Automatically Guided Vehicle System

Automatically Guided Vehicle System

INTRODUCTION As mechanized and automated production plants are expanded, the problems of transport, handling and storage became increasingly important, since once these have been overcome, there is considerable scope for rationalization for both industry and commerce. Bearing in mind the trend towards increased automation in the manufacturing areas, the internal transport systems in the form of Automated Guided Vehicle Systems, i.e. the AGVS occupy an important place in general field of materials handling. Within the framework of this study, internal transport systems will be defined as all trucks that are used for handling if material flow throughout industrial and commercial enterprises. Material flow is horizontal & mainly inside the buildings but may include transport between the buildings provided that the public transport is not involved. AGVs are driver-less industrial trucks, usually powered by-electric motors and batteries. AGVs range in size from carrying small loads of a few kilograms up to loads over 100 tons. The working environment may vary from offices with carpet floor to harbor dockside areas. Automatic load handling is used in many AGV-systems. The AGV can pick up and drop off pallets or transfer loads automatically using fork attachments, conveyors, lift tops etc. depending on the type and size of the load units to handle. Modern AGVs are computer-controlled vehicles with onboard microprocessors. Most AGVsystems also have system management computers, optimizing the AGV utilization, giving transport orders, tracking the material in transfer and directing the AGV traffic.

1.1 Historical Development: The first Automated Guided Vehicles (AGVS) were developed in USA by Barrette Electronics 1950s. The first system was installed in 1954 at Mercury Motor Freight in Columbia. It was a tugger system, following an inductive guidance path and with a controller based on vacuum tube technology. Many factors hindered the early growth of AGV industry. The controllers were bulky & had very limited capabilities. Also the labour unions saw them as a direct threat & even resorted to the sabotage of AGV systems. During 1960's and early 1970's, the controllers were first transistorized & then later replaced with integrated circuits (IC) technology. This permitted more compact controllers with more computing powers. Today AGV systems are highly developed & are making use of sophisticated techniques like laser guidance and complete computerised controls. Thus AGVs are offering the industries a viable solution because of their flexibility & ability to offer material tracking & inventory support, asynchronous assembly, and readily integrate with other automation such as robots, automatic storage & retrieval systems of CNC machines. It is also one of the few material handling systems that will allow unmanned manufacturing to become a reality.

1.2 Basic Functions Carried Out By AGVS: 1) Supply and disposal at store and production areas. This area includes many different applications in the entire internal material flow from the time of goods-in, through the store areas & production sections right up to the dispatch. 2) Production-integrated application of AGVS trucks as assembly platforms. C.O.E.& T;Akola

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Automatically Guided Vehicle System

This application is based upon the idea that the manufacturing process can be structured in more flexible way with this transport system. 3) Retrieval especially in wholesales trade. This application is very useful in order picking in a wholesale trade where there is a large turnover and frequent access of the material. 4) Supply and disposal in special areas, such as hospitals and movement of files within the offices. With regard to the high-level of organisational integration in the overall system of operations the following special applications have become particularly important. 1. Servicing high-bay stores with central process control. 2. Servicing of engine test cells in the car industry, especially in the electrical test station as well as in the performance testing. 3. Servicing of production work places according to the principle of central work distribution. 4. Integration of the AGVS in packaging and palletising processes such as travel through shrink-wrapping ovens and automatic palletisers. 5. Integration of AGVS in the servicing of the flexible manufacturing systems. 6. Use in the areas having the health hazards, such as the cold stores or areas with the risk of radiation. 7. Use in war times for remote inspection, detection and disarming of bombs. 8. Use as a space Tele-operator for moving and collecting information on remote planets like Mars, Moon etc.

