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英文原文
Us Bureau of Mines Coal Mining Automation Research
J H WELSH and J E BEVAN
ABSTRACT
The US Bureau of mines is conducting research to improve the health and safety for underground coal miners, and the efficiency of the mining systems that are used. In 1986, the Bureau began a major research effort on the technology for computer-assisted mining systems for underground coal mines. The initial target was technology for continuous mining machines that would allow them to extract coal by computer-assisted operation, Technology areas being investigated include guidance systems, computer systems, machine control, human-machine interfaces and planning. In each of these areas, individual system development has progressed to where underground testing of these systems will begin in 1991.
In addition to coal extraction, the Bureau has also begun research for the development of technology for computer-assisted roof bolting. The Bureau is developing technology for a “smart” roof bolter that would be able to sense and analyze strata conditions to determine the location of the hole, drill the hole to length, and select and install the appropriate bolt.
The research on the continuous mining and the roof bolter are well advanced.
INTRODUCTION
Working in underground coal mines continues to be one of the most hazardous of occupations, Between 1984 and 1989, 14181 accidents occurred at the face area of continuous mining section in US underground coal mines. This was 18 percent of all injuries and 21 percent of all fatalities and permanent disabilities. In addition, face workers are exposed to health hazards such as equipment noise, where in 1988, 6981 new black lung cases were filed in the US.
The traditional approach to health and safety problems in mines has been to reduce the hazard through ground control, dust control, methane control, and noise control. While this approach has been very successful in the past in reducing the hazards in mines, health and safety hazards still exist, and accidents and health problems are still occurring. To make a further significant reduction in the number of accidents and exposures to health hazards, a new approach is needed.
In 1986, the Bureau of Mines initiated a new approach that would allow workers to be relocated from the face to a safe, healthful environment, where they could perform their jobs.
Although this approach had been thought of earlier, only recent advancements in computer and sensor technology have made it a viable alternative.
While health and safety is a major concern, technology that would also provide for improvements in mining efficiency was also desirable. Recent statistics show that continuous miners only extract coal about 32 percent of the available shift time.
This means that even small improvements in mining efficiency could result in dramatic in productivity.
Over the last several years, a Bureau of Mines program for computer-assisted mining has been developed that is centered around a comprehensive long-range research plan that targets the goals of the program and provides a coordination of research. This research effort involves multiple projects and researchers at different Bureau centers. In the near term, research targets current, commercially available mining equipment operating in typical mining section. The target is further defined to a continuous mining section with room-and- pillar, longwall development. This scenario was selected because it has wide applicability to US mining, and stands to make a significant impact on the health, safety, and efficiency of the US mining industry. Research for computer-assisted mining systems includes coal extraction with a continuous mining machine, roof bolting, haulage, and ventilation. For the longer term, researchers will investigate mining systems and concepts to determine if new mining systems that can take advantage of advances in robotics technology should be pursued, and/or if changes in the mining methods show promise of health, safety, and efficiency improvements.
COMPUTER-ASSISTED MININNG, DEFINED
A typical continuous mining section consists of a continuous mining machine, a roof bolting machine, and one or two shuttle cars. The face area where this equipment is operating, and where unsupported roof is exposed during the extraction process, poses the greatest threat in terms of health and safety to the workers. With computer-assisted mining, sensors and computer technology would be added to the face equipment to allow the operator to be relocated to a control room positioned 150 to 180 meters outby the face.
The control room would be positioned in fresh air, and the environment would be controlled to provide a healthful work area with little or no dust and noise. Various levels of computer-assisted mining exist, from teleoperation to computer-assisted operation, and are described in the remainder of this section.
To operate mining equipment at the face from a control room which is not im line-of-sight view of the equipment, the operator must rely on information from sensors and video cameras installed on the equipment. Initial research will involve teleoperation, where the operator essentially performs the same job as he/she would when operating the mining equipment, only at a remote location. The operator will rely on input from the video cameras installed on the machine and/or in the area of operation, sensors that provide the position of the movable parts(cutting boom, gathering pan, conveyor, etc.) of the machine, guidance sensors that provide information that an operator would normally have available at the face, such as face noise.
A computer system will collect the data from the sensors, present the information to the operator through a human interface such as graphics or dials and gauges, and control movements of the machine based on operator initiated commands.
As more sensors are installed on the equipment and more intelligent computer software is developed, the machine-control scenario will evolve to computer-assisted operation. The computer control system will progressively make more of the routine decisions to where the operator only intervenes when an abnormal situation arises, such as when a completely new situation is encountered. Machine actions are automaticallly initited by the control computer based on sensor input and software analysis and decision-making. For this type of operation, additional sensors and intelligent software are required than for teleoperation. Sensors for machine position and heading, machine condition, the position of the moveable parts of the machine, and the type of material the machine is cutting are needed. The software must guide the mining machine following a plan that can be altered by local conditions and events as determined from real-time sensor input.
