A coal-rock interface detector is presented which employs a radioactive source and radiation sensor. The source and sensor are separately and independently suspended and positioned against a mine surface of hydraulic pistons, which are biased from an air cushioned source of pressurized hydraulic fluid

Crouch, C. E.

Jones, E. W.

Rose, S. D.

English

NASA Technical Reports Server

United States Patent [ I ~ I  
Rose et al. 
11 11 4,165,460 
[45] Aug. 21, 1979 
[54] COAL-ROCK INTERFACE DETE(;TOR 
[76] Inventors: Robert A. Frosch, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Stephen D. Rose; Charles 
E. Crouch, both of Huntsville, Ala.; 
Elborn W. Jones, Mississippi State, 
Miss. 
[21] Appl. No.: 848,793 
[22] Filed: Nov.4,1977 
[51] ht. c1.2 ........................ GOlV 5/00; GOlN 23/20 
[52] US. CI. ..................................... 250/253; 250/272 
[58] Field of seprcb ........... 250/253, 254, 256, 358 R, 
250/272,273; 299/1 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,019,338 1/1962 Monaghan et al. .................. 250/253 
3,723,727 3/1973 Wogman et al. .................... 250/253 
Primary Examiner-Alfred E. Smith 
Assistant Examiner-Janice A. Howell 
Attorney, Agent, or Firm-George J. Porter; John R. 
Manning; L. D. Wofford, Jr. 
1571 ABSTRACT 
A coal-rock interface detector employing a radioactive 
source and radiation sensor wherein the source and 
sensor are separately and independently suspended and 
positioned against a mine surface of hydraulic pistons 
which are biased from an air cushioned source of pres- 
surized hydraulic fluid. 
5 Claims, 4 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19790023535 2020-03-20T19:31:24+00:00Z
U.S. Patent Aug. 21, 1979 Sheet 1 of 4 4,165,460 
U.S. Patent Aug. 21,1979 Sheet 2 of 4 4,165,460 
U.S. Patent Aug. 21, 1979 Sheet 3 of 4 4,165,460 
M 
U.S. Patent Aug. 21,1979 Sheet 4 of4  4,165,460 
4,165,460 
1 
COAGROCK INTERFACE DETECTOR 
ORIGIN OF THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(74 Sta. 435; 42 U.S.C. 2457). 
5 
10 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to devices for measuring the 
depth of coal remaining on the roof or floor of a coal 15 
mine, and particularly to devices which accomplish 
measurement by measurement of backscatter from a 
radioactive source. 
2. General Description of the Prior Art 
It has heretofore been known that the distance from 20 
the surface of coal to underlying rock may be measured 
by positioning a radioactive source adjacent to the sur- 
face of the coal, and positioning a radiation detector or 
sensor nearby and measuring the reflected radiation. In 
this process, gamma photons are emitted by the source 25 
and scattered by the coal and rock, redirecting a num- 
ber of photons back toward the sensor. The lower den- 
sity of coal does not absorb as many scattered photons 
as does the higher density rock. Consequently, the more 
coal between the detector and rock, the greater number 30 
of photons which reach the sensor. The exact number is 
proportional to the coal depth. Ideally, such a device is 
directly mounted on a coal cutting machine and its cut 
determined by the depth information obtained from the 
device. As far as is known, all prior devices of this type 35 
have employed a radiation source and radiation detec- 
tor commonly contained in a single module or housing, 
which housing contacts a cut coal surface over a rela- 
tively large solid plane area. The difficulty with this is 4o 
that there are often substantial air gaps between the 
source and detector and coal surface because of irregu- 
larities in the surface, and these air gaps produce signifi- 
cant errors in measurement. 
vide a gamma backscatter type of coal interface detec- 
tor which eliminates the above problem and, when 
mounted on a coal shearing machine, will provide con- 
tinuous and accurate coal-rock depthsf-interface infor- 
mation. 50 
SUMMARY OF THE INVENTION 
In accordance with the invention, a gamma backscat- 
ter coal interface detector is mounted on an arm sup- 
porting a coal cutting head, and, by means of parallelo- 55 
gram coupled arms, supports a platform member for 
movement vertically without angular change of the 
platform member. A radiation source and radiation 
sensor of the detector are separately positioned on the 
platform member, and each is independently raised or 60 
lowered from the platform member by means of an air 
cushioned hydraulic system, whereby as cutting pro- 
gresses and irregularitks in the top surface occur, the 
radiation source and sensor individually follow the 
smaller area portions of the surface, and thereby sub- 65 
