WO2020061598A1 - Rock bolt with strain detection means - Google Patents

Rock bolt with strain detection means Download PDF

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Publication number
WO2020061598A1
WO2020061598A1 PCT/ZA2019/050058 ZA2019050058W WO2020061598A1 WO 2020061598 A1 WO2020061598 A1 WO 2020061598A1 ZA 2019050058 W ZA2019050058 W ZA 2019050058W WO 2020061598 A1 WO2020061598 A1 WO 2020061598A1
Authority
WO
WIPO (PCT)
Prior art keywords
strain
rock bolt
rod
processing module
measuring rock
Prior art date
Application number
PCT/ZA2019/050058
Other languages
French (fr)
Inventor
Greig KNOX
Original Assignee
Epiroc Holdings South Africa (Pty) Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Epiroc Holdings South Africa (Pty) Ltd filed Critical Epiroc Holdings South Africa (Pty) Ltd
Publication of WO2020061598A1 publication Critical patent/WO2020061598A1/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/0004—Force transducers adapted for mounting in a bore of the force receiving structure
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
    • E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
    • E21D21/02—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection having means for indicating tension
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B1/00—Measuring instruments characterised by the selection of material therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B5/00—Measuring arrangements characterised by the use of mechanical techniques
    • G01B5/30—Measuring arrangements characterised by the use of mechanical techniques for measuring the deformation in a solid, e.g. mechanical strain gauge
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B31/00—Screwed connections specially modified in view of tensile load; Break-bolts
    • F16B31/02—Screwed connections specially modified in view of tensile load; Break-bolts for indicating the attainment of a particular tensile load or limiting tensile load
    • F16B2031/022—Screwed connections specially modified in view of tensile load; Break-bolts for indicating the attainment of a particular tensile load or limiting tensile load using an ultrasonic transducer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2210/00—Aspects not specifically covered by any group under G01B, e.g. of wheel alignment, caliper-like sensors
    • G01B2210/66—Rock or ground anchors having deformation measuring means

