3_Material Handling_Plan, set up , and control

Gives a comprehensive explanation on how to plan and set up a material handling system for your facility which adhere to your QMS

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5. Material Handling

Material Handling Defined:
1. Material Handling is the art and science of moving, storing, protecting, and
controlling material.
2. Material handling means providing the right amount of the right material, in
the right condition, at the right place, at the right time, in the right position, in
the right sequence, and for the right cost, by using the right method(s).
3. The systems perspective defines the scope of material handling as all activities
involved in handling material from all suppliers, handling material within the
manufacturing or distribution facility, and distributing finished goods to
customers.

Material Handling System Design:
Material handling equipment is usually assembled into systems. These systems must
be specified and configured for the particular application. The design of the system
depends on the parts, materials, or products to be handled, the quantities to be moved
the distances of the moves, the type of production system that the handling equipment
will serve, etc.

I. Material Handling Principles:
1. Planning principle: Establish a plan to include basic requirements and
desirable options for all material handling and storage activities.
2. Unit load principle: Materials to be moved should be aggregated into a larger
unit size, and the unit size should be the same for all materials. The materials
are typically placed on a palette or other standardized container. The materials
and container are referred to as the unit load. The unit load should be as large
as practical.
3. Avoid partial loads: Transport the full unit load whenever possible. Load the
material handling to its maximum safe limit.
4. Standardization principle: Standardize handling equipment and methods
whenever possible.
5. Shortest distance principle: Movements of materials should be over the
shortest distances possible.
6. Straight line flow rule: The material handling path should be in a straight line
from point of origination to destination.
7. Minimum terminal time principle: Minimize loading, unloading, and other
activities times that do not involve actual transport of the materials.
8. Gravity principle: Use gravity to assist the movement of materials to extent
possible.
9. Carry loads both ways: The handling system should be designed and
scheduled to carry loads in both directions whenever possible.
10. Mechanization principle: The handling process should be mechanized where
possible to increase efficiency and economy.
11. Systems principle: Integrate the material handling system with other systems
in the facility.
12. Systems flow principle: Integrate the flow of material with the flow of
information in handling and storage systems.
13. Computerization principle: Consider computerization in material handling
and storage whenever possible.

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14.
Part orientation principle: The orientation of the material should be
established and maintained throughout the material handling process. This is
especially important in automated production systems.
15.
Flexibility principle: Use methods and equipment that can perform a variety
of tasks under a variety of operating conditions.
16.
Space utilization principle: Make effective utilization of all cubic space.
17.
Ergonomics principle: Design material handling equipment and procedures
for effective interaction with the people in the system.
18.
Safety principle
19.
Simplification principle: Simplify handling by eliminating, reducing, and/or
combining unnecessary movements or equipment.
20.
Layout principle: Select the material handling system which best integrates
efficiency and effectiveness.
21.
Cost principle: Economic justification of alternate solutions in equipment and
methods.
22.
Maintenance principle: Plan for preventive maintenance and scheduled
repairs on all material handling equipment.
23.
Obsolescence principle: Make a Long term economically sound plan for
replacement of obsolete methods and equipment.
24.
Ecology principle
25.
Energy principle

II. Consideration of material and movement conditions:
The planning for a material handling system must begin with an analysis of the
materials to be moved.

Characteristics of materials
Category Measures or descriptors
Physical form Solid
Liquid
Gas
Size Length, width, and height
Volume
Weight Weight per piece
Weight per unit volume
Shape Long and flat
Round
Square
Risk of damage Fragile
Brittle
Sturdy
Safety risk Explosive
Toxic
Corrosive
Condition Hot
Wet
Dirty
Sticky

Other factors to be considered are factors relating to the movement and handling
conditions, including:
1.
The quantity of material to be moved.
2.
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3. The scheduling of the moves.
4. The route by which the materials are to be moved.

III. Effect of plant layout:
Plant layout is an important factor influencing the design of a material handling
system. In the case of a new facility (i.e., not yet constructed), The design of the
handling system should be considered as part of the layout design. In the case of an
existing facility, there are usually constraints that inhibit the realization of optimum
flow patterns.

