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l/> no/I/I BUREAU OF MINES 
 
 U SJ244 INFORMATION CIRCULAR/1990 
 
 Longwall Automation: A Ground 
 Control Perspective 
 
 By Jeffrey M. Listak and Deno M. Pappas 
 
 U.S. BUREAU OF MINES 
 1910-1990 
 
 THE MINERALS SOURCE 
 
Mission: Asthe Nation's principal conservation 
 agency, the Department of the Interior has respon- 
 sibility for most of our nationally-owned public 
 lands and natural and cultural resources. This 
 includes fostering wise use of our land and water 
 resources, protecting our fish and wildlife, pre- 
 serving the environmental and cultural values of 
 our national parks and historical places, and pro- 
 viding for the enjoyment of life through outdoor 
 recreation. The Department assesses our energy 
 and mineral resources and works to assure that 
 their development is in the best interests of all 
 our people. The Department also promotes the 
 goals of the Take Pride in America campaign by 
 encouraging stewardship and citizen responsibil- 
 ity for the public lands and promoting citizen par- 
 ticipation in their care. The Department also has 
 a major responsibility for American Indian reser- 
 vation communities and for people who live in 
 Island Territories under U.S. Administration. 
 
Information Circular 9244 
 
 Longwall Automation: A Ground 
 Control Perspective 
 
 By Jeffrey M. Listak and Deno M. Pappas 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Manuel Lujan, Jr., Secretary 
 
 BUREAU OF MINES 
 T S Ary, Director 
 

 Library of Congress Cataloging in Publication Data: 
 
 Listak, Jeffrey M. 
 
 Longwall automation : a ground control perspective / by Jeffrey M. Listak and 
 Deno M. Pappas. 
 
 p. cm. - (Information circular, 9244) 
 
 Includes bibliographical references. 
 
 Supt. of Docs, no.: I 28.27:9244. 
 
 1. Longwall mining-Data processing. 2. Ground control (Mining). I. Pappas, 
 Deno M. II. Title. III. Series: Information circular (United States. Bureau of 
 Mines); 9244. 
 
 TN295.U4 
 
 [TN275] 622 s-dc20 [622\334] 
 
 89-600351 
 CIP 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 2 
 
 Background 3 
 
 Longwall ground control 4 
 
 Problems inherent in longwall mining 5 
 
 Pressure distribution 5 
 
 Bumps 5 
 
 Sloughing 5 
 
 Cavities 5 
 
 Geologic conditions 5 
 
 Lithologic changes 7 
 
 Structural relief 8 
 
 Panel continuity 8 
 
 Longwall layout and design 8 
 
 Subsidence 9 
 
 Multiple-seam mining 9 
 
 Gate road pillar design considerations 9 
 
 Longwall automation state of the art 9 
 
 Roof supports 9 
 
 Shearer automation 11 
 
 Cutting horizon 11 
 
 Face alignment 12 
 
 Shearer position 12 
 
 Component integration 12 
 
 Constraints affecting longwall automation 13 
 
 Ground control constraints 13 
 
 Shearer 13 
 
 Roof supports 14 
 
 General constraints 14 
 
 Bureau research 15 
 
 Conclusions 15 
 
 References 15 
 
 ILLUSTRATIONS 
 
 1. Number of U.S. longwall faces 2 
 
 2. U.S. longwall production 2 
 
 3. Cost breakdown of longwall components 2 
 
 4. Representation of gamma-ray backscatter device 4 
 
 5. Relationship between backscatter count rate and coal thickness 4 
 
 6. Natural gamma radiation sensor 4 
 
 7. Stress distribution profile in roof of typical longwall section 6 
 
 8. Entry after bump occurrence 6 
 
 9. Face sloughing 7 
 
 10. Cavity or void along longwall face 7 
 
 11. Fence diagram showing changing lithology above a longwall panel 7 
 
 12. Stream valley profile 8 
 
 13. Sandstone channel 8 
 
 14. Fault- 9 
 
 15. Trends in longwall shield controls 10 
 
 16. Schematic showing two types of electrohydraulic systems for shield control 10 
 
 17. Infrared technique used for shearer-initiated face advancement 13 
 
 18. Rock on face conveyor 14 
 
TABLES 
 
 Page 
 
 1. Intelligent mining machines critical systems and technologies 11 
 
 2. Status of shearer automation devices 12 
 
 3. Summary of longwall automation monitoring devices 12 
 
 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 
 
 cps 
 
 count per second min minute 
 
 ft 
 
 foot pet percent 
 
 ft/min 
 
 foot per minute s second 
 
 in 
 
 inch 
 
LONGWALL AUTOMATION: A GROUND CONTROL PERSPECTIVE 
 
 By Jeffrey M. Listak 1 and Deno M. Pappas 2 
 
 ABSTRACT 
 
 This U.S. Bureau of Mines report describes the implications of in-mine ground control on the 
 automated or remotely controlled operation of longwall mining equipment. Perhaps the greatest 
 challenge to longwall automation researchers is the development of systems that will continuously 
 function in the complex and unpredictable underground environment. The high degree of environmental 
 variability, together with conditions brought about by the extraction process, makes complete automation 
 of longwall mining a difficult task. The intellectual thought processes and split-second decision making 
 required to avert disasters are lost when workers are removed from the face. As many mine operators 
 can attest, minor problems, left unresolved, can eventually accumulate and lead to catastrophic 
 consequences. The automation process will have to assess and manage various routine problems that 
 are otherwise resolved through worker observation and experience. 
 
 fining engineer. 
 
 2 Research civil engineer. 
 
 Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 
 
INTRODUCTION 
 
 In 1983, the number of operating longwall faces in U.S. 
 mines peaked at 118 faces (i), 3 producing an estimated 
 16 pet of the underground coal mined (figs. 1-2). By 1987, 
 the number of faces had dropped to 101 (2), yet longwall 
 mining produced over 21 pet of the underground coal 
 mined. It is apparent that longwall productivity is increas- 
 ing at an accelerating rate. Productivity statistics support 
 this trend. In 1983, 64.7 face tons per worker day were 
 being produced. By 1987, this number had doubled to 139 
 face tons per worker day (3-4). This marked increase in 
 productivity maybe attributed to improvements in longwall 
 operation techniques, a leaner work force, and equipment 
 sophistication. This trend will probably continue, espe- 
 cially with the development of semiautomated and, in the 
 future, completely automated longwall faces. 
 
