GB2170784A

GB2170784A - Web tension control

Info

Publication number: GB2170784A
Application number: GB08503449A
Authority: GB
Inventors: Anthony John Sissons; Reginald Robert Green
Original assignee: Interfic Engineering Ltd
Current assignee: Interfic Engineering Ltd
Priority date: 1985-02-11
Filing date: 1985-02-11
Publication date: 1986-08-13
Also published as: GB8503449D0

Abstract

An apparatus varies the supply of power, from a constant source (9), to a web-braking means (4) to control tension in the web (2). A tension-sensing means (5) traversed by the web produces an output signal which is proportional to the tension and which is variable (at 6) in accordance with a first parameter of the web material. The resultant modified signal passes to a relay (8) governing the proportion of the constant power fed to the web-braking means, the relay itself permitting the introduction of a variable ratio in accordance with a second parameter of the web material. <IMAGE>

Description

SPECIFICATION Web tension control This invention relates to automatic control of tension in a web which is being fed to a user apparatus. Whilst not restricted to such application, it is of particular utility in the control of tension in a web of paper being fed from a supply roll to a corrugating machine. Tension in the web can be varied by applying a braking force to the supply roll, and varying the braking force in accordance with one or more parameters of the nature of the web.

In a corrugating apparatus, parameters of interest are (i) the width of the web, (ii) the weight per unit area of the paper, and (iii) the quality of the paper.

The object of the present invention is to provide apparatus for sensing tension in a web downstream of the application of braking force, and permitting modifying of the braking force by a factor which is a resultant of the tension sensed and two factors each of which is a parameter of the nature of the web.

According to the present invention apparatus, for varying the supply of power to a web braking means to control tension in the web, comprises tension-sensing means to be traversed by the web and arranged to produce an output signal which is proportional to the tension in the web, a relay for connecting between a source of constant power and the web braking means to determine the proportion of the constant power actuating the web braking means, means connecting the tension-sensing means to the relay including an adjustable control for modifying the output signal in accordance with a first parameter of the web material, and means in or associated with the relay for introducing a variable ratio between the modified output signal and the degree of reduction of power by the relay in accordance with a second parameter of the web material.

In a preferred form, the tension-sensing means produces an output electrical signal, and the relay is a device for varying pneumatic pressure and is connected between a source of constant pressure and a pneumatically-operable braking means for the web. The adjustable control between the tension-sensing means and the relay advantageously comprises a signal-transducer, and means may be provided for visual display of the modified output signal. The tension-sensing means may include a roll traversed by the web and shiftable radially against loading in accordance with tension in the web, and means such as an electrical load cell originating the output signal proportionally to the extent of radial shift.

Further, in accordance with the invention, there is provided the combination of power supply varying apparatus as set forth above, and a web braking means positioned upstream, in the path of the web, of the tension-sensing means. The web braking means may act on a feed roll for the web.

Still further, in accordance with the invention, there is provided the combination of power supply varying apparatus as set forth above, and a web braking means positioned upstream, in the path of the web, of the tension-sensing means, and a corrugating apparatus positioned downstream, in the path of the web, of the tension-sensing means.

In order that the nature of the invention may be readily ascertained, an embodiment of paper corrugating apparatus incorporating the invention is hereinafter particularly described with reference to the figures of the accompanying drawings, wherein: Figure 1 is a schematic block diagram of the corrugating apparatus and its braking control system; and Figure 2 is an axial section of part of a feed roll assembly to show a pneumatically-operable brake.

Referring to Figure 1, there is shown a corrugating apparatus 1 the details of which do not form any part of the invention and which is therefore illustrated purely diagrammatically. It suffices to state that the corrugating apparatus needs feeding with a continuous web 2 of paper which in practice is commonly supplied from feed rolls 3. It is convenient to have at least two feed rolls 3 placed either side by side, or stacked, so that when one such roll is emptied, paper from a next roll can be spliced to the tail end of the paper from the first roll, and the feed then continued from the second roll.

To control the rotation of the feed roll 3, and thus the tension at which the web enters the corrugating apparatus 1, each feed roll is provided with a brake 4 acting on each end of its spindle. The brake 4 is actuated pneumatically from a constantpressure air supply 9, with the interpolation of a relay device 6 which varies the pressure supplied to the brake. Structural details of the brake are described later herein with reference to Figure 2 of the drawings.