The layout should provide the following information for use in the design of the
handling system:
1. Locations where materials must be picked up, i.e., load stations.
2. Locations where materials must be delivered, i.e., unload stations.
3. Possible routes between locations.
4. Distances that must be traveled to move materials.
5. Flow patterns, opportunities to combine deliveries, possible places
where congestion might occur.
6. Total area of the facility and areas within specific departments in the
layout.
7. Arrangement of equipment in the layout.

For example, in the case of fixed position layout, the product is large and heavy and
remains in a single location during its fabrication. Heavy components and
subassemblies must be moved to the product. Handling systems used for these moves
are large and mobile, e.g., cranes, hoists, and trucks.

In process layouts, there is a variety of product manufactured and the quantities made
per product are medium or small. The handling system must be flexible and
preferably programmable, e.g., hand trucks, forklift trucks, and Automated Guided
Vehicles (AGV).

In product flow layouts, standard, nearly identical products in relatively high volumes
are produced. The handling system typically exhibits the following characteristics:
fixed installation, fixed route, and mechanized or automated, e.g., conveyor systems.

IV. Material handling system equation:

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V. Attributes and characteristics by which to classify material handling equipment:
1.
Manual vs. mechanized vs. automated.
2.
Mobile vs. fixed in-position.
3.
Floor mounted vs. overhead.
4.
Fixed route vs. programmable route.
5.
Flow in one direction vs. flow in multiple directions.
6.
Discrete loads vs. continuous.
7.
Multiple items per carrier vs. single item per carrier.
8.
Delivery only vs. delivery and storage.
9.
Single pickup station and single drop-off station vs. multiple pickup and
multiple drop-off stations.
10.
Pickup and drop-off at the same station vs. pickup and drop-off stations
separate.
11.
Equal rates of loading and unloading vs. unequal rates of loading and
unloading.
12.
Continuous placement of items on handling system vs. uniformly spaced
discrete placement vs.
randomly spaced discrete placement.

VI. Quantitative measures:
In general, let:
Tc
: Time to complete a delivery (min) (delivery time).
Rdv
: delivery rate per carrier (deliveries / hr).
nC : Number of carriers in system.
TL
: Time required for loading (min) (terminal time for load).
TU
: Time to complete unloading (min) (terminal time for unload).
Ld
: Distance required to make a delivery (ft) (delivery distance).
Le
: Distance for empty return trip (ft) (empty travel distance).
VC
: Velocity of material handling equipment (ft / min).
AT:
available time per hour per carrier (min/hr/carrier)
WL:
workload (total time needed to make all delivers neglecting the
traffic factor
FT
: Traffic factor. 0  FT  1, related to traffic congestion.
EH
: Material handling system efficiency.
AH
: Material handling system availability.
Then,
Time for a carrier to make a delivery is:
Tc
= ((Ld / VC ) + TL + TU + (LE / VC )) (min).

The number of deliveries that can be made by a carrier is:
Rdv
= 60 * EH *AH *FT/ Tc ( d eliveries / hr).
Available time:
AT = 60 * EH *AH
*FT min per hour per carrier


The number of deliveries that can be made by a carrier is:
Rdv
= AT / Tc ( deliveries / hr).

Work load: number of min needed to make all delivers
:
WL= R * Tc
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Material Handling Equipment:
a. Classification of Material Handling Equipment:
1. Hand trucks: platforms with wheels for manual movement of items, unit
loads, and bulk materials.
2. Powered trucks: powered vehicle with platform for mechanized movement
of items, unit loads, and bulk materials. Driven by human beings and
powered by battery, gasoline, or propane gas.
3. Cranes, monorails, and hoists: handling devices, usually manually
operated, designed for lifting, lowering, and transporting heavy objects.
4. Conveyors: Large family of handling devices, often mechanized, sometimes
automated, designed to move materials between specific locations over a
fixed path, generally in large quantities or volumes.
5. Automated Guided Vehicle Systems (AGVS): battery-powered,
automatically steered vehicles designed to follow defined paths. Some are
capable of automatically loading and unloading unit loads. Usually
interfaced with other automated systems to achieve full benefits of
integrated automation.
6. Containers and unitizing equipment: create a convenient unit load to
facilitate and economize material handling and storage operations. These
devices also protect and secure materials.
7. Storage and Retrieval equipment: its primary function is to house material
for staging or building inventory and to retrieve material for use. Sometimes
the retrieval equipment is one of the material transport equipment described
above. In other cases a new equipment type is introduced.
8. Other handling equipment including:
• Industrial robots.
• Dial indexing tables.
• Flow line transfer mechanisms.
• Parts feeding and delivery devices.