 With few exceptions, large mining companies have 
 come to realize that the only way their mines can stay 
 competitive in the domestic and world markets is to adopt 
 
 Italic numbers in parentheses refer to items in the list of references 
 at the end of this report. 
 
 1979 1981 1983 1985 1987 1989 
 Figure 1. -Number of U.S. longwall faces. 
 
 longwall mining methods (5). Consequently, underground 
 coal mining is moving toward high-production longwall 
 systems. Currently, much time and effort are being spent 
 in the development of semiautomated and automated 
 production longwall systems. Although advances have 
 been made, several key factors related to underground 
 conditions need to be integrated into the overall design 
 of an automated longwall system. Adverse geomechanical 
 conditions are one of the most debilitating problems faced 
 by longwall operators in terms of both production losses 
 and accidents. A seemingly insignificant ground control 
 condition could eventually interrupt the activity of the 
 shearer, shields, or conveyor, any of which interruptions 
 would halt the production of coal. Therefore, the success 
 of an automated longwall system will depend on the ability 
 of all the automated components to overcome geomechan- 
 ical problems encountered during the course of longwall 
 panel extraction. The initial capital expenditure required 
 for providing face support to a longwall system emphasizes 
 the necessity of coping with ground control conditions. 
 Figure 3 shows that over 70 pet of the total cost of long- 
 wall face equipment goes toward the cost of the longwall 
 supports. 
 
 It is the intent of this report to review the state of the 
 art in longwall automation and to identify ground control 
 conditions that may affect the operation of an automated 
 longwall system. This research is in support of the 
 U.S. Bureau of Mines goal to develop longwall systems 
 that allow for continuous and autonomous operation. 
 
 I983 I984 I985 I986 
 
 Figure 2.-U.S. longwall production. 
 
 I987 
 
 Figure 3.-Cost breakdown of longwall components. 
 
BACKGROUND 
 
 The need for longwall automation was first recognized 
 and addressed by the British in the early 1960's, with the 
 Remotely Operated Longwall Faces (ROLF) program of 
 the National Coal Board (NCB). This ambitious program 
 attempted to automate the longwall system as a whole; 
 however, at the time, mechanization was not developed to 
 the level of reliability necessary to make automation fea- 
 sible (6). By the end of the 1960's, the program was ter- 
 minated; the lesson learned was that, for an automation 
 program to be successful, a step-by-step approach of 
 looking at each longwall component separately is required. 
 The results of this work laid the foundation for the de- 
 velopment of electrohydraulically controlled supports, 
 which utilize an electrically activated compacted solenoid 
 valve for controlling the hydraulic systems for the roof 
 supports (7). Although it took nearly 20 years for the 
 electrohydraulically controlled supports to become com- 
 mercially available, this technology was a major contri- 
 bution to automating the longwall mining system. A de- 
 tailed description of electrohydraulic control of supports 
 is presented later in this report, in the section "Roof 
 Supports." 
 
 Another NCB initiative, known as the Advanced Tech- 
 nology Mining (ATM) program, was aimed at improving 
 production and productivity on longwall faces by consol- 
 idating the reliability of proven equipment and moving in 
 small steps toward automation (6-7). Out of this program 
 developed two types of nucleonic sensors for detecting the 
 coal-roof interface as the shearer is cutting. The first 
 nucleonic probe basically consists of a transmitter with a 
 radioactive source, usually cesium- 137, and a receiver that 
 detects the radiation. The gamma-ray backscatter device 
 consists of a gamma radiation source that is directed onto 
 the roof material and a method of radiation detection to 
 monitor the backscatter ed radiation from the roof (8). As 
 shown in figure 4, the sensor, known as the gamma-ray 
 backscatter sensor, is enclosed in a housing positioned 
 near the surface to be measured (9). A narrow beam of 
 gamma rays is directed against the rock and is subject to 
 scattering processes and attenuation. The amount of in- 
 cident rays that are backscattered is inversely proportional 
 to the density of the rock type. Figure 5 (10) illustrates 
 the relationship between backscatter and coal thickness. 
 In order for the probe to work accurately, it has to be in 
 close contact with the surface of the roof; an air gap or 
 void significantly reduces the accuracy of the results. In 
 addition, the presence of a radioactive source in the probe 
 was a major detriment toward further development. From 
 these disadvantages evolved the second sensor, referred to 
 
 as the "natural gamma background sensor" (fig. 6/1). This 
 system allows the coal thickness above the shearer to be 
 measured using the background radiation naturally emitted 
 by most strata composed of shale (6). Radiation from the 
 roof rock is attenuated exponentially by any coal left in 
 place (8, 11-12). The coal thickness can be measured 
 using an empirically determined attenuation curve, shown 
 in figure 6B. Voids and air gaps are not a problem with 
 the natural gamma background sensor; however, the probe 
 does not work for nonshale strata. 
 
 By 1980, the second probe was refined and mounted on 
 the shearer along with a computer-based control data 
 transmission system and was termed the "System 70000" 
 (6). This system has recently become commercially avail- 
 able as the Machine Information Display and Automation 
 System (MIDAS) 4 (13). 
 
 At the same time the NCB's ATM program was being 
 developed, the U.S. Bureau of Mines began its longwall 
 automation program focusing on shearer guidance sensors 
 to detect the seam roof or floor interface. Three types of 
 systems were developed (14): 
 
 • Vertical Control System (VCS).-VCS sensors in- 
 clude coal interface detectors, last cut height sensors, and 
 interface connections to the shearer drum arm actuators 
 and controls. 
 
 • Face Alignment System (FAS) -FAS sensors include 
 coal face alignment sensors measuring the yaw and roll, 
 and interface connections to the roof support and shearer 
 tilt actuators. 
 
 • Master Control System (MCS).-MCS components 
 include the software, controls, and information display 
 necessary for operators to control the longwall operation 
 from the headgate location. 
 
 When the U.S. Department of Energy (DOE) took over 
 some of these Bureau projects, the VCS was field tested. 
 Unfortunately, ?}>& trial run was discontinued owing to very 
 severe ground control conditions. The DOE continued to 
 work on surface recognition and coal depth measuring 
 sensors. These sensors and detectors included nucleonic, 
 electromagnetic, radar, and machine vibration types. 
 
