Chapter 2
An automated guided vehicle system ( AGVS ) is a stuff handling system that uses an independently operated, automotive vehicle that is guided along defined tracks in the floor. The vehicle is powered by agencies of an AC Servo motor. The definition of tracts is by and large accomplished by utilizing wires embedded in the floor, painted chevrons or by utilizing tracks to steer the vehicle.
types of agv
There are different types of AGV ‘s each which works based on a specific rule. The types can be classified as follows:
Driverless trains
This type consists of a towing vehicle ( which is an AGV ) that pulls one or more dawdlers to organize a train. It was the first type of AGVS to be introduced and is still popular. It is used in applications where heavy warheads must be moved in big distances in warehouses or mills with intermediate pickup and slump point along the path.
Fig 2.1 Driverless Trains
AGV palette trucks:
Automated guided palette trucks are used for palletized tonss along determined paths. In this typical application the vehicle is backed into the laden palettes by human workers. The driver drives the palette truck to the guide way, plans its finish and the vehicle returns automatically to the estination for droping. The capacity of the AGVS palette truck ranges up to6000 pound, some trucks are capable of managing two palettes instead than one. A recent debut related to pallet trucks
AGV is the Forklift AGV. This vehicle can accomplish important perpendicular motion of its forks to make tonss on shelves.
Fig 2.2 AGV Pallet trucks
AGVS Unit Load Carrier:
This type of AGVS is used to travel unit tonss from one station to another station. They are frequently equipped for automatic burden and unloading by agencies of powered rollers, traveling belts, mechanized lift platforms, or other devices. Variations of the unit burden bearers include light burden AGV ‘s. The light burden AGV is a comparatively little vehicle with a corresponding visible radiation burden capacity. It does no necessitate the same big aisle breadth as the conventional AGV. Light-load guided vehicles are designed to transport a partly completed subassembly through a sequence of assembly workstations to construct the merchandise.
AGVS engineering is far from mature, and the industry is continually working to develop new systems in response to new application demands. An illustration of a new and germinating AGVS design involves the arrangement of a robotic operator on an automated guided vehicle to supply a nomadic automaton for executing complex handling undertakings at assorted locations of the works. These robot vehicles are seen as being utile in clean suites in the semi music director industry.
Fig 2.3 AGV Pallet trucks
applications of agv:
Automated guided vehicle systems are being used in a turning figure and in a assortment of applications. The application tendency is parallel to the vehicle types described supra. We group the applications into the undermentioned five classs:
Driverless train operations:
These applications involve the motion of big measures of stuff over comparatively big distances. For illustration, the moves are within a big warehouse or mill edifice, or between edifices in a big storage terminal. For the motion of trains dwelling of 5 to 10 dawdlers, this becomes an efficient handling method.
Storage/distribution systems:
Unit burden bearers and palette trucks are typically used in these applications. These storage and distribution operations involve the motion of stuffs in unit tonss from or to other specific locations. The application ever involves the interface of the AGV with some other machine-controlled handling or storage system, such as machine-controlled storage and retrieval system ( AS/RS ) in a distribution centre. The AGVS delivers the incoming tonss or unit tonss from the having dock to the AS/RS ; the AS/RS retrieves the palette loads or points from the storage and transportations them to vehicles for bringing to the transportation dock. When the rates for the entrance tonss and surpassing tonss are in balance, this manner of operation licenses loads to be carried in both waies by the AGVS vehicle, thereby increasing the managing the system efficiency.
This type of storage/distribution operation can besides be applied in light fabrication and assembly operations in which the work-in-progress is stored in a cardinal storage country and distribution to single workstations for assembly or processing. Electronicss assembly is an illustration of these types of applications. Components are “ knitted ” at the storage subdivision and are delivered in carryall pans or trays by the guided vehicle to the assembly workstations in the works. Light burden AGV systems are used in these applications.
Assembly line operations:
AGV systems are being used in a turning figure of assembly line applications, based on the tendency that began in Europe. In these applications the production rate is comparatively low and there are a assortment of different theoretical accounts made on the production line. Between the workstations, constituents are knitted and placed on the vehicle for the assembly operations that are to be performed on the partly completed merchandise at the following station. The workstations are by and large to be arranged in parallel constellation ton attention deficit disorder to the flexibleness of th1e line. Unit load bearers and light burden vehicles are the types of AGVS used in these assembly lines.
