GB2189320A

GB2189320A - Detection of loose particles in containers

Info

Publication number: GB2189320A
Application number: GB08708196A
Authority: GB
Inventors: Dr Christopher Brian Scruby; Adrian Carey Tolchard
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1986-04-21
Filing date: 1987-04-06
Publication date: 1987-10-21
Also published as: GB8708196D0; GB8609687D0

Abstract

An apparatus and a method are provided for detecting small particles such as glass fragments in a glass jar, in which the jar (20) is supported in an acoustically absorbent frame (18, 30) and is given an abrupt vertical blow. A transducer (24) acoustically coupled to the outside of the jar by a resilient solid couplant (28) detects the high frequency noise made by impacts of glass fragments with the jar. Signals from the transducer are passed through a filter (46) to cut out the low frequency noise from the blow, while passing the noise of the particle impacts. A frequency range of 100kHz to 3MHz is suitable for this purpose. <IMAGE>

Description

SPECIFICATION Particle detection This invention relates to a method and an apparatus for detecting a loose particle in a container, and particularly but not exclusively detecting glass fragments in glass jars or bottles.

According to the present invention there is provided an apparatus for detecting the presence of a loose particle in a container, comprising a support for the container, the support comprising an acoustically absorbent material, a transducer acoustically coupled by a solid, resiliently deformable couplantto the outside of the container, meansforsubjectingthecontainertoanabrupt vertical blow, andafilterforsignalsfrom the transducer arranged to pass onlythose signals above the frequency range of sounds made bythe blow.

The acoustically absorbent material might be polytetrafluoroethylene (PTFE) or nylon, and the couplant might be silicone rubber. Preferably the filter is arranged to pass only those signals above 100 kHz.

The apparatus of the invention is applicable to the testing of bottles orjars in a production-line where several hundred jars may have to be tested every minute. It has been found capable of detecting glass particles in a glass jar reliably down to particles of volume about 1 mm3, and for particles largerthan that size enables the particles to be at least approximately sized.

The invention will now be described by way of example only and with reference to the accompanying drawing, which shows a glass fragment detector 10, partly in vertical section and partly diagrammatically.

The detector 10 comprises a base 12 supporting three vertical PTFE-coated steel guide rods 14 (only two are shown) arranged (in plan view) at three cornersofa square, and fourvertical pillars 16 (only three are shown) arranged atthefourcorners of a largersquare.A PTFE support plate 18fora glass bottle 20 is slidable on the guide rods 14 and is resiliently supported, resting on zig-zag springs 22 mounted atthetopsofthepillars 16.Abroadband piezoelectrictransducer24, sensitive to frequencies between about 10 kHz and 3MHz, is mounted on the underside ofthe support plate 18 and extends into a hole 26 through the support plate 18, and a coupling block 28 of resiliently deformable silicone rubber locates in the hole 26 above the transducer 24, being slightly proud ofthe top surface of the support plate 18 when uncompressed so as to accommodate any slight concavity in the base ofthe bottle 20 and to couple ultrasound effectively from the bottle 20 and to couple ultrasound effectively from the bottle 20 to the transducer 24.

Above the bottle 20 is an upper PTFE plate 30 which is also slidable on the guide rods 14 and linked to the support plate 18 bythree hydraulic piston-and-cylinder assemblies 32 (only two are shown) adjacent to the guide rods 14. Flexible hoses 34 supply hydraulicfluid to the assemblies 32. A shorttube 36 of PTFE extends down from the plate 30, its lower, inwardly chamfered, end resting on the shoulder of the bottle 20. A rubber block 38 is attached centrally on the upper side of the plate 30.

Above the upper plate 30 is an electromagnetically operated hammer40 (shown diagrammatically) arranged when energised to impart a vertical blowto the rubber block 38 and hence through the tube 36to the bottle 20.

