GB2178413A - Web transport system - Google Patents

Abstract

In a cigarette making machine comprising a rod forming section and a web transport system for supplying a web of cigarette paper to the rod forming section, the means for transporting the web of cigarette paper from a supply bobbin include a capstan and a pinch wheel between which the web is firmly held; drive means for driving the capstan; means for monitoring the tension in the web between the capstan and the supply bobbin by detecting the torque applied to the capstan to drive the web; and means for varying the speed of the drive means in response to the measured tension so that the tension in the web does not exceed a predetermined value.

Description

SPECIFICATION Web transport system This invention is concerned with transporting webs, and is particularly concerned with a system which avoids applying excessive tension to the web while it is being transported.

In many manufacturing processes articles are produced from or with a section of sheet material (for example, paper, cellophane, foil, filter tow, reconstituted tobacco, etc.) which is transported to an assembly region as a continuous web. The web may be continuous for a substantial working period (for example filter tow) or a continuous supply may be maintained by splicing together finite lengths. However, as machines are required to operate at ever increasing speeds, excessive tension may be applied to the web which may stretch the material, thus changing its properties, or break the web, thus disrupting production.

According to a first aspect of this invention there is provided a method of transporting a web, comprising the steps of transporting a web from a store to a machine by means of a transport device; detecting the tension in the web between the store and the transport device; and controlling the transport device in response to the measured tension so that the tension in the web does not exceed a predetermined level.

In a cigarette making machine, for example a Molins Mark 10, a continuous cigarette rod is formed by sealing tobacco in a paper web which is supplied to a rod forming section from a bobbin. before the bobbin runs out of paper the paper from a new bobbin must be spliced to the existing paper without stopping the machine. Production is maintained during a splicing cycle by supplying paper to a rod forming section of the machine from a previously filled reservoir. Increasing and decreasing the speed of the web in order to achieve this increases the web tension, and the web will break if the tension exceeds a value of typically 17 to 21 newtons (3.8 to 4.7 pounds).

According to a second aspect of this invention there is provided a web transport system comprising a transport device for transporting a web from a store to an assembly machine; means for detecting the tension in the web between the store and the transport means; and control means for controlling the transport device in response to the measured tension so that the tension in the web does not exceed a predetermined level.

In a preferred apparatus the drive unit consists of a capstan and a pinch wheel between which the web is firmly held, and a drive unit for driving the capstan.

Preferably the tension in the web is determined by monitoring the torque applied to the capstan by the web.

In the preferred apparatus the capstan consists of two coaxial members which are connected by at least one spring so that the relative displacement between the members is indicative of said applied torque.

Preferably the capstan consists of an outer member supported by bearings on an inner member which is connected to an output shaft of the drive means.

In the preferred apparatus a first vaned disc extends from the inner member and a second vaned disc extends from the outer member, a beam of light is directed at the vanes of both discs, and a transducer receives light which has passed between the vanes to produce a displacement signal indicative of the relative displacement of the discs; the displacement signal may be a square wave having a variable mark/space ratio.

The web tension indicated by the displacement signal is used to control automatically the braking applied to a bobbin from which the web is drawn. The drive unit may be an eddy current coupled drive. It is arranged to run at a speed determined basically by the speed of the machine consuming the web. One of the vaned discs may have a larger diameter than the other and a second beam of light may be directed between the vanes of the larger disc, where they extend beyond the smaller vanes, to produce a speed signal indicative of the speed of the capstan. The speed signal is preferably a square wave having a variable frequency and a constant mark/space ratio. In the preferred apparatus the inner member is also connected to the outer member via a rotating dash-pot to damp out rapid fluctuations and oscillations between the two said members.The eddy current coupled drive is preferably arranged to apply tension to the web when the capstan is not actually rotating.

The invention is particularly suitable for controlling paper tension in a cigarette making machine.

