US3009364A

US3009364A - Guide for alignment of moving band

Info

Publication number: US3009364A
Application number: US772786A
Authority: US
Inventors: Edward D Beachler
Original assignee: Beloit Iron Works Inc
Current assignee: Beloit Iron Works Inc
Priority date: 1958-11-10
Filing date: 1958-11-10
Publication date: 1961-11-21
Anticipated expiration: 1978-11-21
Also published as: FI46420B

Description

Nov. 21, 1961 E. D. BEACHLER 3,009,354

GUIDE FOR ALIGNMENT OF MOVING BAND Filed Nov. 10, 1958 4 Sheets-Sheet 1 "6 o S 1H w n n m Em t W an we 2 D .2

.EE 3528 W M Nov. 21, 1961 E. D. BEACHLER GUIDE FOR ALIGNMENT OF MOVING BAND 4 Sheets-Sheet 2 Filed Nov. 10, 1958 0:44 AB-HZZLHE Nov. 21, 1961 E. D. BEACHLER GUIDE FOR ALIGNMENT OF MOVING BAND 4 Sheets-Sheet 3 Filed Nov. 10, 1958 r. l immu e Hu l vh LE'EZZZEJ" Edward D. .Beaclxler Nov. 21, 1961 E. D. BEACHLER 3,009,364

GUIDE FOR ALIGNMENT OF MOVING BAND Filed Nov. 10, 1958 4 Sheets-Sheet 4 Edward D. Beach/er United States Patent 3,009,364 GUIDE FOR ALIGNMENT OF MOVING BAND Edward D. Beachler, Beloit, Wis., assignor to Beloit Iron Works, Beloit, Wis., a corporation of Wisconsin Filed Nov. 10, 1958, Ser. No. 772,786 10 Claims. (Cl. 74-241) This invention relates to paper-making machines, and more particularly to a guide mechanism to retain a web such as a felt or Wire in proper alignment as it travels over supporting rolls.

Various devices have heretofore been made to retain a web centered on rolls of a paper-making machine, and maintain it in that position. These devices have often been delicate in operation, have required a large amount of space, have been easily damaged by foreign materials and water, have not had a large range of operation and have not been fully satisfactory.

Accordingly, an object of the invention is to provide a web guide for paper-making machines which will be improved in operation over devices heretofore provided, and will be rugged and relatively free from failure.

Another object of the invention is to provide an improved operating mechanism for a web guide of the type which shifts the position of a guide roll to vary the lateral position of a moving web.

Another object of the invention is to provide an improved web guide suitable for use in a paper-making machine, which has an improved range of operation.

A still further object of the invention is to provide an improved web guide which is suitable for use in a Fourdrinier paper machine, and Which requires a minimum of head room and which is particularly well adapted to automatically controlling the position of a looped foraminous belt for supporting a Fourdrinier wire over a suction box for dewatering a paper web.

A further object of the invention is to provide an improved web guide with a roll for supporting the web which is pivotal about one end, and which is provided with improved apparatus for shifting the other end and improved bearing support apparatus for the shiftable end.

Other objects and advantages will become more apparent with the teaching of the principles of the invention in the disclosure of the preferred embodiments thereof, in the specification, claims and drawings, in which:

FIGURE 1 is a side elevational view of a Fourdrinier paper-making machine employing a guide for a web in the form of a traveling looped support belt for a Fourdrinier wire in accordance with the principles of the present invention;

FIGURE 2 is a graph presenting the relationship between force and deflection of the air springs of the guide mechanism;

FIGURE 3 is a top plan view, shown partially in schematic form, of the web guide mechanism;

FIGURE 4 is an enlarged detailed side elevational view, with parts in section, of a bearing support for a roll of the guide mechanism;

FIGURE 5 is a vertical sectional view taken along line VV of FIGURE 1;

FIGURE 6 is a side elevational view of the guide mechanism at one end of the roll; and,

FIGURE 7 is a top plan view, shown partially in section, of a control valve for the guide mechanism.