Flexible fabricating systems:
Another turning application of AGVS engineering is in Flexible Manufacturing Systems ( FMS ) . In this application, the guided vehicles are the material managing systems in FMS. The vehicles deliver work from the presenting country to the single workstation, the vehicle besides moves work between Stationss in the fabrication system. At a workstation, the work is transferred form the vehicle platform into the work country of the station for processing. At the completion of processing by that station a vehicle comes to pick up the work and transport it to the following country. AGVS systems provide a various stuff managing system to complement the flexibleness of the FMS operation.
Assorted applications:
Other applications of Automated Guided Vehicle system includes non-manufacturing and non-warehousing application, such as mail bringing in the office edifices and infirmaries material managing operations. Hospital guided vehicle conveyance, repast trays, linen, medical and laboratory supplies and other stuffs between assorted sections in the edifice. These applications typically require motion of the vehicle between different floors of the infirmary. AGV systems have the capableness to cite and utilize lifts for this intent.
VEHICLE GUIDANCE AND ROUTING
There are several maps that must be performed to run any machine-controlled guided vehicle system successfully. These maps are:
Vehicle counsel and routing
Traffic control and safety
System direction
The term counsel system refers to the methods by which the AGVS tracts are defined and the vehicle control system that follows the tracts, as indicated above, there are two principle methods presently in usage to specify the tracts along the floor: Embedded usher wires and pigment chevrons. Of the two types, the usher wire system is more common in warehouse and mill applications.
In the usher wire method, the wires are normally embedded in a little channel cut into the surface of the floor. After the usher wires are installed, the channel slot is filled so as to extinguish the discontinuity in the wire. The signal is of comparatively low electromotive force, low current and as the frequence is in the scope of 1-15 KHz. These signal degrees creates a magnetic field along the tract that is followed by detectors on-board each vehicle. Two detectors are mounted on the vehicle on either side of the usher wire. When the vehicle is traveling along the class such that the usher wire is straight between the two spirals, the strength of the magnetic field measured by each spiral will be equal. If the vehicle strays to one side or the other, or if the usher wire way curves, the magnetic field strength at the two detectors will me different. This difference is used to command the guidance of the motor, which make the needed alterations in the vehicle way to equalise the two detector signals, thereby tracking the defined tract.
When pigment chevrons are used to specify the vehicle tracts, the vehicle possesses an optical detector system that is capable of tracking the pigment. The pigment can be taped sprayed, or painted on the floor. One system uses a 1-in-wide pigment strip incorporating fluorescent atoms that reflect an UV ( UV ) light beginning on the vehicle. An on board detector detects the reflected visible radiation in the strip incorporating fluorescent atoms that reflects an UV visible radiation beginning on the vehicle. An onboard detector detects the reflected visible radiation in the strip and controls the maneuvering mechanism to follow it. The pigment counsel system id utile in environments where electrical noise would render the usher wire system undependable or when the installing of usher wires in the floor surface would non be appropriate. One job with the paint-strip counsel system is that the pigment strip must be maintained.
A safety characteristic used in the operation of most counsel systems is automatic fillet of the vehicle in the event that is by chance strays more than a few inches on the guide way. The automatic fillet characteristic prevents the vehicle from traveling off the usher way. It is capable of locking on to the usher wires or pigment strip. If moved within the same few inches of it. The distance is referred to as vehicle acquisition distance.
The usage of micro procedure or controls on board the vehicles has led to the development of characteristic called dead-reckoning. This term refers to the capableness of the vehicle to go along the path that does non follow the defined tract in the floor. The microprocessor computes the figure of wheel rotary motions and the operation of the maneuvering motor required to traverse a steel home base in the mill floor, or to go from the guide way for positioning at a load/unload station. At the completion of a dead-reckoning manoeuvre, the vehicle is programmed to return to within the acquisition distance of the guide way to restart normal counsel control.
Routing is an AGVS system which is concerned with the job of choosing among alternate tracts available to the vehicle in its travel to a defined finish point in the system. A typical guided vehicle layout, one that exploits the capablenesss of modern AGVS engineering, contains characteristics such as multiple cringles, subdivisions, side-tracks and goads, in add-on to the required pickup and slump Stationss. Vehicles in the system must make up one’s mind which way to take to make a defined finish point.
