US3032245A - Apparatus for controlling web tension - Google Patents

Description

May 1, 1962 H. F. GEORGE ET AL Filed April 25, 1960 FIG. I.

VACUUM PUMPN ELEcTROPNEuMATIc POsITIONER 5 Sheets-Sheet 1 MANUAL VALVE FlLTER 25 sPRING MANUAL CONSTANT ROLLER SET POINT\B.I vOLTAGE INPUT 1 SUPPLY N l 23 AUTOMATIC I9 ELECTRONIC I7 CONTROLLER I6 REEL AND UNWIND PRINTING cOuPLE r l l l i I MANUAL I AUTOMATIC SET POINT F 2 i 2 ELECTRONIC INPUT E CONTROLLER i I l ERROR- I sENsING ELEcTRO-PNEuMATIc C|RCU|T POSITIONER ----6O P.s.I. AIR

CONSTANT sTRAIN GAGE VOLTAGE LOAD CELL suPPLY A VARYING I BALANCING TENSION LEVEL 3 TENSION FROM I FROM REEL VACUUM BO TI-IROTTLE ATMOSPHERE FILTER VALVE VACUUM VACUUM ATMOSPHERE INvENTORs i JS II N S 'KI ITAL FILTER I MANUAL BY ATMOsPI-IERE VALVE 5 ,W

ATTORNEYS.

THROTTLE VALVE OPERATION May 1, 1962 H. F. GEORGE ET AL 3,032,245

APPARATUS FOR CONTROLLING WEB TENSION Filed April 25, 1960 5 Sheets-Sheet 2 FIG. 3. STRAIN GAGE I CONSTANT LOAD CELL I 4! VOLTAGE .I SOURCE i i l VOLTAGE 523351 AMPLIFIER I CIRCUIT E5: E1: ER I I l i T CONSTANT I e. VOLTAGE l l SOURCE l l l l""""5 g "i i I i I AUTOMATIC I 1l- I I CONTROLLER I L I 56 I I I l I 57 I t l I AIR .L ELECTROPNEUMATI C/ POSITIONER INVENTORS HARVEY F. GEORGE JOHN J. KIMBALL BY MWrM ATTORNEYS.

May 1962 H. F. GEORGE ET AL APPARATUS FOR CONTROLLING WEB TENSION 5 Sheets-Sheet 3 Filed April 25, 1960 AT TORNE YS.

&

LOAD CELL FIG.

y 1962 H. F. GEORGE ET AL 3,032,245

APPARATUS FOR CONTROLLING WEB TENSION- Filed April 25, 1960 5 Sheets-Sheet 4 flmfiflhi g 96 SENSING ROLLER 98 7* SENSING ROLLER FIG. II.

INVENTORS HARVEY F. GEORGE JOHN J. KIMBALL BY %,WMM

AT TORNEYS.

VACUUM BOX May 1, 1962 F. GEORGE T AL 3,032,245

APPARATUS FOR CONTROLLING WEB TENSION Filed April 25, 1960 5 Sheets-Sheet 5 VACUUM pUMpj MANUAL VALVE FIG, 7 THROTTLE VALVE PNEUMATIC I3I LOAD CELL SIGNAL PRESSURE 0-60 RS. l.

REEL AND UNWIND PNEUMATIC CONTROLLER SWITCH PRINTING COUPLE FIG. 8.

CONSTANT AIR SUPPLY-6O P.S.l. CONSTANT AIR SUPPLY-2O P.S.|.

g' z' EVEL SIGNAL PRESSURE TENSI L 0-60 P.S.|. PNEUMATKL MANUAL FROM REEL PNEUMATIC f LOAD CELL CONTROLLER BALANCING TENSION ADDED BY VACUUM'\-! BOX ' FILTER VACUUM A VACUUM ATMOSPHERE ATMOSPHERE BOX PUMP THROTTLE l VALVE '\MANUAL VALVE FILTER INVENTORS r HARVEY F. GEORGE JOHN J. KIMBALL ATMOSPHERE BY AT TORNEYS.

