Transcript Document 7143412

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 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
b
BEHAVES AS AN M /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 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. 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