As shown on the drawings:

A preferred embodiment of the web guide mechanism of the present invention is illustrated in FIGURE 1 combined with a Fourdrinier paper-making machine. The machine includes a looped support belt or blanket 11, which supports a traveling Fourdrinier wire W. The belt or blanket 11 is supported on rolls, as will be deice scribed, and its lateral position is controlled by a guide roll 12, over which the blanket 11 travels. As illustrated in FIGURE 3, the roll 12 is supported by a pivotal bearing assembly 10 on one end, and a shiftable bearing assembly 16 on the other end. The

bearing assemblies

10 and 16 include shaft support bearings 13 and 14, respectively which permit the roll to rotate about its axis, with movement of the blanket or web 11. The

assemblies

10 and 16 permit shifting or canting of the axis of the roll approximately parallel to the plane of the web 11 (usually at right angles to the bisector of the angle of wrap of the Web around the roll), thereby causing the Web to run toward either side of the roll depending on the direction in which the roll is canted, as will be appreciated by those skilled in the art. This, of course, will change the lateral position of the web and the present mechanism is used for co-rrectively maintaining the web in a predetermined running position. For shifting the guide roll 12, the bearing 13 is mounted in a pivotal support 15, and the bearing 14 on a shiftable support 16a. The roll 12 is pivoted substantially parallel to the web 11 about the bearing assembly 10, and an arm 17 is connected to the bearing 14 and is shifted to control the position of the roll by

air springs

18 and 19,

An air spring, as the term herein is used, incorporates an expansible chamber defined by an outer axially expandable bellows-like wall of flexible material with one end anchored and the other end movable. The spring is preferably provided with a connection for directing air under pressure into the chamber which may be varied in pressure or held constant. The expandable wall is shaped to provide an expansion force which is a particular function of the expanded length of the chamber.

The air spring 19 is a balancing spring and is maintained at a constant air pressure and behaves as a variable rate spring. The air spring 18 is larger to move against the balancing spring and is attached to a control pressure and exerts a variable force dependent on the pressure. The control pressure is varied by a valve 22, which is operated by a shoe 21 riding against the edge of the web 11.

It will be understood that the guide mechanism is illustrated in a preferred form in combination with a wire supporting belt on a Fourdrinier machine to control the position of the belt. iIt is contemplated that the 'belt may be in the form of a looped rubber blanket with openings therein for communicating sub-atmospheric pressure from the suction box to the wire on the belt, for dewatering a paper web on the wire. 1

The wire is supported on the upper surface of the upper run of the looped blanket and the paper web on the wire is dewatered. The water drains down through the openings in the wire and through the openings in the web into the suction box. For various operational reasons it is important'that the lateral position of the belt be accurately maintained. Thus the guide arrangement is provided.

The guide arrangement, however, may be used on felts, belts, conveyor belts, and various forms of moving bands or loops, and for the purpose of the present description, the moving member to be controlled will be referred to as a web.

Turning to details of construction, as illustrated in FIGURE 1, the moving blanket or web 11 is supported on supporting rolls 23 and 24 on the inside of the looped web. The web passes over a suction box 26 suitably supported on the frame 27 of the machine. Also supported on the frame 27 are bearings 28 and 29 for the supporting rolls 23 and 24. The upper course 11a of the web 11 passes over the suction box and the lower course 11b is supported or received on the guide roll 12 and on a roll 31. The roll 31 is supported on bearings 32 mounted on the frame. It will, of course, be understood that the rolls extend horizontally across the machine and similar bearings are provided at the other side of the frame 27. Paper stock is deposited on the Wire W by suitable means as will be appreciated by those skilled in the art.

As illustrated in FIGURE 1, and as illustrated in greater detail in FIGURES 3 and 5, the guide roll 12 has journal ends 33a. and 34a projecting axially from the ends and mounted in the bearings 13 and 14. Conventional journal arrangements may be employed, but the journals must be mounted in self-aligning type bearings.