United States Patent ()fiice 3,032,245 Fatented Il lay 1, 19 3 2 This inventionrelates to machinery for handling material in'web form and aims to provideapparatus for correcting variations from a selected levelin the tension of a travelling web. While our-invention may be practiced with advantage in conjunction with the'handling of a variety of flexible materials such as paper, cardboard, plastic film and metal foil, it is a particular feature of our invention that it can be'used' to suppress variations in the tension of a travellingweb of paper on a rotary printing press. In the operation of a rotary printing press, one of the conditions that must be maintained as nearly uniform as possible, if satisfactory printing is to be achieved, is the tension to which the web ofpaper is subjected as it travels through the press. Variations in the paper itself or in the treatment" which it receives on the press may result in fairly wide fluctuations in the web tension. For-instance, variations in web tension caused by flying pasters" when a new roll of paper is spliced to the end of the web of an expiring roll of paper at running speeds on multicolor presses used for the printing of magazines may result in colors being so badly out of register that it is commonly necessary to scrap anywhere'from several dozen to several hundred of the magazines because they are printed'in out of register colors during the flying splice.

Various expedients have been resorted to in the past to attempt to mitigate the difiiculties created through variations in the tension of a web travelling through a rotary printing press but 'they have been far from successful. Apparatus that has been used in the past in an attempt to gain some measure of control over web tension has not only been costly and subject to excessive wear but it has also been possessed of excessive inertia so that the response to the necessity of effecting corrections of tension variations has been too slow.

We have discovered that it is possible to apply a regulable tension to a web as it travels through a rotary printing press by means of a stationary brake whose action is governed through a system of basic control units that are readily available at moderate cost, and wherein there are a very few moving parts which are of such small size that the inertia of the apparatus is negligible and web tension variations are sensed and'compensated for as they occur.

In accordance with our invention, a transverse vacuum box equipped with a perforated cover plate is located along the path of the paper Web so that, as the web travels through a printin press, it slides across that cover plate. Air is evacuated from the vacuum box to maintain sub atmospheric pressure within the box. The friction between the paper web and the cover plate against which the web is pressed by atmospheric pressure causes the vacuum box to function as a brake for the web, the amount of the braking efiect exerted by the web being a function of the difference between the pressure inside the vacuum box and atmospheric pressure.

The rate at which air is evacuated from the vacuum box is regulable so that the braking exerted by the vacuum box can be adjusted to produce a selected net tension upon the web during normal operating conditions. Variations from the selected web tension level are sensed by automatic means that cause a controller to vary the rate at which air is evacuated from the vacuum box. When the web tension sinks below the selected level, thejcontroller causes the rate at which air is evacuated from the vacuum box'to' be increased. When the web tension rises above the selected level, the controller causes the rate at which air is evacuated from the vacuum box to be decreased. In this manner the web tension is immediately restored to the selected level when variations occur therein. I 2

Apparatus embodying .our invention in the form which we now prefer is illustrated in the accompanying drawings in which:

FIG. 1 is a diagrammatic view in elevation ofone form of the web tension correcting apparatus embodying our invention; a.

FIG, 2 is, a block diagram illustrating the interrelationship of the control units for the web tension correcting apparatus shown in FIG. 1; V

FIG. 3 is a circuit diagram of the control apparatus illustrated in FIG. 2.including vertical sections of the strain gage load cells and electropneumatic positioner forming part of such control apparatus; FIG. 4 is a front elevation, broken away in part, of the sensing roller that actuates the pair of strain gage load cells illustrated in FIG. 3; f v

FIG. 5 is a section along the lines 5-5 of FIG. 4;

FIG. 6 is an isometric view of a vacuum box;

FIG. 7 is a diagrammatic view in elevation of another form of Web tension correcting apparatus embodying our invention; 7

FIG. 8 is a block diagram of the control units shown in FIG. 7;

FIG. 9 is a vertical section of the pneumatic load celland pneumatic controller illustrated diagrammatically in FIG. 8;

FIG. 10 is a front elevation of the sensing roller thatactuates the pneumatic controller illustrated in FIG. 9; and

FIG. 11 is a section along the lines 1111 of FIG. 10.--

The web tension correcting apparatus illustrated in FIG. 1 is located between the web supply reel and the first printing couple of a rotary printing press. The portion of such a press that is illustrated in FIG. 1 includes, in addition to the printing couple and the supply reel, a belt 15.

um box and sensing roller forming part of the web tension:

correcting apparatus are located between the rollers 20 and 21 and above the plane along which the web 25 con--- tacts those rollers so that the Web 25 slides across the upper cover plate 26 of the vacuum box and presses down wardly against the sensing roller.

The vacuum box extends transversely across the path,

of the web and has a rectangular body 27 Whose cover plate 26 is provided with a series of perforations 28.

