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Safety and health in mines research advisory board

Annual Review 2005


Mine Communications

Extending the Utility of Underground Data Transmission Networks

MRSL completed work on ECSC project 7220 PR-133 in June 2005.  Within the project an important set of new high speed data transmission devices and technologies were developed or adapted for use in the coal mining industry.  These technologies cover all currently used transmission media: wired, fibre optic and wireless, and constitute the foundations for further research that has already begun within the Iamtech and Rainow RFCS projects reported below.  These technologies will allow the presence of near ubiquitous real time digital voice and video transmission to be achieved, plus high volume data transmission, which is needed in the teleoperation and automation of modern longwall faces and in maintenance applications.  The main specific results and conclusions of the MRSL part of the study were as follows:

  1. Design studies undertaken on the feasibility of using wireless data sondes for transmitting telemetry from inaccessible locations, such as the waste, showed that such a scheme is feasible, with any limitation on transmission distance being overcome by utilising a network of devices.  An alternative is where the power and data are transferred by inductively coupling the device to a single wire cable. However, the safety issues of operating electrically powered systems in inaccessible locations remain unresolved, particularly where electrical protective systems may be potentially compromised.
  2. The issue of addressing telemetry system resilience and survivability involved research into the use of high resilience wireless systems based on the emergent technology field of mesh topology wireless personal area networking.  The practical research work focused on establishing the feasibility of using low-power wireless mesh networks in an underground environment. Depending on conditions, transmission ranges within tunnels ranged from 80m to beyond 150 m, sufficient for many applications. The mesh network tests confirmed excellent coverage around complex, large fixed and mobile plant infrastructure and acceptable behaviour regarding tunnel wall proximity and body shielding effects. Several important potential applications of mesh wireless techniques were identified.
  3. Wireless based safety systems are feasible in other applications. One application addressed the safety issues available for communicating a warning between drivers and pedestrians underground using high integrity data transmission and hazard status warning techniques. A second application concerned the provision of zonal location information underground.  A preliminary investigation of the respective merits of RFID (Radio Frequency Identification Devices, known as 'tags' or transponders) versus emerging wireless networking technologies was undertaken. Both Bluetooth and Zigbee technologies could meet an application requirement of providing an intelligent tag function.

The full report is expected to be published by the EU later in the year.

Enhancing the performance of mine communication and warning systems

EC project RFC-CR-03003 (EPCWCMS) is concerned with achieving substantial improvements in the performance of speech communication systems and auditory alarm and warning systems across a wide range of underground and surface mining applications.  Progress made by MRSL during the year against the three objectives was:

Researching the Applications of Open Innovative Wireless Technologies.

MRSL and RMT are the UK partners in this new RFCS project,RFC-CR-0503 (RAINOW), which is due to continue until 2008.  The main target of this research is to innovate mining operations through the widespread introduction of wireless technologies, including smart open wireless sensor networks, wireless digital voice communications and wireless position tracking systems. 

During initial tunnel tests by MRSL, it was found out that sharp bends and the close proximity to large metallic objects caused low attenuation rates of wireless signals.  The trials indicate that Zigbee seems to be the most promising transmission method for smart sensor applications.  Underground ambient energy sources were characterised and their potential power was estimated.  Energy sources in terms of small rechargeable nickel metal hydride packs could be sufficient for the needs of the m-Com wireless link.

Zigbee could lead to more energy efficiency and lower cost solutions of an intelligent RFID tag.  It was determined that a key objective is the replacement of low frequency transponders and read stations with compact ISM technology.  Candidates for sensors were chosen and guidelines for real-world implementation of sensor nodes defined.  Market available energy harvesting micro-generators were found.  An extended reading range and a resistance to signal fade outs were achieved.

Other work by MRSL focussed on temperature monitoring in the proximity of conveyor belt drives with smart senor technology, with the aim to eliminate false alarms (e.g. caused by diesel exhaust gas emissions or blasting emissions). Also it is intended to detect incidents (e.g. blocked belt rolls) at an early stage to prevent fires. For the development of navigation and tracking systems for machines, material flow and personnel, it was found out that an active RFID approach is more feasible than a passive one. Moreover it was acknowledged that IEEE 802.15.4/Zigbee specification technology appears to offer the best prospects for engineering a low cost device able to provide a zonal detection capability with relatively low costs of implementation.

RMT’s work under the Project will be to develop, to full commercial exploitation, a new version of the m-Comm mine rescue communications system which incorporates a local wireless voice and data link between units worn by the rescue team members and the m-Comm life line/ information transmission system.

