The history of AGVS

First AGV in 1953

 

Automated guided vehicles have been used for more than 40 years in the movement of materials and products. The first AGV system was built and launched in 1953. It is a modified tractor that is used to tow the trailer and overhead wires along the grocery store. By the end of the 1950s and early 1960s, traction AGV operated in many types of factories and warehouses.

The history of AGVS

1973 Volvo Assembly Plant

 

In 1973, Volvo, Kalmar, Sweden, began developing non-synchronous assembly equipment as an alternative to traditional conveyor assembly lines. The result is 280 computer controlled assembly of the AGV.

The history of AGVS

First unit load in the 1970s

The first major development in the AGV industry was the introduction of unit loaders in the mid-1970s. These unit load AGVs are widely accepted in the material handling market because of their multiple functions; work platforms, transportation equipment and links to plant control and information systems. Today hundreds of systems that use units to load vehicles are produced by several manufacturers. These systems transport materials in warehouses, factories, factories, hospitals and other industrial and commercial environments.

The history of AGVS

Smart floor and dumb

 

In the 1970s, the main guiding technique was to induce electron frequencies through wires buried in the floor. A device called a “floor controller” turns the frequency on the wire on and off and directs the AGV to its intended route. The car is considered a “stupid” because the vehicle just signaled on the floor. The information on the vehicle route is in the floor controller. Therefore, this day’s system is considered to be “smart floor” and “dumb”.

The antenna on the AGV will find the frequency and guide the vehicle based on the strength of the signal. This technique requires multiple wires to be embedded on the floor to handle intersections or other decision points. The system will energize the wires corresponding to the intended direction of travel. For example, at an intersection, three separate lines may be required.

These first generation navigation schemes are expensive to install. All floor cuts need to follow the exact path of the AGV. The cutting of the turn must follow the radius curve that the vehicle will produce when cornering. Many systems must embed four wires – three wires for guidance and one for communication. Usually steel or electrical signals will interfere with the pilot signal applied to the wires.

The history of AGVS

Calculation ability

 

With the advancement of electronics and microprocessors, so is the AGV application. As vehicles become more intelligent, the path becomes more and more complex. One of the first major breakthroughs was the development of projections. Dead reckoning is a term used to describe the ability of a vehicle to pass through a steel expansion joint or through a steel grid at a factory floor. The biggest advantage is that dead reckoning eliminates the need to change the cutting radius at the intersection. The vehicle can leave the wire, rotate at the programmed radius, and then pick up the wire to continue driving. The path still requires multiple wires on the floor, but the installation is greatly simplified.

The history of AGVS

Non-line guidance in the 1980s

 

In the late 1980s, wireless guidance for the AGV system was introduced. Laser and inertial guidance are two examples of nonlinear guidance that can increase the flexibility and accuracy of the system. When a change to the original tour guide is required, no floor replacement or production interruption is required. The navigation section will provide a more comprehensive introduction to these navigation methods.

The history of AGVS

Computer function

As with all high-tech products based on electronic and computer software, there is no doubt that AGV is affected by the increased cost and reduction of microcomputers and microelectronic devices. Computers used in the AGV system can store instructions, make decisions and execute programs. In fact, AGV is able to perform almost all of the decision-making and control functions that humans currently manage in the processing of materials. They can schedule plant time, maintain inventory, manage system details, and control many types of mechanical systems throughout their operations.

The history of AGVS

Application and control

 

The use of AGV has evolved from traditional distribution-oriented applications to complex computer-controlled automotive assembly systems with robotic interfaces on the other end. They can be stand-alone systems, part of another system, and can help integrate automated islands. Originally designed for horizontal transport of palletized materials, the design and application of vehicles and controls are now different from industrial robots.

The history of AGVS

AGV manufacturer

The market demand for AGV can be measured by increasing the number of AGV manufacturers. In the late 1970s, there were only six AGV suppliers in the United States, and there were only three different types of vehicles. By 1990, there were more than 40 suppliers and more than 15 models worldwide, and more and more attention was paid to standard design. The future will be characterized by more changes, in part because of technological advances. But it will also be driven by the increased use of AGVS, which in turn will promote investment in research and development.

