Page 128 - Advances In Productive, Safe, and Responsible Coal Mining

112 Advances in Productive, Safe, and Responsible Coal Mining

Also, it is not required in some applications that use continuous haulage. Whenever
the cutter head on the CMM is not active, such as when the machine is tramming
between locations, mining mode is not active, and thus the zones are not reduced. Field
test results show that mining mode significantly reduces warning and stop zone sizes
at the rear of the CMM, in some cases to zero. Although there are no recorded fatal
striking/pinning accidentsthat have occurred while cutting coal, this reduction in warn-
ing and stop zones could allow contact with the CMM by an operator and could be a
safety hazard.
A principle known as parasitic coupling has been reported [15] by a number of
mine operators, where it has been suggested that MWCs located near a trailing cable
are causing spurious machine shutdowns even though the operator is not near the
machine. It is suggested that parasitic coupling may occur when the magnetic field
generated on the CMM couples to the trailing cable, effectively extending the warning
and stop zones farther than intended. Because of this possibility, the influence of a
trailing cable on zone measurements was examined in field tests. The test protocol
called for the MWC to be held 46 and 16in. from the trailing cable in these tests at
test point #3 or test point #9 (depending on which side the training cable exited the
machine) while measuring warning and stop zone distances. These measurements
were then compared to baseline test measurements for determining any effects from
the training cable.
Data collected from these tests provide no indication that parasitic coupling has any
effect on warning and stop zone distance measurements. Additional testing would be
required using closer distances from the MWC to the trailing cable to further inves-
tigate reports of false alarms caused from parasitic coupling.
Also, when a shuttle car maneuvers into the loading position while the CMM is
mining coal, a large mass of metal (the shuttle car) is introduced nearby the CMM.
This could possibly reshape the field toward the rear of the machine. Specific field
tests were designed to quantify the effect that the presence of a shuttle car has on
the PDS system. This field test data show that the effect of the shuttle car being present
was to enlarge warning and stop zones slightly.
Overall test results indicate that while system performance is generally good, there
is still room for improvement due to large variations between field test sites. Since all
approved PDS have adjustable zone distances, this variability is due to preferences set
at installation. Site-specific conditions need to be considered when defining warning
and stop zone distances. A number of measurements showed stop zones to be less than
3ft (91.4cm). This distance may be inadequate for a CMM operating under adverse
traction conditions, such as a wet floor on a slope. These zone distance settings should
be tailored to mine conditions, keeping safety in mind. Field test measurements for
both warning and stop zones were repeatable, and the majority of readings only
required two measurements. Detailing complete results is beyond the scope of this
chapter, but interested readers are referred to a comprehensive NIOSH report [16].
Future development and installations of PDS should take this information into consid-
eration and work to improve system precision. Additionally, mine operators and PDS
installers may want to consider minimum distances when setting zones for production.