Definitions

  • the invention relates to a rock bolt with means to measure the strain on the rock bolt as it yields under load.
  • rock wall support such as installed rock bolts
  • [0G04J ft would be desirable to be able to monitor a rock bolt and to detect when the rock bolt is approaching overload or maximum strain. The bolt can then indicate that it is approaching its load or strain limit and action can be taken to avoid a catastrophic failure event. However it is difficult to measure strain on an installed bolt,
  • a strain gauge typically is used to measure strain.
  • the device measures a change in resistance over the device as a function of the strain of an element to which the device is attached.
  • a rock bolt is designed to elongate significantly over its length. The magnitude of the strain would render compatible a strain gauge or the like.
  • the invention at least partially solves the aforementioned problems.
  • the invention provides a strain measuring rock bolt which includes: a yielding rod of a malleable material which extends between a distal end and a proximal end; a bore which extends through the rod between the distal and proximal ends; an strain sensor comprising an elongate member of a conductive elastomeric material, which is fixed to the rod within the bore to elongate as the rod elongates under load, and a power source which is electrically connected to the member in a power circuit; a processing module electronically connected to the power circuit; wherein the processing module is adapted to measure a change in an electrical property of the elongate member, as the member elongates under strain; and wherein the processing module is adapted to calculate the strain on the rod based on the change and to communicate with an output means based on the calculated strain.
  • the conductive elastomeric materia! of the elongate member preferably is a silicone carbon composite material.
  • the electrical property maybe resistance, capacitance or inductance.
  • the output means may be a means that visually, audibly or by data communicates the difference.
  • the output means may be an LED, an audible alarm or a transmitter.
  • the processing module may communicate with the LED, alarm or transmitter, to illuminate, sound or transmit data respectively, when the calculated strain exceeds a predetermined limit.
  • the LED may be visible from the proximal end of the rod.
  • the processing module may be electronically interposed between the power circuit and the output means.
  • the processing module may include a microcontroller with an Analog-to- Digital Converter ADC”)
  • the power source may be a battery.
  • Figures 1 and 2 are diagrammatic representations of a strain measuring rock bolt in accordance with the invention and an electronics module of the rock bolt respectively
  • the invention provides a strain measuring rock bolt 10 which is illustrated in Figure 1
  • the rock bolt includes a yielding rod 12, of a suitable malleable metal material, which extends between a distal end 14 and a proximal end 16.
  • the rod has a bore 18 which extends the entire length of the rod, between the ends (14, 16).
  • the rod is partially externally threaded along a proximal end portion 20.
  • a nut 22 is engaged to the threaded portion.
  • the rock bolt 10 further includes a strain sensor 24, comprising an elongate member 26 of a suitable conductive elastomeric materia! which is fixed to the rod 12 within the bore 18, a battery 28 and a resistor 30.
  • the member, battery and resistor are electrically connected in series in a power circuit.
  • the battery and the resistor are part of a PCB 32.
  • the PCB 32 is housed in a housing 33 which is attached to the proximal end [0024] An LED 34 is partially contained within the housing.
  • the PCB includes a processing unit 36 which is electronically interposed between the power circuit of the sensor 24 and the LED.
  • the elastomeric elongate member 20 extends between a first end 38 and a second end 40.
  • the member extends within the bore, fixed to the rock bolt in any suitable way so as to allow the member to elongate proportionally to the rod when the rod elongates, in use, under load in this example, the member is fixed at the first end 38, to the distal end 14 of the rod 12.
  • the member 26 is attached to the RGB 30 in electrical communication.
  • the member is a transducer, to the processing unit 36, of the strain of the rock bolt.
  • the processing unit 36 includes a microprocessor 42, an ADC 44 and a memory unit 48, such as ROM or RAM.
  • input into the memory unit are at least the following values: resistance (“RT) of the resistor 30, voltage (“Vin”) of the battery 28, resistance (“Rx”) of the elongate member 26 before elongation and the physical dimensions of the elongate member.
  • the processing unit 26 As the rod 12 experiences strain, elongating under load when in use, inserted into a rock hole, the elongate member 26 elongates proportionally, The elongation of the elongate member changes its resistivity and increases its resistance to an electricai current flowing through the power circuit. [0028] As the processing unit 26 is connected to a centre tap between the resistor
  • Vout the voltage across the elongate member
  • the microprocessor 42 can compute the resistance (“Ry”) of the elongate member 26 after the event or period. From R y, strain can he calculated from resistivity to length data pertaining to the particular elastomeric material.
  • the processing unit 36 can be pre-set with a stress limit. If the measured strain exceeds the stress limit, the microprocessor can cause the LED 34 to energise to emit light as a visual signal. As the LED is in the housing, and the housing protrudes from the rock hole in which the rock bolt 10 is inserted, the visual signal is easily seen by a mine worker as an indication that the rock bolt is overloaded.

Abstract

The invention provides a strain measuring rock bolt (10) which includes a yielding rod (12) of a malleable material which extends between a distal end (14) and a proximal end (16), a bore (18) which extends through the rod between the distal and proximal ends, an strain sensor (24) comprising an elongate member (26) of a conductive elastomeric material, which is fixed to the rod (12) within the bore to elongate as the rod elongates under load, and a power source which is electrically connected to the member in a power circuit, a processing module electronically connected to the power circuit, wherein the processing module is adapted to measure a change in an electrical property of the elongate member, as the member elongates under strain and wherein the processing module is adapted to calculate the strain on the rod based on the change and to communicate with an output means based on the calculated strain.