The ends 29, 30 of the cover plate 26 are bent down-.

wardly so they will not interfere with the sliding movement of the Web across it. The vacuum box is connected with a vacuum pump through a conduit 31 which contains a throttle valve so that air is evacuated from the vacuum box by the vacuum pump at a rate that is governed by the position of that throttle valve.

The sensing roller has its ends 32,33 j ournaled .in, the

outer ends of a pair of arms 34, 35 whose inner ends are pivoted to the side frame members 36, 37 of the press... The outer ends of the arms 34, 35 are connected, through set screws 38, 35', with buttons 41, 42 extending from the tops of the strain gage load cells, as best illustrated in FIGS. 4 and 5, so that the sensing roller is supported in level position. Each strain gage load cell, as illustrated.

in FIG. 3, includes a housing 44 that contains a high strength steelcolumn 45 that is capped by the button 41. As the web 25 travels past the sensing roller the tension illustrating the interrelation of the strain gage load cells under compression. Such compression will be increased with increases in the tension of web 25 and decreased with decreases in that web tension.

Four strain gages, each of which consists of a continuous length of fine resistance wire 43, are bonded to the surface of the column 45 and they are electrically connected to each other in the form of an initially balanced Wheatstone bridge. A constant voltage circuit, such as an ordinary battery, is connected to the two input terminals of the bridge circuit. The resistance of the wires 48 varies in accordance with changes in the height of column 45 as the compressive force applied to button 41 is increased or decreased. When the strain gages are connected as by means of the line 50, 51 to the constant voltage source, the net output of the two strain gage load cells used in our tension correcting apparatus is a measure of the compressive force applied to the button 41 and varies directly with variations in the tension of web 25. Strain gage load cells that are well adapted for use in the practice of our invention are marketed by Baldwin- Lima-Harnilton Corp. of Waltham, Mass. (see Baldwin- Lima-Hamilton Corp. Bulletin 4355, SR4 Load Cells and Load Beams).

Variations in the sum of the output voltages of the two strain gage load cells are utilized to correct the variations in web tension that cause them. To accomplish this the strain gage load cells are connected through the line 52, 53 with an error sensing circuit. Since the voltages (E derived from the strain gage load cells are of the order of millivolts, the lines 52, 53 are connected to the terminals of a direct current voltage amplifier included in the error sensing circuit. The error sensing circuit also includes a constant voltage source which, in combination with a potentiometer, provides an adjustable set point voltage (E that opposes the output voltage (E of the direct current voltage amplifier so that variations in the amplifier voltage (E will produce an error signal (E whose magnitude and polarity are governed by the magnitude and type of change in the voltage (E That error signal (E is fed to the input of a controller which consistsoi a servo-amplifier containing a set of three controls, namely, a proportional gain control, a rate control, and a reset time control. Such a servoamplifier is marketed by Taylor Instrument Companies of Rochester, New York (see Taylor Instrument Companies Catalog 98335 of August 1959). As illustrated diagrammatically in FIG. 3, it includes, an addition to the amplifier 55, a proportional gain control indicated generally at 56, a rate control indicated generally at 57, and a reset control indicated generally at 58.

The output of the controller is utilized to actuate an electro-pneumatic positioner which regulates the throttle valve located in conduit 31 connecting the vacuum box with the vacuum pump. To effect this, the controller is connected through the line 60, 61 with the winding of a coil 62 that is associated with a permanent magnet 63 to provide a voice coil motor. The coil 62 is mounted adjacent the end of a balance beam 65 pivoted at one end so that it may be moved toward or away from nozzle 66 of the conduit 67 that communicates with the interior of the electro-pneumatic positioner. The electro-pneumatic positioner includes a casing 63 that houses a flexible transverse partition 69 forming an expansion chamber 79. The air pressure in expansion chamber 70 is normally balanced by a coil spring 71 located between the lower face of partition 69 and the lower wall of casing 68. The stem 72 of the vacuum pump throttle valve located in conduit 31 is attached to the lower face of the partition 69 and extends from the casing 63 to that throttle valve. Longitudinal movement of this valve stem 72 when the air pressure in expansion chamber 70 is increased moves the throttle valve in conduit 31 toward closed. position,

while a decrease in the pressure in expansion chamber 70 causes that throttle valve to be moved toward open position.

