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 AGV plays an important role in the design of new factories and warehouses, safely moving goods to their rightful destination.
Navigation
Wired
A slot is cut in to the floor and a wire is placed approximately 1 inch below the surface. This slot is cut along the path the AGV is to follow. This wire is used to transmit a radio signal. A sensor is installed on the bottom of the AGV close to the ground. The sensor detects the relative position of the radio signal being transmitted from the wire. This information is used to regulate the steering circuit, making the AGV follow the wire.
Guide tape
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. 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. A flexible magnetic bar can also be embedded in the floor like wire but works under the same provision as magnetic tape and so remains unpowered or passive. Another advantage of magnetic guide tape is the dual polarity. small pieces of magnetic tape may be placed to change states of the AGC based on polarity and sequence of the tags.
Laser target navigation
The navigation is done by mounting reflective tape on walls, poles or fixed machines. The AGV carries a laser transmitter and receiver on a rotating turret. The laser is transmitted and received by the same sensor. The angle and (sometimes) distance to any reflectors that in line of sight and in range are automatically calculated. This information is compared to the map of the reflector layout stored in the AGV's memory. This allows the navigation system to triangulate the current position of the AGV. The current position is compared to the path programmed in to the reflector layout map. The steering is adjusted accordingly to keep the AGV on track. It can then navigate to a desired target using the constantly updating position.
Modulated Lasers The use of modulated laser light gives greater range and accuracy over pulsed laser systems. By emitting a continuous fan of modulated laser light a system can obtain an uninterrupted reflection as soon as the scanner achieves line of sight with a reflector. The reflection ceases at the trailing edge of the reflector which ensures an accurate and consistent measurement from every reflector on every scan. By using a modulated laser a system can achieve an angular resolution of ~ 0.1 mrad (0.006°) at 8 scanner revolutions per second[citation needed].
Pulsed Lasers A typical pulsed laser scanner emits pulsed laser light at a rate of 14,400 Hz which gives a maximum possible resolution of ~ 3.5 mrad (0.2°) at 8 scanner revolutions per second[citation needed]. To achieve a workable navigation, the readings must be interpolated based on the intensity of the reflected laser light, to identify the centre of the reflector.
Inertial (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 the inertial method is ±1 inch.
Inertial can operate in nearly any environment including tight aisles or extreme temperatures.[2] Inertial navigation can include use of magnets embedded in the floor of the facility that the vehicle can read and follow.
Natural feature (Natural Targeting) navigation
Navigation without retrofitting of the workspace is called Natural Features or Natural Targeting Navigation. One method uses one or more range-finding sensors, such as a laser range-finder, as well as gyroscopes 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 for on-demand delivery to any location. They can handle failure without bringing down the entire manufacturing operation, since AGVs can plan paths around the failed device. They also are quick to install, with less down-time for the factory.
Vision guidance
Vision-Guided AGVs can be installed with no modifications to the environment or infrastructure. They operate by using cameras to record features along the route, allowing the AGV to replay the route by using the recorded features to navigate. Vision-Guided AGVs use Evidence Grid technology, an application of probabilistic volumetric sensing, and was invented and initially developed by Dr. Hans Moravec at Carnegie Mellon University. The Evidence Grid technology uses probabilities of occupancy for each point in space to compensate for the uncertainty in the performance of sensors and in the environment. The primary navigation sensors are specially designed stereo cameras. The vision-guided AGV uses 360-degree images and build a 3D map, which allows the vision-guided AGVs to follow a trained route without human assistance or the addition of special features, landmarks or positioning systems.
Geoguidance
A geoguided AGV recognizes its environment to establish its location. Without any infrastructure, the forklift equipped with geoguidance technology detects and identifies columns, racks and walls within the warehouse. Using these fixed references, it can position itself, in real time and determine its route. There are no limitations on distances to cover number of pick-up or drop-off locations. Routes are infinitely modifiable.
Steering control
To help an AGV navigate it can use three different steer control systems.The differential speed control is the most common. In this method there are two independent drive wheels. Each drive is driven at different speeds in order to turn or the same speed to allow the AGV to go forwards or backwards. The AGV turns in a similar fashion to a tank. This method of steering is the simplest as it does not require additional steering motors and mechanism. More often than not, this is seen on an AGV that is used to transport and turn in tight spaces or when the AGV is working near machines. This setup for the wheels is not used in towing applications because the AGV would cause the trailer to jackknife when it turned.
The second type of steering used is steered wheel control AGV. This type of steering can be similar to a car's steering. But this is not very manoeuvrable. It is more common to use a three-wheeled vehicle similar to a conventional three wheeled forklift. The drive wheel is the turning wheel. It is more precise in following the programmed path than the differential speed controlled method. This type of AGV has smoother turning. Steered wheel control AGV can be used in all applications; unlike the differential controlled.Steered wheel control is used for towing and can also at times have an operator control it.
