Material Handling Module7 Definitions Material Handling Equipment & Classifications Analysis and Design of Material Handling Conveyor Systems AGV systems.

Material HandlingModule7

•Definitions

•Material Handling Equipment & Classifications

•Analysis and Design of Material Handling •Conveyor Systems•AGV systems•AS/RS

Material Handling in Production Systems

Introduction• Purpose of Material handling (MH) is the movement, storage, tracking (or control) of all

materials during manufacturing; and; also during distribution, consumption, and disposal.

• Materials include raw materials, finished parts, tools, and supplies

• Cost of MH could be a significant portion (10 to 70%) of total production cost

• MH equipment is the conduit for materials flow and physical integration within a factory (95% of time).

• Automated MH is a key element in any flexible manufacturing system (primary and secondary systems)

• Because of movements, MH equipment are associated with many accidental injuries on the job.

Requirements

• Safety (humans and products including fragile items)

• Efficient (low cost)• Effective (Timely, Accurately)

Equipment: Classification by Types

• Hand Trucks: dollies, wheeled trucks for manual transport of all material.

• Powered Trucks: forklifts (powered by propane, battery or gasoline), tractor-trailer trains, and other vehicles.

• Cranes and Hoists: specialized overhead equipment for lifting and manipulating heavy objects usually powered.

• Conveyors: move large quantities of materials over a fixed path. Can be continuously moving or use gravity.

• Automated Guided Vehicle Systems (AGVS): powered vehicles that automatically follow a fixed path.

• Automated Storage/Retrieval Systems (ASRS): mechanized systems that automatically store and retrieve items.

• Others indexing table, pipelines

Non-Powered Trucks

Powered Trucks

Cranes and Hoist

Conveyor Systems:Types of Conveyors

• Roller: a series of short tubes roll under the action of gravity or powered ( belts or chains). Very common.( Skate – wheel conveyors)

• Belt: a continuous belt loop driven by pulleys for moving pallets, parts or bulk materials (troughed).

• Overhead trolley: an endless moving cable or chain carries trolleys on overhead rails. Hooks or baskets suspended from the trolleys to carried loads.

• In-floor tow line: a moving cable or chain buried in the floor moves wheeled trailer carts along a fixed path.

• Cart-on-track: individual carts ride on tracks driven by rotating tube. (high positioning)

Types of Conveyors-1

Types of Conveyors-2

Conveyor Accessories

• Angle Pushers• Diverters• Turntable• Switches• Flow Control – traffic cop• Gates• Sorting

Automated Guided Vehicle Systems (AGVS):Vehicle Types

• Driverless train: a guided vehicle tows several trailers carrying heavy loads (up to 50,000 lbs) over long distances.

•Unit-load carrier: a lighter duty (500-1000 lbs) version of the pallet truck with its own automatic load/unload mechanisms.

•Pallet truck: a manually loaded guided vehicle for dispatching medium-duty (<6000 lbs) pallets along a guide path on demand.

Tow train

Pallettruck

Unit loadcarrier

Maximum speed for all is 3 mi/hr = 264 ft/min

Automated Guided Vehicles -AGVs

Automated Guided Vehicle Systems (AGVS): Factory Applications

• Warehousing, shipping and receiving: moving large quantities over large distances in large factories and warehouses typically require drivereless trains.

• Storage and distribution: unit load carriers and pallet trucks typically move materials randomly and in varied quantities to and from automated storage systems.

• Assembly-Lines: extra light duty (<500 lb) unit-load carriers move part kits between workstations assembling several variations of the product on the assembly line

(4-10min cycle time)• FMS: unit-load carriers and pallet trucks move parts and

tools between workstations, staging areas and storage areas under the control of the FMS supervisory controller.

Vehicle Guidance Technologies• Fixed Pathway

– Impeded Guide Wires (magnetic (coil) sensors)– Paint Strip (UV sensors)

Vehicle Guidance Technologies

• Flexible Pathway– Self-Guided Vehicle (SGV)

Has on board navigation computer Term “Dead Reckoning”

Vehicle Management and Safety

• Objectives

– Minimize waiting time at loading/unloading stations– Equipment utilization and service time management

issues– Minimize traffic congestions– Operate safely

AGVS: Vehicle Management and Safety• Traffic Control (on-board sensing)

• Zone Control (control units on pathway)

• Vehicle Dispatching – On-board control panel– Remote call stations– Central computer

• Safety (speed, safety bumper, obstacle detection, etc)• Additional technologies that can improve above issues

are ?????