For sensing the tension existing in the web 2 between the feed roll 3 and the corrugating apparatus 1 there is provided a sensing device indicated schematically at 5.

Structural details of the sensing device 5 need not be supplied for those skilled in the art, and it is sufficient to state that the device includes an input roll 5a, an output roll 5b, and a sensing roll 5c.

Rolls 5a, and Sb are of fixed position but freely rotatable. Sensing roll Sc is also freely rotatable and its shaft is supported in the structure of the device for radial shifting upon a load cell 5d. In practice, it is convenient to have each end of the shaft of the sensing roll Sc supported in bearings carried by a respective load cell. The web 2, issuing from the feed roll 3, passes under the input roll 5a, over the sensing roll 5c, under the output roll 5b, and thence to the corrugating apparatus 1. Increase and decrease of tension in the web 2 are sensed by the load cell 5d and originate a signal, for example an electircal milli-voltage, or milli-amp current, which is fed to a respective signal modifier 6.

The load cell may comprise, for example, semiconductors arranged in a bridge circuit and utilising an excitation voltage to produce a high-level milli-volt output which is linearly proportional to load imposed. Suitably, the load cell may be a Cleveland-Kidder Type UPB Tension Transducer (manufactured by Cleveland Machine Controls Inc, Cleveland, Ohio, USA).

Each signal modifier 6 is connected to a respective visual display unit 7 so that an operator may check visually the current strain, indicated for example in kilograms, imposed on the respective load cell 5d.

The signal modifiers 6 modify, under the control of an operator, the signal received from the respective load cell and pass it to a respective adjustable-ratio relay valve 8. Suitably, the signal modifier may be an R15 SC-1390 strain gauge transmitter (manufactured by Rochester Instrument Systems of Rochester, New York, U.S.A.).

A constant pressure air supply, e.g. at 80 Ibis/ sq.in., originates at 9 and is fed through a common line 10 and, reduced to 20 Ibs/sq.in., through pilot lines 11 to each of the relay valves 8. The pilot air supply, through lines 11, serves for activation of the moving parts of the relay. Main feed air pressure is also fed through main feed lines 12,12 to a valve section 8a of each relay valve, for feed through main output lines 13,13 to a respective pneumatic switching panel 14. Output air lines 15,15, lead from the panels. Each output line 15 is connected to a brake 4. Only one such connection has been shown in the drawing, for clarity of the drawing.The system illustrated is assumed to have two feed rolls, with a pneumatic brake 4 at each end of the shaft of each roll 3, and each panel 14 therefore has two output lines 15 for the pneumatic brakes of its respective feed roll 3.

A relay suitable for use as the relay 8 is available commercially in the United Kingdom from Fairchild Industrial Products Company of 1501, Fairchild Drive, Winston-Salem, NC27105, U.S.A. under their catalogue reference T5221 I/P Transducer. The Transducer converts a 1-5 m.a., 4-20 m.a., or 10-50 m.a. input signal, or 1-5 and 1-9 V. DC signal into a 0-150 Psig resultant or 10" to 50" WC. The principle of operation is that increase of signal strength to a coil increases its flux density, opposing a permanent magnetic field and creating a thrust on the coil which causes the coil to move. The coil is coupled to a flapper which is moved away from a nozzle to increase flow of air, the resultant increase of air flow causing output pressure to decrease. The change in output pressure is directly proportional to change of input to the coil.The operating signal for relay 8 is obtained from signal modifier 6, and the output pressure passes to the pneumatic brake 4. Increase of tension in the web provides an increase of signal which results in a lowering of output pressure and a diminution of the braking force to reduce tension in the web.

The system is provided with two means for insertion, by an operator, of a variable factor, e.g. (i) paper width, and (ii) paper weight.

To permit the operator to insert the paper width factor, the signal modifier 6 is inserted in the electrical line between the load cell 5d and the relay 8.

According to the setting of the control 16 of the signal modifier 6, the information supplied from the load cell Sdto the relay valve 8 is varied.

To permit the operator to insert the paper weight factor, the relay valve 8 itself has an adjustable control valve 8b in its pilot air supply which varies the extent to which the pilot air supply, as a result of the modified electrical signal received from the signal modifier 6, actuates the mechanical parts of the valve to reduce the pressure of air, supplied from air line 10, to feed lines 13,13. By way of example, if the signal current received by the relay valve 8 (with paper width factor already inserted at 6) is 20 m.a., the control 8b of the relay valve can vary the degree of control of the air pressure, for that given current, through a range of 30:1 to 1:30.

