Material Transport Systems

Zone Control System

The AGVS layout is divided into separate zones Operating rule prohibits vehicles entering a zone already occupied by another vehicle Zone length sufficient to hold 1 vehicle plus other considerations: • Allowance for safety • Number of vehicles in system • Size and complexity of layout • Objective of minimizing number of separate zones

Paint strips - AGV

Using an optical sensor to track the paint Strips can be taped, sprayed, or painted on floor A paint strip containing fluorescent particles reflects UV light emitted from the vehicle Paint strip guidance is useful in environments where electrical noise interferes with guide wire system Since paint deteriorates with time, it must be kept clean and periodically replaced

Inertia navigation (inertial guidance)

Using on-board gyroscopes and/or other motion sensors to determine vehicle position by detecting changes in speed and acceleration Magnetic transponders imbedded in floor along the pathway are detected by AGV to correct errors in its position The advantage of inertia navigation systems are generally about flexibility. Path network can be changed New docking points can be defined Pathway can be extended by installing new beacons Quick changes without major alterations

On-board sensing (forward sensing)

Using sensors to detect obsticles and other vehicles Optical and ultrasonic sensor can be used. Mopre effective in straight pathways

Process Layout

Various products are manufactured in small or medium batch sizes Flexibility in handling system to deal with variations

Fixed-position layout

a layout that brings all resources required to create the product to a central location Fabrication of large and heavy products in a single location

Non-powered industrial trucks

human workers push or pull loads It can be reffered as hand trucks as they are pushed or pulled manually Quantities and travel distances are low. • Multiple-wheel trucks: dollies, pallet trucks, etc. • Dollies: fixed-wheel, caster-type wheel, etc.

Cranes

machines with long, movable arms used to lift things • Used for horizontal movement of materials • They include a variety of material handling equipment for lifting and moving heavy loads (+100 Tons) using overhead beams • A crane always includes hoist, since it's the hoist that lifts the load and crane moves it horizontally • Main types of cranes • Bridge cranes • Gantry cranes • Jib cranes

Hoists

to raise or lift, especially by some mechanical appliance • Mechanical devices to raise and lower loads • Consist of one or more fixed pulleys, one or more moving pulleys, rope, cable, and chain between pulleys • Load is attached via a hook or a similar tool

Conveyor - Types

• A mechanical device for moving items or bulk materials internally • Used for moving materials in large quantities between specific locations over fixed path (on floor, above floor, overhead) Powered conveyors: Power mechanism contained in fixed path using chains, belts, rolls, etc. to drive loads Non-powered conveyors: Humans push loads along the fixed path, or gravity is used from a higher elevation Types of conveyors: 1-Roller 2-skate-wheel 3-belt, chain 4-in-floor towline 5-overhead trolley 6-power-and-free overhead trolley 7-cart-on-track, others

Unit load principle

• A unit load is the mass that is to be moved or otherwise handled at one time • It could be one part, a container loaded with multiple parts, or a pallet loaded with multiple containers of parts • It should be as large as is practical for the material handling system that will move or store it • Considerations of safety, convenience, and accessibility to the materials that make up the unit load must be observed Reasons for using unit loads 1. Simultaneous handling of multiple items 2. Reduction of the required number of trips 3. Reduction of loading/unloading items 4. Decreasing product damage Unit loads result in lower cost and higher operating efficiency

Overhead trolley conveyors

• A wheeled carriage running on overhead rail with loads suspended • Multiple trolleys equally spaced along fixed track • Trolleys moved along track by chain or cable forming a loop • Often used for moving parts and assemblies between production departments

Reasons for using asynchronous motion type

• Accumulate loads • Temporary storage of items • Allowing for different production rates between adjacent processing areas • Smooth production when different stations have variable cycle times along the conveyor • Accommodate different conveyor speeds in a path

Chain conveyors

• Chain loops in over-and-under config • One or more chains operating in parallel • Chains slide along the channel or ride on rollers in channel

Recirculating conveyors

• Continuous loop conveyors that allow for parts to remain on the return loop for one or more revolutions are recirculating • So, storing and delivering are both feasible • Possible problems could be lack of empty carriers at loading station when needed, or lack of loaded carriers at the unloading station

Positioning equipment

• Equipment to handle parts and other materials at a single location (loading/unloading from production machine) • Positioning accomplished by industrial robots that perform material handling, and part feeders in automated assembly • Hoists at single location can be included in this category

Transport Equipments

• Industrial trucks • Automated guided vehicles (AGVs) • Rail-guided vehicles • Conveyors • Hoists and cranes

Continuous motion conveyors

• Move materials at a constant velocity along a path • Examples: belt, roller, skate-wheel, and overhead trolley

Unit Load Formation Equipment

• Refers to containers (pallets, boxes, baskets, pails, drums) used to hold individual items during handling, and equipment used to load and package the containers (palletizing) • Containers include pallets, tote pans, boxes, baskets, barrels, drums • Factories, warehouses, and distribution centers use forklift trucks to move unit loads on pallets • Using automatic transport and/or storage equipment to handle loads means the facility needs to standardize on a specific type and size of container

Continuous loop conveyors

• They form a complete circuit • They allow materials to be moved between any two stations along a path • Any conveyor type can be configured as a loop (even the single direction ones) • Empty carriers automatically return from unloading station back to loading station • No loads in the return loop (items loaded at load stations are unloaded at unload stations

