Alternative Control Architectures Research Articles

Alternative Control of an Electrically Assisted Tensile Forming Process Using Current Modulation

Electrically assisted forming is a technique whereby metal is deformed while simultaneously undergoing electric current flow. Using this process, electric current level becomes a new degree of freedom for process control. In this work, we present some alternative control architectures allowing for new avenues of control using such a process. The primary findings are architectures to allow for forming at constant force and forming at constant stress levels by modulating electric current to directly control material strength. These are demonstrated in a tensile forming operation, and found to produce the desired results. Combining these control approaches with previous and contemporary efforts in modeling of the process physics will allow for system identification of material response properties and model-based control of difficult-to-observe process parameters such as real time temperature gradients.

A model for improving microbial biofuel production using a synthetic feedback loop

Cells use feedback to implement a diverse range of regulatory functions. Building synthetic feedback control systems may yield insight into the roles that feedback can play in regulation since it can be introduced independently of native regulation, and alternative control architectures can be compared. We propose a model for microbial biofuel production where a synthetic control system is used to increase cell viability and biofuel yields. Although microbes can be engineered to produce biofuels, the fuels are often toxic to cell growth, creating a negative feedback loop that limits biofuel production. These toxic effects may be mitigated by expressing efflux pumps that export biofuel from the cell. We developed a model for cell growth and biofuel production and used it to compare several genetic control strategies for their ability to improve biofuel yields. We show that controlling efflux pump expression directly with a biofuel-responsive promoter is a straightforward way of improving biofuel production. In addition, a feed forward loop controller is shown to be versatile at dealing with uncertainty in biofuel production rates.

Metrics for evaluating distributed manufacturing control systems

In this paper, two classes of metrics are proposed that can be used to evaluate alternative manufacturing control architectures: those dealing with the controlled system (i.e. the manufacturing system) and those dealing with the control system. In order to illustrate the use of these metrics, the problem of scheduling a simple manufacturing cell is tackled using two test control architectures and the performance of these alternative approaches is evaluated using a modular discrete-event simulation model. The results of the paper suggest that it is worthwhile to use both manufacturing and control system performance measure to evaluate alternative control architectures, especially when considering dynamic architectures such as a Holonic Manufacturing System (HMS; i.e. architectures that adapt to changes in the manufacturing environment).

Evaluating the performance of reactive control architectures for manufacturing production control

The requirement for adaptable and re-configurable control systems for manufacturing has highlighted the inadequacies of traditional centralised control approaches, leading researchers to focus on decentralised approaches. The question of what is the most appropriate control architecture for a given system has led industrial and academic researchers to develop a spectrum of decentralised control architectures ranging from hierarchical to non-hierarchical structures. While current research has confirmed the potential of decentralised architectures, neither extreme of this control architecture spectrum has proven to be the most appropriate choice for a given manufacturing system. Recent research into providing an objective comparison of alternative control architectures has shown that some degree of hierarchy is important for distributed manufacturing control architectures. This paper is concerned with our current investigations into why these partial hierarchies appear to display superior performance.

Performance comparison and analysis of reactive and planning-based control architectures for manufacturing

Although numerous distributed architectures ranging from hierarchical to non-hierarchical (or heterarchical) have been proposed for the control of manufacturing systems, very little research has focused on quantitative comparisons of these architectures. In this paper, an objective comparison of two architectures, each required to control the same manufacturing cell, is presented. The objective of this work is to gain insight into the behaviour of alternative control architectures that will ultimately be used to determine the best control architecture for a given manufacturing system. In particular, this research focuses on the role of planning horizon in control architecture design to determine whether intelligent control agents should plan ahead or simply react to change in their environment.

The Tempest-a practical framework for network programmability

The Tempest framework provides a programmable network environment by allowing the dynamic introduction and modification of network services at two levels of granularity. First, the switchlet and associated virtual network concepts enable the safe introduction of alternative control architectures into an operational network. The timescales over which such new control architectures can be introduced might vary from, for example, a video conferencing specific control architecture, which is active only for the duration of the conference, to a new version of a general purpose control architecture, which might be active for several months or longer. Second, the Tempest framework allows refinement of services at a finer level of granularity by means of the connection closure concept. In this case modification of services can be performed at an application-specific level. These attributes of the Tempest framework allows service providers to effectively become network operators for some well defined partition of the physical network. This enables them to take advantage of the knowledge they possess about how the network resources are to be used, by programming their own specially tailored control architecture. This, as our work with the Tempest shows, is a spur to creativity allowing many of the constraints imposed on operators and end users to be rethought and for new techniques to be quickly and safely introduced into working networks.

Semantics in an intelligent control system

Much research on intelligent systems has concentrated on low level mechanisms or limited subsystems. We need to understand how to assemble the components in an architecture for a complete agent with its own mind, driven by its own desires. A mind is a self-modifying control system, with a hierarchy of levels of control and a different hierarchy of levels of implementation. AI needs to explore alternative control architectures and their implications for human, animal and artificial minds. Only when we have a good theory of actual and possible architectures can we solve old problems about the concept of mind and causal roles of desires, beliefs, intentions, etc. The global information level ‘virtual machine’ architecture is more relevant to this than detailed mechanisms. For example, differences between connectionist and symbolic implementations may be of minor importance. An architecture provides a framework for systematically generating concepts of possible states and processes. Lacking this, philosophers cannot provide good analyses of concepts, psychologists and biologists cannot specify what they are trying to explain or explain it, and psychotherapists and educationalists are left groping with ill-understood problems. The paper outlines some requirements for such architectures showing the importance of an idea shared between engineers and philosophers: the concept of ‘semantic information’.