stantially reduce cavities between each of these and the 
surface. As a result, the accuracy of the detector is 
greatly increased. 
Accordingly, it is an object of this invention to pro- 45 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a pictorial view illustrating the overall as- 
sembly and organization of components of the inven- 
tion. 
FIG. 2 is a pictorial view illustrating the radiation 
source unit of the invention. 
FIG. 3 is a pictorial view of the radiation detection 
unit of the invention. 
FIG. 4 is a diagrammatic illustration of the hydraulic 
circuit by which the radiation source and detection 
units are biased against a coal surface. 
DETAILED DESCRIPTION OF THE 
DRAWINGS 
Referring to FIG. 1, radiation source unit 8 employs 
a radiation source 10, such as Cesium 137, which is 
positioned in chamber 12 of cylinder 14. Chamber 12 
extends radially from the approximate axis of cylinder 
14 to the periphery of the cylinder. Cylinder 14 is en- 
closed by and rotates within lead enclosure 16, and, 
depending upon the rotational position of cylinder 14, 
chamber 12 is either closed off by lead enclosure 16 or 
it connects through passageway 18 of the enclosure and 
opening 20 in housing 22 to the outside of the housing. 
The rotation of cylinder 14 is effected by rotation of 
lever 24 and connected shaft 26, the latter extending 
inward through housing 22. Rotatable force is coupled 
from shaft 26 to collar 30 on shaft 26 by spring 31 which 
connects between shaft 26 and collar 30. The rotatable 
movement of collar 30 is transmitted to gear 32 by link 
34 through ball joint connections 36 and 38, respec- 
tively, of link 34. In tum, gear 32 drives a smaller gear 
44 which is attached to and rotates cylinder 14. By the 
employment of spring 31 as a torsional link, a cushioned 
response is achieved between lever 24 and cylinder 14. 
In a normal or resting state, lever 24 is biased upward 
(90" from the shown position), biasing being by means 
of a biasing lever 45 on shaft 26 which is coupled by 
spring 46 to bracket 47 on housing 22. This causes cylin- 
der 14 to be turned approximately 180" from the indi- 
cated position, whereby outward radiation from source 
10 is blocked by lead enclosure 16. Lever 24 would be 
moved to the indicated or operating position by virtue 
of the combination of forward motion (along arrow 48) 
and upward movement of source unit 8, which would 
cause lever 24 to be triggered by the roof or floor sur- 
face of a mine, and thus be rotated clockwise. In an 
operating mode, chamber 12 is aligned, as shown, with 
passageway 18 and opening 20, and thereby radiation 
will be emitted outward from source unit 8. To protect 
the interior of chamber 12 from debris, a polyurethane 
diaphragm 49 is positioned in opening 20, it being 
largely transparent to gamma radiation. 
Outwardly, housing 22 is formed of vertical sides 50 
and 51 and a roof 52, the latter sloping upward from 
leading edge 54 (with respect to the direction of travel 
indicated by arrow 48) to flat surface 58 and then slopes 
downward to trailing edge 60. Alternately, the roof of 
the housing would be circular. In use, surface 22 is in 
constant sliding contact with a coal mine surface. 
Referring to FIG. 2, radiation detection unit 62 em- 
ploys a conventional scintillation detector 64 which 
provides an electrical output on leads 157 to meter 158 
proportional to the radiation it receives. Meter 158 
would be conveniently positioned for viewing by the 
operator of a mining machine on which the system of 
this invention is mounted, and would be scaled in a 
4,165,460 
3 4 
conventional scale in terms of coal depth to a rock 122, and shaft I20 rigidly connects to end 128 of lower 
interface. arms 127 of parallelogram assembly 102. 
Scintillation detector 64 is generally enclosed by a Hydraulic cylinders 104 and 116 are hydraulically 
lead enclosure 66, but open at end 68 to coincide wth an coupled in a parallel fashion to coupling points 130 and 
opening 70 in housing 72, through which radiation is 5 132 of four-way valve 134. Coupling point 136 is simply 
a drain connection and connected to a drain 138, and received. The opening in housing 72 is plugged by a 
polyurethane diaphragm 73 to generally provide pro- 
tection for scintillation detector 64, but still enabling the 
penetration of radiation without significant (10%) atten- 
uation. As shown, housing 72 is identical in contour to 
that of housing 22 of radiation source unit 8. 
FIG. 3 illustrates the mounting of radiation source 
unit 8 and detection unit 62 on a coal mining machine 
74, such as a longwall shearer. The longwall shearer 