The third type is a combination of differential and steered. Two independent steer/drive motors are placed on diagonal corners of the AGV and swivelling castors are placed on the other corners. It can turn like a car (rotating in an arc) in any direction. It can crab in any direction and it can drive in differential mode in any direction.
Path decision
AGV must make a decision on path selection. This can be done in different ways: frequency selection mode (wire navigation only) and path selection mode (wireless navigation only), or guide the AGV through a tape on the floor, and can also issue steering commands and speed commands.
Frequency selection mode
The frequency selection mode is determined based on the frequency emitted by the floor. When the AGV approaches a point on the wire, the AGV detects these two frequencies separately and determines the best path through a table stored in its memory. Different frequencies are needed only at the decision point of the AGV. After that, the frequency can be changed back to a set signal. This method is not easy to expand and requires additional cutting, which means more money.
Path selection mode
The AGV using the path selection mode selects the path according to the pre-programmed path. It uses the measured value obtained from the sensor and compares it with the value provided by the programmer. When the AGV reaches the decision point, it only needs to decide whether to follow paths 1, 2, 3, etc. The decision is fairly simple, because it already knows the path from programming. This method may increase the cost of the AGV, because a group of programmers are required to program the AGV with the correct path and change the path if necessary. This method is easy to change and set up.
Tape mode
The tape is placed on the floor surface or buried in a 10mm channel; it not only provides a path for the AGV, but also tells the AGV to change lanes, accelerate and decelerate in different combinations of polarity, order and distance along the track. And stop.
Traffic control
Flexible manufacturing systems containing multiple AGVs may require traffic control, so the AGVs will not collide with each other. Traffic control can be done locally or through software running on fixed computers elsewhere in the facility. Local methods include zone control, forward induction control and combined control. Each method has its advantages and disadvantages.
Zone control
Zone control is the favorite in most environments because it is easy to install and easy to expand. Area control uses wireless transmitters to send signals in a fixed area. Each AGV contains a sensing device to receive this signal and send it back to the transmitter. If the area is empty, set the signal to "clear" to allow any AGV to enter and pass through the area. When an AGV is in this area, it will send a "stop" signal, and all AGVs trying to enter the area will stop and wait for it to turn. Once the AGV in the area moves out of the area, the "clear" signal will be sent to one of the waiting AGVs. Another way to set up area control flow management is to equip each individual robot with its own small transmitter/receiver. Then, each AGV sends its own "Do Not Enter" message to all AGVs approaching the area. The problem with this method is that if one area drops, all AGVs are at risk of colliding with other AGVs. Area control is a cost-effective way to control AGV in the area.
Collision avoidance
Forward sensing control uses collision avoidance sensors to avoid collisions with other AGV in the area. These sensors include: sonic, which work like radar; optical, which uses an infrared sensor; and bumper, physical contact sensor. Most AGV's are equipped with a bumper sensor of some sort as a fail-safe. Sonic sensors send a “chirp” or high frequency signal out and then wait for a reply from the outline of the reply the AGV can determine if an object is ahead of it and take the necessary actions to avoid collision.[7] 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.
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
Towing Vehicles (also called "tugger" 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 2,000 pounds to 160,000 pounds.
Tugger AGVs can move trailers or trains of trailers more safely than a manually operated tugger.
Tugger AGV towing multiple trailers in a warehouse environment
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.
Unitload AGV (dual)
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. They can sometimes lift up to 30' to store or retrieve on high-bay racking.
Forklift AGV with Stabilizer Pad
AGVS Hybrid Vehicles are adapted from a standard man-aboard truck so that they can run fully automated or be driven by a fork truck driver. These can be used for trailer loading as well as moving materials around warehouses. Most often, they are equipped with forks, but can be customized to accommodate most load types.[8]
Hybrid AGV picking load
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.
Common applications
Automated Guided Vehicles can be used in a wide variety of applications to transport many different types of material including pallets, rolls, racks, carts, and containers. AGVs excel in applications with the following characteristics:
Repetitive movement of materials over a distance
Regular delivery of stable loads
Medium throughput/volume
When on-time delivery is critical and late deliveries are causing inefficiency
Operations with at least two shifts
Processes where tracking material is important
Handling raw materials
AGVs are commonly used to transport raw materials such as paper, steel, rubber, metal, and plastic. This includes transporting materials from receiving to the warehouse, and delivering materials directly to production lines.
Work-in-process movement
Work-in-Process movement is one of the first applications where automated guided vehicles were used, and includes the repetitive movement of materials throughout the manufacturing process. AGVs can be used to move material from the warehouse to production/processing lines or from one process to another.[10]
Pallet handling
Pallet handling is an extremely popular application for AGVs as repetitive movement of pallets is very common in manufacturing and distribution facilities. AGVs can move pallets from the palletizer to stretch wrapping to the warehouse/storage or to the outbound shipping docks.
