CA1197604A - Conveyor belt monitor - Google Patents
Conveyor belt monitorInfo
- Publication number
- CA1197604A CA1197604A CA000409621A CA409621A CA1197604A CA 1197604 A CA1197604 A CA 1197604A CA 000409621 A CA000409621 A CA 000409621A CA 409621 A CA409621 A CA 409621A CA 1197604 A CA1197604 A CA 1197604A
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- CA
- Canada
- Prior art keywords
- belt
- zone
- ultrasound
- belting
- transducer
- Prior art date
- Legal status (The legal status 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 status listed.)
- Expired
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- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
- Control Of Conveyors (AREA)
Abstract
ABSTRACT
Flaws may be detected in conveyor belting in motion by transmitting ultrasound to the belting at one zone, detecting ultrasound propagated by the belting from the one zone to another zone spaced apart from the first and issuing a signal responsive to ultrasound if any detected whereby a signal is obtained which is indicative of discontinuities in the belting intermediate the zones. Preferably a column of water extending between an ultrasonic transducer and the belt is used for ultrasonic coupling during motion of the belt and tracking means are provided to maintain the column at constant length.
Flaws may be detected in conveyor belting in motion by transmitting ultrasound to the belting at one zone, detecting ultrasound propagated by the belting from the one zone to another zone spaced apart from the first and issuing a signal responsive to ultrasound if any detected whereby a signal is obtained which is indicative of discontinuities in the belting intermediate the zones. Preferably a column of water extending between an ultrasonic transducer and the belt is used for ultrasonic coupling during motion of the belt and tracking means are provided to maintain the column at constant length.
Description
6~'1 This invention relates to a method and apparatus for detecting a rip or flaw in a conveyor belt.
Conveyor belts comprising rubber or rubber-like materials are in some uses susceptible to failure by tearing or ripping. Early detection of such flaws is desirable to prevent loss of conveyed materials and complete failure of, or damage to, conveyor belts.
For that purpose various means such as trip cords and tilt trays have been used mechanically to detect material falling through a tear in the conveyor belt. Such monitors are only sensitive to a gaping rip sufficient to permit material to fall through, or to gross belt failure.
In another method the electrical continuity of electrical conductors embedded in the belt composition is monitored. However, that method requires the use of expensive and non-standard belts and it is difficult to maintain the conductors in a production environment.
of the methods employed to-date all are either insensitive to some ways in which a belt can rip or are otherwise impractical.
It would be particularly advantageous if a flaw or incipient flaw likely to result in belt failure could be detected so that preventative maintenance could be conducted. None of the methods hitherto proposed for monitoring conveyor belts has been useful for that purpose The present invention uses ultrasonic vibrations, referred to hereinafter as "ultrasound", for the purpose of detecting discontinuties in the belting.
I, 2a It has hitherto been believed that transmission of ultrasound in rubber over distances of more than a few centimeters was impracticable due to the high level of attenuation of ultrasound in rubber. It was also thought tihat attenuation would decrease continuously with decreasing frequency.
The present invention stems from the discovery that ultrasound may be propogated in belting comprising a rubber or rubber like composition, and that particular frequencies of ultrasound are attenuated to a much lesser degree than expected and to a lesser degree than other higher or lower frequencies.
The particular frequencies may be ascertained by experiment for a particular belting composition and belting thickness. There may be more than one particular frequency at which the attenuation is low in comparison with neighbourlng frequencies.
Surprising, it has been found possible to select an ultrasound frequency at which attenuation in belting is sufficiently low that a transmitter and receiver may be spaced apart over a long path length, for example a meter or more, enabling a transmitter and receiver to be situated adjacent opposite side edges of an industrial scale conveyor belt. Moreover the low attenuation enables a reLiable signal to be propogated and detected at a distance from the transmitter even when the intervening conveyor belting is of a poor quality but intact.
,.
Preferred embodiments ox the method of-the invention also permit small discontinuities throughout the length of a belt to be discovered while the belt is in normal use and enable identification of portions requiring preventative maintenance to reduce the risk of a rip subsequently occurring.
According to a first aspect the invention consists in a method fox detecting a ri? in a conveyor belting comprising rubber or rubber-liXe composition, the method comprising the stews of:
(a) trans,nit'ing ultrasound of a particular frequency to the belting at a first æone;
(D) detecting ultrasound of said particular frequency propagated by the belting from the first zone to a second zone spaced apart from the first; and (c) issuing a signal responsive to the intensity of ultrasound, if any, so detected whereby said signal is indicative of discontinuities in the belting intermediate said zones.
According to a second aspect the invention consists in apparatus comprising:
a conveyor belt comprising a rubber or rubber liXe material, the belt passing throuc3h a first zone and a second zone spaced from the first, go tran~lucer means or producing uLtrasound at a prede.ermined frequency, cou?ling means for transmitting said ultrasound Jo the Dell wnile it is in motion through the first zone, and sensor jeans producing a signal responsive to said ul~rasoun~ toe welt at toe second zone.