In operation of the detector 10, with the hydraulic assemblies 32 operated to raise the upper plate 30, a bottle 20 is placed in the position shown, on the support plate 18. The assemblies 32 arethen operated to lower the upper plate 30 until the tube 36 is pressing firmly on the shoulderofthe bottle 20.

The hammer 40 is then energized so as to impart a vertical impulsetothe bottle 20, such that it accelerates downwards, moving a distance of about 5 mm against the force ofthe springs 22 supporting it. Any loose fragments or glass particles in the bottle 20 are shaken loose by the impulse, and then hit the inside of the bottle 20 generating high frequency vibrations; these vibrations are detected by the transducer 24 which generates corresponding electrical signals. These signals are amplified by a pre-amplifier 44, passed through a bandpassfilter 46, amplified by a second amplifier48, and then supplied to an output or display module 50. The filter 46 is arranged to pass only those signals in the frequency range 100 kHz to 3 MHz.

It has been found that whereas the noise produced by the blowfrom the hammer 40 is below about 30 kHz, the noise produced by impacts from small particles of glass is white noise extending over a wide frequency band above about 50 kHz, up to 3MHzoreven higher. The filter 46 thus cuts outthe noise of the hammer blow, but transmits the noise emitted by any small glass particles. This noise after amplification can either be used to illuminate a display to warn an operator of the presence ofthe particles, or can be used to trigger a reject mechanism to reject the bottle 20; the module 50 fulfils one or both of these roles.

It has also been found that although there is some variation (less than 3dB) in the noise produced by an individual glass particle, there is nevertheless a systematic increase in noise with the size of the particle. The signals received by the output or display module 50 can therefore be used to provide an indication of the sizes of the particles.

It will be appreciated that where the method is applied to glass jars which have no significant shoulder, the tube 36 can be dispensed with, so the upper plate 30 rests directly on the top ofthejar.

