AUTOMATED GUIDED VEHICLE SYSTEM INTRODUCTION

AUTOMATED GUIDED VEHICLE SYSTEM INTRODUCTION: An automated guided vehicle or automatic guided vehicle (AGV) is a portable robot that follows markers or wires in the floor, or uses vision, magnets, or lasers for navigation. They are most often used in industrial applications to move materials around a manufacturing facility or warehouse. Application of the automatic guided vehicle broadened during the late 20th century. An automated guided vehicle system is a material handling system that uses independently operated , self propelled vehicle that are guided along defined pathways on the floor. The vehicles are powered by means of on board batteries that allow operation for several hours (8-16 hrs.) between recharging. Guidance is achieved by using sensors on the vehicles that follow the guide wires. The vehicle is controlled by an off board controller or a micro- processor. This controller sends commands to the vehicle such as identification of load, its destination and other special instructions. An AGV system provides a material handling system i.e. both flexible and readily adaptable to either production or production changes. AGV systems are originally developed for the distribution of material in warehouse environments although this is an imp. use, two major growth areas have been evolved the movement of material to and from production areas in manufacturing facilities, reflecting manufacturing work lifts and use of carriers of work in progress in assembly plants, replacing serial type asynchronous or fixed index assembly conveyor system and small packages, in hospitals to deliver meals, and for material handling. In manufacturing units, material spends more time in a shop moving than being machined, which means that there is more time wasted thereby adding to the cost of the product. Thus, material handling methods used are important in improving the profitability of a manufacturing organization. The major automated material handling systems that are generally used in advanced manufacturing are automated guided vehicles (AGV) or mobile robots, storage and retrieval systems (AS/RS) The primary objective of this project is to design a fully autonomous “line following AGV” capable of following a pre-designed path marked on a surface. AGV system were first introduced in 1950 in USA and later in Europe in early 1960, the technology caught on much faster in Europe. TYPES OF VEHICLES Towing Vehicles: These vehicles consist of an AGV with no load carrying facility but with a hitch or tow bar that can pull trailers, carts pallets jacks and wheeled racks. They are used where large volume of product to be moved or in retro fit applications where product in historically been moved by trailers. These vehicles can move loads up to 50,000 pounds. Unit load Transporters: These vehicles are designed to carry individual loads. Unit load transporter can have an extremely versatile deck design, which permits them to be equipped with rollers, belt conveyors, power lifts, special fixtures, or on board robot arm, These AGV can be either bi-directional or unidirectional and are used in house as well as on factory flowers. Unit load transporter scan lift loads ranging between 12,000 to 60,000 pounds. Standard Automatic Guided pallet Trucks: These vehicles are designed to service palletized loads to and from floor level positions. The shadow fork region has limited fork travel and is designed to move pallets to and from floor positions exclusively. The fork truck version has travel up to 20 feet and can move pallets both at floor level and on stands or racks. Assembly Line Vehicles: These vehicles have a fixture on board that accept the frame initial parts of the product that is to be assembled. The vehicle is routed through the various manufacturing stations of the factory where parts and assembly are added to the product. these AVG can provide total automatic transfer of material these are known as material handling system on automated assembly line. They can skip assembly section if required in particular section breaks down. Light Load Transporters: These vehicles are design to carry boxes, baskets, small parts, etc. with any other unitized container. It generally has a footprint allowing its use in tight spaces and narrow aisles. These vehicles are used for a wide range of functions from mailrooms to clean rooms in every type of manufacturing and office environments. Advantages and Disadvantages : Advantages of AGV: Reduction in labor force. Improved productivity and quality. Job enrichment and worker satisfaction. Reduction in space requirement Reduction in product damage. Improvement in house keeping. Ease of removal and relocation. Integration with other type of automations. System adaptability and flexibility. Disadvantages of AGV External use is limited. Requirement of specially designed floor space. Performance is affected if guide path bed is not stable. Sufficient support from management is required. Equal support from worker is required. Obstructions are created. Maintenance is required. Other considerations are : The vehicle must not be used for inventory storage or acts as buffers. It is not