Patent Publication Number: US-6041980-A

Title: Dosing apparatus and method

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus and method for dispensing doses of particulate material. 
     SUMMARY OF THE PRIOR ART 
     In the production of packets by the form-fill process, a web of the packet material is shaped into a tubular form around a downwardly extending dosing tube as it is led down the tube, and is sealed transversely at intervals and separated at the transverse seals to form a series of sealed packets. Filling material is fed through the dosing tube into the tubular web in alternation with the formation of the transverse seals, so that each packet has a dose of filling material sealed within it as it is formed. 
     WO95/01907 (U.S. Pat. No. 5,548,947) describes such a process in which the filling material is dispensed from the dosing tube by a reciprocating plunger valve that expels the material in discrete doses into the tubular web. Such an arrangement is capable of operating at relatively high rates of packet production but control of the size of dose expelled by the valve requires regulation of the flow of material into the former tube. When the material is in the form of small particles, e.g. tea for tea bags, this has the disadvantage that close control of the doses is difficult, for example because of the tendency of the material to spread out as it falls through the former tube and because of the influence of random perturbations of the flow through the dosing tube. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a dosing apparatus is provided for use in a form-fill process comprising a former tube through which filling material is supplied to a tubular envelope formed around the tube, means within the former tube defining a dosing opening for passage of the filling material, a dosing valve within the former tube being arranged to reciprocate to dispense discrete doses of the filling material from the former tube, and means being provided to vary the flow of the filling material through said dosing opening to control the quantity of material dispensed in each dose. 
     Apparatus according to the invention is preferably employed in a form-fill process in which the dosing valve is displaceable into an outlet opening at the outlet end of the former tube to expel each dose of the filling material therefrom. Preferably, it is arranged that the valve ends each dosing stroke closing the outlet opening so as to space the doses of material being dispensed therethrough. 
     In a preferred form of the invention, means within the former tube define a dosing opening the size of which is adjustable for said dosing control. Thus, an inner member can be provided which is located within the former tube adjacent to the dosing valve and is relatively displaceable to the former tube to adjust the size of said dosing opening. 
     If the inner member comprises a tubular element spaced from an internal wall of the former tube and defining said dosing opening therewith, it can be arranged that the tubular element forms a guide in which the dosing valve is reciprocable. The tubular element can thus extend coaxially with the dosing valve and with the former tube and may also form the outlet opening which is closed by the valve to terminate each dose. 
     The inner member may extend from the former tube remote from said dosing opening to an adjustment mechanism for displacement of the member in the former tube to obtain said variation of the size of the dosing opening. 
     In another aspect of the invention, there is provided a dosing apparatus for use in a form-fill process comprising a former tube through which filling material is supplied to a tubular envelope formed around the tube, a dosing opening defined within the former tube for passage of the filling material, a dosing valve within the former tube for reciprocation to dispense discrete doses of the filling material from the former tube, and means being provided to vary the flow of the filling material through said dosing opening to control the quantity of material dispensed in each dose. 
     According to a further aspect of the invention, a dosing apparatus provided for use in a form-fill process comprises a former tube through which filling material is supplied to a tubular envelope formed around the tube, a dosing valve within the former tube being arranged to reciprocate to dispense discrete doses of the filling material from the former tube, means being provided to vary the mean position of reciprocation of the valve relative to the tube to control the quantity of material dispensed in each dose. 
     In particular, if the dosing valve is displaceable into an outlet opening of the former tube to expel each dose, such adjustment of the valve mean position varies the stage in each stroke at which it enters the outlet opening and so terminates the feed of material into the opening. With this latter form of control, more generally it is not necessary to provide a specific dosing opening for the flow of material to the valve. 
     If an inner member defining a dosing opening is provided in the former tube of such an apparatus, it is similarly possible to exercise control of the dosing by causing the change of mean position of the valve to vary the stage at which the valve opens the dosing opening for delivery of the material therethrough. In such an arrangement, the inner member may remain fixed in position. 
     According to another aspect of the invention, a method of controlling dosing in a form-fill process is provided in which the material to be dosed is supplied to a a former tube around which a tubular packaging envelope is formed and is dispensed into said envelope by reciprocating valve means at an outlet from the former tube, a reservoir of the material being maintained in said tube upstream of the valve means and the rate of supply of the material to downstream of the valve means is controlled to vary the quantities of the doses of material dispensed by the valve means. 
