Frequently Asked Questions
Search below to find answers to your most frequently asked questions about automatic guided vehicle systems.
- When were automatic guided vehicles first developed?
Barrett Electronics Corporation invented the world’s first AGV for industrial applications in 1954. The term AGV (Automatic Guided Vehicle) was actually introduced in the 1980’s. Previously, AGVs were called driverless vehicles.
One of the first driveless vehicles is on permanent display at Savant Automation in Walker, MI near Grand Rapids, MI. Barrett Electronics was acquired in 1983 allowing the Barrett AGV product line to evolve as part of Savant Automation and now consists of over 13 distinct AGV vehicle types.
- How many systems have been installed?
In the United States there have been over 3,000 AGV systems installed during the last 50 years. These systems range from one vehicle to well over 100 vehicles. There are approximately half a dozen major AGV manufacturers in the US. These companies account for about 80% of the systems installed each year. Approximately 12 other companies supply the remaining 20% of the systems.
- What are the general types of AGVs?
Tow Type — Used for pulling carts, trailers, dollies, etc. Typically range from 10,000 to 50,000 pounds towing capacity. Train lengths depend on capacity, space and trailer tracking performance.
Unit Load Type — Self-contained AGVs that carry products on their built-in load decks. Typically transport pallets, totes, rolls and racks, usually one or two at a time. Often incorporates automatic load transfers at pick and drop stations.
Fork Type — Utilizes a fork/mast lift mechanism for interfacing with loads at various elevations. Often loads are at floor or stand level and are retrieved and deposited automatically.
Commercial/Office Type — Smaller type units with capacities of less than 500 pounds. Designed to transport small totes or small loads in light manufacturing or clean environments. Versions are also used to distribute mail in offices.
Heavy Carrier Type — Designed to transport large or very heavy loads. Typically used in primary metal and paper industries. Capable of transporting dies, rolls, coils, ingots weighing in excess of 250,000 pounds.
- What are the basic functions performed by AGVS controls?
AGV systems with multiple vehicles perform some type of AGV routing, traffic control and communications.
Routing is the method by which AGVs navigate through an AGV system path network to arrive at a designated destination. Different approaches to routing logic can be implemented included shortest time, shortest distance and fixed pattern.
Traffic control assures that AGVs do not collide with each other while operating on the path. Traffic control can be provided with fixed or variable vehicle separation capabilities.
Communications is used for various functions in an AGV system. It can be between vehicles, between vehicles and a central device or for local interfaces. Communications can be implemented via RF or infrared means.
- How do AGV control systems differ?
Most major US AGVS manufactures use proprietary control system designs. However, they tend to fall into two categories. Either they use a centralized controller or a decentralized vehicle control approach.
The centralized controller approach utilizes a PC or other computer device to manage the movement of vehicles along the path. Often, this is called the smart central approach. Either or both the routing or traffic control functions would be performed by the central controller. The AGVs would take appropriate direction from the central controller via a communications link.
The decentralized control approach does not require a central controller device for basic vehicle movement. Instead, the vehicles perform their own routing and traffic control functions. This is often referred to as the smart vehicle approach. The AGVs would use their onboard intelligence to select their route to a destination and they would avoid running into other AGVs operating on the path by communicating directly between AGVs.
- What are the types of AGV navigation systems?
The methods of AGV navigation include wire guided, inertial guided, laser guided, grid and chemical path guided. By far, the most popular methods are wire, inertial and laser guided system.
Wire guided systems have been available since the invention of the AGV in the early 1950’s. Although variations exist, most wire guided technologies employ a series of wires embedded in a shallow slot in the floor. The slot is cut in the floor using a concrete saw. The slot is approximately 1″ deep and 1/4″ wide and is backfilled once the wire is installed. The wire in the floor slot carries a low voltage, milliamp strength high frequency signal. The wire guided AGVs have sensing devices under their frames to detect the wire signals and allow the AGV to steer appropriately.
Inertial navigation systems were introduced in the early 1990’s. It is based on the use on a gyroscope onboard the AGV. Similar to gyroscopes used on airplanes, cruise missiles, etc., the gyroscope can detect minute changes in vehicle direction. Each vehicle has a CAD type map of the system layout in its memory. The vehicles steer by comparing information from the gyroscope and odometry sensors to the map and making necessary course corrections. Typically, the tracking of inertial navigation systems is +/-1″ of the true path. Small markers in the floor are used periodically to maintain the tracking accuracy.
Laser navigation systems were introduced in the early 1980’s. These systems are based on target triangulation to keep the vehicles on course. The vehicle is equipped with a rotating laser beacon mounted approximately seven feet above the floor. This beacon scans 360 degrees around the vehicle for laser targets mounted on columns, walls, etc. The reflections from these targets are measured relative to angles from the vehicle and triangulated to allow the vehicle to determine its position. This position is compared to a CAD type map stored in the vehicle’s memory. The targets are typically located 20 to 30 feet apart, on both sides of the path to provide sufficient navigation resolution. Laser navigation is supplemented by onboard vehicle odometry sensors to obtain tracking accuracy of about +/- 1″.
