The present invention relates to a method and a device for controlling functions in a machine for processing material webs, especially a napkin-manufacturing machine, e.g. its cutting position relatively an em¬ bossed edging in a running material web for the manu- facture of napkins, by sensing level changes exhibited by the web material in question and by generating a corresponding signal for carrying out said control.

In the manufacture of e.g. napkins from a running tissue paper web there are encountered problems in connection with the cutting-off of the napkins central¬ ly in an embossed, transverse edging in the web. The accuracy is today about ± 4 mms at the cutting of the napkins, which leads to an unacceptably high degree of rejection and/or waste. The reason for this is that up to now it has been difficult to select and to maintain the control of the cutting position in relation to an embossed edging in a running tissue paper web.

The object of the present invention is to solve that problem and to provide an accuracy in the control of the cutting position relatively the embossed edging in the running tissue paper web for the manufcture of napkins, so that the accuracy can be substantially higher than what has sofar been possible to achieve.

This has been made possible by means of a method and a device of the type mentioned above. The characteristic features of the invention are set out in the accompany¬ ing claims.

Thanks to the invention there has now been provided a method and a device, which in an excellent manner

satisfy their purposes, in addition to which the inven¬ tion is both simple and cheap to work. The special device for controlling the functions of especially a napkin-manufacturing machine - e.g. the cutting posi- tion relatively an embossed edging in a running tissue paper web used in the manufacture of the napkins - yields a very accurate control of the cutting position, so that the cutting will with a great precision sever the edging centrally. By arranging a signal transmitter on a resilient member in sliding contact with the material web it becomes possible accurately to fix the cutting positions on the web in relation to e.g. an embossed edging creating a level change, which by means of the signal transmitter generates a signal controll- ing the cutting position in relation to the embossed edging. Further, disturbances caused by conventional surface irregularities in the material can be reduced resulting in better signal characteristics as far as the sensed level changes in the material web are con- cerned. This is achieved by mounting the signal trans¬ mitter on a separate resilient element forming part of the resilient member, especially in the shape of a shorter leaf spring, which has been provided with a vibration damper and is in contact with a longer and more flexible spring element contacting the web. The presence of an intended level change appears clearly and separated from any background noise, because the special resilient element in the form of a leaf spring has its bending end in contact with the resilient element, past which the web slides triggering a move¬ ment due to the level change. That movement is perpen¬ dicular to the feeding direction of the web, i.e. the resilient sliding element is arranged to create a spring movement in the contact portion substantially perpendicular to the web.

A preferred embodiment of the invention will be de¬ scribed below in greater detail and with reference to the attached drawings.

Fig. 1 is a diagrammatic lateral view of a device designed in accordance with the invention for gene¬ rating a signal triggered by a level change in a conti¬ nuously fed material web for the purpose of controlling machine functions.

Fig. 2 is a diagrammatic plan view of the signal trans¬ mitter unit illustrated in Fig. 1, when removed from its carrier.

Fig. 3 is a diagrammatic plan view of a machine for the manufacture of napkins including the device according to the invention.

As appears from Figs. 1 and 2, it is there shown a preferred embodiment of a device for controlling func¬ tions in, especially, a napkin-manufacturing machine. The control does generally concern e.g. the cutting position relatively an embossed edging 31 in a running web used in the manufacture of napkins and the control is governed by level changes in the web material 1 in question. This generates a signal for carrying out said control so that the cutting position can, at a high accuracy, take place a number of napkin blank sections downstream the sensing position. The device according to the invention is constituted by a signal transmitter 3 mounted on a resilient member 2 in sliding contact with the material web 1 for the purpose of sensing a level change and generating a control signal, which e.g. after the determination of an average value feeds a control signal to the function units upstream as well as downstream the sensing position.

In accordance with a preferred embodiment the resilient member 2 is constituted by at least two spring leaves 4 and 5 and the signal transmitter 3 is mounted on the spring leaf 4, which shall be in resilient contact with the spring leaf 5 in sliding contact with the web material. The signal transmitter used may be e.g. a piezo-electric cell, a strain gauge, an inductive gauge, an accelerometer or an optical signal system.

The spring leaf 4 supporting the signal transmitter 3 comprises a portion 7, which is freely movable above the web 1 and spaced from its mounting portion 6 in a carrier means 13 and it is in contact with the central portion 9 of the leaf spring 5 in sliding contact with the material web 18 and a movement-equalizing portion 8 is arranged outside thereof. On the opposite side of the web 1 there is arranged a support 18, where the end 30 of the movable portion 7 is in contact with the central portion 9. Further, the leaf spring 4 support- ing the signal transmitter 3 is provided with a vibra¬ tion-damping element 10 in the position 11, where it is in contact with the leaf spring 5, which by means of two screws 19 is likewise fixed in a mounting portion 12 secured to the carrier member 13 extending across the web 1. Thanks to this mounting arrangement of the leaf springs 4 and 5 and to the fact that the leaf spring 4 is provided with said vibration-damping ele¬ ment 10 level changes in the web can be sensed without the control signal from the signal transmitter 3 being disturbed by irregularities in the tissue material.

In order to create a stronger signal from the leaf spring 4, which is exposed to a flexing force and supports the signal transmitter 3, it has been provided with a portion having a reduced resistance against flexing. According to the embodiment in Fig. 2 cut-outs 14, 15 have been made at the outer edges 16, 17 and

further there is an orifice 27 at the location of the signal transmitter 3 on the leaf spring 4. The leaf springs 4 and 5 are by screws 19 mounted in the carrier 13, which by means of a set screw 28 can be adjusted for the purpose of bringing the signal transmitter unit 29 in contact with the web 1. Thanks to this mounting arrangement the resilient slide leaf 5 will, at its contact or central portion 9, carry out a spring move¬ ment almost perpendicular to the material web 1.

Fig. 3 is a diagrammatic top view showing a tissue paper web passing through a napkin-manufacturing machine exemplifying the invention. As appears from the drawing figure, the tissue paper web 1 is fed between embossing cylinders 20 and 21 and further via posi¬ tioning means 22 to the level change sensor 23 de¬ scribed above and consisting of the resilient member 2 with the signal transmitter 3 mounted above the web by means of the carrier 13. From there the web 1 continues through a pair of folding cylinders 24 and 25, which fold the paper web into a zigzag shape, whereupon a knife 26 divides the web 1 into two napkin strings, which are then counted and packeted.

The method according to the invention for the genera¬ tion of signal controlling functions in, especially, a napkin-manufacturing machine is characterized in that level differences in the passing material web are sensed by a signal transmitter mounted on a resilient member, the spring element of which is in sliding contact with the material web 1 and exposed to a bend¬ ing movement when the napkin surface passes below it and a level difference is encountered, e.g. in the shape of an embossed edging 31. Figs. 1 and 2 show details according to a preferred embodiment of the spring member 2. When an embossment in the material web 1 passes below the resilient member 2 comprising the

signal transmitter 3 the lower leaf spring 5 forming part of the spring member 2 will move in an outward direction and thereby actuate the signal transmitter 3 via the spring 4 supporting it, so that a signal is generated. The signal is treated in an electronic unit with automatic level control and continues to a PLC- system. Unreasonable measured values are discarded by the program, whereas reasonable measurements form an average value from a number of measurements so that the accuracy of the value will be as high as possible. The position reference for the embossment operation is the embossing cylinders 20, 21, to which there is connected a pulse transmitter and the calculated average value is compared with the reference value. Consequently, the program uses the position reference value and the average value for controlling the adjustment motors used to control the functions of the machine.