2. CONSTRUCTIONAL DETAILS In this chapter, we will be looking into the various components of AGVS & characteristic features of the systems. The main components of AGV-system are: 1) The truck or tractor, pallet truck, tow skid basic type. 2) The floor system with the installation of the wire guidance system and the information transfer system. 3) The load transfer equipment, which can be both on board the truck and /or in a stationary position, including the station structure. 4) The truck and traffic control systems. 5) The flexible safety guard and the safety system. Following are the constructional features of the vehicle as shown in fig. 2.1 with a brief description of each: C.O.E.& T;Akola

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Automatically Guided Vehicle System

2.1 Control Enclosure: The electrical control enclosure of a forklift AGV includes all controls of the AGV. Normally there are a control board with an I/O board, chopper units for drive, steer and lift motors. The design of the enclosure makes it very easy to access all the components, which makes it easier to service and troubleshoot. Another advantage is that the control enclosure can be prefabricated as a standard unit, which lowers the cost of the AGV and shortens the lead-time during manufacturing. On the front part of the control enclosure is the control terminal located. It is used for entering information when inserting an AGV to an AGV traffic control system. It is also used for all kind of trouble shooting on the vehicle. Control terminal display features are: Current error messages; a history of the 16 latest error messages; status of all on-board software: status of all digital I/O's guidance status; hour counters for power, drive and lift motors; battery voltage ; memory content which may be changed from keypad; etc. A separate safety control module is located in the enclosure. All safety signals from bumpers, E-stop's etc. are connected to the safety control module. It supervises the safety parts of the AGV making sure all safety equipment is in function at all times. The safety module has doubled safety circuits and safety relay outputs. It detects single faults in safety components and safety circuits. The principle of operation is that both safety circuits must have the same status. If only one circuit is opened up, the module can not be restarted. On the side of the control enclosure are normally a key switch used to select OFF / AUTOMATIC / MANUAL mode. In the OFF status is the power turned off. The AUTOMATIC mode is the normal mode for the AGV when used automatically in the system. The MANUAL mode is only used for manual operation when inserting an AGV to a system or for moving the AGV manually. The control enclosure has an E-stop (Emergency stop) push button on each side. The E-stop will stop all functions of the AGV by disconnecting power to motors as well as giving an E-stop signal to the microprocessor. The manual control unit (MCU) is located on the side of the control enclosure. To each AGV is normally one MCU included. It is used for manually controlling all functions of the AGV. 2.2 Battery: The battery of a forklift AGV is located above the drive unit and below the electrical control enclosure. The battery may be tractionary lead acid, gel or Ni-Cd type. The location of the battery makes it very easy to access for maintenance. It is covered by a cover plate, which also holds it in position. A normal AGV has a 48-volt battery. The capacity depends of type of battery, AGV and operation. The battery may stand on a roller bed in an AG from where the battery is exchanged when discharged. This makes it easy to replace the battery by simply rolling it on and off the AGV. 2.3 Drive Unit : The drive unit on a forklift AGV is located under the battery and behind the front bumper. It is an integrated unit with a drive motor and a fail safe brake. The drive unit is mounted on a mounting plate, which is attached to a turntable. A steering motor is C.O.E.& T;Akola

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Automatically Guided Vehicle System

