GB2118297A - Checking contents of tubular casing - Google Patents

Abstract

A tubular casing (1) to be checked moves longitudinally in a continuous manner through a passage (24) in a head (16). At one side, this passage (24) comprises a light-emitting source (41) and on the other side, a photoelectric pick-up member (42). The passage (24) has a U-shaped section with parallel walls and the base of which has a surface in the form of a projecting dihedron (25), the edge of which is situated at least approximately in the bissecting plane of the U, at a distance from the trajectory of light ray equal to at least one and a half times the width of the passage (24). The head (16) may be raised by pivoting. <IMAGE>

Description

SPECIFICATION Device for the continuous checking of the contents of a tubular casing The present invention relates to a device for the continuous checking of the contents of a tubular casing moving longitudinally in a continuous manner, in particularfor checking a continuous filter rod for a cigarette, atthe time of its manufacture and controlling the cutting of this continuous rod into individual rods, as well as for checking the filling of the cigarettes themselves. This device comprises a head having a passageforthe casing to be checked and supporting a light-emitting source radiation transversely with respectto the passage, in the direction of a photoelectric pick-up member located behind a transverse slot, on the other side ofthe passage and associated with a circuitfor processing the signal picked up.

The continuous optical checking ofthe density of a continuous filter rod for a cigarette manufactured continuously, has been proposed in Swiss Patent No.

576242. The continuous rod passes through a checking head comprising an annular passage allowing as little clearance as possible. Bundles of optical fibres terminate on each side ofthe passage, one emitting light and the other picking it up. This idea was adopted, with a photo-electric pick-up, in Swiss Patent No. 621 245 and Swiss Patent No.62711 for controlling the device for cutting a composite filter, necessitating cutting at a predetermined point.The passage, through the checking head, forthe continuous rod to be checked, is always annular.The annular shape was indispensible for reasons of guidance, since logically one sought two limitthe play of the continuous rod to the minimum, transverse movements of the continuous rod having the effect of modifying the optical signal measured. Henceforth, the radial play was also kept to a minimum. In orderto reduce the reflection ofthe light by the innerwall of the annular passage, the latter was coated with an anti-reflective optical varnish. A non-reflective synthetic material was also used in order to form the body of the ring. Despite this, stray light exists, which in the recording of the optical signal measured results in instability ofthe latter.This is due to the fact that inspite of everything a certain reflection occurs on the cylindrical wall ofthe passage, in particulartowards the points oftangency of the planes parallel to the trajectory of the light ray. Moreover, the friction ofthe continuous rod on the wall ofthe passage produces the formation of more or less white dust, paper dust, even white filter material, which constitutes a source of indirect stray light, this being all the more so when it is necessary to leave a sufficient radial clearance, taking into account the variation in diameter of the continuous rod formed by the sticking of two webs of paper.

The essential objectofthe invention isto eliminate the stray light due in particularto reflections.

To this end, the device according to the invention is characterised by the fact that the said passage has a U-shaped section with parallel walls, which are preferably vertical and the base of which has a surface in the form of a projecting dihedron, with plane or concave faces, the edge of which is situated at least approximately in the bissecting plane ofthe U, at a distance from the trajectory of the light ray equal to at least one and a half times the width of the passage.

The U-shaped passage is preferably arranged vertically, its opening at the lower end, in the direction of the greatest movements of the continuous rod due to the system for guiding the cylinders of the cutting device which immediately follows the optical checking device. Consequently, contrary to what has always been sought after, the continuous rod to be checked may move freely vertically in the U-shaped passage. Now, despite this play, the optical signal measured has great stability and there is virtually no longer any stray signal. Owing to the shape of the section of the passage, the reflections on the walls of the passage no longer influence the pick-up. On the other hand, dust tends to be evacuated automatically. It is also easierto clean the passage.

But, as a natural consequence, one obtains another important advantage, namely the possibility of disengaging the headforchecking the continuous rod by raising it or removing it from the latter, which facilitates starting up, since it is no longer necessary to introduce the end of the continuous rod into the annular passage of the head and this facilitates any inspection or maintenance of the mach ine without it being necessarytocutthecontinuous rod in the making.

