Unit – II Unit Material handling and Storage: Unit load concept, Industrial Hand trucks, Powered
industrial trucks, Automated Guided Vehicles(AGV), Basic storage and equipment system,
Automated Storage and Retreival System(AS/RS),Carosel storage system and its applications
A unit load is a single item or a group of items that are combined to be handled and moved as a
single, manageable object. The main goal is to minimize the number of moves required to transport a
large quantity of material, thereby reducing handling time and cost.
Key Concepts
• Unit Load Principle: This principle, also known as the "unit size principle," emphasizes
moving the maximum amount of load at a time. The optimal size of a unit load is the largest
amount of material that can be safely and efficiently handled by the available equipment.
• Unitization: This is the process of combining small, individual items or bulk materials into a
single, cohesive unit. This is often done for materials whose individual size and weight are
too small to be efficiently moved one by one.
• Types of Unit Loads:
• Unit Load (Single Object): A single item that is too large for manual handling on its
own. Examples include a large piece of machinery or a heavy steel beam.
• Unitized Load (Collection of Objects): A group of smaller items that have been
arranged or secured together to be moved as a single mass. Examples include a pallet
of bricks, a container of small castings, or a bundle of sticks tied together.
Unitized vs. Packaged Loads
While both unitization and packaging can involve combining items, they have different primary
purposes.
• Unitized Loads are primarily created for efficient materials handling over short distances,
typically within a plant or facility. The focus is on moving large volumes quickly.
• Packaged Loads are primarily created for protection during storage and transport over long
distances. Packaging protects items from damage, contamination, and theft. Advantages of
Unitization
• The main advantages of unitizing loads are centered on efficiency, safety, and cost
reduction.
• Reduced Handling Costs: Moving larger loads at once minimizes the number of trips, which
lowers labor and transportation costs.
• Faster Operations: Loading and unloading are significantly faster compared to handling
individual items.
• Improved Safety: Unitized loads are more stable and easier to handle, reducing the risk of
damage to the goods and injuries to workers.
• Better Storage: Unit loads, even if made of irregularly shaped items, are often well-shaped
and stable. This allows for uniform stacking, better utilization of vertical storage space, and
improved warehouse organization.
• Simplified Labeling: Labeling a single unit load is often sufficient, eliminating the need to
label each individual item.
• Standardization: Unitization often leads to the standardization of handling systems and
equipment within a facility, as well as at shipping and receiving points.
Disadvantages of Unitization
• While beneficial, unitization also has some drawbacks, primarily related to cost, weight, and
equipment dependency.
• Additional Costs: There are costs associated with the process of unitizing and de-unitizing
materials.
• Increased Weight: The materials used to restrain the load (e.g., pallets, containers, straps)
add extra weight, which can slightly increase handling and transportation costs.
• Capital Investment: Unitization requires specialized equipment (like forklifts, pallet jacks,
or automated systems), which represents a capital investment.
• Container Management: If containers are used for unitization, there's an additional cost and
logistical challenge associated with moving and storing empty containers.
• Risk of Damage: While safer in many ways, mishandling a large, heavy unit load can
potentially cause more significant damage than mishandling a single item.
• Equipment Dependency: The inability to move a unit load without the proper equipment can
create bottlenecks in the workflow.
Industrial Vehicles / Trucks
• Industrial vehicles or trucks are essential equipment used to handle materials efficiently in
industries, warehouses, large stores, and transport depots.
• They are distinct from general transport vehicles like buses or lorries since they are designed
specifically for material handling tasks.
• Industrial trucks are mainly divided into two categories:
• Non-powered trucks (Hand trucks): These rely on manual effort or can be attached
to powered equipment for movement.
• Powered trucks: These have their own source of power and include power trucks,
forklift trucks, and tractors.
Hand Trucks
• Hand trucks operate without any engine or motor and depend on manual pushing or pulling.
• They come in three common types based on their design and load-handling capabilities: two-
wheel hand trucks, multiple-wheel hand trucks, and hand lift trucks.
Two-Wheel Hand Trucks
• These are commonly used for moving single-unit loads such as bags, boxes, barrels, cartons,
bales, and cylinders by manually pushing.
• The basic design consists of two long handles connected by several crossbars forming a
sturdy frame.
