AUTOMATED GUIDED VEHICLE(AGV) GUIDANCE AND MANAGEMAENT

AUTOMATED GUIDED VEHICLE(AGV)GUIDANCE AND MANAGEMENT1

AGVS DEFINATIONHigh Tech material handling systems that uses self independent and propelled vehicles guided along definite pathways.

Unlike other rail guided and conveyor system vehicles their pathways are Un-obtrusive.

They are most prominent to areas suitable for automated material handling system for batch production and mixed model production.

TYPES OF AGVS:- *Towing vehicles *Assembly line vehicles *Unit load transporters/carriers *Robotic arm vehicles * Flexible machining vehicles *Autonomous vehicles

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AGVS GUIDANCE 3Guidance is a method by which AGVS pathways are defined and vehicle are controlled to follow that pathways.Generally three technology are used-* IMBEDDED GUIDE WIRES- 1.Electrical wires are placed in a small channel in or out the surface generally 3 to 12mm in width and 13-26mm deep

2.Guide wire is connected to a frequency generator which emits a lo voltage and current signal with frequency in the range 1-15 KHz.

3. It induces a magnetic field along the pathway that an be controlled by a sensor on board each vehicle

CONTD4

AGVFloor spaceGuide wire

Sensor coilEM Field

Two sensor coils are mounted on both side of guide wires.

Intensity of magnetic field measured by each coil is equal when guide wire is in between the two coil.

If vehicle strays to one side of or the other guide wire path changes magnetic field intensity changes

This difference is used to control the steering motor which makes the required changes in vehicle direction to equalize the two sensor signal thereby tracking the guide wire.

PRINCIPAL METHODS OF ROUTING IN GUIDE WIRE SYSTEM5

Frequency Select Method-: 1.Guide wire leading to different paths have different frequencies and requires different frequency generator for each different frequency used 2.As the vehicle enters the switch it reads an identification code on the floor to determine its location and depending upon its programmed destination, the vehicle selects the correct guide path. Path switch select method-: 1. Operates with single frequency though out the guided path2.Guide path layout is divided into blocks that are electrically insulated from each other 3.For vehicle control power is turned off in all other branches except that left for vehicle travel by the help of a central control computer.

PAINT STRIP GUIDANCE TECHNOLOGY 6In this method the vehicle uses an optical sensor system capable of tracking the paint.

The paint contain fluorescent particles which reflect UV light received by the sensor on the vehicle.

The strips can be taped, sprayed or painted on the floor.

System uses an 1 inch wide paint strip containing fluorescent particle that reflect an UV light source from the vehicle.

CONTD7An onboard sensor detects the reflected light in the strip and control the steering mechanism to follow it.

Useful in environment where electrical noise renders the guide wire system unreliable or installation of guide wire in the floor surface is not practical

Disadvantage with paint strip us that the paint strips deteriorates with time.

Must be kept clean and replaced periodically.

SELF/AUTO GUIDED VEHICLES(SVG)8Latest AGV guidance technology.Uses a combination of dead reckoning(capability to follow a given route in absence of a defined pathways on floor) and beacons located through the plant and can be controlled by onboard sensors.Movement of vehicle is accomplished by computing the required no. of wheel rotation in a sequence of specified steering angles.The most common type of beacons used are:- 1.Bar coded beacons 2.Magnetic beacons These beacons are preinstalled in the entire factory that will actually send signal received by a rotating laser scanner on vehicle or vice versa.Accuracy of dead reckoning decreases over long distances

AGVS MANAGEMENT 9Management needed for efficient working of AGV, allocation of delivery tasks for minimising waiting times at load/unload stations.There are TWO aspects of vehicle management-

1. TRAFFIC CONTROL-To minimise interference between vehicles and to prevent collision between vehicles. Two Methods of traffic control are-

1. ONBOARD VEHICLE SENSING(FORWARD VEHICLE SENSING)- * Have one or more sensors on each vehicle to detect obstacles ahead on the guided path and stops the vehicle if an obstacle is encountered.

* Are less affective at turns and convergence points where the vehicle may not be directly in front of the sensor.

2.Zone control10

Guide pathZONE 1 ZONE 2ZONE 3ZONE 4AGVs layout is divided into different zones and the rule is that no vehicle is allowed to enter a zone already occupied by another vehicle.

Allowance is given for length to sufficiently hold one vehicle and allowance for safety, no. of vehicles in the system, size and complexity of the layout.

When one vehicle occupies a given zone ,any trailing vehicle is not allowed to enter that zone, the leading vehicle must proceed into the next zone before the trailing vehicle can occupy the current zone.

By this forward movement in the separate zones is controlled, collisions are prevented

CONTD11When a vehicle enters a given zone, it activates a block in that zone to prevent any trailing vehicle from moving forward and colliding with the present vehicle. VEHICLE DISPATCHING:-Dispatching to the point in the system where they are needed.

1.On board control panels-*Dispatching through Onboard computer control panels.*Used for manual vehicle control vehicle programming and other functions*Lowest level of sophistication but flexible.*Changes in delivery requirements are easy.2.Remote call stations -:*Call stations is a push button mounted on the load/unload stations

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CONTD12*It transmit a hailing signal to any available AGV within the dock and either pick/drop a load.*A more automatic dispatching method capable of automatically loading/unloading operations

3. Central computer control-:*Have a central computer control for automatic dispatching of vehicle*Central computer issues a command to the vehicle and the operations they must perform*Vehicle is always communicating with the central computer controller. * Radio frequency is commonly used for communication links.