Material Handling System Design Consideration

Material Handling System Design• Objectives

– Safety (humans and products ‘fragile’)– Efficient (low cost)– Effective (Timely, Accurately)

• Factors that influence design– Material Characteristics– Flow rate, Routing, and Scheduling– Plant Layout

Material Characteristics

Flow rate, Routing, and Scheduling• Flow rate (dedicated and shared?)

• Routing (distances? conditions?)

•Scheduling (MH system response?)

Plant Layout • Information required for system design are:

– Path of materials flow and potential obstacles– Load and unload locations– Materials flow pattern and potential congestion points– Distances traveled – Arrangement of equipment within each department– Storage requirements and location for WIP– Total area of the facility

• Plant layout strongly influences the type and the configuration of equipment in a MH system (new ?)- Fixed-position, Process (or Cellular) Type, Product-Flow

Plant Layout

The 10 Principles of MH (Table 9.3)

• Planning Principle• Standardization Principle• Work Principle• Ergonomics Principle – human capabilities and limitations• Unit Load Principle• Space utilization principle• System principle• Automation principle• Environmental principle• Life Cycle Cost principle

Analysis of Materials Handling Systems

• Flow diagram

• From-to chart

Conveyor Systems: Common Characteristics

• Are generally mechanized and sometimes automated• Follow fixed path (single direction, continuous loop,

recirculating)• Mounted on the floor or overhead• Move materials mostly in one-direction• Move discrete parts or bulk (continuous load)• Used for transport and dynamic storage (Later?)• Non-powered individual carriers or pallets ride on the

powered or gravity-driven conveyor

Conveyor Analysis:Single Direction Conveyors

vc

c

dd v

LT

where:Td = delivery time (min/carrier)Ld = conveying distance between load

and unload stations (m,ft)vc = conveyor speed (m/min, ft/min)Rf = material flow rate (parts/min)

Assumptions:1. Belt moves in one direction2. One load station at the input end3. One unload station at the output end

L

p

c

cpLf T

n

s

vnRR

RL= loading rate (parts/min)np= number of parts per carriersc = carriers spacing on conveyor

(m/carrier, ft/carrier)TL= loading time (min/carrier)TU= unloading time (min/carrier)

Ld

sc

LoadStation

UnloadStation

TLTU

TU < TL

Conveyor Analysis:Example 1

It takes 20 sec to load 18 parts into each tote pan and 4 sec to load the tote pan onto the single direction belt conveyor. Find: (a) delivery time, Td (min)

(b) minimum tote pan spacing, sc (ft)

(b) maximum possible parts flow rate, Rf (parts/min);

(c) maximum unload time TU

vc= 50 ft/min

Ld =200 ft

scTL

TU

ft/min50

ft200

c

dd v

LT = 4.0 min (for a specific tote)

sc = vc TL = (50 ft/min) (20 s + 4 s) (1 min/60 s) = 20 ft

ft 20

)ft/min50(parts18

c

cpf s

vnR = 45 parts/min TU < TL < 24 s/pan

0.40 min/pan

Belt conveyor

Conveyor Analysis:Continuous Closed-Loop Conveyors

vc

Return legLe

Delivery leg Ld

c

edc s

LLn

Empty carrier

Load station

Unload station

np

Full carrier

Consider a continuous closed-loop conveyor, such as an overhead trolley system with one load and one unload station. Assume that all carriers are emptied at the unload station.

ed

dcp

c

dpp LL

Lnn

s

LnN

L

p

c

cpf T

n

s

vnR

nc = number of carriers in the systemLd = length of the delivery leg (ft or

m)Le = length of the return leg (ft or m)sc = carriers spacing (ft or m/carrier)

Np = total number of parts in the systemnp = number of parts in each carrierRf = part feed rate (parts/min)vc = conveyor speed (ft/min or m/min)

Conveyor Analysis:Recirculating Conveyors

• Continuous loop conveyors can be used for storage, if loaded carries are allowed to flow back on the return leg raising the following possibilities:– Empty carriers are not available when needed for

loading

– Full carriers are not immediately available for unloading (airport conveyor)

Conveyor Analysis:Recirculating Conveyors

• Kwo’s recirculating conveyor design requirements with ONE load station and ONE unload station. Three rules

– Speed rule: Operating speed within a certain limit determined by #carriers/min (vc/ sc ). The lower limit should be greater than or equal the required loading or unloading rate whichever is the greater.