In preferred embodiments the invention is used to monitor a conveyor belt while in motion. ultrasound generated by a piezo-electric transducec is transmitted to moving belting via a liquid or aqueous medium impinging on the underside of the belting at a first zone. The ultrasound is propogated along the belting to a second zone at which a detector produces a signal responsive to ultrasound, also coupled to it via a liquid or aqueous medium. Vaciatio;;s in the received signal are indicative of discontinuities or flaws of the belting intermediate the zones. or preference the zones are s`paced apart on a line perpendicular to the direction ox travel of the belt.
ay way of example only an embodiment of apparatus according to the invention will now be described with reference to the accompanying drawings wherein:-Fig. 1 is a general arrangement according to the invention.
Fig. 2 is a cross-section of a transducer assembly useful for transmitting ultrasound to a conveyor belt in motion.
Fig. 3 shows one part oE the means foc mounting the apparatus of Fig. 2 in the arrangement of Fig. 1.
Fig. 4 shows a second part of the means for mounting the apparatus of Fig. 2 in the arrangement of Fig. 1.
Fig. 5 shows a third part of the means for mountiny the apparatus of Fig. 2 in the arrangement of Fig. 1.
Fig. 6 is a grapih showing the attenuation of ultrasound in belting of 25 and 20 mm thickness at various frequencies.
With reference to Fig. 1 there is shown a cross-section through an endless conveyor belt 1, transverse the direction of conveyor travel.
The conveyor has a trough shaped cross-section and belting 1 is supported along its length by means not shown in Fig. 1.
The conveyor belting is typical of the wind used in the mining industry comprising a steel cord reinforced rubber-like composition having a width edge to edge of 1-2 meters and having a thickness in the present example of 2~ or 25 mm.
- 4a -A first transducer assembly 2 is mounted adjacent to and beneath conveyor belt 1 near one edge of the conveyor and a second transducer assembly 2 is similarly mounted near the opposite edge. One transducer assembly 2 together with associated circuitry is a means for producing ultrasound and the other with associated circuitry acts as a detector of ultrasound.
In use a column of water extends between each transducer assembly 2 and a zone 3 of belt 1 overlying that transducer assembly.
Ultrasound may thus be transmitted from one transducer assembly 2 via a water column extending from the transducer to a zone 3 of belt 1, through belt 1 to a second zone 3 overlying the other transducer assembly, and via a water column to ultrasound detection means associated with the other transducer assembly 2.
A discontinuity in belt 1 between zones 3 may thus be detected.
With reference to Fig. 2 there is shown in cross-section a transducer assembly 2 useful either for transmitting ultrasound to a belt in motion or for detecting ultrasound in the belt. The transducer assembly comprises an upper tubular case part 10 and a lower tubular case part 11 connected at respective radially extending flanges 12 and 13 by fasteners 14.
Upper case part 10 has an upper radially extending flange 15 to which is mounted a head 16 defining a chamber 17 provided with a water inlet tube 18 and a water outlet orifice 19.
7~
Case parts 10 and 11 house a sub-assembly comprising two discs 21,22 of pizeo-electric material (such as Philips PXE42)separated at adjacent faces by metallic foil 23 and clamped coaxially between metal cylinders 24 and 25 by sleeve mounting on bolt 26 which extends through cylinder 24, disks 21 and 22, foil 23 and threadibly engages a threaded blind bore 27 of cylinder 25.
A cylindrical plug 28 of a non-metallic solid material, typically a plastics substance, is fixed at one end 28 to the upper face of metal cylinder 25. The other end 30 of plug 28 is of reduced diameter over a length extending into cavity 17. O-rings 31 provide a seal between plug 28 and case 16.
Cylinder 25 is provided with a radially extending flange 32 which is clamped between O-rings 33 grooved in case flanges 12 and 13 whereby the pizeo-electric crystal sub-assembly is mounted.
Electrlcal connection 34 with metallic foil 3 serves as a connection to one electric pole of pizeo-electric disks 1,2.
The other electrical pole is kept at earth potential by connection 35 of the end face of each disc remote from foil 3 to earth potential. Cylinders 24 and 25 are of dissimilar metal and the axial lengths are chosen having regard to the velocity of ultrasound in the respective metals. The combined sub-assembly connected by bolt 26 can vibrate substantially in the axial direction at ultrasonic frequencies with a fundamental resonance frequency occurring when the wavelength of the vibration is equal to twice the combined axial dimension.
761~
In use as a transmitter water fed under pressure via inlet tube 18 to cavity 17 flows outwardly from orifice 19 and impinges on the underside of an overlying conveyor belt 1.