1. An apparatus for detecting the presence of a loose particle in a container, comprising a support for the container, the support comprising an acoustically absorbent material, a transducer acoustically coupled by a solid, resiliently deformable couplantto the outside of the container, meansforsubjecting the container to an abrupt vertical blow, and a filter for signals from the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Particle detection This invention relates to a method and an apparatus for detecting a loose particle in a container, and particularly but not exclusively detecting glass fragments in glass jars or bottles. According to the present invention there is provided an apparatus for detecting the presence of a loose particle in a container, comprising a support for the container, the support comprising an acoustically absorbent material, a transducer acoustically coupled by a solid, resiliently deformable couplantto the outside of the container, meansforsubjectingthecontainertoanabrupt vertical blow, andafilterforsignalsfrom the transducer arranged to pass onlythose signals above the frequency range of sounds made bythe blow. The acoustically absorbent material might be polytetrafluoroethylene (PTFE) or nylon, and the couplant might be silicone rubber. Preferably the filter is arranged to pass only those signals above 100 kHz. The apparatus of the invention is applicable to the testing of bottles orjars in a production-line where several hundred jars may have to be tested every minute. It has been found capable of detecting glass particles in a glass jar reliably down to particles of volume about 1 mm3, and for particles largerthan that size enables the particles to be at least approximately sized. The invention will now be described by way of example only and with reference to the accompanying drawing, which shows a glass fragment detector 10, partly in vertical section and partly diagrammatically. The detector 10 comprises a base 12 supporting three vertical PTFE-coated steel guide rods 14 (only two are shown) arranged (in plan view) at three cornersofa square, and fourvertical pillars 16 (only three are shown) arranged atthefourcorners of a largersquare.A PTFE support plate 18fora glass bottle 20 is slidable on the guide rods 14 and is resiliently supported, resting on zig-zag springs 22 mounted atthetopsofthepillars 16.Abroadband piezoelectrictransducer24, sensitive to frequencies between about 10 kHz and 3MHz, is mounted on the underside ofthe support plate 18 and extends into a hole 26 through the support plate 18, and a coupling block 28 of resiliently deformable silicone rubber locates in the hole 26 above the transducer 24, being slightly proud ofthe top surface of the support plate 18 when uncompressed so as to accommodate any slight concavity in the base ofthe bottle 20 and to couple ultrasound effectively from the bottle 20 and to couple ultrasound effectively from the bottle 20 to the transducer 24. Above the bottle 20 is an upper PTFE plate 30 which is also slidable on the guide rods 14 and linked to the support plate 18 bythree hydraulic piston-and-cylinder assemblies 32 (only two are shown) adjacent to the guide rods 14. Flexible hoses 34 supply hydraulicfluid to the assemblies 32. A shorttube 36 of PTFE extends down from the plate 30, its lower, inwardly chamfered, end resting on the shoulder of the bottle 20. A rubber block 38 is attached centrally on the upper side of the plate 30. Above the upper plate 30 is an electromagnetically operated hammer40 (shown diagrammatically) arranged when energised to impart a vertical blowto the rubber block 38 and hence through the tube 36to the bottle 20. In operation of the detector 10, with the hydraulic assemblies 32 operated to raise the upper plate 30, a bottle 20 is placed in the position shown, on the support plate 18. The assemblies 32 arethen operated to lower the upper plate 30 until the tube 36 is pressing firmly on the shoulderofthe bottle 20. The hammer 40 is then energized so as to impart a vertical impulsetothe bottle 20, such that it accelerates downwards, moving a distance of about 5 mm against the force ofthe springs 22 supporting it. Any loose fragments or glass particles in the bottle 20 are shaken loose by the impulse, and then hit the inside of the bottle 20 generating high frequency vibrations; these vibrations are detected by the transducer 24 which generates corresponding electrical signals. These signals are amplified by a pre-amplifier 44, passed through a bandpassfilter 46, amplified by a second amplifier48, and then supplied to an output or display module 50. The filter 46 is arranged to pass only those signals in the frequency range 100 kHz to 3 MHz. It has been found that whereas the noise produced by the blowfrom the hammer 40 is below about 30 kHz, the noise produced by impacts from small particles of glass is white noise extending over a wide frequency band above about 50 kHz, up to 3MHzoreven higher. The filter 46 thus cuts outthe noise of the hammer blow, but transmits the noise emitted by any small glass particles. This noise after amplification can either be used to illuminate a display to warn an operator of the presence ofthe particles, or can be used to trigger a reject mechanism to reject the bottle 20; the module 50 fulfils one or both of these roles. It has also been found that although there is some variation (less than 3dB) in the noise produced by an individual glass particle, there is nevertheless a systematic increase in noise with the size of the particle. The signals received by the output or display module 50 can therefore be used to provide an indication of the sizes of the particles. It will be appreciated that where the method is applied to glass jars which have no significant shoulder, the tube 36 can be dispensed with, so the upper plate 30 rests directly on the top ofthejar. CLAIMS

1. An apparatus for detecting the presence of a loose particle in a container, comprising a support for the container, the support comprising an acoustically absorbent material, a transducer acoustically coupled by a solid, resiliently deformable couplantto the outside of the container, meansforsubjecting the container to an abrupt vertical blow, and a filter for signals from the transducer arranged to pass onlythose signals above the frequency range of sound made by the blow.

2. An apparatus as claimed in Claim 1 wherein the acoustically absorbent material comprises polytetrafluoroethylene (PTFE) or nylon, and the couplant comprises silicone rubber.

3. An apparatus as claimed in Claim 1 or Claim 2 wherein the filter is arranged to pass only those signals above 50 kHz.

4. An apparatus as claimed in Claim 3 wherein the filter is arranged to pass only those signals above 100 kHz and below 3 MHz.

5. An apparatus as claimed in any one of the preceding Claims wherein the support includes a plate to stand the container on, the plate being resiliently supported to be able to move several millimetres vertically in response to the blowto the container.

6. An apparatus for detecting the presence of a loose particle in a container substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.