Conveyor Systems:
A conveyor system is used when materials must be moved in relatively large
quantities between specific locations over a fixed path. Most conveyor systems are
powered to move loads along the pathways.
- Conveyors have the following attributes:
- Generally mechanized, some are automated.
- Fixed-in-position to establish pathways.
- Either floor mounted or overhead.
- Almost always limited to one-directional flow of materials.
- They generally move discrete loads.
- Used for either delivery-only or delivery-plus-storage of items.

A common feature of powered conveyor systems is that the driving mechanism is
built into the conveyor pathway itself. The individual carriers are not individually
powered.

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Conveyor systems can be designed to operate in a single direction or in continuous
closed loop for two-way flow. Single direction conveyors are suitable when there is
no need to return the carriers to the loading station. Loop conveyors are used for
temporary storage of work-in-process in production systems.

It is possible to construct branches, spurs, and sidings into the conveyor pathway. This
allows for different routings of loads.

Types of Conveyors:
1.
Roller conveyors: The pathway consists of a series of tubes (rollers) that are
perpendicular to the direction of flow. The rollers are contained in a fixed
frame which elevates the pathway above the floor. Flat pallets or tote pans
carrying unit loads are moved forward as the rollers rotate.

Roller conveyors are used to deliver loads between manufacturing operations,
delivery to and from storage, and distribution applications.



2.
Overhead trolley conveyors: A trolley in material handling is a wheeled
carriage running on an overhead rail from which loads are suspended. A trolley
conveyor consists of multiple trolleys along the rail by means of an endless
chain. The chain is attached to a drive wheel that supplies power to the
systems. Suspended from the trolleys are hooks, baskets, etc. to carry the loads.

Overhead trolley conveyors are used to move parts and assemblies between
major production departments.
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3. Towline conveyors: Towline conveyors make use of wheeled carts powered by
means of moving chains or cables located either overhead or in trenches in the
floor. The pathways of the conveyor system are defined by the cable system.
Selector-pin or pusher-dog arrangements allow automatic switching between
power lines or onto an unpowered spur line for accumulation.

Tow conveyors are generally used when long distances and high frequency of
movement are involved.

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4.
Cart-on-track conveyors: These conveyor systems use individual carts riding
on a two
-railed track in a frame. The carts are not individually powered. They
are driven by means of a rotating tube that runs between the rails. One of the
advantages of the cart-on-track systems is that the carts can achieve high
accuracy of position. This permits their use for positioning work in
production.

Applications of cart-on
-track systems include robotic spot welding lines and
mechanical assembly systems.





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5. Power-and-free conveyors: The power-and-free conveyor utilizes two tracks:
one powered and the other unpowered or free. Carriers are suspended from a
set of trolleys that run on the free track. Linkage between the power chain and
the trolleys is achieved by a “dog”.

The advantage of the power-and –free design is that the carriers can be
disengaged from the power chain and accumulated or switched onto spurs.

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Automated Guided Vehicle Systems
(AGVS)
:

AGVS Defined:
An automated guided vehicle system (AGVS) is a materials handling system that uses
independently operated, self-propelled vehicles that are guided along defined
pathways in the floor. The vehicles are powered by means of on-board batteries. The
definition of the pathways is generally accomplished by means of wires in the floor or
reflective paint on the floor surface. Guidance is achieved by sensors on the vehicle.

Types of AGVS:
1.
Driverless trains: This type consists of a towing AGV that pulls one or more
trailers. It is useful in applications where heavy payloads must be moved over large distances in warehouse or factories with intermediate pick-up and drop- off points along the route.



2.
AGVS pallet trucks: Automated guided pallet trucks are used to move
palletized loads along predetermined routes.


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3. AGVS unit load carriers: This type of AGVS is used to move unit loads from
one station to another station. They are often equipped for automatic loading
and unloading by means of powered rollers, moving belts, mechanized lift
platforms, etc.