     Said variation of the quantities of the doses of material dispensed can be achieved by maintaining a reservoir of the filling material within the former tube and allowing the material to pass from the reservoir to the valve means through a dosing opening the size of which can be adjusted. Alternatively, the mean position of reciprocation of the valve means relative to the outlet opening can be adjusted. In a further possibility, the head of material held in the reservoir within the tube is adjusted to vary the rate at which it can escape into the zone of action of the valve means. In each instance it is possible to vary the size of dose while maintaining the stroke of the valve means constant. 
    
    
     By way of example, the invention will be described in more detail with reference to the accompanying drawings, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 are axial sectional views of a former tube of a form-fill apparatus having a dosing apparatus according to the invention, a dosing valve of the apparatus being shown in the extended and retracted positions in FIGS. 1 and 2 respectively, and 
     FIG. 3 is a similar view of the former tube showing a tubular dosing control element associated with the valve in an opposite end position to that which it occupies in FIGS. 1 and 2, 
     FIGS. 4 and 5 are detail views of modifications of the apparatus in FIGS. 1 to 3, and 
     FIGS. 6 to 9 illustrate some further modifications of the apparatus in accordance with the invention, and 
     FIG. 10 is an oblique illustration of the form-fill apparatus in which the forms of dosing apparatus of the preceding figures can be incorporated. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The form-fill apparatus in the drawing comprises a static outer tube 2 which acts as a former around which a descending web of heat-sealable packaging material is wrapped to overlap its side edges which are then welded together by heat sealing rollers while travelling down the tube. The web is thereby given a tubular shape in which, below the former tube, transverse welds are formed in known manner by a heat sealing arrangement to produce a series of welded compartments which can then be separated to form individual packets. 
     The filling material is dispensed from supply means (not shown) through the interior of the former tube 2 in a manner which allows it to be dispensed in discrete doses. Alternately with the formation of each transverse weld seal, a dose of material is delivered into the tubular web so that each compartment is filled before its upper end is sealed closed by a transverse weld. 
     As described so far, the process can operate as a conventional form-fill process. Reference can be made, for example, to WO95/01907 for further details of an apparatus in which such a process can be performed. The content of WO95/01907 is incorporated into the present application by reference, therefore, and only those features are illustrated and described that relate directly to the novel subject matter of the present invention. 
     The interior of the tube is rotationally symmetrical about a central axis AA (FIG. 3), apart from the optional presence at one side of a small cross-section guide 4 containing a drive (not shown) for a spreader finger mechanism (which may be of the kind that is illustrated in WO95/01907). At its lower, exit end the tube has a concentrically tapered throat 6 leading into a cylindrical outlet nozzle 8 that is also concentric with the tube. 
     An inner tubular element or sheath 10 extends concentrically within the former tube 2 to near the outlet nozzle 8. The tubular element 10 has an extension 10a above the former tube to an adjustment mechanism (described below) by means of which it can be displaced progressively between a lowermost position shown in FIGS. 1 and 2 and an uppermost position shown in FIG. 3. To maintain the tubular element centralised within the former tube, radial fins 12, only one of which is shown projects inwards from the former tube into sliding contact with the tubular element. It will be noted that over its entire range of adjustment, the lower end of the tubular element 10 lies within the former tube 2, above the outlet nozzle 8. An essentially annular gap 14 is therefore always present between the former tube and the lower end of the tubular element and provides a dosing opening. 
     A dosing valve comprises a piston 16 concentric with the former tube is a free sliding fit within the tubular element and is axially displaceable between the positions shown in FIGS. 1 and 2 respectively. In the lower position the piston 16 extends into the outlet nozzle 8. In its upper position the piston is spaced above the tapered throat 6 of the former tube and is withdrawn wholly or mainly into the tubular element 10. The piston 16 is mounted on a central stem 16a that extends through the top of the tubular element 10 to a drive mechanism (not shown) to be reciprocated between the end positions illustrated, in order to expel a discrete dose of material from the nozzle on each down stroke. 
     The apparatus further comprises supply means (not shown) for dispensing material into the upper end of the former tube 2, in the annular free space 18 between the former tube and the tubular element 10. As the material falls to the bottom of the former tube 2, the piston 16 reciprocates to expel the material from the tube in the manner described in WO95/01907. The movement of the piston 16 is coordinated with the operation of the unillustrated heat sealing arrangement below the former tube so that the doses are dispensed in alternation to the formation of the transverse welds compartmenting the tubular web. 
     The upper extension 10a of the tubular element 10 is located in a guide mounting 22 above the former tube, in which it is held non-rotationally but is axially slidable. On top of the mounting a captive nut 24 is rotatably held, the internal thread of which engages an external thread on a sleeve 26 fixed to the extension 10a. A servo motor 28 is connected by a belt drive 30 to the captive nut 24 to rotate it, whereby the tubular element 10 is displaced axially. In this manner the tubular element is adjustable continuously between the end positions shown in the figures. 
