Are you planning to buy Automated Guided Vehicles for your manufacturing unit/office or maybe just curious to know what the heck it is? You have landed to the best domain for detailed and updated information about Automated Guided Vehicle technology. This article initiates with its historical background and flows through its technology and working mechanism then reveals the various types of Automated Guided Vehicles to help you understand what you should buy, in addition to the Automated Guided Vehicle applications. To further aid you, some important points are discussed before you buy the AGV. Finally, the specific advantages and disadvantages of Automated Guided Vehicle system have been exposed to help you understand AGVs better.
Since its inception, humans have tried to attain knowledge and applied it innovatively to simplify life. Carts, cycles, bikes, cars, ships, planes are classic examples in the navigation domain. These all have simplified navigation of humans and goods miraculously if visualized being in the stone age. But, there is a next-level innovation in the navigation domain i.e. unmanned navigations or computer operated navigations. You must be well aware of unmanned space missions and unmanned aerial vehicles (drones) and fully automated unmanned GPS enabled cars. But you may have not heard about the Automated Guided Vehicles.
Let’s have a look at it…
What is an Automated Guided Vehicle
In short, an Automated Guided Vehicle (AGV) is a computer-programmed, wheel-based robot that functions as a load carrier from one place to another within a manufacturing unit, warehouse or office. It is not driven by a human instead pre-programmed with routes and tasks to operate.
There are no footprints of AGVs until the start of the 1950s. In 1953, Arthur Mac Barrett Jr. modified his towing tractor which he used to tow the trailer. He configured the tractor to follow an overhead wire (in the ceiling) and operated the first Automated Guided Vehicle in a grocery shop. He called his invention Guide-o-Matic (the term AGV was not coined by then). Later, the overhead wires were laid down on the floor.
His company Barrett Electronics, Illinois introduced its driverless vehicle in 1954 calling it Guide-o-Matic. This driverless vehicle was a tow truck that followed an embedded wire on the floor. Soon his invention and automation became very popular within the manufacturing units and warehouses.
Minor improvisations kept on coming till the late 90s and no significant innovation was done until the start of the 70s.
In 1973, the engineers at Volvo auto assembly plant in Kalmar, Sweden invented a replacement for the conveyor-centric assembly line. It was a non-synchronous 280 computer-operated driverless vehicles. It became so popular that almost every industry started requesting for it, to replace their conveyor lines. Later, Volvo marketed its unit load driverless units to other car companies as well.
Till this time there was no such term as AGV. It was just called a driverless vehicle. The industry leaders coined the term Automated Guided Vehicle (AGV) during the 80s. This was also the time when the embedded wires were being replaced by UV technology.
The first UV based AGV was deployed in the Willis Towers (formerly Sears Tower) in Chicago, Illinois to deliver mail throughout its offices.
In 1987 laser technology was introduced in the AGV for navigation and by 1989 the AGVs were fully controlled by a computer. In 1992, a system was developed to control both the wired and wireless AGV. In 2003, a new system was developed which could command an AGV to change the path. Besides navigation, today’s AGV can lift, lower and transfer the loads quite easily and safely.
No doubt, Arthur Mac Barrett handed over an innovative and a millennial idea to the manufacturing industry. He kept himself busy with various innovations during his whole life and passed away on 17 August 2010 at the age of 89 in Lake Forest, Illinois.
AGV Technology & Working Mechanism
A battery-powered AGV system navigates through a pre-defined path without a driver on-board. The AGVs navigate throughout the warehouse, unit or office using several guidance technologies viz. floor-surface mounted magnetic tape, laser or optical sensor. With the help of these guidance technologies, the AGV can change the route or its navigational area can be expanded/shrank as per the facility’s open space.
The computer-controlled wireless AGV system uses software provided by the AGV manufacturer. With the help of this software the location of the AGV is identified and the relevant commands for the specific tasks can be issued. These commands include but are not limited to start-stop, lift-lower, speed-change, reverse-forward, turn-points, diversion from the guide paths and interacting with other material handling equipments & systems both automated and static.
Various Navigation Types for Automated Guided Vehicles
By now you know some of the navigation types of the AGVs. Let’s elaborate a bit more on the navigation of the AGVs.
There are seven types of AGV navigation viz.
For wired navigation inside the unit first, you need to map the route on a paper. Then a slot is cut on the floor approx 1 inch below the surface throughout the route. In this cut slot, a wire is placed which is followed by the AGV. This placed wire transmits a radio signal and there is a sensor beneath the AGV which detects this signal. The sensor detects the relative position of the wire and the steering circuit uses this information to maintain the AGVs position along the route.