AGVS Applications:
1. Driverless train applications: These applications involve the movement of
large quantities over large distances.
2. Storage/Distribution systems: Unit load carriers and pallet trucks are typically
used in these applications. The applications often interface the AGVS with
other automated handling and storage systems, such as automated storage and
retrieval systems (ASRS). They can also be applied in manufacturing and
assembly applications to deliver loads to and from WIP storage.
3. Assembly line operations: Unit load AGVS are used. Between the
workstations, components are kitted and placed on the vehicle for the
assembly operations to be performed on the partially completed product at the
next station. The workstations are arranged in parallel to add to line flexibility.
4. Flexible manufacturing systems: In this application, the AGV delivers work
from the staging area to the individual workstations in the system. At a
workstation, work is transferred from the vehicle into the work area of the
station. At the completion of the work the AGV returns to transport it to the
next station.

AGVS Operation:
1. Vehicle guidance and routing: Guidance system refers to the method by which
the AGVS pathways are defined and the vehicle control systems that follow the
pathways.

In the guide wire method the wires are either embedded in the floor or taped on
the surface. A frequency generator provides the guidance signal carried in the
wire. The signal creates a magnetic field along the pathway that is followed by
sensors on-board the vehicle. Two sensors (coils) are mounted on either side of

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the guide wire. In the paint strip method, optical sensors on the vehicle track the
paint.

Microprocessor controls mounted on board of the vehicle provide the AGV with
Dead reckoning
capability, i.e., the ability of the vehicle to travel along a route
that does not follow the defined pathway. For example, to load or unload on a
station away from the guide wire or to cross areas where wires can not be
mounted.

Routing in AGVS refers to the problem of selecting between different
pathways
available to the vehicle. Two method are applied. Frequency select method
where
different paths provide different frequencies and the AGV follows the
appropriate frequency for its route. Path switch method
where only one path is
active while the others are switched off.

2. Traffic control and safety:
The purpose of traffic control is to prevent collisions
between vehicles travelling along the same paths. This is achieved by two
methods.

On-board vehicle sensing:
Sensors on-board the vehicles detect the presence of
other vehicles ahead of it.

Zone control:
The AGVS layout is divided into separate zones, and the operating
rule is that no vehicle enters a zone if that zone is occupied by another vehicle.

3. System management:
Managing the operations of an AGVS is concerned with
the problem of dispatching vehicle to the points where they are needed. This can
be achieved by:
•
On-board vehicle control panel.
•
Remote call station.
•
Central computer control.


















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Automated Storage and Retrieval Systems:
The general objective of a storage system is to store materials for a certain period of
time. The performance of the storage system must be sufficient to justify its cost.
• Storage capacity is the total maximum number of individual items that are
expected to be stored. It is determined by the size of the storage system relative
to the physical size of the materials in storage.
• System throughput is defined as the number of loads per hour that the storage
system can: 1. Receive and put in storage, 2. Retrieve and deliver to the output
station. Each of these two cycles are referred to as storage transactions.
• Utilization of the storage system is defined as the percentage of time the system
is in use relative to the time available.
• Uptime reliability is defined as the percentage of time the system is up and
operating relative to the total scheduled operation time of the system.

Typical types of materials stored in a factory are:
2. Raw materials: raw stock to be processed or assembled.
3. Purchased parts: parts from vendors to be processed or assembled.
4. Work-in process: partially completed parts between processing or assembly
operations.
5. Finished product: product ready to be shipped to customer.
6. Rework and scrap: parts that are out of specifications to be either reworked or
scrapped.
7. Tooling: cutting tools, jigs, fixtures, welding rods, etc used for manufacturing
and assembly operations.
8. Spare parts: spare parts used to repair machines and equipment.
9. Office records.
10. Plant records.

Automated Storage and Retrieval Systems (ASRS):
An ASRS is defined as: A combination of equipment and controls which handles,
stores, and retrieves materials with precision, accuracy, and speed under a defined
degree of automation. The ASRS consists of:
• A series of storage aisles.
• The aisles have storage racks for holding the materials.
• The aisles are serviced by one or more storage/retrieval (R/S) machine to
deliver materials to or retrieve materials from the storage aisle.
• The ASRS has one or more pick-and-deposit (P&D) stations where materials
are delivered to or from the ASRS.