A basic understanding of the behaviour of electromagnetic (EM) wave propagation in coal mines is fundamental to success of this project.  Hence, much of the initial research effort has been devoted to this task. Firstly, background information on radio propagation, and its limitations, in confined spaces and tunnels has been gained mainly through researching past tunnel propagation measurements and published papers. Secondly, the use of numerical modelling is being explored as a way of gaining propagation coverage data in a more efficient way.  It is fortunate that the increased demand for wireless technology is forcing companies worldwide to explore similar coverage problems in modern offices with high density of metal cabinets and furniture. At this stage, it is predicted that electromagnetic noise and interference in deep mines will be more predictable than in general industrial applications.  There will be a study and tests at a later stage to evaluate the tolerance of the m-Comm wireless system to likely EM interference,

It is becoming clear that the multi-path propagation patterns in underground mines, particularly when encountering metal infrastructure, will cause the greatest difficulties in securing reliable transmission over a given distance/range. Wireless digital transmission measurements are equally concerned with the consequence of multi-path, i.e., signal delay or arrival times and the relative multi-path total received power. The two standard methods of reducing this type of signal loss (known as fading) are frequency and space diversity reception. Frequency diversity is the main driver force behind ‘wideband’ wireless systems such as direct sequence and frequency hopping spread spectrum, e.g., Bluetooth and DECT products.  The other diversity method is based on having two, or more, receiving aerials quarter of a wavelength apart. In this way, the probability of both aerials receiving near zero signals at any one time is very small.  

In the examination of candidate wireless technologies it is first necessary to list the main requirements for the m-Comm wireless link, they are:

In addition to the primary function of voice communication there should be the ability to send (automatically) limited data from the forward rescue team members to the base station.

The majority of candidate wireless technologies are based on low power chip-set, operate at 2.4GHz and designed to transmit high speed data.  They are further standardised by a commercial need to have interchangeably (termed connectivity), e.g., 802.11x standard. Close investigation of the Bluetooth and DECT products/technologies, which seemed at first the most suitable, has revealed fundamental problems for m-Comm applications.  These technologies rely on a two way transfer of digital information to maintain synchronisation and optimisation of channel hopping frequencies.  This basically restricts them to a point to point wireless link application.  m-Comm ideally needs the flexibility to be both one to one and one to group with each able to be the transmitter as and when required.  It would be unjustifiably expensive to rewrite the embedded ‘stack’ protocol to accommodate the simple needs of a press-to-talk (simplex) voice link. 

Currently, the best technical options for m-Comm are based on wireless microphone, wireless headphone and wireless surround rear speaker mass market applications.   A selection of these products are currently undergoing tests, they include; Circuit Design’s WA-TX/RX, 960 MHz modules and a number of AIRWAVE  2.4 GHz audio short range modules. 

Increasing the Efficiency of Roadway Drivages through the Application of Advanced Information, Automation and Maintenance Technologies

MRSL is contributing to RFCS project RFC-CR-04001 (IAMTECH), which is due to run until June 2007.  The aim is to improve the efficiency of roadway drivages through the use of the latest advances in information and automation technologies, applied to:

Satisfying the programme goals will involve applying advanced information, automation and maintenance technologies, including:

State-of-the-Art reviews of Automation, Maintenance and Wireless technologies were undertaken at the start of the project, together with a Human Factors review addressing issues associated with the operation of mining equipment and electronic devices underground.  These reviews enabled the preparation of functional specifications for the research to be undertaken within the other work packages of the project.

EON Studio was chosen for 3D modelling of mining machines because it meets all the requirements of the project.  First specifications for the development, use and ergonomic analyses of wearable interface devices were identified.  Activities regarding the evaluation of 3D profiling techniques were started. The first results are that two equipment-level and three component-level manufacturers were identified as promising sources of instruments and/or components in this field.

Evaluation of wireless technologies was progressed.  Network test software was selected and a significant number of surface tests conducted, which included IEEE 802.11 (a)/b/g/super g/pre-n (MIMO) and Bluetooth Class 1 devices.  Initial underground trials suggested that considerable benefits would be obtained by constraining transmissions to be line-of-sight.  The research into EM propagation at GHz frequencies in underground tunnels has also progressed, with both theoretical studies and methods of measuring signal strength experimentally having been investigated.

Data for modelling of both a road header and an SL 300 took place during the year. Some difficulties appeared during modelling the AM105 G, but the modelling of the shearer loader has been very successful. In close cooperation with DSK in Germany and the machine manufacturers, certain underground repair procedures were identified for the SL300/420. The processes were described in film scripts, to prepare Virtual Reality (VR) modelling.

Updated 2013-12-23