• Two wheels mounted on an axle are fixed at one end of the frame, while short legs near the
handles keep the truck horizontal during loading and unloading.
• Variations include pry trucks with a crowbar-shaped nose, which help lift very heavy loads
and are usually operated by two people together.
1. Handle 2. Side rail 3. Leg 4. Leg
brace 5. Top crossbar 6. 3rd crossbar 7.
2nd crossbar 8. 1st crossbar 9. Nose
10. Axle brace 11. Axle 12. Pressed
steel wheel 13. Retaining ring 14. Axle
bracket 15. Nut, bolt and lock washer
Fig. 5.1.1. Parts of common 2- wheel hand truck
Different varieties of 2-wheel trucks are in use based on the type of loads to
be handled. Some of these, which are variations of the basic design, are
illustrated in Figure 5.1.2 below indicating the type of load they are used for.
Fig. 5.1.2. Different types of 2-wheel hand trucks
Multiple-Wheel Hand Trucks
• These trucks have a platform or frame mounted on three or more wheels, often equipped with
a handle for pushing or pulling, although some models may have detachable or no handles.
• Types include:
• Dollies:
• Low platforms made from wood or metal, available in various shapes and
sizes.
• Equipped with fixed or swivel caster wheels.
• No handles are provided, and the load itself is pushed to move the dolly.
• Platform Trucks:
• Larger and sturdier than dollies, typically rectangular metal frames.
• Have handles at one or both ends for ease of movement.
• Wheel configurations vary:
• Tilt or balance type: rigid wheels centered under the platform with
swivel casters at the ends for easier turning.
• Non-tilt type: rigid wheels at one end and swivel casters at the other, so
all wheels remain active.
• Often fitted with racks or posts to prevent load slipping or spilling.
• Can be reinforced and equipped with couplers for towing or use in light trailer
systems.
Fig. 5.1.5. Various types of rack bodies used on platform trucks
• Semi-live Skid Platforms:
• Flat platforms with two load wheels on one end and two legs on the other.
• A special lift jack handle is used to raise the legs off the floor, converting the platform
into a three-wheel rolling truck.
Fig. 5.1.6. Semi-live skid platform
Hand Lift Trucks
• Hand lift trucks combine manual movement with a lifting mechanism to raise pallets or skids
off the ground, facilitating easier transport.
• Lifting mechanisms include:
• Hydraulic: Uses a hydraulic ram and oil pump activated by pumping the handle;
capacities typically range from 0.5 to 10 tons.
• Mechanical: Uses lever and pawl systems to raise and lower the load; capacities are
usually up to 1 ton.
• Common types based on construction and use:
• Pallet Trucks:
• Feature two sturdy metal forks (called fingers) forming a U-shape that slide
under pallets.
• The forks have wheels at the ends, and larger steering wheels at the back.
• Used widely for lifting and moving palletized loads.
(a) (b)
Fig. 5.1.7. Hydraulic hand pallet truck : Fig. 5.1.8. Operation of a pallet truck
(a) low-lift (b) high-lift
Fig. 5.1.9. Typical dimensions of a pallet truck
• Platform Lift Trucks:
• Similar to pallet trucks but use a solid or open platform instead of forks.
• Mainly used to lift loads on skids, with capacities ranging from 0.5 to 3 tons and
various platform sizes and lifting heigh
ts.
(a) (b)
Fig. 5.1.10. Scissor design platform lift trucks : mechanical type (a) or hydrautic type (b)
• Special Hand Lift Trucks:
• Designed for specialized industrial tasks such as coil or reel handling, incorporating
customized lifting features.
Powered Trucks
Powered trucks are a vital category of industrial vehicles equipped with their own source of
power usually an internal combustion engine or electric motor that enables them to move
materials efficiently within industrial settings, warehouses, and distribution centers. Unlike non-
powered hand trucks that depend solely on manual effort, powered trucks handle heavier loads,
travel longer distances, and offer better maneuverability and speed, improving operational
productivity.
Powered trucks are generally classified into three main types based on their design and
application:
Power Trucks
Power trucks are motorized industrial vehicles designed primarily for transporting heavy
materials horizontally within industrial premises, manufacturing plants, or warehouses. They are
versatile machines equipped with controls for speed, steering, and braking, allowing operators to
maneuver bulky or heavy loads safely and efficiently. Power trucks are commonly used to tow
trailers or carts loaded with materials, helping to transport goods over large areas without manual
effort.
