US3482954A

US3482954A - Manufacture of sheet material in ribbon form

Info

Publication number: US3482954A
Application number: US556189A
Authority: US
Inventors: Ng Wing Yuen
Original assignee: Pilkington Brothers Ltd
Current assignee: Pilkington Group Ltd
Priority date: 1965-06-15
Filing date: 1966-06-08
Publication date: 1969-12-09
Anticipated expiration: 1986-12-09
Also published as: ES327874A1; SE326617B; DE1499090B1; CS166192B2; LU51337A1; BE682569A; NL6608325A; GB1136262A

Description

Dec. 9, 1969 N6 WIN'G YuEN MANUFACTURE OF SHEET MATERIAL IN.R IB'BON FORM Filed June 8, 1966 8 Sheets-$heet 1 v B ZMW S Dec 9, 1969 3,482,954

MANUFACTURE OF SHEET MATERIAL IN RIBBON FORM NG WINGYUEN 8 Sheets-Sheet 2 Filed June 8, 1966 Inventor Attorney 5 Dc. 9, 1969 M c; WING Y-U'EN MANUFACTURE OF SHEET MATERIAL I-N RIBBON FORM Filed June 8. 1966 8 Sheets-Sheet 5 9 /7 1 1 RR i Dec. 9, 1969 N6 WING YUEN 3,482;954

MANUFACTURE OF SHEET MATERIAL IN RIBBON FORM Filed June a. 1966 s sheets-sheet 4 Fl... .I 2

221 -27 a m 1/ wuyl} X44 7 L A Horneyg 1969 N6 WING YUE'N 3,482,954

MANUFACTURE OF SHEET MATERIAL IN RIBBON FORM Filed June 8. 1966 8 Sheets-Sheet 6 I nvenlor Attorneys Dec.'9,- 1969 wm UE 3,482,954

MENUFACTURE OF SHEET MATERIAL IN RIBBON FORM Filed June 8. 1966 8 Sheets-Sheet 7 WI-I- :Z:

D} Q to Q %L JA 3 T Inventor Dec. 9, 1969 NE; WINGQYU EN 3,482,954

MANUFACTURE OF SHEET MATERIAL IN RIBBON FORM Filed June 8, 1966 i 8 Sheets-Sheet 8 Inventor tlorney5 United States Patent U.S. CI. 6529 9 Claims ABSTRACT OF THE DISCLOSURE The position of an edge of a ribbon of sheet material is continuously sensed by projecting an annular gas stream towards the ribbon edge, sensing the back pressure existing in the zone surrounded by that annular stream, and using the result of the sensing to control the manufacture of sheet material.

This invention relates to the manufacture of sheet material in ribbon form, and more particularly to methods and apparatus for determining the position of an edge of the ribbon as it advanced.

It is a main object of the present invention to provide a method of determining the position of an edge of an advancing ribbon of sheet material which can be applied in methods of manufacture where the ribbon of sheet material is in contact with a surface, and the detecting means can therefore detect the position from one side of the ribbon only.

In accordance with the present invention, there is provided in the manufacture of sheet material in ribbon form, a method of determining the position of an advancing ribbon, comprising the steps of continuously sensing pneumatically in the neighborhood of an edge of the ribbon by determining the back pressure existing in an aperture around which gas is ejected in an annular stream, and deriving from said continuous pneumatic sensing information regarding the position of the edge of the ribbon for use in controlling the manufacture of the sheet material.

Advantageously the pneumatic sensing is performed in a to and fro motion in transverse relation to the advancing ribbon.

According to the broadest aspects of the invention, the method of determining the position of an edge of the advancing ribbon may be employed in any method of manufacture of sheet material in ribbon form. The present invention does, however, have particular application in the manufacture of flat glass during which the glass is advanced in ribbon form in contact with molten metal, and in accordance with this aspect of the invention, the method of determining the position of the advancing ribbon of glass comprises the steps of continuously sensing pneumatically in the neighborhood of the edge of the ribbon by determining the back pressure eixsting in an aperture around which a gas which is substantially inert to the molten metal is ejected in an annular stream, and deriving from said continuous .pneumatic sensing information regarding the position of the edge of the glass ribbon for use in controlling the manufacture of the glass.

More particularly, according to this aspect, there is provided in the manufacture of flat glass in ribbon form on a bath of molten metal, the steps of continuously sensing pneumatically in the neighborhood of one or both edges of the glass ribbon by determining the back pressure existing in an aperture around which a gas which is substantially inert to the molten metal is ejected in an annular stream, deriving from said continuous pneumatic ice sensing information regarding the position of the glass ribbon on the bath of molten metal and utilising the derived information to control either the advancing glaSS or a subsequent operation performed on the glass ribbon.

As will become evident from the detailed description of one embodiment of the invention, the information regarding the position of the glass ribbon on the bath of molten metal may be utilised in any one of a number of ways, and as one example, the information may be utilised to steer the glass ribbon down a desired path on the surface of the bath of molten metal.

As another example, when the position of both edges of the ribbon is determined by a method in accordance with the invention, information concerning the width of the ribbon may be obtained.

In the particular example of a special method of manufacturing a glass ribbon, there is therefore provided in accordance with this aspect of the present invention in the manufacture of flat glass in ribbon form on a bath of molten metal, wherein a layer of molten glass is permitted to flow freely and a glass ribbon is developed on the surface of the bath of molten metal, a method of determining the width of the glass ribbon formed on the surface of the bath of molten metal comprising the steps of continuously sensing pneumatically in the neighborhood of both edges of the glass ribbon by determining the back pressure existing in respective apertures around each of which a gas which is substantially inert to the molten metal is ejected in an annular stream, deriving from said continuous pneumatic sensing information indicative of the width of the glass ribbon, and, in the event of the sensed width of the glass ribbon differing from a predetermined value, utilising the information indicative of the difference from the said predetermined value for changng the conditions under which the glass ribbon is formed in a. manner to correct for the departure from the said predetermined width.

There are a number of ways in which the information indicative of the difference in the width of the glass ribbon from the said predetermined value may be utilised to apply the necessary correction to obtain from the process a glass ribbon of the predetermined width.

In general, the glass ribbon formed on the surface of the bath of molten metal is taken up from the bath and advanced by rollers which are driven at an appropriate speed and which apply a tractive force to the glass ribbon as it is formed on the bath of molten metal. In

one example, the information indicative of the difference of the Width of the glass ribbon from the said predetermined value is used to change the speed at which the said rollers are driven, and thereby to correct for the departure of the width of the glass ribbon from the said predetermined value.