ASRS can be divided into five categories:
1. Man-on-board ASRS.
2. Automated item retrieval system.
3. Deep-lane ASRS.
4. Unit load ASRS
5. Miniload ASRS.

Applications of ASRS include:
• Unit load storage and handling.
• Order picking.
• Work-in-process storage systems.

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Carousel storage systems:
A carousel storage system is a series of bins or baskets fastened to carriers that are
connected together and revolve around a long, oval track system. The track system is
similar to a
trolley conveyor system. Its function is to position bins at a load/unload
station.

The typical operation of the storage carousel is mechanized rather than automated.
The load/unload station is manned by a human worker who activates the powered
carousel to deliver a desired bin to the station. Manual controls include the following:
•
Foot pedal control.
•
Hand control.
•
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Carousel storage applications include:
• Storage and retrieval operations.
• Transport and accumulation.
• Storage for assembly operations.
• Store items for inspection and testing.

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Sample questions on material handling equipment (AGVS)
1. Name the four major categories of material handling equipment.
2. What is the unit load principle?
3. What are the five categories of material transport equipment commonly used to move parts and
materials inside a facility?
4. Name three categories of automated guided vehicles.
5. What is forward sensing in AGVS terminology?
6. What are some of the differences between rail-guided vehicles and automated guided vehicles?
7. Name some of the different types of conveyors used in industry.
8. What is a recirculating conveyor?
9. What is the difference between a hoist and a crane?
10. A planned fleet of forklift trucks has an average travel distance per delivery = 500 ft loaded and an
average empty travel distance = 350 ft. The fleet must make a total of 60 deliveries per hour. Load
and unload times are each 0.5 min and the speed of the vehicles = 300 ft/min. The traffic factor for
the system = 0.85. Availability = 0.95, and worker efficiency = 90%. Determine (a) ideal cycle
time per delivery, (b) the resulting average number of deliveries per hour that a forklift truck can
make, and (c) how many trucks are required to accomplish the 60 deliveries per hour.
Solution: (a) Tc = 0.5 + 500/300 + 0.5 + 350/300 = 3.83 min/delivery
(b) Ideally, Rdv = 60
383.
= 15.66 deliveries/hr per truck
Accounting for traffic factor, availability, and worker efficiency,
Rdv = 15.66(0.85)(0.95)(0.90) = 11.39 deliveries/hr per truck
(c) nc = 60/11.39 = 5.27  6 forklift trucks
11. An automated guided vehicle system has an average travel distance per delivery = 200 m and an average empty travel distance = 150 m. Load and unload times are each 24 s and the speed of the AGV = 1 m/s. Traffic factor = 0.9. How many vehicles are needed to satisfy a delivery requirement of 30 deliveries/hour? Assume that availability = 0.95.
Solution: Tc = 24 + 200/1 + 24 + 150/1 = 398 s = 6.63 min
Rdv = 60090095
663
( .)(. )
.
= 7.73 deliveries/hr per vehicle
nc = 30/7.73 = 3.88  4 vehicles
12. Four forklift trucks are used to deliver pallet loads of parts between work cells in a factory. Average travel distance loaded is 350 ft and the travel distance empty is estimated to be the same.
The trucks are driven at an average speed of 3 miles/hr when loaded and 4 miles/hr when empty.
Terminal time per delivery averages 1.0 min (load = 0.5 min and unload = 0.5 min). If the traffic
factor is assumed to be 0.90, availability = 100%, and worker efficiency = 0.95, what is the
maximum hourly delivery rate of the four trucks?
Solution: When loaded, vc = (3 miles/hr)5280 1
60
ft
mile
x
hr
min.






= 264 ft/min
When empty, vc = (4 miles/hr)5280 1
60
ft
mile
x
hr
min.





