WO1999030004A1

WO1999030004A1 - Remote monitoring safety system

Info

Publication number: WO1999030004A1
Application number: PCT/US1998/025994
Authority: WO
Inventors: Thomas E. Marshall; Craig S. Compton; Anthony Iannacchione; Gerald Finfinger; Thomas Mucho; Dennis Dolinar; David Oyler
Original assignee: The Government Of The United States Of America, As Represented By The Secretary Of The Department Of Health And Human Services
Priority date: 1997-12-09
Filing date: 1998-12-08
Publication date: 1999-06-17
Also published as: AU1716199A

Abstract

A roof monitoring safety system which is especially adapted for use in underground mines, especially underground stone mines, is provided. More specifically, this roof monitoring safety system can accurately and inexpensively gauge movement at single or multiple points in a structure (e.g., a mine roof or wall) relative to a fixed point and can, therefore, provide warning of an impending unsafe condition. Movement of the rock strata overlying the mine is measured directly by use of one or more potentiometers connected via cables to the rock strata at differing locations (normally vertically displaced) in a bore hole in the roof surface. Movement is precisely determined by measuring the output of the potentiometer(s) and comparing it to the control level calibration value (generally determined at the time of installation). Depending on the depth of the bore hole and the location of anchors within the bore hole, movement can be detected within the layers of rock up to 20 feet (or even more) above the surface layer. By providing early warning of an unstable and potentially hazardous condition, efforts can be made to eliminate the unstable condition and/or remove personnel from the potentially hazardous area until the unstable condition is eliminated. The present invention can also be used in and during building or other construction to increase worker safety.

Description

REMOTE MONITORING SAFETY SYSTEM

Field of the Invention

This invention provides a roof monitoring safety system which is especially adapted for use in underground mines, especially underground stone mines. More specifically, the present invention provides a roof monitoring safety system which can accurately and inexpensively gauge movement at multiple points in a structure (e.g., a mine roof or wall) relative to a fixed point and can, therefore, provide warning of an impending unsafe condition. By providing early warning of an unstable and potentially hazardous condition, efforts can be made to eliminate the unstable condition and/or remove personnel from the potentially hazardous area until the unstable condition is eliminated. The present invention can also be used in and during building or other construction to increase worker safety.

Background of the Invention

Underground mining ranks as one of the most hazardous occupations in the United States and throughout the world. Certain types of underground mining are especially hazardous. For example, underground stone mining is significantly more hazardous than underground coal mining. During the period 1991 through 1995 in the United States, twelve miners were fatally injured at underground stone mines even though the total number of underground stone miners is relatively small (approximately 2000 at the present time). Nine of the twelve fatalities were a result of roof or rib (i.e., side wall) collapse. The number of such miners world-wide is, no doubt, much higher. The number of underground stone mines and miners is likely to grow since the public and environmental groups increasingly oppose the development and/or expansion of surface quarries. Thus, the need to provide new and better methods to recognize and monitor hazardous ground conditions will significantly increase in the 21st century. A number of devices and techniques have been used in various attempts to monitor unsafe ground conditions in underground mines. For example, Waters et al., U.S. Patent 3,949,353 (April 6, 1976), provided an underground mine surveillance system in which the seismic energy in the mine area was continuously monitored. Graham, U.S. Patent 4,136,556 (January 30, 1979), provided a system for monitoring the creep rate or velocity of the strata (e.g., mine roof) wherein a single top anchor was attached to a stable portion of the rock formation and the bottom anchor was attached to the mine roof. If the creep rate or velocity exceeds a predetermined value, a warning device was triggered. Conkle, U.S. Patent 4,156,236 (May 22, 1979), provided a single position sensing device mounted in a bore hole wherein, once the device is triggered by movement in excess of a preset amount, an alarm system (e.g., an indicator lamp) was activated. The triggering and warning systems were mounted outside of the bore hole.