A continuous column of water thus extends between the ultrasound transmitting face 30 of plug 28 and the overlying zone ox belt 1 providing an ultrasound coupling medium, notwithstanding motion of the belt. Flange 33 surroundiny orifice 19 assists to maintain the water column while conveyor belt 1 is in motion. '' The ultrasonic receiver and transmitter are similar in design and differ in respect of the electric circuit 36 shown schematically. This circuit is of a type well known in the art and comprises an impedance matching inductor in the transmitter and in the receiver a similar inductor in addition to a pre-amplifier. In the case oE the transmitter electrical signals supplied through cable 37 are converted to ultrasonic vibrations according to the piezo-electric effect and in the receiver the vibrations are converted to electric signals by the piezo-electric effect and amplified by the pre-amplifier for subsequent analysis. A lug 38 is fixed to case 11 to facilitate mounting.
Figure 3 shows a means of mounting the transducer assembly 2 (referring collectively to the receiver and transmitter) relative to a conveyor belt 1. Transducer assembly 2 is fixed to a lever arm 40 by bolts through the lug 38 in such a way that allows a small rotation about an axis through bolt 41 so as to adjust and fix the angle of the axis of the transducer to the surfaces of the belt. The .~_ ~g~
lever arm 40 is fixed to a pipe clamp 42 by a lug ~3. Pipe clamp 42 attaches over a roller 5 shown in Fig. 1 and in part sectioned view in Fig. 4. Roller 5 is modiEied from a typical idler roller and forms a pivot axis for transducer assembly 2 such that the transducer assembly can follow the random vertical movements of belt 1.
With reference to Fig. 4, roller 5 is provided with a helical spring 51 mounted co-axially in the roller and whereby a restoring torque acts on the roller with respect to the fixed shaft 52 and in turn provides an upward force to the transducer relative to the conveyor belts. Spring 5,1 is secured at one end 54 to the roller by a collet 53 fastened by a screw (not shown) to the inside wall of roller 5 and is free of the shaft 52.
The other end of spring 51 is secured to the shaft 52 by a similar collet 55 which is free of the inside wall of roller 5. Each end of the spring is fastened to the respective collet by a grub screw 56 (not sectioned).
Attached to the same roller 5 is a wheel arrangement 6 shown in Fig. 5.
The separation of the face of the transducer at the or.ifice 17 from the surface of belt 1 is controlled by wheel arrangement 6. Wheel 61 is mounted on an axle 62 and fork 63 which is in turn mounted on a lever arm 64 at pivot axle 65.
This arrangement allows for the rotation of the wheel about the axis of axle 65 so as to effectively adjust the separation of the axle 65 from belt 1. Adjustment is made by screw 66 which is screwed into lug 67 attached rigidly to the ~3~
lever arm 6~ and acts on t.he lug 6~ whicii is rigidly attached to the York ~3. 'rhe assembly is clamped adjacent to the transducec on the roller 5 by a clamp 69 similar to clamp ~2. Adjustment ox screw 66 results in rotation of the roller 5 and a change in the separation of the transducer from tne belt. Contact ox the wheel and the belt is maintained by roller spring 51.
With re~erènce to Fig. 1, rollers 5 are mounted in the usual way on an idler frame 4. The transmitter transducer assembly 2 and associated wheel 6 is mounted so as to transmit ultrasound into one edge of the belt and the receiver transducer assembly 2 with associated wheel 6 is mounted on the opposite roller 5 to detect ultLasound at the other edge of the belt.
Electrical energy is supplied to the transmitter at a frequency for preference equal to the fundamental resonant frequency of that transmitter in a series of short pulses.
Also for preference the frequency is such that the wavelength of ultrasound in the conveyor belt is equal to one thickness of belt.
When the ultrasound is of a particular frequency such that the wavelength in beLting is equal or similar in dimension to the belting thickness dimension, the ultrasound attenuation is of the order of only 0.5-0.65 dB per cm of path length, whereas at neighbouring higher and lower frequencies the attenuation is significantly greater.
When reference to Fig. 6 there is shown a plot of ultrasound attenuation in decibels per centimeter of path _ 9 _ g7~
length against requency in belting of thicknesses. In a steel cord reinforced belting of 25 mm thickness and at frequency of 43.6 XHz the wavelength is about 25 mm and the attenuation is at or near a minimum. By selecting a frequency of 43.5 XHz ultrasound can be propogated and detected over a path length exceeding one meter in the 25 mm thick belt. At frequencies in excess of 100 kHz ultrasound is Darely detectable over a path length in the belting of 20 cm and at lower frequencies the attenuation i5 also greater.
Likewise for a belt of similar construction but of thickness 20 mm, at a frequency of 47.6 kHz the ultrasound wavelength is about 21 my and attenuation is at or near a minimum.
As is apparent from Fig. 6 there is another attenuation minimum for~the 25 mm thicXness belting at around 39 ~Hz.
As will be apparent to those sifted in the art the frequency is desirably selected having regard both to the level of attenuation and the sensitivity of attenuation to slight change in frequency.
