AU624858B2

AU624858B2 - Detection of presence of a glass plate

Info

Publication number: AU624858B2
Application number: AU41305/89A
Authority: AU
Inventors: Philippe Boutier; Benoit D'iribarne; Hubert Havenith; Hans-Werner Kuster; Denis Mathivat; Dany-Ange Plebani; Luc Vanaschen
Original assignee: Saint Gobain Vitrage SA
Current assignee: Saint Gobain Vitrage SA
Priority date: 1988-06-17
Filing date: 1989-09-12
Publication date: 1992-06-25
Anticipated expiration: 2009-09-12
Also published as: FR2632949B1; ES2031379T3; JP2896164B2; CA1337965C; JPH0238908A; DE68901008D1; FI892974A; AU4130589A; KR0126676B1; EP0348266B1; FI892974A0; BR8902923A; YU47321B; MX169565B; FI106751B; EP0348266A1; DD285086A5; KR900000304A; ATE73928T1; FR2632949A1

Abstract

The invention relates to a method and a device for detecting a moving glass sheet heated to a temperature above its softening point. A jet of pressurised gas, in particular compressed air, is sent through the path which the sheet of glass takes, and the variation in pressure of the jet when the latter is intersected by the sheet of glass is detected. <IMAGE>

Description

AUSTRALIA

PATENTS ACT 1952 COMPLETE SPECIFICATION 624858 Form

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: Related Art: 9 4 99r 9 9 0 *9 TO BE COMPLETED BY APPLICANT

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Name of Applicant: Address of Applicant: SAINT-GOBAIN VITRAGE "Les Miroirs" 18 AVENUE D'ALSACE F92400 COURBEVOIE

FRANCE

Actual Inventor: Address for Service: GRIFFITH HACK CO., 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

Complete Specification for the invention entitled: DETECTION OF PRESENCE OF A GLASS PLATE.

The following statement is a full description of this invention including the best method of performing it known to me:-

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2 The present invention relates to detection of the precise position of a glass plate in movement, in particular a glass plate heated, by traversing a furnace, to a temperature above that required for softening to allow for its moulding to shape.

The invention is applicable, in particular to plants for curving and/or thermal treatment of glass plates for the purpose of obtaining, for example, windscreens for motor vehicles.

Lnr rrvr- n 4 1 4 nc1 rrvr A n n i- 4 rrn-r. n 1I.F4. 4 A -S 0 4. l.4oc 4-U'+-ILVL t 4 U..Lih0( nJ. -(I4 production with the use of ever more complex curving moulds, it has become necessary to know, with ever greater precision, the position occupied by a glass plate during the course of treatment. This is necessary to anticipate, for example, the displacement of an operational member or the start of its functioning. Thus, it would be possible to initiate the movement $S into position of a frame for retrieval of the glass plate even S before the plate had been lifted up from the conveyor, or to 1 commence the blowing with tempering gas after the glass plate has been directed towards the tempering zone. In all cases, the objective is the total, or partial., elimination of dead time.

20 On the other hand, as the desired shapes become more and *4 I

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*45 Li (4 more complex, so the precision of positioning the glass plates should become greater, which necessitates a preliminary knowledge of its actual position.

All these considerations lead to the development of a system of detection of the glass plate which is, at the same time, very precise and very reliable. These detection systems should not entail marking of the glass plates, which are at a temperature higher than that required for softening to mould them to shape, ti t by contact with a solid body which could be the source of :O optical defects in the windscreen. For a windscreen of very high quality, such defects cannot be tolerated, even in the marginal zones, because motor vehicle windscreens are frequently mounted flush at the edges, with adhesive applied directly to the framework and, for this reason, their entire surface is visible from the outside of the vehicle.

The usual types of optical detectors which register the cutting-off of a light beam directed across a path travelled by iYJ 3 a glass plate are not sufficiently reliable under the temperature conditions encountered. Actually, at such temperatures, close to 700 degrees Celsius, for example, in a curving and tempering plant, the light rays are subjected to strong diffraction and, especially all variations in the temperature of the environment, even of only small magnitude, entail a modification of the angle of diffraction such that the light beam is no longer intercepted by the receiver cell and this could lead to erroneous information about the position and passage of a glass plate.

It is also known from the German Patent 36.38.659 that a glass plate can be detected by a light barrage functioning by reflection, of which the measuring head is placed in proximity to the trajectory of the glass plate and is connected by means o of optical glass fibres to a photoelectric unit placed outside the hot environment. The free trajectory of the light rays, that is to say where they are not guided by the optical fibres, is 9 S very short in this case, so that the system should be less S sens±tive to temperature variations. However, this solution is 20 rather burdensome, because the optical fibres should be chilled, X taking into account the high temperatures prevailing in the j environment of the equipment.

