MODELING AND ANALYSIS OF MANUFACTURING SYSTEMS Session 13 MATERIAL HANDLING SYSTEMS E. Gutierrez-Miravete Spring 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.- SIMPLIFY 13.-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 c ij X ij +  i C i Y i SUBJECT TO  i X ij = 1 (for all j)  j t ij X ij < T i Y i (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 M b /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 (M l ) NUMBER OF UNLOADING STATIONS (M u ) NUMBER OF WORKSTATIONS (M w ) 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 M u  > /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 (f i (j)) LOAD/UNLOAD PERIOD (p)

CARRIER CAPACITY FOR CONVEYOR STABILITY OVER THE CYCLE p NEED LOADING = UNLOADING  i  j f i (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 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?)

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 (O)

VEHICLE REQUIREMENTS WHAT ABOUT BLOCKING? –DIVIDE PATH INTO ZONES –PREVENT TWO VEHICLES FROM BEING IN SAME ZONE –See Ex (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 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