mounted to the mounting plate and rotates the complete unit when running. The drive unit is very reliable and requires very little maintenance. The drive unit is mounted with spring suspension on five-wheel forklift AGVs. The spring presses the drive wheel to the floor with a constant force. This will ensure good contact and friction between drive wheel and floor surface at all times. The DC motors of the drive and steer unit are always permanent magnetized (PM) motors. The motor size is depending on load capacity of the AGV. The motor requires normally only brush changes as maintenance. An incremental encoder is mounted direct on the drive motor. The encoder gives pulses to the AGV control board, which are used for distance measuring, and speed control. A potentiometer is located on top of the drive unit in the AGV. It is direct linked to the steering and gives a feedback signal to the control board of the AGV, telling exact angle of the steering wheel. In an AGV used for inductive wire guided systems a front main guide antenna is located in front of the drive wheel. This antenna is used for guiding on main paths. In an AGV used for inductive wire guided systems normally a cross antenna is mounted next to the drive unit, in line with the wheel. The antenna is mounted perpendicular to the guide antennas and is used to detect cross wires that the AGV is passing or stopping over. By counting cross wires the AGV can move long distances controlled by a simple command telling how many cross wires to count. At stop positions where very high accuracy is required the AGV can stop with the cross antenna positioned exactly over a cross wire. The drive and steer motor are controlled by four quadrant choppers in the electrical control enclosure. The choppers gives smooth start and stops and makes it possible to stop the AGV with high accuracy. At emergency stop the drive chopper is disconnected by a contactor and the drive brake is braking as power disappears. 2.4 Lift Unit: The lift unit is covered by the cover plate. It is mounted on a cross-tie welded to the fixed mast. Always an electromechanical design of the lift unit consisting of a ball screw with a ball nut, a DC motor, worm gear box and a brake is used. This is a very efficient design, which gives high positioning accuracy for the lift height position, which is very important at high lift heights. The lift screw is normally a ball screw with a ball nut attached to it. The lift screw is attached to the worm gear box in the top. The lift ball nut is attached to the fork carriage or the duplex mast in the AGV. The worm gear box is mounted between the DC motor and the lift screw, it has also an electromechanical brake mounted to it. The brake is used at E-stops and as a parking brake for the lift. The DC motor of the lift unit is normally a permanent magnetized (PM) motor. The motor size is depending of load capacity and lift frequency of the AGV. An incremental encoder is mounted direct on top of the lift screw. The encoder gives pulses to the AGV control board, which are used for height measuring. The lift motor is controlled by a special electronical lift control unit. It is located in the electrical control enclosure. The lift control unit gives smooth start and stops and makes it possible to stop the lift unit with high accuracy. C.O.E.& T;Akola

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Automatically Guided Vehicle System

2.5 Fixed Mast: The fixed mast of a forklift AGV is made of pre-fabricated C-profiles of a type commonly used in manual forklift trucks. The mast is welded to the bottom plate of the vehicle and makes an integrated part of the AGV structure. Inside the mast there is the fork carriage running up and down. The fork carriage has four rollers rolling inside the mast C-profiles. On a high lift AGV with duplex mast there are the duplex mast rollers running inside the fixed mast C-profiles. The battery is standing on beams welded to the fixed mast. The electrical control enclosure is bolted to the fixed mast. At the top of the mast is a cross-tie welded to the mast. On this cross-tie is the lift unit mounted. 2.6 Duplex Mast: A high lift AGV uses a duplex telescopic mast for enabling high lift height with a normal height of the vehicle. The duplex mast of a forklift AGV is made of pre-fabricated C-profiles of a type .commonly used in manual forklift trucks. The mast has rollers welded to it and these rollers runs inside the fixed mast C-profiles. The fork carriage runs with its rollers inside the duplex mast C-profiles. The duplex mast is lifted by the lift nut and it lifts the lift chains over the chain wheels. The lift chains are attached to the top cross-tie of the fixed mast and to the fork carriage. The fork carriage will run twice as fast as the lift nut and the duplex mast. As an option the fork can have a separate lift unit making it possible with high lift heights and a low vehicle. There may also be a third mast for very high lift heights, up to seven meters. 2.7 Fork: The fork of an AGV is normally made from a profile welded to the fork carriage. The fork may be open on the underside or closed depending on AGV type and load capacity. For some applications massive forged forks may also be used. In the tip of each fork arm is normally a bumper mounted, it is used for protection and will stop all movement of the vehicle if it is obstructed by an object. This may happen if a load is mispositioned at pickup or during manual operation. On the fork back is a load detection sensor mounted close to the fork back. Other load sensors may be located in the fork. 2.8 Front Bumper: The front bumper is a safety device, which should stop the AGV immediately if it is obstructed by an object. The front bumper of an AGV is normally designed with a polycarbonate shield around the front part of the AGV. The shield is mounted on two hinges, which are fixed to the AGV chassis. The shape of the bumper shield is controlled by strings attached to the shield and AGV chassis. The main purpose of the bumper is to protect people and the AGV itself from damage. It is normal for a bumper in an industrial environment with combined AGV traffic and manual forklifts, to be damaged and worn as it is obstructed. This bumper is designed with this in mind and is very easy to repair to a low cost. The sensor of the front bumper is made in two main designs with a photocell or limit switches. The standard design is with a photocell on top of the control C.O.E.& T;Akola

