Radiant energy – Photocells; circuits and apparatus – Housings
Reexamination Certificate
2001-05-30
2002-09-17
Le, Que T. (Department: 3673)
Radiant energy
Photocells; circuits and apparatus
Housings
C250S214100
Reexamination Certificate
active
06452163
ABSTRACT:
BACKGROUND
The invention described herein generally relates to an apparatus for detecting the presence of rock during coal mining operations, and more particularly, to an armored detector system, utilizing sensitive monitoring equipment, such as radiation detecting equipment, which is used in mining operations to allow removal of essentially all the coal with very little cutting into the rock above and below the coal.
The use of sensitive monitoring equipment in mining operations is well known. It is further known that radiation sensors in particular are well suited for use in coal mining operations. Their conventional use allows for limited control of the cutting depth for a variety of continuous excavators used in mining operations. However, effective use of gamma detectors has been impaired due to the inability to place the detectors such that they can accurately measure the thickness of the coal remaining to be cut or, in effect, to accurately measure the distance between the cutter and the rock that is to be avoided. Conventionally, suitably sized detectors have only been able to make real-time measurements at locations other than in the region actively being cut and then have inferred or calculated, in a somewhat indirect manner, the parameter that ultimately must be known; namely, the distance from the cutter to the rock. Further, such conventional approaches have tried to project cutting decisions to future or succeeding cuts rather than making real time cutting decisions during the current cutting stroke. Such approaches have only had limited success, particularly on continuous miners, because of the large variations in the formations, cutting conditions and other operational variables.
In coal mining operations, radiation sensors, such as gamma sensors, are currently used to detect radiation emissions from layers of fireclay and shale and other non-coal materials in the surrounding ground. Radiation is emitted from non-coal layers in various quantities dependent upon the type of non-coal material. As the radiation passes through the coal from the rock, it is attenuated. It is this attenuation that is measured, or counted, to determine when cutting should be halted to avoid cutting into the rock. Counting gamma rays must be accomplished over a period of time because the nature of radiation is statistical, having an emission rate that is represented by a Gaussian distribution around some central value.
The most accurate measurements of the distance from the cutter to the rock to be avoided is to place the sensor near the region of the mineral being cut, rather than at a distance away or near some other region. Data must be accumulated over time in order to average the readings so as to establish that central value. Since the radiation in a coal mines is relatively weak, the view angle needs to be large in order to obtain data in a sufficiently short time in order to be used to control real-time cutting actions. But, large view angles in conventional devices have resulted in viewing radiation sources other than from the region that needs to be measured so this makes the measurement inaccurate. In other words, choosing a narrow viewing angle has reduced the count rate, requiring more time which resulted in decreasing the accuracy since the miner is active and must continue. But, making the view angle wider also has reduced the accuracy.
It is also known that radiation detecting equipment is sensitive and must be protected from harsh environments to survive and to produce accurate, noise free signals. This protection must include protection from physical shock and stress, including force, vibration, and abrasion, encountered during mining operations. However, the closer in proximity equipment is to the mineral being mined, the greater is the shock, vibration and stress to which the equipment is subjected. Thus, there is a tension between placing conventional radiation detectors close to the surface being mined to make accurate measurements and providing adequate protection to ensure survival of the sensor and to avoid degradation of the data by the effects of the harsh environment. Conventionally, the need to assure survival of the sensor has resulted in placement of the sensor away from the target of interest. Another conventional approach has been to make the sensing element smaller so that it can be more easily placed in a strategically desirable location, but the sensitivity of the element drops as the size is reduced, and again, the accuracy reduces in a corresponding fashion.
One method of mining coal is continuous mining, in which tunnels are bored through the earth with a machine including a cutting drum attached to a moveable boom. The operator of a continuous mining machine must control the mining machine with an obstructed view of the coal being mined. This is because the operator is situated a distance from the cutting made by the picks on the cutting drum and his view is obstructed by the portions of the mining machine as well as dust created in the mining operation and water sprays provided by the miner. Another method of mining coal is longwall mining, which also involves the use of a cutting drum attached to a boom. In longwall mining, as compared with continuous mining, the drum cuts a swath of earth up to one thousand feet at a time. Both continuous mining machines and longwall mining machines are used in very harsh conditions.
Mining operations are more efficient when the coal-rock boundary is accurately determined. By accurately determining the coal-rock boundary, the unnecessary removal of rock is minimized, while the amount of coal removed is optimized. Due to the impaired ability of mining machine operators from accurately visualizing the surface being mined, operators often cut beyond the coal-rock boundary, often cutting into rock, adding tremendously to the cost of mining due to increased removal costs, lower coal yield efficiency, and greater replacement costs for the cutting tools on the cutting drums.
It is known that sensors can be mounted on the mining machines somewhat near the cutting drum. See, for example, U.S. Pat. No. 4,981,327 (Bessinger, et al.). Bessinger, et al. describes a method and apparatus for sensing a coal-rock interface during longwall mining by placing the sensor in a cowl adjacent the shearer drum. A disadvantage of conventional devices such as the device described in Bessinger, et al. is that such devices measure radiation after the leading drum of the mining machine has completed its cutting pass, rather than measuring ahead of the cutting. Hence, the Bessinger device may lead to the disadvantage of incompletely cutting the coal seam or cutting beyond the coal-rock boundary and into the rock before determining that the cutting operation had extended beyond the coal layer. If the leading drum has removed all the coal, the sensor cannot distinguish between the conditions of barely having removed all the coal to the interface to having removed some of the rock as well. On the other hand, if some coal is left so as to provide a basis for control, this residual coal is left unmined. Without being able to differentiate between these two cutting conditions, the control system does not know how to effectively respond and either may not respond fast enough or may respond inappropriately. The detector will not be able to determine if the control system has overreacted or under-reacted until the detector reaches the region that has been cut. More importantly for continuous miners, placement of a sensor in front of a cutter drum, as for the follower drum in Bessinger, et al., is obviously not possible.
Other sensors have been known to be positioned approximately where the schematically illustrated sensor D (
FIG. 1
) is shown on a mining machine. As with the Bessinger device, sensor D senses radiation after the cutting pass has occurred and cannot determine distance to the rock unless some coal is left through which measurements are made. Furthermore, the known sensors lack the requisite ruggedness to be properly positioned to acc
Frederick Larry D.
Medley Dwight
Dickstein , Shapiro, Morin & Oshinsky, LLP
Geosteering Mining Services LLC
Le Que T.
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