Automated Guided Vehicle

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The automated guided vehicle or automatic guided vehicle (AGV) is a mobile robot used in industrial applications to move materials around a manufacturing facility or a warehouse.

[1] Heavy-duty AGV

[2]Light-duty assembly AGV

[3]Laser Guided Forklift AGV

[4] Inertial-guided automatic trailer loading vehicle

[5]Laser Guided Unitload AGV

1 Introduction
- 1.1 Flexible manufacturing system
2 Navigation
3 System Management
4 Vehicle Types
5 Battery Charging
6 References

Introduction

Automated guided vehicles (AGVs) help to reduce costs of manufacturing and increase efficiency in a manufacturing system.^[1] AGVs can tow objects behind them in small trailers which they can autonomously hook up to. These trailers can be used to move raw materials into line to get them ready to be manufactured. The AGV can also store objects on a bed. The objects can be placed on a set of motorized treads and then pushed off by reversing them. Some AGVs use fork lifts to lift objects for storage. Transporting materials such as medicine in a hospital situation is also done.

An AGV can also be called a laser guided vehicle (LGV) or self-guided vehicle (SGV). In Germany the technology is also called Fahrerlose Transportsysteme (FTS) and in Sweden förarlösa truckar.

The first AGV was brought to market in the 1950s, by Barrett Electronics of Northbrook, Illinois, (now Savant Automation of Walker, Michigan) and at the time it was simply a tow truck that followed a wire in the floor instead of a rail. Over the years the technology has become more sophisticated and today automated vehicles are mainly Laser navigated e.g. LGV (Laser Guided Vehicle). In an automated process, LGVs are programmed to communicate with other robots to ensure product is moved smoothly through the warehouse, whether it is being stored for future use or sent directly to shipping areas. Today, the LGV plays an important role in the design of new factories and warehouses, safely moving goods to their rightful destinations.

Flexible manufacturing system

To begin to understand AGV it is necessary to understand the fundamentals of flexible manufacturing systems (FMS). FMS is a means by which to manufacture a product. FMS is more of a philosophy rather than a tangible item.^[2] FMS is the idea that faster is better and uses machines to produce their products. Rather than using humans to perform repetitive tasks a machine is used to perform that task 24 hours a day. FMS uses computer numerical controlled machines (CNC) to form a work cell.^[2] Each cell performs a specific task to assist in the manufacturing of a product. Although FMS is fast and efficient it is not cheap as it requires a lot of expensive machines in order to work. Typically, it costs millions of dollars to introduce an FMS into a factory.^[2] Rather than using a complete FMS, most companies use part of an FMS called a flexible manufacturing cell. This is used to produce part of a product by machine and maybe part by other methods. Often one or more AGV’s are used in FMS to connect work cells together.

Navigation

AGVs in FMS are used to transport an object from point A to point B. AGVs navigate manufacturing areas with sensors. There are two main sensors AGVs use for navigation, a wired and a wireless sensor.^[1]

Wired

The wired sensor is placed on the bottom of the robot and is placed facing the ground. A slot is cut in the ground and a wire is placed approximately 1 inch below the ground. The sensor detects the radio frequency being transmitted from the wire and follows it.

Guide Tape

Many light duty AGVs (some known as automated guided carts or AGCs) use tape for the guide path. The tapes can be one of two styles: magnetic or colored. The AGV is fitted with the appropriate guide sensor to follow the path of the tape. One major advantage of tape over wired guidance is that it can be easily removed and relocated if the course needs to change. It also does not involve the expense of cutting the factory or warehouse floor for the entire travel route. Additionally, it is considered a "passive" system since it does not require the guide medium to be energized as wire does. Colored tape is initially less expensive, but lacks the advantage of being embedded in high traffic areas where the tape may become damaged or dirty.

Laser Target Navigation

The wireless navigation is done by mounting retroreflective tape on walls, poles or machines. The AGV carrys a laser transmitter and receiver on a rotating turret. The laser is sent off then received again the angle and (sometimes) distance are automatically calculated and stored into the AGV’s memory. The AGV has reflector map stored in memory and can correct its position based on errors between the expected and received measurements.^[3] It can then navigate to a destination target using the constantly updating position.

