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Developing effective proximity detection systems for underground coal mines 113

7.5 Development of intelligent proximity detection (iPD)

In 2009, NIOSH researchers began developing Intelligent Proximity Detection (iPD)
technology designed to provide improved protection for miners working near CMMs.
The iPD system continuously tracks the position of all miners near the CMM and com-
pares these positions to known hazardous locations around the machine. When a miner
is detected in a hazardous location, the machine functions that could cause an accident
are automatically disabled. For example, if the operator is standing behind the
machine, there is no safety concern in allowing the machine to move forward, regard-
less of how close the operator is to the back of the machine, but reverse movement is
prohibited. In this way, safe mining practices are allowed to continue uninterrupted,
but the safety of miners is protected at all times.
Because iPD disables only the hazardous machine functions dependent on the
miner’s position around the CMM, this is expected to improve operator acceptance
by minimizing the impact on the operator’s normal mining routine. In addition, since
only the hazardous motions of the machine are blocked, miners are permitted more
freedom with respect to where they position themselves. This enables them to better
avoid other hazards such as other equipment in the area and unsupported roof or ribs.

7.5.1 Localization methods

NIOSH researchers developed a sophisticated mathematical model of the shape and
size of EM fields as previously described in this chapter. At the core of this model is an
equation for the shapes of three-dimensional magnetic “shells” formed around
magnetic-field generators. Shells close to the generator have a more abnormal shape
because as the distance between the generator and the MWC is increased, shells
become larger and more uniform in shape. This nonlinear variation in size and shape
is very well described by this model. For any measured field strength, an associated
shell exists that can be approximated using this model. This means that if an MWC
detects a given field strength, the associated shell can be determined by the proximity
detection system, indicating that the MWC must be located somewhere on that shell.
This does not, however, give an exact position.
In order to implement iPD, it is necessary to continuously track the position of
MWCs. To accomplish this, the position of the MWC is found using multiple
magnetic-field generators on the CMM. The magnetic-field strength for each of the
generators is measured by the MWC, and a magnetic shell is determined for each gen-
erator based on the magnetic-field model. The position of the MWC is given by the
intersection of two or more magnetic shells.
Although this concept for calculating miners’ positions is fairly simple, calculating
the intersection of the magnetic shells is not a trivial task. Shell shapes are irregular and
vary nonlinearly with distance, making it difficult to find a direct mathematical solution
for the intersection. Therefore, NIOSH researchers have developed a new search
method using a series of geometric approximations to calculate shell intersections.