According to a third aspect of the invention there is provided a cigarette making machine including a rod forming section and a web transport system for supplying a web of cigarette paper to the rod forming section, comprising means for transporting a web of cigarette paper from a supply bobbin including a capstan and a pinch wheel between which the web is firmly held; drive means for driving the capstan; means for monitoring the tension in the web between the capstan and the supply bobbin by detecting the torque applied to the capstan by the web; and means for varying the speed of the drive means including means for controlling said speed variations so that the tension in the web does not exceed a predetermined value.

The invention will now be described, by way of example only, with reference to the accompanying Figures of which: Figure 1 shows part of a Mollins Mark 10 cigarette making machine; Figure 2 shows a splicing unit of the machine of Figure 1 Figure 3 shows a drive unit for driving a paper supply capstan of the machine in Figure 1; Figure 4 shows a cross-section of the paper supply capstan of Figure 1; Figure 5 is a section on line V-V of Figure 4 showing an arrangement of springs for the capstan; and Figure 6 is a section on line VI-VI of Figure 4 showing an arrangement of vaned discs.

Figures 7a, 7b and 7c are examples of waveforms obtained from a displacement detector mounted adjacent to the capstan of Figure 4.

Part of a cigarette making machine is shown in Figure 1 in which a web cigarette paper 1 is transported by means of a rotating capstan 2 and pinch wheel 3 from a bobbin 12 via a splicing unit 4.

After being firmly held between the capstan 2 and pinch wheel 3 the web then passes into a reservoir 5, under a "dancing arm" 6, through a printing unit 7 and into a rod forming section 8. Each bobbin provides enough paper for approximately ten minutes of production after which paper from a new bobbin must be spliced to the existing paper. During a splice cycle production must be maintained at normal operating speed.

The capstan is driven by a variable speed motor (e.g.

an eddy current coupled a.c. motor) under the control of a control unit 9. During normal operation the speed of the capstan is dependent upon the position of the dancing arm 7; when the dancing arm goes above a predetermined height the speed of the capstan is automatically increased, and when it goes below a predetermined height the speed of the capstan is reduced.

A bobbin is supported by an upper spindle 10 and a second bobbin is supported by a lower spindle, 11 which are usually free to rotate but may be held firm by a diaphram brake controlled by the control unit 9.

The diaphram brake may also be applied when decelarating the web to prevent the formation of loops which is a facility provided by the present invention.

The spindles 10, 11 are not required to move perpendicular to their axes of rotation as paper is supplied alternately from a bobbin supported by the upper spindle 10, and then from a bobbin supported by the lower spindle 11.

The diameter of a bobbin in monitored by generating a series of bobbin pulses at a frequency proportional to the speed of the bobbin which are compared with similar capstan pulses produced at a frequency proportional to the speed of the capstan 4. When the web is running at constant speed the capstan pulses will maintain a constant frequency while the frequency of the bobbin pulses will increase as the diameter of the bobbin decreases. The control unit 12 is arranged to detect a predetermined relationship between the frequency of the capstan pulses and the frequency of the bobbin pulses, for example frequency equality, and then perform the necessary operations. In previous arrangements for detecting bobbin diameter arms have been provided which rest on the bobbins and therefore swing as the bobbin diameter is reduced.

A similar arrangement may be provided for maintaining the required amount of paper between the capstan 2 and the rod forming section 8. Pulses generated by the rod forming section may be compared with pulses generated by the capstan to calculate the length of paper which has passed through each over a predetermined time interval, thus eliminating the dancing arm.

However, with such a system care must be taken to ensure that the web does not slip over the rotating parts from which pulses are generated.

In Figure 1 paper is being unwound from a bobbin 12 which is supported by the lower spindle 11. On detecting that very little paper remains on bobbin 12 the control unit 9 increases the speed of the capstan 2 to provide a surplus of paper in the reservoir 7. When sufficient paper has collected in the reservoir the capstan slows down and eventually stops. This allows the splicing unit 4 to cut the paper from bobbin 12 and form a splice with the paper from a new bobbin 14 which is supported by the upper spindle 10. Once the splice has been formed the capstan is accelerated to 98% of its normal operating speed (thus emplying the reservoir 5) until capstan control may be returned to the dancing arm 6.