When a vehicle approaches a ramification point in which a usher way splits into 2 waies, a determination must be made as to which path the vehicle should take. This is sometimes referred to as a determination point for the vehicle. There are two methods used in commercial AGV systems to allow the vehicle to make up one’s mind which way to take:
Frequency select method
Path switch select method
In the frequence select method, the usher wires taking into the two separate waies have different frequences. As the vehicle enters the determination point, it reads an designation codification on the floor to place its location. Depending on its programmed finish, the vehicle selects one of the usher waies by make up one’s minding which frequence to track this method requires a separate frequence generator for each frequence that is used in the guide way lay out.this normally means that two or three generators are needed in the system. Extra channels must frequently be cut into the floor with the frequence select method to supply for by base on balls channel where merely the chief channel needs to be powered for vehicle trailing.
The way switch selects utilizing a individual frequence through out the guide way layout. In order to command of a vehicle at a determination point, the power is switched off at all subdivisions except the 1 on which the vehicle is to go. To carry through a routing by the way select switch method. The guide way layout must be divided into blocks that can be independently turned on and off by agencies of control mounted on the floor-mounted shift device connected to the control unit for the relevant block. The control unit activates the coveted usher waies and turns off the options subdivisions or subdivision.
In the rail usher method, the AGV travels on tracks. The tracks are fitted with micro-switches at the several places wherever necessary and the vehicle in guided by the tracks to the several storage subdivision, the micro-switches placed on the tracks are used to observe the range of place by the vehicle these micro-switches are connected to the PLC and trigger the reset of the pulsation train end product being generated by the PLC. The micro-switches besides determine the distance of return travel the AGV has to travel in order to make the beginning or the finished merchandise roll uping subdivision. The routing and ramifying method adopted is similar to that of the embedded wire or pigment strips counsel method as explained above.
traffic control and safety:
The intent of traffic control for the AGV is to forestall hit between the vehicles going along the same guide way in the layout. This intent is normally accomplished by agencies of a control system called the blocking system the term “ barricading ” suggest that a vehicle in front of it. There are several agencies used in the commercial AGV system to carry through the blocking. They are:
on board vehicle feeling
zone barricading
On-board vehicle feeling involves the usage of some signifier of detector system to observe the presence of vehicle and carts in front of the same usher wire. The detector used on commercial guided vehicle includes optical detectors and supersonic systems. When the on-board detector detects an obstruction in forepart of it, the vehicle Michigans. When the obstruction is removed, the vehicle is avoided and the traffic is controlled. Unfortunately, the effectivity of forward detection is limited by the capablenesss of the detector system to observe vehicles in forepart of its guide way. Since the detectors themselves are more effectual in feeling obstructions straight in front of the vehicle, these systems are most appropriate on layouts that contain long stretches of consecutive tracts. They are less effectual at bends and convergence points where forward vehicles may non be straight in forepart of the detector.
The construct of zone control is simple. The AGV layout is divided into separate zones, and the operating regulation is that no vehicle is permitted to come in a zone if that zone is already occupied by another vehicle. The length of a zone is sufficient to keep one vehicle plus an allowance safety and other considerations. These other considerations include the figure of vehicle in the system, the size and complexness of the layout, and the aim of minimising the figure of separate zone controls. When one vehicle occupies a given zone, any draging vehicle is non allowed into that peculiar zone. The taking vehicle must continue into the following zone before the tracking vehicle can busy the given zone. By commanding the forward motion of the vehicles in the separate zones, hits are prevented and the traffic in the overall system is controlled. The construct is in its simplest signifier. More complicated zone control schemes separate any two vehicles by a out of use zone.
One means of implementing zone control is to utilize separate control units for each zone. These controls are mounted along the guided way are actuated by the vehicle in the zone. When a vehicle enters a given zone, it activates the block in the old zone to barricade any draging vehicle from traveling frontward and clashing with the present vehicle. As the present vehicle moves into the following zone, in consequence, zones are turned on and off to command vehicle motion by the blocking system.
