MODELING AND ANALYSIS OF MANUFACTURING SYSTEMS Session 13 MATERIAL HANDLING SYSTEMS E. Gutierrez-Miravete Spring 2001

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MODELING AND ANALYSIS OFMANUFACTURING SYSTEMS
Session 13MATERIAL HANDLING SYSTEMS E.
Gutierrez-MiraveteSpring 2001

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MATERIAL HANDLING SYSTEM TASKS

• DISTRIBUTE VITAL MATERIALS TO THE PLANTS CELLS
• IMPLEMENT FLOW PATHS PLANNED IN THE FACILITY
  LAYOUT
• CONTROL THE FLOW OF PARTS, TOOLS AND WASTES
  WITHIN AND BETWEEN DEPARTMENTS

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MHS DESIGN GOALS

• TO CONTRIBUTE TO THE EFFECTIVENESS AND EFFICIENCY
  OF THE PLANT
• USUALLY, LESS IS BETTER

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MHS FEATURES

• CORRECT PRODUCT (WHAT)
• LOCATION (WHERE)
• TIMING (WHEN)
• METHOD (WHO HOW)
• CONDITION (HOW)
• ORIENTATION (HOW)
• QUANTITY (HOW MUCH)

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QUESTIONS

• WHAT IS POINT OF USE STORAGE?
• WHAT IS A UNIT LOAD?
• WHY IS NOT ALWAYS TRUE THAT LESS IS BETTER?

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MHS EQUIPMENT TYPES

• CONVEYORS (Fig. 9.3)
• CRANES AND HOISTS
• AUTOMATED STORAGE/RETRIEVAL SYSTEMS (AS/RS)
  (F9.4)
• INDUSTRIAL TRUCKS
• AUTOMATED GUIDED VEHICLES (AGV)

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MHS OTHER COMPONENTS

• CONTAINERS
• ROBOTS
• BAR CODES
• RADIO FREQUENCY SYSTEMS

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MHS PRINCIPLES

• 9.-ECOLOGY
• 10.- MECHANIZE
• 11.- FLEXIBILITY
• 12.- SIMPLIFY
• 13.-GRAVITY
• 14.- SAFETY
• 15.- COMPUTERIZE
• 16.- SYSTEM FLOW

• 1.- ORIENTATION
• 2.- PLANNING
• 3.- SYSTEMS
• 4.- UNIT LOAD
• 5.- SPACE USE
• 6.- STANDARDIZE
• 7.- ERGONOMIC
• 8.- ENERGY

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MHS PRINCIPLES

• 17.- LAYOUT
• 18.- COST
• 19.- MAINTENANCE
• 20.- OBSOLESCENCE

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EQUIPMENT SELECTION

• NUMBER OF EQUIPMENT TYPES AVAILABLE (M)
• NUMBER OF PRODUCT MOVES PLANNED (N)
• EQUIPMENT i MAKES MOVE j
• ASSUME THAT THE FREQUENCY AND DISTANCE FOR EACH
  MOVE ARE ALREADY KNOWN

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EQUIPMENT SELECTION

• VARIABLE COST PER PERIOD cij
• FIXED COST PER UNIT-PERIOD Ci
• TIME PER MOVE tij
• AVAILABLE TIME PER UNIT-PERIOD Ti
• NUMBER OF UNITS OF EQUIPMENT i ACQUIRED Yi
• DECISION VARIABLES Xij
• See Ex. 9.1, p. 297

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DECISION MODEL

• MINIMIZE (cost/period)
• ?i ?j cij Xij ?i Ci Yi
• SUBJECT TO
• ?i Xij 1 (for all j)
• ?j tij Xij lt Ti Yi (for all i)
• See Ex. 9.2 (O) Ex. 9.3 (Yi removed) Ex. 9.4
  (Heuristic)

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TWO KEY FEATURES OF MODERNS MHS