The pivotal support 15 for the bearing 13 is mounted on a bracket 36 connected to a side 27a of the frame. The shiftable bearing support 16a for the bearing 14 is mounted on a bracket 37 supported on the side 27b of the frame. The

bellows air springs

18 and 19 which shift the arm 17 (so as to pivot the arm 17 and the roll 12 about the pivotal support 15 for the bearing 13) are mounted at their fixed ends on

brackets

38 and 39, also secured to the side 27b of the frame.

The arm 17 is split at its inner end to form a yoke with sides 17a and 17b, which are attached to a collar 41. The outer end of the arm 17 has a boss 170 which connects between the

bellows air springs

18 and 19.

The collar 41 is supported on the shiftable support bearing 16a. For this purpose, the collar has a lower flange 41a, which is suitably secured, such as by bolting, to a mount 42. The mount 42 is part of the shiftable bearing 16a, and provides vertical support for the guide roll 12 at the shiftable end, and permits the guide roll end to be shifted laterally in either direction for the corrective effect on the web 11. The collar supports the bearing 14 which can slide axially a small distance therein as the roll pivotally shifts about the support 15 at the other end. The supports for the bearings 13 and 14 may be in the form of spherical bearing surfaces.

The shiftable support bearing 16a. includes a pair of parallel shafts 43 and 44. The shafts are horizontally and slidably supported at their respective ends in bearing

hubs

46 and 47, which are mounted on the bracket 37, as is illustrated particularly in FIGURES 1, 3, 4, and 6. Each of the hubs 46 and 47 i provided with a pair of cylindrical openings to receive each of the shafts 43 and 44. The ends of the openings are closed by

caps

48, 49, 51 and 52. These caps are suitably connected to the ends of the bearing hubs and protect the openings against foreign matter. The support for each of the shafts within the hubs is of identical construction and, therefore, only one need be described and shown, as illustrated in detail in FIGURE 4. The hub 46 has a cylindrical opening 53. Within the cylindrical opening is a bearing sleeve 54. The bearing sleeve supports a collection of ball bearings 56, which are held in the retainer 57, and which ride on the inner surface of the sleeve 54 to support the shaft 44. To seal the other end of the sleeve, a rubber or neoprene expansible tubular jacket seal 58 surrounds the shaft 44 and is connected at one end to the hub 46 and at the other end to the support 42, such as by suitable clamps, not shown. Similar jacket seals 59, 61 and 62 are placed over the other exposed parts of the shafts 44 and 43.

Thus, a strong, reliable support has been provided and it is to be particularly noted that the support requires little head room. The support may be situated below or above the bearing for the shaft, and in either instance, can be easily maintained in space requirements within the limits of the radius of the guide roll 12.

As illustrated particularly in FIGURES 3 and 6, the bellows air springs 18 and 19, which are mounted between the

brackets

38 and 39, apply opposing forces to the arm 17 to control its lateral position and thereby control the position of the axis of the roll 12. The bellows air springs are supported at their inner ends by the boss 17c and have fittings 63 and 64, respectively, at their outer ends which pass through openings in the

brackets

39 and 38, and are threaded to receive attachment nuts 65 and 66. The fittings 63 and 64 are internally threaded and internally bored for the flow of pressurized fluid, such as air, and for the connection of

air lines

67 and 68.

Air is supplied to the air springs 18 and 19 through an air supply line 69 which is furnished by a suitable supply of pressurized air. Connected in the supply line 69 is a pressure regulating valve 71 which delivers a constant downstream pressure and which is variable to obtain a predetermined pressure. Connected downstream of the regulator valve 71 is a gauge 72 for observing the pressure. The air line 67 is connected downstream of the regulator valve so that a constant pressure air is maintained in the bellows air spring 19. The air spring 18 receives a variable pressure supply of air, and the pressure is varied by the valve 22 in order to apply a varying force and thereby shift the position of the arm 17.