Brown et al., U.S. Patent 4,217,839 (August 19, 1980), provided another mine warning device. The shifting of the roof applied pressure to a tensioned arm of the device which, when activated, triggered an alarm. The device was designed to be mounted directly on the roof surface using a roof bolt. Kehrman et al., U.S. Patent 4,271,407 (June 2, 1981), provided a single point induction coil extensometer mounted in a bore hole. A ferrite core was suspended within the bore hole and positioned with coil turns located within the bore hole near the roof surface. Changes in frequency of the oscillator were monitored. Frequency changes above a predetermined threshold triggered an alarm.

Pavlov et al., Russian Patent Application SU 1213194 (March 23, 1986), provided a roof monitoring system using acoustical sensors to detect crack formation. Perry et al., U.S. Patent 4,581,712 (April 8, 1986), provided a warning system wherein the loading pressure on various roof bolts and roof supports were continuously monitored. The sensors were mounted on the roof bolts or supports at the roof surface. Stolarczyk, U.S. Patents 4,968,978 (November 6, 1990) and 5,087,099 (February 11, 1992), provided a method by which data in underground mines could be transmitted using burst transmission of digitally encoded radio signals. Types of data included, for example, carbon monoxide concentrations, longwall roof support pressure, or uncut coal thickness. Butcher et al., International Patent Publication WO 96/39610 (December 12, 1996), provided a system for remotely monitoring roof displacement in underground mines. A single movement sensor (a cable with a tensioning weight) was mounted in a bore hole. The cable was looped around a pulley attached to a rotary encoder which generated a signal upon movement of the strata. The sensoring mechanisms were exposed on the roof surface.

Although these systems, when used properly, generally provide an increase in safety in underground mines, they also suffer from several significant disadvantages. First, they are limited to one data point per device in the roof structure layers. Since the rock structure and stability can vary significantly in the mine roof (both vertically and horizontally), the accuracy and timeliness of the data can depend in large part on the actual placement of the sensor. In many cases, the measuring device is mounted directly on the roof surface and only monitors the surface layer of the roof structure. Even where the measuring device is located in a bore hole, it can only monitor the strata in the immediate vicinity of its actual location in the bore hole (generally at the top or terminus of the bore hole). Thus, significant movement either above or below the actual location of the measuring device may not be detected as early as desirable. In addition, many of these devices have their critical measuring and sensoring components located in exposed areas (e.g., mounted on and hanging down from the roof surface itself) and are, therefore, subject to damage during normal mining operations. Furthermore, in many cases, these devices are generally complex and not as reliable as desired. Moreover, these devices are generally expensive; the devices currently in use today can cost over $1000 per sensor location. Since the mining industry is highly competitive, the cost of monitoring will be a critical factor as to whether such sensors are used at all and, if used, their numbers and locations.

Thus, there remains a need for an improved roof monitoring safety system. Such an improved system should ideally be relatively inexpensive, easy to install and operate, protected from damage from normal mining operations, and capable of providing multiple data points per sensor location at varying locations in the roof structure or strata. As one of ordinary skill in the art can determine from the present specification, the present roof monitoring safety system meets these objectives.

Summary of the Invention

The present invention relates to a roof monitoring safety system in which a single point or multiple points in a single bore hole can be measured to detect movement or sag in the roof strata of an underground mine. Movement of the rock strata overlying the mine is measured directly by use of one or more potentiometers connected via cables to the rock strata at differing locations

(normally vertically displaced) in a bore hole in the roof strata. Movement is precisely determined by measuring the output of the potentiometer(s) and comparing it to the control level calibration value (generally determined at the time of installation). Depending on the depth of the bore hole and the location of anchors within the bore hole, movement can be detected within the layers of rock up to 20 feet (or even more) above the surface layer. The movement of the rock at multiple locations within the bore hole is measured relative to a single fixed point near or on the surface of the roof. By measuring movement at different levels above the roof surface, a more detailed and accurate profile of roof stability can be obtained, thereby allowing for more accurate warning of hazardous conditions in the mine roof. Preferably the entire sensor is located with the bore hole, thereby minimizing the risk of damage to the sensor from normal mining operations. For multiple point measuring systems, where the sensor may be mounted on the roof surface, it is preferred that the sensor have a low profile and/or be encased in a protective case or cabinet. Data from the sensors can be remotely gathered using either manual or automated recording devices.

