Real-time Control Software Research Articles

SFC++: a tool for developing distributed real-time control software

This paper describes a visual tool for developing real-time control software for distributed industrial systems. The aim of this project currently in progress, is to obtain a visual programming environment which integrates both the advantages of object-oriented modelling for the design and simulation of systems and the power of modern distributed control systems (i.e. computers with real-time operating systems interconnected by means of industrial real-time networks). To bridge the gap between the object-oriented system model and the implementation level, at which we have multiple parallel tasks running on a network, sequential function charts (SFCs) are used as a standard formalism [12,16] for the description of system dynamics and control software programming.

An integrated framework for development of real-time distributed control software based on can-bus

Embedded systems are computer-based systems which must respond to external stimuli within time scales determined by the external environment. Such systems are required to achieve ever more demanding behavioural. performance and safety requirements. Embedded systems are found in applications such as primary flight control, gas-turbine engine control and railway traffic managementOften complex embedded systems are distributed, typically to achieve demanding performance or dependability requirements, and must operate within hard real-time constraints. Considerable effort is required to select optimal design solutions and ensure adherence to specified requirements. In embedded systems safety, reliability and response-times are considered as strict constraints on the system design. Achievement of these constraints requires meticulous analysis, typically through the use of specialist modelling and simulation techniques. Integration of knowledge and understanding obtained from disparate detailed models remains a considerable challenge.Ideally, a system which has both continuous dynamics and event-driven parts. would be modelled in one environment, using the most appropriate techniques for each part, and allowing the analysis of the whole system to be carried out simultaneously.The paper presents an integrated approach in order to translate automatically the information manipulated during the different phases of the design: specification. analysis, design and implementation.

H-Astral and Its Use in the Development of Real-Time Control Systems

An important issue in the design and implementation of real-time control software is the verification of (time continuous) properties during system development such that even in early stages of the development adequate feedback on design decisions can be given. It is beyond any doubt that formal methods play an important role in this kind of verification. Our research of the past few years focused on applying formalisms in requirements specification and in developing tools for modeling, design and verification of specifications for real-time systems. The development approach builds upon requirements specifications constructed using the formal real-time specification language Astral. In this paper we discuss issues in the use of Astral in development and verification of real-time control systems and give an example of its use.

A Distributed Architecture for Real-Time Traffic Management

The aim of this paper is to present a software and hardware architecture for real time control of traffic light signals, and prediction of congestion in traffic flow. The system presented here is under development within the framework ofa European Esprit Project: ASTORIA.The hardware architecture is based on the ZELT-2 system, which is unique and specially developed for experimentation, test and validation of new research approaches in the urban traffic domain.

X-Control: A Graphical Application for Implementing Real-Time Controllers

This paper describes the X-Control application. This is a Linux based application to facilitate the implementation of real-time control software, which provides an intuitive graphical user interface. The application makes use of a POSIX.4 compliant scheduler, and a system of real-time software components to provide a flexible, easily extendible real-time control generation method.

A Building-Block Approach to the Temporal Modelling of Control Software

This paper describes a formal process model used in a real-time control software development environment. This model allows the generation of a time Petri net representation of the processes within a system that is intended to enable temporal simulation. Processes are categorised, for the purpose of modelling, as either: data-transforming, control or choice (ALT) processes. Models which represent the temporal behaviour and the synchronisation of these individual process types are presented. It is then shown how these models may be extended to support varying numbers of process inputs and outputs. An illustrative example is presented to demonstrate the interconnection of individual process models into an integrated model of the system under development. The process model represented in time Petri net form provides the semantic basis for automatic translation from designs to temporal models.

Teaching software engineering through real-life projects to bridge school and industry

To educate graduates to succeed in industries which demand high quality software engineers is not easy due to rapidly changing organization styles and working environments. The major limitation of university education may be the lack of opportunity to expose students to real field problems. In this article, we present our experience of exposing graduate students to a real-time plant monitoring and control software development project and show how the software engineering process has been customized to educate them and satisfy the user requirements at the same time.

Sensor-based collision avoidance: Theory and experiments

A new on-line control strategy for sensor-based collision avoidance of manipulators and supporting experimental results are presented in this article. This control strategy is based on nullification of virtual forces applied to the end-effector by a hypothetical spring-plus-damper attached to the object's surface. In the proposed approach, the real-time arm control software continuously monitors the object distance measured by the arm-mounted proximity sensors. When this distance is less than a preset threshold, the collision avoidance control action is initiated to inhibit motion toward the object and thus prevent collision. This is accomplished by employing an outer feedback loop to perturb the end-effector nominal motion trajectory in real-time based on the sensory data. The perturbation is generated by a proportional-plus-integral (PI) collision avoidance controller acting on the difference between the sensed distance and the preset threshold. This approach is computationally very fast, requires minimal modification to the existing manipulator positioning system, and provides the manipulator with an on-line collision avoidance capability to react autonomously and intelligently. A dexterous RRC robotic arm is instrumented with infrared proximity sensors and is operated under the proposed collision avoidance strategy. Experimental results are presented to demonstrate end-effector collision avoidance both with an approaching object and while reaching inside a constricted opening. © 1996 John Wiley & Sons, Inc.