The air springs 18 and 19, acting in combination, are preferably designed to have a self-centering characteristic, as illustrated in FIGURE 2. The vertical axis represents the forces applied by air springs 18 and 19 to the shiftable end of the roll. The horizontal axis represents expansion of the springs. The force curve of the spring 19 is line 77a which is under constant pressure and the characteristic of the spring is obtained by design of the air spring. The force curves of the spring 18 are shown at 78, 78a and 78b. The three curves represent the action of the spring at three pressures, P P P These pressures are achieved, of course, by variation in position of the core 79 of the valve 22.

The guide roll 12 will have a zero running position, which may be assumed to be substantially parallel to the other supporting rolls for the web 11. This position is where curves 77a and 78a cross, or where their opposed outputs cancel and where the spring forces cancel. This position is represented by O on the graph of FIGURE 2 and is achieved at pressure P Any outside force that tends to shift the roll 12 in either direction will cause the force on one spring to increase and the force of the other spring to decrease, and the tendency of the air springs 18 and 19 will thus be to maintain the arm 17 in a centered position.

This self-centering effect is in operation at any pressure in the variable pressure spring 18. At pressure P equilibrium is reached at 0 on the graph. This is a pressure which causes the roll to shift and shift the belt to the left. At pressure Pm, equilibrium is reached at O which causes the belt to move to the right. At either of these pressures, the roll will stop where equilibrium is reached in the opposing spring forces. Thus the operation of the guide roll will be stable and the tendency to hunt will be reduced. As will also be noted from the curves of FIGURE 2, each air spring not only has a diminishing force versus displacement characteristic (the force decreasing as the roll swings away from the spring) but the force decreases at an increasing rate with expansion of the air springs. Conversely the force increases at a decreasing rate with compression of the air springs. This enhances the self-centering elfect.

The air spring 18 is supplied with air through the line 68, and the line connects to the supply line through a needle valve 73. A varying quantity of air is bled from the line 68, by a line 76, which leads to the control valve 22. Thus by adjustment of the needle valve 73, the pressure in the spring 18 will be selectively changed, thus enabling the operator to choose the location at which the belt 11 will run. In other words, the operator is selecting the position of the curve 78 in FIGURE 2, and thus is changing the location at which the curves 77a and 78 will cross, which is the location where the forces will balance. As will be appreciated, a valve such as valve 73 could be located in the line 67 so that the posirestored to its predetermined position.

tion of the curve 77a could be changed. If an air spring arrangement such as shown is also placed at the other end of the roll 12, the running position of both ends or either end of the roll could be changed.

The control valve is illustrated in detail in FIGURES 3 and 7, and includes a housing 77 with a conically shaped inner chamber 78. Movably mounted within the chamber is a conical valve plug 79. The valve plug has a centrally located annular groove 81 which substantially registers with the location at which the line 76 enters the housing 77. It will be recognized that air flowing through the line 76 will flow through the groove 81 and escape between the outer surface of the valve plug 79 and the surface of the valve chamber 78, in an amount dependent upon the depth of the insertion of the valve plug into the chamber.

To vary the position of the valve plug, a boss 82 is secured to the large end of the conical plug and pivotally connected to a rocker arm 83. The rocker arm is pivotally mounted on a link 84, secured to a bracket 86 on the side of the housing 77. The rocker arm is pivoted by movement of the shoe 21, which is mounted on a block 87 secured to the rocker arm. The shoe 2 1 rides along the side of the web 11 in a manner illustrated in FIG- URE 3. As the web is laterally displaced in either direction, the rocker arm 83 will pivot, changing the position of the valve plug 79 thereby increasing or decreasing the escape of air through the line 76. This results in a change in pressure in the air spring 18 to change the force against the arm 17. A spring 88 connected to a bracket 92 in the side of the housing urges the rocker arm in a direction to hold the shoe 21 against the side of the web. An adjustable stop bolt 89 is threaded into the rocker arm and engages an ear 91 on the side of the housing 77, and an adjustable stop bolt 93 is threaded into a bracket 94 at the end of the housing and engages an end 79a of the valve plug. These stop bolts limit the movement of the parts and prevent binding of the valve plug in the chamber 78.