The AGVs which use tapes are usually called Automated Guided Carts (AGC). The tape navigation is a better way than the wire navigation as you need not cut throughout the route to place the wires. In the tape navigation, both the magnetic and the colour tapes can be used. The AGV is equipped with the appropriate sensor to detect the tape beneath and follow the route. The major advantage of tape as compared to wire is that it can be easily removed and the route of AGV can be changed as per the need. The coloured tape is less expensive than the magnetic tape but if installed in high traffic areas can become dirty too quickly thus create problems for the sensor to detect it. Dual polarity is the main advantage of using magnetic tapes. You can place the small pieces of magnetic tapes to change the state of the AGC based on the polarity.
For laser navigation, reflective tapes are fixed on the walls, poles or any appropriate location. The reflectors’ positions are then stored in the memory of the AGV. The AGV is also equipped with a laser transmitter and receiver on a rotating turret. The laser is transmitted and received by the same sensor. The sensor calculates the angle and distance to the reflective tapes which are in the line-of-sight and in the range. This information is used by the navigation system to triangulate the present position of the AGV by analysing the reflectors’ layout in the memory. This present position is then analysed with the route stored in the memory, then the navigation system steers the AGV as per the route.
The laser AGV navigation is of two types
Pulsed lasers provide coarser resolution than the modulated ones. Its scanner emits pulsed laser light at a rate of 14,400 Hz resulting in a resolution of ~3.5 mrad (0.2o) with 8 revolutions of scanner per second. Then based on the intensity of the reflected laser light the centre of the reflector is calculated by interpolating the intensities. This way workable navigation is achieved with the pulsed laser AGV.
The modulated lasers on the other hand provide better range and finer resolution as compared to the pulsed lasers. It emits a continuous fan of modulated lasers which results in an uninterrupted reflection as soon as a reflector comes in the line of sight. At the trailing edge of the reflector, the reflection ceases which improves the accuracy of the AGV position. A modular laser can provide the angular resolution of ~0.1 mrad (0.006o) with 8 revolutions of the scanner per second.
In the inertial AGV navigation, transponders are embedded on the floor of the unit and a computer-controlled system assigns routes and tasks to the AGV. The transponders help AGV to stay on the course. The gyroscope within the AGV helps to detect the slightest change and rectifies the steering to keep in on the course. The gyroscope has an accuracy of ±1 inch.
Natural Feature Navigation
With this type of navigation system, you need not alter anything within the unit. One of the natural feature navigation methods uses one or more range finding sensors like laser range-finders along with gyroscope or inertial measurement units with Monte-Carlo/Markov localization technique. With the help of these techniques, the AGV calculates its shortest permitted route to its goal. Finding the shortest permitted route and reaching it fast makes this navigation system quite popular.
This system also comes with the promise of an unaltered unit. You need not change anything within the unit. The AGV comes installed with a specially designed stereo camera. The 360o camera generates a 3D map of the route and the surrounding. This way the AGV can repeat the route as and when desired. The technology used within these systems is called Evidence Grid Technology, a probabilistic volume sensing application that was initially developed by Dr Hans Moravec at Carnegie Mellon University.
In the Geo-navigation technique, the AGV calculates its position by recognizing the nearby features. These features may be racks, poles, walls or columns. The AGV uses these fixed features as a reference to determine its current position and proceeds through the route.
Steering Control in Automated Guided Vehicles
Now that we have seen the various navigation mechanisms, let’s understand the various steering mechanisms for different AGVs.
There are three types of AGV steering viz.
Differential Speed Control
The type of steering controlled mechanism of AGVs is simplest as it does not require any additional steering motor or mechanism. That’s why such steering AGVs are most commonly used. In this steering method, the two front wheels are independently controlled. Both the wheels have different speeds while taking a turn on the other hand while moving ahead or reversing the wheels’ speed remains in sync. But this type of steering is not suggested for towing AGVs as they may cause the trailer to jackknife while turning.
Steered Wheel Control
Usually, such steering is used in the three-wheeled AGVs. The front-wheel keeps the AGV on track and the same is responsible to change the course. This steering AGV is much appreciated for better track accuracy. Due to the smoother turning, this type of steered AGV can be used for towing AGV as well, unlike the former steering type AGV.
Combo of Above
This type is the combo of the above two. In this type of AGV, two independent drive/steer motors are placed on the diagonal wheels and swivelling castors are placed on the remaining corner. This type of AGV can take a turn like a car (arc), crab in any direction as well as it can drive in the differential mode in any preferred direction.
Path Decision in Automated Guided Vehicles
Different navigation systems use different path decision mechanisms. It’s important to understand beforehand as it may help you buy the AGV system as per your need and budget.
There are broadly three types of path decisions for the navigation systems viz.