System approach to design generic software for real-time control of flexible manufacturing systems

Potentially, flexible manufacturing systems (FMSs) possess the ability to attain efficiency and versatility in small batches, variable mix production. However, the FMS potentiality is not yet fully used, because of the high cost of specific control software. Hence, a generic software, usable in an arbitrary FMS, producing an arbitrary part mix, appears as an important means to minimize programming and re-programming effort. In this context, modeling and control problem formalization emerge as a main issue. In this paper the authors refer to Zeigler's system-theoretic formalism for modeling the dynamics of a generic FMS at the job release and job how levels. The authors' discrete event dynamic system (DEDS) model establishes an abstract comprehensive framework for developing a generic control software at such levels. The model is able to represent both hardware/software components of the FMS and processing activity plans with a common "language". A modular structure underlies the description of both the shop-floor dynamics and control rules. So, the software architecture emerges as a direct consequence of the proposed approach and consists of three main parts: the system state knowledge base, the job release manager and the job flow manager.

Learning controllers for industrial robots

One of the most significant cost factors in robotics applications is the design and development of real-time robot control software. Control theory helps when linear controllers have to be developed, but it doesn't sufficiently support the generation of non-linear controllers, although in many cases (such as in compliance control), nonlinear control is essential for achieving high performance. This paper discusses how Machine Learning has been applied to the design of (non-)linear controllers. Several alternative function approximators, including Multilayer Perceptrons (MLP), Radial Basis Function Networks (RBFNs), and Fuzzy Controllers are analyzed and compared, leading to the definition of two major families: Open Field Function Approximators and Locally Receptive Field Function Approximators. It is shown that RBFNs and Fuzzy Controllers bear strong similarities, and that both have a symbolic interpretation. This characteristic allows for applying both symbolic and statistic learning algorithms to synthesize the network layout from a set of examples and, possibly, some background knowledge. Three integrated learning algorithms, two of which are original, are described and evaluated on experimental test cases. The first test case is provided by a robot KUKA IR-361 engaged into the “peg-into-hole” task, whereas the second is represented by a classical prediction task on the Mackey-Glass time series. From the experimental comparison, it appears that both Fuzzy Controllers and RBFNs synthesised from examples are excellent approximators, and that, in practice, they can be even more accurate than MLPs.

Dependable, intelligent voting for real-time control software

An intelligent and dependable voting mechanism for use in real-time control applications is presented. Strategies proposed by current safety standards advocate N-version software to minimize the effects of undetected software design faults (bugs). This requires diversity in design but presents a problem in that truly diverse code produces diverse results; that is, differences in output values, timeliness and reliability. Reaching a consensus requires an intelligent voter, especially when non-stop operation is demanded, e.g. in aerospace applications. This paper, therefore, firstly considers the applicable safety standards and the requirements for an intelligent voter service. The use of replicated voters to improve reliability is examined and a mechanism to ensure non-stop operation is presented. The formal mathematical analysis used to verify the crucial behavioural properties of the voting service design is detailed. Finally, the use of neural nets and genetic algorithms to create N- version redundant voters, is considered.

Advanced process control for photolithography.

Process control in photolithography will be a key requirement for the successful manufacturing of 0.25 micron semiconductor products. A program to study photolithography process control techniques was recently undertaken at Texas Instruments. The target for this program was 0.35 micron technology, and the lithography used a combination of conventional wet developed resists and surface-imaging dry developed resists along with both i-line and deep UV steppers. Advanced process control techniques were applied in order to achieve lithography control without lot send-ahead wafers or test wafers. A notable conclusion was the need for the development of real-time sensor technology, particularly for the stepper exposure process. Lithography for the program demonstration was performed both with conventional i-line processing and with surface imaging and dry develop. Acceptable process control was achieved without lot send-ahead wafers or test wafers by a program of short-loop SPC and regular monitoring of equipment states. The fundamental lithography processes appear to have sufficient short term control in general, but sudden excursions and long term drifts still occur. The goal of fully automated process control can only be met when there are real time sensors and control software on the key steps in the lithography process. The most pressing need is for a sensor that could control the exposure on the stepper. With such a system variations in the incoming wafer state could be compensated, even for short run ASIC lots, to provide an on-target pattern every time.

CSYSLAB: A Versatile Software for Undergraduate Laboratory in Control

A real-time control software is developed using analog computer like modelling approach. This software has graphical user interface to help in modelling and in measuring system performance. This is used for simulation study and control of external systems using linear/nonlinear building blocks provided in the software. The software has been tested in an undergraduate control laboratory and was found to be versatile and efficacious.

An Object-Oriented Specification of a Control Logic for An FMS

The paper concerns with the application of object-oriented modelling to the development of real-time control software for FMS. Object- oriented model integrates the features of object-oriented database, features of real-time system and features of artificial intelligence aspects. The goal is to develop intelligent decision making logic for automatic creation of the control actions in both the standard and the nonstandard (error) situations. The knowledge is represented by the rules and the constraints. Three type of rules are described in the paper: process rules (create the dynamic model of the devices), production plan rules (define the production sequence of the technological operations), and expert knowledge rules (create reasoning model for solving the fault situations). The cooperation among these rules is also discussed in the paper.