Description

ROCK BOLT WITH STRAIN DETECTION MEANS
FIELD OF THE INVENTION The invention relates to a rock bolt with means to measure the strain on the rock bolt as it yields under load.
BACKGROUND OF INVENTION
[0002] To improve mine safety, it is important to be able to assess the integrity of rock wall support, such as installed rock bolts.
[0003] Passive and dynamic forces are imposed on a rock bolt by the surrounding rock mass to which the bolt offers load support. These forces strain the rock bolt. A rock bolt is prone to catastrophically fail when the bolt is subjected to load that exceeds a maximum tolerance of the bolt. This event is termed“overload”.
[0G04J ft would be desirable to be able to monitor a rock bolt and to detect when the rock bolt is approaching overload or maximum strain. The bolt can then indicate that it is approaching its load or strain limit and action can be taken to avoid a catastrophic failure event. However it is difficult to measure strain on an installed bolt,
[0005] A strain gauge typically is used to measure strain. The device measures a change in resistance over the device as a function of the strain of an element to which the device is attached. o
[0006] Use of a strain gauge is limited in the mining context as it is difficult to adhere the device to the bolt with any degree of permanence and, even if this problem was overcome, the device is designed to measure sma!l changes in resistance, proportional to small strain Furthermore, complexity in the electronics to measure the change comes with small changes in an electronic parameter. With complexity comes cost and size, neither of which lend to a high volume, commoditised product
[0007] A rock bolt is designed to elongate significantly over its length. The magnitude of the strain would render inutile a strain gauge or the like.
[0008] The invention at least partially solves the aforementioned problems.
SUMMARY OF INVENTION
[0009] The invention provides a strain measuring rock bolt which includes: a yielding rod of a malleable material which extends between a distal end and a proximal end; a bore which extends through the rod between the distal and proximal ends; an strain sensor comprising an elongate member of a conductive elastomeric material, which is fixed to the rod within the bore to elongate as the rod elongates under load, and a power source which is electrically connected to the member in a power circuit; a processing module electronically connected to the power circuit; wherein the processing module is adapted to measure a change in an electrical property of the elongate member, as the member elongates under strain; and wherein the processing module is adapted to calculate the strain on the rod based on the change and to communicate with an output means based on the calculated strain.
[0010] The conductive elastomeric materia! of the elongate member preferably is a silicone carbon composite material.
[0011] The electrical property maybe resistance, capacitance or inductance. [0012] The output means may be a means that visually, audibly or by data communicates the difference.
[0013] The output means may be an LED, an audible alarm or a transmitter.
[0014] The processing module may communicate with the LED, alarm or transmitter, to illuminate, sound or transmit data respectively, when the calculated strain exceeds a predetermined limit.
[0015] The LED may be visible from the proximal end of the rod.
[0016] The processing module may be electronically interposed between the power circuit and the output means.
[0017] The processing module may include a microcontroller with an Analog-to- Digital Converter ADC”)
[0018] The power source may be a battery. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention is described with reference to the following drawings in which Figures 1 and 2 are diagrammatic representations of a strain measuring rock bolt in accordance with the invention and an electronics module of the rock bolt respectively
DESCRIPTION OF PREFERRED EMBODIMENTS
[0020] The invention provides a strain measuring rock bolt 10 which is illustrated in Figure 1
[0021] The rock bolt includes a yielding rod 12, of a suitable malleable metal material, which extends between a distal end 14 and a proximal end 16. The rod has a bore 18 which extends the entire length of the rod, between the ends (14, 16). The rod is partially externally threaded along a proximal end portion 20. A nut 22 is engaged to the threaded portion.
[0022] The rock bolt 10 further includes a strain sensor 24, comprising an elongate member 26 of a suitable conductive elastomeric materia! which is fixed to the rod 12 within the bore 18, a battery 28 and a resistor 30. The member, battery and resistor are electrically connected in series in a power circuit. The battery and the resistor are part of a PCB 32.
[0023] The PCB 32 is housed in a housing 33 which is attached to the proximal end
Figure imgf000006_0001
[0024] An LED 34 is partially contained within the housing. The PCB includes a processing unit 36 which is electronically interposed between the power circuit of the sensor 24 and the LED.
[0025] The elastomeric elongate member 20 extends between a first end 38 and a second end 40. The member extends within the bore, fixed to the rock bolt in any suitable way so as to allow the member to elongate proportionally to the rod when the rod elongates, in use, under load in this example, the member is fixed at the first end 38, to the distal end 14 of the rod 12. At the opposed second end 40, the member 26 is attached to the RGB 30 in electrical communication. The member is a transducer, to the processing unit 36, of the strain of the rock bolt.
[0026] The processing unit 36 includes a microprocessor 42, an ADC 44 and a memory unit 48, such as ROM or RAM. input into the memory unit are at least the following values: resistance (“RT) of the resistor 30, voltage (“Vin") of the battery 28, resistance ("Rx”) of the elongate member 26 before elongation and the physical dimensions of the elongate member.
[0027] As the rod 12 experiences strain, elongating under load when in use, inserted into a rock hole, the elongate member 26 elongates proportionally, The elongation of the elongate member changes its resistivity and increases its resistance to an electricai current flowing through the power circuit. [0028] As the processing unit 26 is connected to a centre tap between the resistor
30 and the elongate member 26, it can measure the voltage across the elongate member (“Vout”) to determine the strain (difference in length) of the yielding rod 12 This measurement can occur after a loading event or it can occur periodically.
[0029] Calling on the invariable values from the memory unit 48, with the Vout fed from the ADC 44, the microprocessor 42 can compute the resistance (“Ry") of the elongate member 26 after the event or period. From Ry, strain can he calculated from resistivity to length data pertaining to the particular elastomeric material.
[0030] The processing unit 36 can be pre-set with a stress limit. If the measured strain exceeds the stress limit, the microprocessor can cause the LED 34 to energise to emit light as a visual signal. As the LED is in the housing, and the housing protrudes from the rock hole in which the rock bolt 10 is inserted, the visual signal is easily seen by a mine worker as an indication that the rock bolt is overloaded.