Vehicle navigation

The principle of navigating the AGV between any two locations is really simple. All navigation methods use paths. Instruct the vehicle to follow a fixed path or take an open path.

Fixed path navigation

Follow the road

The earliest method of using AGVS navigation for vehicles following the path. The general characteristics of these methods are:

The road surface is marked well on the floor
Continuous path
These paths are fixed but can be changed

AGVS的历史

Fixed path navigation:

Create path

The main techniques for creating paths are:

Apply a narrow tape to the floor surface
Apply a narrow photosensitive chemical strip to the floor surface
Apply a narrow photo reflective tape to the floor surface
Bury wire is just below the floor surface

The first three methods require a sensor on the underside of the vehicle that can detect the presence of a surface mount path. The task of the sensor is to keep the vehicle directly above the rail. If the path is rotated, the sensor detects a turn and provides feedback to the onboard vehicle controller, which in turn causes the vehicle to turn in the direction of the path. The role of the sensor in relation to the onboard controller and steering mechanism is to cause the vehicle to follow the path.

 

Buried line

Apply a narrow tape to the floor surface
Apply a narrow photosensitive chemical strip to the floor surface
Apply a narrow photo reflective tape to the floor surface
Bury wire is just below the floor surface

When the fourth “path following” method is used using the current-carrying buried line, the on-vehicle sensor takes the form of a small antenna composed of a magnetic coil. As the current flows, the magnetic field surrounds the buried line. The closer the buried wire is to the AGV antenna, the greater the field strength.

The magnetic field is completely symmetrical around the conductor or buried line. The cable has the same strength on both sides of the cable at a given distance from the wire. The field strength is detected by the magnetic coil of the antenna and causes the voltage in the coil.

AGVS的历史

Fixed path navigation:

Steering correction coil

Like the other three paths, the vehicle turns itself around the magnetic field around the buried line. To obtain the steering correction signal, the vehicle’s inductive antenna consists of two coils. When the vehicle is directly above the buried line, an equal voltage is produced in both coils. If one side of the vehicle guide wire moves a little, the induced voltage will have a different intensity. The difference in signal strength in the coil is proportional to the lateral displacement of the coil. This difference is amplified and fed back to control the onboard servo motor, which turns the wheel or wheel until the two coils receive an equal signal and corrects the process.

Fixed path navigation:

Path Selection

 

In this example, the vehicle on “A” has two options for how to reach “B”. A computer on a vehicle or at a central location selects a path according to established criteria. The standard can be the shortest distance or path with the least amount of traffic in the current time. Once the vehicle is selected, start navigation. All “PATH FOLLOWING” navigation methods allow routing options including boot path switching and merging.

Open path navigation:

walk

The navigation method that guided the vehicle to “walk” took its own development from the early 1990s to the mid-1990s. They use different technologies. Unlike “path tracking navigation”, the guiding path is fixed and more or less permanent, and the vehicle running in the “walking path” category is actually providing more changes, if not an unlimited number. The way to navigate the open space between two points.

Open path navigation:

Navigation requirements

From a practical point of view, the choice is limited by known permanent or temporary obstacles and path selection criteria, such as taking the shortest path.

In order to navigate within an open, unrestricted space, without the benefits of a fixed path, the vehicle must have a way to know where it is and be able to head its way to where it is going. All open space navigation methods require:

A map of the area in which the vehicle is operable is housed in the computer memory of the vehicle.
A plurality of fixed reference points located within the operating area that can be detected or “seen” by the vehicle.

Open path navigation:

Navigation method

 

The three most common open space navigation methods are laser guidance, inertial guidance, and Cartesian guidance. The choice of a navigation method for a particular application is usually a simple preference issue. Each method provides different advantages and costs associated with application-related system setup and operation. Unless there is a clear preference, users should work closely with the vendor to evaluate options related to the intended application. Each method has a rich history of its successful use in practice.

     Laser navigation
     Inertial navigation
     Descartes navigation

AGVS scheduling

 

AGVS scheduling is critical for every AGVS, whether simple or complex. Dispatch AGVS is roughly the same as taxi rental. The scheduling function ensures that all customers get the best service request service from the vehicle in time. No scheduling function, no action. Due to the inefficient scheduling, the system will not get the most benefit.