Alternatively, the information indicative of the dif ference of the width of the glass ribbon formed on the bath of molten metal from the predetermined value is used to alter the temperature of the molten glass from which the ribbon of glass is formed on the bath to correct for the departure of the width of the glass ribbon from the said predetermined value.

A third possible alternative is that the information indicative of the difference in Width of the glass ribbon formed on the bath of molten metal from the said predetermined value is used to regulate the rate of flow of molten glass to the bath of molten metal and thereby to correct for the departure of the width of the glass ribbon from the said predetermined width.

The present invention also comprehends apparatus for determining the position of an edge of an advancing ribbon, the apparatus comprising pneumatic sensing means including an inner tube located co-axially with an outer tube to define an annular nozzle, gas delivery means for supplying gas under pressure to the space between said inner and outer tubes whereby a jet of gas is discharged therefrom, and a pressure sensitive switch responsive to the back pressure set up in the said inner tube, driving means for moving the pneumatic sensing means laterally with respect to the advancing ribbon, control means arranged to control the said driving means and to produce a signal indicative of the position of the pneumatic sensing means as the pneumatic sensing means is moved by the said driving means, and sampling means controlled by said pressure sensitive switch for sampling the signal produced by said control means at the instant that said pneumatic sensing means experiences a change in the back pressure in the said inner tube: consequent upon the movement of the said pneumatic sensing means over the edge of the said ribbon.

More particularly, according to this aspect of the present invention, there is provided apparatus for determining the position of an edge of an advancing ribbon of sheet material, the apparatus comprising pneumatic sensing means including an inner tube located co-axially with an outer tube to define an annular nozzle, gas delivery means for supplying gas under pressure to the space between said inner and outer tubes whereby a jet of gas is discharged therefrom, and a pressure sensitive switch responsive to the back pressure set up in the said inner tube, pneumatic driving means arranged to move the pneumatic sensing means laterally with respect to the advancing ribbon, electro-pneumatic control means arranged to produce a pneumatic signal which controls the said driving means and which is indicative of the position of the pneumatic sensing means as the pneumatic sensing means is moved by the said pneumatic driving means, electrically operated sampling means controlled by said pressure sensitive switch for sampling the pneumatic signal produced by said electro-pneumatic control means at the instant that said pneumatic sensing means experiences a change in the back pressure in the said inner tube consequent upon the movement of the said pneumatic sensing means over the edge of the said ribbon, and detector means for analysing, indicating or recording the signal passed by said sampling means and indicating the position of the edge of the advancing ribbon.

Advantageously the said pressure sensitive switch is arranged to control the electronic current generator which in turn operates to change the condition of the said electro-pneumatic control means, whereby the pneumatic driving means is reversed to move the pneumatic signal means in the opposite direction in relation to the edge of the advancing ribbon.

More particularly, apparatus in accordance with the present invention is apparatus for determining the width of a glass ribbon manufactured on the surface of a bath of molten metal. The apparatus for determining the width of a glass ribbon will include duplicate apparatus for determining the position of an edge of an advancing ribbon as set forth above and will additionally include comparator means for comparing the distance between the indications of the respective edges of the advancing ribbon with a predetermined value for the width of the advancing ribbon and a pneumatic recorder controller dependent upon the output of the said comparator means for changing one condition under which the glass ribbon is formed in a manner to correct for the departure from the said predetermined width.

As has been indicated already, there are a number of ways in which the correction to the width of the glass ribbon may be applied. The pneumatic recorder controller is arranged to change the rate at which the glass ribbon is withdrawn from the bath of molten metal.

As an alternative, the pneumatic recorder controller may be arranged to control the rate of delivery of glass to the bath of molten metal.

As a third alternative, the pneumatic recorder controller 4 is arranged to vary the temperature of the glass supplied to the bath.

In order that the invention may 'be more clearly understood, a preferred embodiment thereof will now be described by way of example, with reference to the accompanying diagrammatic drawings of an embodiment of the invention in which the position of the edges of the glass ribbon advanced along the surface of a bath of molten metal is determined, and in which:

FIGURE 1 is a flow diagram of a pneumatic servomechanism for reciprocating a probe over an edge of a ribbon of glass and indicating means for recording signals produced by the probe,

FIGURE 2 is an elevation in section of the nozzle for a probe for use in the apparatus of FIGURE 1,

FIGURE 3 is an elevation, partly in section of the probe,

FIGURE 4 shows the electrical circuit details of the apparatus of FIGURE 1,

- FIGURE 5 shows in a simplified block diagrammatic form the sampling apparatus, the electrical detail of which is shown in FIGURE 4,

FIGURE 6 shows one form of recorder for recording the pneumatic signals passed from the sampling apparatus of FIGURE 5,

FIGURE 7 shows an electro-pneumatic relay for use in the apparatus of FIGURE 1,

FIGURE 8 shows the driving means for moving the probe over the ribbon of glass,

FIGURE 9 shows a pressure switch for use in the apparatus of FIGURE 1,

FIGURE 10 shows a plan view of apparatus for manufacturing a ribbon of glass of desired width on a bath of molten metal and including apparatus according to the invention,

FIGURES 11 and 12 show details of apparatus included in FIGURE 10, and

FIGURE 13 shows an alternative form of sampling apparatus.

In the drawings like reference numerals designate the same or similar parts.

Referring to the drawings, there is shown in FIGURE 1 a block diagram of the detecting apparatus used to determine and record the position of one edge of a ribbon of glass advancing along the surface of a bath of molten metal.

In FIGURE 1, there is indicated diagrammatically a part of a structure 1 containing a bath 2 of molten metal, preferably molten tin, on the surface of which a ribbon of glass 3 is continuously advanced. A protective atmosphere based on nitrogen which is chemically inert to the molten metal of the bath is maintained within the structure 1 in the headspace over the bath. For simplicity, there is shown in FIGURE 1 only one lateral edge 4 of the advancing glass ribbon 3, and the detecting apparatus of FIGURE 1 is designed to determine and record the position of this edge 4 of the glass ribbon 3.

The structure 1 includes a side wall 5 in relation to which the position of the edge 4 of the glass ribbon is to be determined and through a gas seal in the side wall 5 of the structure 1 there extends a probe 6 consisting of a nozzle 7 carried at the end of an arm 8. The arm 8 is arranged to be operated by a pneumatic driving means 9 so that the nozzle 7 is moved either progressively towards or away from the side wall 5 of the structure. The pneumatic driving means 9 is itself controlled in a manner to be described by a pressure-operated electrical switch 10, an electronic current generator 11 and an electropneurnatic relay 12.

