During surface-mining operations, large mobile reclamation machines are used to recover bulk materials. On each machine, a bucket-wheel excavator collects material and deposits it onto a conveyor. As an area is cleared of material, the machine moves along parallel steel travel rails to the next area, allowing continuous operation without interruptions for machine repositioning.
The distance between the travel rails is around 100 metres (300 ft) and travel speeds may reach 2m/sec (4.5 mph). If machine movement along the two rails is not controlled accurately, the two sides of the structure become misaligned, causing the machine to skew. In this event, production is halted while the machine is realigned; in the worst case, costly damage occurs.
A sensing system is required that detects the position of each side of the machine structure accurately and reliably along the entire length of the travel rails, allowing coordinated control of the drive systems. Sensors must accommodate up to 10mm lateral movement of the machine structure across either rail and must withstand the hot, dusty environment of a desert climate.
Contrinex high-frequency RFID read/write modules and 30mm-diameter RFID transponder tags are ideal for this application. Rated up to IP67, the M30-diameter read/write modules have PBTP sensing faces and V2A stainless-steel housings, making them ideal for the demanding environment.
The ConIdent passive transponders require no internal power source and, with PBTP synthetic housings, have the same IP67 rating. The selected combination provides read/write distances of up to 45mm (nearly 2 in), ideal for the specified operating conditions. Tags are mounted at one-meter intervals along each travel rail, each programmed with a unique identification number.
As the machine passes a tag, the read/write module reads its identification number at high speed; this is transmitted via a PROFIBUS DP interface to the customer’s control system. A simple look-up table confirms the location of the tag and thus the position of the machine, allowing movement of both sides of the structure to be synchronized without skewing. Operation is independent of the direction of travel.
Contrinex ConIdent RFID devices allow accurate and highly reliable sensing of machine position and the long sensing distance avoids any risk of collision damage. The customer enjoys extended service life and robustness not available from alternative position-detection systems, together with excellent value for money.
Contrinex sensors and more information are available from PLUS Automation.