One object of the present invention is to provide a roof monitoring safety system comprising:

(a) a movement sensor rigidity mounted within or adjacent to a bore hole formed in strata above a mine roof, wherein the movement sensor has one or more electromotive recording devices;

(b) one or more cables, each cable having a sensor end and an anchor end, wherein the sensor end of each cable is attached to one of the electromotive recording devices of the movement sensor and the anchor end of each cable is attached to its own anchor and wherein the anchor for each cable is rigidly mounted in the bore hole such that the anchors are located along the length of the bore hole and at varying distances from the mine roof; wherein the numbers of electromotive recording devices, cables, and anchors are equal such that each electromotive recording device is connected to a single corresponding anchor through a single corresponding cable; and wherein movement of the strata located at or near any of the anchors causes the corresponding cables attached to anchors at or near the location of the movement to move which, in turn, causes a change in electromotive force at the corresponding electromotive recording device which can be directly correlated to the movement.

Still another object of the present invention is to provide a method for monitoring movement in the strata above a roof surface in an underground mine, said method comprising:

(a) providing a bore hole in the strata above the roof surface of at least five feet in length; (b) rigidly attaching one or more anchors to points along the length of, and within, the bore hole, wherein each anchor has a corresponding cable, having an anchor end and a sensor end, attached thereto via the anchor end;

(c) rigidly mounting a movement sensor within or adjacent to the bore hole, wherein the movement sensor contains one electromotive recording device for each anchor;

(d) connecting the sensor end of each cable to the corresponding electromotive recording device for each anchor, whereby movement at any of the anchors can be measured at its corresponding electromotive recording device via movement of its corresponding cable by a change in the electromotive force at the corresponding electromotive recording device;

(e) measuring the electromotive force over time at each electromotive recording device; and

(f) correlating the measured electromotive force over time at each electromotive recording device with movement at the corresponding anchors.

Other objects and advantages of the present invention will be apparent upon consideration of the instant specification.

Brief Description of the Drawings

Figure 1 illustrates, in expanded view, the basic components of the roof monitoring safety device.

Figure 2 illustrates, in assembled form, the sag measuring portion of the roof monitoring safety device.

Figure 3 illustrates the anchor with attached cable and the insertion tool.

Figure 4 illustrates the installation and anchoring of the roof monitoring safety device in a bore hole. Figure 5 illustrates the attachment of the monitor cable from the anchor to the roof monitoring safety device.

Figure 6 illustrates a roof monitoring safety device with multiple measuring point capabilities.

Figure 7 provides typical data generated by a multipoint roof monitoring safety device.

Description of the Preferred Embodiments

The present invention relates to a roof monitoring safety system in which a single point or multiple points in a single bore hole can be measured to detect movement or sag in the roof strata of an underground mine. Movement of the rock strata overlying the mine is measured directly by use of one or more potentiometers connected via cables to the rock strata at differing locations (normally vertically displaced) in a bore hole in the roof strata. Movement is precisely determined by measuring the output of the potentiometer(s) and comparing it to the control level calibration value (generally determined at the time of installation). Depending on the depth of the bore hole and the location of anchors within the bore hole, movement can be detected within the layers of rock up to 20 feet (or even more) above the surface layer. The movement of the rock at multiple locations within the bore hole is measured relative to a single fixed point near or on the surface of the roof surface. By measuring movement at different levels above the roof surface, a more detailed and accurate profile of roof stability can be obtained, thereby allowing for more accurate warning of hazardous conditions in the mine roof. Preferably the entire sensor is located with the bore hole thereby minimizing the risk of damage to the sensor from normal mining operations. For multiple point measuring systems, where the sensor may be mounted on the roof surface, it is preferred that the sensor have a low profile and/or be encased in a protective case or cabinet. Data from the sensors can be remotely gathered using either manual or automated recording devices. The movement sensors illustrated in the Figures having one electromotive recording device can generally be built and sold for about $25 to $125. Movement sensors having more than one electromotive recording device, although they will cost more, are still relatively inexpensive.