The pressure-operated electrical switch 10, in addition to controlling the direction of movement of the probe 6, also controls a sampling apparatus 13 which permits the transmission of signals indicative of the position of the edge 4 of the glass ribbon to a pneumatic recording apparatus 14 where the signals are recorded.

The nozzle 7 will now be described with reference to FIGURE 2, which is an enlarged cross-sectional view and which shows the nozzle 7 comprising an outer casing 15 coaxial with an inner tube 16.

The inner tube 16 is connected directly to the pressureoperated electrical switch 10 by a gas line 17 so that the pneumatic signal constituted by a gas pressure within the inner tube 16 is communicated immediately to the pressure-operated electrical switch 10.

The pressure-operated electrical switch 10 is arranged such that its contacts are open when there is a sub-atmospheric pressure within the inner tube 16, and its contacts are closed when the pressure in the inner tube 16 is greater than atmospheric pressure. In the ensuing description, a gas pressure greater than atmospheric pressure in the inner tube 16 will be referred to as a positive signal, and a gas pressure less than atmospheric in the inner tube 16 will be referred to as a negative signal.

The outer casing 15 of the nozzle 7 is sealed about the inner tube 16 by appropriate locking means 18 and a conduit 19 connected to a gas line 20 opens into the outer casing 15 as shown in FIGURE 2. The gas line 20 is connected to a source of gas which is inert to the molten metal of the bath 2 at the temperature of the molten metal bath and conveniently there is used a source 21 of gas similar in composition to the protective atmosphere maintained in the headspace over the bath. The gas from the source 21 is arranged to flow through the gas line 20 and conduit 19 and so out of the nozzle 7 comprised by the annular space 22 between the inner tube 16 and the outer casing 15.

It will be appreciated that, when gas is flowing through the gas line 20, the conduit 19 and the annular space 22, an annular jet is continuously emitted from the nozzle 7. Provided that the gas in the annular jet can escape freely, that is to say there is no object immediately in the path of the emitted gas, the flow of gas from the nozzle 7 will draw gas from the inner tube 16, thus decreasing the pressure in the inner tube and setting up a negative signal. On the other hand, if there is an object closely in front of the nozzle 7 and obstructing the path of the gas flowing from the nozzle, the escape of this gas is prevented so that there is a build-up of pressure in front of the nozzle 7 and gas is deflected from the object back into the inner tube 16 so that a pressure greater than atmospheric pressure is created in the inner tube 16 and this constitutes a positive signal communicated from the interior of the inner tube 16 to the gas line 17.

Consequently, if the nozzle 7 is suitably positioned in relation to the surface of the molten metal bath 2 and the glass ribbon 3 on the surface of the molten metal bath 2, a change from a negative signal to a positive signal may be obtained as the nozzle 7 is traversed across the edge 4 of the glass ribbon 3 in a direction away from the side wall of the structure 1.

FIGURE 3 shows a preferred arrangement of the probe 6 in which the arm 8 includes a gas reservoir 23 interposed in the gas line 20. The reservoir 23 clamps small variations in the pressure of the gas supplied from the gas source 21 so that a substantially even flow of gas is fed to the nozzle 7 through the conduit 19.

The probe 6 is sealed into the side wall 5 of the structure 1 (FIGURE 1) so that ingress of air into the structure 1 is prevented. The probe 6 including the gas reservoir 23 is arranged for axial reciprocation by the arm 8 of the pneumatic driving means 9, the reciprocation taking place in the sealing means in the side wall without ingress of air into the structure 1.

The operation of the apparatus will now be described commencing from the rest position in which the probe 6 is at the side of the bath near to the wall 5.

Assuming that the bath atmosphere supply from the source 21 is already applied to the probe 6 and to the gas seal in side wall 5 of the structure 1 and that air is already supplied to the other pneumatic parts of the apparatus, the detecting apparatus is then put into operation by switching on the electrical power. The points at which the air is supplied to the other pneumatic parts of the apparatus will be mentioned in the course of the description.

In the rest position of the apparatus with the nozzle 7 and the probe 6 away from the glass ribbon 3, there will be a negative signal passed from the inner tube 16 to the line 17 and consequently the contacts of the pressureoperated electrical switch 10 will be open.

The way in which the pressure-operated electrical switch 10 acts in the electrical part of the apparatus is illustrated in FIGURE 4 of the accompanying drawings.

With the contacts of the switch 10 open, the operating conditions of the transistor 24 are determined by the base current drawn out of transistor 24 by the setting of a potentiometer 25.

The transistor 24 is connected to operate as a miller integrator so that, in the conditions shown in FIGURE 8 with the switch 10 open and electrical power applied, the current flowing through transistor 24 increases linearly.

The linearly increasing current passing through transistor 24 also passes through a coil 27 of the electro-pneumatic relay 12 and the electro-pneumatic relay 12 responds to this increase in current to give a continually increasing air pressure in the output line 28 (FIGURES l and 4). A detailed description of the electro-pneumatic relay 12 will be made with reference to FIGURE 7 of the accompanying drawings.

Referring again to FIGURE 1, the output line 28 feeds air pressure to

further lines

29 and 30. Line 29 supplies this increasing air pressure to the sampling apparatus 13 whose operation Will be described later.

The linearly increasing pressure in the line 30 operates the driving means 9 to move the arm 8 continually towards the left as seen in FIGURE 1, in a manner which will be described in detail with reference to FIGURE 8 of the accompanying drawings. The continual movement of the arm 8 to the left as seen in FIGURE 1 causes the nozzle 7 of the probe 6 to be moved inwards from the side wall 5 of the structure 1 towards the central part of the bath 2 of molten metal.

During this inward movement of the nozzle 7 it passes over the edge 4 of the glass ribbon 3 with the result that there is a change from a negative signal to a positive signal in the line 17, and the contacts of the pressureoperated electrical switch 10 close.

The closing of the contacts of the switch 10 connect the base of the transistor 24 (FIGURE 4) to the common line through a potentiometer 31 with the result that the potential applied to the base of the transistor 24 is changed to a lower value which is dependent upon the setting of the potentiometer 31. This change in the value of the potential applied to the base of the transistor 24, which is acting as a Miller integrator, causes the current through the transistor 24 to commence to fall at a uniform rate.