The operation of the apparatus that we have described, and which is illustrated in FIGS. 1-6, inclusive, is as follows:

The tension to which a paper web is normally subjected as it travels through a rotary printing press is about one pound per inch of web width. It will be assumed that half of this tension is to be produced by the vacuum box and that the balance of this tension will be produced through the normal operation of other components of the press. The controls are adjusted so that air is evacuated from the vacuum box at a rate that will maintain a pressure therein that will exert a braking effect that is the equivalent to one-half pound per inch of web width. Then, when the amplified load cell voltage (E is 10 volts, the balancing set point voltage (E is also 10 volts.

If the operating conditions of one of the press components were to change so that it would increase the web tension by one-quarter pound per inch, while the vacuum box was producing a web tension of one-half pound per inch, the net web tension would then total one and onequarter pounds per inch. This would cause the amplified cell voltage (E to increase from 10 volts to 12 /2 volts. As the set point voltage (E remains at 10 volts, the voltage (E will now be 2 /2 volts with a positive polarity. If the tension had decreased by one-quarter pound per inch, the voltage (E would be 2 /2 volts with a negative polarity. The 2 /2 volt error signal (E is fed to the controller which is now required to emit a signal which will cause the vacuum box tension to be reduced to one-quarter pound per inch so that the total web tension returns to one pound per inch. When this has been done, the voltage (E returns to 10 volts and the error signal voltage returns to 0.

The controller circuit is arranged so that a positive error signal (E will cause the vacuum pump throttle valve to be moved toward closed position while a negative error signal (E will cause that valve to be moved toward open position and the proportional gain control 56 is adjusted so that the correct amount of valve movement will be eltected. When there is a rapid and substantial change in the web tension because of a change in operating conditions, a proportional initial change in control output voltage would result in an undesirably slow realization of the desired web tension correction. The rate control 57 overcomes this by making it possible for the controller to deliver an initial voltage change that is disproportionately greater than that which would occur in the absence of such a control, which voltage change is then gradually reduced until the desired proportional voltage is reached. This rate control 57 is made adjustable in order that it may be readily accommodated to the characteristics of the particular system in which it is installed.

It is desired that for a change in press operating conditions the controller should adjust the vacuum tension so as to completely compensate for the change in press operating conditions and maintain constant web tension. The action of the proportional gain control 56 is such that for each value of web tension there is :1 corresponding throttle valve opening. This relationship between web tension and valve opening is adjustable to suit the characteristics of the particular system and press operating conditions. For each error signal, or deviation of actual web tension from the desired web tension, the valve is moved to a new position proportional to the magnitude of the error signal. If the press operating conditions change from those for which the proportional control is set originally, then it is apparent that when the proportional voltage corresponding to the error signal is reached the control valve will reach a throttle position that will not completely eliminate the web tension error.

The residual web tension erroris called-.ofiset and is compensated for by the resetcontrol. Thevreset control continl fils to change thecontroller.outputvoltage, hence the valve throttle position, in the same direction. as did the proportional, control until a. new' valve position is reached that makes the' error signalzero.

Whenthe output voltage. of the controller isincreasecl, the voice coil motor, is. actuated, to .move balance'beam 65 toward the nozzle 66. Such movement increases the back pressure at nozzle 66. to. produce, .in conjunction with thelaction of a pilot valve 74, .a proportional increase in the pressure in expansion chamber 7% This moves valve stem 72 in a direction to.close. the throttle valve for the vacuum, pump. Such movement is. re.- sisted by the coilspringl71 which createsa fixed throttle valveopeninglfo'r each value of pressure in compression nherl l- The valve stem 72 carries a pin 75 that bears against arm/76 of bell crank lever, 77. A spring 78 .urges arm 79 015 the bell crankalever 77 away from the balance bearnfiS so thata point is reached whenv the forces produced by the pressurefrom nozzle 66 and the feed back spring 78 balance the force exerted by the voice coil motor. Hence, the vacuum pumpthrottle valve will. remain inthe position towhich ,it is shifted by virtue of a variation in the web tension so l'ongas the controller output voltagecorresponding thereto,is applied to the voice coil motor and thernechanism automatically compensates for changesin air supply pressure. such as.are due to air leakages and the like, 7

Theweb tensioncorrecting apparatus illustrated in FIG. 7, like that illustrated in FIG. 1, is located'between the web supply reel and the first printing couple of a rotary press which is equipped with. belt .to govern the speed of the supply reel as it unwinds and rollers 16', 17', 18', 19', 29,,21',,22, 23 and 241,.all of conventional construction, across which the web 25 is drawn as it travels from the supply reel to the press. The apparatus illustrated in FIG. 7 alsoincludes a vacuum box and a sensing roller located between the rollers 20 and 21', and above the planealong which the web25' contacts those rollers so that the web.25' slides across the upper cover plate of the vacuum box, which is also of the.

construction illustrated in FIG. 6, and presses. down wardly against the ,sensingroller Whose ends 91,92 are journalled in bearings 93,, 94 mounted on the upper endsof armsj 95,,96. The lower endsof the arms 95, '96 are fixedto a shaftfiS mounted in bearingsltlft, 102 that are supported by the frame 163 of the press.