     In operation, particulate filling material is supplied by the unillustrated supply means at a rate that will keep a reservoir of the material at least in the lower part of the annular space 18 between the former tube 2 and tubular element 10, to above the lower end of the tubular element, although it is preferred to maintain the former tube filled to the top. In its lowermost position shown in FIG. 1, the piston 16 blocks the annular gap 14 but as it is raised from the outlet nozzle 8 the material is allowed to escape through the annular gap 14 and the following down stroke of the piston then drives it into the tubular web. It will be understood that this arrangement is intended to operate at relatively high rates of reciprocation of the piston, so that there is little if any opportunity for the material to fall from the nozzle 8 under the action of gravity alone. 
     Because the material must first pass through the annular gap 14 between the former tube and the tubular element in order to escape below the piston to be expelled from the former tube, the size of that gap will determine the size of the dose. As the element is lowered from the position shown in FIG. 3, it narrows the gap 14 to increasingly restrict the path of the filling material, limiting the rate of flow. The position of adjustment of the tubular element can therefore determine the amount of material that will form the dose to be expelled by the piston. 
     In this manner, the dosing of the tubular web can be controlled independently of the drive of the piston, the speed and stroke of which can be kept constant. Furthermore, as this control is exercised immediately adjacent the former tube outlet, its effect is substantially instantaneous. The supply means feeding material into the former tube do not have to be regulated so closely as it is only required to ensure that they maintain a supply at a rate sufficient to keep a substantially constant head of material above the annular gap 14. The dosing of the compartments being formed in the tubular web can thus be controlled rapidly and easily, even at filling rates of more than 1000 doses per minute. The power requirement of the dosing control is minimal because only relatively small movements need to be made, at a rate far slower than the piston reciprocation rate. 
     In order to keep the valve plunger aligned with the outlet nozzle, the lower end of the tubular element must also be held in alignment with the nozzle. FIGS. 4 and 5 show two alternative ways of doing this in place of the radial fins 12 of the example described above. 
     In FIG. 4, the tubular element 40 extends into the outlet nozzle 48 and its end portion 42 is a sliding fit in the nozzle 48. Large cut-outs 44 in the element above the end portion 42 form dosing openings and allow the filling material to escape from the reservoir of material in the annular space 18 to be expelled under the control of the valve piston 16 which operates in the manner already described, except that it now closes off the flow by entering the end portion 42 of the tubular element. In the same manner as the tubular element 10 already described, the tubular element 40 can be axially displaced, and the passage for the material is progressively restricted as the cut-outs 44 move downwards into tapered throat 46 and the outlet nozzle 48, so reducing the doses delivered by the dosing valve. 
     FIG. 5 shows a support for the tubular element 50 in the form of a segment 52 fixed to the wall of the former tube 2. Tie bolts 54 fixed to the tubular element 50 extend through elongate slots 56 in the support 52 and bear on the outer face of the support through spring washers 58. The tubular element 50 is thus resiliently clamped against the support but is able to slide axially in the former tube 2. In other respects the tubular element 50 can be identical to the tubular element 10 of FIGS. 1-3. 
     It is also possible to employ other means to vary the doses dispensed by the dosing valve while maintaining the stroke of the piston constant. 
     In the manner shown in WO95/01907, from which FIG. 6 is derived, the valve piston 16 is operated by a drive mechanism such as the cam drive mechanism 62 mounted in a frame 64 above the former tube 2. (As explained in U.S. Pat. No. 5,548,947, FIG. 6 shows a pair of counter-rotating drives, which balance out transverse forces, for identical, parallel production paths by the following description will be given with reference to only one of those paths). By mounting the frame 64 movably on support means 66, it can be displaced up and down, as indicated by the arrows V, relative to the former tube Z so that the mean position of the piston 16 in the former tube is varied, although the cam drive mechanism can continue to reciprocate the plunger valve with the same stroke. If, for instance, the mean position of reciprocation is lowered relative to the former tube 2, the outlet nozzle 8 is closed earlier in the downward stroke of the piston. It will be seen that the dose delivered from the reservoir of filling material maintained in the former tube is then reduced. 
     FIG. 6 also shows how the connection of the illustrated cam drive to the valve stem 18 is by a rocking lever 72 pivoted on a pillar 74 on the frame 64. A similar effect to that described in the preceding paragraph can be achieved by making the position of the pivot 76 adjustable on the frame upwardly and downwardly relative to the cam disc rotary mountings 78. The lever is thereby tilted in one direction or the other to change the mean position of reciprocation of the dosing valve upwards or downwards. 