In the European Patent Application 217 708, the Applicant has described a purely mechanical detection device for a glass plate which reacts to the pressure exerted by the glass plate.

Vi .1 In this system, the integrity of the surface of the glass is S entirely preserved, and the detection is perfectly guaranteed.

However, this device has the disadvantage of possessing mechanical components which become heated and can seize-up. On S the other hand, it can only be moved across the plant with S' difficulty. Lastly, it is poorly adapted to detection of glass plates of which the leading edge is not at right angles to the direction of forward travel of the glass plates.

The objective of the present invention is to devise a very precise and very reliable detection system for a moving glass plate which has been heated above its deformation temperature, this system being more flexible in its utilisation than 71A 44 4 2.ee 0 H 3 o 30 detectors which have been developed previously.

According to the present invention there is provided a method for detecting the presence of a moving glass plate, in a bending/tempering installation, said plate being heated to a temperature above that required for softening to facilitate moulding of the plate to a preselected shape, comprising projecting a jet of gas under pressure, across the path travelled by the moving glass plate, and detecting the variation of the pressure when the jet is interrupted by the glass plate, wherein the pressure of gas supplied to the jet is such that the pressure variation detected is in the range from 10 to 300 pascal.

This method allows for detection without physical contact and without mechanical components, is insensitive to temperature variations and well suited for use at temperatures prevailing in the moulding environment. In practice, it has been established that air movement caused by blowing for tempering or during the moulding procedure does not interfere with the detection method.

Preferably, the pressure of the compressed air supplied to the jet is selected so that the pressure variation detected is in the range from 10 to 300 pascal.

Very satisfactory results are obtained if the pressure variation is of the order of 200 pascal. The working pressures are thus very low, advantageously eliminating any risk of marking the glass surface by the impact of the air jet.

Furthermore, the compressed air is heated to a temperature approximately equal to that of the glass plate, that is to say, to that of the shaping mould. The detection will thus have no adverse influence on the windscreen. The heating of the compressed air can advantageously be achieved by providing a sufficient length of an air-supply circuit through the moulding unit. Taking into account the low pressures use, a length less than 1 metre is generally sufficient for continuous emission of the air, which does not introduce any mechanical impediments.

According to a first form of embodiment of the

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-*~CILI 4Apresent invention, the detection of the jet is effected in transmission. For this purpose an air-emission nozzle is disposed in proximity to the plane of transport of the glass plate so that the compressed-air jet passes through the plane of transport in a direction substantially perpendicular to the direction of forward travel of the glass plates. The detection is effected by a sensor of the type of a transmitter of differential *44, a a .1 IIr t g c I t i 2 pressure, of which the admission opening faces towards the emitter and is disposed on the opposite side of the plane of transport. The compressed-air jet is emitted continuously. Thus, after the leading edge of the glass plate has interrupted the current of hot air, the sensor detects a lowering of the pressure and then it detects the absence of pressure until the air current is re-established, that is to say when the trailing edge of the glass plate has passed the jet.

A detector in conformity with this first form of embodiment consists, for example, of an emitter including a source of compressed air or other gas under pressure, optionally an airfilter unit for preventing the projection of powder particles or droplets of oil onto the glass surface, a pressure-control unit, a means of heating the air in the emission tube. Preferabse 5 ly, and for an air-supply pressure of the order of 200 pascal, S the emission tube has an internal diameter between 3 and 4 millimetres.

With a very small orifice, the device would be sensitive to vibrations in the system generated by the gas-blowing for tempering and the movements of the moulding tools. On the contrary, if the diameter of the orifice is greater than millimetres, the time of the measuring response increases and could prove to be inadequate. However, larger diameters, for example between 5 and 10 millimetres, may be used in a device t t intended solely for detection of the presence of a glass plate without any attention being devoted to its precise position. The S' sensor consists of a receptor tube with an orifice diameter equal to, or greater than, that of the emission tube. The receptor tube is connected to a transmitter of pressure differ- 0 entials which converts the pressure measurement into an eleci tt trical signal registered by a voltmeter and then the signal is sent to a programmable relay device.

According to another equally preferred form of embodiment, the detection is achieved by a measure in reflection of the pressure difference. In this case, the whole device is situated on the same side of the plane of transport of the glass plates.