The upper limit should be less or equal to the capabilities of the material handlers.

c

cp

LUs

vn , RMax R

c

c

s

v<Min 1

TL TU

1,

parts/min

min/carrier

Conveyor Analysis:Recirculating Conveyors

– Capacity constraint: The flow rate capacity of the conveyor must be at least equal to the flow rate requirement to accommodate reserve stock and allow for the time elapsed between loading and unloading due to delivery distance.

– Uniformity Principle: empty and full carriers should be uniformly distributed along the line to avoid excessive waiting for carriers.

c

cp

fs

vnR

Conveyor Analysis: Example 2A recirculation conveyor has a total length of 300m. Its speed is 60m/min, and the spacing of part carriers along its length is 12m. Each carrier can hold 2 parts. The time required to load 2 parts into each carrier is 0.20min and the unload time is the same. The required loading and unloading rates are both defined by the specified flow rate, which is 4parts/min. Evaluate the conveyor system design with respect to Kwo’s three principle.

Find: Specified flow rate , Rf = 4 parts/minConveyor speed, vc = 60m/minSpacing of carriers, Sc =12m Number of parts per carrier, np = 2 parts

Loading TL = Unloading TU = 0.2 min/carrier

Solution: 1) Speed Rule

c

cp

LUs

vn , RMax R

c

c

s

v<Min 1

TL TU

1,

Example 2 (continue)

2) Capacity Constraint

Actual flow rate capacity = 10 parts/min (> 4 parts/min)

c

cp

fs

vnR

3) Uniformity Principle

-Loading rate = unloading rate

-Other

Flow rate capacity (10 parts/min) is substantially greater than

required loading / unloading rate (4parts /min)

AGVS: Common Characteristics

• An AGVS is a automated material handling system consisting of independently operated, self-propelled vehicles that are automatically guided along defined paths.

AGVS: Common Characteristics

• On-board batteries usually power AGVS vehicles for 10 to 16 hrs of operation.

• On-board control system uses sensors to detect the position of wires buried in the floor or strips of reflective paint and guide the vehicle along the desired path within a certain margin of error (pp387-393).

• Vehicles automatically (sensors) detect obstacles and avoid collisions with other objects

AGVS: Factors to Consider in System Design

• Guide path type (?) and vehicle type• Path routing and layout• Flow direction along each path segment• Number and location of docking points for

loading and unloading• Number and locations of vehicle parking sites• Required number of vehicles• Dispatching rules and frequency of pickups and

deliveries

AGVS Analysis: Delivery Cycle Time

• Analysis begins with estimating the total time Tc in a delivery cycle of a vehicle on the average, ignoring effects of traffic congestion:

Tc = delivery cycle time for one vehicle (min/del) TL = loading time (min)Ld = average distance traveled while loaded per delivery (ft or m)vc = AGV speed which is assumed to be constant (ft/min, m/min)TU = unloading time (min)Le = average distance traveled while empty per delivery (ft or m)

Other Assumptions?

c

eU

c

dLc v

LT

v

LTT

AGVS: Factors affect Delivery Cycle Time

• Availability (A)

• Traffic congestion (Tf )

• Efficiency of manual elements (E)

ETAAT f60

e)per vehiclhr (min/

AGVS: Rate of deliveries

e)per vehicl/hr Deliveries(

cdv T

ATR

AGVS: Number of Vehicles

Vehiclesdv

fc R

Rn

hour per deliveries (Designed) Required isfR

AGV: ExampleIt is desired to design a particular AGVS system that iscapable of making 40 deliveries/hr. The performance characteristics of the system are: Vehicle velocity = 150 ft/min Average distance traveled per delivery = 450 ft Average distance traveled empty = 450 ft

Pick up time = 45 sec Drop-off time = 45 sec

Traffic factor = 0.90Determine the required number of vehicles.

Storage Systems

Storage System- Types of Materials

Storage System- Location Strategies• SKU?

Most Common:• Randomized Storage

– Designed based on the average inventory level

• Dedicated Storage – Designed based on max inventory level

• Class-based dedicated storage– Designed based on activity level

Which uses less Space?

Which is Faster?

Storage Capacity : Example 4

Determine the number of storage locations required in the system based on the randomized storage and dedicated storage strategies

Note : a different SKU arrives each day

Total 50 SKU

Storage System- Performance• Storage cycle (pick, travel, place, travel)• Retrieval cycle?