Vibration-based systems

• They use a flat track connected to an electromagnet to create vibratory angular motion in a certain direction • Same concept used in vibratory bowl feeders to deliver components in automated assembly systems

Single direction conveyors

• To transport loads one way from point of origin to destination • Suitable for situations where there is no need to move loads in both directions, or return carriers and containers from unloading station back to loading station • Examples: roller, skate-wheel, belt, chain-in-floor

Material Handling Equipment

• Transport equipment • Positioning equipment • Unit load formation equipment • Storage equipment • Identification and control equipment

In-floor towline conveyors

• Use four-wheel carts powered by moving chains or cables (towline) located in trenches in floor • Cable and trench define pathway • Cable is driven as a powered pulley system • Switching between powered pathways possible (increased flexibility) • Used in manufacturing plants and warehouses

Material Transport Equipments

1. Industrial trucks, manual and powered 2. Automated guided vehicles 3. Monorails and other rail-guided vehicles 4. Conveyors 5. Cranes and hoists

Categories of Material Handling Equipment

1. transport equipment 2. positioning equipment 3. unit load formation equipment 4. storage equipment 5. identification and control equipment • Transport equipment • Positioning equipment • Unit load formation equipment • Storage equipment • Identification and control equipment

Asynchronous conveyors

Asynchronous motion type can accomodate different conveyor speeds in a path Operate with stop-and-go motion Loads in carriers (baskets, carts, hooks) are moved between stations, stop and remain in a station until released • This allows for independent movement of carriers • Examples: overhead power-and-free trolley, in-floor towline, and cart-on-track conveyors

Belt conveyors

Continuous loop, half of the length is for delivering and the other half for return run Made of reinforced elastomer (rubber) for high flexibility and low extensibility A drive roll at the end of conveyor powers belt

Plant Layout

Design of the handling system should be considered part of the new facility planning to optimize material flow in the building Three types of plant layout: Process layout Product layout Fixed position layout

Categories of AGV

Driverless trains: a towing vehicle (AGV) pulling one or more trailers, heavy payloads, long distances, with/without intermediate pickup/drop-off • Pallet trucks: to move palletized loads along determined routes • Unit load carriers: to move unit loads from one station to another

Imbedded guide wires - AGV

Electrical wires are placed in a small channel cut into the floor (cemented later) Guide wire is connected to a frequency generator which emits active power low-voltage low-current signal (1-15kHz) A magnetic field is induced along the pathway that can be followed by sensors on board

Powered industrial trucks

Guided by an operator • Common types: walkie trucks, forklift rider trucks, and towing tractors • Walkie trucks: for insertion into pallet openings, Max speed 5km/hr • Forklifts: load capacity of 450-4500 kg

Automated guided vehicle systems (AGVS)

Independently operated and self-propelled systems guided along a defined path The power source is rechargeable on-board batteries Suitable for moving different materials from various load points to various unload points AGV principal applications in production and logistics • Driverless train operations • Storage and distribution • Assembly line applications • Flexible manufacturing systems

Cart-on-track conveyors

Individual carts riding on a track elevated from floor • Carts are driven by a rotating shaft • Carts can be positioned with high accuracy (advantage compared with others) • Applications include robotic spotwelding lines in automobile body plants and mechanical assembly systems

Skate-wheel conveyors

Like roller type but with skate wheels rotating on shafts connected to the frame Similar applications as roller but with lighter loads Light weight makes them portable for loading/unloading points

Magnetic tape - AGV

Magnetic tape installed on floor to define pathways No cutting on floor required

Vertical lift conveyors

Mechanical elevators designed to provide vertical motion (between floors, or to link floor-based conveyor with overhead conveyors)

Vehicle guidance technology

Method by which AGVS pathways are defined and vehicles are controlled to follow the pathways Five common technologies • Imbedded guide wires • Paint strips • Magnetic tape • Laser-guided vehicles LGVs • Inertial navigation

Laser-guided vehicles (LGVs)

More flexible than other applications Operating without continuously defined pathways Dead reckoning accuracy decreases over long distances "Dead reckoning" is a method of determining a vehicle's position based on its initial position, speed, orientation, and elapsed time. Calculated position needs to be compared with known locations established by beacons all over the plant (columns, walls, machines, etc.)

Roller conveyors

Pathway consists of a series of tubes perpendicular to direction of travel Pallets, tote pans, cartons serve this type Rollers are contained in a fixed frame elevate from floor Can be powered (driven by belts or chains) or non-powered (driven by gravity) Applications include manufacturing, assembly, packaging, sorting, distribution

Product Layout

Products are standard (or very smilar), variety among products is limited, and the required production rate is high. Involves production of a standard or nearly identical types of products in high quantities

Rail-Guided Vehicles

Self-propelled vehicles that ride on a fixed-rail system Motorized vehicles guided by one fixed rail (monorail) or two fixed parallel rails Vehicles operate asynchronously (like AGVs) and are powered by on-board batteries Rail-guided systems are more versatile than conveyor systems but less than AGVs

Design Considerations in Material Handling

System design depends on • Materials to be handled • Quantities and distances to be moved • Type of production facility served by the handling system • Budget, etc • Materials can be classified by the physical characteristics