While paper is being unwound from bobbin 14 an operator removes the remnants of bobbin 12 and loads a new bobbin onto the lower spindle 11. The end of the new bobbin is located in the splicing unit 4 so that the new bobbin may be spliced to the paper from bobbin 14. Preferably an exhausted bobbin is rejected by the operation of a foot pedal so that the operator has both hands free to hold the new bobbin. A second operation of the pedal may then lock the new bobbin into place.

The splicing unit may be similar to the type used in conventional cigarette making machines in which cigarette paper is spliced together with a piece of adhesive tape and paper from the old bobbin (bobbin 2 in Figure 1) is cut away. Such arrangements require an operator to place the tape in the required position before each splice may be formed. In addition to this inconvenience the edges of the tape may catch closely fitting rod guides which may result in the rod jamming before the offending section can be removed. To avoid this problem the machine may be arranged such that a piece of tape placed on the cigarette paper 1 at the splicing unit is contained on the inside surface of the cigarette rod. The tape cannot therefore catch any of the rod guides before the continuous rod has been cut.

However, in a preferred arrangement (shown in Figure 2) the splice is formed by two impact hammers 20, 21 which quickly hammer the two webs of paper together at three or more impact positions effectively welding the two webs together.

Before such an impact splice is formed two pairs of scissors on a common mounting member cut the paper 1 from the old bobbin 2 at position 23 and cut the loose end from the new bobbin 10 at position 24.

The impact hammers are brought together by arranging each hammer as an electro magnet (supplied by voltage sources V1 and V2) with opposing poles thus forcing the hammers together. Just before the hammers are about to contact the control unit 12 operates a ganged switch 24 which reverses the current supplied to one of the electromagnets thus after the impact the hammers quickly retract.

in an alternative arrangement one of the hammers may be forced into contact with the other by a piston supplied with compressed air via an electrically controlled valve.

The capstan drive unit is shown in Figure 3 and provides an eddy current coupling between an output shaft 30 (which drives the capstan 4) and a continuously running a.c. motor formed by a fixed stator winding 31 and a rotor winding 32. A quill 33 extends from the rotor winding 32 to an iron ring 34 (having a low magnetism retention characteristics) which surrounds an output rotor winding 35. The speed of the output rotor is determined by the current applied to the output rotor winding through brushes 36. However, a ballrace 37 and a ballrace 38 (allowing the continuously running rotor 32, 33, 34 to rotate around the output rotor) have a degree of friction which will in turn supply a tension of typically 1.1 Newton (4 ounces) to the paper when current is not passing through the output rotor winding 35.

The drive unit is provided with a diaphragm brake 39 and an eddy current brake 40. The diaphragm brake 39 is used for holding the capstan stationary and effecting large braking operations during the splice cycle. The eddy current brake 40 provides smaller measures of braking and is used to slow down the drive output 30 if the tension in the paper goes above a predetermined maximum. In order to complete the control loop back to the control unit 12 a voltage signal proportional to the speed of the drive output 30 is measured by a tachometer formed by a rotor winding 41 and a stator winding 42.

A cross section of the capstan 2 is shown in Figure 4. The web of cigarette paper 1 is held between the pinch wheel 3 (Figure 1) and a capstan roller 60 which is secured to an outer rotating member 61 by a bolt 62 and a spring 63. The capstan roller 60 and the outer member 61 are separated by friction pads 64.

The outer rotating member is supported on an inner rotating member 65 by two bearings 66 and the inner rotating member is coupled to the capstan drive via a gear 50.