Fault-tolerant control of real-time systems in the presence of single event upsets

Abstract High energy radiation environments, such as in space or in the presence of a nuclear event can adversely affect the operation of digital devices, presenting significant problems of reliable control to both Hardware and Software Engineers. These problems, although only recently addressed, have important implications for both military aircraft and space vehicles. The phenomenon known as Single-Event-Upset (SEU) occurs when bistable devices, such as memory, are corrupted by a collision with an high energy particle. These particles are found in abundance in radioactive environments and in outer space. An SEU can produce a variety of undesirable scenarios for a computer that range from annoying to catastrophic and can be either temporary or permanent. Some of these scenarios are; alteration of program memory, corruption of RAM or of a CPU register, and spurious or missed interrupts. A variety of techniques employing hardware, or both have been developed to enable recovery from an SEU. These schemes include RAM scrubbing, coding, fault-tolerant software, and judicious selection of hardware. A unique set of these and other techniques were developed for use on the Space Shuttle Inertial Measurement (IMU) computer. This paper provides an introduction to the phenomenon of the SEU, a review of some of the existing software techniques and hardware selection considerations to combat the effects of SEUs, and a discussion of the application of the techniques in the fault-tolerant, real-time control software for the Space Shuttle IMU's embedded computer.

Control of Complex Mechanical Systems

Complex mechanical systems, those with such interacting components as motion control loops. process or thermal control loops, intelligent subsystems such as robots. etc ., require a design methodology for representation of control software. Transition logic has been found to be effective for design of real time control software and is used here for mechanical systems. The definition of the transition logic has been extended to include a formal function set associated with each state, and rules for how those functions must operate. This provides added formality and modularity to the software design process, and also establishes a discipline in which implementation of cooperative multitasking is simple and direct.

Artificial Intelligence Techniques in Real-time Control Systems

Applying artificial intelligence techniques in real-time control is still a challenge. In order to be effective in reducing the cognitive load in a real-time environment, problems to overcome are, for example: Representation of time and reasoning about events in time; handling of asynchronous events; inferring within a given interval of time; and integrating knowledge-based components into conventional real-time control software with a real-time operating system. The paper addresses these fundamental problems and presents the state of the art in providing solutions. Results of current research are presented. Additional unsolved problems, such as validating control systems with AI components and proving their reliability and safety, are mentioned

Control systems software

A short historical perspective is given of the evolution of the use of software for the realization of increasingly complex control systems. The state-of-the-art in designing computer-based control systems is discussed and highlighted with an example. Two major aspects of the difficulties encountered with the current approach to designing these systems are discussed as an introduction to a solution. The solution is in the form of SPICE, a system that makes large real-time control software less complex by adopting a highly modular and expandible software architecture. A description of the system's architecture developed is given and illustrated with a simple example.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Real-time software methodologies: Are they suitable for developing Manufacturing control software?

Computer-Integrated Manufacturing (CIM) systems may be classified as real-time systems. Hence, the applicability of methodologies that are developed for specifying, designing, implementing, testing, and evolving real-time software is investigated in this article.The paper highlights the activities of the software development process. Among these activities, a great emphasis is placed on automating the software requirements specification activity, and a set of formal models and languages for specifying these requirements is presented. Moreover, a synopsis of the real-time software methodologies that have been implemented by the academic and industrial communities is presented together with a critique of the strengths and weaknesses of these methodologies.The possible use of the real-time methodologies in developing the control software of efficient and dependable manufacturing systems is explored. In these systems, efficiency is achieved by increasing the level of concurrency of the operations of a plan, and by scheduling the execution of these operations with the intent of maximizing the utilization of the devices of their systems. On the other hand, dependability requires monitoring the operations of these systems. This monitoring activity facilitates the detection of faults that may occur when executing the scheduled operations of a plan, recovering from these faults, and, whenever feasible, resuming the original schedule of the system.The paper concludes that the set of surveyed methodologies may be used to develop the real-time control software of efficient and dependable manufacturing systems. However, an integrated approach to planning, scheduling, and monitoring the operations of these systems will significantly enhance their utility, and no such approach is supported by any of these methodologies.

Data base design for real-time adaptations

The performance of embedded real-time control software depends on its ability to adapt to changing operating conditions in a timely and predictable manner. CHAOS (concurrent hierarchical adaptable object system) has been designed for programming such adaptable real-time applications. Applications in CHAOS are structured as concurrent objects that interact via invocations. The adaptation control system in CHAOS, responsible for monitoring the execution environment, detecting the need for adaptations, and enacting selected adaptations, is structured around an extended entity relationship data base. Here we describe the design of this entity relationship data base, the mapping of objects and their attributes into it, the mechanisms for performing adaptations, and the data base manipulation language interface (used to encode adaptations) to the data base.