The web 25' exertsardownwardpressure on the sensing roller that urges it to rotate shaft 518. The extent to' which shaft 98 maybe rotated through thedownward pressure exerted by web 25 on the sensing roller and the direction of such rotation are a function of the tensionto which ,the web 25 is subjected. .Variations in this tensionare measured by a pneumatic load cell of known construction which is attached to a support 103athat is carried bythe frame of the press.

Such ineasurements are accomplished by mounting a head 104cm a'link lil tatfixed to shaft '98. so that the head 104 bears against thev loading platform 105 of the pneumatic load cell. The loading platform 1.05. is mounted on a plunger 1G6thatis supported by partition members 1117, 108 and 1119 which are respectively con-- nected to the load cell, casing .111 through flexible diaphragms 111, 112 and 113 to provide atare chamber114 and a compression chamber. 115 in the pneumatic load 4 cell, as best illustrated in F1G..,9. 1 Air is supplied at a constant pressurethrough the'conduit116. which cornmunicates with tare chamber 114 and compression chamber 115, respectively, through branch conduits 117,118.

A constant differential pressure regulator, indicated gen-,

erallyat 119, maintains a constant flow of air through conduit 118to compression chamber 115. The plunger 1% suppo ts a flapper 120 mm s tes sicu wa dly;a over the nozzle 1 21 so that air is permitted'to escape from compression chamber 115 through nozzle 121 with a back pressure that is-dependent upon the proximity of flapper 129 to that nozzle. The pressure of the air-in tare chamber 114may be regulated through-manual valve 123 so that it will counterbalance the force normally exerted on loading platform 165 by the head 164' and the flapper 121) is maintained at a selected distance from nozzle 121 so long as the force exerted on loading platform 105 remains unchanged.

Air is evacuated from the vacuum box through conduit 130 at a rate that is governed by the pneumatically actu ated throttle valve located in that conduit. The position of that pneumatically actuated throttle valve is governed by a pneumatic controller (illustrated in FIG. 9) that is located between-the pneumatic load cell and the pneu matically actuated throttle valve and which is connected to the pneumatic load cell by conduit 131 and to the pneumatically actuated throttle valve by conduit 132;

The conduit 131 leads from the compression chamber 11510 the bellows l33 in the pneumatic controller. The pneumatic controller also includes a pilot valve, indicated generally at 141, whose action is governed by the position of fiapper134, which is adjustably pivoted at one end to link 135 fixed to the movable end 136 of bellows- 133. Pilot valve 141 communicates through the conduit 132.with the pneumatically'actuated throttle valve located" in the vacuum line 130.

a The pilot valve 141 includes an air chamber 145 that surrounds bellows 146 and a valve chamber 147that con-' tains valve plug 148 which is supported by the movableend of bellows 146- The pilot valve'141 also has an exhaust port 149 leadingfromchamber 147 and which is closed when the plug'148 is moved from the position shown in FIG. 9 to the left side of chamber 147. Compressed air at fixed pressure is supplied to thechamber 147-through conduit 150 except when plug 148 is positioned at the right side of chamber 147-. A bypass 151 justable valve 161. A link 162-that extends from the movable end of negative feedback bellows 158 is adjustably pivoted to flapper 134.

The operation .of the apparatus illustrated in FIGS.

7-11 is as follows:

The controls are adjusted so thatthe tension to which the web-is subjected under normal operating conditions is "set. ata value which will be selected, for purposes of illustration, as one pound per square inch of web width, and it maybe assumed that one-half pound thereof is contributed through the braking action of thevacuum box.. In this condition the pressure'in the tare chamber 114 just balances the force, other than the web tension force, exerted against loading platform 105 by the head 104;.tl1'epressure in the chamber 115 balances the web tension force; and. the entire system is in balance. If the operating conditions of oneof the press components werevto. change so that it would increase the web tension by one-quarter pound per-inchwhile the vacuum box was producing a web tension of one-half pound per-inch, the,

65 ,net web tension would then total one and one-quarter pounds per inch.