The scheduling function maximizes the benefits of AGVS and ensures that all customers receive service in a timely manner. Remote and local scheduling are most often described as offline and onboard dispatchers, respectively.

Remote scheduling

Communication method

 

Remote scheduling occurs when the AGV receives scheduling information from the central controller. This type of scheduling requires a communication method to send commands from the scheduler to the AGV. These communication methods include:

     An RF network (broadband or spread spectrum) including a base station, and an antenna in which a radio wave transmission signal of a receiver is mounted on each vehicle.
     Inductive RF is mounted on each vehicle through an antenna through wires on the floor. In many cases, the guide line will be used as an RF communication antenna, and in other cases, the sensed signal is transmitted through a separate buried line.
     Infrared communication and multiple infrared emitters are installed throughout the unit and are equipped with an infrared receiver on the AGVS.

Remote scheduling

Dispatcher

 

Remote scheduling functions are typically located in a computer (PC), programmable logic controller (PLC), or other microprocessor called a scheduler. The dispatcher accepts input from various system components (usually a transfer request) and instructs the AGVS to complete the command in the most efficient manner. This function is directly compared to the taxi dispatcher on the terminal, receives calls from many customers, and then sends each driver to the pick-up station by radio. Remote scheduling may occur for vehicles at a single or individual dispatch point.

Remote scheduling

Single point dispatch

A single scheduling point requires the AGV to return to the same location each time to receive commands and transmission requests. Single point scheduling typically has a predetermined shortest path route and works on strict FIFO requests. As the vehicle is available and arrives at the dispatch point, they are given shipping instructions.

Remote scheduling

Vehicle manager

 

Using various dispatch locations, transportation instructions are given once the vehicle has completed its previous transportation. The dispatcher attempts to select the closest available vehicle to complete the command. If the vehicle is commanded and a more recent vehicle is available, a more complex dispatcher will be able to reassign the shipping request to a more recent vehicle. Dispatchers, also known as vehicle managers, typically include an algorithm that controls the motion priority of the system.

Remote scheduling

Scheduler command

The Dispatcher command can also take many forms, where the AGV can send a full command, a semi-command or a peer-to-peer command.

E.g:

Complete command (take up “A” and deliver to “B”)

Semi-command (retrieved with “A”)

Point-to-point (moving from point 1 to 2, moving from point 2 to 3, etc.)

Using full and semi-command, the AGV has a system map that resides on its onboard controller. With point-to-point routing, the system map resides with the scheduler.

 

Local delivery

Signal and occurrence

Local transmission occurs when the AGV is transmitted by a signal or event that occurs at the AGV location. Local scheduling is usually associated with a simpler AGV system, and repetitive tasks predominate.

 

Signals and events include:

      An optoelectronic or data coupler that gives a simple command at the dispatch point.
      Automatic identification of bar codes, RF tags, magnetic strips, etc.
      Onboard sensor for load presence, buttons, keyboards, etc.

Local delivery

Taxi analogy

Local scheduling is simple and almost always requires the system map to reside on the onboard controller. Going back to the taxi analogy, the local dispatch is equivalent to a taxi driving the street, and they charge the fare when they yell for the taxi. A central dispatcher is not required and the vehicle reacts to simple, usually single source inputs of sensors, keyboards and devices.

Local delivery
Common input source

 

The following are more common input sources for local scheduling:

      When the button is pressed, the AGV controller is programmed to advance the stop point and wait for release. The release signal is the onboard button input, which causes the AGV to automatically send to the next stop point.
      In addition, the system may include multiple destinations that require a series of buttons (one for each button), or a keypad that can accommodate more of the selected starting point and destination.

Local delivery

Signal Detection

A data coupler or optoelectronic external to the vehicle can also be used to send a signal indicative of the origin and/or destination to the AGV vehicle controller. These devices can be in a single location or at multiple points along the path.

 

A load signal from an optical power source or proximity switch can be used to detect the presence of a load transmitted or placed on the AGV. This signal is sufficient in a simple system, each starting point has a singular destination that allows the AGV on-board vehicle controller to schedule itself.

