Control system for gap measuring

A control system for measuring a gap in an apparatus for pressing a traveling paper web as the paper web travels through the gap accompanied by at least one belt or felt, the apparatus including a press apparatus and a support surface defining a gap therebetween. A frame is provided for moveably supporting the press apparatus. An actuator is operatively disposed between the frame and press apparatus for selectively moving the press apparatus toward and away from the support to control the gap size. A transducer is mounted in either the press apparatus or support for producing a signal indicative of the pressure on the paper web as the paper web, belt and felt pass through the gap beneath the transducer. A controller is operatively linked with the transducer for receiving the signal, determining the measure of the gap as a function of the pressure, and causing the actuator to selectively move the press apparatus to control the gap size.

BACKGROUND OF TIE INVENTION

1. Field of the Invention

The present invention relates to the measurement of a gap between nipped components through which a paper web is being passed, and, more particularly, this invention relates to a system for measuring the nip gap in a paper-making press apparatus through which a traveling flexible material is passed for dewatering the paper web.

2. Description of the Related Art

In the press section of a paper-making machine, water is typically removed mechanically by passing the paper web through a nip between structural components, such as two rotating rolls. The nascent paper web is carried on a felt for absorbing the water expressed from the paper web as it passes through the nip.

One of the characteristics of a quality paper product is uniformity of caliper in a cross-machine direction of the paper-making machine. Such uniformity of caliper is difficult to obtain, particularly in bulky products, such as tissue and towel grades, due to deflection of machine components caused by gravity.

Rolls of different design, such as control-deflection rolls and plain rolls, deflect different amounts along their lengths extending in a cross-machine direction. A non-uniform gap, or uneven gap loading in the cross-machine direction, will produce undesirable variations in both caliper and moisture in the web passing through on its way to the dryer section. Such variations undesirably affect the processing of the web, such as by requiring costly special profiling downstream of the press section, increasing expensive thermal removal moisture in the dryer section, or slowing the entire paper-making machine.

What is needed in the art is a way of measuring the gap between the surface which presses the belt against the support surface and signals that measurement so that the gap can be changed or adjusted according to predetermined design parameters.

SUMMARY OF THE INVENTION

The present invention provides one or more transducers mounted in the press for measuring the gap between press elements mounted on either side of the traveling belt, paper web and felt.

The present invention comprises, in one form thereof, a control system for measuring a gap in an apparatus for pressing a traveling paper web as the paper web travels through the gap accompanied by at least one belt or felt, the apparatus including a press apparatus and a support surface defining a gap therebetween. A frame is provided for moveably supporting the press apparatus. An actuator is operatively disposed between the frame and press apparatus for selectively moving the press apparatus toward and away from the support to control the gap size. A transducer is mounted in either the press apparatus or support for producing a signal indicative of the pressure on the paper web as the paper web, belt and felt pass through the gap beneath the transducer. A controller is operatively linked with the transducer for receiving the signal, determining the measure of the gap as a function of the pressure, and causing the actuator to move the press apparatus to control the gap size, as desired.

This system thereby controls the cross-machine uniformity of the sealing or pressing nip. Such uniformity results in the least sealing nip for the pressing operation commensurate with optimal water removal and maintenance of the desired, uniform paper web caliper at a given speed. Cross-machine non-uniformity in the paper web in the form of wet streaks is controlled, and bulk in tissue paper grades is maximized because the nip load is dispersed as evenly as possible over the entire operating face which extends along the axial length of the support roll.

Accordingly, an advantage of the invention is to provide a system for measuring the gap and apparatus for processing a traveling paper web in a paper-making machine.

Another advantage of the invention is to provide a system for adjusting the nip or sealing pressure in the press section of a paper-making machine, which nip or sealing pressure is decreased commensurate with the maximum water removal in the press.

Yet another advantage of the invention is to provide an air press which maximizes the pressing operation without compromising the speed of production.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, as shown inFIGS. 1 and 1A, a traveling composite web W is guided over a guide roll8to begin its processing in an air press apparatus10, and subsequently over guide roll8A.

Air press apparatus10includes a frame12, a U-shaped pressure body14having a pair of spaced, parallel arms15,15awhich extend toward a rotatable support roll16. On the ends of leading and trailing arms15,15aare mounted a seal18,18a, respectively, canted to bear tangentially against the composite web W when the web is disposed to be carried on the surface of support roll16during operation as support roll16rotates about its axis13. Seals18,18aare secured with their flat back surfaces21to the distal ends of arms15,15aby wedges24and screws26.

Seals18,18adefine, with the pressure body14(including the lateral sides thereof) and composite web W, a pressure chamber20. The composite web W is formed of a flexible belt B, the flexible felt F with a nascent paper web P disposed in between. The belt B is positioned to be between the paper web P and curved surfaces19,19aof the seals to prevent abrasion between the seal surfaces and the paper web as the composite web W passes through the nip N1, N2between each respective seal18,18A. An optional water shower6provides lubrication between belt B and the curved surface of seals18and18A. In an alternative embodiment the positions of felt F and belt B are transposed.

