MODELING AND ANALYSIS OF MANUFACTURING SYSTEMS Session 13 MATERIAL HANDLING SYSTEMS E....
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Transcript of MODELING AND ANALYSIS OF MANUFACTURING SYSTEMS Session 13 MATERIAL HANDLING SYSTEMS E....
MODELING AND ANALYSIS OFMANUFACTURING SYSTEMS
Session 13
MATERIAL HANDLING SYSTEMS
E. Gutierrez-MiraveteSpring 2001
MATERIAL HANDLING SYSTEM TASKS
• DISTRIBUTE VITAL MATERIALS TO THE PLANT’S CELLS
• IMPLEMENT FLOW PATHS PLANNED IN THE FACILITY LAYOUT
• CONTROL THE FLOW OF PARTS, TOOLS AND WASTES WITHIN AND BETWEEN DEPARTMENTS
MHS DESIGN GOALS
• TO CONTRIBUTE TO THE EFFECTIVENESS AND EFFICIENCY OF THE PLANT
• USUALLY, LESS IS BETTER
MHS FEATURES
• CORRECT PRODUCT (WHAT)
• LOCATION (WHERE)
• TIMING (WHEN)
• METHOD (WHO & HOW)
• CONDITION (HOW)
• ORIENTATION (HOW)
• QUANTITY (HOW MUCH)
QUESTIONS
• WHAT IS POINT OF USE STORAGE?
• WHAT IS A UNIT LOAD?
• WHY IS NOT ALWAYS TRUE THAT LESS IS BETTER?
MHS EQUIPMENT TYPES
• CONVEYORS (Fig. 9.3)
• CRANES AND HOISTS
• AUTOMATED STORAGE/RETRIEVAL SYSTEMS (AS/RS) (F9.4)
• INDUSTRIAL TRUCKS
• AUTOMATED GUIDED VEHICLES (AGV)
MHS OTHER COMPONENTS
• CONTAINERS
• ROBOTS
• BAR CODES
• RADIO FREQUENCY SYSTEMS
MHS PRINCIPLES
1.- ORIENTATION
2.- PLANNING
3.- SYSTEMS
4.- UNIT LOAD
5.- SPACE USE
6.- STANDARDIZE
7.- ERGONOMIC
8.- ENERGY
9.-ECOLOGY
10.- MECHANIZE
11.- FLEXIBILITY
12.- SIMPLIFY13.-GRAVITY
14.- SAFETY
15.- COMPUTERIZE
16.- SYSTEM FLOW
MHS PRINCIPLES
17.- LAYOUT
18.- COST
19.- MAINTENANCE
20.- OBSOLESCENCE
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
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
DECISION MODEL• MINIMIZE (cost/period)
i j cij Xij + i Ci Yi
• SUBJECT TO
i Xij = 1 (for all j)
j tij Xij < Ti Yi (for all i)• See Ex. 9.2 (O); Ex. 9.3 (Yi removed); Ex.
9.4 (Heuristic)
TWO KEY FEATURES OF MODERNS MHS
• FLEXIBILITY
• MODULARITY
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)
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
CONVEYOR ANALYSIS
CONVEYOR DESIGN GOAL
• TO PROVIDE THE DESIRED LEVELS OF PERFORMANCE IN THE INTENDED ENVIRONMENT
DECISION VARIABLES
• SPEED
• LENGTH
• CARRIER SPACING
• CARRIER CAPACITY
• NUMBER OF LOAD AND UNLOAD STATIONS
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
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)
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
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
CRITERIA
• FOR BLOCKING
k = d/v > 1• FOR SUCCESSFUL HANDLING OF
CONVEYOR TRAFFIC THROUGH UNLOADING
Mu > /k
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)
CARRIER CAPACITY
• FOR CONVEYOR STABILITY OVER THE CYCLE p NEED
• LOADING = UNLOADING
i j fi(j) = 0• See Fig. 9.6; Ex. 9.7
PATH FLEXIBILITY
• CONVEYORS: FIXED PATH
• MANNED TRUCKS: FLEXIBLE PATH
• AGV’S: SEMI-FLEXIBLE PATH
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
QUESTIONS
• HOW ARE AGVS CONTROLLED?– CENTRAL COMPUTER & LOCAL
CONTROLLERS
• HOW DO AGV’S NAVIGATE?– INDUCTIVE GUIDEPATHS– OTHER SYSTEMS
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
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
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?)
PATH DESIGN RULES3.- 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?)
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
PATH DESIGN
• MATERIAL HANDLING PATHS (See Ex 9.8)
• TANDEM APPROACH (See Fig 9.8)
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
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)
VEHICLE REQUIREMENTS
• WHAT ABOUT BLOCKING?– DIVIDE PATH INTO ZONES
– PREVENT TWO VEHICLES FROM BEING IN SAME ZONE
– See Ex. 9.11 (O)
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
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
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)
PALLET SIZE AND LOADING