Imagine this: a potash mine in which the operator of a large continuous-mining machine is seated at a remote console contained in a climate-controlled, ergonomically-designed, mobile control pod connected to, and located a safe distance behind, the mammoth machine. This may become a reality if recent trends in automation continue. Automation promises to improve the operator performance by placing the miner in an environment with lower exposure to heat, dust, noise and loose ground. Automation of the miner will also increase machine utilization during shift changes and lunch breaks, and it should make machines more available through reduced downtime by sensing operating conditions which might lead to serious equipment failure.
A co-operative research and development program between the Potash Corp. of Saskatchewan (pcs) and Prof James Wilson, in the division of Control Engineering at the University of Saskatchewan, is aimed at automating one production mining machine at the pcs mine in Rocanville, Sask. The automation modules delivered to date include a Sonar Guidance System and an Automated Advance Unit. In a separate project with Integrated Sciences Incorporated (isi) of Longmont, Co., pcs has developed a machine-mounted ore-analyser (MMOA) which is capable of detecting high grade potash.
Potash mining in Saskatchewan makes extensive use of face-cutting techniques, employing large, continuous-mining machines. At the Rocanville division, mining is performed with a room-and-pillar method, using Marietta miners. Each room consists of multiple (usually three) parallel cuts or passes. A room conveyor is installed during the first pass and ore is fed to this location by a cross-conveyor on subsequent passes. The miner is about 11.5 m long, cuts a 2.4×7.8-m face, and weighs 226 tonnes. Typical advance rates are 30 cm per minute. Two views of the mining machine are shown on pages 76 and 78. The machine is made up of two main sections:
* The tractor frame and drive assembly–This section consists of the track and tramming motors used to drive the machine, and the frame on which the rest of the miner is carried. Tramming power is provided by either dc electric motors and solid state drive systems or through a hydrostatic drive.
* The cutting and conveying assembly–This assembly is supported on the tractor frame by hydraulic trim cylinders. Four motors containing changeable, hardened, steel-cutting tools, are used to remove most of the ore from the mine face. Trim chains run along the top and bottom to remove the rough edges left by the rotors. The rotors and trim chains are driven through the rotor drive gear case by four head motors. The rotors and head motors are mounted to the gear case to form the cutting mechanism. The cutting mechanism is joined to the conveying mechanism, which transports the mined material from the front of the machine to the rear.
The co-operative project between PCS, Prof Wilson and Carl Fisher of isi is directed toward automation of a continuous potash mining machine; it was initiated in 1983. To date expenditures have been about $800,000. The approach has been to automate the continuous miners in incremental steps — each element of automation being economically justified on its own merit. Development of automated ore grade analysis at the mine face and development of automated steering and advance rate control were identified as prime candidates for increased productivity, reduced operator fatigue, and health and safety risks.
Plans include integration of the various monitoring and control elements to provide fully automated, triaxial guidance of the continuous miners.
The MMOA developed by James Vance of pcs and Carl Fisher provides the operator with continuous analysis of ore grade at the face and provides instructions for vertical steering of the miner in order to maximize ore grade produced. In addition, it allows for storage and retrieval of detailed records of ore grade distribution. The MMOA relies on radiometric determinations of potash ore grade. Sylvite contains the radioactive isotope potassium-40 which is used to detect the richest potash ore. The MMOA uses an array of detectors to provide distribution of ore grade in the back, wall and floor. The grade-sensing system consists of seven thallium-doped sodium iodide scintillometers encased in lead shielding and steel plate. The individual sensors are arranged so that a detailed profile of ore grade may be provided.
The system is built around a rugged microcomputer — the Otrona Attache. This unit has been repackaged in a sturdy cast-aluminum chassis. Information is provided to the operator via a CRT screen, as well as LED and LDC indicators. A continuous power supply was developed to provide 110-volt output to the system. This power supply includes battery backup for two hours of operation, as well as high-speed switching to battery power during line power interruptions.