Finished product handling
Moving finished goods from manufacturing to storage or shipping is the final movement of materials before they are delivered to customers. These movements often require the gentlest material handling because the products are complete and subject to damage from rough handling. Because AGVs operate with precisely controlled navigation and acceleration and deceleration this minimizes the potential for damage making them an excellent choice for this type of application
Trailer loading
Automatic loading of trailers is a relatively new application for automated guided vehicles and becoming increasingly popular. AGVs are used to transport and load pallets of finished goods directly into standard, over-the-road trailers without any special dock equipment. AGVs can pick up pallets from conveyors, racking, or staging lanes and deliver them into the trailer in the specified loading pattern. Some Automatic Trailer Loading AGVs utilize Natural Targeting to view the walls of the trailer for navigation. These types of ATL AGVs can be either completely driverless or hybrid vehicles.
Roll handling
AGVs are used to transport rolls in many types of plant including paper mills, converters, printers, newspapers, steel producers, and plastics manufacturers. AGVs can store and stack rolls on the floor, in racking, and can even automatically load printing presses with rolls of paper.
Roll handling
AGVs are used to transport rolls in many types of plant including paper mills, converters, printers, newspapers, steel producers, and plastics manufacturers. AGVs can store and stack rolls on the floor, in racking, and can even automatically load printing presses with rolls of paper.
Container handling
Container terminals showing a container being loaded onto an unmanned automated guided vehicle
AGVs are used to move sea containers in some maritime container terminal. The main benefits are reduced labour costs and a more reliable (less variable) performance. This use of AGVs was pioneered by ECT in the Netherlands at the Delta terminal in the Port of Rotterdam.[citation needed]
Primary application industries
Efficient, cost effective movement of materials is an important, and common element in improving operations in many manufacturing plants and warehouses. Because automatic guided vehicles (AGVs) can deliver efficient, cost effective movement of materials, AGVs can be applied to various industries in standard or customized designs to best suit an industry's requirements. Industries currently utilizing AGVs include (but are not limited to):
Pharmaceutical
AGVs are a preferred method of moving materials in the pharmaceutical industry. Because an AGV system tracks all movement provided by the AGVs, it supports process validation and cGMP (current Good Manufacturing Practice).
Chemical
AGVs deliver raw materials, move materials to curing storage warehouses, and provide transportation to other processing cells and stations. Common industries include rubber, plastics, and specialty chemicals.
Manufacturing
AGVs are often used in general manufacturing of products. AGVs can typically be found delivering raw materials, transporting work-in process, moving finished goods, removing scrap materials, and supplying packaging materials.
Automotive
AGV installations are found in Stamping Plants, Power Train (Engine and Transmission) Plants, and Assembly Plants delivering raw materials, transporting work-in process, and moving finished goods. AGVs are also used to supply specialized tooling which must be changed.
Paper and print
AGVs can move paper rolls, pallets, and waste bins to provide all routine material movement in the production and warehousing (storage/retrieval) of paper, newspaper, printing, corrugating, converting, and plastic film.
Food and beverage
AGVs can be applied to move materials in food processing (such as the loading of food or trays into sterilizers) and at the “end of line,” linking the palletizer, stretch wrapper, and the warehouse. AGVs can load standard, over-the-road trailers with finished goods, and unload trailers to supply raw materials or packaging materials to the plant. AGVs can also store and retrieve pallets in the warehouse.
Hospital
AGVs are becoming increasingly popular in the healthcare industry for efficient transport, and are programmed to be fully integrated to automatically operate doors, elevators/lifts, cart washers, trash dumpers, etc. AGVs typically move linens, trash, regulated medical waste, patient meals, soiled food trays, and surgical case carts.
Warehousing
AGVs used in Warehouses and Distribution Centers logically move loads around the warehouses and prepare them for shipping/loading or receiving or move them from an induction conveyor to logical storage locations within the warehouse. Often, this type of use is accompanied by customized warehouse management software.[16]
Theme parks
In recent years, the theme park industry has begun using AGVs for rides. One of the earliest AGV ride systems was for Epcot's Universe of Energy, opened in 1982. The ride used wired navigation to drive the 'Traveling Theatre' through the ride. Many rides use wired navigation, especially when employees must frequently walk over the ride path such as at (the now-closed attraction) The Great Movie Ride at Disney's Hollywood Studios.Another ride at Hollywood Studios that uses wired navigation is The Twilight Zone Tower of Terror, a combined drop tower/dark ride. The elevator cars are AGVs that lock into place inside separate vertical motion cab to move vertically. When it reaches a floor requiring horizontal movement, the AGV unlocks from the vertical cab and drives itself out of the elevator.
A recent trend in theme parks is a so-called trackless ride system, AGV rides that use LPS, Wi-Fi, or RFID to move around. The advantage of this system is that the ride can execute seemingly random movements, giving a different ride experience each time.