 Recent developments in longwall automated systems 
 are presented in the section "Longwall Automation State 
 of the Art." 
 
 Reference to specific products does not imply endorsement by the 
 U.S. Bureau of Mines. 
 
Rock 
 
 0M&0MMXM&Mi 
 
 A 
 
 Scattering and attenuation 
 of gamma rays 
 
 Protective mounting 
 
 Detector - 
 
 Arm 
 
 on shearer 
 
 Source surrounded 
 by heavy metal 
 shielding 
 mounted 
 
 
 //»'•' 
 
 Shale 
 ( radiation source) 
 
 Coal 
 
 ( absorber) 
 
 Sensor to 
 detect roof 
 contact 
 
 Figure 4. -Representation of gamma ray backscatter device. 
 [Adapted from Wood (9)] 
 
 Gamma 
 detector 
 
 £ 400 
 
 i i 
 
 i i 
 
 o 
 
 
 
 LU 
 
 
 
 b 300 
 
 — 
 
 / - 
 
 < 
 
 
 
 rr 
 
 
 
 £ 200 
 
 
 - 
 
 3 
 
 
 
 O 
 
 
 
 ° 100 
 
 i i 
 
 i i 
 
 300 
 
 2 4 6 8 
 
 COAL THICKNESS, in 
 
 10 
 
 Figure 5.-Relationship between backscatter count rate and 
 coal thickness. [Adapted from Clayton (10)] 
 
 2 4 6 8 10 12 14 
 
 COAL THICKNESS, in 
 
 Figure 6.-Natural gamma radiation sensor. A, Schematic 
 representation; B, calibration curve. [Adapted from Tregelles 
 (12)] 
 
 LONGWALL GROUND CONTROL 
 
 Longwall ground control can be defined as a method 
 of managing an unstable underground opening resulting 
 from the redistribution to roof support elements of forces 
 induced in the roof, rib, and floor during the mining pro- 
 cess. Longwall mining ground control is of paramount 
 
 importance because effective strata control is to the coal 
 operator's advantage in mining the coal, while ineffective 
 control is to the coal operator's detriment in that bad 
 conditions could result in the abandonment of the mine 
 section or entire mine. 
 
There are three major aspects of ground control that 
 need to be considered when addressing the longwall auto- 
 mation program: the ground control problems inherent in 
 the longwall method of mining, the ground control prob- 
 lems stemming from the changing geologic conditions 
 found in all underground mines, and the unique ground 
 control problems related to the different designs and 
 layouts of longwall panels. 
 
 PROBLEMS INHERENT IN LONGWALL MINING 
 
 The longwall system of mining coal in 665- by 5,000-ft 
 panels (average dimensions) with the roof caving behind 
 the face and several gate road entries separating the panels 
 presents ground control problems unique to underground 
 mining. The total extraction of a large block of coal 
 causes high stress concentrations, along the face and in the 
 gate roads, and poses some difficult ground control prob- 
 lems depending upon the competency of the immediate 
 and main roof rock. The following areas need to be con- 
 sidered for the successful design and implementation of 
 an automated longwall system. 
 
 Pressure Distribution 
 
 When the mine entries are developed, the preexisting 
 stress equilibrium is destroyed because of the extraction of 
 the coal. The weight of the overburden previously sup- 
 ported by the excavated coal must now be carried by the 
 neighboring solid coal in the panel and the pillars. These 
 regions, where the vertical pressures exceed the average 
 overburden pressure, are referred to as the "abutments" 
 (15). Figure 7 shows a typical pressure redistribution 
 pattern including the front and side abutment and the 
 pressure buildup in the gob. In the overall design of an 
 automated longwall system, the pressure distribution along 
 the face and gate roads needs to be examined for the 
 following reasons: (1) pillars must be sized to support 
 anticipated loads, (2) roof falls are inevitable under some 
 extremely poor roof conditions and the automated system 
 must be protected from such events when they occur, and 
 (3) system flexibility is required to respond to changing 
 conditions. 
 
 Bumps 
 
 In some longwall mines the problem of mountain 
 bumps or pressure bursts has become a major ground 
 control concern. It is thought that bumps or bursts are 
 triggered by the excessive loading of the pillars because 
 of the massive overburden, which exceeds the bearing 
 strength of the coal and results in a sudden and violent 
 rupture of the face or supporting gate road pillars. Al- 
 though bumps can occur in all types of mining methods, 
 this phenomenon is usually more pronounced in deep 
 mines with massive lithologic members present in the 
 overburden (16) and to some degree is affected by the 
 
 physical properties of the coal being mined. Some bumps 
 are so large they generate seismic waves that register 
 between 3 and 4 on the Richter scale, cause tremors on 
 the surface, and result in serious consequences under- 
 ground (fig. 8). Research into bump phenomena con- 
 tinues, and although it is thought that the proper design 
 of gate road pillars can guard against or control bump 
 occurrence, a solution does not appear imminent. 
 
 Sloughing 
 
 One of the repercussions resulting from the weight of 
 the overburden being transferred to the gate road pillars 
 and longwall face is the sudden failure of portions of the 
 outer skin of the pillar or longwall face (fig. 9). Although 
 most rib sloughing incidents are minor, they may inhibit 
 the movement of coal out of the headgate or halt the 
 production of coal because large pieces of coal or rock fall 
 and choke the conveyor at the stage loader. Consequently, 
 these occurrences would have to be dealt with when 
 considering an automated longwall system. 
 
 Cavities 
 
 During the longwall mining process, highly fractured 
 roof may be encountered, resulting in falls between the 
 face and support canopy tips (fig. 10). Consequently, these 
 cavities cause the support to lose contact with the roof. If 
 this condition persists, large roof voids develop above the 
 longwall supports, disabling their movement and halting 
 production. Correction of this problem often requires that 
 miners climb on top of the supports and construct cribs 
 to reestablish roof contact. If this condition occurs, it 
 defeats the purpose of having an automated longwall since 
 the miners are subjected to hazardous roof while con- 
 structing the cribs. Therefore, it is imperative that mea- 
 sures be taken to prevent the occurrence of cavities. 
 