 = 352 ft/min
Tc = 1.0 + 350
264
350
352
 = 3.32 min/delivery
Rdv = 6010 090095
332
( . ( .)(. )
. = 15.45 deliveries/hr per vehicle
With four trucks, Rd = 4(15.45) = 61.8 deliveries/hr.
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18. 17
13. An AGVS has an average loaded travel distance per delivery = 400 ft. The average empty travel
distance is not known. Required number of deliveries per hour = 60. Load and unload times are
each 0.6 min and the AGV speed = 125 ft/min. Anticipated traffic factor = 0.85 and availability =
0.95. Develop an equation that relates the number of vehicles required to operate the system as a
function of the average empty travel distance Le.
Solution: Tc = 0.6 + 400
0.6
125 125
e
L
 = 4.4 + 125
e
L
AT = 60(0.95)(0.85)(1.0) = 48.45 min/hr per vehicle
WL = 60(4.4 + Le
125 ) = 220 + 0.4 Le
nc = 220 0.4
48.45
e
LWL
AT

 nc = 4.54 + 0.00825 Le
14. An AGVS will be used to satisfy material flows indicated in the from-to Chart in the table below,
which shows deliveries per hour between stations (above the slash) and distances in meters
between stations (below the slash). Moves indicated by "L" are trips in which the vehicle is
loaded, while "E" indicates moves in which the vehicle is empty. It is assumed that availability =
0.90, traffic factor = 0.85, and efficiency = 1.0. Speed of an AGV = 0.9 m/s. If load handling time
per delivery cycle = 1.0 min, determine the number of vehicles needed to satisfy the indicated
deliveries per hour? Assume that availability = 0.90.
To: 1 2 3 4
From: 1 0/0 9L/90 7L/120 5L/75
2 5E/90 0/0 0/NA 4L/80
3 7E/120 0/NA 0/0 0/NA
4 9E/75 0/NA 0/NA 0/0
Solution: vc = 0.9 m/s(60 s/min) = 54 m/min
Route 1  2  1: Tc = 1.0 + (90 + 90)/54 = 4.33 min, 5 deliveries.
Route 1  3  1: Tc = 1.0 + (120 + 120)/54 = 5.44 min, 7 deliveries.
Route 1  4  1: Tc = 1.0 + (75 + 75)/54 = 3.78 min, 5 deliveries.
Route 2  4  1*: Tc = 1.0 + (80 + 75)/54 = 3.87 min, 4 deliveries.
Route 1  2*: Tc = 1.0 + 90/54 = 2.67 min, 4 deliveries.
* Assumes vehicles on route 1  2 are used to make deliveries on route 2  4  1.
Average Tc = 54337544537843874267
25
(.)(.)(.)(.)(.)    = 4.192 min/delivery cycle
Rdv = 60085
4192
(.)
. = 12.166 deliveries/hr per vehicle
Including effect of availability factor, Rdv = 12.166(0.90) = 10.95 deliveries/hr per vehicle
nc = 25/10.95 = 2.28  3 vehicles
Alternative solution: Total time (workload, WL) to make all deliveries, neglecting traffic factor:
WL = (9 + 7 + 5 + 4)(1.0) + + 5907120975
54
()()()  = 104.8 min
Time available per vehicle per hour, AT = 60(.90)(.85)(1.0) = 45.9 min
nc = 104.8/45.9 = 2.28  3 vehicles
15. An automated guided vehicle system is being proposed to deliver parts between 40 workstations in
a factory. Loads must be moved from each station about once every hour; thus, the delivery rate =
40 loads per hour. Average travel distance loaded is estimated to be 250 ft and travel distance
empty is estimated to be 300 ft. Vehicles move at a speed = 200 ft/min. Total handling time per
delivery = 1.5 min (load = 0.75 min and unload = 0.75 min). Traffic factor Ft becomes
increasingly significant as the number of vehicles nc increases; this can be modeled as:
Ft = 1.0 - 0.05(nc-1) for nc = Integer > 0
Determine the minimum number of vehicles needed in the factory to meet the flow rate
requirement. Assume that availability = 1.0 and worker efficiency = 1.0.