Grid navigation systems rely on a floor pattern to guide the AGV. This floor pattern can be a grid of magnets, wires, colored tiles, RF devices, etc. The AGVs monitor their position along the grid following a pre-established route in their onboard memory.
Chemical path navigation systems employ an optical guidance system onboard the AGV. Typically, a chemical line is applied to the floor surface. Under normal lighting conditions the line is not visible. However, the AGV utilizes a special path illumination light under the vehicle to detect the floor line and thereby track it. This type of path is not typically used in factories or warehouses because the floor line needs to reapplied periodically depending on wear caused by other traffic.
- How big is the AGVS market in the United States?
The AGVS market has ranged from $40-100 million per year over the last 10 years. This generally represents 30-80 systems. The average system has about 4-5 vehicles. The largest material handling AGV systems have 50-100 vehicles. There are numerous small systems with 1-3 AGVs.
- How many companies supply AGV systems and how can I compare these companies?
There are approximately a dozen companies in the US supplying AGV systems. Of those, the top four companies have a combined 60% (approximate) of the market. Some of the ways to compare AGV suppliers are:
Longevity — How long have they been in the AGV business?
In-House Capabilities — Do they manufacture their own vehicle chassis? Do they buy or build the AGV controls?
Financial Strength — Do they have financial resources of a large or small company?
Complimentary Products — Are they a one product company or do they offer other products (conveyor, controls, storage products, sortation equipment, etc.)
Reputation — What do reference customers say about quality and service?
Product Design — Is the vehicle type for your system a standard model or a special design?
Customer Support — Do they have local service? How large is their parts and service organization? Is 24/7 help included with system?
System Training and Documentation — How much operator and maintenance training is included? Are service manuals well documented with parts lists, troubleshooting diagrams, descriptions of component operation? Does the maintenance manual come on CD?
- What are some general considerations for AGVS?
There are a number of issues to be considered:
Nearly all AGV systems operate indoors. If traveling outdoors a concrete surface is usually recommended. This is because other softer surfaces (asphalt, blacktop, etc.) will develop ruts from repetitive AGV traffic. These ruts will hold water, cause excessive wear to steering components, and eventually crack out.
Insure in-plant paths are in good condition (no broken concrete, large cracks, etc.)
Consider marking the AGV path. Painted lines, arrows, etc. are often used to identify the route of the AGV for plant personnel. Mark safety areas so that people are aware of AGV tracking patterns at turns or congested pedestrian areas.
AGV paths need to be kept open, so ‘housekeeping’ needs to be maintained.
It is generally best to limit the mixing of AGV traffic with manned vehicle traffic. As much as possible, manned forklifts, etc. should use aisles separate from AGV aisles. If possible, a dedicated space should be provided for AGV travel.
AGVs need maintenance. Reserve an area in the facility for AGV maintenance.
Spare parts should be procured with the AGV system. Insure your budget includes this.
AGV systems should have champions. This would be someone who has the responsibility to insure the AGV system is properly used and maintained. This person would also identify any changing system requirements and deal with adapting the systems to meet those needs.
Consider a maintenance contract. The major suppliers offer various packages to provide periodic preventive maintenance or full time maintenance to meet user needs.
- Can AGVS be leased?
Yes. This is an increasingly popular approach. Leases of 3-7 years are typical. Leases can include just the equipment or the entire system (equipment, engineering, installation, software). Contract maintenance is often bundled with a system lease, which improves potential residual value at the end of the lease reducing lease payment.
- What level of technical expertise is required to maintain AGVs?
Most AGV maintenance is mechanical. Background in maintaining forklifts, conveyors or machinery is sufficient to provide normal AGV maintenance. Electronic troubleshooting expertise is usually required when there is an AGV problem. Typically this includes knowledge or skill with diagnostic tools and software. Electronic problem resolution usually involves following a troubleshooting diagram/flowchart and either repairing a connection or replacing a PC board or sensor. Major AGV suppliers who provide their own control systems also provide telephone support to help in-plant technicians troubleshoot problems.
- What factors affect the useful life of AGVs?
The useful life of an AGV depends on a number of factors:
Environment — Clean, dirty, abusive, indoors or outdoors
Floors — Smooth, rough, wet, dry, cracks, holes
Application life — How long system is needed
Maintenance — Level of preventative maintenance, quality of servicemen
User discipline — Commitment to support proper AGV use
Operating time — Number of shifts, percent time running
Equipment quality — Robustness for application, accessibility for maintenance
Vendor support — Timely/knowledgeable supplier support, parts availability
Management commitment — Dedication to system operation
Documentation/training — Quality of support materials and guides
Vendor condition — Financial strength, control of technology, market leadership
There are AGVs that have been in service 15-20 years. However the norm is more like 7-10 years in most industrial applications. Many users opt to rebuild or refurbish their AGVs when they reach significant increased maintenance cost. Rebuilt equipment generally costs half the price of new equipment and generally yields 5-7 more years of useful AGV life.