includes an elongated arm 76 which is pivotally 
mounted at one end by pin 78 on the frame of the ma- 
chine. Coal shearing drum 80 is mounted on the oppo- 
site end of arm 76 and is rotably driven, by means not 
shown. Coal is continuously sheared or cut from a wall 
of a mine by movement of rotating drum 80 on arm 76 
about pin 82, by means not shown. It is a particular 
function of this invention to determine the height or 
elevation of a cut by determining the location of a coal- 
rock interface. 
Radiation source unit 8 and detection unit 62 are 
individually supported on a mounting arm 84 through 
identical parallelogram mounting brackets 86 which 
enable the units to maintain their angle of orientation 
despite vertical movement with respect to mounting 
arm 84. Mounting brackets 86 are affixed to arm 84 
through mounting blocks 88 and 90. In case of a tunnel 
cave-in, brackets 84 will shear (by means not shown) 
from blocks 88 and 90 to hang downward in a more 
protected position. Mounting arm 84 is supported on 
the mining machine through supporting members 
which maintain an essentially level reference for the 
mounting arm while moving it coordinately with verti- 
cal movement of shearing drum 80. This is accom- 
plished by a parallelogram arrangement of arms 
wherein an arm 92 is pivoted at end 94 to vertical arm 
% attached to frame 97 of the mining machine. The 
opposite end of arm 92 is pivotally attached to arm 98 
which is pivotally mounted at an opposite end to shaft 
82 of shearing drum 80. Arm 98 in turn is connected at 
right angles to mounting arm 84. The distance between 
pivots of arms 98 and 96 are identical, and the distance 
between pivots of arms 92 and 97 are identical. Thus, 
mounting arm 84 is maintained in the desired reference 
plane, e.g., level, as shearing drum 80 is raised and low- 
ered. 
Referring additionally to FIG. 4, identical four-bar 
parallelogram assemblies 100 and 102, which mount 
source unit 8 and detector unit 62 on mounting arm 84, 
are biased to a desired elevation and contact force be- 
tween these units and the surface of a mine by hyraulic 
cylinders. Thus, referring to the mounting of source 
unit 8, one end coupling of hydraulic cylinder 104 is 
pivotally connected to lever arm 106, and lever arm 106 
is connected to shaft 108, rotably supported by bracket 
110, and shaft 108 rigidly connects to end 112 of lower 
arm 114 of parallelogram 100. Thus, the effect of the 
application of a hydraulic pressure across cylinder 104 
is to rotate lever 106 and thereby raise (or apply greater 
pressure to) or lower (or apply less pressure to) source 
unit 8 through bracket 110. Similarly, hydraulic cylin- 
der 116 is coupled to lever arm 118, and lever arm 118 
is connected to shaft 120, rotably mounted by bracket 
coupling point 140 is connected through line 142 to a 
source of hydraulic fluid pressure which is illustrated by 
hydraulic fluid 144 in the lower portion of accumulator 
10 146. Compressed air 148 is in the upper portion 150 of 
accumulator 146. Initially, hydraulic fluid under pres- 
sure is supplied from a source 151 of hydraulic fluid 
under pressure through pressure reduction valve 152 
and shut-off valve 154 of the hydraulic cylinders and 
15 accumulator 146. Relief valve 155 is connected to line 
156 above valve 154 and simply provides a safety relief 
function in the event that pressure in the line should 
become excessive. 
The procedure for charging the system is as follows: 
20 1. Close valve 154. 
2. Operate four-way valve 134 to allow both hydrau- 
lic cyliners 104 and 116 to extend fully. 
3. Operate four-way valve 134 to retract both cylin- 
ders. This should allow accumulator 146 to force its 
25 remaining oil into both cylinders. 
4. Repeat step 2. 
5. Pressurize accumulator 146 through valve 154 to a 
gas (e.g., air) pressure of approximately 250 PSIA. This 
may be revised upward in the event that the system 
6. Adjust pressure reducing valve 152 for oil pressure 
commensurate with a value of air pressure for a desired 
hydropneumatic response. Thus, with a value of 250 
PSI for air pressure, it has been found that 277 PSIG is 
7. Open manual shut-off valve 152 between accumu- 
lator 146 and the coil supply. 
8. After accumulator oil reaches 277 PSIG, as read by 
gauge 156, turn off valve 152 to the oil supply. 
9. Operate four-way valve 134 to a position to retract 
pistons of both cylinders. 
Assuming that this procedure has been carried out 
correctly, the pistons should be fully retracted at this 
time, and the cylinder pressure should be slightly larger 
Considering that the pressure drop in the system 
