Transcript Document

Materials Handling
Objectives
•To review modern technologies for material handling:
- Part handling
- AGV’s
- AS/RS
- conveyors
•To consider application conditions (student presentations)
•To introduce assessment criteria
•To test understanding of the material presented
Material handling principles
( from Groover )
Principle 1 - PLANNING PRINCIPLE: All material handling should be the result of a
deliberate plan where the needs, performance objectives, and functional specification
of the proposed methods are completely defined at the outset.
• The plan should be developed in consultation between the planner(s) and all who will
use and benefit from the equipment to be employed.
• Success in planning large-scale material handling projects generally requires a team
approach involving suppliers, consultants when appropriate, and end user specialists
from management, engineering, computer and information systems, finance, and
operations.
• The plan should promote concurrent engineering of product, process design, process
layout, and material handling methods as opposed to independent and sequential
design practices.
• The plan should reflect the strategic objectives of the organization as well as the more
immediate needs.
Material handling principles
( from Groover )
Principle 2 - STANDARDIZATlON PRINCIPLE: Material handling methods,
equipment, controls, and software should be standardized within the limits of achieving
overall performance objectives and without sacrificing needed flexibility modularity,
and throughput.
• Standardization means less variety and customization in the methods and equipment
employed.
• Standardization applies to sizes of containers and other load forming components as
well as operating procedures and equipment.
• The planner should select methods and equipment that can perform a variety of tasks
under a variety of operating conditions and in anticipation of changing future
requirements.
• Standardization, flexibility, and modularity must not be incompatible.
Material handling principles
( from Groover )
Principle 3 - WORK PRINCIPLE: Material handling work should be minimized without
sacrificing productivity or the level of service required of the operation.
• The measure of material handling work is flow rate (volume, weight, or count per unit
of time) multiplied by distance moved.
• Consider each pickup and set-down, or placing material in and out of storage, as
distinct moves and components of the distance moved.
• Simplifying processes by reducing, combining, shortening, or eliminating unnecessary
moves will reduce work.
• Where possible, gravity should be used to move materials or to assist in their
movement while respecting consideration of safety and the potential for product
damage.
Material handling principles
( from Groover )
Principle 3 - WORK PRINCIPLE: Material handling work should be minimized without
sacrificing productivity or the level of service required of the operation.
• The Work Principle applies universally, from mechanized material handling in a
factory to over-the-road trucking.
• The Work Principle is implemented best by appropriate layout planning: locating the
production equipment into a physical arrangement corresponding to the flow of work.
This arrangement tends to minimize the distances that must be traveled by the
materials being processed.
Material handling principles
( from Groover )
Principle 4 - ERGONOMIC PRINCIPLE: Human capabilities and limitations must be
recognized and respected in the design of material handling tasks and equipment to
ensure safe and effective operations.
• Ergonomics is the science that seeks to adapt work or working conditions to suit the
abilities of the worker.
• The material handling workplace and the equipment must be designed so they are safe
for people.
• The ergonomic principle embraces both physical and mental tasks.
• Equipment should be selected that eliminates repetitive and strenuous manual labor
and that effectively interacts with human operators and users.
Material handling principles
( from Groover )
Principle 5 - UNIT LOAD PRINCIPLE: Unit loads shall be appropriately sized and
configured in a way which achieves the material flow and inventory objectives at each
stage in the supply chain.
• A unit load is one that can be stored or moved as a single entity at one time, such as a
pallet, container, or tote, regardless of the number of individual items that make up the
load.
• Less effort and work are required to collect and move many individual items as a
single load than to move many items one at a time.
• Large unit loads are common in both pre- and post-manufacturing in the form of raw
materials and finished goods.
• Smaller unit loads are consistent with manufacturing strategies that embrace operating
objectives such as flexibility, continuous flow and just-in-time delivery. Smaller unit
loads (as few as one item) yield less in-process inventory and shorter item throughput
times.
Material handling principles
( from Groover )
Principle 6 - SPACE UTILIZATION PRINCIPLE: Effective and efficient use must be
made of all available space.
• Space in material handling is three-dimensional and therefore is counted as cubic
space.