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Automatically Guided Vehicle System

enclosure detecting a reflector on the bumper shield. The photocell has a testable input, which is used by the control board to test the complete bumper electrical circuit each second. The option to the photocell is two limit switches attached via strings to the bumper shield. The above sensors are combined with limit switches on the sides to detect obstruction from the sides. 2.9 Rear Support Leg: The support legs are welded to the bottom plate and make an integrated part of the AGV structure. The rear wheels are mounted in the support legs and are covered. In an AGV used for inductive wire guided systems is a rear guide antenna located behind the rear wheel. A front leg antenna is located in front of the support leg. The rear leg antenna is used for guiding in reverse travel, and the front leg antenna for guiding in forward travel. Some AGVs may have guide antennas in both support legs to simplify the floor installation. At the rear end of each support leg is a rear bumper located. The rear bumper is a spring mounted plastic plate. The plate is made in durable plastic and activates sensors when obstructed by an object. The rear bumper may also carry additional sensors, such as miniature photocells used for load detection. 2.10 Characteristics: The current market situation is characterized by demanding requirements. The characteristics of the transport system are: 1) The conveying technique - continuous or discontinuous as well as overhead or floor mounted. 2) The conveying speed. 3) The economic transport path. 4) The type of drive. 5) The goods being transported or handling aid.

3. AGV NAVIGATION TECHNIQUES 3.1 Mechanical Guidepath: This uses some form of rails, directly or indirectly (i.e. through a steering mechanism) to guide the vehicle. (This technique being of minor importance in the modern AGV systems scene is considered mainly for reference purposes.) The characteristics of this navigation system are: 1) Range: Excellent, as guidepaths i.e. rails of any length can be installed. 2) Accuracy: Excellent. Guidance accuracies in the sub-millimeter range can be achieved if necessary. 3) Flexibility: Poor. As rails are fixed rigidly to the ground, considerable effort is necessary if it is required to rearrange the guidepath. 4) Reliability: Good. If there is only a mechanical guidance slot sunk in the floor then in working with a finger guided vehicle the problem of clogging of the slot has to be considered. 5) Controllability: Acceptable. The technique of building remotely controlled switches is well known for all kinds of rail structures. C.O.E.& T;Akola

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Automatically Guided Vehicle System