• FLEXIBILITY
• MODULARITY

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BULK LOAD RECEIVAL

• NUMBER OF LOADS/ARRIVAL (b)
• LOAD ARRIVAL RATE (?)
• LOAD SERVICING RATE (?)
• AVERAGE NUMBER OF LOADS WAITING TO BE SERVICED
  (L)
• AVERAGE TIME BETWEEN LOAD ARRIVAL AND SERVICE
  COMPLETION (W)

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BULK LOAD RECEIVAL

• WITH A SINGLE SERVER AND POISSON ARRIVALS, SYSTEM
  BEHAVES AS AN Mb/M/1/inf QUEUE
• Eqn. 9.3
• Ex. 9.5

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CONVEYOR ANALYSIS

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CONVEYOR DESIGN GOAL

• TO PROVIDE THE DESIRED LEVELS OF PERFORMANCE IN
  THE INTENDED ENVIRONMENT

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DECISION VARIABLES

• SPEED
• LENGTH
• CARRIER SPACING
• CARRIER CAPACITY
• NUMBER OF LOAD AND UNLOAD STATIONS

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CLOSED LOOP CONVEYORS

• REVOLVE AT CONSTANT SPEED ALONG A FIXED PATH WITH
  PART CARRIERS EQUALLY SPACED ALONG THE CONVEYOR
  LENGTH
• See Fig. 9.5 Ex. 9.6

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CLOSED LOOP CONVEYOR ANALYSIS

• NUMBER OF LOADING STATIONS (Ml)
• NUMBER OF UNLOADING STATIONS (Mu)
• NUMBER OF WORKSTATIONS (Mw)
• CONVEYOR VELOCITY (v)
• NUMBER OF CARRIERS (N)
• NUMBER OF PARTS/CARRIER (c)

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CONVEYOR LOAD/UNLOAD CAPACITY

• UNITS ARRIVE AT A SINGLE LOADING STATION WITH
  FREQUENCY ????DETERMINISTIC?
• EACH CARRIER HOLDS ONE UNIT
• CARRIERS ARE A DISTANCE d APART ON CONVEYOR
• UNLOADING FREQUENCY ? IS ALSO DETERMINISTIC

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QUESTIONS

• WHAT HAPPENS IF UNITS ARRIVE FASTER THAN THEY CAN
  BE LOADED?
• WHAT HAPPENS THE FIRST TIME A UNIT PASSES AN IDLE
  UNLOAD STATION?
• WHAT HAPPENS IF ALL UNLOADING STATIONS ARE BUSY?
  (BLOCKING)
• Ex. 9.6, p. 304

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CRITERIA

• FOR BLOCKING
• k ? d/v gt 1
• FOR SUCCESSFUL HANDLING OF CONVEYOR TRAFFIC
  THROUGH UNLOADING
• Mu ? gt ?/k

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CARRIER CAPACITY SETTING

• ASSUME VOLUME AND TIMING OF LOAD/UNLOAD REQUEST
  ARE KNOWN
• AMOUNT OF MATERIAL LOADED ONTO THE j-th CARRIER
  ON PASSING STATION i (fi(j))
• LOAD/UNLOAD PERIOD (p)

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CARRIER CAPACITY

• FOR CONVEYOR STABILITY OVER THE CYCLE p NEED
• LOADING UNLOADING
• ?i ?j fi(j) 0
• See Fig. 9.6 Ex. 9.7

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PATH FLEXIBILITY

• CONVEYORS FIXED PATH
• MANNED TRUCKS FLEXIBLE PATH
• AGVS SEMI-FLEXIBLE PATH

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AUTOMATED GUIDED VEHICLES

• USEFUL FOR THE SUPPORT OF ASYNCHRONOUS ASSEMBLY
• CAN PROVIDE CONTROL IN ADDITION TO TRANSPORT
• CAN FUNCTION TO PICK UP AND DROP OFF LOADS ONLY
• CAN FUNCTION AS MOBILE PART FIXTURES

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QUESTIONS

• HOW ARE AGVS CONTROLLED?
• CENTRAL COMPUTER LOCAL CONTROLLERS
• HOW DO AGVS NAVIGATE?
• INDUCTIVE GUIDEPATHS
• OTHER SYSTEMS