Surface19of seals18,18A is contoured to substantially curve to conform with the cylindrical surface of support roll16. To accommodate the lubricating qualities of the water shower, the curvature of the outer, belt-contacting surface of seals18,18A might be somewhat larger than the radius of the surface of support roll16. At least surface19of seals18,18A is made of a hard, wear-resistant material, such as a ceramic. However, the entire seal could be made of a ceramic.

As shown more clearly inFIG. 1A, in the face of at least one of seals18,18A is a transducer22which is linked to a controller32by line30. Power supply28is linked with controller32by a line34. Transducer22is preferably an inductive or magnetic type, but may be a pressure type.

Intermediate frame12and body14are a plurality of flexible, expandable and contractible tubes36disposed on three sides, including15,15a, of pressure body14. A source of pressurized air, such as pump38, is linked with the plurality of tubes36via corresponding air lines39, and controlled by controller32via line40.

With further reference toFIG. 1A, there is a gap G between the curved surfaces17,19of support roll16and seals18,18A, respectively. At the location of pressure transducer22, gap G is measured normal to planes PB, PF tangent to the outer curved surface of belt B against seal18or18A and tangent to the surface of felt F against support roll16.

The presence of belt B, paper sheet or web P and felt F in the space forming the gap between seal18or18A and support roll16creates a force or pressure nip between seal18or18A and support roll16. Since belt B and felt F are manufactured to exacting standards, any variation in the caliper of the web is reflected in a corresponding variation in the gap and nip pressure at the location of the variation.

Another embodiment is shown inFIGS. 2 and 3. In this embodiment, the frame includes the center shaft42of a so-called controlled deflection roll44which serves as the pressure roll in a nipped-roll couple. A support roll46forms a gap G with roll44when rolls44,46are engaged along a nip line of contact N as shown in FIG.2. Support roll46has a plurality of sensors in the form of transducers22a. . .22emounted in its surface. Both rolls44,46have journals48,50, respectively, about which the hollow, cylindrical roll shell52of the controlled deflection roll, and support roll16rotate.

Controlled deflection roll44has a plurality of end-aligned shoes54,54a,54b. . .54iextending longitudinally of roll44so as to be arrayed in the cross-machine direction when controlled deflection roll44is in an operating position. Shoes54a-54iare individually linked to controller32avia lines39a,39b. . .39i. These shoes are individually actuated which in turn controls the corresponding contour of the face surface and nip line of contact with roll46.

In the surface of support roll46are a plurality of transducers22a,22b. . .22ewhich are respectively linked via lines30a-30eto a controller, in a manner similar to that shown inFIGS. 1,1A. The individual transducers can accordingly measure the gap at their respective locations across the face of the support roll.

In operation, with reference toFIGS. 1,1A, the traveling composite web is guided by guide roll8into the interface between the curved surface of seal18and the surface of support roll16. The composite web W comprises a traveling paper web P held between a substantially impervious belt B on its upper side against the seal, and a substantially pervious felt F against the support roll. The thickness of the composite web creates a gap between seal18and support roll16.

The air pressure in actuators in the form of flexible tubes36on pressure body14produces a nip pressure against the paper web P in gap G. This seals the air pressure in chamber20against modification of the air pressure from an air source38to tubes36to increase, decrease or maintain the desired nip load and corresponding gap G. Gap G is measured by the pressure on transducer22which in turn signals controller32to control the air pressure from air source38, acting in tubes36.

Such action maintains maximum and consistent paper bulk through the seal nip consistent with the dehydration desired over the pressurized air in air press chamber20.

In operation of the embodiment shown inFIGS. 2 and 3, a plurality of transducers are mounted in the surface of the support roll to produce signals over lines30a. . .30eindicative of gap G at longitudinal locations along the nip line between support roll46and controlled deflection roll44. Measurement of gap G is done in the same general manner as described in conjunction with the embodiment shown inFIGS. 1,1A utilizing signals to and from controller32, via lines30.

Control of the measured gap or nip at corresponding cross-machine locations along the length of the roll faces is accomplished by the controller signaling actuators in the form of individual shoes54a. . .54ivia lines39a-39iwithin controlled deflection roll44to provide increased or decreased shoe actuation pressure against inside surface56of hollow cylindrical roll shell52of controlled deflection roll44. This action adjusts gap G at one or more locations along the longitudinal working length of the nipped rolls44,46, as desired, according to the corresponding gap measurements. Such control of the measurement of gap G also affords corresponding control of the nip load against the composite web W and paper web P to provide the stated advantages as well as other advantages readily discernable by those skilled in the art.