2009 AMTS Symposium Reconfigurable Assembly Systems v1

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2009 AMTS Symposium Reconfigurable Assembly Systems v1 Powered By Docstoc
					    Reconfigurable Assembly System

         Anton Basson (Stellenbosch University)
    Herman Vermaak (Central University of Technology)

                      Reconfigurable Assembly Systems
    •   Target Application
    •   Target Assembly System Characteristics
    •   Mechanical Architecture
         ♦ Fixtureless Mechanical Architecture

         ♦ Fixture-based Mechanical Architecture

         ♦ Fixture-based vs. Fixtureless

    •   Cell-level Control Architecture
    •   Process Planning, Monitoring and Control
         ♦ Characteristics of the Software System

         ♦ Information Flow between Factory and Software System

         ♦ Software System Agent Types

         ♦ Features of the Software System

    •   Planned Further Work

                          Reconfigurable Assembly Systems
                                           Target Application
     •     Domestic circuit breaker spot welded assembly
                                                                                               Coil 20A
Moving contact + tip
                                                                                                                   Arc runner

                       Pigtail Ø2.5– length 60mm
                                                            Handle frame assembly
                                                                                     Pigtail Ø 2.5 – length 20mm

                                                   Reconfigurable Assembly Systems
                         Target Application
    •   Dynamic over short timescales
        ♦   Multiple product variants concurrently in assembly process
        ♦   Revision of demand prediction and scheduling
             • Requires continual status feedback
        ♦   Assembly disruptions occur
             • Incorrect or insufficient parts at assembly plant
             • Labour disruptions (also in mechanised situations)
             • Equipment or tooling failures
    •   Dynamic over long timescales
        ♦   Shortening product life
        ♦   Increasing product variety and customisation

                                  Reconfigurable Assembly Systems
    Target Assembly System Characteristics
     • Accommodate large product variety
        ♦   Flexibility: handle some part families autonomously
        ♦   Adaptability: quick changeovers for other variants
        ♦   Modularity and Extendibility:
             • Simple interfaces amongst functional units and their controllers
        ♦   Integratability + diagnosability
             • Rapid ramp-up after reconfiguration
    •   Combine manual and automated assembly
    •   Investment payback within 2 years
    •   Suitable for rural Southern Africa

                                   Reconfigurable Assembly Systems
                  Mechanical Architecture
    •   Reconfigurable fixtures
        ♦   Not feasible
    •   Reconfigurable feeding and orienting
        ♦   Possibly feasible
    •   Investigated two approaches
        ♦   Fixture based
        ♦   Fixtureless

                                Reconfigurable Assembly Systems
    Fixtureless Mechanical Architecture

                                                   Vertical resistance
                                                   welding station



                 Reconfigurable Assembly Systems
    Fixture-based Mechanical Architecture
                    Pallet with fixture                                                               n
                    and data tag                                                              sta
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                                                           cti stati
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                                                    Ins ova
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                                                e                                                                     t io
                                             zin                                                               s   ta
                                        ga                                                                 ing
                                   t ma                                                                  ed
                             lle                                                                      Fe
                                                                               t ion
                                                                       g   sta

        Data read/write
        heads at stations

                                      Reconfigurable Assembly Systems
               Fixture-based vs Fixtureless
    •   Fixture-based                                •   Fixtureless
        ♦   Fixtures not reconfigurable                    ♦   Avoid fixtures by using
        ♦   Conventional approach                              dextrous robot pair
        ♦   Facilitates concurrent                         ♦   Reconfigurable feeder
            operations                                     ♦   Serial operations
        ♦   Lower cost per assembly for                    ♦   Higher cost per assembly for
            given configuration                                given configuration
             • Higher initial cost                               • Lower initial cost
             • Higher throughput                                 • Lower throughput
        ♦   Higher reconfiguration cost                    ♦   Lower reconfiguration cost

                                     Reconfigurable Assembly Systems
     Cell-level Control Architecture

               Decentralised control

                Reconfigurable Assembly Systems
 Process Planning, Monitoring and Control
  • Software Platform Overview
     ♦   Multi-Agent based Java software system running on
         Windows server(s) (Linux also possible due to Java)
     ♦   OPC used to enable communication between factory
         devices and software system
          • PLC, serial device, etc <> TCP <> OPC <> Software System
     ♦   Software System controlled primarily through web interface
         although other interfaces are possible
     ♦   Relational MySQL database used for all persistent data
         storage needs