3.2 Inductive Guidepath: It is the 'classical' AGV guidance system using a floor-embedded wire carrying alternating current. Wire guidance is the most widely used method of AGV guidance today, and for good reason. Wire has been around since the advent of the AGV technology. It sports high accuracy, dependability, and the simplest initial setup of all the methods. Wire guidance in an AGV is based on the fact that an electrical conductor through which an AC current is flowing will create an electromagnetic field around itself (as shown in fig. 3.1). This field is stronger close to the conductor and is reduced with increased distance from the conductor. An electromagnetic field, which passes through a coil, will induce an electric voltage across the coil ends. This voltage can be detected across the termination of the coil. The voltage is proportional to the strength of the field. A guide antenna contains two coils positioned on each side of the wire, which is embedded in the floor. The difference in electric voltage between the two coils will, after amplification, create the steering signal to the steering motor of the AGV. When the antenna is centered over the wire, the voltage in the coils will be the same and the steering is equal to zero. If the antenna is positioned to either side of the guide wire, the voltage will be increased in one coil and reduced in the other. This voltage difference will generate a steering which will control the rotation direction of the steering motor. Floor installation is made very easy today as there are several companies specializing in this technique. Special floor cutting machines are developed which cut the floor without excessive noise, concrete dust or water spillage and leaves a clean slot ready for installation of the wires. With the improvements in programming capabilities, it is no longer necessary to cut radiuses for vehicle turns. The vehicle is also able to leave the guide path for several feet and return with no interruption in operation. The characteristics of this navigation system are: 1) Range: Good. The length of an inductive guidewire loop limited only by the drive of the capability alternating current amplifier used. 2) Accuracy: Good. Accuracy is limited by distortion of the electromagnetic field caused by metallic objects in the vicinity of the guidewire. 3) Flexibility: Medium. To move an existing guidepath a new slot has to be cut into the floor and the guidewire loop reconnected. 4) Reliability: Excellent. As guidepath is embedded in the floor it is almost ideally protected from environmental influences. 5) Controllability: Excellent. As switches can be implemented by using several distinct frequencies and data communication is possible by modulation of frequencies. 3.3 Optical / Chemical / Magnetic Guidepath: This uses a passive strip on the floor that is detectable by proximity sensors (magnetic) or optically. Of the late a principle is known where a 'chemical' guidepath is exited with ultraviolet waves re-emits in the visible range, thereby vastly improving the contrast ratio. The figure 3.2 shows a system designed to guide an industrial vehicle along a painted track. This mode of guidance is intended for long outdoor ways between two C.O.E.& T;Akola

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Automatically Guided Vehicle System

buildings, where classical inductive methods require too costly equipments of the ground. Optoguiding along a painted track is too much sensitive to track quality, so its use is limited to clean working areas. To overcome this problem, a video sensor is used, which obtains much larger view far from the cart's front. So local defaults of the painted track to be followed have no fatal consequences on the guiding security. The sensor can also be used as a security detector for objects taking place on the cart's way. The system includes three parts: 1) A 256 photodiodes linear array analyses the path, one meter in front of the carts driving wheel. 2) A filter, based on a digital processor, delivers information on the detection quality and on the offset between the camera axis and the detected painted track. This last data allows control of the driving wheel. 3) A last module ensures driving in case of detection failure on a length upto 0.5m. In such cases guiding has to be hold without vision. It takes into account the last detection before failure. The characteristics of this navigation system are: 1) Range : Excellent. The cost of an optical, chemical or magnetic guidepath is proportional to its installed length. 2) Accuracy: very much dependent on the working principle applied. Simple magnetic or optical systems suffer substantial errors due to poor selectivity of sensors used. 3) Flexibility: Good. As the guidepaths are painted or pasted to the ground, they can be removed easily. 4) Reliability: Medium. As guidepath is mostly attached to the floor surface it is vulnerable to environmental influences. 5) Controllability: Poor. As optical chemical and magnetic guidepaths are all passive in their nature there is no inherent means of switch control or start / stop control. 3.4 Magneto-Gyro Guidance: The Magnet-Gyro guiding and navigation system has a special made magnet position sensor used to find small magnets installed in the floor, and Gyroscope technology to keep the AGV heading direction continuously under control. In addition,

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Automatically Guided Vehicle System

there are odometer wheel and steering angle feed back, the same as used on vehicles with inductive wire guidance system. The magnet sensors give information about the AGV position deviations and updates the odometer distance counting as the magnets are passed. All this combined makes a system that can guide vehicles with the help of small magnets installed along the guide path, in the floor. A pair of magnets for every five to ten meters of AGV guide path is normally required. Magnets can easily be installed in wood floors and other types of environment not well suited for guide wire installations. The Magnet-Gyro guidance system has higher cost for the onboard navigation compared with wire guided systems but the cost of installation of guidance wire C.O.E.& T;Akola