The accompanying drawings illustrate, byway of example, one embodiment of the invention.

Figure 1 shows diagrammatically the terminal part of a machineforthe manufacture of cigarette filters, equipped with a checking device and a device for controlling cutting.

Figure 2 is a side view, to an enlarged scale, ofthe optical checking device.

Figure 3 is a front view ofthis optical checking device.

Figure4is a plan viewofthe same device.

Figure 5 is a diagram illustrating the insensitivity of the optical checking device to the vertical movement ofthe continuous rod to be checked, compared with a device according to the prior art.

The installation illustrated diagrammatically in figure 1 is described in Swiss Patent No. 621 245. It is intended for the continuous manufacture of cigarette filters, in particular of composite filters and of filters having a cavity filled with a granulated filtering substance. Filters formed continuously by placing end to end cylinders of cellulose acetate and cavities filled automatically with granulated material and wrapped in two webs of paper arrive in theform of a continuous rod 1 carried by an endless belt 2 through the optical checking device 3 in front of a cutting device 4which cuts the continuous rod 2 into individual rods 5, which are deflected laterally from their trajectory by a distribution wheel 6 comprising helical grooves, whichenablestheindividual rods to engage in the grooves 7 of a receiving drum which distributes them on a conveyor belt moving at right angles to the plane ofthe drawing. Faulty rods are eliminated pneumatically by a nozzle 8 controlled by a solenoid valve 9.

Faulty rods are driven into a discarge hopper 10. The optical signal supplied by the checking device 3 makes it possible to checkthefilling ofthe cavities ofthe filters quantitatively, to check the location and the length ofthefiltersegments and to control the cutting device 4depending on the position ofthe filter members. To this end, a circuit is provided for processing the signal picked up, for example a circuit such as that described in Swiss Patent No. 627 119.

The continuous rod 1 is introduced manually into a pre-guiding cylinder 11 preceding the cutting unit4 provided with two guiding cylinders 12 and 13 between which the cutter 14 ofthe cutting unit operates.

The detection device 3 will be described in relation to figures 2,3 and 4. The device is mounted on a vertical plate 1 fixed to the frame 40 ofthe machine.

The measuring head proper 16 is mounted to pivot on this plate about a horizontal pivot 17 integral with a crank 18 at the end of which is pivoted, about a pivot 19, the piston rod 20 of a single-acting pneumatic jack 21, the cylinder of which is pivoted on the plate 15 about a pivot 22.

The head 16 is composed of two asymmetrical parts 16a and 16b of solid metal, joined one to the other along a vertical joint plane 23. The part 1 6a is cut out in orderto form a prismatic passage 24 in the head, the passage having a cross-section in the general form of an inverted U, the base 25 of which is in the form of a projecting dihedron, whereof the edge is situated in the bissecting plane of the passage 24. The part 1 6b comprises a recess 26 in which is mounted an infrared emitting diode 27 mounted on a cheek 41 and supplied by a source of pulsating light.Mounted in front of this emitting diode 27, whose hemispherical emitting surface has a diameter less than 2mm is a window pane 28 constituted by a small saphire plate having a thickness of 0.6 mm, located at several tenths of a millimetre from the diode 27 and embedded in a metal cover 29 closing off the recess 26 and which is flush with the joint plane 23. The part 16a ofthe head also comprises a recess 30 in which a receiving cell 31 is housed, for example a Si-PIN photodiode mounted, with part of a circuitfor processing the signal, on a side plate 42.This photodiode is virtually in contact with a metal screen having a thickness of 0.05 mm, coated adjacent the rod with an absorbent optical layer and stuck to a saphire plate 32 identical to the plate 28 stuckto and embedded in a recess in a metal cover 33 closing off the recess 30 and provided with a central cut-outforthe receiving diode 31, like the cover 29. The screen located in front of the receiving diode 31 comprises a vertical slot having awidth of approximately 0.8 to 1 mm and a height equal to 0.4 to 0.6 times the width of the passage 24, i.e. the diameter of the rod 1 which passes through the slot with the least possible lateral clearance, for example ofthe order of 0.7 mm on each side. The dimensions ofthe slot are for example 1 mm by 4.5 mm.The edge ofthe dihedron 25 is situated at a distance from the trajectory 34 of the light ray emitted by the emitting diode 27 equal to one and a halftimesthe width of the passage 24,that is to say slightly more than one and a half times the diameter of the rod 1. Naturally, this distance could be greater, but it has proved perfectly adequate in orderto eliminate the effects of stray light dueto reflection.Thewallsofthe passage 24, including the dihedron 25 are also treated in order to obtain diffusing, absorbent surfaces. They are for example sand-blasted, then coated in matt black or covered with an optical black dye. The vertical slot of the screen of the receiving diode 31 is naturally located on the trajectory 34 of the light ray emitted by the emitting diode 27.The emitting diode and the circuit associated with the receiving diode are connected to flexible conducting wires (not shown,} The same is true forthetube supplying the pneumatiejack 21.