possible to operate vehicles made by different manufacturers on same guide path and control system. Vehicles are not suited for situations where ambient temperature exceeds 49ºC. It is difficult to upgrade a simple system in to complex one. AGV SYSTEM COMPONENTS Although all AGV system are different, in general they consist of following components: 3.1 Vehicles: The component of an AGV system that is most readily identified is vehicle itself. The vehicle consists of a frame, batteries on board charging unit, electrical system drive unit, steering, precision stop unit, on board controller, communication unit, safety system and work platform. Frame : The frame is usually constructed of welded steel member with aluminum cover Plate. Batteries and charging : AGV systems are typically powered by 24 or 48v D.C. industrial batteries. Battery charging is accomplished by one of two techniques viz. Opportunity charging or full cycle charging. Drive unit : The main components of motor speed controller and drive mechanism. The driver speed controller mechanism is usually a pulse width modulated four-quadrant servo drive unit. The carrier drive commands are generated either through the microprocessor or at the hand control unit. Steering: Vehicles are designed to maneuver in three different ways forward only, forward and reverse, four directional. The major components of power steering system are the steering antenna, the steering motors and their controllers, steering linkage and steering limit switches. Precision stop controller : A precision stop controller is used to stop AGV with close location accuracy at workstation and charge station. At some point before an up coming precision stop location, the vehicle will receive a precision stop command from off board controller or by code bar on board on the floor. AS it approaches stop point the vehicle’s metal detector is activated and AGV slows to the end of the plate. On board controller : The vehicle controller is used to monitor vehicle performance through encoder data to determine position and velocity discrete digital input, monitor functions as controls, activation of safety devices, battery conditions, steering limit, break release, running light drive controller status. Communication Unit : Instructions to the vehicle microprocessor are usually generated by the Area controller and then relayed to the vehicle. The communication System may be either continuous or discrete. Safety : Safety systems may be divided in to three specific categories, vehicle to Vehicle, vehicle to object, and vehicle to people. The first system uses photo cells mounted on AGVs leading edge and reflecting material on trailing edge to avoid collision of vehicles. Vehicle to object system uses bumpers , toe born limit switches, proximity sensors to protect both vehicle and any object in AGV path generally vehicle have warning light buzzers or toner which flashes or sounds to indicate automatic mode. 3.2 GUIDE PATH AND GUIDENCE SYSTEM; Generally most AGV s need guide path to follow. The guide path techniques used are known as passive or active tracking. Passive tracking depends upon either optical or metal detection principles where as active tracking involves inductive principle’s Passive Tracking : The optical method may be simply involved a light sensitive photocell mounted on the vehicle, which follows the tape on floor. It depends upon contrasting floor surface so that variation in reflecting light that is sensed by photocell can be detect ed when the vehicle begins to stray from them guide path. If guide path becomes dirty, faded, or damaged or if the ambient light distorts the light level sensed, the vehicle may stray from guide path. A variation of optical method is lightening patented optical system. It is based on bonding fluorescent particles to the floor surface and stimulating these particles with ultra violet light and causing them to omit a generated light in the sensing head an oscillation mirror scans the guide path and reflect the generated light in to photo reflector, which intern relays signal to microprocessor. The other passive tracking techniques involve vehicle with metal detecting sensor s following a stainless steel ribbon. Tran scar patterned guidance system consists of two sensors packs each containing five sensors and located at each end of AGV. The three central sensors allow the vehicle to center itself on the guide path. The two remaining sensors assist the vehicle in transverse curve. The sensor locates the presence of guide tape and transmit this information to the onboard microprocessor. Active Tracking : Active tracking involves use of guide wire and most commonly used Technique in industry. A low voltage ( less than 40 v), low current (less than 400 ma), low frequency (Ñ to 15 kHz.) and signal is conducted through a wire buried in a slot in the floor. A small electromagnetic field is radiated from the wire and two inductive type sensors are compared and as long as they are equal, the vehicle is centered on the guide path if vehicle begins to stray, signal magnitudes sensed are no longer equal and sensor difference is used to steer the vehicle back on the guide path. 3.3 Floor and system