19. 18
Solution: Tc = 1.5 + 250 300
200
 = 4.25 min/cycle
Rdv = 60(1.0 0.05( 1))
4.25
c
n = 60(1.05 0.05 )
4.25
c
n = 14.824 - 0.706 nc deliveries/hr per vehicle
nc = 40
14.824 0.706
c
n
nc (14.824 - 0.706 nc) = 40
14.824 nc - 0.706 nc
2
= 40
0.706 nc
2
- 14.824 nc + 40 = 0
Use quadratic equation to find roots:
nc =    ( . ) . ( . )()
( . )
14 824 14 824 4 0706 40
2 0706
2 = 17.82 or 3.18  Use nc = 4 vehicles
Check: Ft = 1.0 - 0.05(4 - 1) = 1.0 - 0.15 = 0.85
Rdv = 60085
425
( . )
. = 12 deliveries/hr per vehicle, nc = 40/12 = 3.33  Use n = 4 vehicles
16. An automated guided vehicle system is being planned for a warehouse complex. The AGVS will
be a driverless train system, and each train will consist of the towing vehicle plus four carts. Speed
of the trains will be 160 ft/min. Only the pulled carts carry loads. The average loaded travel
distance per delivery cycle is 2000 ft and empty travel distance is the same. Anticipated travel
factor = 0.95. Assume reliability = 1.0. The load handling time per train per delivery is expected to
be 10 min. If the requirements on the AGVS are 25 cart loads per hour, determine the number of
trains required.
17. The from-to Chart in the table below indicates the number of loads moved per 8-hour day (above
the slash) and the distances in ft (below the slash) between departments in a particular factory.
Fork lift trucks are used to transport materials between departments. They move at an average
speed = 275 ft/min (loaded) and 350 ft/min (empty). Load handling time per delivery is 1.5 min,
and anticipated traffic factor = 0.9. Assume reliability = 1.0 and worker efficiency = 110%. Use an
availability factor = 95% and worker efficiency = 110%. Determine the number of trucks required
under each of the following assumptions: (a) the trucks never travel empty; and (b) the trucks
travel empty a distance equal to their loaded distance.
To Dept. A B C D E
From Dept A - 62/500 51/450 45/350 0
B 0 - 0 22/400 0
C 0 0 - 0 76/200
D 0 0 0 - 65/150
E 0 0 0 0 -
18. An AGVS will be implemented to deliver loads between four workstations: A, B, C, and D. The hourly flow rates (loads/hr) and distances (m) within the system are given in the table below (travel loaded denoted by “L” and travel empty denoted by “E”). Load and unload times are each
0.45 min, and travel speed of each vehicle is 1.4 m/sec. A total of 43 loads enter the system at station A, and 30 loads exit the system at station A. In addition, six loads exit the system from
workstation B each hour and seven loads exit the system from station D. This is why there are a
total of 13 empty trips made by the vehicles within the AGVS. How many vehicles are required to
satisfy these delivery requirements, assuming the traffic factor is 0.85 and the reliability
(availability) is 95%?
Hourly rate (loads/hr) Distances (m)
To A B C D A B C D
From A - 18L 10L 15L A - 95 80 150
B 6E - 12L B - 65 75
C - 22L C - 80
D 30L, 7E - D - ®??? ?] ¦v]¦ ®Âvo ?]  Z?? ÏÍÎÑ  ÏÍÎÐ `v???¦ `??? `?l? `???^?d?¦ ¿????¦ `??Zk `^?? ~?l? ?]???¦ ????¦ ??lc

20. 19
Solution: Ld = 
302212151018
15030802265121501580109518


Ld = 11,800/107 = 110.28 m
Le = 
107
1507956 = 1620/107 = 15.14 m
Tc = 0.45 + 110.28/(1.4 x 60) + 0.45 + 15.14/(1.4 x 60) = 2.393 min
WL = 107(2.393) = 256.04 min of work per hour
AT = 60(0.85)(0.95) = 48.45 min/hr per vehicle
nc = 256.04/48.45 = 5.28 rounded to 6 vehicles