     FIG. 6 shows two counter-rotating drive mechanisms 62 for two dispensing mechanisms arranged in parallel. With the first form of adjustment of the preceding paragraph both dispensing mechanisms are adjusted jointly. With this second form of adjustment, each may be adjusted independently. 
     In another alternative, the mean position of the dosing valve in the former tube can be left unchanged and the dose varied by varying the height of the reservoir of material held in the former tube. For example, as shown schematically in FIG. 7 the filling material can be supplied from a hopper 80 at the outlet from which is a conventional dosing wheel 82 to control the supply of the material into the former tube 2. The rate at which the material is fed to the tube can be changed by varying the speed of the wheel 82, so building up the head of material in the reservoir or allowing it to fall to increase or decrease the dose size respectively. 
     In these alternative arrangements, it may not be required to have a discrete inner tubular element between the valve plunger and the former tube. The entry to the outlet nozzle then forms the dosing opening. However such a tubular element is preferably retained because it is found to contribute to uniformity of dosing. The tubular element may then be fixed or, where the mean position of the piston is adjustable, it may be adjustable with the piston so as to have a similar effect at all positions of adjustment. 
     In a further form of the invention the stroke of the piston is varied in order to control the dose size dispensed. In this example also the sleeve 10 is preferably retained because it contributes to the uniformity of dosing. The sleeve may be displaceable, although the dose size is now determined by the piston stroke, or it may be completely fixed. If fixed in place, it may assume a position such as that shown in FIG. 3, in which it will not throttle the flow when the piston is set to its maximum stroke. If movable, its displacement is preferably synchronised with the change of stroke of the piston by interlinking the mechanisms for these two adjustments. 
     In one embodiment, shown in FIGS. 8 and 9, the piston is driven from a crank mechanism. Crank shaft 86 has crank pin 88 attached to it through a mounting bar 90 that is diametrically displaceable relative to the crank shaft axis. The crank shaft and a control shaft 92 extending through the craft shaft are rotated together by an input drive 94. The control shaft is mounted coaxially in the crank shaft on bearings 92a and the input drive 94 includes means for adjusting the relative angular positions of the crank shaft and control shaft. Such means for adjustment of a pair of co-rotating shafts are known in the art and are not illustrated in detail. The control shaft terminates in an arm 96 carrying an eccentric pin 98 that is located in a transverse slot 100 in the mounting bar. Rotational adjustment of the control shaft pivots the arm 96 and, through the pin and slot engagement, displaces the mounting bar 90 diametrically to the crank shaft. The radial offset of the crank pin 88 from the crank shaft axis is then altered. As a result, the throw of a connecting rod 102 journalled to the crank pin 88 is altered and the stroke of the piston is changed. FIG. 8 shows the connecting rod 102 connected to the piston stem 16a through a coupling 104 that ensures rectilinear motion of the valve stem 16a. 
     FIG. 10 is a general view of the form-fill apparatus in which dosing apparatus as already described can be incorporated, although FIG. 10 shows only the dosing valve piston 16 and piston stem 16a of the dosing apparatus. The filler material is fed through a feeder tube to the tube 2. The web W of packaging material is drawn over a shaping guide 120 near the upper end of the former tube 4. Here the initially flat web W turns downwards from an upwardly inclined path to take up the tubular form of the former tube exterior, as indicated by the chain-like outline W&#39;, and is drawn down the tube while its opposite side edges are sealed together as it approaches the lower end of the tube. Immediately below the feed tube the web is first sealed transversely by sealing means 122 in synchronism with the delivery of the doses of particulate filling from the interior of the former tube to form individual packets containing doses of the material, and the chain of packets is then separated by a cutting operation. 
     The web is drawn down the outer face of the former tube 2 by pairs of rollers. These include pairs of heating and pressing rollers 124,126 between which the opposite edges of the web are sealed together longitudinally with a butt weld. The welded seam is then laid down against the tubular web by a roller and disc pair 128. 
     The transverse sealing means 122 for each path comprise two pairs of rotors 130, the axes of the two pairs of roters being at 90° to each other and to the web axis and the arms 132 of the rotors 130 interdigitating or interlacing to operate in alternation on the tubular web in order to produce tetrahedral-form packets. In the form illustrated, the apparatus has a corresponding arrangement of cutting rotors (not shown) below the sealing rotors. It is of course possible, however, to employ a single pair of rotors for compartmenting the web and a parallel pair of rotors for severing the compartmented packets to produce flat packets containing the filling material.