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Automatically Guided Vehicle System

is reduced. Cost of onboard navigation is less compared to laser guidance system. The magnets in the floor may collect small magnetic particles in the environment; this will however not cause any big problem under normal conditions. The gyro sensor is a solid state, single axis, and angular rate sensor. The gyro sensor gives direction of the vehicle and provides an output voltage proportional to the rate of turn at its sensitive axis. The gyro sensor uses the Coriolis effect to detect angular rate. The magnet sensor is microcomputer based and is using hall elements to detect magnetic field from magnets. The magnet sensor detects small magnets installed in the floor with high accuracy. The magnet sensor gives X and Y coordinates of the AGV when updating on magnets. The magnets are rare earth type and normally 10 mm in diameter and 15 mm long. They are installed in a drilled hole in the floor and covered with epoxy giving a smooth and flat floor surface. The distance between the magnets in the floor is depending on the type of vehicle and accuracy demands. Typical is to install a pair of magnets every five to ten meters, and after a programmed turn perhaps closer.

4. AGV SYSTEM SAFETY Where and When Do Accidents Occur? Before considering how to approach the problem of safety, it is necessary to consider where and when accidents happen. It has been found that a large proportion of accidents occur during nonstandard situations. The first example is where personnel are in areas which are totally forbidden. This may be due to curiosity, because they are going to speak a friend or because they are taking a short cut. Other accidents occur during breakdown situations. Typically a service engineer might be working on a breakdown. He has been told that everything must be running by the morning. However, he is still at it late at night. He is tired and his reactions are slow. He makes a wrong electrical connection and suddenly the AGV starts to move. This is the type of accident, which has occurred at many places. Other accidents occur due to human fallibility. For ex., if a manual operation has not been carried out correctly; perhaps a load is misplaced on a carrier or verbal instructions have not been understood. Lastly, accidents occur due to product failure. This can be the result of the AGV not performing correctly due to programming or component failure. It might also be due to safety devices not functioning properly. 4.1 Safety Considerations for AGV Systems: There are four basic categories to consider regarding the safety of Automated Guided Vehicle Systems: C.O.E.& T;Akola

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Automatically Guided Vehicle System

   

Training Procedures. System specifications. AGV specifications.

1.) Training: All persons involved with AGVs should receive adequate training. These include: 1) Maintenance personnel. 2) Operators. 3) Supervisors 4) Management. Anybody who is entering the area where AGVs are being used should also be included, such as plant designers, contractors and visitors. The required level of training may be small but should be properly established. 2.) Procedures: Written standard procedures regarding the safe operation of the AGV system are essential. These procedures will ensure a consistent standard and provide a checklist for management. This is parallel to standard procedures in other aspects of business management. 3.) System Specifications: The type of AGV system will have a strong influence on the safety specifications. Originally, AGVs were used mostly in warehouses involving a few personnel. Today, the fastest growth is in AGV systems used in assembly areas where there are many people and correspondingly higher risks. The areas in which AGV will operate can be divided into three alternative types as follows: Closed Zones: - Some warehouse systems can be considered as closed zones with no people at all. It is then possible to stop people entering the operating area by the use of fencing and the use of pressure sensitive mats or light beams at entrances. Even so, it is difficult to count people entering and leaving closed zones and difficult to know if somebody has been left inside. Mixed Zones: - These are areas where there may be a limited number of personnel. These may be pedestrians, people working on machines or driving manual vehicles. Restricted access should be enforced so that only trained personnel are present. Open Zones: - Open zones exist wherever AGVs are working in open factory areas alongside other production processes. Historically, the open zone system is the area where the greatest number of accidents has occurred. Well-designed systems should take into account the following: • Layout: - A good layout will ensure that there are no trapping points such as with narrow aisles where pedestrians and AGVs are in the same area. • Lighting: - Lighting should be to a good level with no dark patches. • Interfacing Traffic: - This may need similar control to road traffic. • Warning Signs: - These should be clear well lit and at the right height. • Vehicle Breakdown: - This must be allowed for in the design of operating systems. • Computer Programming Integrity: - This must be of a high order. 4.) AGV Specifications: The specifier should consider the following points with regard to safety: -

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Automatically Guided Vehicle System