As illustrated in FIGURE 3, if the web 11 moves downwardly due to conditions of the machine, the shoe 21 will move downwardly, moving the valve plug out of the housing 77, and increasing the escape of bleed air. This will decrease the pressure in the bellows 18, pivoting the guide roll in a clockwise direction to cause the traveling web to move upwardly. The reverse eifect is accomplished ifthe web displaces upwardly; with the pressure in the bellows air spring 18 being increased, and the air spring 19 urging the arm 17 to pivot the guide roll 12 in a counterclockwise direction, in FIGURE 3.

In operation, the belt or web 11 of FIGURE 1 is driven in the direction indicated by the arrows, such as by driving the roll 23. The guide roll 12 supports the web and when the web is deflected downwardly, as illustrated in FIGURE 3, the shoe 21 moves downwardly withdrawing the valve plug 79 to increase the air bled through line 76 and decrease the air pressure in the air spring 18.

' This will shift the bearing 14 of the guide roll 12 to the left, pivoting the roll 12 about its support 15, thereby shifting the axis of the roll and causing the web to be Shifting movement of the web beyond the predetermined desired position in the opposite direction will cause an opposite effeet with the guide roll being pivoted in a counterclockwise direction.

In first setting up the automatically operating guide mechanism, the valve 71 is adjusted to apply a desired constant pressure to the bellows air spring 19, for example, on the order of thirty pounds per square inch. The bleed valve 73 is then opened to apply pressure to the air spring 18 to bring the arm 17 to centered position, and the control valve 22 with its guide shoe 21 is then set up. Minor adjustments in the control of the bleed oif of air can be made by pivotally shifting the valve housing 77 on a pivotal support, not shown. Adjust- 6 ments can also be made by varying the opening of the bleed valve 73.

The position of the guide roll 12 is automatically and quickly changed to correct the position of the web and the shift of the roll end is substantially parallel to the direction of web travel, which is preferably perpendicular to the bisector of the angle of wrap of the web on the roll.

Thus, it will be seen that I have provided an improved guide for the alignment of a moving web which meets the objectives and advantages hereinbefore set forth. The mechanism has a wide range of operation, is not aifected by foreign materials and water, such as are encountered in a paper-making machine, and is rugged and durable in operation.

I have, in the drawings and specification, presented a detailed disclosure of the preferred embodiments of my invention, and it is to be understood that I do not intend to limit the invention to the specific form disclosed, but intend to cover all modifications, changes and alternative constructions and methods falling within the scope of the principles taught by my invention.

I claim as my invention:

1. A guide mechanism for a traveling web comprising a roll adapted to receive a traveling web, first and second bearings rotatably supporting the roll for rotation about its own axis, a pivotal support for pivotally supporting the first bearing, a shiftable support for the second bearing accommodating pivotal movement of the roll about the first bearing, a frame carrying said supports, an expansible bellows air spring having an axially expandable chamber defined by a flexible wall having one end mounted on the frame and the other end connected for applying a force in one pivotal direction to said second bearing to change the pivotal position of said roll, means for applying a force to said second bearing in the opposite direction against said air spring, said air spring and said force applying means each having a diminishing force versus displacement output at constant internal pressure, a pressurized fluid supply means for supplying a controlled fluid pressure to said air spring, valve means connected to said fluid supply means to control the pressure in said air spring, and means positioned to be responsive to a change in lateral position of said web and connected to said valve means to control the pressure in the air spring, said air spring and force applying means coaoting to reach a selfcentering position at any given fluid pressure.