In add-on to avoid hits between vehicles, a related aim is the safety of human existences who might be located along the path of the vehicle going in the system. There are several devices that are normally included on an automated guided vehicle to accomplish this safety aim. One of the safety devices is an obstacle-detection detector located at the forepart of each vehicle. This is frequently the same on-board detector as that used in the blocking system to observe non merely other vehicles, but besides people and obstructions in the way of the vehicle. These obstacle-detection systems are normally based on optical, infrared, or supersonic detectors. The vehicles are programmed either to halt when an obstruction is sensed in front of it, or to decelerate down. The ground for decelerating down is that the perceived object may be located off to the side of the vehicle portion, or straight in front of the vehicle beyond a bend in the guide way. In either of these instances, the vehicle should be permitted to continue at a slower velocity until it has passed the object or rounded the bend.
Another safety device included on virtually all commercial AGV vehicles is an exigency bumper. The bumper surrounds the forepart of the vehicle and protrudes in front of it by a distance which can be a pes or more. When the bumper makes contact with an object, the vehicle is programmed to brake instantly. Depending on the velocity of the vehicle, its burden, and other conditions, the braking distance will change from several inches to several pess. Most vehicles are programmed to necessitate manual restarting after an obstruction brush with exigency bumper.
Other safety devices on the vehicle include warning visible radiations and/or warning bells. These devices alert people that the vehicle is present.
Finally, another safety characteristic that prevents runaway vehicles is the built-in operating feature of the counsel system: if the system strays by more than a few inches from the defined way, the vehicle is programmed to halt.
system direction:
Pull offing the operation of an AGVS trades chiefly with the job of despatching vehicles to the points in the system where they are needed inn a timely and efficient mode. The map depends on dependable operation of other system maps discussed supra. There are a figure of methods by and large used in combination to maximise reactivity and effectivity of the overall system.
The despatch methods include:
On-board control panel
remote call Stationss
cardinal computing machine control
Each guided vehicle is equipped with some signifier of control panel for the intent of manual vehicle control, vehicle scheduling, and other maps. Most commercial vehicles have the capacity to be dispatched by agencies of this control panel to a given station in the AGV ‘s layout. Dispatching with an on-board control panel represents the lowest degree of edification among the possible methods. Its advantages are that it provides the AGV ‘s with the flexibleness and reactivity to altering demands on the handling system. Its advantage is that it requires manual attending.
The usage of remote call Stationss is another method that allows the AGVS to react to altering demand forms in the system. The simplest signifier of call station is a imperativeness button mounted near the load/unload station. This provides a signal to any passing vehicle to halt at the station in order to carry through a burden transportation operation. The vehicle might so be dispatched to the desired location by agencies of the on-board control panel.
More sophisticated call Stationss consists of control panels mounted near the assorted Stationss along the layout. This method permits the vehicle to be stopped at a given station, and its following finish to be programmed organize the distant control panel. This represents a more machine-controlled attack to the dispatching map and is utile in AGV systems that are capable of automatic burden and unloading operations.
Both of the cal station methods described here affect a human interface with the AGVS at the loading/unloading station. One illustration is an machine-controlled production workstation that receives natural stuffs and sends completed parts by agencies of the AGVS. The workstation is interfaced with the AGVS to name for vehicles every bit needed to execute the burden and unloading processs.
In big mills and ware houses systems affecting a high degree of mechanization, the AGVS serving the mill or warehouse must besides be extremely automated to accomplish efficient operation of the full production- storage-handling system. Central computing machine control is used to carry through automatic dispatching of vehicles harmonizing to a preplanned agenda of pickups and bringings in the layout and/or in response to calls from assorted loads/unload Stationss in the system. In the dispatching method, the cardinal computing machine issues commands to the vehicles in the system refering their finish and operation to execute. To carry through the dispatching map, the cardinal computing machine must possess real-time information about the location of each vehicle in the system so that it can do appropriate determinations refering with vehicles to despatch to what locations. Hence, the vehicle must continually pass on their whereabouts to the cardinal accountant.
There are difference in the manner these cardinal computing machine despatching system operate. One of the differences involves the distribution of the determination duties between the cardinal accountant and the single vehicles. At one extreme the cardinal computing machine makes about all the determinations about the routing of vehicles and other maps. The cardinal computing machine plans out the paths for each vehicle and controls the operation of guide way zones and other maps. At the opposite utmost each single vehicle possesses significant decision-making capablenesss to do its ain routing choice and to command its ain operations. The cardinal computing machine is still needed to command the overall programming and determine which vehicles should travel to the assorted demand points in the system. However the vehicles themselves decide which path and command their ain burden transportation operations. Vehicles in this 2nd class are frequently referred to as “ smart ” vehicles.
