Alternate Technologies Applicable To Proximity Detection on Mobile Machines In Underground Coal Mines

"There have been about 42 fatalities in underground coal mines between 1984 and 2015 where the victim was struck, pinned, or run over by a mobile machine (MM) such as a shuttle car, scoop, or battery hauler. MSHA has issued a proposed rule requiring proximity detection systems (PDS) on MMs in an effort to prevent future fatalities. Currently approved PDSs use electromagnetic (EM) technology to detect the presence of a miner and impose machine controls to prevent contact. The disadvantages of an EM-based PDS on MMs include the need for a miner-wearable component (MWC), environmental interferences, EM interferences from other devices, and low localization range and accuracy. NIOSH researchers are investigating alternate technologies that could improve the capabilities of the current PDSs. Many technologies were reviewed, and NIOSH researchers identified RFID, LIDAR, RADAR, ultrasonic detection, and computer vision as candidates for PDS development. The performance characteristics of each technology and its applicability to an underground mining environment will be discussed, along with international developments and implementations, and the concept of sensor fusion. INTRODUCTION PDSs provide safety to mine workers by detecting their presence (and in some cases location) around a machine. These PDSs provide a warning zone, which triggers an alarm, and a stop zone, which halts the machine before it contacts the miner. The Mine Safety and Health Administration (MSHA) issued a final rule requiring that PDSs be installed on all continuous mining machines (CMMs) on the working section, with the exception of full-faced machines, according to a phase-in schedule for newly manufactured and existing equipment [1]. The PDSs that were designed for CMMs have since been adapted to other mobile machines. Mobile machines include scoops, which are used as general utility vehicles, as well as coal hauling machines, such as shuttle cars, ram cars, and continuous haulage systems. MSHA has examined all accident reports from 1984 to 2014, and determined that 42 fatalities could have been prevented on mobile machines had a PDS been installed [2]. As such, MSHA issued a proposed rule that would require mobile machines on working sections (with the exception of longwall sections) to be equipped with a PDS. This rule would follow a phase-in schedule for newly manufactured and existing equipment. Currently available PDSs are based on electromagnetic (EM) technology. NIOSH researchers developed a shell-based magnetic flux density distribution model [3] for determining the position of a miner near a machine. A typical system would consist of four generators positioned around the perimeter of the machine. Each generator is a coil of insulated wire wrapped around a ferrite core. The magnetic field strength is proportional to the current running through the coil. Miners working on the section have an MWC, which is a transceiver that measures the field strength emitted by the generators and transmits a data packet over an RF link which contains the field strength reading to the PDS controller mounted on the machine. The magnetic field generators are pulsed sequentially such that the MWC can identify which generator’s field strength it is reading. This type of system utilizes the principle of magnetic flux density: the closer the MWC is to the field generators, the higher the field strength reading. Thus a miner’s presence can be determined once he gets too close to the machine, because his MWC will measure a magnetic flux density beyond a certain threshold. These thresholds are utilized on a per-generator basis to “shape” the fields for both warning and stop zones around a machine, as illustrated in Figure 1."