Signals from the receiver are amplified, rectiied and sampled at a certain time following each pulse of electrical energy supplied to the transmitter. This delay takes into account the time that the resultant pulse of ultrasound travels from the transmitter to the receiver. An alarm circuit monitors the level of ultrasound and issues an alarm if this level falls below an adjustable threshold for an adjustable period of time. This alarm is also inhibited if - 9a -,~, ~97~
certain functions of the apparatus are not operational. Such functions include power supplies and coupling water supply.
Thus the apparatus can be adjusted to be responsive to rips and other faults that are of a predetermined severity and/or oE a certain minimum length. The conveyor belt drive motor is stopped if all alarm conditions apply.
The apparatus described is normally mounted at a location on the conveyor belt so that it monitors the belt immediately after passing through areas where rips are likely to occur. These locations are usually immediately after the belt is loaded. One problem occurs when the conveyor belt contains relatively long sections that, because of their poor physical condition, do not satisfactorily transmit ultrasound. The belt rip detector can be made insensitive to these sections by increasing the response time (and hence rip length) of the alarm circuit. This, however, also increases the minimum length of rip capable of being detected. To overcome this problem a second rip detector is mounted to monitor the belt immediately before passing through the area where a rip is most likely to occur. The conveyor belt drive motor is stopped only if the condition of the belt has deteriorated between the two rip detectors.
Another application of the apparatus relates to its use for detecting long term degradation of the belt and identifying sections that require preventative maintenance.
This is done by compiling a log of the level of received ultrasound throughout the entire length of the belt. In addition, as an alternative condition for raising an alarm . I_ ..
3'~, _ the 109 is compared in real time with the actual received level of ultrasound and an alarm is raised when the actual level differs from the log.
. ..
Conveyor belts comprising rubber or rubber-like materials are in some uses susceptible to failure by tearing or ripping. Early detection of such flaws is desirable to prevent loss of conveyed materials and complete failure of, or damage to, conveyor belts.
For that purpose various means such as trip cords and tilt trays have been used mechanically to detect material falling through a tear in the conveyor belt. Such monitors are only sensitive to a gaping rip sufficient to permit material to fall through, or to gross belt failure.
In another method the electrical continuity of electrical conductors embedded in the belt composition is monitored. However, that method requires the use of expensive and non-standard belts and it is difficult to maintain the conductors in a production environment.
of the methods employed to-date all are either insensitive to some ways in which a belt can rip or are otherwise impractical.
It would be particularly advantageous if a flaw or incipient flaw likely to result in belt failure could be detected so that preventative maintenance could be conducted. None of the methods hitherto proposed for monitoring conveyor belts has been useful for that purpose The present invention uses ultrasonic vibrations, referred to hereinafter as "ultrasound", for the purpose of detecting discontinuties in the belting.
I, 2a It has hitherto been believed that transmission of ultrasound in rubber over distances of more than a few centimeters was impracticable due to the high level of attenuation of ultrasound in rubber. It was also thought tihat attenuation would decrease continuously with decreasing frequency.
The present invention stems from the discovery that ultrasound may be propogated in belting comprising a rubber or rubber like composition, and that particular frequencies of ultrasound are attenuated to a much lesser degree than expected and to a lesser degree than other higher or lower frequencies.
The particular frequencies may be ascertained by experiment for a particular belting composition and belting thickness. There may be more than one particular frequency at which the attenuation is low in comparison with neighbourlng frequencies.
Surprising, it has been found possible to select an ultrasound frequency at which attenuation in belting is sufficiently low that a transmitter and receiver may be spaced apart over a long path length, for example a meter or more, enabling a transmitter and receiver to be situated adjacent opposite side edges of an industrial scale conveyor belt. Moreover the low attenuation enables a reLiable signal to be propogated and detected at a distance from the transmitter even when the intervening conveyor belting is of a poor quality but intact.
,.
Preferred embodiments ox the method of-the invention also permit small discontinuities throughout the length of a belt to be discovered while the belt is in normal use and enable identification of portions requiring preventative maintenance to reduce the risk of a rip subsequently occurring.
According to a first aspect the invention consists in a method fox detecting a ri? in a conveyor belting comprising rubber or rubber-liXe composition, the method comprising the stews of:
(a) trans,nit'ing ultrasound of a particular frequency to the belting at a first æone;
(D) detecting ultrasound of said particular frequency propagated by the belting from the first zone to a second zone spaced apart from the first; and (c) issuing a signal responsive to the intensity of ultrasound, if any, so detected whereby said signal is indicative of discontinuities in the belting intermediate said zones.
According to a second aspect the invention consists in apparatus comprising:
a conveyor belt comprising a rubber or rubber liXe material, the belt passing throuc3h a first zone and a second zone spaced from the first, go tran~lucer means or producing uLtrasound at a prede.ermined frequency, cou?ling means for transmitting said ultrasound Jo the Dell wnile it is in motion through the first zone, and sensor jeans producing a signal responsive to said ul~rasoun~ toe welt at toe second zone.