controls: The controller is the brain of the whole system, trying the vehicle to the guide path and integrating the system. Not only does it control the AGV system but it also integrates with automatic assembly facility. The AGV system itself will usually contain three levels of controller architecture, vehicle control system, floor control system and vehicle on board processor. vehicle control system : The top level of vehicle control system often communicates with and under the control the facility’s host computer. Most of the decision making takes place at this level as it oversees the system operation. The vehicle system stores in memory exact vehicle location at all the times and provides network access. Floor control Unit : This level is referred to as the data concentrator and acts as traffic manager and communicating directly with the vehicles and providing them with formatted detailed commands. Vehicle processor : Generally the vehicle processor knows the vehicle location, and it can interpret commands received from floor control unit and can monitor on board safety devices. The two type of vehicle control processors are intelligent type and non-intelligent type. CHAPTER 4 AGV GUIDENCE & CONTROLES INTRIDUCTION Some AGV system use vehicles, which have sophisticated microprocessor on board and are known as smart or intelligent vehicles. Other systems have minimal vehicle computing ability and use a central computer for all process. In such systems central computer decides location, direction, proper rout and path of the vehicle. This is accomplished by turning on and off the path at decision points or by commanding vehicle to follow a particular frequency. All decision is making is made by central computer in smart vehicles. The central computer dispatches the vehicle to next location, though it’s on board microprocessor, the vehicle it self makes decision as to which path it takes. 4.1 method of Programming the smallest system uses manual programming to direct the vehicle to specific destination and to dispatch the vehicle. These system ranges from basic toggle switches, thumbwheel switches or push button numeric pad for programming the vehicle to go to specific station. The advantage of manual system is that it is the least expensive and simplest system. The disadvantages of manual system are that its efficiency depends upon operators. Finally these types of systems controller cannot determine vehicle location while it is in transits. The second level of sophistication in control system is referred to as remote dispatch. In such systems operator intersects with the local controller who in turn transmit information such as destination , rout and automatic load/ unload commands to the vehicle this control system allows the vehicle to circulate on guide path looking for work. this system does not allowed tracking capabilities. The third level is more complex and expensive and is referred to as the central computer controlled system. 4.2 Guide Path Techniques: a. passive techniques: It involves the use of chemical, paint and adhesive strips or tape where by the AGV focuses a beam of light on the reflective tape and tracks the path by measuring the amplitude of reflected beam. Another passive method involves vehicles with metal detecting sensors following stainless steel tape. Communication of commands and positional information to the vehicle may be accomplished by placing guide path codes along the guide path. Active Techniques : By for most commonly used method in industry is the wire guide path. This method involves cutting a slot in the floor (1/8 to ¾ inch wide ) and (1/2 to 1.5 inch deep), in to which one or more wires are placed and grouted and epoxyed. There are two different wire guide path techniques, one using either one wire in the slot operating on one frequency or one multiple overlaid frequencies and other using several wires in the slot each operating at a different frequency. With multiple wire method a path is selected at decision points according to the assigned frequency. The vehicle can be programmed by system controller at decision points to follow the appropriate frequencies and thus the vehicle is directed on the desired path. 4.3 Communication Technique : Irrespective of guidance technique used it is essential for individual vehicle to be able to communicate with the system controller. The vehicle must be able to receive such commands as work assignments, destinations, route frequency, speed, blocking instruction, when to start and stop and auxiliary equipment commands used similarly vehicle must be able to transmit it’s status to the system controller by sending such informations as vehicle identification, location, direction of travel speed of travel & battery status. There are two AGV systems viz. continuous & discrete. Continuous indicates that the area controller always communicates with any vehicle where as discrete means that area controller can only communicate with a particular vehicle at times. Radio frequency communication is widely used from in an continuous communication. Each AGV is equipped with transmit / receive antenna. Each AGV may be on a different frequency. The majority of AGV systems prefer discrete communication method. The two type of discrete control are inductive and optical. Inductive method utilizes A set of wires buried beneath the ground along guide path in squares or rectangles. Each communication point is assigned a unique address through area controller. Yo communicate, vehicles either come to a stop with their communication antenna immediately above a communication loop or while in motion over an elongated loop. The optical method involves stopping the AGV at set stations along the guide path where information is passed to the vehicle using infrared light. CHAPTER 5 APPLICATION OF AGVS Introduction : AGV is used in various growing number and a variety of applications. 