Figure 1 illustrates, in expanded view, a movement sensor having one electromotive recording device 10. Figure 2 illustrates the same electromotive recording device 10 with the main components in assembled form. (For clarity, many of the screws, bolts, nuts, washers, and the like shown in Figure 1 are not specifically labeled. One of ordinary skill in the art would clearly recognize and appreciate their use and purpose in the assembly. As one of ordinary skill will also realize, the specific materials of construction for the various components are not critical so long as each component can serve its intended function.)

The electromotive recording device 10 has a bracket 12 having a bottom end (or cable end) 13 and a top end (or spring end) 11. The electromotive measuring device 14 (e.g., a potentiometer) is mounted on bracket 12 roughly midway between the two ends 11 and 13. The potentiometer 14 can be protected, if desired, by bracket 30. The electromotive measuring device 14 has a shaft 15 for mounting a gear 22. The gear 22 is matched with sliding gear rack 16 such that linear movement of the gear rack 16 along the longitudinal axis of bracket 12 (i.e., along the directions of the arrow 17 in Figure 2) is converted to rotational movement of the gear 22 . Gear rack 16 is attached to the bracket 12 via spring 32. Spring 32 is rigidly attached to the bracket 12 at the top end 11; the opposite end of the spring 32 is attached to the gear rack 16. The opposite end of the gear rack 16 has two cable ends 18 and 20 one of which (cable end 18) is to be attached to the cable 40 which will extend into, and be anchored via anchor 38 in, the bore hole in the mine roof. The other cable end 20 is used with indent 25 on the bottom end 13 of the bracket 12 during installation to hold the gear rack 16 in proper position for installation (see Figures 4 and 5). The bracket 12 has mounting and guiding mechanisms located at its bottom end 13. As shown in Figures 1, 3, and 4, mounting mechanism consists of cylinder 24, threaded member 26, and locking nut 28, all of which are mounted on the bottom end 13. Threaded member 26 is attached to bracket 12 through hole 15 (Figure 2). Once placed in the bore hole, the threaded member 26 can be adjusted to provide a rigid friction or compression fit in the bore hole which is then locked in place via locking nut 28. Spring clamps 34 and 36, which can be attached to the top end 11 of bracket 12, can be used to help position or center top end 11 of the sensor mechanism in the bore hole. Of course, other means could be used to attach or fix the sensor within the bore hole. The actual mechanism for attaching the sensor within the bore hole is not critical so long as the sensor is rigidly fixed since the positioning of the sensor will provide the fixed point from which all measurements of movement will be determined or referenced. Cylinder 24 also provides a guiding mechanism for the cable (comprising cable end 18 and cable 40).

Figure 3 illustrates the anchor 38 which is placed within the bore hole. The anchor can be any type of spring loaded or expansion clamp that, once placed in the desired position within the bore hole, it will remain fixed. Anchor 38 has two arms 37 and 39 which grip the side of the bore hole. Insertion tool 42, which is a long pole (preferably telescopic) used to place the anchor 38 into the bore hole, preferably has length markings (not shown) so the position of the anchors 38 can be determined. Cable 40 is attached to anchor 38 at its top cable end 41. Cable 40 will extend down the bore hole, around cylinder 24, and connect to gear rack 16 via cable end 18.

The installation of a movement sensor having a single electromotive recording device 10 is illustrated in Figures 3-5. First, a suitable bore hole is drilled in the roof strata in a suitable location. Normally, the bore hole has a diameter of about 1 to 3 inches, preferably about 1.5 to 2 inches, and a length of greater than about 5 feet, preferably about 10 to 25 feet. Of course, the diameter and length of the bore hole can be smaller or larger than these measurements if appropriate for a particular installation. For example, larger diameters (especially immediately adjacent to the roof surface) could be used, if desired, to accommodate more than one single electromotive recording device 10. Although it is generally preferred that the bore hole is vertical or near vertical, the present invention will operate in non-vertical bore holes in the mine roof or in horizontal bore holes in sidewalls or even in vertical or non-vertical bore holes in the mine floor (i.e., downward oriented bore holes).