In preferred embodiments the invention is used to monitor a conveyor belt while in motion. ultrasound generated by a piezo-electric transducec is transmitted to moving belting via a liquid or aqueous medium impinging on the underside of the belting at a first zone. The ultrasound is propogated along the belting to a second zone at which a detector produces a signal responsive to ultrasound, also coupled to it via a liquid or aqueous medium. Vaciatio;;s in the received signal are indicative of discontinuities or flaws of the belting intermediate the zones. or preference the zones are s`paced apart on a line perpendicular to the direction ox travel of the belt.
ay way of example only an embodiment of apparatus according to the invention will now be described with reference to the accompanying drawings wherein:-Fig. 1 is a general arrangement according to the invention.
Fig. 2 is a cross-section of a transducer assembly useful for transmitting ultrasound to a conveyor belt in motion.
Fig. 3 shows one part oE the means foc mounting the apparatus of Fig. 2 in the arrangement of Fig. 1.
Fig. 4 shows a second part of the means for mounting the apparatus of Fig. 2 in the arrangement of Fig. 1.
Fig. 5 shows a third part of the means for mountiny the apparatus of Fig. 2 in the arrangement of Fig. 1.
Fig. 6 is a grapih showing the attenuation of ultrasound in belting of 25 and 20 mm thickness at various frequencies.
With reference to Fig. 1 there is shown a cross-section through an endless conveyor belt 1, transverse the direction of conveyor travel.
The conveyor has a trough shaped cross-section and belting 1 is supported along its length by means not shown in Fig. 1.
The conveyor belting is typical of the wind used in the mining industry comprising a steel cord reinforced rubber-like composition having a width edge to edge of 1-2 meters and having a thickness in the present example of 2~ or 25 mm.
- 4a -A first transducer assembly 2 is mounted adjacent to and beneath conveyor belt 1 near one edge of the conveyor and a second transducer assembly 2 is similarly mounted near the opposite edge. One transducer assembly 2 together with associated circuitry is a means for producing ultrasound and the other with associated circuitry acts as a detector of ultrasound.
In use a column of water extends between each transducer assembly 2 and a zone 3 of belt 1 overlying that transducer assembly.
Ultrasound may thus be transmitted from one transducer assembly 2 via a water column extending from the transducer to a zone 3 of belt 1, through belt 1 to a second zone 3 overlying the other transducer assembly, and via a water column to ultrasound detection means associated with the other transducer assembly 2.
A discontinuity in belt 1 between zones 3 may thus be detected.
With reference to Fig. 2 there is shown in cross-section a transducer assembly 2 useful either for transmitting ultrasound to a belt in motion or for detecting ultrasound in the belt. The transducer assembly comprises an upper tubular case part 10 and a lower tubular case part 11 connected at respective radially extending flanges 12 and 13 by fasteners 14.
Upper case part 10 has an upper radially extending flange 15 to which is mounted a head 16 defining a chamber 17 provided with a water inlet tube 18 and a water outlet orifice 19.
7~
Case parts 10 and 11 house a sub-assembly comprising two discs 21,22 of pizeo-electric material (such as Philips PXE42)separated at adjacent faces by metallic foil 23 and clamped coaxially between metal cylinders 24 and 25 by sleeve mounting on bolt 26 which extends through cylinder 24, disks 21 and 22, foil 23 and threadibly engages a threaded blind bore 27 of cylinder 25.
A cylindrical plug 28 of a non-metallic solid material, typically a plastics substance, is fixed at one end 28 to the upper face of metal cylinder 25. The other end 30 of plug 28 is of reduced diameter over a length extending into cavity 17. O-rings 31 provide a seal between plug 28 and case 16.
Cylinder 25 is provided with a radially extending flange 32 which is clamped between O-rings 33 grooved in case flanges 12 and 13 whereby the pizeo-electric crystal sub-assembly is mounted.
Electrlcal connection 34 with metallic foil 3 serves as a connection to one electric pole of pizeo-electric disks 1,2.
The other electrical pole is kept at earth potential by connection 35 of the end face of each disc remote from foil 3 to earth potential. Cylinders 24 and 25 are of dissimilar metal and the axial lengths are chosen having regard to the velocity of ultrasound in the respective metals. The combined sub-assembly connected by bolt 26 can vibrate substantially in the axial direction at ultrasonic frequencies with a fundamental resonance frequency occurring when the wavelength of the vibration is equal to twice the combined axial dimension.
761~
In use as a transmitter water fed under pressure via inlet tube 18 to cavity 17 flows outwardly from orifice 19 and impinges on the underside of an overlying conveyor belt 1.