As shown in figure 2,the head may be raised into position 16' shown in dot dash line, by pivoting about its pivot 17, in the direction of arrow F, in order to occupy the position 16' shown in dot dash line, under the effect oftheforce of the pneumatic jack 21. When the pressure in the jack 21 is released, the return spring ofthe latter restores the head to the working position shown in full line. It can be seen that in the raised position of the head 16, the continuous rod 1 is completely disengaged from the head, which facilitates easy starting-up and also prevents accidental damagetothe head. The inspection and cleaning of the saphire plates, in particular ofthe glue deposits left bycontactwith the continuous rod 1, are also facilitated.

The vertical position of the passage 24 is favourable since itfacilitatesthe automatic evacuation, by gravity, of the dust formed by a abrasion on the outside ofthe continuous rod 1. As regards the optical result and the possibility of disengaging the head, the slot could however also be oblique, even horizontal.

In the form of a measuring diagram,figures 5 shows the surprising result obtained by the shape of the passage 24. The vertical deviation d, in millimetres, of the continuous rod 1,from a stationary position 0 is drawn on the X axis and the ratio VNo between the signal measured in the inoperative state (1) and the signal measured in various positions remote from the stationary position is shown on theY axis. The curve a is the measuring curve obtained with a measuring head according to the prior art, that isto say a head comprising a cylindrical annular passage with minimum clearance. The curve b is the measuring curve obtained with the measuring head according to the invention. It is appropriate to consider that in the head according to the prior art, the vertical play ofthe continuous rod is very limited by the wall ofthe annular passage, whereas in the head according to the invention, this vertical play is absolutely not limited. It will be seen that with the head according to the prior art, the ratio VNo is of the order of 1 .3to morethan 1.5 for a distance of 1 mm, whereas this ratio VNo is only 0.97 to 0.99 for a distance of i 1 mm.

Claims (5)

1. Deviceforthe continuous checking of the contents of a tubular casing moving iongitudinally in a continuous manner, comprising a head having a passage forthe casing to be checked and supporting a light-emitting source emitting radiation transversely with respecttothe passage, in the direction of a photo-electric pick-up member located behind a transverse slot, on the other side of the passage and associated with a circuit for processing the signal picked up, characterised by the factthatthe said passage has a U-shaped section with parallel walls and the base of which has a surface in the form of a projecting dihedron,the edge ofwhich is located at least approximately in the bissecting plane ofthe U, at a distance from the trajectory of the light ray equal to at least one and a half timers the width ofthe passage.

2. Device according to claim 1, characterised by the fact that the walls of the U-shaped passage are vertical andthatthe passage is open on the underside.

3. Device according to claim 1 or2, characterised by the fact that the length ofthe transverse slot situated in front of the pick-up member is comprised between 0.4 and 0.6 times the width ofthe passage.

4. Device according to claim 1,2 or3, characte- rised bythefact that the light source and the pick-up member are located respectively behind a small saphire plate flush with the surface of the passage.

5. Device according to claim 1,2,3 or4, characte- rised by the fact thatthe head is able to move in a plane parallel to the bissecting plane ofthe U, in order to be able to be disengaged from the tubular casing to be checked.