• In storage areas, the objective of maximizing storage density must be balanced against
accessibility and selectivity.
• When transporting loads within a facility, the use of overhead space should be
considered as an option. Use of overhead material handling systems saves valuable
floor space for productive purposes.
Material handling principles
( from Groover )
Principle 7 - SYSTEM PRINCIPLE: Material movement and storage activities should be
fully integrated to form a coordinated, operational system that spans receiving,
inspection, storage, production, assembly, packaging, unitizing, order selection,
shipping, transportation, and the handling of returns.
• Systems integration should encompass the entire supply chain, including reverse
logistics. It should include suppliers, manufacturers, distributors, and customers.
• Inventory levels should be minimized at all stages of production and distribution while
respecting considerations of process variability and customer service.
• Information flow and physical material flow should be integrated and treated as
concurrent activities.
• Methods should be provided for easily identifying materials and products, for
determining their location and status within facilities and within the supply chain, and
for controlling their movement.
Material handling principles
( from Groover )
Principle 8 - AUTOMATION PRINCIPLE: Material handling operations should be
mechanized and/or automated where feasible to improve operational efficiency,
increase responsiveness, improve consistency and predictability, decrease operating
costs, and eliminate repetitive or potentially unsafe manual labor.
• In any project in which automation is being considered, pre-existing processes and
methods should be simplified and/or re-engineered before any efforts to install
mechanized or automated systems. Such analysis may lead to elimination of
unnecessary steps in the method. If the method can be sufficiently simplified, it may
not be necessary to automate the process.
• Items that are expected to be handled automatically must have standard shapes and/or
features that permit mechanized and/or automated handling.
• Interface issues are critical to successful automation, including equipment-toequipment, equipment-to-load, equipment-to-operator, and in-control communications.
• Computerized material handling systems should be considered where appropriate for
effective integration of material flow and information management.
Material handling principles
( from Groover )
Principle 9 - ENVIRONMENTAL PRINCIPLE: Environmental impact and energy
consumption should be considered as criteria when designing or selecting alternative
equipment and material handling systems.
• Environmental consciousness stems from a desire not to waste natural resources and to
predict and eliminate the possible negative effects of our daily actions on the
environment.
• Containers, pallets, and other products used to form and protect unit loads should be
designed for reusability when possible and/or biodegradability after disposal.
• Materials specified as hazardous have special needs with regard to spill protection,
combustibility, and other risks.
Material handling principles
( from Groover )
Principle 10 - LIFE CYCLE COST PRINCIPLE: A thorough economic analysis should
account for the entire life cycle of all material handling equipment and resulting systems.
• Life cycle costs include all cash flows that occur between the time the first dollar is spent
to plan a new material handling method or piece of equipment until that method and/or
equipment is totally replaced.
• Life cycle costs include capital investment, installation, setup and equipment
programming, training, system testing and acceptance, operating (labor, utilities, etc.),
maintenance and repair, reuse value, and ultimate disposal.
• A plan for preventive and predictive maintenance should be prepared for the equipment,
and the estimated cost of maintenance and spare parts should be included in the economic
analysis.
Material handling principles
( from Groover )
Principle 10 - LIFE CYCLE COST PRINCIPLE: A thorough economic analysis should
account for the entire life cycle of all material handling equipment and resulting systems.
• A long-range plan for replacement of the equipment when it becomes obsolete should be
prepared.
• Although measurable cost is a primary factor, it is certainly not the only factor in
selecting among alternatives. Other factors of a strategic nature to the organization and
that form the basis for competition in the market place should be considered and
quantified whenever possible.
Automated Guided Vehicle (AGV)
Definition - An AGV is an independently operated vehicle
that moves material along defined paths between defined
delivery points or stations. Typically the paths are defined
by either using wires embedded in the floor or reflecting
paint strips on the floor.
Some of the more advanced
technologies use laser
triangulation or inertial guidance
systems on-board the vehicles,
with distributed calibration
stations for position updating.
AGV classification
Driverless trains - AGV is a towing vehicle used to tow one or more trailers
forming a train between stations.
Pallet trucks - Used to move palletized loads along predetermined routes.
