Page 118 - Advances In Productive, Safe, and Responsible Coal Mining

102 Advances in Productive, Safe, and Responsible Coal Mining

and noise. In the 1980s, CMMs were redesigned with radio remote controls. By
removing the operator from the machine cab, several safety hazards associated with
having the operator near the coal face were alleviated. With the implementation of
remote controls, operators also became free to position themselves for best visibility
to perform job tasks and were no longer subjected to machine vibrations during oper-
ation. However, this freedom of movement exposed the operator to the hazard of being
accidently struck or pinned by the CMM and other nearby large moving machinery,
since operators and their helpers often stand in close proximity to the machine in order
to see visual cues needed to operate the machinery. Since 1984, there have been
42 fatalities involving striking and pinning of the operator and other workers by
the CMM. In 2009, the Mine Safety and Health Administration (MSHA) conducted
an analysis of 38 striking and pinning accidents involving CMMs. MSHA estimated
that of these 38 fatal striking and pinning accidents between 1984 and 2009, the use of
proximity detection could have been a preventative factor in at least 28 cases. Further-
more, MSHA estimates that proximity detection could prevent 20% of all deaths
throughout the industry [2].
In August 2011, MSHA published a proposed regulation that would require prox-
imity detection systems on all continuous mining machines except full-face machines
[4]. These systems are designed to stop machine motion to protect miners from
striking/pinning hazards. The final rule was published in 2015 and several MSHA-
approved proximity detection systems are commercially available.

7.3 Technologies for PDS in underground applications

7.3.1 Radar

Radar systems transmit a radio signal from a directional antenna that is mounted—for
the purposes of this discussion—on a vehicle. The radio signal is reflected off of
objects that are within the transmitted beam and a portion of the reflected energy
returns to the receive antenna. Depending on desired system performance character-
istics, transmit and receive antennas can be combined or separate. From this reflection,
the distance from the radar unit to the object can be determined. There are two primary
measurement methods for a radar sensor—pulsing and continuous wave. Pulsed or
ultra-wideband (UWB) radar detects obstacles by measuring the time of flight
(ToF) of a pulsed signal that is transmitted and then reflected from an object within
the radar’s beam with distance between transmitter and reflector being proportional to
this time. The continuous-wave method works by transmitting a radar signal of a
known, stable frequency, and then measuring the Doppler shift of the reflected signal.
The Doppler shift indicates the change in frequency of the reflected signal, which is
proportional to the speed of the target.
Typically, these systems operate in the microwave (300MHz–40GHz) portion of
the radio spectrum. Doppler radar detects the relative motion of an obstacle; i.e.,
detection requires either movement of the obstacle or the vehicle. Both types of radar
are effective for detecting people, other vehicles, large rocks, and buildings. Some