This allows us to direct the behavior of large decentralized systems of robots. The grammatical approach also allows us to compose multiple subsystems into a larger whole in a principled manner. In this paper, we illustrate the approach by proving the correctness of a cooperative control system called the load balanced multiple rendezvous problem. I

Modular Self-Reconfigurable Robot Systems

The field of modular self-reconfigurable robotic systems addresses the design, fabrication, motion planning, and control of autonomous kinematic machines with variable morphology. Modular self-reconfigurable systems have the promise of making significant technological advances to the field of robotics in general. Their promise of high versatility, high value, and high robustness may lead to a radical change in automation. Currently, a number of researchers have been addressing many of the challenges. While some progress has been made, it is clear that many challenges still exist. By illustrating several of the outstanding issues as grand challenges that have been collaboratively written by a large number of researchers in this field, this article has shown several of the key directions for the future of this growing fiel

The Role of Reflexes Versus Central Pattern Generators

Animals execute locomotor behaviors and more with ease. They have evolved these breath-taking abilities over millions of years. Cheetahs can run, dolphins can swim and flies can fly like no artificial technology can. It is often argued that if human technology could mimic nature, then biological-like performance would follow. Unfortunately, the blind copying or mimicking of a part of nature [Ritzmann et al., 2000] does not often lead to the best design for a variety of reasons [Vogel, 1998]. Evolution works on the just good enough principle. Optimal designs are not the necessary end product of evolution. Multiple satisfactory solutions can result in similar performances. Animals do bring to our attention amazing designs, but these designs carry with them the baggage of their history. Moreover, natural design is constrained by factors that may have no relationship to human engineered designs. Animals must be able to grow over time, but still function along the way. Finally, animals are complex and their parts serve multiple functions, not simply the one we happen to examine. In short, in their daunting complexity and integrated function, understanding animal behaviors remains as intractable as their capabilities are tantalizing

Symbolic Control and Planning of Robotic Motion [Grand Challenges of Robotics]

Mobile robots are complex systems that combine mechanical elements such as wheels and gears, electromechanical devices such as motors, clutches and brakes, digital circuits such as processors and smart sensors, and software programs such as embedded controllers. They have mechanical constraints (e.g., a car-like robot cannot move sideways), limited energy resources, and computation, sensing, and communication capabilities. They operate in environments cluttered with possibly moving and shape changing obstacles, and their objectives can change over time, such as in the case of appearing and disappearing targets. Robot motion planning and control is the problem of automatic construction of robot control strategies from task specifications given in high-level, human-like language. The challenge in this area is the development of computationally efficient frameworks allowing for systematic, provably correct, control design accommodating both the robot constraints and the complexity of the environment, while at the same time allowing for expressive task specifications

Synthesis, structure, magnetism, and high temperature thermoelectric properties of Ge doped Yb_(14)MnSb_(11)

The Zintl phase Yb_(14)MnSb_(11) was successfully doped with Ge utilizing a tin flux technique. The stoichiometry was determined by microprobe analysis to be Yb_(13.99(14))Mn_(1.05(5))Sb_(10.89(16))Ge_(0.06(3)). This was the maximum amount of Ge that could be incorporated into the structure via flux synthesis regardless of the amount included in the reaction. Single crystal X-ray diffraction could not unambiguously determine the site occupancy for Ge. Bond lengths varied by about 1% or less, compared with the undoped structure, suggesting that the small amount of Ge dopant does not significantly perturb the structure. Differential scanning calorimetry/thermogravimetry (DSC/TG) show that the doped compound's melting point is greater than 1200 K. The electrical resistivity and magnetism are virtually unchanged from the parent material, suggesting that Yb is present as Yb^(2+) and that the Ge dopant has little effect on the magnetic structure. At 900 K the resistivity and Seebeck coefficient decrease resulting in a zT of 0.45 at 1100 K, significantly lower than the undoped compound