Typically, personnel will steer the AGV to the pallet, acquire the pallet, then
steer it to the guide-path where the automated guidance system will then
move it to its destination. In a sense, it can be thought of as an automated
forklift.
Unit load carriers - Move unit loads from from one station to another
station. A unit load is a collection of items that is delivered repetitively as a
unit.
AGV applications
Driverless train operations - Movement of large material quantity over large distances
(between buildings, warehouses).
Storage/distribution systems - Uses unit load carriers and pallet trucks to transfer material
between stations, sometimes interfacing with other automated systems such as an AS/RS
(Automated Storage and Retrieval System). Works well in assembly operations where the
unit loads (or kits) can be transferred from a central storage area to assembly sites.
Assembly line operations - AGV’s become part of the assembly operation by transferring
material along an assembly line (such as moving an engine block between operational
stations)
Flexible manufacturing systems (FMS) - AGV’s are used to transfer parts, materials and
tooling between the FMS process stations.
Miscellaneous applications - Non-manufacturing applications include the handling of
sensitive waste, transportation of material at hospitals, mail transportation.
AGV guidance and control
Guidance and control functions:
Vehicle guidance - on-board control system to move the vehicle along pre-defined paths by
a feedback loop between the control system and the guide wire (or paint). More modern
systems use inertial guidance to move the AGV between calibration stations. In situations
where the guide wire or paint is discontinuous, the control system uses dead reckoning to
transition these points.
Traffic control - collision avoidance between multiple AGV’s. The control system is
designed with blocking algorithms that use a combination of on-board vehicle sensing
and zone control.
Systems management - programming interfaces and algorithms for moving AGV’s between
stations, and for scheduling the movement of multiple AGV’s.
AGV material handling analysis
Terms:
vc - AGV average speed
(c = conveyor, carrier, cart, etc.)
ve - AGV empty speed
Th - load handling time
Ld - destination distance
Le - empty move distance
Tf - traffic factor (<= 1)
Rdv - rate of deliveries per vehicle
nc - number of carriers required
Rf - specified flow rate of system (del/hr)
Tc - delivery cycle time (min/del)
TL - time to load at load station (min)
TU - time to unload at load station (min)
WL - workload (total work in min per hour)
Eh - handling system efficiency
A - proportion of time vehicle is operational
AT- available time in min/hr/veh
E - worker efficiency
AGV material handling analysis
Equations:
del cycle time
Tc = TL + TU + Ld / vc + Le / ve
available time
AT = 60 A Tf E
(min/hr/veh)
rate of del per vehicle
Rdv = AT / Tc
(num del/hr/veh)
work by handling system per hr
WL = Rf Tc
(min/hr)
num of vehicles for workload nc = WL/AT = Rf / Rdv
(min)
(num of veh for work load)
AGV example (from text)
Given the AGV layout in the figure and the info listed,
determine the number of vehicles required for a
delivery (flow) rate of 40 del/hr.
Info:
Loading time = 0.75 min
Unloading time = 0.5 min
Vehicle speed = 50 m/min
Availability = 0.95
Traffic factor = 0.9 (from fig) =>Ld = 110 m ; Le = 80 m
E=1
Solution:
Ideal cycle time/del/veh = Tc = 0.75 + 0.5 + 110/50 + 80/50 = 5.05 min
Compute workload = WL = (40) (5.05) = 202 min/hr
Available time = AT = (60) (0.95) (0.90) (1.0) = 51.3 min/hr/veh
Num of vehicles = nc = 202/51.3 = 3.94 veh => 4 vehicles!
AGV questions
• Who are major vendors of AGV’s?
• Describe their components (power source, transmission system,
communication system, etc.)?
• What are typical costs?
• What type of interfaces do they have? How are they programmed?
• How fast do they move?
• What are load to weight ratios?
• Unusual maintenance requirements?
• How do they avoid collisions?
• How are they scheduled?
Automated Storage and Retrieval System
(AS/RS)
Definition - An AS/RS is a
combination of equipment and
controls which handles, stores,
and retrieves materials with
precision, accuracy, and speed
under a defined degree of
automation. (Materials Handling Institute)
AS/RS classification
Unit load AS/RS - Large automated system designed to use S/R machines to
move unit loads on pallets into and out of storage racks.