A continuous column of water thus extends between the ultrasound transmitting face 30 of plug 28 and the overlying zone ox belt 1 providing an ultrasound coupling medium, notwithstanding motion of the belt. Flange 33 surroundiny orifice 19 assists to maintain the water column while conveyor belt 1 is in motion. '' The ultrasonic receiver and transmitter are similar in design and differ in respect of the electric circuit 36 shown schematically. This circuit is of a type well known in the art and comprises an impedance matching inductor in the transmitter and in the receiver a similar inductor in addition to a pre-amplifier. In the case oE the transmitter electrical signals supplied through cable 37 are converted to ultrasonic vibrations according to the piezo-electric effect and in the receiver the vibrations are converted to electric signals by the piezo-electric effect and amplified by the pre-amplifier for subsequent analysis. A lug 38 is fixed to case 11 to facilitate mounting.
Figure 3 shows a means of mounting the transducer assembly 2 (referring collectively to the receiver and transmitter) relative to a conveyor belt 1. Transducer assembly 2 is fixed to a lever arm 40 by bolts through the lug 38 in such a way that allows a small rotation about an axis through bolt 41 so as to adjust and fix the angle of the axis of the transducer to the surfaces of the belt. The .~_ ~g~
lever arm 40 is fixed to a pipe clamp 42 by a lug ~3. Pipe clamp 42 attaches over a roller 5 shown in Fig. 1 and in part sectioned view in Fig. 4. Roller 5 is modiEied from a typical idler roller and forms a pivot axis for transducer assembly 2 such that the transducer assembly can follow the random vertical movements of belt 1.
With reference to Fig. 4, roller 5 is provided with a helical spring 51 mounted co-axially in the roller and whereby a restoring torque acts on the roller with respect to the fixed shaft 52 and in turn provides an upward force to the transducer relative to the conveyor belts. Spring 5,1 is secured at one end 54 to the roller by a collet 53 fastened by a screw (not shown) to the inside wall of roller 5 and is free of the shaft 52.
The other end of spring 51 is secured to the shaft 52 by a similar collet 55 which is free of the inside wall of roller 5. Each end of the spring is fastened to the respective collet by a grub screw 56 (not sectioned).
Attached to the same roller 5 is a wheel arrangement 6 shown in Fig. 5.
The separation of the face of the transducer at the or.ifice 17 from the surface of belt 1 is controlled by wheel arrangement 6. Wheel 61 is mounted on an axle 62 and fork 63 which is in turn mounted on a lever arm 64 at pivot axle 65.
This arrangement allows for the rotation of the wheel about the axis of axle 65 so as to effectively adjust the separation of the axle 65 from belt 1. Adjustment is made by screw 66 which is screwed into lug 67 attached rigidly to the ~3~
lever arm 6~ and acts on t.he lug 6~ whicii is rigidly attached to the York ~3. 'rhe assembly is clamped adjacent to the transducec on the roller 5 by a clamp 69 similar to clamp ~2. Adjustment ox screw 66 results in rotation of the roller 5 and a change in the separation of the transducer from tne belt. Contact ox the wheel and the belt is maintained by roller spring 51.
With re~erènce to Fig. 1, rollers 5 are mounted in the usual way on an idler frame 4. The transmitter transducer assembly 2 and associated wheel 6 is mounted so as to transmit ultrasound into one edge of the belt and the receiver transducer assembly 2 with associated wheel 6 is mounted on the opposite roller 5 to detect ultLasound at the other edge of the belt.
Electrical energy is supplied to the transmitter at a frequency for preference equal to the fundamental resonant frequency of that transmitter in a series of short pulses.
Also for preference the frequency is such that the wavelength of ultrasound in the conveyor belt is equal to one thickness of belt.
When the ultrasound is of a particular frequency such that the wavelength in beLting is equal or similar in dimension to the belting thickness dimension, the ultrasound attenuation is of the order of only 0.5-0.65 dB per cm of path length, whereas at neighbouring higher and lower frequencies the attenuation is significantly greater.
When reference to Fig. 6 there is shown a plot of ultrasound attenuation in decibels per centimeter of path _ 9 _ g7~
length against requency in belting of thicknesses. In a steel cord reinforced belting of 25 mm thickness and at frequency of 43.6 XHz the wavelength is about 25 mm and the attenuation is at or near a minimum. By selecting a frequency of 43.5 XHz ultrasound can be propogated and detected over a path length exceeding one meter in the 25 mm thick belt. At frequencies in excess of 100 kHz ultrasound is Darely detectable over a path length in the belting of 20 cm and at lower frequencies the attenuation i5 also greater.
Likewise for a belt of similar construction but of thickness 20 mm, at a frequency of 47.6 kHz the ultrasound wavelength is about 21 my and attenuation is at or near a minimum.
As is apparent from Fig. 6 there is another attenuation minimum for~the 25 mm thicXness belting at around 39 ~Hz.
