State-of-the-art ultrasonic sensor designed to improve longwall production rates and operation safety

measuring the distance from the end of the shield support canopy to
the face of the longwall panel. The sensor's task is to detect rock falls
because in such a case, empty spaces in the coal seam below the roof
are generated. The sensor is a part of the system which task is to
predict unfavourable behaviour of the longwall roof affecting the
continuity of mining. Due to an untypical workplace and difficult
conditions prevailing there, it was not possible to use a typical sensor.
The ultrasonic technique was used for this purpose. The next research
stages related to the development of the sensor were described. Tests
of various types of ultrasonic transducers, working at different
parameters, were described. Only transducers with a closed structure
were considered because they can operate in the presence of high
dustiness and humidity. The sensor casing was adapted to a specific
type of shield support. The installation location should not be
accidental, as an additional hinged shield is mounted at the end of the
canopy, which is an obstacle in the measuring track and can even
completely cover it, making measurements impossible. The sensor is
mounted close to the side edge of the shield support canopy using
small free space, enabling a measurement. Structural elements of the
canopy are obstacles in the measuring track and are a source of
interference of the received signals. The ultrasonic transducers are
built-in tubes, which direct the ultrasonic wave and amplify the
received signals. The results of laboratory tests of the model of the
path measurement sensor are presented. They describe the impact of
analysed aspects, i.e. the type of transducers used, the structure of the
surface that the wave is reflected from and the mechanical solutions
on the quality of received signals. A prototype of a sensor installed
on shield support is presented.