Mini-load AS/RS - Smaller automated system designed to move smaller
loads into and out of storage bins or drawers.
Man-on-board AS/RS - Uses personnel to pick items from racks or bins,
reducing transaction time.
Automated item retrieval system - Items to be moved are stored in single
file lanes, rather than in bins or drawers.
AS/RS applications
Unit load storage and handling - Warehousing for finished goods/products.
Order picking - Used to store and retrieve materials in less than full unit
load quantities, such as man-on-board or mini-load applications.
Work-in-process - Support just-in-time production activities, buffer storage,
and as integral part of assembly systems.
AS/RS control
The S/R is a large Cartesian type robot that integrates
modern control technology, I/O, and sensors
(compartment identification) to move between storage
compartments. AS/RS control is integrated with modern
material management software for real-time inventory
control, storage transactions, and material delivery.
AS/RS material handling analysis
Terms:
C – capacity per aisle
vz - vertical speed (m/min, ft/min)
x - width of unit load
vy - horizontal speed (m/min, ft/min)
y - length of unit load (in horizontal direction)
tz - vertical travel time (min)
z - height of unit load (in vertical direction)
ty - horizontal travel time (min)
nz - number of vertical compartments
Tcs - single command cycle time (min/cycle)
ny - number of horizontal compartments Tcd - dual command cycle time (min/cycle)
U - system utilization per hr
Tpd – pickup and deposit time (min)
W - width of AS/RS rack
Rcs - num of single commands per hr
H - height of AS/RS rack
Rcd - num of dual commands per hr
L - length of AS/RS rack
Rc - total cycle rate in cycles/hr
Rt - num transactions per/hr
AS/RS material handling analysis
Equations:
AS/RS dimensions
W = 3 (x + a)
a = 6 in
L = ny (y + b)
b = 8 in
H = nz (z + c)
c = 10 in
capacity per aisle
C = 2 ny nz
single command cycle
Tcs = Max {L/vy , H/vz } + 2 Tpd
“uniform racks,
random
storage”
dual command cycle
Tcd = Max {1.5 L/vy , 1.5 H/vz } + 4 Tpd
utilization
60 U = Rcs Tcs + Rcd Tcd
hourly cycle rate
Rc = Rcs + Rcd
num transactions per hr
Rt = Rcs + 2 Rcd
AS/RS example (from text)
Given a 4 aisle AS/RS layout, each aisle contains 60 horizontal racks and 12 vertical racks.
Unit load dimensions are x = 42 in, y = 48 in, and z = 36 in. The S/R machine has a horizontal
speed of 200 ft/min and vertical speed of 75 ft/min. It takes 20 s for a P&D operation. Find
a) Num of unit loads that can be stored
b) Total dimensions of AS/RS
c) Single and dual command cycle times
d) Throughput per aisle assuming utilization = 90% and num of single command
cycles equals the num of dual command cycles
Solution:
Total capacity = 4C = (4) 2 ny nz = (4)(2)(60) (12) = 5760 unit loads
Width = 3 (42 + 6) = 144 in => 12 ft/aisle
Length = 60 (48 + 8) = 3360 in = 280 ft
Height = 12 (36 + 10) = 552 in = 46 ft
AS/RS example (cont)
Solution:
Single command cycle time = Tcs = Max{280/200,46/75} + 2(20/60) = 2.066 min/cycle
Dual command cycle time = Tcd = Max{(1.5)(280/200), (1.5)(46/75)} + 4(20/60) = 3.432 min/cycle
Utilization = 0.9:
2.066 Rcs + 3.432 Rcd = 60 (0.9) = 54 min, but Rcs = Rcd
Thus, solve and get
Rcs = Rcd = 9.822 command cycles/hr
System throughput is the total number of S/R transactions per hour = 4 Rt
Throughput = 4 Rt = 4(Rcs + 2 Rcd) = 4(29.46) = 117.84 transactions/hr
AS/RS questions
1.