- How safe are AGVs compared with other material handling methods?
AGVs are very safe, particularly when compared with manual material handling methods. There are hundreds of injuries per year resulting from manual forklifts, however there are probably less than a dozen AGV injuries per year.
The exemplary safety record of AGVs is due to a number of factors. They travel at 2 mph, which is walking speed. They have numerous safety devices to prevent accidents such as flashing lights, audible devices, physical emergency bumpers, passive infrared and sonar devices. In addition, ANSI regulations specify layout requirements, stopping distances and other safety related items to insure safe implementation of AGV systems.
- How do AGVs avoid running into each other while operating on the same path?
AGV traffic separation is generally performed two different ways:
Central Traffic Controller — This method employs a centralized computer to control the movement of the AGVs in the system. Each AGV communicates with the central controller, which in turn keeps track of the AGV locations. When two AGVs get close to each other along the path or at intersections, the central controller instructs one AGV to wait until the other passes.
Decentralized Traffic Control — Each AGV performs its own traffic control without the need of a central traffic control computer. As the AGVs catch up with each other along the path or cross each other’s path at intersections, they communicate with each other to coordinate their movements. This is via direct AGV to AGV communication.
Systems that do not require a centralized controller have greater redundancy because a central controller failure would otherwise stop all vehicle movement. However, with AGVs that have onboard traffic control intelligence, a failure only affects that AGV — not the whole fleet.
All traffic control schemes are based on maintaining either variable or fixed spacing between vehicles. In the case of fixed spacing methods, the AGVs are separated by specific distances or zones created along the path. Variable spacing methods allow dynamic changes in vehicle spacing to occur. Typically, variable spacing methods bunch vehicles closer together and can result in greater system throughput. Some AGV systems utilize a combination of variable and fixed vehicle separation in the same system.
- How are destinations given to AGVs?
AGVs receive destination information either locally (onboard the AGV) or remotely (via a central controller). Some AGV system technologies support both methods, others support only one method.
The need for one or both dispatching capabilities depends on the system operation. Many times, especially in tow type AGV systems, operators will key in destinations directly onboard the AGV using the AGV’s built-in keypad. This would be the preferred and less expensive method to use when operators (like forklift personnel) load or unload the AGVs and then desire to dispatch the AGV according to their needs.
More sophisticated AGV system requirements usually demand the ability to remotely dispatch the AGVs in response to operator or system needs. These system applications require AGV technologies that support remote AGV communication for determining AGV status, location and command instructions. Such applications could include an AGV call system when operators use terminals in the facility to call for AGV service, or in systems where the AGV control system is interfaced to a higher level computer system which issues transport tasks to the AGV system controller.
- How do AGVs route themselves to selected destinations?
There are two general methods for routing AGVs to destinations:
Centralized Routing Controller — The AGVs are directed through the path network by a central control device. At path branches, the central controller directs the AGV on which path to take.
Onboard Vehicle Routing — Each AGV is capable of making its own routing decisions as it proceeds to its next destination. At path branches, the AGV determines which path should be taken depending on the current destination.
Systems that do not require a centralized controller have greater redundancy because a central controller failure would otherwise stop all vehicle movement. However, with AGVs that have onboard routing intelligence, a failure only affects that AGV — not the whole fleet.
- What are the possible ways to call or dispatch AGVs?
In systems that require the ability to remotely call and dispatch AGVs there are several methods possible:
Simple Call Button — At each AGV calling location a button, lanyard or switch can be provided. The call signal is usually routed to a central controller. The controller will store the calls first in – first out order. When an AGV becomes available for a new task, the controller will send it to the next calling station on its wait list.
Keypad Terminal — The AGV call location is equipped with PC terminal or touch type keypad/display. The operator can give the AGV controller more specific information regarding the call task. This information can include the destination for the load once it is picked up, the type of load, priority or even allow the operator to queue multiple calls for different load pickups.
Automatic Call — The call station can be part of an automatic process such as the output from a stretchwrapper, palletizer or production line. In such cases an interface can be provided between the device controller (stretchwrapper, etc.) and the AGV call controller to permit automatic signaling when a load is ready for pickup. Automatic calls can also be generated by sensors (limit switches, photoeyes, etc.) mounted at the load point of the call station.
- How is AGV battery charging done?