1) Warning lights: - these are most desirable on moving vehicles and should be visible allround. 2) Audible signals: - these are useful and important at blind corners. 3) Brakes: - these must be of high integrity. 4) The load: - this must be secure so hat it will not move under emergency braking or cornering. 5) The computer program: -this must be of high integrity. The hardware must not be affected by voltage variations or electrical interference. 6) Color: - A- bright color is easier to see than dark one. 7) Stop buttons: - The emergency stop buttons must be accessible from all sides of the vehicle. 8) Non contact sensing devices: - Non contact sensors such as infrared or ultrasonic detectors have the advantage of being able to sense a considerable distance in front of the path of the vehicle. They are normally used as the first line of defense to slow the machine down. Following things must be taken into consideration: • Some systems are affected by environmental noise such as from pneumatics and magnetic or radio interference. • The sensing field can be over a wide or narrow angle in front of the vehicle as shown in fig 4.1. If it is very wide it will give somer protection against cornering and crabwise movement of the AGV. However, it may also be affected by other AGVs passing in the opposite direction and by objects on the side of the path of the vehicle. A narrow angled beam will avoid these problems but can still create difficulty when an AGV approaches a wall before cornering (fig. 4.2) and when it is arriving at a loading point. 9) Contact sensors: - These are limited in their size and as a result in their sensing field. After a contact sensor has operated, the AGV must stop before it can cause an accident. In worst condition, a loaded AGV going at a certain speed will have a maximum associated stopping distance. The contact sensor should have built in overtravel to allowlforothis topping distance, i.e. the distance between operation of the sensor and it finally being squashed flat must be greater than the maximum stopping distance of the AGV. It is also desirable that the sensor should not have sharp edges, which will cause cuts or bruising if pressed in this way through human contact. Many AGVs in use today use a suspended skirt as a bumper. The types of designs generally preferred are: 1) The bumper is held up by wires, which are connected to interlock switches inside the AGV. 2) An alternative design uses a photoelectric cell on the AGV reflecting off a disc on the inside of the skirt. 3) Pressure sensitive bumpers use intrinsic fiber optic sensor created by bending glass fiber at regular predetermined intervals, achieving the phenomenon known as microbending loss. Thus a displacement of only 0.03mm will switch off 95% of the light which is passing through. The fiber optic system can then be compared with a photoelectric control.

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Automatically Guided Vehicle System

5. THE NEW VEHICLE ON BLOCK : SELF GUIDED VEHICLES 5.1 General characteristic features of the vehicles :Operations These vehicles feature a full function microprocessor controller on-board the vehicle. The controller automatically activates and monitors all vehicle electronic and mechanical components. All on-board I/O is also processed by the controller which handles photo-eyes, limit switches, safety sensors and serial communications. Safety These vehicles are designed to provide full personnel protection which includes safety devices, flashing warning lights and audible horn, tactile bumpers, emergency stop buttons, key operated lockout switch and non-contact object sensors. Diagnostics These vehicles include a full complement of detailed multi-level diagnostics of vehicle components and functions through the on-board display panel. This easy-to-read diagnostic system allows fast error detection and correction. Controls These vehicles use the most reliable on-board and stationary controllers available today - proven through years of service, in vehicles worldwide. The vehicles wire or non-wire guidance provides safe, accurate guide path tracking. Continuous RF communication between the vehicle and the central controller allows constant monitoring of vehicle position and functions. Maintenance Easily accessibie mechanical and electrical components simplify vehicle maintenance. Removable panels expose electrical controls while extensive use of common standardized components and quick disconnects minimizes service downtime.