 GEOLOGIC CONDITIONS 
 
 Whereas the first set of conditions affecting ground 
 control is a result of the mining-induced stresses during 
 coal extraction, the second set of conditions is a result of 
 the geologic features already present in the coal measure 
 rocks. These naturally occurring phenomena consist of 
 major and minor geologic features and structures, includ- 
 ing changing lithology, structural relief, faults, sand chan- 
 nels, slickensides, seam height, clay veins, joints, kettle- 
 bottoms, seam undulations, and soft floor. The occurrence 
 and implication of these features can vary greatly from 
 region to region and often within the same coalbed and/or 
 mine. The effects of these geologic features are magnified 
 by the mining-induced stresses mentioned previously. 
 These geologic conditions need to be confronted for 
 longwall automation to be successful in the U.S. mining 
 industry. 
 
Direction 
 of mining 
 
 Head 
 entry 
 
 41 ! i** 
 
 Figure /.-Stress distribution profile in roof of typical longwall section. [Adapted from Whittaker (75)] 
 
 Figure 8.-Entry after bump occurrence. 
 
Figure 9.-Face sloughing. 
 
 -Cavity 
 
 ~^ — — /s n° o /> o» 
 rlmmediate roo1-=-^j&frSm0osCp 
 
 Figure 10.-Cavity or void along longwall face. 
 
 Lithologic Changes 
 
 Over the extent of a mine, it is not unusual to encoun- 
 ter coal measure rocks that vary in type, property, and 
 thickness (fig. 11). Variation in lateral continuity of roof 
 and floor strata present numerous problems to an auto- 
 mated system. As roof and/or floor rock gradually grade 
 into other rock types, adjustments to equipment are re- 
 quired as the face advances. For example, floor rock that 
 had sufficient bearing strength at the beginning of a panel 
 can become soft as the panel is retreated and thus pose 
 serious problems with the performance of face supports. 
 Similarly, the immediate roof can change from being very 
 uniform and stable to being fractured or friable and, sub- 
 sequently, prohibitive to mining and damaging to equip- 
 ment. In extreme cases, massive sandstone roof, which 
 does not readily cave, can create conditions that can lead 
 to excessive loading and, eventually, pressure bursts 
 (bumps). 
 
 As the dimensions of longwall panels continue to in- 
 crease, system flexibility will be required to control the 
 different types of strata encountered throughout the length 
 of the panel. 
 
 
 
 1,000 
 
 Scale, ft 
 
 LEGEND 
 
 H2J Sandstone 
 Shale 
 Coal 
 
 IShaly limestone 
 Limestone 
 
 Figure 11. -Fence diagram showing changing lithology above longwall panel. 
 
Structural Relief 
 
 Overburden thickness often varies over the length of 
 longwall panels. Topographic relief from to 2,000 ft 
 over short horizontal distances (less than 1 mile) is not 
 uncommon in drift mines located in mountainous regions. 
 Extreme changes in overburden must be considered prior 
 to selection of support equipment so that proper capaci- 
 ties of both face and supplemental support can be imple- 
 mented to control changes in cover loads. 
 
 Stream valleys located above coal reserves also create 
 a unique set of stress-related problems. Topographic 
 relief, formed by years of normal erosion of weak, flat- 
 lying sediments, creates a zone of lateral compression, as 
 shown in figure 12 (17). These premining stress field 
 concentrations beneath stream valleys are often the cause 
 of roof failure brought about by the persistent shearing of 
 the rock at the rib-roof interface. This type of roof failure, 
 commonly known as cutter roof, is nearly impossible to 
 support by conventional support methods. 
 
 Panel Continuity 
 
 Successful automation of longwall mining equipment is 
 very promising because of the repetitive nature of the 
 extraction process inherent in the longwall mining method 
 and the fact that most coal seams are generally homoge- 
 neous and flat lying. However, geologic anomalies such as 
 faults, clay veins, sand channels, kettlebottoms, seam un- 
 dulations, interbedded seams, variation in seam height, 
 and coal quality create challenges for developers of au- 
 tomation technology. For instance, sand channel and clay 
 vein intrusions can occur periodically without warning and 
 interrupt the otherwise uniform interface between the coal 
 and the roof (fig. 13). In general, operators cut through 
 the intrusion in order to maintain uniform roof height. On 
 the other hand, a sensor that detects the coal-rock 
 interface may attempt to follow the irregularity, causing 
 inconsistencies in the roof and subsequent problems for 
 roof supports. In the Western United States, the presence 
 of faults can signify a sudden and complete loss of coal 
 reserves, requiring complex mining adjustments (fig. 14). 
 Fortunately, retreat longwall mining offers an advantage in 
 that many of these features are recognized during the 
 development of the longwall panel and prior to the setup 
 of the face equipment. In addition, some of these 
 conditions can be detected and managed with various 
 devices (i.e., remote sensing and electromagnetic 
 instruments). 
 
 LONGWALL LAYOUT AND DESIGN 
 
 Mines in existence prior to the use of longwall methods 
 were limited subsequently in the use of longwall mining 
 because of Federal subsidence laws, which restrict the 
 
 complete extraction of coal beneath surface structures 
 (buildings, highways, cemeteries, etc.). This means careful 
 planning, and oftentimes interruptions, of panel layout and 
 projections to avoid populated areas. More recently, coal 
 mines are being designed to include longwall practices, 
 and as a result, wider and longer panels (super panels) are 
 being developed away from populated areas. Super long- 
 wall panels have widths greater than 900 ft and lengths 
 greater than 10,000 ft. The motivation behind this trend 
 in super longwalls is to maximize the production of coal 
 and minimize the long-term effects of surface subsidence. 
 Mining larger panels and mining continuously using an 
 automated longwall face could significantly increase pro- 
 duction. For instance, as panel dimensions increase, the 
 frequency of setup and transfer of equipment, a very time 
 consuming process, decreases. However, at some point, 
 equipment transfer to the next panel is required when the 
 current panel is depleted of coal. Equipment recovery 
 areas require special preparation near panel recovery 
 points and have yet to be addressed by the automated 
 process. 
 
 Zone of high 
 lateral compression 
 
 LEGEND 
 
 Resultant of 
 overburden stresses 
 
 400 
 
 I 
 
 Approx scale, ft 
 
 Figure 12.-Stream valley profile. 
 