2. A guide mechanism for a traveling web comprising a roll adapted to receive a traveling web, first and second bearings rotatably supporting the roll for rotation about its own axis, a pivotal support for pivotally supporting the first bearing, a shiftable support for the second bearing accommodating pivotal movement of the roll about the first bearing, a frame carrying said supports, a first expansible bellows air spring having one end mounted on the frame and the other end connected to said second bearing to apply a force thereto to pivot said roll, a second expansible bellows air spring having one end mounted on the frame and the other end connected to said second bearing and positioned to apply a force in opposition to saidfirst air spring, each of said air springs having an axially expandable chamber defined by a flexible wall and each having a diminishing force versus displacement output, in which the rate of increase of force in each air spring decreases with compression of the spring so that said air springs will coact to reach a self-centering position at a given air pressure in each spring, means for pressurizing said first air spring, means for pressurizing said second air spring, control means for varying the pressure in said second air spring, and means positioned to be responsive to a change in the lateral position of said web and connected to said control means to control the pressure in the second air spring as a function of web position to tend to maintain the web in a constant lateral position.

3. A guide mechainsm for a traveling web comprising a roll adapted to receive a traveling web, first and second bearings rotatably supporting the roll for rotation about its own axis, a pivotal support for pivot-ally supporting the first bearing, a shiftable support for the second bearing accommodating pivotal movement of the roll about the first bearing, a frame carrying said supports, a first air spring mounted on the frame and connected for applying a corrective force to said second bearing to change the pivotal position of said roll with deviation from a predetermined position, a second air spring connected in opposition to said first air spring, said air springs having a characteristic of increasing force as a function of increase in deflection of the roll from said predetermined position at constant internal pressure, said air springs coacting to reach a self-centering position at any given fluid pressure, said web running in a predetermined lateral position on the roll in said predetermined roll position, control means connected to vary the pressure in said first air spring, and means positioned to be responsive to a change in the lateral position of said web and connected to said control means to control the pressure in the first air spring as a function of deviation of Web position from said predetermined position and as a function of direction of deviation to move the roll to a corrective position to tend to maintain the web in a constant lateral position.

4. In a traveling Web guide of the character described, a guide roll for supporting a traveling web, a pivotal bearing supporting one end of said roll, a shiftable hearing supporting the other end of said roll for pivotal movement of the roll about said pivotal bearing, said bearings accommodating rotation of the roll about its axis, an expansible bellows air spring having an axially expandable chamber defined by a flexible wall having one end mounted on the frame and the other end connected for applying a force in one pivotal direction to said shiftable bearing to change the pivotal position of said roll, means for applying a force to said shiftable bearing in the opposite direction against said air spring, said air spring and said force applying means having diminishing force versus displacement outputs at constant pressure in the air spring, said air spring and force applying means coacting to reach a self-centering position at any given fluid pressure, a pressurized fluid supply means for supplying a controlled fluid pressure to said air spring, valve means connected to said fluid supply means to control the pressure in said air spring, and means positioned to be responsive to a change in lateral position of said web and connected to said valve means to control the pressure in the air spring.

5. A guide mechanism for a traveling web comprising a roll adapted to receive a traveling web, first and second bearings supponting said roll for rotation about its axis, a first expansible bellows air spring having one end mounted on the frame and the other end connected to said second bearing to apply a force thereto to pivot said roll, a second expansible bellows air spring having one end mounted on the frame and the other end connected to said second bearing and positioned to apply a force in opposition to said first air spring, said air springs each having an axially expandable chamber defined by a flexible wall and having a diminishing force versus displacement output at constant pressure and coacting to reach a self-centering location at a given pressure for each spring, means for pressurizing said first air spring, means for pressurizing said second air spring, control means for varying the pressure in said second air spring, means positioned to be responsive to a change in the lateral position of said web and connected to said control means to control the pressure in the second air spring as a function of web position to tend to maintain the web in a constant lateral position, a pivotal support for said first bearing, a support for said second bearing member including a pair of parallel shafts connected at a midportion to the second bearing and extending in the direction of movement of the second bearing, and including sliding bearings mounted on the frame and journalling both of the ends of the shafts for free sliding movement therein, and flexible sleeves for excluding foreign matter surrounding the shafts and connected between the sliding bearings and the second bearing.