A 25% increase in web tension also changes the total forceapplied to the pneumatic load cell through the pressurev of the head 104 against platform 105 by 25 Asa" consequence, the platform 105 is displaced bringing the flapper 120 into-contact with the nozzle 121 so that "air may 'riot escape from that nozzle. This results in an ine creasein the pressure in compression chamber 115 until it reaches a valuethat lifts the loading platform ,1051 and.moves-.fiapper-120 away from the nozzle to'permit a small air flow. The increase in pressure in the compression chamber 115 is transmitted through conduit 131 to the bellows 133, expanding the bellows and moving flapper 134 toward nozzle 155. As a consequence, there is an increase in the back pressure at that nozzle accompanied by a change in the pressure differential between chambers 145 and 147, shifting valve plug 148 to a position where the pressure in conduit 132 is proportionately decreased. This decrease in pressure in the conduit 132 causes the pneumatically actuated throttle valve located in vacuum line 130 to be closed by a corresponding amount, thus reducing the rate at which air is evacuated from the vacuum box and effecting a corresponding decrease in the braking etfect of that vacuum box. When the force exerted on the pneumatic load cell platform 105 is reduced, the action of the control system is the converse.

In order that the pneumatic control may alter the rate at which air is evacuated from the vacuum box to just the extent necessary to correct a variation in the Web tension, the pneumatic controller is provided with a proportional gain control, a rate control and a reset control, each of which is adjustable, and whose functions correspond, respectively, to the functions of the proportional gain control, rate control and reset control included in the electronic system that is contained in the embodiment of our invention which is illustrated in FIGS. 1-6, inclusive, of the drawings:

For each tension change the movable end 136 of bellows 133 is repositioned causing the combination of flapper 134, nozzle 155, negative feedback bellows 158 and pilot valve to produce a pressure change in conduit 132 proportional to the magnitude of the tension change or error. The pressure change in conduct 132 causes the throttle valve to move to a new position also proportional to the magnitude of the error signal.

The proportional gain control is adjusted by changing the point on the flapper 134 at which the link 162 is pivoted thereto. Accordingly, the amplitude of the response of the vacuum pump throttle valve to given changes in the position of the moveable end 136 of bellows 133 can be set at the appropriate value by locating the pivotal connection between link 162 and flapper 134 at the appropriate distance from the upper end of the latter.

Rate control is effected by the extent to which valve 159 is opened since the bellows 158 is adapted to produce a negative feedback. When the pressure in conduit 132 is changed as a result of the action of bellows 133, there is a lag in the rate at which the pressure in negative feedback bellows 158 reaches that level because of the restriction that is provided by the adjustable valve 159. As a result of this lag, the action of negative feedback bellows 158 in moving the upper pivot of flapper 134 is gradual, thereby effecting a delay in the corresponding change in the back pressure at nozzle 155 to the point where the desired proportional pressure in conduit 132 is reached.

When the proportional valve position described above is reached the Web tension error will have been eliminated for only one initial load or tension level; at all other tension levels the error or deviation has been reduced but not eliminated. This residual error is called offset and is compensated for by the reset control.

The reset control, which is effected through the positive feedback bellows 160 in conjunction with the adjusta ble valve 161 is used to reduce the offset error to zero. When the flapper 134 has been repositioned at the stable proportional pressure level through the action of the negative feedback bellows 158 there is a pressure differential across the valve 161 as a result of the restriction provided thereby. As air gradually flows through valve 161 the change in pressure in positive feedback bellows 160 causes the flapper 134 to be moved in a direction to effect the desired change in the output pressure in conduit 132. This change in pressure causes a. continuing change in the valve throttle position, in the same direction as the proportional control action, until a throttle position is reached that will reduce the web tension error to zero.

. While the tension control shown in the drawing is located in front of the first printing couple of a rotary press, it will be appreciated that such a control may be combined with a press at other locations, such as the point at which a printed web enters a folder; indeed our tension control may be used with advantage with web handling machinery other than printing presses. Also, it is to be understood that the terms that have been used in describing the illustrative embodiment of our invention that is shown in the accompanying drawings are terms of description and not of limitation and various changes can be made therein without departing from the spirit of our invention as it is defined in the appended claims.

What is claimed is:

1. Apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said Web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; means for sensing variations from the selected web tension level; and a controller responsive to said sensing means for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tension to said level.

2. Apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall, a pump adapted to evacuate air from said vacuum box'to maintain reduced pressure therein, and a throttle valve located between the vacuum box and the pump for regulating the rate at which air'is evacuated from said vacuum box; means for sensing variations from the selected web tension level; a pneumatic positioner for said throttle valve; and a controller responsive to said sensing means adapted to cause said pneumatic positioner to actuate the throttle valve so that the rate at which air is evacuated from the vacuum box is increased when the web tension sinks below the selected level and the rate at which air is evacuated from said vacuum box is decreased when the web tension rises above said selected level to restore the web tension to said level.

3. Apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; a sensing roller mounted along the path of said web for perpendicular movement with respect thereto so that it is caused to move perpendicularly by a change in the tension of said web; and a controller responsive to perpendicular movement by said sensing roller for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box 'when the web tension rises above said selected level to restore the web tension to said level.

4. Apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate .to maintain reduced pressure therein; means for sensing variations from the selected web tension level; and a controller provided with an adjustable proportional gain control and responsive to said sensing means for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing therate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tension to said level.

5. Apparatus -for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said Web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate tomaintain reduced pressure therein; means'for sensing variations from the selected web tension level; and a controller provided with an adjustable rate control and responsive to said sensing means for increasing the rate at which air is evacuated from the vacuum box when the web'tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box -when the web tension rises above said selected level to restore the web tension to said level.

6. Apparatus for correcting variations from as selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path ofsaid web so that the web slides across-the surface of saidwall and a pump adapted to-evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; means. for sensing variations from the selected web tension level; and a controller provided with an adjustable reset control and responsive to said sensing means for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tension to said level. i

7. Apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said Web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable.

rate to maintain reduced pressure therein; means for-sensing variations from the selected web tension level; and a controller provided with adjustable proportional gain,- rate and reset controls and responsive toisaid sensing means for increasing the rate at .which air is evacuated. from the vacuum box when the web tensionsinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension risesabove said selected level to restorethe web tension to said level.

8. The combination with Web handling machinery of apparatus for correcting variations from a selected level in, the tension of a flexible webtraveling through saidmachinery including: a brake comprising a transverse vacuumrbox having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from: said vacuum box at a regulable rate to maintain reduced inks below the selected leveland for decreasing the rate: at which air is evacuated from saidvacuum box when the web tension rises above said selected levelto restore'the web tension to said level.

9. T he combination with a rotary printing press of apparatus for correcting variations from a, selectedlevel in the tension of a web ofpapertraveiing through said press including: a brake comprising a transverse vacuum-box having a perforated wall located along the path ofsaid web.

10 so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; means for sensing variations from the selected web tension level; and a controller responsive to said sensing means for increasing the rate at which air is' evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected'level to restore the web terision to said level.

10. Electroniccontrol apparatus for correcting varia tions from a selected level in the tension of a traveling web including: abrake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate 'air from 'said vacuum box at a regulable'rate to maintain reduced pressure therein; means for sensing variations from the selected Web tension level including a sensing roller and a strain gage actuated by said sensing roller to produce an output voltage whose magnitude is proportional to the tension'of saidweb; and a controller responsive to changes in said output voltage for increasing ther'at'e at which air is evacuated from the vacuum box When the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tenQ sion to said level. 1 l

11. Electronic control apparatus for correcting varia tions from a selected level in the tension of atraveling webv including: a brake comprising a transverse vacuum box having a perforated walllocated along the path of said Web so that the web slides across the surface of said wall and a pump adapted to. evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; means for-sensing variations from the selected web tension level including a current supply whose output voltage is proportional to and changed'by variations in the tension of said web, and an error sensing circuit adapted to produce a signal upon a change in said output voltage whose magnitude and polarity are governed by the magnitude and type of said change; and a controller responsive to said-signal forincreasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the Web tension-rises above said selected level to restore the web tension to said level. t Y

12. Electronic control. apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of'said web so that the Web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a 'regulable rate to maintain reduced pressure therein; means forsensing variations from the selected web tension level and adapted to deliver a signal whose magnitude and polarity are governed by the magnitude and type of said variations; and a controller including an adjustable proportional gain control and responsive to said signal for increasing the rate'at which'air is evacuated from the vacuum box when the web tension sinks below the so-- lccted level and for decreasing the rate at which air isevacuated from said vacuum box when the'web tension rises above said selected'level-to restore the web tension' to said level.

l3.- Electronic control apparatus for correcting variations from 'a' selected level in the tension of a traveling" web including: a brake comprising a transverse 'vacuum' box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable' rate to maintain reduced pressure" therein; means for sensing variations from the selected web tension level and adapted to deliver a signal whose magnitude and polarity are governed by the magnitude and type of said variations; and a controller including an adjustable rate control and responsive to said signal for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tension to said level.