 Figure 13.-Sandstone channel. 
 
Figure 14.-Fault 
 
 Subsidence 
 
 Longwall mining allows the roof to cave quickly, uni- 
 formly, and completely, thus significantly reducing the 
 long-term damaging and unpredictable effects of surface 
 subsidence usually associated with room-and-pillar mining. 
 Furthermore, a faster advance rate lessens surface defor- 
 mations by reducing the magnitude of the inclination, 
 curvature, and tension and compression zones ahead of the 
 face, thus enabling the surface to settle with less damaging 
 effects. An automated longwall system will allow for a 
 
 faster rate of advance and tend to reduce the damaging 
 effects of subsidence. 
 
 Multiple-Seam Mining 
 
 As mines expand, mining below or above previously 
 mined-out areas or presently active mines will become 
 more common, especially in the eastern U.S. coalfields. In 
 West Virginia alone, there are over 50 minable seams in 
 multiple-seam configurations (18). Analysis of ground 
 control multiseam problems shows that factors contributing 
 to interactions may be classified into variables that are 
 fixed by the geologic environment and those that depend 
 on engineering design (79). Although with proper design 
 considerations automated longwall mining can be realized 
 in multiple-seam situations, caution must be exercised 
 when designing gate road and panel projections. 
 
 Gate Road Pillar Design Considerations 
 
 Another problem related to panel layout is that the 
 design of gate roads often depends upon the prevailing 
 roof conditions in a particular area during development, as 
 well as supply, ventilation, and escapeway requirements. 
 These conditions influence the number of entries and the 
 type of pillar design, either desired or deemed necessary, 
 in longwall gate roads. However, the best pillar configu- 
 ration for developmental purposes does not always coin- 
 cide with the most effective ground control methods for 
 maintaining entry stability during longwall retreat mining. 
 
 LONGWALL AUTOMATION STATE OF THE ART 
 
 Longwall mining is a repetitive process and one con- 
 ducive to automation; however, the extremely harsh un- 
 derground environment and unpredictable geologic con- 
 ditions have seriously impeded automation progress. In 
 general, the health and safety benefits that can be achieved 
 from an automated longwall process are the removal of 
 personnel from the hazards associated with immediate face 
 exposure (i.e., dust, roof falls, noise, pinch points, etc.), 
 while the economic benefits are a higher quality product, 
 lower maintenance costs (less bit wear), increase in speed 
 of operation, and better personnel utilization. 
 
 Various avenues of automation technology are being 
 explored. Peterson (20) believes that the currently existing 
 longwall component configuration is not the best basis for 
 automation and that if a longwall system were designed 
 specifically for automation, a differently designed system 
 would be produced. However, other researchers (11, 21- 
 24) and manufacturers are working within the currently 
 available equipment specifications. As previously stated, 
 automation of a longwall face is not a new concept; how- 
 ever, initial attempts failed because the technology was 
 not available to make complete automation of individual 
 components an integrated, error-free process. Today, 
 positive technological advancements have been made in 
 automation of individual components, particularly shield 
 
 supports. Although advances in shearer automation have 
 been realized, no current breakthrough can be reported. 
 
 ROOF SUPPORTS 
 
 Shield supports now make up 98 pet of the longwall 
 face support installations in the United States (7). Two 
 major groups of shield manufacturers have clearly influ- 
 enced the development of shield support application in the 
 United States. The basic structural design parameters of 
 the caliper and lemniscatic shields were introduced by 
 West German manufacturers, and the hydraulic and later 
 electrohydraulic auto-control concepts were innovations of 
 the British (25). Perhaps the most significant advance 
 toward automation has come from the development of 
 electrohydraulic control systems for shield supports. The 
 earlier pilot-operated valve systems have been superseded 
 by electrohydraulic control systems. Electrohydraulic 
 shields were introduced in the United States in 1984. 
 Since then, the technology has been readily adopted by 
 longwall operators (fig. 15). Initially, the move to an 
 electrohydraulically controlled support was made because 
 electrohyraulics provided the ability to move a group or 
 batch of supports from one dustfree location. Also, these 
 types of supports were able to achieve a uniform set 
 
10 
 
 120 
 100 
 80 
 60 
 40 
 20 
 
 KEY 
 Manual 
 Electrohydraulic 
 Shearer initiated 
 
 1985 
 
 1986 
 
 1987 
 
 1988 
 
 1989 
 
 15.-Trends in longwall shield controls. 
 
 pressure against the roof and a much faster cycle time (6 
 to 10 s per support). Base lifting to overcome soft floor, 
 which had been available on hydraulically controlled sup- 
 ports, has been successfully incorporated into the electro- 
 hydraulic systems. 
 
 In general, the four major components of an electro- 
 hydraulic control system are (1) the hydraulic directional 
 control valves, (2) the solenoid valves, (3) the electronic 
 control unit, and (4) the headgate computer. General 
 schematics of the two systems currently in use are shown 
 in figure 16 (26). The major difference in the systems is 
 the function of the microprocessor contained in each elec- 
 tronic control unit. In system A, the signals are sent to a 
 master computer for interpretation. The commands are 
 then issued to cycle the next support in the batch. Each of 
 the supports in the system is dependent on the headgate 
 computer for cycling. In system B, the microprocessor on 
 each shield interprets signals and relays commands to the 
 next support to initiate the support cycle. In this system 
 each support is "smart," thus eliminating the need for a 
 master computer. 
 
 System A 
 
 Power 
 supply 
 
 Headgate 
 computer 
 
 Master cable 
 
 KEY 
 E Electronic control unit 
 
 H Hydraulic control valve block 
 
 S Solenoid valve 
 
 System B 
 
 Master and slave cable 
 
 Figure 16.-Schematic showing two types of electrohydraulic systems for shield control. [Adapted from S. Peng (26)] 
 
11 
 
 Initially, electrohydraulic control units were easily in- 
 capacitated by dust and moisture migration into the unit's 
 electronics. As a result, supports, although equipped to 
 operate in batch mode, were being activated singularly 
 from an adjacent support. However, reliability has greatly 
 improved and batch advance of supports is now the rule 
 rather than the exception for installations utilizing electro- 
 hydraulic control. Support manufacturers agree that, al- 
 though there is room for improvement, the dependability 
 problems first encountered with electronic components 
 have been sufficiently overcome so that today few, if any, 
 support installations are purchased without electrohydrau- 
 lic control technology. 
 
