DEVICE FOR VARYING THE OPENING BETWEEN THE WELDING ELEMENT AND THE COUNTER-WELDING ELEMENT IN PACKAGING MACHINES

Abstract: In machines for the continuous packaging of products inside a film of a plastic material, folded above said products, so as to form a continuous tubular wrapping, a device for changing the opening between the welding (12) element and the counter-welding element (13) makes it possible the operating distance between said elements (14, 13) to be changed as a function of the height of the products in course of packaging, thus ensuring the highest packaging speed for both low- and high-thickness products.

Description: The present invention relates to a device for varying the spacing between the welding element and the counter-welding element in packaging machines. In the packaging machines for the automatic packaging of products fed in sequence inside a continuous film of a thermoplastic material, e.g., suitably folded above and/or under said products, so that a continuous tubular element is obtained, a device is provided, which comprises a transversal upper welding element and lower counter-welding element, such as to realize a set of wrappings which enclose the products inside the thermoplastic material and separate them from one another. One of such devices is disclosed in FR-A-2 297 773 wherein on a carriage, alternatively movable in the direction of running of the conveyor belt on which products fed above said film of thermoplastic material are positioned, an upper welding element and a lower counter-welding element are provided, which constitute the welding unit and are positioned on opposite sides relatively to said material, and provided with a vertical reciprocating motion. Said welding unit, by combining the essentially horizonal movement of the carriage with the vertical reciprocating motion of the bars, results therefore in a substantially elliptical trajectory. The relative distance between the two bars is fixed, independently from the height of the products to be packaged, and from the fact that the counter-welding element too is more or less movable in a vertical direction. In fact, if on one hand an adjustment can be carried out by modifying the position of the point at which the counter-welding element has its operating top stop point, on the other hand, by so doing, a corresponding shift upwards of the welding bar is determined, because the relative operating distance, or spacing, between the two bars in their resting position must remain unchanged, and equal to the factory setting carried out when the packaging machine was manufactured. Such an arrangement considerably limits the speed of the machine, above all in the presence of limited-height products, because the actual stroke of both bars remains fixed, and has always its maximum value. A purpose of the present invention is to provide a device which makes it possible the maximum height of spacing of the welding unit to be changed with varying heights of the product to be packaged, so as to make it possible as-high-as-possible packaging speeds to be taken advantage of, with such values of the welding pressure between the welding bar and the counter-welding bar being simultaneously secured, as to optimize at the same time both the cutting and the welding of the thermoplastic material. These and still other purposes according to the present invention are achieved by providing a device according to claim 1. The structural and functional characteristics, and the advantages of a device for packaging machines according to the present invention will be better understood from the following disclosure, given for exemplifying and non-limitative purposes, referred to the schematic drawings, wherein: Figure 1 shows a perspective view of a device according to the present invention, with the welding element and the counter-welding element being in their opened position for a product to be packaged having a minimum height; Figure 2 shows a schematic side view equivalent to that of Figure 1, with the welding element and the counter-welding element being in their opened position, and with the device being adjusted for handling a product to be packaged having a minimum height; Figure 3 shows the same view of Figure 2 in the welding position; and Figure 4 shows a view equivalent to that of Figure 2, with the device being adjusted for handling a product having a considerable height. In a packaging machine, not shown in the figures, products to be packaged, positioned in sequence after each other at regular distances, and already wrapped inside a continuous film of plastic and/or thermoplastic material in a tubular arrangement, are fed above a conveyor belt, schematically shown in 11, towards a per se known welding unit, essentially constituted by an upper welding element 12 and a lower counter-welding element 13. Said welding unit is of the type wherein the welding element 12 and the counter-welding element 13 are vertically movable by a reciprocating motion, and are borne by a carriage schematically indicated by the reference numeral 14, which is provided with a substantially horizontal reciprocating motion in a parallel direction to the direction of the conveyor belt 11. In such way, the welding unit can be moved according to an elliptical movement relatively to the product-containing thermoplastic material, so that said motion makes that the welding element and the counter-welding element accompany the feeding movement of the conveyor belt while they perform their stroke of mutual approaching. Furthermore, such a movement makes the welding element and the counter-welding element remain into contact, in a temporary position of engagement for a long enough time, so as to secure that the transversal cutting and welding of the interposed film are perfectly carried out, realizing the leading end and the trailing end of the packaged products. The essentially horizontal reciprocating movement of the carriage driven in a known way, and its stroke can be adjusted by means of also well-known control means. The vertical reciprocating motion of the welding unit is performed inside a vertical guide 10 for said carriage 14, so that the welding element 12 and the counter-welding element 13 can be driven to move to be shifted between resting, mutual spaced-apart positions and a mutual-engagement position. In the device according to the present invention, the movement