67 A guide and support mechanism for a traveling Web in a paper-making machine having a looped supporting band for supporting a traveling Fourdrinier wire, a horizontal suction box positioned to apply a suction to said band, horizontally spaced supporting rolls for the band, a guide roll between said supporting rolls carrying the band on the upper surface of the roll, bearings supporting the guide roll for rotation about its axis, means for pivotally supporting one of said bearings for pivotal movement about a vertical axis, means for shiftably supporting the other of said bearings for horizontal movement, means for selectively applying a positioning force to move said other bearing, and means positioned to be responsive to change in lateral position of said band and connected to said force applying means to control the position of the guide roll and the position of the band as it is moved over the supporting rolls, said force applying means including opposed air springs each having an axially expandable chamber defined by a flexible wall and each having a diminishing force versus displacement output at a constant air pressure in each spring so that they apply self-centering forces to position the guide roll.

7. A guide mechanism for a traveling web comprising a roll adapted to receive a traveling web, bearing means supporting said roll for rotation about its longitudinal axis, means for movably supporting said bearings, an expansible bellows air spring having an axially expandible chamber defined by a flexible wall connected to apply a force tending to change the position of the roll axis with expansion or contraction of the spring, means for applying a force in opposition to the force of said air spring, said air spring and said force applying means each having diminishing force versus displacement outputs for a constant air pressure in said air spring, and means responsive to change in position and positioned to be responsive to change in the lateral position of the web and connected to control said force applying means as a function of web position so that the roll will be positioned to maintain the web in a predetermined position.

8. In a traveling web guide of the character described, a guide roll for supporting a traveling web, a pivotal bearing supporting one end of said roll, a shiftable bearing supporting the other end of said roll for pivotal movement of the roll about said pivotal bearing, said bearings accommodating rotation of the roll about its axis, an arm connected to said shiftable bearing to change the pivotal position of said roll and thereby change the position of said web, a first pressure responsive expansible control member connected to the arm having a characteristic of decreasing force with increasing expansion, a second pressure responsive control member having a characteristic of decreasing force With increasing expansion connected to said arm in opposition to said first member, a pressure line for supplying fluid under substantially constant pressure, a first line leading from said pressure line to said first pressure responsive control member, a second line leading from said pressure line to said second pressure responsive control member, a controllably variable flow restricting means restricting flow through said second line to selectively control the balance position of said control members and the position of said roll, a bleed valve connected to bleed fluid from said second line downstream from said flow restricting means, and means positioned to be responsive to the lateral position of said web relative to the roll and connected to operate said bleed valve and control the pressure at said second pressure responsive control member as a function of Web position.

9. In a traveling web guide of the character described, a guide roll for supporting a traveling Web, a pivotal bearing supporting one end of said roll, a shifitable hearing supporting the other end of said roll for pivotal movement of the roll about said pivotal bearing, said bearings accommodating rotation of the roll about its axis, an arm connected to said shiftable bearing to change the pivotal position of said roll and thereby change the position of said Web, a first pressure responsive expansible control member connected to the arm having a characteristic of decreasing force with increasing expansion, a second pressure responsive control mem her having a characteristic of decreasing force With increasing expansion connected to said arm in opposition to said first member, a pressure line for supplying fluid under substantially constant pressure, a first line leading from said pressure line to said first pressure responsive control member, a second line leading from said pressure line to said second pressure responsive control member, a controllably variable flow restricting means connected in one of said first and second lines to selectively control the balance position of said control members and the position of said roll, a bleed valve connected to bleed fluid from said second line, and means positioned to be responsive to the lateral position of said Web relative to the roll and connected to operate said bleed valve and control the pressure at said second pressure responsive control member as a function of web position.

10. A guide mechanism for a traveling web comprising a roll in guiding engagement with a traveling web, said roll having a predetermined running position wherein the Web is at a predetermined lateral position, roll centering means connected to the roll including a first force applying member and asecond force applying member connected in opposition to said first force ap plying member, each of said force applying members having a diminishing force versus displacement output characteristic With the force decreasing at an increasing rate as the roll moves away from each of the centering means toward the other force applying member so that a self-centering force is applied, and means responsive to the position of said Web connected to said first force applying member for changing the force applied thereby to change the position of the roll and return the web to its predetermined running position.

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