Traditional Systems– Storage Capacity– Density– Accessibility– Throughput

Mechanized and Automated Systems:– Utilization– Availability (Uptime Reliability)

Storage Capacity/ Density/Accessibility

• Storage Capacity is defined by the number of total unit loads stored in the system

– Physical capacity should be greater than the MAX number of unit loads anticipated to be stored (Why?)

• Storage Density is defined as the volumetric space available for actual storage relative to the total volumetric space in the storage facility (floor area?)

• Accessibility refers to the the capability to access any desired unit load in the system

– Trade-offs are made between storage density and accessibility

System Throughput

• Defined as the hourly rate at which the storage system– Receives and puts loads into storage (storage

transaction) and/or– Retrieves and delivers loads to the output station

(retrieval transaction)

– Single command cycle or Dual command cycle

• System is designed to handle the MAX hourly rate required.

Utilization and Reliability

• Utilization is defined as the proportion of time that the system is actually being used for performing storage and retrieval operations compared with the time it is available (80-90%)– Utilization varies throughout the day

• Availability is a measure or reliability. It is defined as the proportion of time that the system is capable of operating (not broken down) compared with the normally scheduled shift hours. – General approaches to improve reliability (preventive

maintenance, redundancy)

Some Formulas

• Scheduled time/shift = hrs in a shift (8 hrs)

• Available time/shift = (Scheduled time/shift) – (Downtime/shift)

• Utilization = (Actual time used )/ (Available time)

• Availability = (Uptime) / (Scheduled time)

Automated Storage and Retrieval Systems (AS/RSs)

• An AS/RS is an automated system of storage, control and actuating devices which handles, stores and retrieves materials with precision, accuracy and speed.

• An AS/RS automatically:

– Stores an item at predetermined storage site– Removes a specified item from a storage site– Transports the item to a processing or transfer point

Automating Storage Operations

AS/RS Common Characteristics

• Custom designed• Computer Controlled (or manual)• Storage locations serviced by S/R (storage/Retrieval)

machines • One or more P&D stations (Pick up and Deposit).

Manually operated or interfaced to handling system • Two basic types of AS/RS:

– Standard (unit load) or Conventional – Carousel storage systems

Unit Load AS/RS

AS/RS : Standard Systems

Several types

– Unit load– Miniload– Man-on-board– Others

Carousel AS/RS

Unit Load vs Carousel Storage

Adapted from: Groover, M.P, “Automation Production Systems,” Prentice-Hall, 1987, p. 409.

Unit-Load LayoutTop view

Front view

Aisles

Pickup/Deposit (P/D) stations

Storage/RetrievalS/R machine

Interfaceconveyor

Storageracks

Bay

Row

Unit Load AS/RS (most common)

• A Unit load AS/RS is a massive structure for handling individual bulky items or groups of items on pallets or in containers

• Unit load systems have the following physical features:– Storage Structure. A series of storage racks arranged horizontally

in rows and vertically in bays separated by aisles for access– A Storage/Retrieval (S/R) machine servicing each aisle– One or more Pickup/Deposit (P/D) stations– Storage modules (unit load containers-pallets)

• Special features– Aile Transfer Cars (when S/R car services more than ONE aisle)– Full-Empty Detectors– Sizing Station– Load Identification Stations (tracking)

AS/RS Design:System Requirements Specification

• Storage capacity:– load sizes– size and number of storage compartments– number of rows and number of bays in each row

• Space requirements:– bay width, bay depth, rack length and rack height (30-90')– aisle spacing, number of racks and system overall size

• System performance:– required number of (store/retrieve) cycles per hour,– capacity of each S/R machine in (cycles/hr)– number of S/R machines required – cycle time for retrieve, store or for both

AS/RS : Sizing and Space Requirements• The dimensions Ls , Hs and Ws of an aisle unit are

given in terms of the dimensions x, y and z of the basic unit load and clearance:

The size of the overall system is determined by the number of aisle units Na needed to hold the inventory levels

Ls = nh (x + a)

Hs = nv(y + b)

Ws = k (z + c)

For a standard pallet:x = 42 inch and a = 8 inchy = 48 inch and b = 10 inchz = 36 inch and c = 6 inchK = 1-3

Aisle unit

Hs

Ls

W s

x+a

y+b

z+c

Basic storage compartment containing a unit load

nv is the number of rows and nh is the number of bays. Each aisle unit contains 2nv nh compartments.

nv nh

Sizing AS/RS system : Example A four –aisle AS/RS is to contain 60 storage compartments in the length direction and 12 compartments vertically. All storage compartments will be the same size to accommodate standard size pallets. Determine Storage capacity and dimensions of the storage rack structure.