because of pipe friction in the hydraulic lines will have 
an adverse effect on dynamic performance, this has 
been minimized by utilizing 0.5 inch diameter tubing for 
Referring to FIG 3, it is to be noted that in order to 
maintain a desired adjustable separation and distance 
between source 8 and detector 62 of from 10.5 to 22.5 
inches, detector 62 is positioned 51" behind the source. 
55 This moves the center of the gamma ray path to 54.5 
inches behind the shearing drum center line for a 22.5- 
inch separation distance. 
To commence operation, and with the shearing drum 
being moved upward, and the machine being moved to 
60 the left as shown in FIG. 3, lever 24 is rotated down by 
engagement with the roof or ceiling of a mine (not 
shown). This effects rotation of cylinder 14 and the 
exposure of the surface of the mine to radiation from 
source 10. Depending upon the depth of coal in the 
65 surface, that is, distance from the surface of coal to the 
surface of rock, the quantity of radiation is picked up by 
radiation detector 62, decreasing as rock is approached. 
The output of scintillation detector 64 is typically indi- 
30 response at the top of a piston stroke is too slow. 
35 appropriate. 
40 
45 than 250 PSIA. 
50 the lines. 
4,165,460 
5 6 
cated by meter 158 observable by the operator of ma- 
chine 74 to thus enable him to operate the shearing 
d m  to a desked position of cut to shear the coal close 
to the coal-rock interface. As the shearing head pro- 
gresses, the source a d  detector ud& separately follow 5 
the surface of the mine. Thus, since the upper contact 
surface of each of these units is relatively small, approxi- 
in surface relief is small, and thus the depth of air cavi- further comprising means generally surrounding said 
ties the and mine surfaces are source of radiation for shielding against the emission of 
SXder. As a resulk this bent ion enables a substantial radiation, and means responsive to said Source of radia- 
improvement in accuracy of measurement Over Prior tion being positioned adjacent to a said surface for pro- 
art devices. viding a passageway for emission of radiation along a 
Having thus disclosed our invention, What is claimed 15 selected path only when said source of radiation is adja- 
is: cent to said surface and for blocking said passageway 
1. A coal-rock interface detector comprising: when said source of radiation is moved away from said 
a source of gamma radiation; surface. 
a radiation detector; 4. A coal-rock interface detector as set forth in claim 
a frame; 
first support means mounted on A d  frame for in&- a first housing generally surrounding said radiation 
pendently, and vertically variably, positioning said source, and including a generally flat contact area 
and a radiation window across said passageway; source of gamma radiation adjacent to a coal sur- 
face as said frame is moved along the coal surfxe; first force biasing means for urging said contact area 
housing against a said surface; second support means mounted on said frame, inde- a second housing generally surrounding said radia- 
tion detector, and including a generally flat contact pendent of said frame and independent of the posi- 
area and a window for the reception of radiation; tion of said source of gamma radiation, for verti- 
and cally variably, positioning said radiation detector 
adjacent o said second force biasing means for urging said second 
moved along the coal surface. housing and its flat contact area against a said sur- 
2. A coal-rock interface detector as set forth in claim face. 
5. A coal-rock interface detector as set forth in claim 
said first support means includes means for raising 4 wherein each said force biasing means comprises a 
and lowering said source of radiation, and for 35 hydropneumatic cylinder and means for providing a gas 
maintaining the orientation of said source of radia- cushioned source of hydraulic fluid to said cylinder. 
to a vertical line as said source of radiation is raised 
and lowered; and 
said second support means includes means for raising 
and lowering said radiation detector and for main- 
taining the orientation of said radiation detector at 
a discrete angular orientation with respect to a 
vertical line as said radiation detector is raised and 
lowered. 
mately 3t inches (Or round), the 3. A interface detector as set forth in claim 
20 3 further comprising: 
25 
surface as said frame is so 30 
1 wherein: 
tion at a discrete angular orientation with respect * * * * *  
40 
45 
50 
55 
60 
65 


Coal-rock interface detector

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