The human element for machine operation is always expected to be needed in underground coal mines because of the variability of conditions that are encountered and the difficulty to develop sensors and computer software that can provide the same level of intelligence and perception as a human.
The objective of this research is to evaluate and develop the enabling technology for computer-assisted continuous mining and roof bolting machines. Work is also on-going in other areas such as ventilation for computer-assisted mining(Volkwein, Goodmanand Thiemens,1990) and continuous haulage systems(Bhatt,1990). The remainder related to these two machines. Additional details on the computer-assisted mining program can be found in the references(Schnakenbenberg, 1988,1989,1990).
COMPUTER-ASSISTED CONTINUOUS MINING MACHINE
Technology components
The technology components required for any intelligent machine system are the guidance system, machine condition system, computer system, machine control, human-machine interface and planning. For a computer-assisted machine, the same list applies, where the basic machine is a drum-type continuous mining machine.
Guidance system involve both horizontal movements of the mining machine in the mine space and vertical movements of the cutting boom. For a horizontal guidance, a computer-assisted mining machine must not only be able to guide itself while it is extracting coal, but also while moving throughout the entire mine. This requires sensors to provide information on machine location coordinates(x,y), machine yaw(heading), and the location and distance to mine walls and obstacles. The computer system must to take this sensor information, and using stored knowledge, plan machine moves, position the machine at the face so cutting can occur, and construct or update maps, all in real-time. The Bureau has divided the horizontal navigation problem into there areas: the face , the section, and the whole mine. The face navigation problem is being investigated first. Once this problem is solved, navigation in the section and the whole mine will be relatively easy.
A computer-assisted mining machine must also be able to keep its cutting boom within the coal seam and mine only coal, or to some other particular pattern depending on the requirements and geology at the mine site. For vertical guidance of the cutting boom , a sensor system is needed that can determine the thickness of coal left on the roof or floor, or that can determine when the cutting action crosses the boundary from coal to rock. This research is known as coal-rock interface detection(CID).
Machine condition involves the determination, in real-time, of the condition of the major electrical and hydraulic components of a continuous mining machine, to aid in the efficient and timely repair of the machine when a failure occurs. Ultimately, this system should be able to predict a component failure in advance of its occurrence so that maintenance can be scheduled during nonproduction times. Since machine downtime is a significant factor in the low production time experienced with continuous mining machine, an increase in machine availability will have a significant impact on efficiency and productivity.
Computer systems provide the backbone for computer-assisted mining. The computer must interface to a variety of internal(machine system) and external(surrounding environment) sensors, gather data from the sensors, make decision based on the real-time sensor data, and initiate and carry out machine control.
Machine control involves establishing accurate computer(Sammarco,1988a) of the moving parts of the mining machine including cutting boom, gathering pan, conveyor, stabilizer jack, and locomotion tracks. Closed-loop computer control or control based on sensor feedback must be established which is accurate and stable. To establish closed-loop control, the following tasks are required: select a sensor that provides the position of the machine part to be controlled; develop the computer-sensor and machine-sensor interface; test the machine and sensor system; analyze the data; formulate control algorithms; test the control in free space; test the control under mining conditions(cutting simulated coal); analyze data.; repeat the above steps as necessary.
Human-machine interface are required so that an operator can interact with a computer-assisted machine to provide efficient machine control. An operator may interact with the machine through an interface to provide new information, change priorities or plans, or intervene when a new condition or situation is encountered.
Planning refers to the software that is necessary to control the whole machine process, to make a mining machine operate according to some predetermined sequence. In a robot factory floor application, where a robot is performing a routine, repetitive action, software to control the robot is simple. However, with a mining machine, the situation is much more complex. The environment can change; and the mine geometry changes as coal is mined. The planner software must be able to react to changing conditions and initiate an appropriate action for the condition encountered, all in real-time.
These are the areas in which researchers are evaluating and developing the enabling technology for computer-assisted mining. The status of this development is discussed in the next section.
Technology evaluation and development
Since the start of the computer-assisted mining program, significant progress has been made in each of the technology areas required. A navigation scheme for horizontal guidance(Anderson,1989a) was defined for a computer-assisted mining machine operating in a room-and-pillar, two-pass mining scenario. The navigation scheme, makes use of both on-and-off machine sensors that work together to provide the information needed for navigation. Sensors selected for evaluation and development are a laser gyroscope, ultrasonic rangers, a mechanical line pull system, and clinometers. (Note: A fluxgate compass was tested early in the program and was determined to be unsuitable for mining machine navigation, Sammarco, 1990). The laser scanner system (Anderson, 1989b) uses commercially available laser units that are mounted on an off-machine reference structure. It scans a horizontal plane for retroreflective targets within its 11m range and 105°field of view.
