Framework of a Simulation Based Shop Floor Controller Using HLA Pramod Vijayakumar Systems and Industrial Engineering University of Arizona

Topics Covered Control Architecture of Mfg Systems Simulation based control Integration of simulations Proposed system Work Ahead

Control Architecture - Centralized All planning and information processing performed at a single Location The Advantages are Less no of Computers Global decisions are easy to make Works well with a product mix which is fairly stable Disadvantages Central computer needs to have high computing power (Mainframe) Failure of the central controller paralyses the system Low fault tolerance Reconfigurations difficult

Hierarchical Top down approach for passing control Status is send upward and decisions are send downward Advantages Modularity Modularity Computation is more distributed Planned Extension possible Disadvantages Rigid Master Slave Relationships Low fault tolerance Modification possible is limited

Heterarchical It has a flat structure characterized by peer communication High Level of autonomy and no master slave relationships Advantages High levels of distribution of control Easy to make modifications High fault tolerance Computers with significantly less processing powers Disadvantages High number of conflicts Behaviour could be unpredictable

Implementation philosophies AGENTS Software that is AutonomousAdaptive Goal oriented HOLONS similar to agents Holon could be part of another holon or many holons More cooperation SIMULATION Used for modeling and analysis Representation of the real system Could be used in real time to control a system

Roles of Simulation Simulation Dynamic Scheduler Status Update Instructions Decision Maker Mfg System Present Strategy And status Better Strategy

Proposed Change

Advantages Individual Models means better analysis and debugging Models are reusable More distributed control Easy to extend the model Easy To make Modifications to the model

Integrating Simulations Different vendors different representations Coordination with respect to time Standard Method for exchanging information

High Level Architecture ( HLA) The efforts were initiated by DMSO An Architecture to allow dissimilar simulations to talk The 3 main components are Rules –Regarding the federate and federation behaviour Interface Specification –Regarding the interactions between the federates and RTI Object Model Template –Data model for the Federation (FOM) and Federate (SOM )

Run Time Infrastructure Acts as the mediator between all the simulations 6 Basic Functions Federation Management –Creating, Joining, Resigning and Destroying federates Declaration Management –Publishing and Subscribing data Object Management –Attribute updates and interactions Ownership management –Transfer of ownership of objects and attributes Time management –Coordinating time of federates and managing time-stamped delivery of events Data Distribution management –Manages object instances

Process Planning AND/OR Graphs Precedence Relations exhibited Alternative ways of machining a single part – AND Node Redundancies can be built into the model – OR Node Each Node represents an operation to be carried out. The graph determination is an offline activity Node contains –NC Filename –Tools Required –Fixtures –Processing Machine M1SA M3 JAM4 M2 NC Filename, Tools, Fixtures, Machine Names

Proposed Architecture MH MP RMHMR Guide MT Manager MT Visualization Status

Proposed System Characteristics Loose Master Slave Relationships Peer to peer communication Extendable architecture Modular design Good Fault Tolerance Reusable Code Manufacturing System Raw Part AND/OR Graph Finished Part

Federates in the system Equipment Material Processor Material Transporter Material Handler –Controls the equipment –Keeps check of the tools and fixtures –Monitors the machine and updates status –Interacts with the Resolver or Managers for part Resolver –Resolves the AND/OR Nodes –One resolver for each cell –Interacts with the Material Processor for the part –Communicates with peer resolvers in case of “foreign machines” in the cell

Federates in the system Guide –Has a supervisory role –Make the initial assignment of ownership and initial AND/OR resolution –Comes into play in the case of “foreign machines” MT Manager –Interacts with the Material Transporter and Material Processor MH Manager –Interacts with the Material Handler and Material Processor Visualization Federate –Gives a Current status summary of the entire system

Scheduling and Operation Resolver MP1 MP3 Do you want to process the part MP2 Do you want to process the part Yes No Yes You Win

Work Ahead Algorithms for the different federates –Roughly determined as SPT for MP Federate Due Date of the part for Resolver Transportation time for MT Manager Handling time for MH Manager Message formats for communication Structure of Databases

Summary A modular approach suggested to simulation based control of manufacturing systems An easily extendable and modifiable architecture Online Collection of data for analysis possible