 The successful application of support advance technol- 
 ogy is currently evolving into what eventually will become 
 a completely automated longwall face. Currently, the use 
 of automatic support advance by shearer initiation is 
 gaining in popularity, and there are several installations 
 with this capability. However, the use of shearer initiation 
 for the automatic advance of face supports is at the same 
 stage as that of batch control several years ago (i.e., mines 
 have the technology but are not utilizing it). Two mines 
 that have installed shearer-initiated support advance are 
 reluctant to use it, for different reasons. One operator 
 recognizes its benefits, but mine officials fear that miners 
 are threatened by its presence; they are therefore allowing 
 for an extended training and breaking-in period. The 
 other operator does not see production advantages over its 
 current method of mining. In general, operators are able 
 to meet their contractual obligations by employing meth- 
 ods that do not require the added expense of automated 
 equipment. In addition, some operators are reluctant to 
 adopt technology that is not yet fully proven and thus will 
 wait for the development of more reliable systems. 
 
 SHEARER AUTOMATION 
 
 To manage the complex conditions that will be encoun- 
 tered underground, it is not enough for shearing machines 
 to be automated. Instead, machine "intelligence" will be 
 required, not only to perform normal operations, but to 
 detect, interpret, and respond to possible changes in nor- 
 mal operations (many of which are ground control relat- 
 ed). Computerization has provided the integration of once 
 stand-alone electronic components, enabling on-board 
 intelligence. With the existence of a proven interface on 
 the machine, the addition of feedback sensors can allow 
 for the use of on-board intelligence (27). Some of the 
 early technical endeavors that were the basis for the cur- 
 rent state of the art are presented in the "Background" 
 section of this report. A synopsis of the Bureau's robotics 
 and automation research program, by Schnakenberg (28), 
 lists the critical path technology categories for intelligent 
 mining machines (table 1). 
 
 Three important areas must be addressed before 
 shearer automation can become practical (9): (1) cutting 
 horizon, (2) face alignment, and (3) shearer position. 
 
 Table 1 .-Intelligent mining machines critical systems 
 and technologies (28) 
 
 System 
 Basic machine 
 
 Computer systems 
 
 Machine control 
 
 Guidance systems 
 
 Coal interface 
 detection. 
 
 Diagnostics 
 
 Planning 
 
 Dominant components and issues 
 
 Mechanical, electrical, and hydraulic 
 systems. 
 
 Processor boards, operating system; 
 communication networks for real- 
 time, multiple-processor operations. 
 
 Position, electrical, and hydraulic 
 sensors; computer data acquisition, 
 closed-loop control algorithms, and 
 command language. 
 
 Position and heading sensors and 
 systems, obstacle and mine rib 
 detection and registration to map 
 data, computer software for data 
 fusion and filtering. 
 
 Coal-strata properties and differences, 
 multidisciplinary systems for real- 
 time sensing of cutting position, 
 artificial intelligence data interpreta- 
 tion. 
 
 Sensors of machine condition, expert 
 system interpretation and analysis, 
 human interfacing. 
 
 Data interpretation, knowledge repre- 
 sentation, artificial intelligence, and 
 human interfacing. 
 
 Cutting Horizon 
 
 The automated shearing machine will replace the ma- 
 chine operator and therefore must execute the functions 
 a human operator would perform using sensory perception. 
 Machine operators maintain horizon control by observing 
 the position of the cutting drums and making adjustments 
 according to the coal-rock interface or the desired thick- 
 ness of the cut. Shearing can take place at the coal-rock 
 interfaces of the roof and floor, or coal may be left un- 
 mined either at the roof or at the floor depending on the 
 competency of the rock or the seam height desired. Sen- 
 sors have been developed to maintain cutting horizon in a 
 variety of ways; however, the primary purpose is either to 
 differentiate between coal and rock or to determine the 
 thickness of coal left at the roof. 
 
 These sensors are in various stages of development, and 
 thus far, no one sensor has been a total success. The 
 sensitized pick transducer uses pick force to guide the 
 ranging drum along the correct horizon by maintaining a 
 continuously updated hardness profile of particular bands 
 within the coal seam (6). The vibration transducer dis- 
 criminates between the coal-rock interface, while other 
 sensors, such as the natural gamma radiation, doppler 
 radar, and electromagnetic wave sensors, can be used to 
 detect coal thickness left at either the roof or floor. Main- 
 taining horizon control at the floor presents problems for 
 
12 
 
 many of the sensors because there is no way to mount 
 sensors on either the shearer or face conveyor to transmit 
 signals into the floor. The type of sensor utilized on a 
 particular shearing machine would depend on the appli- 
 cation desired or on ground control conditions either pres- 
 ent or expected. 
 
 Face Alignment 
 
 During the retreat of a longwall panel, it is not unusual 
 for face equipment to gradually wander out of alignment 
 (i.e., the longwall face is no longer perpendicular to the 
 head and tailgate entries). To correct this occurrence, 
 shearer operators make angle or wedge cuts to straighten 
 the face. British Coal is developing sensors to maintain 
 face alignment (24). Transducers on the support advance 
 rams and distance measurements using a cord transducer 
 located in the gob are two promising face alignment 
 techniques. 
 
 Shearer Position 
 
 As the shearer traverses the face, cutting coal, the 
 shields are advanced to support the exposed roof, followed 
 by the push or advance of the conveyor, which in turn 
 enables the cycle to begin over again. Since the latter two 
 operations (shield advance and conveyor push) depend 
 upon the position of the shearer along the face, timing 
 during the cycle is critical. An automated system must 
 continually monitor shearer position so that effective ad- 
 vance of supports and conveyor can be performed in prop- 
 er sequence. 
 
 Two types of systems have been developed and suc- 
 cessfully implemented to monitor shearer direction and 
 position along the face. One system employs the shearer 
 haulage drive gear as an odometer. As the drive gear 
 rotates, pulses are generated, incremented, and relayed to 
 a central control unit in the headgate at regular distance 
 intervals along the face. The control unit is linked to the 
 roof supports and, by recognizing the position of the 
 shearer, is able to relay commands to activate the support 
 advance and conveyor push at a preset distance behind the 
 shearer. 
 