Who are major vendors of AS/RS?
2.
Describe their components (power source, transmission system,
communication system, etc.)?
3.
What are typical costs?
4.
What type of interfaces do they have? How are they programmed?
5.
How fast do they move?
6.
What are load capabilities?
7.
Unusual maintenance requirements?
8.
What type of S/R control is used? PID?
9.
Who are primary users?
Conveyors
Definition - A conveyor is a
mechanized device to move
materials in relatively large
quantities between specific
locations over a fixed path.
Conveyors
Roller conveyors - Series of tube rollers perpendicular to motion direction, which can be
powered or use gravity for motion.
Skate-wheel conveyors - Similar to rollers but use skate wheels parallel to motion direction.
Belt conveyors - Drives move flat or belts shaped into a trough.
Belt
Skate
wheel
Conveyors
Trolley
Chain conveyors - Uses loops of chain
that are typically moved by sprockets as
driven by motors.
Overhead trolley conveyors - Items are
moved in discrete loads by hooks or
baskets suspended from overhead rails.
Conveyors
In-floor towline conveyors - Similar to
overhead trolley but carts are pulled by
hook to in-floor conveyor.
Cart on track conveyors - Items are
moved by a cart attached to a rail system,
which uses a rotating tube to move the
cart along the rail.
Towline
Conveyor material handling
Terms:
vc – carrier average speed
(c = conveyor, carrier, cart, etc.)
sc – material spacing on conveyor
TL – loading time (min)
TU – unloading time (min)
Rf – material flow rate (parts/min)
Ld – distance between load and unload
Le –distance of return loop (empty)
L – length of conveyor loop
Td – delivery time
np – number of parts per carrier
nc – number of carriers
RL – loading rate (parts/min)
RU – unloading rate (parts/min)
Tc – total cycle time (min)
Np – total number of parts in system
Note: If one part per carrier, then part flow rate
is carrier flow rate.
Conveyor handling analysis
Equations – single direction:
time from load to unload
Td = Ld /vc
(min)
“delivery time = delivery distance divided by carrier speed”
material flow rate (np = 1)
Rf = RL = vc /sc 1/ TL
(num carriers/min)
“system flow rate = loading rate = flow rate of carriers on conveyor”
material flow rate (np > 1)
Rf = np vc /sc 1/ TL
(num parts per min)
“system flow rate = loading rate of parts = flow rate of parts on
conveyor”
unloading constraint
TU  TL
(min)
“unloading time must be less than loading time or else pile up carriers”
Conveyor handling analysis
Equations – continuous loop:
time to complete loop
Tc = L /vc
(min)
“full loop carrier time = loop distance divided by carrier speed”
time in delivery
Td = Ld/vc
(min)
“delivery time = delivery distance divided by carrier speed”
number of carriers
nc = L /sc
“num of carriers = loop distance divided by carrier spacing”
total parts in system
Np = np nc Ld/ L
“parts in system = num of parts per carrier times num carriers with parts”
material flow rate
Rf = np vc /sc
(num carriers per min)
“material flow rate = num parts per carrier times carrier flow rate”
Conveyor handling analysis
Equations – recirculating:
Speed rule – operating conveyor speed must fall within a certain range
from load/unload rates
Rf = np vc /sc  Max{RL , RU}
“flow rate of parts on conveyor must exceed the max load or unload part rate to maintain part spacing”
from time to load/unload carriers
vc /sc Min{1/TL,1/TU}
“flow rate of carriers on conveyor must exceed the max load or unload carrier rate to maintain part spacing”
Capacity constraint –conveyor capability (np vc /sc ) must exceed desired/specified
flow rate Rf
conveyor speed and carrier parts
np vc /sc  Rf
Uniformity principle –loads should be distributed uniformly over the conveyor
Conveyor questions
1.
Who are major vendors of conveyors?
2.
Describe their components (power source, transmission system, I/O
subsystem, etc.)?
3.
What are typical costs?
4.
How are they programmed and controlled?
5.
How fast do they move?
6.
What are load capabilities?
7.
Unusual maintenance requirements?
8.
Who are primary users?
Material handling
What have we learned?