Next the anchor or anchors are set using the installation tool 42 to slide the anchor 38 into the bore hole and advance it to the desired position in the bore hole. The installation tool 42 may, if desired, have a slot cut in its upper end for holding the anchor 38. Attached to the anchor 38 is the cable 40 through its anchor end 41. During installation, it is preferred to keep a slight downward tension on the anchor 38 by pulling downward on cable 40 to keep the anchor 38 and the installation tool 42 engaged. Once the anchor 38 is in the correct position within the bore hole, the installation tool 42 is removed. The anchor 38 is locked in place within the bore hole by flexible arms 37 and 39. The flexible arms 37 and 39 will, of course, tend to "dig" into sides of the bore hole when a downward force is applied via the cable 40. Once installed, the anchor 38 should be tested by applying a downward force to make sure it is locked in place. Once installed, the cable 40 will hang from the anchor 38 and extend through the bore hole opening in the mine roof. The location of the anchor 38 or anchors (in the case of multipoint sensors; see Figure 6) for a particular bore hole should be determined on an individual basis. For example, during drilling the bore hole or examination of the bore hole using a scratch tool, it may be apparent that strata at certain heights above the roof may be more prone to failure or movement. Generally, the anchor(s) should be located in these areas to give more advanced warning of hazardous conditions. After placement of the anchor 38, the movement sensor is placed in the bore hole as illustrated in Figures 4 and 5. Generally, the movement sensor is placed so that the threaded member 26 is preferably within a few inches of the roof line. Once the movement sensor is in place in the bore hole, threaded member 26 can be adjusted to provide a friction or compression fit in the bore hole by forcing one end of the cylinder 24 and the opposite end of threaded member 26 against the walls of the bore hole. Once fixed, the locking nut 28 is used to lock the assembly in the bore hole. Of course, other means can be used to fix the movement sensor in the bore hole (e.g., brackets attached to the sensor can extend out of the bore hole for attachment to the mine roof). The cable end 20 can be placed into indent 25 either before or after installation of the movement sensor in the bore hole. By attaching the cable end 20 to indent 25, the gear rack 16 is forced downward in the bore hole thereby expanding spring 32. The other cable end 18, and its associated connector 46, will hang to the mouth of or slightly out of the bore hole. The cable 40 extending from the bore hole is cut so that only an appropriate length (about 3 inches in Figure 5) extends below the roof line. After sliding cable 40 through the connector 46, another connector 44 is attached to the end of cable 40 thereby forming a combined cable (made up of cables 40 and 18) extending down from the anchor 38, around cylinder 24, and up to gear rack 16. At this point, the cable end 20 can be removed from indent 25 so that the gear rack 16 can move upward (pulled by spring 32) to remove the slack in combined cable 40/18 and place the sensor in its operational mode. The various lengths involved (e.g., bracket 12, gear rack 16, cables 18 and 40) should be adjusted so that gear rack 16 has adequate movement possible in either direction once the device is armed. Generally, once armed, the approximate midpoint of the gear rack 16 should contact the gear 22 so that the gear rack 16 can move in either direction to record all ranges of movement of the strata. These various lengths can be adjusted as needed for particular applications.

In its operational mode, movement of the strata at or near the location of the anchor(s) 38 will move the gear rack 16 up or down (depending on the direction of the movement of the strata). Movement of the gear rack 16 will result in rotational movement of gear 22 which will change the electromotive force at the electromotive measuring device 14. The changes in the electromotive force can be monitored at a remote, and preferably protected, area using any appropriate electrical measuring device attached by appropriate electrical cables (not shown) to the electromotive measuring device 14. For example, a multimeter could be used to monitor the output of the electromotive measuring device 14. The output can be correlated with movement of the strata by any suitable method. For example, specific changes in the electromotive force can be directly correlated with the extent of sag in the roof structure by appropriate calibration. Generally, calibration should be undertaken when the sensor is first installed and periodically thereafter (especially if and when the sensor is adjusted for any reason). Figure 7 provides a plot of sag (converted from electromotive force to a distance measurement) as a function of time. Of course, the electromotive force could simply be monitored, without conversion to a distance measurement, with changes from its original value (at the time of installation or modification) noted; warning would be provided if the change exceeded a predetermined value. Generally, however, a plot similar to that of Figure 7 will tend to provide a better representation of the data and better highlight unsafe conditions as they develop.