21. 20


metsys egarots Sample questions on

1. Name and briefly describe four of the six measures used to assess the performance of a storage
system?
2. Briefly describe the two basic storage location strategies.
3. What are the two basic categories of automated storage systems?
4. Identify the three application areas of automated storage/retrieval systems.
5. What are the four basic components of nearly all automated storage/retrieval systems?
6. Each aisle of a six-aisle Automated Storage/Retrieval System is to contain 50 storage
compartments in the length direction and 8 compartments in the vertical direction. All storage
compartments will be the same size to accommodate standard size pallets of dimensions: x = 36 in
and y = 48 in. The height of a unit load z = 30 in. Using the allowances a = 6 in, b = 8 in, and c =
10 in, determine (a) how many unit loads can be stored in the AS/RS, and (b) the width, length,
and height of the AS/RS. The rack structure will be built 18 in above floor level.
Solution: (a) Capacity per aisle = 2(50(8) = 800 loads/aisle
With six aisles, AS/RS capacity = 6(800) = 4800 loads
(b) W = 3(x + a) = 3(36 + 6) = 126 in/aisle
With 6 aisles, AS/RS width = 6(126) = 756 in = 63 ft.
L = ny (y + b) = 50(48 + 8) = 2800 in = 233.33 ft.
H = nz (z + c) = 8(30 + 10) = 320 in = 26.67 ft.
Given that the rack structure is built 18 in above floor level, H = 320 + 18 = 338 in = 28.167 ft.
7. A unit load AS/RS is being designed to store 1000 pallet loads in a distribution center located next
to the factory. Pallet dimensions are: x = 1000 mm, y = 1200 mm; and the maximum height of a
unit load = 1300 mm. The following is specified: (1) the AS/RS will consist of two aisles with one
S/R machine per aisle, (2) length of the structure should be approximately five times its height,
and (3) the rack structure will be built 500 mm above floor level. Using the allowances a = 150
mm, b = 200 mm, and c = 250 mm, determine the width, length, and height of the AS/RS rack
structure.
Solution: Assumption: the L/H ratio does not include the 500 mm foundation.
1000 pallets/ 2 aisles = 500 pallets/aisle. 500 pallets/aisle  250 pallets per aisle side.
Thus ny nz = 250 Eq. (1)
L = ny (y + b) = ny (1200 + 200) = 1400 ny (ny in mm) = 1.4 ny (ny in m)
H = nz (z + c) = nz (1300 + 250) = 1550 nz (nz in mm) = 1.55 nz (nz in m)
Given the specification L/H = 5 1.40
1.55
y
z
n
n
= 0.9032ny / nz = 5 0.9032 ny = 5.0 nz ny = 5.536 nz Eq. (2)
Combining Eqs. (1) and (2): ny nz = (5.536 nz) nz = 250
nz
2
= 250/5.536 = 45.161 nz = 6.72  use nz = 7
ny = 250/nz = 250/7 = 35.71  use nz = 36
W = 3(1000 + 150) = 3450 mm = 3.45 m/aisle.
With 2 aisles, W = 2(3.45) = 6.9 m
L = 1.4 ny = 1.4(36) = 50.4 m
H = 1.55 nz = 1.55(7) = 10.85 m
Given that the rack structure is built 500 mm above floor level, H = 10.85 + 0.5 = 11.35 m
Check on specifications: Capacity = 2 x 2 x 36 x 7 = 1008 pallets.
L/H = 50.4/10.85 = 4.645
8. Given the rack structure dimensions computed in previous problem. Assuming that only 80% of
the storage compartments are occupied on average, and that the average volume of a unit load per ®??? ?] ¦v]¦ ®Âvo ?]  Z?? ÏÍÎÑ  ÏÍÎÐ `v???¦ `??? `?l? `???^?d?¦ ¿????¦ `??Zk `^?? ~?l? ?]???¦ ????¦ ??lc

22. 21
pallet in storage = 0.75 m
3
, compute the ratio of the total volume of unit loads in storage relative to
the total volume occupied by the storage rack structure.
Solution: Number of unit loads = 0.80(1008) = 806.4 unit loads on average
Volume of loads at 0.75 m
3
per load: Vu = 806.4(0.75) = 604.8 m
3

Volume of rack structure, excluding elevation above floor level (using values computed in
Problem 11..2):
Vr = W x L x H = 6.9(50.4)(10.85) = 37773.2 m
3

Ratio u
r
V
V = 6048
37732
.
. = 0.1603 = 16.03%
9. A unit load AS/RS for work-in-process storage in a factory must be designed to store 2000 pallet
loads, with an allowance of no less than 20% additional storage compartments for peak periods
and flexibility. The unit load pallet dimensions are: depth (x) = 36 in and width (y) = 48 in.
Maximum height of a unit load = 42 in. It has been determined that the AS/RS will consist of four
aisles with one S/R machine per aisle. The maximum ceiling height (interior) of the building
permitted by local ordinance is 60 ft, so the AS/RS must fit within this height limitation. The rack
structure will be built 2 ft above floor level, and the clearance between the rack structure and the
ceiling of the building must be at least 18 in. Determine the dimensions (height, length, and width)
of the rack structure.