Background: In underground coal mining, new and innovative machines are being developed to increase production efficiency. An international manufacturer of underground machinery designed a mobile conveyor that needs to maintain precise alignment as it advances and retracts over a distance of 300 feet in the underground mine workings. Product Resources was chosen in the face of international competition to design and build the control system.

Project: Since the alignment of the conveyor must be held to a precision of better than +/- 3 inches over the entire length of 300 feet, a laser was chosen as the alignment reference. Laser targets mounted over each of the four support tractors detect the position of the conveyor with reference to the laser beam. Product Resources designed and assembled the control system based upon a programmable logic controller (PLC), which directly controls the steering and speed of the support tractors. Using the output of the laser targets, the control system coordinates the positions of all four tractors to keep the structure moving in the correct direction and precisely aligned despite the uneven and slippery nature of the ground. The control system uses five PLC's, all communicating with one another and controlling individual segments of the machine. The entire machine is operated from a control panel with a display screen. The screen displays all of the significant control parameters for each tractor including the steering angle, speed, and degree of misalignment.

Technologies: PLC software, electrical to hydraulic control interface, laser beam detection and measurement, intrinsically safe and explosion proof practice to Mine Safety and Health Administration (MSHA) standards, crawler tracked vehicle guidance and speed control

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