Frequency Select Mode
In the wire navigation, frequency select mode is used by the AGV for path selection. The wires in the floor emit a frequency that is received by the AGV. At the split point on the route, the different routes emit different frequencies. At the split point of different frequencies, the AGV with the help of the stored table in its memory decides the route to be taken. The same frequency is emitted throughout the same route and frequency change occurs only at the split point. The AGV costs less but the floor needs to be cut and wires to be laid down along the routes. Assigning a new route requires additional cut and wiring beneath and if the old routes are not needed then the cut on the floor remains there.
Path Select Mode
Within the wireless AGVs, the path select mode is implemented. The AGV is preprogrammed to follow the routes. The AGV, with the help of embedded sensors, locates itself on the map, then calculates the route as per the program. At any split point, the AGV simply needs to follow the installed route. The mechanism is quite simple but costlier than the former one as it needs programming as well. Change of routes and assigning/revoking routes is quite simple.
The magnetic tape provides the path for the AGV. The tape is either laid on the surface or 10mm beneath the surface along the route. Alongside the track, the different combinations of polarity, sequence and distance of the strips of tape, instruct AGV for changing lane, speed up/down and stop.
Types of Automated Guided Vehicles
If classified broadly, there are three types of AGVs viz.
This type of AGV works as a towing vehicle for trailers. There can be just one or more than one trailer to tow. This type of AGVs are used to transport heavy payloads on long-distance routes which have no intermediate pick-up or drop-off points. The driverless trains can bear weight up to 60,000 pounds.
AGV Pallet Trucks
The pallet trucks are used to transport the palletized loads to-from pre-programmed points. These AGVs may also have vertical controls to collect/place the pallets from/on shelves.
Unit Load Carriers
These AGVs are used to move unit loads from one point to another. With the help of rollers, automatic loading/unloading can be performed. Such types of AGVs carry lesser weight as compared to the former ones.
Charging Mechanism of Automated Guided Vehicles
The AGVs work on batteries. Thus, like other batteries, the AGV batteries do get exhausted over time and require recharging.
There are broadly two charging mechanisms for AGVs viz.
In the wired charging, there is direct contact between the battery system and the charging station through a wire. There are three ways, a wired charging can be done
When the battery power is below the predefined threshold, a notification is received and the battery can be either replaced with a charged one by the operator or the AGV can be plugged in for charging.
The is an automated charging and requires an extra automated AGV charging station. When the battery level reaches a threshold, the AGV itself moves towards the charging station and the automated station replaces the drained battery with a fully charged one.
This mechanism is also called opportunity charging for AGV. Whenever a task is over for AGV or a predefined battery threshold is reached, the AGV automatically moves to the charging point and charges its battery. With this mechanism an AGV can charge itself several times a day between the tasks thus it may never have to replace the battery.
Wireless charging is a new entrant in the AGV field thus costlier than the wired one. This mechanism relies on a stationary active fixed coil on the ground or on the wall and a mobile passive coil on the AGV.
The active coil generates a magnetic field that induces an alternate current on the passive coil on the AGV. This current is then used to charge the battery. The charging process is completely contactless. The AGV can charge its battery several times a day with opportunity charging.
Automated Guided Vehicle Applications
There is a long list of industries that use AGVs viz. Automotive, Pharmaceutical, Beverage, Hospitals, printing, chemicals, warehouses and many many more.
The most common operations which are being performed by the AGVs are
To carry load from one point to another.
To collect parts for assembly.
To move products through various production processes
To deliver pallets for the production process
Moving loads within the storage and keeping a record of them.
Taking the ordered products to the trailer-loading point for distribution and transporting a platform for a picker to place selected items on it.
Advantages of Automated Guided Vehicle
Now that we have explored the AGVs in quite detail, let’s have a quick overview of its advantages.
AGVs can cut labour costs to quite an extent.
Better Inventory record
AGVs always keep a track of what they picked up and delivered thus provide better inventory.
AGVs can even work in double shifts thus provide more productivity
Humans make errors depending on their state of mind. This is not the case with the AGVs. They do what they are programmed to do.
AGVs can replace the long conveyor and the production line thus provide more space.
Disadvantages of Automated Guided Vehicle
High Initial Investment
There is a high initial investment to purchase an AGV.
AGVs are machines and do fail from time to time. To fix them also involve cost.
Communication lack between AGV Manufacturers
An AGV from a manufacturer is not compatible with others. Thus you need to stay with the current manufacturer for future assistance.
AGV Favorable Environment required
Even if you get the best AGV with advanced sensors, still it needs a flat surface to work.
Lack of Flexibility
AGVs are designed to do repetitive tasks and wait forever if an obstacle comes in the path which is not removed. Human supervision is always required, even with AGVs.