 The other system utilizes an infrared transmitter 
 mounted on the shearer and receivers located on each of 
 the supports (fig. 17). As the shearer moves along the 
 face, the infrared signals are received by the supports and 
 relayed to the headgate control unit. The control unit 
 defines the position and direction of the shearer and con- 
 veys commands to initiate support advance and, subse- 
 quently, conveyor push. 
 
 A summary of shearer system readiness, as compiled by 
 one automation researcher, is shown in table 2 (21). 
 
 COMPONENT INTEGRATION 
 
 The various sensors being developed for an integrated 
 automated system are presented in table 3. The continual 
 development and reliability of individual components along 
 
 with the introduction of microprocessors (computerization) 
 has enabled some degree of successful automation. The 
 successful interfacing of supports and shearer has been 
 achieved through the use of electrohydraulics and shearer 
 position technology. Although advances are being made, 
 the shearer remains the final obstacle in achieving total 
 longwall automation. 
 
 Table 2 -Status of shear automation devices (21) 
 
 Ready 
 
 Partially complete 
 
 New work 
 
 Shearer face location sensor. 
 
 Pitch and roll sensors. 
 
 Coal thickness sensor. 
 
 Computer and electronics. 
 
 Digital communications. 
 
 Error condition reporting. 
 
 Ability of equipment to with- 
 stand environment. 
 
 Auto floor slave and robotic 
 roof control. 
 
 Roll stability on floor cut. 
 
 Evaluation vibration sensor. 
 
 Addition of high-performance 
 coal thickness data. 
 
 Cut control using coal thick- 
 ness data. 
 
 Shearer turnaround control. 
 
 Integration tests with self- 
 advancing shields. 
 
 Optimizing shearer and pan 
 designs. 
 
 Maintenance procedures, doc- 
 umentation, and training. 
 
 Table 3.-Summary of longwall automation 
 monitoring devices (9) 
 
 Parameter monitored 
 and device used 
 
 Function 
 
 Cutter position: 
 
 Odometer Measure shearer position along face. 
 
 Infrared transmitter ... Do. 
 
 Cutter roll: 
 
 Tilt transducer Measure shearer roll. 
 
 Inclinometer Do. 
 
 Horizon control: 
 Natural gamma Measure roof coal thickness. 
 
 radiation sensor. 
 Doppler radar sensor . . Do. 
 
 Sensitized pick force Differentiate between coal and non- 
 
 sensor, coal. For locating interface or for 
 
 horizon control by using marker 
 bands. 
 
 Vibration sensor Measure roof coal thickness, locate 
 
 coal-rock interface. 
 
 Memory pass Recall preprogrammed cut profile to 
 
 be duplicated on successive 
 shearer passes. 
 Measure roof coal thickness. 
 
 Electromagnetic 
 wave. 
 Face alignment: 
 Cord transducer 
 
 Advance ram 
 transducer. 
 
 Measure straightness of face, de- 
 termine angle of face with road- 
 ways, and measure advance of face. 
 
 Measure advance of face. 
 
13 
 
 
 Figure 17.-lnfrared technique used for shearer-initiated face advancement [Adapted from S. Peng {26)] 
 
 CONSTRAINTS AFFECTING LONGWALL AUTOMATION 
 
 The authors visited several longwall operations through- 
 out the United States to observe the various degrees of 
 automated face equipment in use and to discuss with op- 
 erators constraints that may limit the further development 
 of automated operations. In general, constraints affecting 
 equipment (shearer, roof supports, conveyors) as well as 
 the mine atmosphere (ventilation, dust, methane) emerge 
 as impediments to an automated system. Ideally, auto- 
 mated face equipment will isolate mine personnel from 
 face hazards while providing significant increases in pro- 
 duction; however, compliance with regulations regarding 
 dust and methane concentrations must still be enforced to 
 guard against catastrophic mine explosions. In addition, 
 large production capacities at the longwall face are limited 
 by the capacity of the conveyor, as well as outby haulage 
 systems that transport coal to the surface. 
 
 Since the two major active components of a longwall 
 system are the shearer and roof supports, the following 
 sections present ground control and other general con- 
 straints to automation that affect these two components. 
 
 GROUND CONTROL CONSTRAINTS 
 
 Shearer 
 
 When personnel are present along the face, problems 
 that arise are immediately diagnosed and remedied. Con- 
 sequently, by the routine recognition and correction of 
 small problems, major production-stopping problems are 
 averted. The key to successful automation will be the 
 
 ability of the equipment to overcome problems routinely 
 associated with daily operations. 
 
 Frequent production delays due to shearer stoppages, 
 not related to equipment failure, along the face can usual- 
 ly be attributed to rocks on the face conveyor on the tail- 
 gate side of the shearer that are too large to pass between 
 the shearer and conveyor. These rocks usually fall from 
 the unsupported roof span between the face and the sup- 
 port canopy and must be broken into smaller pieces by a 
 sledgehammer in order to pass beneath the shearer (fig. 
 18). Large rocks that fall on the headgate side of the 
 shearer also have to be broken to pass from the face con- 
 veyor to the stage loader. 
 
 Events such as pressure bursts (bumps) and gate road 
 roof falls occur with less frequency but are major pro- 
 duction hindrances and, in the case of bumps, pose serious 
 safety hazards. The magnitude of a bump is dependent 
 upon the amount of stored energy in an area. In one 
 mine, a large bump damaged shield supports so severely 
 that extreme measures (blasting) had to be employed to 
 remove one-third of the supports from the face area. In 
 another case, a bump near a shearer twisted and bent the 
 ranging arms of the shearer, requiring costly repairs (about 
 $1 million). Some western U.S. longwall faces frequently 
 experience small coal bumps along the face as the shearer 
 cuts. These bumps hurl fragments of coal out into the 
 walkway where longwall crews work. Miners protect them- 
 selves from flying debris by walking between support legs 
 or by hanging lengths of belt from shield supports in bump 
 areas. The shearer operator, however, must remain in the 
 walkway unprotected. 
 