14. Electronic control apparatus for correcting variations from a selected level in the tension of a traveling Web including: a brake comprising a transverse vacuum .box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said 'vacuurn box at a regulable rate to maintain reduced pressure therein; means for sensing variations from the se lected web tension level and adapted to deliver a signal whose magnitude and polarity are governed by the magnitude and type of said variations; and a controller includ ing an adjustable reset control and responsive to said signal for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tension to said level.

15. Electronic control apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; means for sensing variations from the selected web tension level and adapted to deliver a signal whose magnitude and polarity are governed by the magnitude and type of said variations; and a controller including adjustable proportional gain, rate and reset controls and responsive to said signal for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tension to said level.

16. Electronic control apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall, a pump adapted to evacuate air from said vacuum box to maintain reduced pressure therein, and a throttle valve located between the vacuum box and the pump for regulating the rate at which air is evacuated.

from said vacuum box; means for sensing variations from the selected web tension level and adapted to produce a signal whose magnitude and polarity are governed by the magnitude and type of said variations; an electropneumatic positioner for said throttle valve; and a controller responsive to said signal and adapted to cause said positioner to actuate the throttle valve so that the rate at which air is evacuated from the vacuum box is increased when the web tension sinks below the selected level and the rate at which air is evacuated from said vacuum box is decreased when the web tension rises above said selected level to restore the web tension to said level.

17. Pneumatic control apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; means for sensing variations from the selected web tension level including the sensing roller and a pneumatic load cell actuated by said sensing roller to deliver air at a pressure which is proportional to the tension of said web; and a controller responsive to changes in the pressure of the air delivered by said sensing means for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the Web tension rises above said selected level to restore the web tension to said level.

18. Pneumatic control apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; means for sensing variations from the selected web tension level and adapted to deliver air at a pressure which is proportional to the tension of said web; and a controller including an adjustable proportional gain control and responsive to changes in the pressure of the air delivered by said sensing means for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tension to said level.

19. Pneumatic control apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; means for sensing variations from the selected web tension level and adapted to deliver air at a pressure which is proportional to the tension of said web; and a controller including an adjustable rate control and responsive to changes in the pressure of the air delivered by said sensing means for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tension to said level.

20. Pneumatic control apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; means for sensing variations from the selected web tension level and adapted to deliver air at a pressure which is proportional to the tension of said web; and a controller including an adjustable reset control and responsive to changes in the pressure of the air delivered by said sensing means for increasing the rate at which air is evacuated from the vacuum box when the web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tension to said level.

21. Pneumatic control apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall and a pump adapted to evacuate air from said vacuum box at a regulable rate to maintain reduced pressure therein; means for sensing variations from the selected web tension level and adapted to deliver air at a pressure which is proportional to the tension of said Web; and a controller including adjustable proportional gain, rate and reset controls and responsive to changes in the pressure of the air delivered by said sensing means for increasing the rate at which air is evacuated from the vacuum box when the Web tension sinks below the selected level and for decreasing the rate at which air is evacuated from said vacuum box when the web tension rises above said selected level to restore the web tension to said level.

22. Pneumatic control apparatus for correcting variations from a selected level in the tension of a traveling web including: a brake comprising a transverse vacuum box having a perforated wall located along the path of said web so that the web slides across the surface of said wall, a pump adapted to evacuate air from said vacuum 15 vacuum box; means for sensing variations from the selected web tension level and adapted to deliver air at a pressure that is proportional to the tension of said web; a pneumatic positioner for said throttle valve; and a controller responsive to the pressure of the air delivered by said sensing means and adapted to cause said positioner to actuate the throttle valve so that the rate at which air is evacuated from the vacuum box is increased when the web tension sinks below the selected level and the rate at which air is evacuated from said vacuum box is decreased when the web tension rises above said selected level to res-tore the web tension to said level.

References Cited in the file of this patent UNITED STATES PATENTS 2,778,634 Garns et al. Jan. 22, 1957 2,804,275 Saco et a1. Aug. 27, 1957 2,809,582 Crawford Oct. 15, 1957

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