The current flowing through the transistor 24 flows also through the coil 27 of the electropneumatic relay with the result that the closing of the contacts of the pressure-operated electrical switch 10 as a result of a change from negative signal to positive signal in the gas line 17 causes a continually decreasing air pressure to be applied to the output line 28 and thence to the line 30 which is connected to the driving means 9. The change in the air pressure applied to the driving means 9 causes the arm 8 to commence to move to the right in FIGURE 1 (as will be hereinafter described with reference to FIGURE 8) so that the nozzle 7 is moved in a direction away from the centre of the bath 2 towards the side wall 5 of the structure 1. The movement of the nozzle 7 towards the side wall 5 in FIGURE 1 takes place at a controlled rate determined by the preset value of potentiometer 31 and the setting of potentiometer 25.

Accordingly the nozzle 7 moves from over the glass ribbon 3 across the edge 4 thereof until it is over the molten metal bath 2, whereupon there is a change from a positive signal to a negative signal communicated through the gas line 17 to the pressure-operated electrical switch 10. The contacts of the switch therefore open and, as already described, the nozzle 7 is caused to move back to the left again, Consequently a to and fro motion of the nozzle 7 about the position of the edge 4 of the glass ribbon 3 takes place.

During this to and fro motion of the nozzle 7, the air pressure in the line 28 oscillates up and down in consequence of the repeated changing over of the contacts of the switch 10, and the pressure in the line 28 is indicative of the position of the nozzle 7 at any particular time.

In order to record the position of the edge 4 of the glass ribbon 3, the action of the change-over of the position of the contacts of the switch 10 is utilised to sample the air pressure in the line 28 through the line 29, the sampling apparatus 13 and an air line 32 in a manner which will now be described.

This description will be made with reference to FIG- URES 4 and 5 of the accompanying drawings. FIGURE 5 shows diagrammatically the apparatus used, while FIG- URE 4 sets out the electrical circuitry employed in that apparatus.

Referring then to FIGURE 5, the sampling apparatus 13 comprises a first solenoid-operated valve 33 which is supplied with air direct from the line 29, a line 34 joining the valve 33 to a second solenoid-operated valve 35, a branch gas line 36 leading off the line 34 and a reservoir 37 at the end of the line 36. The second solenoidoperated valve controls the output of air to an air-line 32 which leads to the recorder 14.

The principle upon which the sampling apparatus 13 operates is that the solenoid-operated valve 33 is opened while the second solenoid-operated valve 35 is kept closed. The reservoir 37 is thus charged to the pressure existing in signal line 29. In practice, the volume of the reservoir 37 is small so that this reservoir may be charged quickly to a pressure precisely the same as the pressure in the signal line 29 in the comparatively short time interval that it takes the nozzle 7 to cross the edge 4 of the glass ribbon 3. The reservoir 37 therefore becomes charged to the same pressure as exists in the line 29 and, when the first solenoid-operated valve 33 is closed, the pressure in the signal line 29 at that time, which is the time that the nozzle 7 crosses the edge 4 of the glass ribbon, is retained in the reservoir 37.

The pressure to which the reservoir 37 has been charged is then communicated to the recorder 14 by opening the second solenoid-operated valve 35. The time for which the second solenoid-operated valve 35 is open is not confined to short limits because the first solenoidoperated valve 33 is closed at this time and will be open again only when the nozzle 7 traverses the actual edge 4 of the glass ribbon 3 in the reverse direction.

Basically the electrical circuit which controls the sampling apparatus 13 comprises a switching circuit 39, an inverter and a univibrator 41 connected in series, with an output from the switching circuit 39 to the first solenoid-operated valve 33 and an output. from the univibrator 41 to the second solenoid-operated valve 35.

Referring again to FIGURE 4, the parts of the circuit corresponding to the switching circuit 39, the inverter 40 and the univibrator 41 are indicated thereon.

The operation of this electrical circuit is that, immediately the contacts of the pressure-operated electrical switch 10 close, the transistor 42 has its base connected to the common line via diode 43 so that the current through the transistor 42 is cut off, de-energising the electro-magnetic relay 44 and thus de-energising the first solenoid-operated valve 33. Since solenoid-operated valve 33 is held open when energised, closing the contacts of the pressure-operated electrical switch 10 will close off solenoid-operated valve 33.

Switching ofi transistor 45 produces a current step at the base of the transistor 45 and an inversion of this step at the collector of transistor 45. This current step is differentiated to produce a positive going pulse which is fed to the base of transistor 46 and triggers the flip-flop or univibrator action of the combination of transistors 46 and 47. Thus transistor 46 which is normally conducting, is switched oif at contact closure of pressure operated electrical switch 10, and transistor 47 switched on for a period dependent on the resistor 48 and capacitor 49.

Current will then fiow through transistor 47, energising electro-magnetic relay 50, and hence energising solenoidoperated valve 35 to open for the period set by resistor 48 and capacitor 49, allowing the air stored in the reservoir 37 to be transmitted to the pneumatic recorder 14. At the end of this period, transistor 47 reverts to the switched off condition thus closing solenoid-operated valve 35. It only remains for the opening of the contacts of the pressureoperated electrical switch 10 to leave the circuit ready to be triggered again the next time the contacts of the pressure-operated electrical switch 10 close.

The recorder 14 will now be described with reference to FIGURE 6 of the accompanying drawings. The line 32 is connected to a capsule 51 within which a diaphragm 52 is mounted so that the air pressure in the line 37 is applied to move the diaphragm 52. The diaphragm 52 is connected by an arm 53 to a beam 54 pivoted at 55 and the movement of the arm 53 is transmitted to a pen 56 by connecting rods 57 pivoted to one another at 58.

Movement of the diaphragm 52 by a pressure signal impinging thereon from the supply line 32 is transmitted to the pen 56 so that the pen traces on a chart 59, which is continually rotated on the drum on which it is mounted, a line indicative of the position of the edge 4 of the glass ribbon 3 in relation to the side wall 5 of the structure 1 containing the bath 2 of molten metal.

In use there will be similar probes 6, each carrying a nozzle 7 acting to determine the position of each edge 4 of the glass ribbon 3, and there will be similar apparatus connecting each of the probes to the recorder 14 which has two pens each recording the position of one edge of the glass ribbon.

The electro-pneumatic relay 12, the pneumatic driving means 9 and the pressure-operated electrical switch 10 are based on well-known items of equipment which may be obtained readily on the market. However, for the sake of completeness, a preferred form of each of these items of equipment is illustrated respectively in FIGURES 7, 8 and 9 of the accompanying drawings.

As will be understood from the previous description, the electro-pneumatic relay 12, which is shown in more detail in FIGURE 7 is a device for converting an electrical current signal into a proportional output air pressure signal and comprises a permanent magnet 61, a coil 27 mounted on a beam 63 pivoted at 64, one end of the beam 63 carrying an extension spring 65 having its other end fixed at 66, and the other end carrying a baffle 67. An electric current fed to the coil 27 through a connection 68 from the transistor 24 will cause the beam 63 to pivot about the pivot 64 by interaction of the field produced by the current in the coil 27 with the field of the permanent magnet 61.

The electro-pneumatic relay 12 further comprises a diaphragm assembly 69 on which air delivered to the relay from an appropriate air source through a conduit 70 and a T-junction 71 will impinge. One arm 72 of the T-junction is formed as an outlet through which air supplied through conduit 70 may exhaust, but which may be closed by the baflle 67 carried by the beam 63 when the latter pivots about the pivot 64. A junction 73 in the conduit 70 also causes air from the air supply to pass to a poppet valve 74, movement of which by the diaphragm assembly 69 controls the amount of air delivered from the relay 12 through the output signal line 28.

An increase in the input electrical current to the coil 27 suspended in the magnetic field of the permanent magnet 61 moves the beam 63 in the direction of the air outlet 72 allowing less input air from the air line 70 to bleed through it and thus causing more air to contact the diaphragm assembly 69 and, by the pressure on the diaphragm assembly 69, to open the poppet valve 74. The opening of the poppet valve 74 allows air to be delivered through the junction conduit 73 to the air line 28. A balance will be reached when the force on the beam produced by the input current to the coil 27 is balanced by the force on the beam produced by the air issuing from the jet 72.

As already described, the pressure of air in the air line 28 is fed to the sampling apparatus 13 through an air line 29 and to the pneumatic driving means 9 through the air line 30.

The pneumatic driving means 9 is illustrated in FIG- URE 8.

The pneumatic driving means 9 comprises a power cylinder 75 in which the end of the arm 8 is mounted in a piston head 76. The power cylinder 75 is connected to a source of air supply (not shown) through

air lines

77 and 78, which enter at opposite ends of the power cylinder 75, via a pilot valve 79 and air line 80 to which the source of air is connected.

The operating part of the pilot valve 79 consists of a conecting rod 83 carrying two slipper blocks 84 and 85 so arranged that, as the connecting rod 83 is reciprocated, the slipper blocks 84 and 85 will cause air pressure to be applied selectively from the air line 80 either to the air line 78 or to the air line 77.

The connecting rod 83 is mounted in the actuating face or end wall 82 of a bellows 87. The bellows 87 is arranged to be supplied with air pressure from the air line 30. Freely mounted on the flexible connecting rod 83 is a transverse member 88 which is an annular disc and is effectively an end cap arranged to bear against one end of a compression spring 89, the other end of which bears against the actuating face or end wall 82 of the bellows 87. Part of the transverse member 88 also acts on one arm 90 of a crank 91 which is pivoted at 92, and the second arm 93 of which acts as a cam follower bearing against a cam surface 94. The cam surface 94 is mounted on the arm 8 and accordingly moves with the arm 8.

The spring 89 is treated in a discussion of the operation of the pneumatic driving means 9 as a substantially rigid member, the spring being provided to take up play between the arm 90 of the crank 91 and the actuating face or end wall 82 of the bellows 87 and to be compressed slightly as the forces acting increase. Consequently, the system which forms the pneumatic driving means 9 is essentially a two force system, the forces being the pneumatic signal from the air line 30 and the balancing force from the crank 91, both forces being applied to the actuating face or end wall 82 of the bellows 87.

In the rest position of the apparatus when no electrical energy is applied to the system there is no air signal applied to the air line 30. In practice a small air pressure in the air line 30, and consequently in the bellows 87, is equivalent to no signal.

This low signal or air pressure applied to the bellows 87 is balanced by a low force applied by the arm 90 of the crank 91 when the cam follower arm 93 is at a low position on the cam surface 94. With these two forces in balance, the connecting rod 83 is in an equilibrium position in which the slipper blocks 84 and 85 prevent air pressure being supplied from the air line 80 to the

respective air lines

77 and 78. The piston head 76 therefore remains in its rest position near the right hand of the power cylinder 75 as shown in FIGURE 8.

As soon as the apparatus is put into operation and electrical energy is applied to the system, the increasing signal (i.e. the gradually increasing air pressure) is applied to the bellows 87. The connecting rod 83 is therefore displaced to the right so that air pressure from the supply line is connected, when the pilot valve 79 is opened, to the air line 78 by reason of the movement of the slipper block to open the inlet to the air line 78. The force thus applied to the piston head 76 causes this to move to the left, as shown in FIGURE 8, so that the whole arm 8 tends to move in the same direction and the probe 6 moves away from the side wall of the tank structure to seek the edge 4 of the glass ribbon. 5

The movement of the arm 8 to the left means that the cam face 94 is also moved to the left with the result that the cam follower arm 93 rides up the cam face 94 and the crank 91 is caused to turn about its pivot 92 in an anticlockwise direction, and the pressure exerted by the arm on the transverse member 88 and hence on the actuating face or end wall 82 of the bellows 87 is increased.

If the air pressure applied to the bellows 87 from the air line 30 were not continually increasing, the force applied to the actuating face or end wall 82 of the bellows 87 as a result of movement of the cam face 94 would become equal to the increased air pressure in the bellows 87, so that equilibrium would be restored with the return of the actuating face or end wall 82 of the bellows 87 to its neutral position, thus closing the pilot valve 79, and preventing further movement of the piston head 76 in the power cylinder 75.

In practice, however, the input signal from the air line 30 to the bellows 87 is continually increasing until either the probe reaches its fullest extent (i.e. the piston head 76 is moved fully to the left in the power cylinder 75 as seen in FIGURE 8), or until the nozzle 7 of the probe 6 passes over the edge 4 of the glass ribbon. Consequently, the actuating face or end wall 82 of the bellows 87 remains displaced to the right until either of these conditions is reached. When the nozzle 7 passes over the edge 4 of the glass ribbon the input signal to the air line 30 is changed, as already described, with the result that the actuating face or end wall 82 of the bellows 87 is moved to the left, as seen in FIGURE 8', and the piston head 76 is caused to start movement to the right so that the probe 6 and the nozzle 7 are withdrawn from over the glass ribbon.

This movement takes the nozzle 7 clear of the glass ribbon, when the action repeats and an oscillating movement of the nozzle 7 continues, due to the inertia of the system. With a low inertia system the nozzle 7 can be made to lock onto the edge of the glass ribbon, the pilot valve 79 remaining closed. An advantage of keeping the nozzle oscillating is that the continual movement prevents the nozzle from sticking.

Referring now to FIGURE 9 of the accompanying diagrammatic drawings, the pressure switch 10 comprises a limp diaphragm 101 on which a pneumatic signal delivered through the gas line 17 will impinge, a plunger 102 mounted on the diaphragm 101 and abutting, at about its centre, a switching beam 103 pivoted near one end at 104, the other end carrying an electrical contact 105. A second electrical contact 106 is mounted above and close to the electrical contact 105 and is arranged so that, as the diaphragm 101 is deflected upwardly under the pressure from a gas signal, the

contacts

105 and 106 close and complete an electrical circuit. The

contacts

105 and 106 therefore comprise the contacts 10 shown in FIGURE 4.

An adjuster spring 108 is included in the pressure switch 10 to predetermine the strength of the gas signal required to close the

electrical contacts

105 and 106.

Referring to FIGURES 1 and 4, there is shown a nozzle guard switch 99 which is provided to prevent damage arising from large lumps of glass present near the edge of the glass ribbon, or, alternatively, moving down the bath separately from the glass ribbon. When such a lump of glass impinges against the nozzle 7 of the probe 6, the Whole probe 6 rotates and in rotating it actuates the nozzle guard switch 99 which connects the base of the transistor 24 directly to the common line, so that current through the transistor 24 reduces linearly and the probe 6 is caused to retract. When the probe 6 is clear of the glass, the nozzle 7 and the probe will rotate under the action of a return system (not shown), for example a spring, back to their vertical position. The contacts 99 will then open again so that the transistor 24 will again provide a linearly increasing current and the probe 6 will be advanced towards the edge of the glass ribbon in a direction away from the side of the tank structure.

In the embodiment of the invention so far described, the apparatus is employed to obtain a record of the position of the edge of the glass ribbon in the form of a permanent record on paper. In addition or alternatively, a temporary visual indication of the position of the edge 4 of the glass ribbon 3 can be obtained, and this indication can be used by an operator to effect a change in the conditions of operation of the process in order to restore the edge of the glass ribbon to a desired position.

Alternatively the arrangement according to the invention can be employed in a fully automatic system so that any departure of the edge 4 of the glass ribbon from its desired position, a given distance from the side wall of the tank structure, will initiate a correction to restore the edge 4 of the glass ribbon to the desired position. In this case the sampling apparatus 13 is arranged to give an output to control a steering device, for example a carbon fender, which acts to push the glass ribbon towards the centre of the bath when the edge of the glass ribbon moves too near to the side wall of the tank structure. Alternatively the steering correction could be offected by a restrictor tile fitted with a heating control.

More particularly according to this aspect, the invention provides a method of correcting when the glass ribbon departs from a desired width. The embodiment of the invention which will now be described with reference to FIGURE includes a means for obtaining, from the sensing of the two edges of the glass ribbon, an indication of the width and then using any departure of this indication from the desired width to alter one or more of the conditions under which the glass ribbon is formed to make the necessary correction.

Referring then to FIGURE 10, there is shown a plan view of the apparatus for manufacturing a ribbon of glass by delivering molten glass to a bath of molten metal, for example tin or an alloy of tin having a specific gravity greater than that of glass. The molten glass is delivered to a bath 120 of molten metal from a spout 121 and the rate of flow of the molten glass down the spout 121 is controlled by a tweel 122. The molten glass is allowed to'fiow freely on the bath of molten metal to form a ribbon 123 of glass, and the ribbon 123 of glass is withdrawn by taking it up from the surface of the bath 120 of molten metal by appropriate rollers 124 which lead to the lehr in which the ribbon of glass is annealed.

The rollers 124 along which the ribbon of glass is advanced after it has been removed from the bath 120 of molten metal apply a tractive force to the ribbon of glass as this is formed on the bath of molten metal, and an alteration in the speed of the rollers 124 is a convenient method of changing the width of the ribbon 123 of glass formed on the bath.

Indicated diagrammatically in FIGURE 10 by the arrows 127 and 128 are probes which are similar to the probe 6, and each of which tests for the position in relation to the side wall 5 of one edge of the glass ribbon 123 at a position on the bath 120 where the ribbon is being formed from the layer of molten glass developed on the bath after delivery from the spout 121. The block diagrams 129 and 130 indicate the apparatus in accordance with the invention and comprise all the apparatus shown in FIGURE 1 and external to the tank structure containing the bath of molten metal, with the exception of the recorder 14. Two outputs are taken from each of the apparatus 129 and 130, the first output from each being fed to a recorder 14 similar to that already described.

The second output from each of the apparatus 129' and is fed to a respective input of an averaging relay 131. The averaging relay is of a known type, for example it may be of a diaphragm type such as a Kent airoperated controlling unit.

Conveniently the arrangement including the averaging relay 131 works on the system that, when the respective edges of the glass ribbon are in positions equivalent to the desired width of the glass ribbon, equal outputs are applied from the apparatus 129 and 130 to the respective inputs of the averaging relay, and no output is obtained therefrom. However, when one of the edges of the glass ribbon departs from its desired position and the other edge does not make a similar departure, the respective inputs to the averaging relay 131 are no longer equal. The averaging relay 131 then gives an output indicative of the departure from the desired width of the glass ribbon, this output appearing in output line 132.

The output indicative of the departure of the ribbon width from a desired value is fed along the output line 132 to a pneumatic recorder controller 133 (a brief description of one form of pneumatic recorder controller will be made with reference to FIGURE 12 of the accompanying drawings).

Any input signal from the line 132 results in the pneumatic recorder controller 133 giving a mechanical correction signal which is fed to a valve 134, conveniently a hydraulic valve, which controls the position of the tweel 122.

If the width of the glass ribbon being formed is too small, then the correction signal applied by the pneumatic recorder controller 133 to the valve 134 will cause the tweel 122 to be raised to permit a greater mass of glass to flow to the bath 120 of molten metal. The delivery of a greater mass of molten glass to the bath causes the width of the glass ribbon formed to be increased. Conversely, if the width of the glass ribbon 123 formed on the bath 120 of molten metal is found to be too great, then the pneumatic recorder controller 133 will give a mechanical correction signal to the valve 134 to cause the mass of molten glass delivered to the bath of molten metal to be decreased.

An alteration in the control of the mass of molten glass delivered to the bath can itself impart any correction necessary in order to obtain from the bath 120 a ribbon of glass of desired width, but alternatively other alterations in the conditions under which the ribbon is formed may be used for the same purpose, and preferably more than one variable is altered in order to ensure that a ribbon of glass taken from the bath has a desired width and a desired thickness.

In FIGURE 10 of the accompanying drawings, the correction signal given by the pneumatic recorder controller 133 is shown also to be applied to a speed controller 135 which adjusts the speed of a motor 136 (conveniently a DC. motor) which drives the rollers 124 through an appropriate gearing 137.

In general when the width of the glass ribbon formed on the bath is less than the predetermined value, the correction signal applied to the speed controller 135 by the pneumatic recorder controller 133 acts to reduce the speed of the motor 136 so that the rollers 124 rotate more slowly to advance the glass ribbon at a slower speed. The tractive force applied during the formation of the glass ribbon 123 is therefore reduced and the width of the glass ribbon formed is allowed to increase.

Alternatively when the width of the glass ribbon is found to be too great, the output given by the pneumatic recorder controller 133 acts to make the speed controller 135 increase the speed of the motor 136 so that the rollers 124 advance the glass ribbon more quickly and apply a greater tractive force to reduce the width of the 13 glass ribbon at the time of its formation on the bath 120 of molten metal.

The controlling action just described for the speed of the rollers 124 is the control which would be applied to obtain a desired width of glass ribbon if a variation in the rollers 124 was used alone to alter the width of the glass ribbon. In practice, however, the thickness of the glass ribbon is generally of the primary importance and a desired width for the glass ribbon is a matter of manufacturing convenience rather than an essential prerequisite for the product. As the speed of the rollers 124 and the tractive force exerted by them has a particular controlling influence on the thickness of the glass ribbon as well as on its width, in general, some other control, for example the position of the tweel 122, has to be used in conjunction with an alteration in the speed of the rollers 124 in order to obtain a glass ribbon of desired thickness and width.

Additionally, apparatus in accordance with the present invention may be used to alter the temperature of the molten glass supplied to the bath in order to provide a correction when the width departs from a desired value. Such a control of the temperature of the molten glass delivered to the bath may be used on its own as a control, or in conjunction with one or more other variables, such as the two variables already described with reference to FIGURE 10.

Desirably the speed controller 135 is a Ward-Leonard arrangement (see FIGURE 11) associated with a DC. motor 136 and the control of the speed of the motor is eflected by causing the mechanical correction signal to change the setting of a variable resistor 138 in a motor generator set feeding the armature current of the motor 136, the field windings of which are fed from a constant current supply V. The motor generator set comprises a shunt motor 139 mechanically coupled to a drive dynamo 140, and the change in the setting of the variable resistor 138, by altering the armature current of the motor 136, effects a correcting adjustment in the speed of the motor 136.

Referring now to FIGURE 12 there is shown schematically a suitable apparatus for use as the pneumatic recorder controller 133. In FIGURE 12, there is shown a mechanical

arrangement comprising pointers

141 and 142, the first of which is preset and the second of which varies according to the pneumatic output signal applied at 143 from the line 132 leading from the averaging relay 131. The

pointers

141 and 142 are respectively pivoted at 144 and 145 and are connected to a

linkage comprising members

146, 147, 148, 149, 150, 151 and 152. This linkage is also pivoted at 153 and 154, the member 152 which is pivoted at 154 being a flapper for controlling the rate at which air is emitted from a nozzle 155 to which air is supplied from an air line 156, as its position in relation to the nozzle 155 alters in accordance with the pneumatic force applied at 143.

When a predetermined force is applied at 143 in the direction of the arrow shown acting at that point, the apparatus remains in its normal balanced or rest position, and the quantity of air permitted to escape from the nozzle 155 is such that the pressure applied to a diaphragm 157 acts through a member 158 to control the valve 134 at a predetermined setting.

However, when the force applied at 143 in the direction of the arrow increases, the pointer 142 is caused to move downwards and the

linkage comprising members

150 and 149 moves up, as seen in FIGURE 12, with the result that the mid-point of member 149 moves up, the member 151 is also moved in the same direction, and the flapper 152 is moved about its pivot 154 in a direction away from the nozzle 155. Consequently more air is able to escape from the nozzle 155 and the pressure applied to diaphragm 157 decreases so that the member 158, controlled by the diaphragm 157, alters the setting of the valve 134.

The mechanism will move in the reverse direction when there is a decrease in the force applied at 143 or if the force applied at that point is a force in the opposite direction to the arrow shown in FIGURE 12, with the result that a greater pressure is exerted on the diaphragm 157 and the setting of the valve 134 is altered in the reverse direction through the action of member 158.

In the earlier description, the sampling apparatus has been described in FIGURES 4 and 5 as an electropneumatic sampling apparatus. Alternatively the sampling apparatus could be a mechanical/pneumatic component enabling the univibrator 41 and solenoid-operated valves 33 and 35 to be omitted. A simplified form of this alternative mechanical/pneumatic component is shown in FIGURE 13.

In FIG. 13 the signal which is an air pressure indicative of the position of the probe in relation to the side wall 5 of the tank structure is shown applied from the air line 29 to a reservoir 161 via a line 162. This position obtains so long as a member 163 carrying the slipper blocks 164 and 165 remains in the position shown in FIGURE 13 where the line 162 is permitted to be connected directly to the reservoir 161.

At the instant that the contacts 10 close, the member 163 is moved to the left so that the reservoir 161 is connected to the line 166 instead of to the line 162. In FIG- URE 13, the line 166 is shown as being connected directly to a recorder 14 but equally it could be connected to one input of an averaging relay 131.

The mechanism under control of the contacts 10 and causing the movement of the member 163 may be solenoid operated or mechanically operated.

In the embodiments of the invention which have been described, the method and apparatus according to the present invention are used in determining the position of an edge of a glass ribbon advancing along a bath of molten metal and in controlling the position of the edge or alternatively controlling the width of the glass ribbon on the bath of molten metal. Alternatively, however, the information of the position of the edge of the glass ribbon may be used to control the positioning of apparatus for performing some later operation of the glass ribbon, for example in cutting the edge of the glass ribbon or for cutting of the glass ribbon into sheets. The information may further be used for controlling a polishing action on the surface of the glass ribbon if such polishing action is desired to be undertaken.

Instead of determining the position of the glass ribbon on a bath of molten metal, the apparatus may be employed for determining the position of the edge of a glass ribbon as the ribbon is advanced through an annealing lehr, and similarly the information may be used for controlling a subsequent operation on the glass ribbon.

The application of the invention, however, is not limited to the manufacture of glass in ribbon form and may be applied in any industry in which sheet material is manufactured in ribbon form and it is desired to determine the position of the ribbon obtained or the width of the ribbon obtained.

I claim:

1. Apparatus for determining the position of an edge of advancing ribbon, the apparatus comprising pneumatic edge sensing means including an inner tube located co-axially with an outer tube to define an annular nozzle, said nozzle being disposed at a position which is substantially aligned With the edge of the advancing ribbon, gas delivery means for supplying gas under pressure to the space between said inner and outer tubes whereby an annular stream of gas is discharged therefrom, and a pressure sensitive switch responsive to the state of the back pressure set up in the said inner tube, driving means for moving the pneumatic sensing means laterally with respect to the advancing ribbon, control means connected to said drive means and arranged to control the operation of said driving means and to produce a signal indicative of the position of the pneumatic sensing means in relation to the edge of the advancing ribbon as the pneumatic sensing means is moved by the said driving means laterally of the advancing ribbon, and sampling means con nected to said pressure sensitive switch for sampling the signal produced by said control means at the instant that said pneumatic sensing means experiences a change in the state of the back pressure in the said inner tube consequent upon the movement of the said pneumatic sensing means over the edge of the said advancing ribbon.

2. Apparatus for determining the position of an edge of an advancing ribbon of sheet material, the apparatus comprising pneumatic edge sensing means including an inner tube located co-axially with an outer tube to define an annular nozzle, said nozzle being disposed at a position which is substantially aligned with the edge of the advancing ribbon, gas delivery means for supplying gas under pressure to the space between said inner and outer tubes whereby an annular stream of gas is discharged therefrom, and a pressure sensitive switch responsive to the state of the back pressure set up in the said inner tube, pneumatic driving means arranged to move the pneumatic sensing means laterally with respect to the advancing ribbon, electro-pneumatic control means connected to said drive means and arranged to produce a pneumatic signal which controls the operation of said driving means and which is indicative of the position of the pneumatic ensing means in relation to the edge of the advancing ribbon as the pneumatic sensing means is moved by the said pneumatic driving means laterally of the advancing ribbon, electrically operated sampling means in electrical connection with said pressure sensitive switch and in pneumatic connection with said electro-pneumatic control means for sampling the pneumatic signal produced by said electropneumatic control means at the instant that said pneumatic sensing means experiences a change in the state of the back pressure in the said inner tube consequent upon the movement of the said pneumatic sensing means over the edge of the said advancing ribbon, and detector means pneumatically connected to said sampling means for analysing, indicating or recording the pneumatic signal passed thereto by said sampling means and indicating the position of the edge of the advancing ribbon.

3. An apparatus according to claim 2 wherein the said pressure sensitive switch is arranged to control the electronic current generator which in turn operates to change the condition of the said electro-pneumatic control means, whereby the pneumatic driving means is reversed to move the pneumatic sensing means in the opposite direction in relation to the edge of the advancing ribbon.

4. Apparatus for determining the width of a glass ribbon manufactured on the surface of a bath of molten metal, the apparatus comprising duplicate apparatus according to claim 2 for determining the position of respective edges of the advancing ribbon, comparator means connected to the output of each said apparatus for comparing the distance between the indications of the respective edges of the advancing ribbon with a predetermined value for the widthof the advancing ribbon and a pneumatic recorder controller dependent upon the output of the said comparator means for changing one condition under which the glass ribbon is formed in a manner to correct for the departure from the said predetermined width.

5. Apparatus according to claim 4 wherein the pneumatic recorder controller is arranged to change the rate at which the glass ribbon is withdrawn from the bath of molten metal.

6. Apparatus according to claim 4 wherein the pneumatic recorder controller is arranged to control the rate of delivery of glass to the bath of molten metal.

7. Apparatus according to claim 4 wherein the pneumatic recorder controller is arranged to vary the temperature of the glass supplied to the bath.

8. A method of manufacturing fiat glass in ribbon form on a bath of molten metal, comprising delivering glass at a controlled rate to the bath, advancing the glass in ribbon form along the bath, projecting an annular stream of gas towards one edge of the advancing ribbon of glass, sensing the state of the back pressure existing in the zone surrounded by the annular stream, simultaneously. moving said annular stream laterally with respect to the advancing ribbon across said one edge of the ribbon, producing a signal which controls the lateral movement of the annular stream and which is indicative of the position of said stream in relation to the edge of the advancing ribbon as the annular stream is moved laterally of the ribbon, and controlling the manufacture of the advancing glass ribbon in response to that signal at the instant that there occurs a change in the state of the back pressure in said zone surrounded by the annular stream consequent upon movement of the annular stream over the edge of the advancing ribbon to correct for any departure in said edge from a predetermined position.

9. A method of manufacturing flat glass in ribbon form on a bath of molten metal, comprising delivering glass at a controlled rate to the bath, advancing the glass in ribbon form along the bath, projecting respective annular streams of a gas inert to the molten metal downwardly towards the edges of the advancing ribbon of glass, sensing the state of the back pressure existing in the zones surrounded by those annular streams, simultaneously moving each said annular stream laterally with respect to the advancing ribbon across the respective edge of the ribbon, producing two signals which control the lateral movement of the annular streams and which are indicative of the positions of said streams in relation to the edges of the advancing ribbon as the annular streams are moved laterally of the ribbon and thereby indicative of the width of the ribbon of glass, and controlling the formation of the ribbon on the bath in response to those signals at the instant that there occurs a change in the state of the back pressure in the said zones surrounded by the annular streams consequent upon movement of the annular streams over the respective edges of the advancing ribbon s0 as to correct for any departure of the width of the advancing ribbon from a predetermined width.

References Cited UNITED STATES PATENTS 2,244,864 6/ 1941 Witham 73-37.7 2,539,131 1/1951 Gundersen et a1. 73-37.7 2,756,586 7/1956 Nash 7337.7 2,814,487 11/1957 Medketf 24257.1 3,159,170 12/1964 Callan 73-37.7 3,266,880 8/1966 Pilkington 65-99 3,243,992 4/1966 Woods 73--37.5

ARTHUR D. KELLOGG, Primary Examiner US. Cl. X.R.