Key Features:
• Equipped with an engine or electric motor for propulsion.
• Operator’s seat or standing platform with controls for steering and speed.
• Heavy-duty tires or wheels designed for industrial floor surfaces.
• Capability to tow or haul trailers, carts, or dollies.
Flat bed gasolline truck Drop platform truck Drop-centre baggage truck
• Fig. 5.2.1. Different designs of platform truck.
Forklift Trucks
Forklift trucks are the most ubiquitous type of powered industrial truck, specially designed to lift,
carry, and stack loads on pallets or unitized platforms. The distinguishing feature of a forklift is
its pair of forks (also called tines) mounted on a mast assembly that can be hydraulically raised or
lowered to pick up or place loads at different heights.
Forklifts are available in various power types electric, diesel, and LPG making them adaptable to
indoor or outdoor use depending on ventilation and load requirements.
Key Components:
• Two strong forks connected to a mast, capable of vertical movement.
• Hydraulic lifting system powered by a pump or engine.
• Counterweight at the rear to balance heavy front loads.
• Operator cabin or seat with steering wheel, pedals, and controls.
• Durable tires suited for smooth or rough surfaces.
Applications:
• Loading and unloading trucks.
• Stacking goods on warehouse racks.
• Transporting palletized materials within factories.
Industrial Tractors
Industrial tractors are powered vehicles designed primarily for towing or pulling trailers and carts
loaded with materials. Unlike forklifts, industrial tractors are not equipped with lifting
mechanisms but provide robust traction and power to move heavy loads over extended distances
inside industrial or warehouse environments.
They are essential for bulk transport tasks where loads need to be moved quickly and efficiently
between different sections of a plant or storage area.
Key Features:
• Strong engine or motor providing high torque.
• Tow hitch or coupling system to connect trailers or carts.
• Operator platform or seat with driving controls.
• Heavy-duty wheels or tires built for industrial flooring.
Common Uses:
• Towing trailers loaded with goods or raw materials.
• Moving large quantities of material between warehouse zones.
• Supporting conveyor or towline systems in manufacturing.
Coupler
Battery operated tractor without cabin Typical farm tractoR
Trailers can be of different shapes and sizes. Figure 5.4.2 shows a few types of trailers:
Use of tractors with different trailers
Powered trucks enhance material handling by combining motorized propulsion with specialized
attachments like forks or tow hitches. Their ability to lift, move, and transport heavy loads efficiently
reduces labor intensity, increases speed, and improves safety in industrial environments.
What are Automated Guided Vehicles (AGVs)?
Automated Guided Vehicles (AGVs) are driverless, battery-powered vehicles used in industrial
settings to transport materials. They are a core component of automated materials handling
systems and are particularly vital in Flexible Manufacturing Systems (FMS) where they
provide flexible material handling, storage, and retrieval. AGVs are guided along a predefined
path, allowing them to move goods between various loading and unloading stations without a
human operator.
Key Components of an AGV System
An AGV system is a complete solution that includes more than just the vehicles themselves. It
typically consists of four main components:
1. The Vehicle: The AGV itself, which is the mobile unit that carries the load.
2. The Guide Path: The physical or virtual path that the AGV follows.
3. The Control Unit: A central system that manages and directs the AGV's movements,
monitors the system's status, and manages tasks.
4. The Computer Interface: This allows the AGV system to communicate with other systems,
such as a host computer, an Automated Storage and Retrieval System (AS/RS), or a Flexible
Manufacturing System (FMS).
Types of AGVs
AGVs are designed in different configurations to suit various material handling needs:
• Towing Vehicles: These are essentially automated tractors that pull a series of trailers. They
were the first type of AGV and are used for transporting multiple loads over longer distances.
• Pallet Trucks: These AGVs are designed to lift and transport palletized loads. They can pick
up and drop off pallets directly from the floor, eliminating the need for fixed stands.
• Forklift Trucks: The most sophisticated and expensive type of AGV. They can lift and
transport palletized loads at various heights, servicing conveyors or stands. They are
equipped with advanced sensors for precise positioning and stacking.