Claims

1. A strain measuring rock bolt which includes a yielding rod of a malleable material which extends between a distal end and a proximal end, a bore which extends through the rod between the distal and proximal ends, a strain sensor comprising an elongate member of a conductive elastomeric material, which is fixed to the rod within the bore to elongate as the rod elongates under load, and a power source which is electrically connected to the member in a power circuit, a processing module electronically connected to the power circuit, wherein the processing module is adapted to measure a change in an electrical property of the elongate member, as the member elongates under strain, and wherein the processing module is adapted to calculate the strain on the rod based on the change and to communicate with an output means based on the calculated strain.
2. A strain measuring rock bolt according to claim 1 wherein the conductive elastomeric material of the elongate member Is a silicone carbon composite material
3. A strain measuring rock bolt according to claim 1 or 2 wherein the electrical property is resistance, capacitance or inductance.
4. A strain measuring rock bolt according to any one of claims 1 to 3 wherein the output means is a means which visually, audibly or by data communicates the difference.
5. A strain measuring rock bolt according to claim 4 wherein the output means is an LED, an audible alarm or a transmitter.
6. A strain measuring rock bolt according to claim 5 wherein the processing module communicates with the LED, alarm or transmitter, to illuminate, sound or transmit data respectively, when the calculated strain exceeds a predetermined limit.
7. A strain measuring rock bolt according to claim 5 or 6 wherein the LED is positioned to be visible from the proximal end of the rod.
8. A strain measuring rock bolt according to any one of claims 1 to 7 wherein the processing module is electronically interposed between the power circuit and the output means.
9. A strain measuring rock bolt according to any one of claims 1 to 8 wherein the processing module includes a microcontroller with an Analog-to-Digita! Converter.
PCT/ZA2019/050058 2018-09-21 2019-09-16 Rock bolt with strain detection means WO2020061598A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ZA2018/06339 2018-09-21
ZA201806339 2018-09-21

Publications (1)

Publication Number Publication Date
WO2020061598A1 true WO2020061598A1 (en) 2020-03-26

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ZA (1) ZA201906093B (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022251887A1 (en) * 2021-05-28 2022-12-01 Innovative Mining Products (Pty)Ltd Modified spherical seat for a rock bolt assembly

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2600029A (en) * 1946-11-12 1952-06-10 Gerotor May Corp Stress indicating bolt or stud
GB2199952A (en) * 1987-01-16 1988-07-20 Coal Ind Method and apparatus for measuring load on a rock bolt
EP0504676A1 (en) * 1991-03-15 1992-09-23 Straintec AG Sensor for strain measurement
WO2000008342A1 (en) * 1998-08-05 2000-02-17 Hedley Purvis Limited Load indicating device for a threaded fastener

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2600029A (en) * 1946-11-12 1952-06-10 Gerotor May Corp Stress indicating bolt or stud
GB2199952A (en) * 1987-01-16 1988-07-20 Coal Ind Method and apparatus for measuring load on a rock bolt
EP0504676A1 (en) * 1991-03-15 1992-09-23 Straintec AG Sensor for strain measurement
WO2000008342A1 (en) * 1998-08-05 2000-02-17 Hedley Purvis Limited Load indicating device for a threaded fastener

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022251887A1 (en) * 2021-05-28 2022-12-01 Innovative Mining Products (Pty)Ltd Modified spherical seat for a rock bolt assembly

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Publication number Publication date
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