The inner rotating member 65 drives the outer rotating member 61 via three springs 71, 72, 73 (Figure 5). When torque is applied to the outer member (while it is rotating) the springs extend linearly in proportion to the applied torque between a minimum position (shown by spring 71) to a maximum position (shown by spring 71 A). The extension is linear for up to 35 degrees of twist between the inner member and the outer member. The inner member 65 is also connected to the outer member 61 via a rotating dash-pot 67 which prevents rapid speed variations and oscillations between the two said members.

The angular displacement between the inner mem ber 65 and the outer member 61 is measured by means of an inner disc 67 connected to the inner member 65 and an outer disc 68 connected to the outer member 61. Each disc is comprised of six vanes 80, 81 each extending through 30 degrees and separated by a 30 degree gap as shown in Figure 6. When the outer member is not angularly displaced with respect to the inner member the vanes overlap.

In Figure 6 the outer member 61 has undergone 15 degrees of twist. A light emitter and light detector combination 67 (Figure 4) is provided which detects light passing between the vanes of the discs and has associated wave shaping circuitry to provide a square wave output having a variable mark to space ratio; a mark when light is blocked by a vane and a space when light passes between the vanes as shown in Figure 7.

When the angle of twist between the outer member 61 and the inner member 65 is zero, the output waveform is as shown in Figure 7A; i.e. with a mark/space ratio of 1:1. As the angle of twist increases to say 1 5 degrees (as shown in Figure 6) the mark/space ratio becomes 3:1 (Figure 7B) and so on until the outer member 61 has almost been twisted through 30 degrees and the waveform produced is as shown in Figure 7C. In practice the control unit 12 should reduce the speed of the capstan drive before the angle of twist reaches the extreme condition of Figure 7C.

A second light emitter/detector combination is provided to generate a speed reference signal. For this purpose the inner disc 67 has a larger diameter and light emitter by the second emitted only passes between the vanes of the inner disc where they extend beyond the vanes of the outer disc 68. The speed reference signal is supplied to the control unit thus providing that feedback control of the web transport system.

The system as described herein is capable of overcoming the problem of web breaks by controlling the speed of the web in response to the tension measured in the web, and by not allowing a loop to form while a bobbin is stationary. The system may also be used for measuring the tension of other transported webs in the tobacco industry (for example cellophane and foil in cigarette packaging machines and filter tow in filter rod making machines) and of many transported webs outside the tobacco industry.

Claims (8)

1. A method of transporting a web, comprising the steps of transporting a web from a store to a machine by means of a transport device; detecting the tension in the web between the store and the transport device; and controlling the transport device in response to the measured tension so that the tension in the web does not exceed a predetermined level.

2. A web transport system comprising a transport device for transporting a web from a store to an assembly machine; means for detecting the tension in the web between the store and the transport means; and control means for controling the transport device in response to the measured tension so that the tension in the web does not exceed a predetermined level.

3. A system according to claim 2 in which the means for detecting web tension comprises means for monitoring the torque applied to a capstan driving the web.

4. A system according to claim 3 in which the capstan consists of two coaxial members which are connected by at least one spring so that the relative displacement between the members is indicative of said applied torque.

5. A system according to claim 4 in which the capstan consists of an outer member supported by bearings on an inner member which is connected to an output shaft of the drive means.

6. A system according to claim 5 in which a first vaned disc extends from the inner member and a second vaned disc extends from the outer member, a beam of light is directed at the vanes of both discs, and a transducer receives light which has passed between the vanes to produce a displacement signal indicative of the relative displacement of the discs.

7. A cigarette making machine including a rod forming section and a web transport system for supplying a web of cigarette paper to the rod forming section, comprising means for transporting a web of cigarette paper from a supply bobbin including a capstan and a pinch wheel between which the web is firmly held; drive means for driving the capstan; means for monitoring the tension in the web between the capstan and the supply bobbin by detecting the torque applied to the capstan to drive the web; and means for varying the speed of the drive means including means for controlling said speed variations so that the tension in the web does not exceed a predetermined value.

8. A method of apparatus substantially in accordance with any one of the examples described with reference to the accompanying drawings.