As previously, the emission of the jet of compressed air is effected in the proximity of the plane of transport of the glass plates, where the jet of compressed air is directed in an orientation substantially perpendicular to the direction of forward travel of the glass plates. The measurement of the detection is effected by a sensor, namely a transmitter of pressure differentials of which the supply tube is mounted coaxially to the emission tube for the compressed air. A detector in conformity with this second form of embodiment consists, for example, of an emitter including a source of gas under pressure, in particular compressed air, an air-filter unit, a pressure-control unit, optionally a means of heating the air, and an emission device. Preferably, the emission device consists of a nozzle orifice in the form of an annulus located 0 S at the end of a tube and at the centre of this annulus there is S15 located the receptor tube connected to the transmitter of °OQa pressure differentials which converts the pressure measurement into an electrical signal which is treated and sent to an automatic relay device. In this case, the best results are S observed with a distance between the head of the nozzle and the 26 surface of the glass in the range from 1 to 5 millimetres, depending upon the emission pressure of the compressed air.

Other characteristics and advantageous features of the present invention are described in the following text, with reference to the accompanying drawings, in which: Fig. 1 is a diagram of a detector in conformity with a first form of embodiment of the present invention, Fig. 2 is a diagram of a detector in conformity with a second form of embodiment of the present invention, Fig. 3 is a detailed drawing of the emission nozzle shown in Fig. 2.

Fig. 1 is a diagram of a pneumatic device for detection of the presence of a sheet of glass, by measurement in transmission. A glass plate 1 travels through a re-heating furnace on a bed of rotating rollers 2. For preference, the furnace supplies heated glass plates to curving and/or tempering equipment for the purpose of obtaining motor vehicle windscreens. Perpendicular to the direction of forward direction of travel of the m II m. m i i m 7 glass plates, there is a detector which consists of an emitter 3 and a sensor 4, placed on either side of the path of the glass *1

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<>i plates.

The emitter includes a source 5 of compressed air. The air passes through a tube 6 and a filter unit 7, a unit 8 for pressure regulation and a heating unit 9 in which the air is heated to a temperature approximately equal to the temperature of the glass plates (in the range from 600 to 700 degrees Celsius for the furnace). The head 10 preferably consists of a tube of which the orifice is between 3 and 4 millimetres, for S example. The tubing 6 opens at the head 10 at a short distance away from the glass plate 1. This distance is preferably between 2 and 10 millimetres for detection of the precise position of the glass plate. For simply indicating the presence of a glass 13 plate, this distance can be increased to as much as 150 *roo S millimetres. A device 11 is provided to regulate the height of the head 10 as a function of the thickness of the glass plates.

The sensor 4 is located below the plane of transport of the glass plates and consists of a receptor tube in a fixed posir2C tion, of which the diameter is equal to, or greater than, that of the emitter head 10. The receptor tube leads to a transmitter 13 of pressure differentials which measures the variation of pressure of the compressed-air jet during the passage of the glass plate 1 and transforms it into an electrical signal which is registered by a voltmeter 14 and sends it for treatment to a programmable automatic relay device All the components which are sensitive to heat, in particular the transmitter 13 of pressure differentials, the voltmeter 14 and the automatic device 15 are located outside the hot environment to prevent deterioration.

The jet of compressed air is emitted preferably at a pressure of 200 pascal. Under these conditions, the response time of the system is less than one-hundredth of a second.

Fig. 2 is diagram of a pneumatic detector functioning according to the second form of embodiment of the invention.

A glass plate passes through a furnace 17 shown in a part cross-section. The axis of the furnace is indicated by the dotj~l_ i -i

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i 71 ;i dash line 18. The transport of the glas: plates is effected by means of the rollers 19, preferably made from silica, of which the bearings are situated outside the furnace 17. Between two transport rollers 19 there is a member of much smaller diameter for supporting the detector nozzle 21. This support member is preferably a metal tube 22 which is enclosed in a protective silica sheath which is mounted in such a manner that it is able to expand freely against a compensation spring 23. It is carried in a sliding bearing 24 mounted at the upper end of a bearing 10 column 25 standing on the ground.

8 The nozzle 21 is connected to an emitter 26 and a sensor 27.

a The emitter consists of a source of compressed air which is supplied through the tubing 29 to the nozzle 21. The control .a of this supply is effected, for example, by means of a pressure- 1; relief valve 30, a high-precision controller 31 and a micro- 8° manometer 3. with numerical display. The air is cleaned by passage through a pre-filter 33 and then an oil-removal filter 34.

The tubing 29 forms a loop 35 inside the furnace 17. The length of this loop is sufficient for heating the air to the furnace temperature. In another form of embodiment, not depicted, the tubing 29 can be contained in the metal tube 22.