• Light Load Transporters: These are smaller AGVs used for moving light parts and
components over moderate distances, often used for distributing parts between a warehouse
and individual workstations.
• Assembly-Line Vehicles: A specialized version of light load transporters used in serial
assembly. They carry major sub-assemblies (like engines or transmissions) and move them
from one workstation to the next as the product is built. They offer a cost-effective and
flexible alternative to traditional fixed assembly lines.
Guidance and Control Systems
AGVs rely on advanced technology to navigate and operate safely.
• Guidance System: This system ensures the AGV stays on its designated path. The key
advantage of AGVs is that the guide path can be changed easily and inexpensively, unlike a
fixed conveyor system. Common guidance methods include:
• Laser Guidance Technology: The AGV uses an onboard laser to scan reflectors
mounted on walls or columns.
• Magnetic Spot Guidance Technology: Small magnets are embedded in the floor, and
a sensor on the AGV detects them.
• Magnetic Tape Guidance Technology: The AGV follows a magnetic tape strip on
the floor's surface.
• Inductive Guidance Technology (Wire Guidance): A low-voltage wire is buried in
the floor, and the AGV follows the radio frequency signal it emits.
• Control System: This system manages the AGV's overall operation and communication.
AGVs use microprocessor technology to follow their path and avoid obstacles.
Communication is essential to prevent collisions, which is achieved through radio or a floor
wire. There are three main types of control:
• Computer-Controlled: A central system manages all AGV movements and tasks.
• Remote Dispatch Control: An operator uses a remote station to send destination
commands to the AGVs.
• Manual Control: The operator enters the destination on an onboard control panel,
and the AGV follows the path.
STORAGE AND EQUIPMENT SYSTEM
A basic storage and equipment system is a coordinated set of methods and tools used to
efficiently hold and manage materials within a facility. The system's goal is to optimize space,
minimize handling time, and ensure quick access to items. It's built on two core components: the
storage methods themselves and the equipment used to interact with them.
Storage Systems
Storage systems refer to how inventory is organized and housed. The choice of system depends
on product characteristics, inventory volume, and the rate of turnover.
• Bulk Storage: This is the simplest method, where items are stacked directly on the floor
without racks. It's ideal for storing large, uniform, and durable products that don't require
frequent access. A good example is a warehouse storing large quantities of bagged cement or
cases of beverages.
• Rack Storage: This system uses shelving frameworks to store items, maximizing vertical
space.
• Pallet Racks: The most common type, designed to hold palletized loads. This system
provides direct access to each pallet, making it suitable for a wide variety of products.
• Drive-In/Drive-Thru Racks: These are high-density systems where a forklift can
drive into the rack structure to load or retrieve pallets. They are perfect for storing
large volumes of the same product (e.g., cold storage for food).
• Cantilever Racks: These have horizontal arms extending from a central column,
designed specifically for storing long, bulky items like pipes, lumber, or sheet metal.
• Shelving: This is used for storing smaller, individual items that are not on pallets. It is
common in parts departments, retail backrooms, and distribution centers for picking
individual orders.
Equipment Systems
Equipment systems are the tools used to move, retrieve, and organize stored materials. They
range from simple manual devices to complex automated machinery.
• Manual Equipment: These are non-powered tools that require human effort.
• Hand Trucks/Dollies: Used for moving single items or small, non-palletized loads
over short distances.
• Pallet Jacks: Used to manually lift and move pallets at floor level. They are essential
for low-volume, short-distance pallet movement.
• Powered Equipment: These are motor-driven machines that handle larger, heavier loads.
• Forklifts: The workhorse of any warehouse. They lift, move, and stack palletized
loads to significant heights. They come in various types, including sit-down, stand-up,
and reach trucks, each suited for different tasks.
• Conveyors: A system of belts, rollers, or chains that transports items along a fixed
path. Conveyors are highly efficient for moving goods between different stages of a
process, such as from an assembly line to a packing station.
• Automated Systems: These are advanced, computer-controlled systems for high-speed and
high-density operations.
• Automated Storage and Retrieval Systems (AS/RS): Large, automated systems that
use robots and cranes to store and retrieve items from high-density racks. These are
used in highly automated warehouses to minimize human intervention and maximize
speed and accuracy.