There are two ways to do AGV battery charging:
Battery Swap-Out — The AGV’s battery is removed from the vehicle and swapped with a freshly charged battery. Most AGVs have rollers in the battery compartment to facilitate the battery exchange. Typically, the battery is rolled on to a battery cart. This cart then moves transversely across the face of a row of battery charges, each equipped with a battery stand. The used battery is exchanged with the fresh battery, which is then replaced in the vehicle. Batteries in vehicles can also be exchanged using an overhead hoist. Battery swap-out can also be performed by an automated battery change system.
Automatic Battery Charge — Each AGV utilizes a single maintenance-free battery that normally stays in the AGV. The AGV has an automatic charge shoe mechanism that allows the AGV to make contact with a copper contact plate in the floor. This contact plate is wired through the floor to an automatic charger mounted on a column or wall nearby. When the AGV stops over the contact plate and its charge mechanism contacts the plate, the charger automatically turns on. The AGV remains on charge until needed for a load transport task. When it departs, the charger automatically turns off.
There are a number of considerations with respect to the type of battery charging to employ in a given system application. For example, in using automatic battery charging, there must be sufficient AGV idle time to allow the battery recharging to keep up with the battery usage. In an AGV train system there is normally time to charge the AGVs battery while the AGV train is waiting at a station for trailers to be loaded or unloaded. However, in an AGV unit load carrier system, the AGVs are normally kept moving a greater percentage of the time. This limits the time for battery recharging. Unit load carrier AGVs usually pick and drop loads automatically, so there is usually not much idle time at load transfer stations. In these situations additional AGVs would be required to provide sufficient idle time for the whole AGV fleet to allow automatic charging to work. Often this is accomplished by managing the charging process and scheduling AGVs to recharge as needed.
Typical automatic recharge time required can be estimated by determining the expected actual AGV moving time. A good rule of thumb is to plan on a 1:1 relationship between actual running time and required charging time. Therefore, if an AGV is expected to physically be moving for three hours per shift, it should be expected that there needs to be about three hours of automatic charging needed.
- Can AGVs operate on ramps?
Yes, however ramp conditions greatly affect AGV capacity ratings. Most facility ramps vary between 2-10%. AGV unit load carriers are generally allowed to operate on ramps with no more that about 5% inclines. In addition, the level rated capacity of most unit load carriers will be reduced by up to 70% on ramps of 3-5%, depending on the length of the ramp. This means a 4,000 pound rated unit load carrier would only be allowed to handle 1,200 pounds or less when ramps are involved in the system.
Towing AGVs are capable of handling longer and steeper ramps than unit load carriers. They too must be derated for ramp operation. A 30,000 pound towing capacity AGV tow vehicle would be rated for about 10,000-15,000 pounds on a typical 10% ramp. In general, AGV tow vehicles with rear wheel drive systems do better in ramp applications than those with only single front wheel drive construction. Rear wheel drive provides better traction going up the ramp and better stopping performance should the bumper be activated going down the ramp.
Ramp surfaces need to be kept dry. A rough brushed concrete surface is best for traction.
- What are some of the guidelines for laying out an AGV path?
A number of factors must be considered when laying out an AGV path. First and foremost is consideration for safety. It is recommended that 18″ exist from the side of the AGV to any fixed object along the path. This includes any towed trailers as they track around a curve.
Different vehicle types, combined with different steering configurations determine the AGV turning capabilities. Typically a unit load vehicle will use 6-8’ radius curves, whereas tow vehicles use 8-12’ radius curves. The tighter the curve, the less space required in the aisles for the AGV to operate.
Spurs (or sidings) off the main path are another consideration. Including the curves to depart and return to the mainline, plus the straight spur line, the approximate required length of a side spur is — an AGV (and trailers, if tow type) length plus about 30 feet.
It is important to determine where an AGV stop station can be located — how close to the end or beginning of a curve. This is particularly critical in unit load carrier systems where an automatic pickup or drop-off stand is close to a path curve. It takes an AGV a certain distance to straighten out after a curve to line up with a stand. A suggested rule of thumb is to allow a vehicle length after or before a curve before placing the pick/drop stand.
Interface with doors is another layout concern. The AGVs must stop if the door fails to open. Most manufacturers provide a forced stop location prior to an automatic door. The location of this station has to be placed ahead of the door, a sufficient distance to allow the AGV to stop if the door is not completely open. This distance depends on the door opening speed and the speed of the AGV.
Another consideration is to check where an AGV will wait when AGV traffic congestion is ahead. If the AGV waits in an aisle crossing or in a location where it blocks needed access, then the wait point should be relocated.
- Can AGVs from different manufacturers be mixed into the same path?
In general, no. Nearly all US AGVS manufacturers use proprietary AGV designs that are not compatible with each other. Guidance, communications, and control systems differ making path sharing difficult.
- Are there industry standards for AGVS?
Yes, ANSI B56.5 is the accepted standard for AGVS. It focuses on safety requirements and design guidelines.