14 
 
 Figure 18.-Rock on face conveyor being broken up into 
 smaller pieces with sledgehammer. 
 
 Roof falls in gate road entries also inhibit production 
 and provide the potential for the development of danger- 
 ous situations. Tailgate falls block aircourses for venti- 
 lation, which can lead to the buildup of dust and methane 
 concentrations. Extensive maintenance is required to 
 reestablish airflow for face ventilation. 
 
 Roof Supports 
 
 Successful control of the roof and problem-free cycling 
 of longwall face supports are the basic principles required 
 for a productive longwall. However, there are situations 
 that require the constant attention of longwall personnel to 
 prevent support-related production stoppages. The most 
 common ground-control-related occurrence that hinders 
 support functions is soft floor. Floor rock is often com- 
 posed of shale or fire clay. The properties of the rocks 
 vary and may be adversely affected by water. On compe- 
 tent, level floor rock, supports slide forward during the 
 advance cycle. However, support bases penetrate soft rock 
 and dig into the floor, which requires that the base be 
 lifted out of the depression. 
 
 The reaction of the floor to the support is also depen- 
 dent upon support operation. For better control of the 
 roof, support operators bias support force toward the tip 
 of the canopy. This shifts the immediate roof loads toward 
 the front of the base and reduces the bearing area of the 
 support base, causing the base to break and penetrate the 
 floor, resulting in advance problems or, worse, support 
 instability. Support manufacturers have designed support 
 bases to overcome soft floor and, as previously stated, have 
 successfully incorporated this technology into the automatic 
 advance of supports. 
 
 A situation of seemingly less importance but one that 
 requires constant maintenance by face crews is the pushing 
 or plowing of debris (loose coal and floor rock) ahead of 
 support bases. Continuous shoveling of this material is 
 required to allow for unimpeded advance of supports. 
 
 Another roof-support-related problem is that support 
 loads across the face may not be uniform and may require 
 different setting pressures depending upon the location of 
 increased load. Nonuniform loading is determined through 
 observation, and support setting pressure is adjusted ac- 
 cordingly. By incorporating support leg pressure trans- 
 ducers into the automated system, support leg pressures 
 can be continually monitored and adjusted automatically to 
 achieve an appropriate setting pressure. 
 
 Shearer tram times across the face continue to increase 
 and are currently rated at about a 40- to 45-ft/min maxi- 
 mum (29). On a 600-ft-wide face utilizing 120 shield sup- 
 ports, a shearer, moving at 40 ft/min, would take 15 min 
 to cut one direction. The shields, cycling at 10 s, would 
 take 20 min to advance the entire face. This procedure 
 would require the shearer to wait 5 min every cutting pass. 
 However, by cycling shields simultaneously, advance times 
 are dramatically increased. The ground control impli- 
 cations of moving two or three adjacent supports at the 
 same time are obvious; however, manufacturers have de- 
 signed electrohydraulic controls to systematically advance 
 nonadjacent supports simultaneously and thus allow for 
 roof control between advancing supports. 
 
 GENERAL CONSTRAINTS 
 
 Other problems facing complete longwall automation, 
 not necessarily related to ground control, must also be 
 considered. In general: 
 
 • More complex machinery requires more mainte- 
 nance to keep it functional; 
 
 • More highly skilled personnel will be required to 
 perform remedial maintenance measures when equipment 
 malfunctions; 
 
 • The type of sensors utilized may depend upon the 
 specific application desired or geologic conditions present 
 or expected; 
 
 • Electronic devices will have to be rugged to en- 
 dure continual abuse from machine vibration, dust, and 
 moisture; 
 
 • Control and articulation of cutting drum cowls has 
 not been successfully accomplished; 
 
 • Integration of sensor detection, computer inter- 
 pretation, and machine response must occur nearly 
 instantaneously; 
 
 • Work force attitudes toward automation are 
 negative. 
 
BUREAU RESEARCH 
 
 15 
 
 The Bureau's research has been directed to develop 
 automation technology for continuous mining machines, 
 because 75 to 80 pet of underground production (room- 
 and-pillar) is mined by continuous miner and because 
 continuous miners provide development for longwall re- 
 treat, shortwall, and highwall mining. The Bureau is ac- 
 tively involved in the development of intelligent machine 
 control technology. The major thrust of the research is 
 concentrated in the area of coal interface detection (CID) 
 and machine guidance. Several promising CID techniques 
 are currently being investigated, including machine vibra- 
 tion and adaptive signal discrimination, natural gamma 
 radiation, thermography, X-ray florescence, and radar (22). 
 The subsystems being developed can be utilized individ- 
 ually in the near term as aids to remotely controlled 
 
 continuous mining. These sensors, in turn, can be 
 extended to automation of longwall mining systems. 
 
 Bureau research is divided into three categories: (1) 
 a fundamental or core program of research that explored 
 and developed the fundamental knowledge and hardware, 
 (2) an applied research program that brings the pieces 
 or integrated systems to a demonstrable, reliable, and 
 fieldworthy stage, and (3) ad hoc solutions to mining in- 
 dustry needs (28). 
 
 The Bureau is committed to research that will increase 
 coal extraction efficiency by increasing machine availability 
 time and utilization. This goal will be accomplished by 
 developing and integrating systems that will allow for con- 
 tinuous and autonomous operation of mining machines. 
 
 CONCLUSIONS 
 
 Although most technologically advanced automated 
 machinery operates in a highly controlled environment, this 
 is not possible in the underground coal mine. Therefore, 
 the success of an automated longwall system hinges on the 
 ability of the system to handle routine environmental con- 
 straints, including dust and methane, and ground control 
 limitations that all mines cope with on a day-to-day basis. 
 Ground control constraints include mining-induced stresses 
 inherent in longwall mining (e.g., bumps, sloughing, cav- 
 ities), geologic conditions (e.g., lithology, structural relief, 
 
 geologic anomalies), and longwall layout (e.g., panel size, 
 setup, recovery room) that must be considered and incor- 
 porated into the overall operating design of an automated 
 longwall. 
 
 While the various components needed to automate a 
 longwall face are at various stages of maturity, it is evident 
 the mining industry will gradually integrate all of these 
 components into a totally automated longwall system such 
 that they are designed to function within the environmental 
 limitations of an underground mine. 
 
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