Data memory is provided by storage on magnetic disk using shock-mounted floppy disk drives. Ore grade data may be retrieved by either transporting disks to surface, or dumping data via cable to a second transportable data storage unit. The MMOA began commissioning in September, 1986. The system has the capability to interface with potential future systems such as an over-all mine communication network or other miner automation elements.
Using ultrasonic technology from the University of Saskatchewan, a lateral and vertical monitoring system was designed, constructed, installed and commissioned on a mining machine at Rocanville. Encouraged by the performance of the monitoring system, which provided the operator with an indication of the deviation of the actual position of the machine from the desired location, design proceeded on a controller for the automatic guidance in the lateral and vertical directions. Incorporated into the design are sensors for head motor and tram motor currents, which generate signals to control the forward advance rate. The system is being commissioned on a mining machine at PCS.
While the present design is concerned with automating the primary functions performed by the operator, further research and development is required to automate other functions related to conveyor installation (in first pass mining) and cross-conveyor positioning (in second and third passes). The future possibility of automation of guidance and advance rate systems is removal of the operator from the machine to a remote location. Several design challenges are part of this phase. First, the performance status of the machine must, at all times, be presented to the operator in a readily comprehensible form to which the operator can react. Second, information related to the operating status of the machine (for example, temperatures, oil pressures, voltages, currents, shaft speed, etc.) must also be communicated to the operator in a readily comprehensible form.
The research program to automate mining machines in the potash industry has focused on three major performance elements:
* impact on occupational environment;
* impact on productivity (utilization and availability); and
* impact on capital investment considerations.
The working environment of potash mine operators is less than ideal for optimal human performance. However, automation of the continuous miner will allow for relocation of the operator to a safer position of less heat, dust, noise and loose ground.
Direct productivity improvements of the mine may be facilitated by increasing the utilization of continuous miners. These improvements may result from overcoming geological, system and human limitations. The miner automation program will reduce the primary geological constraint by sensing the vertical ore grade distribution and positioning the cutting head at the optimum position within the potash bed. System logistics may be improved with automation. The automation system will provide the capability of miner operation through periods of scheduled downtime by being set into an operating mode before the operator leaves the face. The system would be u
nder the constraint that an automatic shutdown would be effected if any sensors malfunction or if operating conditions deviate outside control setpoints. An automated system will allow for productivity improvement through reduced human error. Control programs may be developed with multiple levels of checks and balances so that, if a malfunction or error occurs, the machine will shut down. The consequences of control system failure can thus be minimized.
A miner automation system may improve mine productivity by making equipment more available. Non- available time consists of the percentage of scheduled mine operating time when the miner is unavailable because of maintenance. An automated system will reduce maintenance requirements by reporting and correlating operating conditions and miner performance. After identification of key conditions which indicate a need for maintenance, the system would provide an alarm signal and readout to alert the operator that performance has deteriorated and that maintenance is required.
The underlying motivation to develop automated continuous miners is to achieve fundamental productivity improvements and economic benefits. There must be a positive return on the investment made in the research and development program, and this return should exceed the return expected from alternatives. Certain risks in the research and development of automation can be mitigated through project design. This may be possible where automation can be accomplished through a progression of relatively low-risk steps. Using this method, the amount of capital required to achieve program goals is reduced, and better measures of performance of the systems are possible during commissioning and evaluation of the automation accessories. Joyce Musial is a Toronto-based geologist and freelance writer. REFERENCES Vance, J. B. (1986): Automation of Large Continuous Miners for the Potash Industry. Presented at Symposium on Application of Automation in Mining: Present and Future, Sudbury, Ont, October, 1986, 19 p. Vance, J. B. and J. N. Wilson (1987): Developments in Potash Miner Automation. Presented at Seminar on Future Mining Technology, Devon, Alta., February, 1987, 21 p. *
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