5.1 Driverless train operation : These applications involved the movement of large quantities of material over large distances. e.g. the moves within a large factory building or buildings in large storage depot. For the movement of trains consisting of ¹ to 10 trailers, this become an efficient handling method. 5.2 Storage / Distribution system : Unit load carriers and pallet trucks are particularly used in these applications. In these storage or distribution operation, the movement of material is in unit load form. The application often interfaces the AGV with some other automated handling or storage system this type of storage / distribution can also be used in light manufacturing and Assembly operation in which work in process is stored in a central storage area and distributed to different work station for assembly or processing. 5.3 Assembly line operation : AGV system is being used in a growing number of assembly line applications. In these applications rate is relatively low and there are variety of different models made on production line. Miscellaneous Applications : Other applications of AGV system including non-manufacturing and non-warehouse applications such as mail delivery in office building and hospital material handling applications between different floors of the hospital. FUTURE TRENDS Although it is difficult to predict the future with absolute certainty, it can be concluded from the trends that seem to indicate future status of AGV systems. Guidance : The research is being accomplished to expand capability and even to eliminate the need for guidance using guide path on board controller. On board controller is becoming more sophisticated and at same time they are becoming smaller and less expensive the vehicle controllers are exhibiting such features as expanding diagnostics. Although vehicle cannot repair themselves, they can at least indicate their problems to maintenance and repair person. Controller sophistification will also allow the vehicle to operator more intelligently in complex handling situation and will increase the system integrity in the event of host computer failure. Vehicle communication: The trend is towards continuous as opposed to discrete communication So that vehicle will be able to communicate and receive updated instruction at any time. system controller: System will be designed to have capability to track material and store this information. They will be able to follow and control material flow to support just in time concepts. The system controller will also be able to be integrated with network allowing it to communicate with any other facility controller. Vehicle : Vehicle will become more standard requiring less engineering to adapt the vehicle to a particulate task, thus lowering the coast of vehicle to a particular task, thus lowering the coast of vehicle to a great extent this will make them easier to justify for many users. Improved Graphical Display : There will be probability the increased use of color graphical display showing entire guide path, every vehicle location, the vehicle identification, the vehicle status and vehicle load. Safety: New safety sensors for proximity detection will be developed and coupled with computing power of on board controller to produce on even vehicle that readily negotiate pedestrian clogged aisle. CONCLUSION This seminar report gives the introductory and brief information about the AGVS. These systems interfaces with automatic storage on one hand and with manufacturing operations on the other. They are coordinated through a centralized computer to provide virtually automatic flow of material through a manufacturing plant, taking row material to machine and carrying finished products in to storage or shipping. Such totally automatic systems are bound to become more prevalent in the future. Another trend ganging momentum is the great sophistification of controls that permits a vehicle to operate more intelligently and thus fit more ifficiently and thus fit more efficiently in to complex handling patterns. The guidance control system of AGVS can be used for other material handling systems such as lift trucks, which permits further reduction of human drivers and materials handling becomes more controllable. REFRANCES M. P. Groover “Automation, Production Systems and Computer integrated Manufacturing “ TATA McGraw Hills Publications,”Second Edition,1995.J.H. Fuchs “Advanced Manufacturing Methods”, Tata McGraw Hills Publications, First Edition,1992. PAGE 18