As will be apparent to those sifted in the art the frequency is desirably selected having regard both to the level of attenuation and the sensitivity of attenuation to slight change in frequency.
Signals from the receiver are amplified, rectiied and sampled at a certain time following each pulse of electrical energy supplied to the transmitter. This delay takes into account the time that the resultant pulse of ultrasound travels from the transmitter to the receiver. An alarm circuit monitors the level of ultrasound and issues an alarm if this level falls below an adjustable threshold for an adjustable period of time. This alarm is also inhibited if - 9a -,~, ~97~
certain functions of the apparatus are not operational. Such functions include power supplies and coupling water supply.
Thus the apparatus can be adjusted to be responsive to rips and other faults that are of a predetermined severity and/or oE a certain minimum length. The conveyor belt drive motor is stopped if all alarm conditions apply.
The apparatus described is normally mounted at a location on the conveyor belt so that it monitors the belt immediately after passing through areas where rips are likely to occur. These locations are usually immediately after the belt is loaded. One problem occurs when the conveyor belt contains relatively long sections that, because of their poor physical condition, do not satisfactorily transmit ultrasound. The belt rip detector can be made insensitive to these sections by increasing the response time (and hence rip length) of the alarm circuit. This, however, also increases the minimum length of rip capable of being detected. To overcome this problem a second rip detector is mounted to monitor the belt immediately before passing through the area where a rip is most likely to occur. The conveyor belt drive motor is stopped only if the condition of the belt has deteriorated between the two rip detectors.
Another application of the apparatus relates to its use for detecting long term degradation of the belt and identifying sections that require preventative maintenance.
This is done by compiling a log of the level of received ultrasound throughout the entire length of the belt. In addition, as an alternative condition for raising an alarm . I_ ..
3'~, _ the 109 is compared in real time with the actual received level of ultrasound and an alarm is raised when the actual level differs from the log.
. ..
Claims (25)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for detecting a rip in a conveyor belting comprising a rubber or rubber-like composition, the method comprising the steps of:
(a) transmitting ultrasound of a particular frequency to the belting at a first zone;
(b) detecting ultrasound of said particular frequency propagated by the belting from the first zone to a second zone spaced apart from the first zone;
(c) issuing a first signal responsive to the intensity of ultrasound, if any, so detected whereby said first signal is indicative of discontiuities in the belting intermediate said first and second zones.
(a) transmitting ultrasound of a particular frequency to the belting at a first zone;
(b) detecting ultrasound of said particular frequency propagated by the belting from the first zone to a second zone spaced apart from the first zone;
(c) issuing a first signal responsive to the intensity of ultrasound, if any, so detected whereby said first signal is indicative of discontiuities in the belting intermediate said first and second zones.
2. A method according to claim 1 wherein said ultrasound is transmitted to the belting while the belting is in motion through the first and second zones.
3. A method according to claim 2 wherein the first and second zones are spaced apart in a direction transverse the direction of belt travel further comprising the steps of:
(a) transmitting further ultrasound to the belting at a third zone spaced apart from the first zone in the direction of travel of the belt, (b) detecting any further ultrasound propagated by the belting from the third zone at a fourth zone spaced apart from the third zone in a direction transverse the direction of travel of the belt, (c) issuing a second signal responsive to said further ultrasound, if any, so detected whereby to indicate a discontinuity between the third and fourth zones, and (d) correlating the second signal with the first signal.
(a) transmitting further ultrasound to the belting at a third zone spaced apart from the first zone in the direction of travel of the belt, (b) detecting any further ultrasound propagated by the belting from the third zone at a fourth zone spaced apart from the third zone in a direction transverse the direction of travel of the belt, (c) issuing a second signal responsive to said further ultrasound, if any, so detected whereby to indicate a discontinuity between the third and fourth zones, and (d) correlating the second signal with the first signal.
4. A method according to claim 2 further including the step of coupling the transducer with a belt in motion via a column of water extending between the transducer and the belt.
5. A method according to claim 4 further comprising the step of tracking vertical movement of the belt and moving the transducer upwardly or downwardly so as to maintain a substantially constant length of water column between the transducer and the belt.
6. A method according to claim 1 wherein the first zone and second zone are at or adjacent to opposite side edges of the conveyor belting.
7. A method according to claim 1 wherein the particular frequency is selected having regard to change in attenuation of ultrasound in the belting with change in ultrasound frequency so that attenuation is at or near a minimum.
8. A method according to claim 7 wherein said ultrasound is transmitted to the belting while the belting is in motion through the first and second zones.
9. A method according to claim 8 wherein the first and second zones are spaced apart in a direction transverse the direction of belt travel further comprising the steps of:
(a) transmitting further ultrasound to the belting at a third zone spaced apart from the first zone in the direction of travel of the belt, (b) detecting any said further ultrasound propagated by the belting from the third zone at a fourth zone spaced apart from the third zone in a direction transverse the direction of travel of the belt, (c) issuing a second signal responsive to said further ultrasound, if any, so detected whereby to indicate a discontinuity between the third and fourth zones, and (d) correlating the second signal with the first signal.