                             Reconfigurable Assembly Systems
     Characteristics of the Software System
     • System is being designed to be as modular as
       possible to enhance reconfiguration capabilities:
       ♦   Multi-Agent abstraction was chosen to enhance high level
           software component modularity
       ♦   Software design patterns employed to enhance lower level
           object oriented software component modularity
       ♦   Standards based components used instead of designing a
           new component if possible:
            • Careful database design in SQL to ensure complete modelling of
              the system and leveraging the proven SQL language
            • Standard communications protocols and platforms, design
              methodologies, software design patterns, etc always first choice

                                 Reconfigurable Assembly Systems
     Information Flow between Factory and
                Software System

                  Reconfigurable Assembly Systems
     Software System Agent Types
     • Human Operator Interface Agent. This agent type will facilitate
       human\system interaction and apply user authentication through the
       Security Provider Agent.
     • Security Provider Agent. This agent type will be responsible for
       processing requests from agents to interact with privileged system
     • Device Agent. This agent type will interact with production
       hardware directly using OPC. It is possible that some “devices” on
       the production floor will be human workers. The device agent will
       then communicate with the human worker through a Human
       Operator Interface agent as a proxy.
     • Product Agent. Each uniquely traceable product will have a
       Product Agent assigned to it. This agent will store the current
       production status, next production step and priority of the product.
       Products that cannot be uniquely traced will have a single Product
       agent assigned to the particular product batch.

                          Reconfigurable Assembly Systems
     Software System Agent Types 2
     • Production Sequence Agent. This agent type will be in charge of a
       particular production sequence that is tasked to produce the correct
       number of products (batch) of a particular configuration from start to
     • Production Planner Agent. This agent will (re)schedule and
       (re)plan production sequences. Production sequences should be
       able to run as concurrently as possible to optimise asset utilisation.
     • Product Tracking Agent. This agent will process product tracking
       events raised by Device Agents assigned to tracking hardware such
       as RFID and or barcode readers.
     • Information Agent. This agent type will handle information queries
       from other agents. This agent can aggregate various information
       sources and or databases and can be used as a proxy to other
       software systems

                           Reconfigurable Assembly Systems
             Features of the Software System
     •   System is being designed with the following features:
         ♦   Process Planning, Control and Monitoring
              • Ability of user to create and execute production plans
                 – The system will determine if a production sequence generated
                     from the production plan is executable and then schedule it to
                        » Is a physical arrangement of devices available to execute
                          the sequence? Are the devices ready or busy with other
                          sequences? What priority is attached to the new sequence,
                          and what priorities do any currently active sequences have?

                                   Reconfigurable Assembly Systems
        Features of the Software System 2
               – The system will execute the steps in the production sequence
                 recursively, checking if pre- and post production device states
                 are favourable during each production step. As one step
                 executes successfully, the next child step is executed
                   » Example step: Start Conveyor 1


     Action                                                       Action to be performed
                                                                  in this step

                                                                  Type 1

                                                                  Type 2
                                Reconfigurable Assembly Systems
     Features of the Software System 3
        – As the system executes the production steps, a collection of
          Type 1 pre-conditions and all post-conditions in the sequence is
          gathered and monitored for changes
            » Should a condition state become unfavourable, upstream
              devices in the sequence will be halted recursively using the
              production step counter action as the system is no longer
              able to execute the production sequence completely
            » If the sequence cannot be re-planned to exclude the faulty
              device and overcome the condition state, human
              intervention is required

                         Reconfigurable Assembly Systems
     Features of the Software System 4
       • Ability to track products as they move through the production
           – As products are scanned by tracking devices the following data
              is logged:
                 » Timestamp
                 » Location in production sequence
           – Through the use of SQL queries, the logging data can be
              converted into useable tracking information
       • Ability to visually represent the status of the system to a human
         operator and to allow the operator to control the system
                 » Human Operator Interface agent can be used to transfer
                   information between any user interface and the system
                   (another example of modularity enhancing re-configurability)

                             Reconfigurable Assembly Systems
                 Planned work:
     Fixture based technology demonstrator
     •   SU                                        •   CUT
         ♦   Feeding subsystem                           ♦   Final inspection subsystem
         ♦   Pallet subsystem                            ♦   Monitor subsystem
              • Fixture by VUT                           ♦   Planner subsystem
         ♦   Transport subsystem                         ♦   Control system modelling
         ♦   Pallet magazine                             ♦   Subsystem control
         ♦   Removal subsystem                           ♦   Platform control analysis
         ♦   Assembly modelling

                                   Reconfigurable Assembly Systems

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