• Automated Guided Vehicles (AGVs): Driverless, robotic vehicles that transport
materials along a predefined path, often used for moving raw materials or finished
goods between workstations and storage areas.
The effective integration of these storage methods with the right equipment is what defines an
efficient and productive materials handling system.
What is an Automated Storage and Retrieval System (AS/RS)?
An Automated Storage and Retrieval System (AS/RS) is a computer-controlled system designed
to automatically store and retrieve materials in warehouses or manufacturing facilities. It reduces
the need for manual labor, which improves speed, accuracy, and efficient use of space.
At its core, an AS/RS is made up of storage racks, aisles, mechanical machines for moving
goods, and a computer system that controls everything. The system ensures items are placed in
their proper locations and retrieved when needed with minimal human intervention.
Primary Functions of AS/RS
• Storage: Automatically places goods in specific storage locations based on an optimized
system logic.
• Retrieval: Automatically picks and delivers goods from storage when required.
• Inventory Management: Tracks every item in real-time, providing precise location and
quantity information, which improves stock control.
Key Components of AS/RS
• Storage Structure:
The shelving or racking system where goods are stored. Modern AS/RS racks can be very tall
sometimes over 100 feet maximizing vertical storage space.
• Storage/Retrieval (S/R) Machine:
A mechanical device that travels horizontally along aisles and vertically up and down racks to
place or retrieve goods. It typically has telescoping forks or shuttles to handle the items.
• Input/Output (I/O) Stations:
Locations where goods enter or exit the automated system, connecting manual processes with
automation.
• Computer Control System:
The “brain” of the AS/RS, managing all operations, directing the S/R machines, tracking
inventory, and integrating with warehouse management software to optimize performance
and accuracy.
Types of AS/RS
• Unit Load AS/RS:
Designed to handle large palletized goods, ideal for heavy or bulky items in factories or
distribution centers.
• Mini-Load AS/RS:
Handles smaller loads like bins or trays, commonly used for small parts or components in
assembly or order fulfillment.
• Carousel Systems:
Rotating shelves or bins bring items to a fixed operator station, increasing picking speed for
small parts storage.
• Vertical Lift Modules (VLMs):
Consist of vertical trays between two columns, with an extractor that brings trays to an
operator at a workstation, efficiently using vertical space in a small footprint.
• Shuttle-Based Systems:
Use robotic shuttles that move along racks to retrieve and transport items, offering flexible
and scalable storage solutions.
Advantages of AS/RS
• Maximized Space Utilization:
Efficient use of vertical and horizontal space allows more storage in less area.
• High Productivity:
Operates continuously with faster retrieval and storage times compared to manual handling.
• Improved Accuracy:
Automated tracking reduces picking errors and ensures inventory accuracy.
• Enhanced Safety:
Reduces human labor in hazardous zones and decreases forklift traffic, minimizing accidents.
• Lower Labor Costs:
Automates repetitive tasks, reducing the number of workers needed for material handling.
Disadvantages of AS/RS
• High Initial Investment:
The cost of purchasing and installing the system is significant.
• Maintenance Requirements:
Needs skilled technicians and regular maintenance to keep running smoothly.
• Risk of System Downtime:
A failure in the control system or machinery can halt the entire operation.
• Limited Flexibility:
Changes to system layout or capacity can be costly and complex once installed.
Carousel storage systems
• Carousel storage systems are automated solutions that improve storage efficiency,
productivity, and safety by delivering items directly to the operator, following the goods-to-
man principle. They eliminate manual searching by rotating bins or shelves on horizontal or
vertical tracks to bring requested items to a fixed access point.
• Originally developed in the 1940s and 1950s, carousels were modular and easy to install.
Today, they are highly automated and integrated with warehouse management software,
enabling precise inventory control, faster picking, and real-time data exchange. These systems
play a key role in modern smart warehouses and align with Industry 4.0 trends.
• Types of Carousel Storage Systems
• Carousel storage systems come in two main types horizontal and vertical each designed for
specific space and operational needs. Choosing between them depends on floor space, ceiling
height, item types, and throughput requirements.