Ls = nh (x + a) = 60 (48 + 8) = 3360 in = 280 ft

Hs = nv(y + b) = 12 (36+10) = 552 in = 46 ft

Ws = k (z + c) = 3 (42 + 6) = 144 in = 12 ft

x+a

Storage capacity per aisle = 2 nv nh = 2(12)(60) = 1440 unit loads

Total Storage Capacity = 4(1440) = 5760 unit loads

Aisle unit

Hs

Ls

W s

y+b

z+c

nv nh

x+a

AS/RS : Throughput • Transaction cycle time Tsc depends on average travel times of the S/R machine and pickup or deposit times:

Assumptions• Single-command cycle initiating a store or retrieve transaction (dual-)

• Randomized storage of pallets

• Storage compartments of equal size

• P/D station located at base and end of aisle

• Uniform horizontal and vertical speed of S/R machine

• Simultaneous horizontal and vertical movement of S/R

Storage System Performance Criteria

There are several standard measures– Storage Capacity– Density– Accessibility– Throughput– Utilization– Reliability (Uptime Reliability)

AS/RS Design: # S/R Machines and Throughput• The number of single-command transactions nsc each S/R machine completes

each hour is

scsc T

An

60

Where: nsc = number of P/D cycles a machine can make per hour Tsc = single-command transaction cycle time per machine (min) A = fraction of time an S/R machine is available

The minimum number of S/R machines required is:

sc

dtm n

nN min,

Where: Nm,min = minimum number of S/R machines requirednsc = number of P/D cycles a machine can make per hr ndt = total number of P/D cycles required per hour

The actual required number of S/R machines Nm should at least equals the number of aisles, Na.

Nm = max (Nm,min, Na)

AS/RS Design: Example 6

Determine the number of S/R machines required to achieve up to 240 pickup or deposit transactions per hour. The horizontal travel speed of the S/R machines is 320 ft/min and the vertical speed is 80 ft/min. Each P/D operation takes about 0.50 min. The horizontal travel is 280 ft and the vertical travel is 46 ft

Solution:Need to determine cycle time Tsc:

th = Ls/Vh = 280 ft/320 ft/min = 0.875 mintv = Hs/Vv = 46 ft/80 ft/min = 0.575 min T = max (th, tv) = max (0.875,0.575) = 0.875 minQ = min (th/T, tv/T) = min (0.875/0.875, 0.575/0.875) = min (1.0,0.657) = 0.657Tsc = T [(Q2/3) + 1] + 2 tpd = 0.875[(0.657)2/3 + 1] + 2(0.50) = 2.00 min

Minimum number of S/R machines Nm,min nsc = 60A/Tsc = 60 (min/hr) (1)/2.00 min = 30 cycles/hr per machine Nm,min = ndt / nsc = 240/30 = 8 machines.

The number of ailes Na?

Combination of Single & Dual cycles?

AS/RS:Storage Carousel

Groover, M., 1987, Automation, Production Systems, and Computer Integrated Manufacturing

Carousel Applications & Advantages

Low cost versatile, and reliable

•Storage and Retrieval applications (kitting, service room)

•Transport and Accumulation (assembly system?)

•Suited for Automated WIP applications (others?)

AS/RS: Advantages (Table 15.2)

• Efficient use of valuable space (up instead of out)• Improved inventory management (find and account for any and all

inventory items)• Increased responsiveness to materials handling service requests• Minimized waste, theft and spoilage• Ease of interfacing with other automated systems such as FMS, CNC

and AGVS• Ease of tracking products for quality and regulatory purposes.

Traditional WIP Storage• Batch and Job shop

• While the cell is processing one order– Several orders awaiting at the cell– Finished orders awaiting to be transported

• WIP placed in Close proximity to cell

• Disadvantages– Lost parts and /or orders– Identification– Priority of processing– Longer lead time– Cost, etc

Automated WIP Storage• Justification

– Kitting of parts for assembly

– Integral part in an assembly system

– Support JIT (critical components)

– Buffer storage (un-equal operation time)

– Improved control and tracking of materials

– Support factory wide automation (including Automated Data Collection)