(a) transmitting further ultrasound to the belting at a third zone spaced apart from the first zone in the direction of travel of the belt, (b) detecting any said further ultrasound propagated by the belting from the third zone at a fourth zone spaced apart from the third zone in a direction transverse the direction of travel of the belt, (c) issuing a second signal responsive to said further ultrasound, if any, so detected whereby to indicate a discontinuity between the third and fourth zones, and (d) correlating the second signal with the first signal.
10. A method according to claim 8 further including the step of coupling the transducer with a belt in motion via a column of water extending between the transducer and the belt.
11. A method according to claim 10 further comprising the step of tracking vertical movement of the belt and moving the transducer upwardly or downwardly so as to maintain a substantially constant length of water column between the transducer and the belt.
12. A method according to claim 7 wherein the first zone and second zone are at or adjacent to opposite edges of the conveyor belting.
13. A method according to claim 1 wherein the particular frequency is selected so that the wavelength of the ultrasound in the belting is of a dimension equal to or similar to the thickness dimension of the belting.
14. A method according to claim 13 wherein said ultrasound is transmitted to the belting while the belting is in motion through the first and second zones.
15. a method according to claim 14 wherein the first and second zones are spaced apart in a direction transverse the direction of belt travel further comprising the steps of:
(a) transmitting further ultrasound to the belting at a third zone spaced apart from the first zone in the direction of travel of the belt, (b) detecting any said further ultrasound propagated by the belting from the third zone at a fourth zone spaced apart from the third zone in a direction transverse the direction of travel of the belt, (c) issuing a second signal responsive to said further ultrasound, if any, so detected whereby to indicate a discontinuity between the third and fourth zones, and (d) correlating the second signal with the first signal.
(a) transmitting further ultrasound to the belting at a third zone spaced apart from the first zone in the direction of travel of the belt, (b) detecting any said further ultrasound propagated by the belting from the third zone at a fourth zone spaced apart from the third zone in a direction transverse the direction of travel of the belt, (c) issuing a second signal responsive to said further ultrasound, if any, so detected whereby to indicate a discontinuity between the third and fourth zones, and (d) correlating the second signal with the first signal.
16. A method according to claim 14 further including the step of coupling the transducer with a belt in motion via a column of water extending between the transducer and the belt.
17. A method according to claim 16 further comprising the step of tracking vertical movement of the belt and moving the transducer upwardly or downwardly so as to maintain a substantially constant length of water column between the transducer and the belt.
18. A method according to claim 13 wherein the first zone and second zone are at or adjacent to opposite side edges of the conveyor belting.
19. Apparatus for use with a conveyor belt to detect a rip therein said conveyor belt comprising a rubber or rubber like material, said belt passing through a first zone and a second zone spaced from the first zone, and said apparatus comprising:
transducer means for producing ultrasound at a predetermined frequency, coupling means for transmitting said ultrasound to the belt while it is in motion through the first zone, and sensor means producing a signal responsive to said ultrasound in the belt at the second zone.
transducer means for producing ultrasound at a predetermined frequency, coupling means for transmitting said ultrasound to the belt while it is in motion through the first zone, and sensor means producing a signal responsive to said ultrasound in the belt at the second zone.
20. Apparatus according to claim 19 wherein the ultrasound is of a frequency selected so that the attenuation of ultrasound in the belting is at or near a minimum.
21. Apparatus according to claim 19 wherein the ultrasound is of a frequency selected so that the wavelength of the ultrasound in the belting is of a dimension equal to or similar to the thickness dimension of the belting.
22. Apparatus according to claim 19 wherein the first zone and the second zone are at or adjacent opposite side edges of the belt.
23. Apparatus according to claim 19 wherein the coupling means includes a liquid medium.
24. Apparatus according to claim 19 further comprising tracking means for maintaining a substantially constant length of a column of liquid medium between the transducer and the belt.
25. Apparatus according to claim 19 wherein a transducer assembly is mounted to a lever arm for pivotal movement towards or away from the belt, bias means urging the transducer assembly towards the belt, and belt tracking means for maintaining a constant separation between the belt and the transducer assembly.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000409621A CA1197604A (en) | 1982-08-18 | 1982-08-18 | Conveyor belt monitor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000409621A CA1197604A (en) | 1982-08-18 | 1982-08-18 | Conveyor belt monitor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1197604A true CA1197604A (en) | 1985-12-03 |
Family
ID=4123428
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000409621A Expired CA1197604A (en) | 1982-08-18 | 1982-08-18 | Conveyor belt monitor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1197604A (en) |
-
1982
- 1982-08-18 CA CA000409621A patent/CA1197604A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |