US3090534A - Web guide control - Google Patents

Description

May 21, 1963 J. c. FROMMER ETAL 3,090,534

WEB GUIDE CONTROL Filed March 24, 1959 2 Sheets-Sheet 1 HYDRAULK. PUMP 92108 ow"; Ij e p Lia-074mg y 1963 J. c. FROMMER ETAL 3,090,534

WEB GUIDE CONTROL 2 Sheets-Sheet 2 Filed March 24, 1959 a Maya 3,090,534 WEB GUmE CONTROL Joseph C. Frommer, Cincinnati, Ohio, and Ulrich R.

Furst, Bellevue, Wash, assignors to Electric Eye Equipment Co., Danville, 1H,, a corporation of Delaware Filed Mar. 24, 1959, Ser. No. 801,503 20 Claims. (Cl. 226-211) This invention relates generally to the control of moving fiem'ble webs and more particularly is concerned with means for continually and automatically maintaining lateral position of a flexible web as it passes through a structure such as a machine which operates upon the web.

The invention will be described in connection with apparatus such as a multi-color high-speed printing press having a continuous paper web passing through the press to be printed in perfect registration, but is not limited to this application, since the invention is applicable as well to any machine which requires a flexible web to pass through the same properly centered with respect to the driving and guiding means thereof.

The invention is especially intended for use with a structure known as a steering roll, such as that described and claimed in a co-pending application which is owned by the assigned hereof, and entitled Steering Roll Construction Serial No. 718,057 filed February 27, 1958 by Carl L. Deeken, now Patent No. 2,940,752. The invention herein is directed especially to the control means per se by means of which the web is maintained in centered position at all time, and as well to a system of a type which has been provided to take the maximum of advantage of the various components thereof for fast and immediate correction of departures from proper centering.

In any machine in which a web must pass through the same properly centered, the purposes for which the machine is intended are defeated if the web is permitted to wander at will over the various rollers and past the various stations of the machine where operations are performed thereon. Only a perfect roll of the material from which the web is made will travel truly, and this cannot occur unless it passes through a perfect machine. There are so many factors which contribute to the webs creeping to one side or the other of center that a complete catalog herein would be impractical, although several such factors can be named as illustrative. Some factors are variations in thickness of the web, variations in width of the web, in consistency of ink, variations of the impression, changes in humidity, variations in mechanical alignment and changes of temperature.

Several solutions for the problem involved have been proposed and indeed placed in operation, 'but none of these are to any degree as efiicacious or sensitive and efficient as the invention herein. Many structures provided for lateral movement of the white roll, the stand which carries the supply of paper for the press. This requires considerable energy and is only capable of application at one end of the reach of the web; can only be done slowly because of the great inertia and weight of the white roll and stand; and provides sluggish and coarse control only. Other methods have utilized mechanical guides which attempt to guide the web itself, and in one instance means are provided for keeping the web centered through the use of pneumatic scanners moving inward and outward of the center of the web in response to the covering and uncover ing of openings in the scanner changing pneumatic pressures. This structure is shown and described in US. Patent 2,666,639, owned by the assignee of this application. Inertia problems of this apparatus did not prevent its becoming commercially successful, because it operated satisfactorily compared with the state of the art at the time of its inception, but greater control and the need for 3,090,534 Patented May 21, 1953 ice speedier response make the present invention a substantial improvement and patentable advance thereover.

The objects of the invention are the provision of a novel and improved web guide control for laterally positioning and guiding the web of a high speed machine, which is greatly simplified and more efiicient and economical than the prior structures.

An important object of the invention is concerned with the provision of a web guide control that will maintain the web centered on the rolls of a machine, irrespective of the changes in width of the web.

In connection with this latter object it is pointed out that most of the prior art structures, with the exception of such structures as those of said Patent 2,666,639, operated upon one edge of the Web. The assumption that the width of the web is constant is a hope rather than a reality, because the opposite is most usually true, especially with very wide Webs. The change of width of the web as it passes through the apparatus operating thereon will also change the position of the web it it is guided from one edge and this materially reduces, if not completely eliminating, the centering control.

The invention herein is primarily concerned with structures in which center line guiding and control is achieved irrespective of the change in width of the web, but in particular instances where single edge guiding is satisfactory, certain phases of the invention are applicable to single edge control of the web.

Many objects and advantages of the invention can only be appreciated and understood through a careful persusal and evaluation of the specification which follows in which a preferred embodiment of the invention is described in detail and illustrated in the drawings, albeit said drawings are diagrammatic in their appearance.

In said drawings:

KG. 1 illustrates the esesntial components of a system using the invention for center line guiding of a web passing through a press.

FIG. 2 is a circuit diagram of the electrical control portion of the structure of FIG. 1 including the two scanners and the amplifier.

FIG. 3 is a circuit diagram of an advantageously modified portion of the circuit of FIG. 2 in accordance with the invention.

The invention is directed to several phases which are concerned with the following: (1) a system for assuring continuous perfect centering and guidance of the high speed web while passing through a machine; (2) a control apparatus used in a system of this kind and which is activated by means of a pair of scanners providing a pair of signals for comparison; (3) a system as described in which the control apparatus uses only one scanner and has a constant signal simulating a second scanner against which the first signal is compared to elfect center line guiding based upon the position of only one edge of the web.

As explained in said copending application Serial No. 718,067, now Pat. No. 2,940,752, it has been found that the maximum control of movement of a web passing through a machine such as a printing press is achieved through the use of a steering roll which is carefully balanced to pivot in a limited plane with a minimum of friction upon an axis which is perpendicular to the axis of the roll and spaced therefrom. The invention herein as embodied in the system depends upon this structure for achieving the unusual and exceedingly high degree of control that is obtained. This steering roll structure is combined with a hydraulic cylinder and a hydraulic system operating the cylinder which is controlled by means of a highly sensitive electromagnetically controlled hydraulic differential valve. The particular valve with which considerable success has been had is one which is available commercially as a Cadillac valve and can be obtained from Cadillac Gauge. Company of Detroit, Michigan. This valve has at least two electromagnetic windings the flow of current through which provides control of the hydraulic fluid pressure applied to one end or the other of the cylinder. The amplifier or comparison device of the invention applies current through the two windings to vary the position of the cylinder and hence pivot the steering roll until the signals from the scanners are equal, at which time there will be no further movement of the steering roll.

In the case of the single edge guide, instead of two scanners a signal is obtained from a fixed source and the signal from a single scanner is continuously compared with this to provide the currents in the windings of the sensitive electrically energized hydraulic valve.

Considering now the illustrations, in FIG. 1 there is 7 shown a portion of a press which has a web of paper passing through the same. The web is designated 10 and the arrows show the direction of movement thereof. The web 10 passes over a steering roll 12 with the incoming reach and the outgoing reach substantially parallel one with the other, an arrangement which has been found most effective and sensitive for steering roll control. The steering roll 12 rotates on an axis 14 which is substantially horizontal and is journalled at the ends 16 of a relatively rigid elongate yoke 18 which is pivotally mounted upon a pivot assemblage 20 suitably secured upon the framework 22 or base of the press. The axis 24 of the pivot assemblage 2G is perpendicular to the axis 14 and is spaced therefrom as indicated by the arrow 26.

The right hand end 16 of the yoke 18 has a pair of cars 28 providing the pivotal journal for the eye 30 formed on the end of the piston rod 32 of a hydraulic cylinder 34 the opposite end of which is pivotally secured at 36 to a part 38 of the framework of the press. Adjustment of the pressure of the hydraulic fluid applied to the cylinder 34 through its end ports 40 and 42 by means of the hydraulic pump 44 operating through the sensitive magnetically controlled valve 46 will swing the yoke 18 one way or the other about the axis 24. The control currents in the valve 46 are provided from the amplifier 48 by way of electrical connections designated generally 50.

The amplifier 48 is a comparison device, which electronically and continuously compares signals obtained from the two scanners 52 and 54 on the outgoing reach of the web 10. These two scanners are of a basic form well-known, comprising photo-sensitive devices such as photoelectric cells activated by projected light from suitable sources such as indicated at 56 and 58. The optical components of these systems are too well-known to require description, but insofar as the application herein is concerned, a narrow slit of light is permitted to impinge against each of the photo-sensitive devices, as for example through the transparent windows diagrammatically indicated at 60 and 62. This narrow slit is intercepted by the edge of the web to decrease or increase the amount of light that the respective scanners receive and hence to vary the amplitude of signals provided thereby and applied to the comparison device 48. Since the valve 46 will continuously change the amount of the piston rod 32 that protrudes until the amplitudes of the signals applied to the comparison device 48 are equal, the web 16 will continuously seek the precise center of the distance between the two scanners 52 and 54 (which are of course adjusted to be equally spaced on opposite sides of the centerline that it is desired the web should follow).

It will be appreciated that for the structure described, the amplitudes of signals from the scanners 52 and 54 will not necesarily remain constant for the condition of perfect centering, although the signal amplitudes will be equal with respect to one another for perfect centering. This means that the width of the web may vary without affecting the centering of the web, since this is automatically compensated for by the system. Likewise, the fogging of the optical systems of the scanners will have no effect upon centering since both will usually fog the same amount over the same period of time.

The system may be varied by eliminating one or the other of the scanners 52 or 54 and providing a source of constant potential in its place against which the signal from the remaining scanner may be compared. This system will not be as effective as that which continuously maintains centering irrespective of the web Width, but is superior to other known structures using one side edge of the web for guiding control.

Such an advantageous detailed modification of the control circuits, to be seen hereafter in connection with the discussion of FIG. 2, is illustrated in FIG. 3. The utility and function of this circuit of FIG. 3 becomes more clear by considering the succeeding description of 'FIG. 2. For the moment, however, in FIG. 3 there is shown an arrangement for substitution in the circuit of FIG. 2 upon eliminating one of the above noted scanners 52 or 54. Associated circuit elements of FIG. 2 are similarly positioned and numbered in FIG. 3 for illustrating the adaptation of these modifying circuits of the latter FIG. 3 to the more general apparatus of FIG. 2;

In this FIG. 3 a control grid of the double triode tube V1 is connected by way of lead 88 to the variable contact of a potentiometer 155. The fixed contacts of this potentiometer, as shown, connect this potentiometer across a source of potential indicated by B+ and a ground symbol.

Thus the bias potential of one control grid 88 of tube V-l is manually adjustable by the potentiometer. As will be seen hereafter, this grid 88 is connected, in another embodiment of the invention, to the cathode electrode of a photoelectric tube, such as tube V-S, for application of grid potentials under control of light rather than under resistor control by a potentiometer.

Referring now to FIG. 2 the DC. amplifier or comparison means 48 is shown in a detailed circuit diagram along with other components of the system. The sources of light are shown as lamps at 56 and 58 directing their light through suitable optical trains past the respective edges of the web 10 through slits 60 and 62 respectively of the scanners 52 and 54. Each scanner has a photoelectric tube as at V5 and V-6, one electrode of each being connected to the B+ supply conductor 74 and the other electrode of each being connected to the scanner signal balancing means indicated generally at 76. The negative electrode of tube V5 is connected through the resistor R201 in lead 78 through the high ohmage variable resistor R311B to the common conductor of the section C of the four-pole five-position switch 80. The negative electrode of the tube V-6 is connected through the resistor R201 in lead 82 through the high ohmage variable resistor R311A to thelead 84, one end of which connects with all four of the first four contacts of section C of switch and the other end of which connects through a voltage divider 86 to ground.

During operation, the wipers of the variable resistors R311A and R311B are adjusted in unison to give equal signal output from tubes V-5 and V-6 for equal amounts of intercepted light.

Flow of current through the resistors R201 produces D.C. potentials at the grids 88 and 90 of the left hand sections of the tubes V-l and V-2. The plates 92 and 94 of the sections of each tube are connected together as shown so that the tubes each have single output circuits, and the potential thereof applied respectively by way of the leads 96 and 98 and resistors R107 and R109 ot the respective grids 160 and 102 of tube V-3. Cathodes 104 of the tube V1 are connected together and extend by the lead 186 to a source of negative potential 108 through resistor R112. Cathodes 110 are also connected together and extend by way of lead 112 through a similar resistor R116 to the same source of negative potential 198. The grid 88 is connected through the resistor R202 to the grid 114 and the grid 90 is connected through a similar resistor R202 to the grid 116.

The resistors R108 and R110 are voltage dropping resistors for the plates 92 and 94 respectively being connected to the B+ supply line 74. The plates 118 and 120 of tube V3 are connected in parallel with the plates 122 and 124 respectively of the tube V4 so that the plate current of both tubes flows through the respective windings 126 and 128 of the valve 46 through the common conductor 130 to the B+ supply line 74 through the dropping resistor R102. The grids 100 and 102 are respectively connected to the grids 134 and 132 of tube V4 through resistors R105 and R104. All of the cathodes 136 and 138 of the tubes V-3 and V4 are C0114 nected to the negative potential source 108 through the resistor R103. The left hand cathodes and right hand cathodes each have a degeneration resistor R106 sepa-. rating same from resistor R103.

The resistors R202, R104 and R105 keep the grids on opposite sides thereof at equal potential and prevent unwanted parasitics, and hence it may be considered that both sections of tube V-1 act as one tube, both sections of V2 act as one tube, the both left hand sections of tubes V3 and V4 act as one tube, and both right hand sections of tubes V-3 and V4 act as one tube. Indeed, the basic invention may be considered as utilizing a total of four single section tubes or two double section tubes, not counting the photo-tubes.

The tubes V-l and V-2 receive D.C. signals which are amplified and applied to the right and left sections of the tubes V3 and V4 respectively resulting in an output current flowing through the windings 126 and 128 which will result in no change in the pressure at opposite ends of the cylinder 34 if the currents are equal, but which will unbalance if the currents are not equal and cause the servo effect to bring the web back to center. Note that changes in line voltage, width of web, fogging of optical systems, and any variation that occurs to both of the scanners 52 in like amount will have no effect upon control.

The amplifier circuit 48 is unusual in that it provides variable sensitivity to the differential between the signals appearing at the grids of the respective tubes V1 and V2, that is, when the scanner signals are not equal; and it provides maximum of degeneration and hence low sensitivity and high stability when the signals are of sub stantially equal amplitude.

The desideratum when equal level signals occur is to keep rated current flowing in the windings 126 and 128 of the valve 46. When signals of different level occur, their difference is to be emphasized so that a speedy and immediate response will be made to bring the web back to centered position.

The plate load resistance R108 and R110 of the respective tubes V1 and V2 is chosen to be approximately half of the cathode resistance R112 and R116. In the actual circuit this ratio was 150,000/ 330,000. Equal signals would therefore be reduced by a factor of one-half. Considering cathode follower action, since the signals on the cathodes and grids of the respective tubes V-l and V2 are substantially the same, the current flow through the resistor R108 and resistor R112 will be the same. The signal across the plate resistor R108 will however be half that of the signal across the cathode resistor R112. This is also true for the tube V2 and its plate and cathode resistors R110 and R116, respectively.

Note that there is a value of resistance between the two cathodes 104 and 110 which may be represented by the broken line equivalent resistor R This resistance R is determined by the following circuitry: the lead 106 connects with the wiper 140 of the multi-position switch 142 connected as a variable resistance element by the lead 144 directly to the cathode 110 through contact No. 5 of the section D of switch 80 and the switch wiper (position 5 of switch 80 is OPERATE) and the lead 6 112; a parallel connection is by way of lead 146 from the lead 106 through resistor R306 and resistor R302 to lead 112. These latter two resistance paths are in parallel. The sensitivity of the compensating effect of the amplifier 48 is controlled by the position of the wiper 140 of the switch 142.

The value of this resistance R the equivalent of the two parallel paths described, is immaterial if the flow of current through the tubes V-1 and V2 is of the same D.C. level. It could be either zero or infinite for inphase signals.

Now we consider what happens if the signals on the two tubes V-l and V2 are not the same and the currents flowing through these tubes are different, related in value to the amount of light lost by one scanner and gained by the other. If R were infinite, then the two tubes Vl and V2 would act in the same manner that they acted when equal D.C. level signals were received, namely, all signals are decreased in their output circuits. This would give an error differential it is true, but one which is of low sensitivity due to the halving of signals, because of cathode degeneration.

If the tube cathodes 104 and 110 were connected in short circuit, the signals at the grids 88, 114 and 90, 116 would have to change the cathode currents of the tubes in opposite directions in order to maintain the same voltages on both cathodes (recalling that one set of grids is receiving a high voltage and the other set of grids is receiving a low voltage) since the cathodes are connected together. There can thus be no cathode follower action or degeneration in the tubes, and all of the signal of each tube will appear at its respective plate with one being substantially greater than the other, to a much greater degree than the difference between the signals that caused the flow of current. The full amplification of the tubes Vl and V2 comes into effect, and the signals applied to the output tubes V3 and V4 are accordingly of much greater differential. This increases the sensitivity of the device.

Instead of having R as a short circuit, which is of course feasible in some installations, it is adjustable, to thereby control the sensitivity of the apparatus.

The necessary power for the amplifier 48, and if desired for the filaments of the lamps 56 and 58, can be obtained from power sources that may be associated with other electrically operated apparatus used in connection with the structure of the invention. In the circuit diagram there is illustrated a suitable power supply which is comprised of a full-wave rectifier tube V-7 having the high voltage secondary winding 162 of a transformer 160 connected across its plates. The transformer primary winding 161 is connected across the power line. The negative potential for the lead 108 is obtained from a center tap 163 of the secondary winding 162 connected to the lead 108 at the point 165. It will be noted that this point is at a negative potential because the point 167 between the resistors R114 and R is at ground potential. The resistor R101 is a voltage dropping and filter resistor and provides a high B+ potential of 260 volts DC. at the point 169. It is shunted to the point 165 by means of the filter condenser C The resistor R102 also drops the voltage of the point 171 to volts DC. and is shunted to point by filter condenser C The filament secondary 174 is connected across the cathode of the tube V7, and there may be additional filament secondaries for other tubes in the apparatus. In the actual device the filaments of the lamps 56 and 58 were energized from a separate transformer and each filament had a variable resistor in series wherewith to adjust its brilliance, but it is not believed necessary to illustrate this since it is a well known arrangement.

As previously stated, the various pairs of tubes act in effect as single tubes, but are used for reliability. Efiort must be taken to prevent the differences between the characteristics of the tubes from affecting the operaconnected directly to the meter M3tl1.

tion of the device. In the case of the outpu tubes V3 and V-4 it has been found that the connection of the low ohrnage resistors R106 to the pairs of cathodes provides some cathode degeneration in the respective sections of the tubes. In this manner the equality of the currents flowing in the coils 126 and 128 of the sensitive valve 46 will be less dependent upon the equality of the characteristics of the sections of the tubes V-3 and V-4.

These two low ohmage resistors Rltifi are respectively associated with dual current paths to coils 126 and 128. The two resistors are together connected in series with a relatively large resistor RitB in the cathode circuits of dual tubes V-3 and V-4. These three resistors all make for degeneration of signal currents passing through the plate circuits of the two tubes. The relatively small size of resistors Riitfi makes the overall degeneration effect of these two resistors small in comparison to the degenerative effect of the large resistor 103.

Now, by reference to the drawing FIG. 2, it is seen that those plate currents of double tubes 1-3, and V-4 which are associated with each of these two small resistors R196, flow to different ones of the control coils 126 and 128. Both these coil currents, however, are degeneratively affected by current flow in the large common resistor R193. What is the effect of this division of currents and the relative sizes of these resistors? As a large current tends to flow through either or both coils 126 and 128 under the'infiuence of light controlled signals from tubes V5 and V6, these large signals are both degenerated by the common cathode resistor R103. But the differential of signals flowing through the respective resistors R106 is not correspondingly degenerated. This follows since resistors R106 are substantially smaller, by an order of magnitude, than common resistor R103.

Accordingly, the overall signal applied to these coils by a large change in light at tubes V-S and V-6 results in a correspondingly degenerated change in overall signal at the coils 126 and 123. But a very much smaller factor of degeneration is applied to the differential signal between the two coils.

As a net result, the overall sensitivity of the coil controlling system is inhibited against overlarge increase and possible physical damage to moving parts. At the same time this inhibiting reduces the system sensitivity to selective operation by valve 46 by only a relatively small amount.

It has been found that the amplifier described above working in conjunction with the components described gives excellent and reliable control. p

In the circuit of FIG. 2 some of the components have ,not been described in detail, and these need not be explained since their purposes and operation should be obvious. The switch 8% is for testing and adjusting the circuit. All of the wipers are ganged as at 180. The various positions may be briefly explained hereinafter without the need for tracing the circuits:

Position 1 shown.

Position 2 In this position the cathode 104 is connected through meter M591 through a. multiplier and cathode 110 is The series con- "8 nection of metersM301 and M501 is through the multiplier resistor R305 between cathodes 104 and 110 so that if the voltage at both cathodes is equal, no voltage drop occurs across the meters and resistor R305. However, if cathode 104 is at one potential and cathode 110 at another potential, the meters both indicate the direction and magnitude of the difference. This gives the difference between the two to enable the balancing of the scanners through the balance 76. Note that in this position as in all others but position 5, the input tubes are connected as pure cathode followers and the low ends of the cathode balance resistors R311-A and R311-B are connected together and to a fixed point between resistors R401 and R402. 1

Position 3 In this position again the cathode voltage of tube V-l is compared against a fixed voltage to enable physical adjustment of the scanner 52 so that exactly half of the light will fall on that scanner.

Position 4 In this position, the cathode voltage of tube V-2 is compared against a fixed voltage to enable physical adjustment of the scanner 54.

Position 5 This is the operating position. When the switch is placed in this position the averages of the voltages of the two cathodes are again being compared at all times. In section B, however, there is a different voltage due to the connecting of other components in its circuit. A variable voltage may now be applied by movement of the fine control of resistor R404 to simulate physical movement of the scanner 52 for fine adjustments of the scanners. This position also connects the sensitivity control into the circuit.

The first stage of the amplifier, namely the tubes V1 and V-2 are usually located in the same housing as the respective photocells of the scanners.

Note that the cathodes 136 and which are slightly higher than the grids of the respective sections of the tubes V-3 and V-4 so that there is always a certain value of current flowing in the windings of the valve 46 as required for most efficient operation thereof. a

The operation of the structure with a fixed voltage applied instead of a signal from one of the scanners is no different than described. There will be a greater difference between the response of the amplifier (i.e., its output) to the signals of different D.C. level than the difference between the signals themselves; while the response at conditions of equal level signals will be relatively smaller, and hence less sensitive. This of course is characteristic of the structure when two scanners are furnishing the signals, but the difference between the response of the equal and unequal signals for the two scanner arrangement is even more marked. This is because as one scanner signal becomes greater the other becomes smaller, and vice versa.

In viewing the overall character of the device, it may be considered that the circuit provides cathode degeneration in the stages at conditions when the respective signals from the scanners are substantially equal and no degeneration when the signals are not equal, thereby enabling the maximum of amplification of the tubes to be available, for the difference. Stating this in another way, since the amplifiers areresponsive to a DC. voltage produced by the respective scanners, the average level of voltage affects the output very little, but the difference between the levels has a very substantial effect.

The construction of a practical embodiment of the invention should be apparentto those skilled in this art,

138 are at voltages be set forth hereinafter:

RESISTORS (in ohms) 2K. (K thousands) 33K.

10 nieg. pct. -10 meg. pot.

A meg. R404 20K. pot. Switch 1'42 Resistance between points to give wide range of sensitivity, from 4.7 K ohms between points 10 and 11, to 330K ohms between points 2 and 3. Total resistagce approximately 665K ms.

M301, M401, M501-" Microam meters.

C-l, 15 mfd. filter condensers.

V-1, V2 12AX7 vacuum tubes.

V3 ,V4 12AT7 vacuum tubes.

V-5, V6 CE34Q photoelectric tubes.

V-7 Y3 rectifier tube.

As stated above, the invention is applicable to a wide variety of apparatus in which a moving web is to be steered to maintain its centering, either with respect to a centerline of the web, or relative to one edge. Considerable changes may be made without departing from the spirit or scope of the invention as defined in the appended claims.

What it is desired to secure by Letters Patent of the United States is:

l. A system for guiding a flexible web through a machine which operates upon the web, and which includes a steering roll mounted for rotation on a first axis transverse of the web and for pivotal swinging on a second axis perpendicular to said first ax-is but spaced therefrom on the side of the oncoming reach of said web, a pair of illuminating means on the outgoing reach of said web, one on each edge thereof and photo-sensitive signal producing means at each edge receiving a defined beam from said illuminating means and the web adapted to intercept an equal portion of each beam to produce an equal signal output from each signal producing means when said web is substantially centered between said signal producing means, an electronic comparison means connected to receive said signals and arranged to provide an output which is amplified to a greater extent for one difference between the signal outputs of said signal pro- 'ducing means than at another difference between the signal outputs of said signal producing means, an electromagnetic hydyraulic control valve receiving said differential output, and hydraulic actuating means connected with said steering roll to swing same about said second axis and controlled by said control valve to pivot said steering roll in a direction for shifting said web laterally to maintain equal signal outputs.

2. A system as claimed in claim 1 in which said comparison means comprise an amplifier having a pair of signal channels including electronic amplifier states having low amplification when said signals are equal and high amplification when said signals are unequal.

3. A system as claimed in claim -1 in which said comparison means comprise a pair of electronic amplifier roll mounted for offset swinging and having a hydraulic actuator for swinging same, a hydraulic system for driving the actuator and controlling the same including an electromagnetic valve including a pair of difierential windings, a scanner on at least one edge of said web on the outgoing reach relative to said steering roll and having illuminating means and a photo-sensitive signal producing means thereat arranged to receive a beam from said illuminating means with the web at least partially intercepting said beam to control the signal from said scanner, a second signal-producing means responsive to another beam which is intercepted to a degree determined by the position of said web, and a comparison circuit receiving the signals from both means and providing a pair of output currents related to one another in a non-linear manner depending upon the difierence between the signals from the photosensitive producing means and the second signal producing means, said differential windings being against which said signal from said photosensitive signal producing means may be compared to guide said web from the position of said one edge thereof.

6. A system as claimed in claim 4 in which there is a second scanner and illuminating means on the opposite edge of said web, and said second signal-producing means is also photo-sensitive and receives a beam from said second illuminating means and the web also at least partially intercepts said beam to control the signal from said second scanner, and the signals from both are compared to guide said web from the geometric center between said scanners.

7. In a system in which a web is steered to keep same centered as it passes through a machine having scanners Y scanning the edges of the web, a comparison amplifier for comparing signals from said scanners and providing difierential current outputs which includes a pair of signal channels each having at least a cathode follower stage with the cathodes connected together, and a pair of Y amplifier stages driven respectively by the cathode folinstance, and the output circuits of said amplifier stages having said current outputs flowing therein.

8. In a device of the character described in which a moving web intercepts light directed at a pair of scanners and means are provided responsive to the signals from I said scanners to maintain the web centered by movement of a steering roll through a control system, an electronic circuit for comparing said signals to provide a pair of output signals whose relative values are related to the difference if any between the signals from said scanners, said circuit including a pair of cathode follower stages each connected with an amplifier stage, and the output signals adapted to appear in the output circuits of said respective amplifier stages, the cathode follower stages each including an electronic tube including a cathode and the cathodes each connected for providing degeneration in the respective cathode follower stage when the scanner signals applied thereto are equal but no degeneration when the scanner signals are unequal whereby the unequal signals will be amplified in said cathode follower stages and said electronic circuit will have greater sensitivity for unequal scanner signals.

"9. A structure as claimed in claim 8 in which adjustable resistance means is connected between said cathodes to vary the sensitivity of said electronic circuit.

10. A structure as claimed in claim 8 in which a constant signal is provided in place of a signal from one of said scanners and the other scanner is located adjacent one edge of said web and its signal varies with respect to the position of the web relative thereto.

11. A structure as claimed in claim 8 in which said scanners are located on opposite edges of said web and the signals therefrom vary with the laterial disposition of said Web and in opposition one to the other.

' 12. In a system for guiding a moving Web of material into locus on a machine wherein a member performs work on the web, means for maintaining proper alignment of the web with said member, said means comprising the combination of means for shifting the position of the web in either direction transverse to its line of travel into said locus, edge scanning means for the web operated responsive to the deviation of said web from said proper "alignment and deriving electrical signals proportional to said deviations, difierential amplifier means connected to receive said signals and responsive thereto to derive an amplified electrical output indicative of the direction and proportional to the extent of said deviations, a bidirectional hydraulic mover connected to said web shifting means to motivate the same, a source of hydraulic fluid for actuating said mover, an electrically actuated flow regulating valve through which fluid from such source is transmitted to said mover to operate the latter in the direction selected, said valve being connected to receive said output from the amplifier and being responsive thereto to select said direction and determine the rate at which fluid is supplied to said mover, the system being further characterized in that, by virtue of the construction, arrangement and inter-connection of the elements of said combination, said web shifting means is moved in a direction to correct said deviations and at a rate which varies proportionally with the extent of the instantaneous web deviation from said proper alignment.

13. The system of claim 12 wherein said scanning means comprises a light source, two photo-sensitive elements and light masking means for the latter disposed adjacent a respective edge of the web, one of said photosensitive elements providing an electrical signal having a potential which serves as a reference in said amplifier and the other photo-sensitive element providing signals to the amplifier which have a potential varying proportionally with the extent of said deviations and which 'are of positive or negative value with respect to said reference signal dependent upon the direction of the deviation.

14. The system of claim 12 wherein said scanning means comprises a light source, a photo-sensitive element and making means for the. latter disposed adjacent opposite edges of the web, each of said photo-sensitive elements providing electrical signals to said amplifier having a. potential which varies proportionally with the extent of the web deviation detected by that element, the instantaneous signal from one of said elements providing a reference potential in said differential amplifier and the instantaneous signal from the other element being of positive or negative value with respect to the said reference signal dependent upon the direction of the deviation at one edge of the web as compared to that at its opposite edge.

15. In a system for guiding a moving web of material into a locus on a machine wherein a member performs work on the web, and in which the proper alignment of the web with said member must be maintained, the combination comprising means for shifting the position of the web in either direction transverse to its line of travel into said locus, scanning means disposed adjacent at least one edge of the web, said scanning means having photo-sensitive means responsive to deviations in the I web from said desired alignment and driving electrical 'error signals the potential of which varies proportionally 'said reference signal and responsive thereto to derive an amplified output varying in positive and negative value, with respect to said reference signal, dependent upon the direction of said deviation and having a magnitude, with respect to said reference signal, which varies proportionally with the extent of said deviation, a bidirectional hydraulic mover connected to said web shifting means to motivate the same, a source of hydraulic fluid for actuating said mover, an electrically actuated flow regulating valve through which fluid from said source is transmitted to said mover to operate the latter in the direction selected, said valve being connected to receive said output from the amplifier and being responsive thereto to select said direction and determine the rate at which fluid is supplied to said mover, the system being further characterized in that, by virtue of the construction, arrangement and interconnection of the elements of said combination, said web shifting means is moved in a direction to correct said deviations and at a rate which varies proportionally with the extent of the instantaneous web deviation from said proper alignment.

16. In a system for guiding a moving Web of material into a locus on a machine wherein a member performs work on the web, and in which the proper alignment of the web with said member must be maintained, the combination comprising means for shifting the position of the web in either direction transverse to its line of travel into said locus, scanning means disposed adjacent each of the opposite edges of the web, each scanning means having a photo-sensitive element responsive to deviations in the position of the corresponding edge of the web and each photo-sensitive element providing electrical signals the potential of which varies with the extent of the deviation detected by that element, a differential amplifier connected to receive said signals from each of the scanning means and responsive thereto to provide an amplified output having a potential proportional to the difference in potential between the signals from the individual scanning means, a bi-directional hydraulic mover connected to said web shifting means to motivate the same, a source of hydraulic fluid for actuating said mover, and an electrically actuated fiow regulating valve through which fluid from said source is transmitted to said mover to operate the latter in the direction selected, said valve being connected to receive said output from the amplifier and being responsive thereto to select said direction and determine the rate at which fluid is supplied to said mover, the system being further characterized in that, by virtue of the construction, arrangement and interconnection of the elements of said combination, said web shifting means is moved in a direction to correct said deviations and at a rate proportional to the extent of deviations of the longitudinal centerline of the web from its desired alignment with said work performing member.

17. In a web scanning system wherein two portions of a moving web are scanned for the purpose of providing a pair of electrical signals the respective amplitude of which is dependent upon the lateral pisition of each portion with respect to the direction of web movement, in which there is a web-adjusting device acting laterally on the web and drive means for operating the web-adjusting device, and in which there is a dilferential signal comparator having its output connected to the drive means, the improvement comprising: a pair of parallel amplifiers each driven by a respective one of said signals and providing an amplified output signal corresponding to the respective input signals received, feedback means connected between said amplifiers providing a variable degree of amplification of said amplifiers the value of which is related directly to the difference between the amplitudes of said electrical signals, whereby for a small difference in signal input amplitudes the degree of amplification will be low, whereas for large difierences in signal input the degree of amplification will be high, the output signals being connected to said differential signal comparator whereby the degree of adjustment of the Web laterally depends upon the degree of amplification of said amplifiers and hence upon the difierence in amplitude between said input signals.

18. The arrangement claimed in claim 17 in which each of said amplifiers is provided with a grid circuit at which the respective signal is received and said feedback means includes a feedback circuit connected between the grid circuits.

19. The arrangement claimed in claim 17 in which said feedback means comprise, first cathode resistor means common to said amplifiers and second cathode resistor means individual to each of said amplifiers connected to one side of said common resistor means.

20. In a system of the character described in which a flexible Web passes over a steering roll in a machine which operates upon said web, and in which means are provided for swinging the web including an actuating device operated by a pair of amplifier output signals Whose relative values determine the extent of actuation; comparison means driven by a pair of input signals at least one of which is related to the position of an edge of said web to produce said output signals, comprising a pair of electronic amplifier stages having connection with one another to provide cathode degeneration in the respective stage accompanied by low amplification while the stages are receiving said input signals and said signals are of substantially the same amplitude, but also eliminating cathode degeneration when the said input signals are of difierent amplitudes whereby substantially to increase the amplification of said stages and therewith the sensitivity of said comparison means to unequal input signals.

References Cited in the file of this patent UNITED STATES PATENTS 2,451,816 Dunn Oct. 19, 1948 2,722,415 Wood Nov. 1, 1955 2,840,371 Frommer June 24, 1958 2,840,722 Frommer June 24, 1958 2,866,407 Hackel et al. Dec. 30, 1958 2,883,559 Bailey Apr. 21, 1959

Claims (1)

1. 7. IN A SYSTEM IN WHICH WEB IS STEERED TO KEEP SAME CENTERED AS IT PASSES THROUGH A MACHINE HAVING SCANNERS SCANNING THE EDGES OF THE WEB, A COMPARISON AMPLIFIER FOR COMPARING SIGNALS FORM SAID SCANNERS AND PROVIDING DIFFERENTIAL CURRENT OUTPUTS WHICH INCLUDES A PAIR OF SIGNAL CHANNELS EACH HAVING AT LEAST A CATHODE FOLLOWER STAGE WITH THE CATHODES CONNECTED TOGETHER, AND A PAIR OF AMPLIFIER STAGES DRIVEN RESPECTIVELY BY THE CATHODE FOLLOWER STAGES, THE CATHODE FOLLOWER STAGES CONNECTED FOR PROVIDING MAXIMUM DEGENERATION WHEN THE SIGNAL INPUTS

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