eastern mediterranean university

Eastern Mediterranean UniversityFaculty of Engineering

Department of Mechanical Engineering

Agenda

Introduction IEC 61499 Function Block Holonic Manufacturing System Real-time Distributed Control System Reconfiguration of Real-time Distributed Control Case Study Application of Virtual Reality

Introduction

• Manufacturing control systems are required to be adaptive and responsive.

• One approach which is closely related to the Multi-agent systems is HMS.

• The motivation is the requirement for manufacturing systems that can automatically and intelligently adapt to changes in the manufacturing environment while still achieving overall system goals.

Introduction

• At the low control level of a HMS, especially at the level of real-time control, reconfigurable holonic controllers are employed (HCs).

• The critical issue for holonic control at this level is how the resources of the HMS are to be organized dynamically during runtime and how the associated controller components are to be reconfigured dynamically at the same time.

• Solution:

Real-time distributed control system that can benefits of holonic control system.

Introduction

• The real-time holonic distributed control systems require:

Stability in the face of disturbance (i,e., Sensor or Robot Failure.)

Adaptability and flexibility in the face of change.

Efficient use of available resource.

To do so, IEC-1499 Function block (FB) standard is employed.

IEC-61499 Function Block

• A standardization project of IEC Technical Committee 65 (TC65) to standardize the use of function blocks in distributed industrial-process measurement and control systems (IPMCSs).

• Work item approved 1991; assigned to Working Group 6 (WG6) 1993

– Experts from USA, Germany, Japan, UK, Sweden, France, Italy

– Also responsible for IEC 61131-3 (Programmable Controller Languages) and 61131-8 (Programmable Controller Language Guidelines)


• Distributed applications• Event and data interfaces• Software encapsulation and reuse• Event-driven state machines• Service interfaces• Management services• Software portability


distributability

programmability

agility!

agility!

distributedconfigurable

programmable

CommonArchitectureReference

Model

Function BlocksIEC 61499

Synthesis

PLCIEC 61131-3

CentralizedProgrammableConfigurable

Thesis

DCSIEC 61804

DistributedConfigurable

Antithesis

dynamicallyreconfigurable

= agile !


• IEC 61499 is composed of 2 IECs standards: IEC-61131-3 and IEC-61804.

• IEC-61131-3 is Centralized Programming Configurable (PLC) with Distributablity property.

• IEC-61804 is Distributed Configurable with Programmibility property.

• The result is Distributed Configurable Programmable which is common architecture reference model.

IEC 61499• Parent organization: IEC• Working group: TC65/WG6• Goal: Standard model

(function blocks) for control encapsulation& distribution

• Started: 10/90• Active development: 3/92• Trial period: 2001-03• Completion: 2005

Holonic Manufacturing Systems (HMS)

• Parent organization: IMS• Working group: HMS

Consortium• Goal: Intelligent manufacturing

through holonic (autonomous, cooperative) modules

• Feasibility study: 3/93-6/94• First phase: 2/96 - 6/00• Second phase: 6/00-6/03

Requirements

Controls architecture

Intelligent Automation architecture


Output variablesInput variables

Event inputs Event outputs

Algorithms

Type identifier

(IEC 1131-3)

Internal variables

Execution Control Chart


• Function Block is consist of two main parts: Head and Body.

• The head of Function Block is Execution Control Chart (ECC) which organizes the flow of events between the blocks as well as the body control.

• The body of Function Block consists of algorithm and the internal data as well as the I/O data.

• The algorithm inside the body operates in IEC-61131-3 standards.

• The body will control the resource capabilities, scheduling, communication and process mapping.

• Events inputs and outputs are used to synchronize function blocks within an application and to schedule the algorithms within the function block.

• Data inputs and outputs are the interface with the external of the function block since internal data is hidden.


Function Block Execution Model


1. Relevant data input values are made available.

2. The event at the event input occurs.

3. The execution control function notifies the resource scheduling function to schedule and algorithm for execution.

4. Algorithm execution begins.

5. The algorithm completes the establishment of values for the output variables associated with the event output.

6. The resource scheduling function is notified that algorithm execution has ended.

7. The scheduling function invokes the execution control function.

8. The execution control function signals an event at the event output.

Holonic Manufacturing System

• Holon is an autonomous and cooperative building block of a manufacturing system for transforming, transporting, storing, and/or validating information and physical objects.

• Holon Autonomy is the capability of a holon to create and control the execution of its own plans and/or strategies.

• Holon Cooperation is the process whereby a set of holons develops mutually acceptable plans and executes them.

• Holon Self-organization is the ability of holons to collect and arrange themselves in order to achieve a production goal.

• Holarchy is system of holons that can cooperate to achieve a goal or objective.

Real-time Distributed Control (Definitions)

• System: A collection of devices interconnected and communicating with each other by means of a communication network consisting of segments and links.• Device: An independent physical entity capable of performing one or more specified functions in a particular context and delimited by its interfaces.• Resource: A functional unit having independent control of its operation, and which provides various services to applications including scheduling and execution of algorithms.• Application: A software functional unit that is specific to the solution of a problem in industrial-process measurement and control. An application may be distributed among devices and may communicate with other applications.