The retroreflective targets are mounted on the mining machine. The laser scanners determine the angular position of the detected targets. In the present configuration, two laser scanners and two targets are used. When the targets are placed in a known, fixed geometry on the mining machine, the x-y position and yaw of the mining machine are determined by triangulation by the angles reported by the laser. Another navigation system, similar to the laser scanner system, is a mechanical position and heading system(Jobes,1990). It uses line-pull liner transducers mounted on the mining machine(two transducers on each corner), with the ends of the transducer pair cords connected to the ribs on opposite sides of an entry or to opposite sides of a reference structure. Through triangulation this mechanical line-pull system also provides x-y position and yaw of the mining machine.
The on-board navigation systems(Sammarco,19988b) include a gyroscope, clinometers, and ultrasonic ranging devices. The gyroscope id used for short-term control of machine heading relative to a previous heading. Clinometers provide pitch and roll of the machine. Ultrasonic ranging devices are used for indicating the position of ribs and corners, and locating obstacles.
At present, each of the navigation sensors, except the ring laser gyroscope, has been individually tested and evaluated on the surface for performance and accuracy. Underground testing is scheduled to begin in February 1991. Since each of the individual sensing system has limitations, the present navigation concept for mining machine guidance will involve the fusion of data from each of the systems, utilizing the most accurate readings to update references for the other systems.
For vertical guidance of the cutting boom, coal-rock interface sensors are being developed. As with horizontal guidance, multiple coal interface sensor systems are being investigated and will work together through fusion of sensor data, this is necessary in most US coal seams because geology varies widely, even locally, to such an extent that a single sensor system will not able to provide accurate guidance. Techniques being investigated include machine vibration, in-seam seismic vibration, natural gamma radiation, infrared thermography, radar, and x-ray fluorescence.
The approach for machine and in-seam seismic vibrations(Mowrey,1990a) are similar. Accelerometers are used to sense vibration signals generated as the mining machine is cutting coal or rock material. In one case they are attached to the mining machine to sense machine vibration, and in the other they are attached to the coal, roof, and/or floor, to sense in-seam seismic vibration. Different signals are generated when the mining machine is cutting coal versus when it is cutting rock. Powerful, intelligent signal processing software, called adaptive signal discrimination networks, are used to discriminate the difference in signals, in practice, for a given geology, the system is initially trained by purposely cutting coal, and then rock, to show the system what the vibration signals look like in each case. The system then develops a set of classifiers that are used to determine what accuracy achieved so far is 65 to 75 percent correctly classified. Efforts are focused on ways to improve the accuracy to better than 90 percent.
Natural gamma radiation sensor systems(Maksimovic and Mowrey, 1990) have been used successfully in Europe to determine remaining roof coal thickness to guide the vertical cutting of longwall shearers.
These sensors are also commercially available from two US suppliers, and have been used in several mines in the US with some successes. To use this sensor system, the immediate roof material must be shale-type, which typically has higher natural gamma radiation than does coal. Bureau research for natural gamma radiation sensors is investigating the geology of the major US coal seams to determine how widespread the applicability of this technique is. In addition, sensor placement, range of accuracy, and guidance off the mine floor are being investigated.
Infrared thermography system(Mowrey,1990b) are able to detect changes in thermography energy produced as a mining machine cuts materials of different hardness. For example, as a mining machine cuts coal, a certain amount of thermal energy is produced. As the cutting picks begin to strike a harder sandstone roof, more thermal energy may be produced. An infrared themography system that can detect thermal energy produced can be used to determine when the cutting action has crossed the boundary from coal to roof strata. Researchers are using both an infrared thermal camera that can view the whole face area, and an inexpensive point thermal sensor that can be aimed at a particular bit, to determine thermal energy produced.
Another technique for CID is a radar coal thickness system. A non-contacting radar sensor that measure the complex reflection coefficient at the surface of any material, as a means to determine the thickness of coal left, is being developed. A network analyzer is used to resolve sub-wavelength dimensions by making matrix measurements in the frequency and apace domains. Research is concentrating on developing the computer models and antenna fixtures for this system. Preliminary underground tests to measure roof coal and rib thickness produced good results, where coal thickness was measured within 6mm.
An X-Ray fluorescence system for coal-rock interface detection is in preliminary stages of investigation.
The bureau is addressing the problem of machine condition and failures by applying computer and sensor technology to the hydraulic and electrical systems of a continuous mining machine. For hydraulic system diagnostics(Mitchell,1990), a sensor-based expert system technique is being used to assist in the detection and determination of the cause of failures in hydraulic components. The knowledge of maintenance and hydraulics expert is incorporated into the knowledge base of an expert system. This knowledge, along with real-time information supplied by hydraulic system sensors on the mining machine, are used by the expert system to detect and diagnose component failures. Sensors include temperature, flow, pressure, fluid level, and contaminents in the hydraulic fluid. A graphic interface is being developed to assist in system operation and diagnosis. A future addition will add prognosis capability so degradation of hydraulic system components can be detected in advance of failure to avoid downtime during production time.
A diagnostic system has also been developed for the electrical control circuit of a continu