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

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