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GPS based truck disptach system at West Bokaro collieries
 Kartikeya Verma, Amit Kr. Montu, V.K. Anand Communication Group, Automation Division, Tata Steel, Jamshedpur, India
Abstract In any mining process, the most expensive operation involves removal of the Over-Burden (OB). The time taken during OB removal , is known as the Haul Cycle time and can be conveniently considered under 4 broad heads viz: Waiting, Loading, Full, and Empty. This cycle is repeated, and involves the rate of utilization of capital equipment, which has a profound impact on the overall productivity and profitability of the mining operation. The HEMM capital equipment are mobile, and operate over a large area. They comprise a fleet of Dumpers and Excavators. It is essential to coordinate the activities from a central location. An efficient and reliable on-line Tracking and Production Monitoring system, is essential for efficient operation. This paper describes Tata Steels application of a Truck Dispatch System at the Opencast Coal Mines located in West Bokaro (in Hazaribagh District of Jhakhand State of India). Truck Dispatch System is based on the GPS technology. Being an opencast mine, GPS was the ideal solution to track location of each Dumper & Excavator inside the pit. Real time location (latitude / longitude) of each mobile equipment is transmitted periodically over UHF Telemetry Data Link from mobile equipment to the On-line Server situated at the Quarry Control Room. Since there are two different quarries, this means in effect that there are two different mines, which are geographically separated viz. Quarry AB & Quarry E. For all practical purposes, operation of both these quarries are independent of each other, therefore there are independent Radio Network, Quarry Control Rooms, Server / Applications / Database and Reporting but it is planned to integrate both these TDS Systems with the help of Wireless LAN to achieve composite reporting and the proposed system is capable of easy integration and future expandability. Besides this, the implementation of the TDS has improved operations so that, the HEMM Operator are capable of having better interaction with real time mining process and provide more value added information which in turn assists better production monitoring system. Introduction Opencast coal-mines operate with periodic blasting and then excavations which in turn is followed by removal of Over Burden (OB) and retrieval of the coal. In the process of coal mining, two main sub processes viz. removal of OB and retrieval of coal are predominant. But most of the effort goes in the removal of OB and this has a dominant influence on the productivity. In the process of OB removal, two of the equipment viz. Rear Dumper and Excavator play a leading role. After the schedule of blasting in an specific zone of the mine has been prepared, the Excavator loads the OB into RD and each RD goes practically through four different machine states i.e. Waiting (near Loading zone), Loading, Full and Empty (at Dumping zone). This sequence of machine states of a RD constitutes one trip. Now it may be understood that to monitor the productivity automatically, one has to monitor the movement of RDs around the corresponding Excavator i.e. Loading zone to Dumping zone and back to Loading zone. Using the facility of GPS Receivers, it is possible to find out the absolute co-ordinates of any mobile equipment. In addition the system incorporates load sensors, limit switches, RF Telemetry etc.  Fig. 1 Site Map of West Bokaro Collieries GPS Technology [1] GPS is a satellite based tracking system. A total of 24 GPS satellites orbit at 11,000 nautical miles above the Earth. They are continuously monitored by ground stations located worldwide. The satellites transmit signals that can be detected by anyone with a GPS receiver. Using the receiver, the exact location can be determined with great precision. GPS has 3 parts: the space segment, the user segment, and the control segment. The space segment consists of 24 satellites, each in its own orbit 11,000 nautical miles above the Earth. The user segment consists of receivers, which can be held in hand or mounted in car. The control segment consists of ground stations (five of them located around the world) that make sure the satellites are working properly. One trip around the Earth in space equals one orbit. Each GPS satellite takes 12 hours to orbit the Earth and is equipped with an atomic clock to let it broadcast signals coupled with a precise time message. Each satellite continuously broadcasts a digital radio signal that includes both its own position and the time, exact to a billionth of a second. A GPS receiver takes this information--from four satellites--and uses it to calculate its position on the planet to within a few hundred feet. The receiver compares its own time with the time sent by a satellite and uses the difference between the two times to calculate its distance from the satellite. By checking its time against the time of three satellites whose positions are known, a receiver could pinpoint its longitude, latitude, and altitude. The GPS system can tell the location anywhere on or above the Earth to within about 300 feet. Even greater accuracy, usually within less than three feet, can be obtained with corrections calculated by a GPS receiver at a known fixed location. The principle behind GPS is the measurement of distance (or "range") between the receiver and the satellites. The satellites also tell exactly where they are in their orbits above the Earth. It works something like this: If we know our exact distance from a satellite in space, we know we are somewhere on the surface of an imaginary sphere with radius equal to the distance to the satellite radius. If we know our exact distance from two satellites, we know that we are located somewhere on the line where the two spheres intersect. And, if we take a third measurement, there are only two possible points where we could be located. One of these is usually impossible, and the GPS receivers have mathematical methods of eliminating the impossible location. For the system to work, the receiver has to know exactly where the satellites are and the satellites have to be able to keep reliable and extraordinarily accurate time.  Fig. 2 Typical Radio Network
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