Gyroscopic Navigation

Another form of an AGV guidance is inertial navigation. With inertial guidance, a computer control system directs and assigns tasks to the vehicles. Transponders are embedded in the floor of the work place. The AGV uses these transponders to verify that the vehicle is on course. A gyroscope is able to detect the slightest change in the direction of the vehicle and corrects it in order to keep the AGV on its path. The margin of error for inertial is method is ±1 inch.^[1]

Inertial can operate in nearly any environment including tight aisles or extreme temperatures and has a longer lifespan than other guidance options. ^[4]

Natural Features Navigation

Navigation without retrofitting of the workspace is called Natural Features Navigation. One method uses one or more range-finding sensors, such as a laser range-finder, as well as gyroscopes and/or inertial measurement units with Monte-Carlo/Markov localization techniques to understand where it is as it dynamically plans the shortest permitted path to its goal. The advantage of such systems is that they are highly flexible and can handle failure without bringing down the entire manufacturing operation, since AGVs can plan paths around the failed device. Cite error: Closing </ref> missing for <ref> tag The optical uses an infrared transmitter/receiver and sends an infrared signal which then gets reflected back; working on a similar concept as the sonic sensor. The problems with these are they can only protect the AGV from so many sides. They are relatively hard to install and work with as well.

Combination control

Combination control sensing is using collision avoidance sensors as well as the zone control sensors. The combination of the two helps to prevent collisions in any situation. For normal operation the zone control is used with the collision avoidance as a fail safe. For example, if the zone control system is down, the collision avoidance system would prevent the AGV from colliding.

System Management

Industries with AGVs need to have some sort of control over the AGVs. There are three main ways to control the AGV: locator panel, CRT color graphics display, and central logging and report.^[1]

A locator panel is a simple panel used to see which area the AGV is in. If the AGV is in one area for too long, it could mean it is stuck or broken down. CRT color graphics display shows real time where each vehicle is. It also gives a status of the AGV, its battery voltage, unique identifier, and can show blocked spots. Central logging used to keep track of the history of all the AGVs in the system. Central logging stores all the data and history from these vehicles which can be printed out for technical support or logged to check for up time.

AGV is a system often used in FMS to keep up, transport, and connect smaller subsystems into one large production unit. AGVs employ a lot of technology to ensure they do not hit one another and make sure they get to their destination. Loading and transportation of materials from one area to another is the main task of the AGV. AGV require a lot of money to get started with, but they do their jobs with high efficiency. In places such as Japan automation has increased and is now considered to be twice as efficient as factories in America. For a huge initial cost the total cost over time decreases

Vehicle Types

AGVS Towing Vehicles were the first type introduced and are still a very popular type today. Towing vehicles can pull a multitude of trailer types and have capacities ranging from 8,000 pounds to 60,000 pounds.

AGVS Unit Load Vehicles are equipped with decks, which permit unit load transportation and often automatic load transfer. The decks can either be lift and lower type, powered or non-powered roller, chain or belt decks or custom decks with multiple compartments.

AGVS Pallet Trucks are designed to transport palletized loads to and from floor level; eliminating the need for fixed load stands.

AGVS Fork Truck has the ability to service loads both at floor level and on stands. In some cases these vehicles can also stack loads in rack.

Light Load AGVS are vehicles which have capacities in the neighborhood of 500 pounds or less and are used to transport small parts, baskets, or other light loads though a light manufacturing environment. They are designed to operate in areas with limited space.

AGVS Assembly Line Vehicles are an adaptation of the light load AGVS for applications involving serial assembly processes.

Battery Charging

AGVs utilize a number of battery charging options. Each option is dependent on the users preference. The most commonly used battery charging technologies are Battery Swap, Automatic/Opportunity Charging, and Automatic Battery Swap.^[5]

Battery Swap

"Battery swap technology"^[5] requires an operator to manually remove the discharged battery from the AGV and place a fully charged battery in its place approximately 8 - 12 hours (about one shift) of AGVs operation. 5 - 10 minutes is required to perform this with each AGV in the fleet.

Automatic / Opportunity Charging

"Automatic and opportunity battery charging"^[5] allows for continuous operation. On average an AGV charges for 12 minutes every hour for automatic charging and no manual intervention is required. If opportunity is being utilized the AGV will receive a charge whenever the opportunity arises. When a battery pack gets to a predetermined level the AGV will finish the current job that it has been assigned before it goes to the charging station.

Automatic Battery Swap

"Automatic battery swap"^[5] is an alternative to manual battery swap. It requires an additional piece of automation machinery, an automatic battery changer, to the overall AGV system. AGVs will pull up to the battery swap station and have their batteries automatically replaced with fully charged batteries. The automatic battery changer then places the removed batteries into a charging slot for automatic recharging. The automatic battery changer keeps track of the batteries in the system and pulls them only when they are fully charged.