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Automatically Guided Vehicle System

Batteries Three battery options are available for the vehicle: standard lead-acid and sealed lead-acid and NiCad. Both lead-acid bettery options provide enough power for a minimum 8 hours of continuous operation and can be replenished through a battery exchange or on-board charging. Manual Operation The Modular Vehicle allows the flexibility to transfer, lift or pick and drop loads manually with the operator pendant. The operator pendant in the manual mode regulates all vehicle forward and reverse travel, and pick and drop functions. 5.2 The New Revolutionary SGV-2000: The vehicle developed by FMC Company has latest features arid is cost effective. The Vehicle starts with a standard control cabinet design concealing the latest electronic controllers and guidance systems along with the vehicle's battery. The rear of the vehicle can be fitted with a variety of attachments depending on the application. FMC currently offers six vehicle configurations illustrated below.

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Automatically Guided Vehicle System

Characteristic Features of the Vehicle: Mechanical: o Large single front dive wheel capable of handling up io a 4000lb (1800Kg) load. o Modular designed upper control cabinet to contain all electronics, lower cabinet for battery. o Front of the vehfcle stays as is for all applications, the rear changes for lift, roller deck, etc.

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Automatically Guided Vehicle System

Electronic: FMC designed 486 processor allows for the following features: o Off the shelf RF modem card for reliable communication. o Steer encoder for self callibrating, accurate steer/drive position feedback. o New laser guidance with a 115ft (35m) range requiring fewer targets to navigate accurately. o User-friendly, menu driven 1/4 VGA operator screen. o RS232 port on the display to download directly from your laptop PC the latest software, or download vehicle code directly from the host computer, via the RF modem card. Software: o New A+ code to move the vehicle around the plant, easily adjusted, quick to install. o Works with new Windows NT® platform host computer. o Communicates to host via new 2.4 GHz wireless LAN RF communication hardware.

5.3 ATLIS hospital vehicle: The ATLIS hospital vehicle provides transportation of materials to fulfill variety of operational and support functions in a hospital. The automated guided vehicles are battery powered, independently mobile vehicles, which pick up, carry, and deliver hospital carts, including dietary trays, surgical supplies, linens, trash, and surgical waste. The essence of the system is a central computer that communicates with each vehicle, eliminating the need for dedicated, full-time operators. Features: 1. Central computer control a. Cart security b. Dynamic vehicle rerouting c. Delivery reports d. Automatic charging 2. Personnel protection a. Bumpers b. Non-contact sensors c. Warning lights and horns 3. NiCad batteries a. Short charge cycles b. Long !ife c. Minimal maintenance d. No ventilation requirements

5.4 ABR Batch Retort Vehicle: The ABR vehicle is designed to transfer pallets of various- mater between other types of automated; machinery. One example of this integration is the transfer of food between processing machinery such as massive pressure cookers in the food industry. While interfacing the ABR vehicle is sometimes faced with steam, wet dripping pallets, and wet floors. For these reasons, the vehicle is equipped with gasketted stainless steel body panels giving the vehicle wash-down capability. variable speed, powered conveyor deck resides on top of the vehicle for automatic transfer of either one or two loads. C.O.E.& T;Akola

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Hidden beneath the conveyer deck, the chassis features a drain pan with a remote drain cock, to keep both the vehicle and floor clean in case of a messy load. Other features include zinc-plated casters, splash proof motors, and splash proof external buttons and switches. A clear, flexible membrane covers the operators panel for waterproofing, while a sheet of plastic provides a water resistant barrier between the floor and the various guidance antennas. Features: 1. Fully automatic operation 2. 4000 lb. (1800kg) capacity 3. Dual load handling 4. Wash-down capability 5. Tight turning radius 6. 360° personnel protection 7. Full-function manual mode 8. Stainless steel components 9. Superior serviceability

CONCLUSION AGVs are being widely used in manufacturing as well as non manufacturing areas where timely, orderly and frequent transportation of materials is required. In India also AGVs are being used in semi automated production shops at a defense production unit. When coupled with an automated stores AGVs can be very effectively used for placing order directly from production area for bringing parts and storing them back automatically.

REFERENCES 1) Engineering Advances, July 1997 2) Automation In Production - By Mikell P. Groover. 3) www. howstuffworks.com 4) www.google.com

C.O.E.& T;Akola

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