is derived, e.g., from a shaft 15 coupled with the central drive means (not shown in the figures) to revolve according to a continuous rotation motion, and driving an oscillatory-motion-generating means, such as a reverser unit 16, from which a shaft 17 protrudes, which is provided with said predetermined, constant-angle oscillatory motion. A set of three idle rolls 18 are installed on the carriage in correspondence of the operating area of the welding unit, so that the conveyor belt 11 is diverted in such a way as not to interfere with the welding element 12 and the counter-welding element 13. The lowest idle roll 18, in cooperation with the other two rolls 18, causes the belt 11 to be diverted from the plane of its advancement and forms a space wherein the welding bar 12 ad the counter-welding bar 13 can run. A device for changing the height of the spacing between the welding element and the counter-welding element according to the present invention is interposed between the welding unit and the shaft 17 provided with oscillatory motion. In particular, said device is composed by crank means and countershafts, such as to transmit the vertical reciprocating oscillatory motion to the welding unit along a variable stroke with varying heights of the products to be packaged. On the shaft 17, a support block 19 is key-constrained, which supports a first adjustment-control unit generally indicated by the reference numeral 20. The first adjustment-control unit 20 comprises a pair of guide studs 21 on which a cross member 22 slides, driven to move by a screw-nut screw coupling constituted by the screw 23 parallel to said guide studs 21, and a nut screw 24 provided inside said cross member 22, with said screw 23 being actuated by means of a handwheel 25 positioned on an upper member, fastened to the guide studs 21 of the same adjustment-control unit 20. Opposite ends of said cross member 22 bear hinge-pivots 26 and 27, protruding outwards according to the direction of an axis of said cross member 22, which is parallel and eccentric relatively to the axis of revolution of the shaft 17, respectively acting as the end drive for a first rod 28 and for a second rod 29. At their other end, said first rod 28 and second rod 29 are respectively hinged, in 30 and 31, to a first bell crank 32 and to a second bell crank 33 supported by an intermediate countershaft 34. The first bell crank 32 is keyed on said intermediate shaft 34, whilst the second bell crank 33 is positioned on said same shaft 34 with the interposition of a freely rotatable support element, which makes it possible the bell crank 33 and the shaft 34 to revolve relatively to each other, such as, e.g., a rolling bearing 35. Onto the respective free ends of the first bell crank 32 and of the second bell crank 33, in 36 and 37 a third rod 38 and a fourth rod 39 are respectively hinged, with said third rod 38 being furthermore provided with an elastic compensation means 40 for the adjustment of the pressure exerted between the welding element 12 and the counter-welding element 13, which are respectively hinged onto said third rod 38 - in 42 - and onto said fourth rod 39 - in 41. The intermediate shaft 34 is supported in its turn by rotatable-support elements 43 integral with a second adjustment-control unit generally indicated by the reference numeral 44. The second adjustment-control unit 44 is at all similar to the first adjustment-control unit 20. In fact, in an exemplifying form of practical embodiment, it is costituted by a cross member 45, with which said rotatable-support elements 43 are integral, with the cross member 45 being slidingly guided by a pair of guide studs 46 integral with the machine frame. The drive for said cross member 45 to slide is supplied by a screw-nut screw coupling constituted by the screw 47 parallel to said guide studs 46, and a nut screw 48, provided inside said cross member 45. An end of the shaft provided with said screw 47 is driven to revolve by means of a bevel gearwheel 49 coupling by a hand-operated handwheel 50, which enables the countershaft 34, or, better, both rotatable-support elements 43, to perform their adjustment movements. Integral with both said cross member 22 of the first adjustment-control unit 20, and directly with the countershaft 34 of the second adjustment-control unit 44, pointer-indicator means 51, 52 are provided, together with fractional scales 53, 54, relating to the translational shift of the cross member 22 and of the intermediate shaft 34 which must be carried out when the product to be packaged has a certain height H. In the figures, as the heights H of a product to be packaged, values of from 0 to 100 mm are indicated, which values should not be construed as having limiting purposes, but are only exemplifying of the operating way of the device according to the present invention . The same remark is true for the angle "β" of oscillation of the shaft 17, which, in the example shown has a predetermined and constant value of approximately 30°, but may have any other advantageous values suitable for supplying the welding unit with the desired reciprocating motion. The operating way of a device according to the present invention can be easily understood on the basis of an observation of the hereto attached drawings. In fact, for a product to be packaged having a relatively small height, the operator firstly acts, by starting from the position depicted in figure 1, on the second adjustment-control unit 44, and revolves the handwheel 50 until the pointer 52 reaches the height of the preselected product to be packaged, as reported on the scale 54. By so doing, one can observe that, with the intermediate shaft 34 rising upwards, the first rod 28 obliges the same intermediate shaft 34 to revolve in counterclockwise direction - frontally observing figure 1 -, and, owing to the presence of the first bell crank 32 causes, through the third rod 38, the welding element 12 to shift downwards. Simultaneously, the presence of the second rod 29, of the second bell crank 33 and of the bearing 35, and, finally, of the fourth rod 39, causes, still through a counterclockwise revolution, the counter-welding element 13 to temporarily move downwards. The operator acts then in an identical way on the first adjustment-control 20, making the cross member 22 move upwards until the pointer 51 reaches the preselected height on the scale 