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AGVS FOR PICK UP/DROP OFF ENVIRONMENT

• DESIGN ISSUES
• NUMBER OF PICK UP POINTS (P)
• NUMBER OF DROP OFF POINTS (D)
• PATH CONNECTING P AND D
• OPERATIONAL ISSUES
• NUMBER OF VEHICLES IN SYSTEM
• ROUTES THE VEHICLES TAKE

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AGV SYSTEM DESIGN ISSUES

• LOCATION OF P AND D
• GUIDE PATH AND FACILITY LAYOUT
• DECISION PROBLEM FIND SET OF ARCS CONNECTING P
  AND D THAT MINIMIZE LOADED TRAVEL
• See Fig. 9.7 Table 9.3

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PATH DESIGN RULES

• 1.- TRAVEL SHOULD BE UNIDIRECTIONAL UNLESS
  TRAFFIC IS VERY LIGHT (WHY?)
• 2.- PICKUP STATIONS SHOULD BE DOWNSTREAM OF
  DROP-OFF STATIONS (WHY?)

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PATH DESIGN RULES

• 3.- FOR EACH PICKUP POINT ALONG A SEGMENT, TOTAL
  DROP-OFFS FROM THE START OF THE SEGMENT TO THIS
  PICKUP SHOULD BE AT LEAST AS LARGE AS TOTAL
  PICKUPS TO THIS POINT IN THE SEGMENT (WHY?)
• 4.- LOCATE P AND D ON LOW USAGE SEGMENTS
  (WHY?)

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PATH DESIGN RULES

• 5.- IF EMPTY VEHICLES ENTER AND STOP ON A SEGMENT
  TO PICK UP, THEN NO VEHICLES SHOULD LEAVE THE
  SEGMENT EMPTY AFTER DROPPING A LOAD IN THE
  SEGMENT
• 6.- BYPASSES AND SHORTCUTS MAY BE CONSIDERED

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PATH DESIGN

• MATERIAL HANDLING PATHS (See Ex 9.8)
• TANDEM APPROACH (See Fig 9.8)

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VEHICLE REQUIREMENTS

• HOW MANY VEHICLES ARE NEEDED TO PERFORM HANDLING?
• VEHICLE UTILIZATION TIME
• LOADED TRAVEL TIME
• UNLOADED TRAVEL TIME
• BLOCKED TIME
• LOAD TIME
• UNLOAD TIME

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VEHICLE REQUIREMENTS

• FINDING LOADING, UNLOADING AND LOADED TRAVEL
  VEHICLE TIME (See Ex. 9.9)
• HOW ABOUT EMPTY TRAVEL TIME?
• TRANSPORTATION MODELING (Eq. 9.7)
• See Ex. 9.10 (O)

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VEHICLE REQUIREMENTS

• WHAT ABOUT BLOCKING?
• DIVIDE PATH INTO ZONES
• PREVENT TWO VEHICLES FROM BEING IN SAME ZONE
• See Ex. 9.11 (O)

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AGV OPERATION

• PICKUP AND DELIVERY DEMANDS MUST BE MET AT EACH
  P AND D
• TWO CASES
• STATIC SITUATION (CONSTANT DEMAND RATE FOR PICKUP
  AND DELIVERY)
• DYNAMIC SITUATION

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STATIC FLOW OPERATION

• ROUTES SHOULD BE SELECTED SO THAT THEY REPEAT
  CONTINUOUSLY SATISFYING THE SPECIFIED DEMANDS
• WHAT IS A CYCLE? (p. 318)
• See Ex. 9.12
• See Table 9.5a T9.5b, T9.6

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DYNAMIC FLOW

• PRIORITIZE PICKUPS BASED ON
• FCFS WORKSTATION REQUESTS
• NUMBER OF REMAINING SPACES AVAILABLE IN OUTPUT
  QUEUE
• CYCLES MAY BE USED (JOB SHOP)
• IMPLEMENT DEMAND DRIVEN MOVE PRIORITIES (JIT)

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PALLET SIZE AND LOADING