A movement sensor capable of measuring movement of several points with a single bore hole can easily be manufactured by effectively ganging the just- described single sensor. Such a multiple sensor can have 2 to 12 (or even more) ganged sensors. A multiple sensor 100 with six measuring points is shown in Figure 6. As shown in Figure 6, each sensor has its own electromotive measuring device 114, gear rack 116, gear 122, spring 132, and cable 118, each of which are contained in enclosure 102. These components can be mounted on mounting brackets similar to the ones shown in Figures 1-2 (reference number 12). The cables 118 are each attached to their own cables 140 via connectors 106; cables 140 extend up the bore hole to individual anchors (not shown) located at various heights above the roof line. The individual cables 140 pass over guide 124 before entering the bore hole. If desired, a cable guard (e.g., a plastic or Teflon sleeve or collar) can be used to protect the cables 140 as they pass over the lip and into the bore hole. Each sensor assembly will measure the sag or movement at its respective anchor position. The output from each sensor can be monitored at a remote location via electrical cable 108 and a suitable readout device (not shown). By monitoring movement of the roof strata at various points along the length of the bore hole, a more accurate and complete representation of movement can be obtained thereby providing a more effective warning system.

As one of ordinary skill in the art will realize, a movement sensor having multiple measuring points will generally not fit into the bore hole as described above for a single sensor unit. Thus, the enclosure 102 can be mounted on brackets 104 which can be attached to the surface of the mine roof near the bore hole using any suitable means. Preferably, the entire assembly, including enclosure 102 and its cover (not shown) are of a low profile so as to fit closely to the roof line. Preferably, the entire assembly is contained within 3 or 4 inches of the roof (more preferably within about 2 inches) so as to avoid damage from normal mining operations. Moreover, the entire assembly can be protected using a metal enclosure 102 and covering (not shown). If desired, the covering can also extend over the cables 140 and bore hole to provide further protection. If desired, a recess in the roof near the bore hole could be cut so that the entire assembly could be installed therein, thereby providing even further protection.

Figure 7 provides a plot of movement (i.e., sag) using a sensor like the one illustrated in Figure 6 having multiple measuring points. The sensor was installed in an operating stone mine. Three anchors were installed in the bore hole at 5, 10, and 14 feet above the roof line. Plot 200 represents movement at 14 feet; plot 300 at 10 feet; and plot 400 at 5 feet. The first notable changes are observed about 220 days after installation with the major movement beginning at about 236 days. Failure (i.e., roof collapse) occurred at about 260 days. As seen in Figure 7, warning of the impending collapse would allow for corrective measures to be taken, including, but not limited to, shoring up the roof and/or keeping personnel out of the area.

As one of skill in the art will realize, the detailed description illustrates preferred embodiments of the invention. The invention is not, however, limited to the specific embodiments illustrated.

Claims

CLAIMSThat which is claimed is:

1. A roof monitoring safety system comprising:

2. A roof monitoring safety system as defined in claim 1, wherein the movement sensor has at least two electromotive recording devices.

3. A roof monitoring safety system as defined in claim 2, wherein the movement sensor has two to twelve, inclusive, electromotive recording devices.

4. A roof monitoring safety system as defined in claim 3, further comprising a data readout device, wherein the readout device is remotely connected to the movement sensor so that the electromotive force at each electromotive recording device can be recorded and analyzed.

5. A roof monitoring safety system as defined in claim 4, further comprising an alarm system wherein an alarm is generated if the movement determined at any of the anchors exceeds a predetermined value.

6. A roof monitoring safety system as defined in claim 2, wherein the sensor ends of the cables are attached to their corresponding electromotive recording devices via corresponding spring-loaded geared racks which are in a geared connection to corresponding gears mounted on the corresponding electromotive recording devices whereby movement of each cable moves its corresponding spring-loaded geared rack which in turn rotates its corresponding gear thereby changing the electromotive force at the corresponding electromotive recording device.