Local delivery

Load identification
An automatic identification system can be placed on the AGV to sense the type of product received on the vehicle. If each load type has a specific destination determined by height, weight, size, barcode ID, RF ID tag or magnetic strip ID, the AGV onboard controller will send the AGV based on the particular load characteristics or identity.

Traffic control

 

The key to all AGV systems is the automatic shutdown, start-up and routing of the vehicle. In order to ensure that a vehicle enters an occupied area or intersection of occupied rails and provides a generally orderly and efficient route, the location of each vehicle will be monitored and decisions made based on this knowledge. In the context of flow control, all forms of automatic stop and start are called blocking.

 

The two types of blockages commonly used are zone blockage and cumulative blockage.

AGVS communication

Communication includes message commands such as where to go, when to start, when to slow down, and when to stop. It may also include a fault condition report. Computer control systems that supervise remote objects require a means of communicating commands between the monitoring computer and the object being controlled, and in many cases confirm the reply. Four types of basic communication media are used in the AGV system depending on the application.

Radio communication

 

The radio provides maximum flexibility in system control. Vehicles can be “instant” programmed to quickly download new roadmaps or maps, increasing the speed at which the system responds to changing load movement demands. It provides almost constant communication between the vehicle and the system and makes the AGVS system a very responsive tool that reacts to the dynamics of changing work environments.

Radio communication

Radio frequency radio wave

 

Radio waves can be used to transfer information and data from a fixed base station to a modem on each vehicle. Radio waves simply perform the function of transferring energy to a remote receiver. The actual information is superimposed on the radio waves so that it can be accurately extracted from the waveform at the receiving end. This provides a continuous two-way data link to the vehicle. There are currently two basic systems, narrowband and spread spectrum. In general, if there is a dead zone in the system that prohibits radio transmissions and determines the number, type, and location of antennas, a factory survey is usually performed to determine how other frequencies are operating in the environment.

Radio communication

Narrowband radio system

A narrowband radio system transmits and receives user information on a particular radio frequency. The narrowband radio makes the radio signal frequency as narrow as possible to pass data. The AGVS system typically operates in the 450 MHz band on the 25-Khz channel. Avoid crosstalk between communication channels by carefully coordinating different users on different channel frequencies. The radio receiver filters out all radio signals except the specified channel frequency.

Radio communication

Spread spectrum channel

The Federal Communications Commission (FCC) assigns frequency channels to the qualified users who request them. This is done by licensing the service at a given frequency in a particular area. Licensing is very effective in providing secure communications, but the burden on the FCC to coordinate and allocate radio channels is increasing. The spread spectrum was established by the FCC to ease the burden by allowing unlicensed radio usage.

Infrared communication

 

Optical infrared communication is highly reliable but not continuous; this is the point. During this data exchange, the vehicle may be stopped, typically occurring at loading stations where the stationary and mobile units are aligned and close. Alternatively, as the vehicle travels through a given area, the vehicle communicates along a fixed point of its guiding path.

The picture shows the optical sensor on the conveyor receiving/storage table. One sensor is used for transmission and the other is for reception.

Vehicles are usually not sent from a point of communication unless there is no call on the path to the next destination. In large systems, this can lead to problems with throughput. Alarm conditions cannot be reported. Therefore, infrared communication is best suited for small systems of small vehicles and loading stations.

AGVS的历史

Wire data communication

The data transmitted by the guideline driver on the wire provides almost the same flexibility as the radio except that the vehicle moves from the wire. Since the distance between the wire and the onboard transponder is constant, there is no transmission dead point because there may be a radio. The technology to complete this kind of data link is not universal.

Induction cycle communication

Induction loops are another means of point-to-point communication. The wire loop on the floor is located near the guide line and is connected to the central controller for data transfer. They are typically 3 to 10 feet long and must be located at every point where communication with the vehicle is required. Simple instructions in the form of electronic information or specified frequencies are sent through the wire loop. The antenna on the underside of the vehicle senses the frequency at which the vehicle decodes and acts. The vehicle can also send a message back to the central controller. This is a cheap but limited method of data transmission. Most systems using this method do not require parking when receiving data from the inductive loop.