There is also return tubing 36, following the same path as the tubing 29, which leads to a transmitter 37 which transforms the measurements of pressure variation into electrical signals registered by the precision voltmeter 38. The registered signal is transmitted to a programmable automatic relay device 39.

S8 A detailed drawing of the nozzle 21 is presented in Fig. 3.

The nozzle 21 consists of a base 40 onto which is screwed a body 41 furnished with a tapped hole 45 for fixing the nozzle to the 30 end of the sheathed support member. The base 40 is provided with drilled holes 42, 43 to the lower ends of which the ends of the tubing 29 and 36 are soldered with allowance for expansion 44.

The base 40 is hollow in the centre to form a channel 46 and the opening 43 has a hole drilled transversely to open into said channel. The nozzle also includes a tube 47 fixed by its lower end to the base 40 at the top of the channel 46 and at its upper end it is fitted with a cap 48. The walls of this tube 47 and I It u T tx.

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the body form the emission nozzle in the shape of a coaxial duct 49. Thus, the jet of compressed air is blown out through an annular orifice, which limits it impact on the glass surface.

The tubing 36 receives, by way of the tube 47, the channel 46 and the bend 43, the counter-pressure induced by the passage of a glass plate across the jet.

Advantageously, the compressed air is emitted at a pressure of 4 kilopascals, which is such that, for a distance of the order of 2 millimetres from the nozzle to the glass plate, the pressure difference induced by the passage of a glass plate over the nozzle will be in the range from 10 to 200 pascal. Because o the air is hot and its impact on the glass surface is reduced by the annular shape of the nozzle orifice, the glass plate will o not suffer any damage by marking.

The mounting of the nozzle on a sheathed support tube aeo presents several advantages: it can be displaced transversely or in an angular manner for the purpose of better taking into account the different shapes of windscreens.

The invention thus proposes a system of detection of the movement of plates of glass in a furnace which is safe and reliable, without the risk of harmful marking of the glass surface.

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Claims

2. The method according to Claim 1 in which the gas under pressure is compressed air.
3. The method according to Claim 1 or 2, wherein the pressure is measured in transmission.
4. The method according to Claim 1 or 2, wherein the pressure is measured in reflection.
5. An apparatus suitable for implementation of the method according to any one of the preceding Claims, comprising an emitter of gas under pressure and a sensor in the form of a transmitter of pressure differentials. 6, An apparatus for implementation of the method according to Claim 3, comprising an emitter of gas including a source of gas under pressure, a gas-pressure control unit, a means of heating the gas, an emission tube, a sensor facing the emitter, and a transmitter of pressure differentials, wherein a receptor tube and the emission tube are placed on opposite sides of the plane of transport of the glass plate. P 25 An apparatus according to Claim 6 further 11 comprising a gas-filter unit.
8. An apparatus according to Claim 6 or 7 in which the gas under pressure is compressed air.
9. An apparatus according to any one of Claims 6 to 8, wherein the diameter of the orifice of the emission tube is between 3 and 10 millimetres. An apparatus according to Claim 9 in which the diameter of the orifice of the emission tube is between 3 and 4 millimetres.
11. An apparatus according to any one of Claims 6 to 1 0, wherein the diameter of the orifice of the receptor tube St 04 is equal to, or greater than, that of the emission tube. e S e e5t555
12. An apparatus for implementation of the method according to Claim 4, comprising an emitter of gas including a source of gas under pressure, a gas-pressure control unit, a means of heating the gas, an emission means and a sensor including a transmitter of pressure differentials, of which a return tube is mounted with an emission tube for the gas under pressure. 2 13. An apparatus according to Claim 12, wherein the emission means comprises a nozzle orifice in the form of an annulus located at the end of the emission tube and at the centre of the annulus there is located a receptor tube connected to the transmitter of pressure differentials.
14. An apparatus according to Claim 12 or 13 further comprising a gas-filter unit. An apparatus according to any one of Claims 12 to 14 in which the gas under pressure is compressed air. S?16. A method for detecting the presence of a moving 0 4, i UI~--PY 12 glass plate in a bending/tempering installation substantially as hereinbefore described with reference to any one of the accompanying drawings.
17. An apparatus suitable for implementation of detecting the presence of a moving glass plate, in a bending/tempering installation substantially as hereinbefore described with reference to any one of the accompanying drawings. Dated this 3rd day of April, 1992 SAINT-GOBAIN VITRAGE By its Patent Attorneys: GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia. i 'a MY**