7. A roof monitoring safety system as defined in claim 3, wherein the sensor ends of the cables are attached to their corresponding electromotive recording devices via corresponding spring-loaded geared racks which are in a geared connection to corresponding gears mounted on the corresponding electromotive recording devices whereby movement of each cable moves its corresponding spring-loaded geared rack which in turn rotates its corresponding gear thereby changing the electromotive force at the corresponding electromotive recording device.

8. A roof monitoring safety system as defined in claim 4, wherein the sensor ends of the cables are attached to their corresponding electromotive recording devices via corresponding spring-loaded geared racks which are in a geared connection to corresponding gears mounted on the corresponding electromotive recording devices whereby movement of each cable moves its corresponding spring-loaded geared rack which in turn rotates its corresponding gear thereby changing the electromotive force at the corresponding electromotive recording device.

9. A roof monitoring safety system as defined in claim 6, wherein the bore hole is at least five feet long and wherein the anchors are located throughout the length of the bore hole.

10. A roof monitoring safety system as defined in claim 7, wherein the bore hole is at least five feet long and wherein the anchors are located throughout the length of the bore hole.

11. A roof monitoring safety system as defined in claim 8, wherein the bore hole is at least five feet long and wherein the anchors are located throughout the length of the bore hole.

12. A method for monitoring movement in the strata above a roof surface in an underground mine, said method comprising:

(a) providing a bore hole in the strata above the roof surface of at least five feet in length;

(b) rigidly attaching one or more anchors to points along the length of, and within, the bore hole, wherein each anchor has a corresponding cable, having an anchor end and a sensor end, attached thereto via the anchor end;

(e) measuring the electromotive force over time at each electromotive recording device; and (f) correlating the measured electromotive force over time at each electromotive recording device with movement at the corresponding anchors.

13. A method as defined in claim 12, wherein the movement sensor has at least two electromotive recording devices.

14. A method as defined in claim 13, wherein the movement sensor has two to twelve, inclusive, electromotive recording devices.

15. A method as defined in claim 12, wherein the movement sensor is remotely connected to a data readout device so that the electromotive force at each electromotive recording device can be recorded and analyzed.

16. A method as defined in claim 15, wherein the data readout device is connected to an alarm system wherein an alarm is generated if the movement determined at any of the anchors exceeds a predetermined value.

17. A method as defined in claim 12, wherein the sensor ends of the cables are attached to their corresponding electromotive recording devices via corresponding spring-loaded geared racks which are in a geared connection to corresponding gears mounted on the corresponding electromotive recording devices whereby movement of each cable moves its corresponding spring-loaded geared rack which in turn rotates its corresponding gear thereby changing the electromotive force at the corresponding electromotive recording device.

18. A method as defined in claim 14, wherein the sensor ends of the cables are attached to their corresponding electromotive recording devices via corresponding spring-loaded geared racks which are in a geared connection to corresponding gears mounted on the corresponding electromotive recording devices whereby movement of each cable moves its corresponding spring-loaded geared rack which in turn rotates its corresponding gear thereby changing the electromotive force at the corresponding electromotive recording device.

19. A method as defined in claim 16, wherein the sensor ends of the cables are attached to their corresponding electromotive recording devices via corresponding spring-loaded geared racks which are in a geared connection to corresponding gears mounted on the corresponding electromotive recording devices whereby movement of each cable moves its corresponding spring-loaded geared rack which in turn rotates its corresponding gear thereby changing the electromotive force at the corresponding electromotive recording device.

20. A method as defined in claim 12, wherein the bore hole is at about 10 to about 25 feet long and wherein the anchors are located throughout the length of the bore hole.

21. A method as defined in claim 14, wherein the bore hole is at about 10 to about 25 feet long and wherein the anchors are located throughout the length of the bore hole.

22. A method as defined in claim 16, wherein the bore hole is at about 10 to about 25 feet long and wherein the anchors are located throughout the length of the bore hole.