Real-time Distributed Control

• A holon is represented by one or more hardware devices and can interact via one or more communication networks.

• Each device comprises of one or more resources (i.e. processor with memory) and one or more interface.

• Interfaces enable the device to interact with either the controlled manufacturing process or with other devices through a communication interface.

• Resources are logical entities with independent control over their operations including the scheduling of their tasks.

• A resource can be created, configured via management model.

Real-time Distributed Control

• Applications are networks of function blocks (FB) and variables connected by data and event flows.

• Such applications aid the modeling of cooperation between the autonomous holons.

• Function blocks receive event/data from interfaces, process them by executing algorithms and produce outputs, all handled by an event control chart.

• Function block algorithms can be written in high-level programming language or in the IEC-61131 language for PLCs.

Reconfiguration of Real-time Distributed Control

• In conventional PLC systems, reconfiguration involves a process of first editing the control software offline while the system is running, then committing the change to the running control program.

• When the change is committed, severe disruptions and instability can occur as a result of high coupling between elements of the control software and inconsistent real-time synchronization.

• Three types of reconfiguration: Simple configuration utilizes the IEC 61499 model to avoid software coupling issues during reconfiguration. Dynamic reconfiguration uses techniques to properly synchronize software during reconfiguration. Intelligent reconfiguration exploits multi-agent techniques to allow the system to reconfigure automatically in response to change.


The Reconfiguration Model


• Function block ports (i.e., event and data connections) are objects that register with the Resource Manager (RM) associated with the function block. The resource manager looks after the interconnection of function block ports (i.e., as is specified by the application) and maintains a record of all function block ports in a FB Port table.

• The Device Manager (DM) looks after the interconnection of the RM’s function block ports and stores this information in an RM Port table.

• Application Manager (AM) looks after the interconnection of the DM’s function block ports and stores this information in a DM Port table.


• The advantage of this approach is that reconfiguration can be managed at various levels (i.e., function block, resource, device, application); all that isrequired is a “map” of the new configuration (i.e., based on the FB, RM, and DM Port tables).

• This approach allows for the “basic reconfiguration” discussed previously, but does not yet address how dynamic and intelligent reconfiguration are performed.

• The fundamental difference between basic and dynamic reconfiguration is the latter’s recognition of timeliness as a critical aspect of correctness.


• Intelligent reconfiguration builds .on dynamic reconfiguration (i.e., timeliness constraints) by focusing on multi-agent techniques to allow the system to reconfigure automatically in response to change.

•For example, as part of a fault recovery strategy, higher-level agents will manage the reconfiguration process using diverse or homogeneous redundancy.

•Two approaches to achieve these more advanced forms of reconfiguration:

Preprogrammed or “contingencies” approach. Softwiring approach.


Contingencies Approach

• Contingencies are made for all possible changes that may occur. • Alternate configurations are pre-programmed based on the system designer’s understanding of the current configuration, possible faults that may occur as well as possible means of recovery.

Disadvantages:

• Inflexibility particularly with respect to the handling of unanticipated changes.• This approach would require constant maintenance in order to keep the reconfiguration tables up to date.


Soft-wiring Approach

• FB, RM, DM port tables are connected to the Configuration Agent (CA).• This agent has information of how two FB, RM or DM can be connected.• CA will use this information, for example, to connect a new function block with an existing function block or to replace an existing one with a new while ensuring that the real-time requirement are met.

Advantages:

• It’s potential to overcome the inflexibility• It’s potential to realize intelligent reconfiguration.

References

Brennan, R.W. Fletcher, M. Norrie, D.H. ” Reconfiguring Real-Time Holonic Manufacturing Systems”, Proceedings of the 12th International Workshop on Database and Expert Systems Applications, Page 611, 2001.

Vrba, P. Marik, V. , “Simulation in agent-based manufacturing control systems”, 2005 IEEE International Conference on Systems, Man and Cybernetics, page(s): 1718- 1723 Vol. 2, Oct. 2005.

Xiaokun Zhang Norrie, D.H. Brennan, R.W. Yuefei Xu, “A multi-level reconfiguration control for holonic PLC” , 2000 IEEE International Conference on Systems, Man, and Cybernetics, page(s): 1762-1767 vol.3, 2000.

Xiaokun Zhang Sivaram Balasubramanian Robert W. Brennan Douglas H. Norrie, “Design and implementation of a real-time holonic control system for manufacturing”, Information Sciences—Applications: An International Journal, Volume 127 , Issue 1-2 (Aug. I 2000).

References

M.Bal, M. Hashemipour, “Applications of Virtual Reality in Design and Simulation of Holonic Manufacturing Systems: A Demonstration in Die-Casting Industry”, Proceedings of the 3rd international conference on Industrial Applications of Holonic and Multi-Agent Systems: Holonic and Multi-Agent Systems for Manufacturing, Pages: 421 – 432, 2007.

Rockwell Automation Company, “IEC 61499 Function Block Model: Application Note”, www.isagraf.com, April 2008.

James H. Christensen, “The IEC 61499 Standard:Concepts and R&D Resources”, http://www.rockwell.comhttp://www.holobloc.com.

http://www.isagraf.com/

http://www.holobloc.com/

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