• Horizontal Carousels
• Horizontal carousels consist of bins or trays linked on an oval track that rotates horizontally,
bringing items to the operator at waist level. Multiple carousels are often grouped into pods of
two to four units operated by one person, allowing one carousel to pre-position the next item
while the operator picks from another. This setup minimizes idle time and maximizes
throughput, making it ideal for high-volume picking.
• They are suited for low-ceiling environments where vertical expansion isn’t possible and help
save space by reducing aisles. Shelves and trays can be customized to fit different inventory
sizes. Horizontal carousels typically handle medium-weight items (from ounces to several
pounds) with shelf capacities up to 75 pounds, though some models can carry much heavier
loads.
FIG. Horizontal Carousels
• Vertical Carousels
• Vertical carousels rotate shelves vertically along an oval track, similar to a Ferris wheel. The
shelves stay horizontal as they move, protecting stored items.
• Their tall, slim design maximizes vertical space, saving over 70% of floor area compared to
traditional racks, and can double storage capacity within the same footprint. Vertical carousels
are perfect for small spaces or facilities aiming to optimize overhead space.
• A key ergonomic advantage is delivering items directly to the operator at a comfortable "golden
zone" height, reducing the need for bending or climbing and enhancing workplace safety. These
systems accommodate various shelf types for different industries, including single-tier shelves
for containers, adjustable shelves for documents, two-tiered shelves for small electronic parts,
and specialized shelves for tooling.
FIG. VERTICAL CAROUSEL
Applications of Carousel Storage Systems
Carousel storage systems are versatile automated solutions widely used across many industries
due to their ability to optimize space, improve efficiency, and enhance safety.
1. Manufacturing and Automotive
• Streamline storage and retrieval of components, tools, and work-in-process materials.
• Vertical carousels store small parts and tooling attachments.
• Automotive industry uses tire storage carousels for efficient, safe tire handling and
organization.
2. Healthcare and Pharmaceuticals
• Provide fast access and precise inventory control for medical supplies and medicines.
• Vertical carousels with stainless steel shelves and sterilization features maintain hygiene in
hospitals and pharmacies.
• Real-time inventory tracking helps prevent shortages and expired products.
3. Retail and E-commerce
• Optimize warehouse floor space and speed up order fulfillment in distribution centers.
• Horizontal carousels are effective for high-speed batch picking.
• Vertical carousels store garments, improving organization and display in retail stockrooms.
• Specialized carousels handle rolls of carpet, textiles, and spools of thread or wire in home
improvement stores.
4. Office and Document Management
• Offer high-density, space-saving storage for files, records, and X-rays.
• Reduce time and effort in retrieving and filing documents.
• Adjustable single-tier shelves enable direct document storage without extra trays.
5. Other Specialized Applications
• Aerospace and Military: Secure, organized storage for high-value and sensitive equipment.
• Media Storage: Efficient storage of electronic media like CDs and computer cartridges.
• Cleanrooms: Stainless steel and sterilization-equipped carousels for storing sterile instruments
and tableware.
Key Benefits of Carousel Storage Systems
• Space Optimization: Vertical carousels save over 70% floor space by using vertical space
efficiently; horizontal carousels reduce aisle space and increase storage density.
• Increased Productivity: Goods-to-man design cuts time spent walking and searching,
boosting pick rates up to 400 lines/hour. Computer controls improve picking and restocking
speed.
• Labor and Ergonomics: Automation cuts manual labor, reducing costs and physical strain by
delivering items at ergonomic heights.
• Accuracy and Inventory Control: Integrated software minimizes errors and uses pick-to-
light and RFID for real-time inventory tracking.
• Security and Safety: Enclosed systems protect items and reduce accident risks with safety
sensors and emergency stops.
• Flexibility: Modular design allows customization and integration with other equipment.
Potential Disadvantages of Carousel Storage Systems
• High Initial Cost: Large upfront investment, though often offset by long-term savings.
• Frequent Restocking: Small bins require more replenishment for fast-moving items.
• Limited Depth: Vertical carousels have fixed depths, limiting large item storage.
• Fixed Shelf Height: Limits flexibility for varying product sizes without reconfiguration.
• Movement Issues: Entire system rotates for each pick, possibly causing inefficiency and motor
overload.
• Single Access Point: Only one pick window can be used at a time, limiting throughput.