To carry through the system direction map, it is helpful to supervise the proctor the overall operations of the AGVS by agencies of some signifier of artworks display. Even with the cardinal computing machine control it is still desirable for human directors to be able to see the overall system operations, in order to supervise its general position and to descry jobs. A CRT coloring material artworks show is frequently used for these intents in modern guided vehicle systems.
Another utile tool in transporting out the systems direction map is a system public presentation study for each displacement of AGVS operation. These periodic studies of system public presentation provide drumhead information about proportion uptime, downtime, and figure of minutess made during a displacement, and more elaborate informations about each station and each vehicle in the system. Hard-copy studies incorporating this type of information permit the system directors to compare operations from displacement to switch and month to month to keep a high degree of overall system public presentation.
2.7 agv building:
The AGV is rectangular construction. The outer frame is constructed utilizing square pipe of size 20mm, length 40cm, width 30cm and height 20cm. the base of the AGV is attached to four PPC wheels on all four corners through and press shrub type rod which is bolted along with the frame. A horizontal shaft of 30cm in length is inserted between the two wheels attached to the shrub.
At either terminals of the horizontal shaft the two PPC wheels are mounted and are bolted at the terminals. The horizontal shaft rod is of 12mm in diameter and an aluminium block of diameter 25mm is fixed in the centre of the horizontal shaft. The other block is mounted on the servo motor shaft, which is besides of diameter 25mm. Two 30 centimeters square pipe are taken welded at the underside of the frame of the AGV, in order to supply support to the vehicle.
Slots are made in the two welded square pipes so as to sit the servo motor absolutely. A channel shaped apparatus is made with a steel home base as per the dimensions of the servo motor so that it can be seated absolutely.
With the aid of a level belt of thickness 15mm and length 50mm the two aluminum blocks, one attached to the shaft of the servo motor and the other to the shaft in between the wheels are coupled. The belt has minimum slippage and the power transmittal from the motor to the wheels is maximal with minimal per centum of power loss.
On top of the outer frame a plyboard board is placed and screwed to the underside which acts as the base and a 50mm overall tallness is maintained to back up the object, so that it does non fall off while traveling on the vehicle.
A detector is placed on the AGV on the plyboard board so that it can feel the objects falling into the AGV ; it helps to enable the servo motor as per the logic fed into the PLC.
AGV Design Specifications:
AGV wheel:
Diameter = 100mm
Square pipe = 18 tens 18mm
Length = 400mm
Width = 300mm
Height = 246mm ( without wheel )
Entire height = 300mm
Wheel linking rod = 10 x 10mm
Diameter = 15mm
Matching diameter = 50mm
Motor support rod = 20 tens 20mm
Pulley support
Height = 140mm
Length = 50mm
Width = 10mm
Fig 2.4 AGV Graphical Representation
2.8 AGV Working:
The Automated Guided Vehicle adopts the Barcode Technology to travel to the several storage subdivisions. An AC servo motor is used to drive the vehicle ; the servo motor has a thrust that controls the motor placement and motion with the aid of a built in encoder.
When of all time an object travels on the conveyer the barcode label pasted on the finished merchandise is sensed by the barcode scanner, a detector nowadays in the AGV besides senses the presence of the object once the object comes skiding down the conveyer. The saloon codification scanner produces an ASCII end product. This is given as an input the PLC. The PLC in bend generates a pulsation train end product ( PTO ) based on the type of merchandise. This PTO end product in bend is fed to the servo thrust. The servo thrust drives the servo motor based on the pulsations received.
If merchandise A is present on the AGV the PLC generates a peculiar sum of pulsations that is adequate to drive the vehicle to the several storage subdivision. The PLC likewise generates different types of pulsation end products for different types of merchandises so that each merchandise can continue to its peculiar storage subdivision.
The AGV moves along with the servo motor on tracks to the several station. The tracks have micro switches attached to them at several places in forepart of each storage subdivision, this helps in maintaining path of the motion of the AGV. It besides acts an input to the PLC to bring forth the pulsations in the rearward way for the AGV to return to the place or origin place in order to roll up other finished merchandises dispatched by the conveyer.