In another major step towards longwall automation, a military-grade inertial navigation system (INS) has been proven capable of measuring the three-dimensional position of an operating shearer over the length of a production block. And with well over two million tonnes under its belt, the INS system has shown it is robust enough to cope with underground conditions.
The technology is being developed as part of the ACARP (Australian Coal Association Research Program) Landmark longwall automation project (www.longwallautomation.org), through key research providers CSIRO (Commonwealth Scientific and Industrial Research Organisation) and others. Key aspects of the automation technology are being developed at Xstrataâs new Beltana mine in New South Wales, which began cutting coal in 2003.
Longwall systems currently have automation functions such as programmable control of both face alignment and the cutting horizon, but quality information on actual shearer positions across the face has not been available until now.
Knowing the real-time position and orientation of the shearer are important pieces of information required to achieve the goals of automated face alignment, horizon control and haulage automation.
Last year at Beltana, a major breakthrough came with the establishment of a reliable face-wide communications link to the shearer to access information for interfacing to roof support and other systems (see article on www.longwalls.com). To cater for much larger volumes of data from intelligent sensors and video equipment required an increase in bandwidth which is currently beyond the capacity of existing shearer cable-based asynchronous serial communications systems.
The data is being collected on a new device developed by CSIRO researchers called the shearer position measurement and display system (SPMDS), which was fitted to the DBT EL3000 shearer at Beltana for testing over the mineâs first block.
Possibly the most exciting news so far is that the accuracy of the INS data about the shearerâs position in space has been verified by a manual survey done underground. The survey compared the SPMDS-indicated position of the shearer with the position as determined by a manual survey of the un-pushed armoured face conveyor (AFC) after the shearer had passed.
In the horizontal position the greatest difference is 100mm and the average difference is 30mm over a 250m face. In the vertical position the greatest difference is 70mm and the average difference is less than 20mm.
Other than putting the broadband comms channel in place, another main challenge in setting up the INS system was where best to locate SPMDS equipment on the shearer, including provision of space, connection to power supplies and other on-board sensors. DBT provided space in the main frame of the shearer to house a flameproof enclosure for the SPMDS equipment rack.
The DBT EL3000 shearer has almost 2000kW of installed power and has cut 2.6Mt in the second half of 2003. In these arduous conditions the SPMDS operated as expected with no failures due to vibration, heat or electrical noise. The few failures experienced so far have been primarily associated with the embedded computer systems and on-board communications interfaces. These systems are being optimised as the trials proceed.
In Figure 2 (see below) there are discontinuities in the shearer position data. This is primarily due to the shearer moving without the INS being aligned and as such no data is recorded. Currently, if the power to the INS is cycled an alignment period of 20 minutes is required before valid position data can be measured, but this time frame will be reduced by the acquisition of new INS hardware where the alignment period is significantly shorter. In addition a backup power supply is being constructed to eliminate many short-term power outages to the INS.
The use of inertial navigation in mining applications is a relatively new development. The US Bureau of Mines conducted tests using the Honeywell modular azimuth positioning system (MAPS) and subsequently the Honeywell Ore Recover & Tunnelling Aid (HORTA) units in the late 1980s for continuous miner guidance applications.
This work was further developed by CSIRO Exploration and Mining, resulting in the development of the first full-survey highwall mining guidance system in the mid 1990s.
INS technology is a logical method to measure machine position in the mining environment as the sensors are robust, having been designed for military operation. They require little or no connection to external sensors and can be located within the machine envelope in protected locations.
The INS-based SPMDS has demonstrated accurate shearer position measurement in production conditions. In the near future, underground tests of automatic face alignment and horizon control are scheduled and results of these tests will be reported when available.