The system thus provides an arrangement for automatic control of tension in the web, by braking the feed roll, as a resuit of feedback supplied by the load cell, and with correction for the two factors which may vary significantly with the width and weight of paper web currently in use. For maintenance of a desired tension it is necessary to decrease the braking effect if the tension is too high, and vice versa, and accordingly the relay valve 8 serves as an inverter, i.e. increase of signal derived from the load cell, as adjusted for paper width, results in corresponding decrease, adjusted for paper weight, in the air pressure supplied to the brakes.

Referring now to Figure 2, there are shown details of a brake 4 for the feed roll 3.

The feed roll 3 includes a shaft 17 the end of which has a bearer 18 for an oil seal 19 within an opening 20 of a mounting plate 21. Extending axially from the end of the shaft 17 there is secured an assembly of a stub shaft 22 fixed by mounting screw 23, and a toothed pinion 24 keyed on the stub shaft. On the mounting plate 21, about the opening 20 there is secured an annular braking plate 25. Coaxial with the braking plate 25 there is fixed an internally-toothed crown ring 26. Coaxially within the crown ring 26 there is meshed an externally-toothed annulus 27 serving as a second braking plate. Axially between the two braking plates 25 and 27 there is disposed a sandwich assembly consisting of an internally-toothed ring 28 on each face of which are secured brake-pad rings 29 which each bear against a respective braking plate. The annulus 27 can be shifted axially to lessen or increase the frictionai braking applied by the braking plates to the ring 28 which is meshed with, and thus rotates with, the pinion 24 and the feed roll shaft 17. For shifting the annulus 27 axially it is abutted on its outer face by a pressure ring 30 which bears against an annular resiliently-deformable air chamber 31 backed by a fixed wall 32 of the structure. The air chamber 31 operates against return spring means 33. Thus, according to the intensity of air pressure applied to the air chamber 31, there is a corresponding degree of braking applied to the feed roll shaft 17.

Claims

1. Apparatus, for varying the supply of power to a web braking means to control tension in the web, comprising: (i) tension-sension means to be traversed by the web and arranged to produce an output signal which is proportional to tension in the web, (ii) a relay for connecting between a source of constant power and the web braking means, to determine the proportion of the constant power actuating the web braking means, (iii) means, connecting the tension-sensing means to the relay, including an adjustable control for modifying the output signal in accordance with a first parameter of the web material, and (iv) means in or associated with the relay for introducing a variable ratio, between the modified output signal and the degree of reduction of power by the relay, in accordance with a second parameter of the web material.

2. Apparatus, as claimed in claim 1, wherein the tension-sensing means produces an output electrical signal, and wherein the relay is a pneumatic pressure-varying device for connecting between a source of constant pressure and a pneumatically-operable braking means.

3. Apparatus as claimed in Claim 1 or Claim 2, wherein the adjustable control between the tension-sensing means and the relay comprises a signal transducer.

4. Apparatus, as claimed in claim 3, comprising means for visual display of the modified output signal.

5. Apparatus, as claimed in any one of the preceding claims, wherein the tension-sensing means includes a roll traversed by the web and shiftable radially against loading in accordance with tension in the web, and means originating the output signal proportionally to the extent of radial shaft.

6. Apparatus, as claimed in claim 5, wherein the originating means is an electrical load cell.

7. Apparatus as claimed in Claim 1 and substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

8. In combination: (a) apparatus as claimed in any one of the preceding claims, and (b) a web braking means positioned upstream, in the path of the web, of the tension-sensing means.

9. The combination of claim 8 wherein the web braking means acts on a feed roll for the web.

10. In combination: (a) apparatus as claimed in any one of claims 1 to 7.

(b) a web braking means positioned upstream, in the path of the web, of the tension-sensing means, and (c) a corrugating apparatus positioned downstream, in the path of the web, of the tension-sensing means.

11. The combination of power supply varying apparatus and braking means substantially as described herein with reference to Figure 1, or Figures 1 and 2, of the accompanyir,g drawings.

12. The combination of web feed roll, power supply varying apparatus, and feed roll braking means substantially as described herein with reference to the accompanying drawings.