53. By so doing, the eccentricity of the hinge points 26 and 27 is changed, and the angle is increased, over which they run when the shaft 17 runs over the predetermined and constant angle "β". The action performed by the first rod 28, the first bell crank 32 and the third rod 38 makes the intermediate shaft 34 revolve clockwise, and the welding element 12 consequently move upwards. Simultaneously, the presence of the second rod 29, of the second bell crank 33, of the bearing 35 and finally of the fourth rod 39 causes, still by means of a clockwise revolution, the counter-welding element 13 to move upwards. Therefore, the device positions itself as shown in figure 2, and the plane of welding and cutting engagement results to be positioned at a distance of H/2 above the plane of the conveyor belt (see figure 3). Thus, the results has been obtained that the transversal welding is carried out at a height corresponding to half height of the product to be packaged, with the consumption of plastic material being minimized, and an aesthetically pleasant and correctly done package being obtained. At the same time, the result has been obtained that the welding element 12 and the counter-welding element 13 are so positioned as to minimize the time required for said elements to run over their operating stroke, making it possible the packaging machine to run at very high packaging speeds, above all if such speeds are compared to those which could be obtained according to the prior art. Figure 2 shows that the lifting and the spacing between the welding element and the counter-welding element is reduced to the essential minimum. Then by looking at figure 4, one can see that, when the product to be packaged has a rather considerable height, by acting on both adjustment-control units 20 and 44, as hereinabove disclosed, the arc over which the hinge points 26 and 27 run in correspondence of the constant angle "β", and, consequently, the spacing between the welding element and the counter-welding element, is increased, with the results being obtained that, while the packaging treatment of a product of considerable height becomes now possible, at the same time all possible dead times are minimized. In both cases, both in case of normally low products, and in case of normally high products, the presence of the two adjustment-control units 20 and 44 and of the compensation means 40 keep unaltered the values of pressure between the welding element and the counter-welding element at the different welding heights H and at the different amplitudes of spacing between both elements. Furthermore, one can observe that with increasing heights H of the product to be packaged, the counter-welding element is shifted towards the plane of the conveyor belt 11, whilst the welding element is positioned at a level slightly higher than the maximum height of the product, so as to prevent any interferences with it.

Claims: Device for varying the spacing between the upper (12) and the lower counter-welding and cutting elements (13) of a packaging machine of the type wherein the products to be packed are positioned in sequence on a conveyor belt (11) and are wrapped inside a continuous tubular film of a plastics material, said device comprising a carriage (14) driven to horizontally reciprocate in the transport direction of said conveyor belt (11), a welding and cutting unit composed by upper and lower counter-welding and cutting elements (12,13), respectively mounted on said carriage (14) at opposite sides in relation to said tubular film, and vertically reciprocatable towards each other in order to perform a temporary engagement operation of said welding and cutting elements with said plastic film held between them, and means (18) for locally diverting said conveyor belt in correspendence of the horizontally reciprocating movement of the carriage downwardly and around said counter-welding and cutting element (13), so as to prevent said conveyor belt (11) from running across the spacing between said welding and said counter- welding and cutting elements, there being provided drive means (15,16) providing said continuously oscillating and vertically reciprocating motion, and an adjustment unit (20) to adjust the inoperative end positions of said welding and counter-welding and cutting elements, respectively, there being further provided a second adjustment unit (44) for adjusting the vertical position of an intermediate common countershaft (34) of linkages (29,33,39; 28,32,38) which connect said first adjustment unit (20) to said welding and counter-welding elements and cutting elements, respectively, in order to displace the operative positions of said welding and cutting elements in accordance with the intermediate height position of the product on said conveyor belt said linkages comprising a first rod (28) and a second rod (29), with both said rods (28,29) being hinged at one of their ends to said first adjustment unit (20) constrained to said vertically oscillating motion supplying drive means (15,16), and, at their other end, to a first bell crank (32) and a second bell crank (33), respectively, which are mounted on said intermediate countershaft (34), with said first bell crank (32) and said second bell crank (33) bearing, hinged to their other end, a third rod (38) and a fourth rod (39), which in their turn are respectively hinged to said element and said counter-welding and cutting elements, with said intermediate counter-shaft (34) being rotatably supported on said second adjustment unit (44), said first bell crank (32) being keyed to said intermediate countershaft (34), and said second bell crank (33) being positioned on a rotatable support element (35) freely mounted on said intermediate countershaft (34), said first bell crank (32) and second bell crank (33) being rotatable in opposite directions. Device according to claim 1, characterised in that said first adjustment unit (20) is positioned on a shaft (17) projecting from said drive means (15,16) supplying the oscillating motion in order to vary the eccentrical position of said linkages (29,33,39; 28,32,38). Device according to claim 1, characterised in that said oscillating motion supplying drive means is a shaft (17) protruding from a reverser unit (16), provided with a predetermined constant-angle oscillating motion. Device according to claim 1, characterised in that said first adjustment unit (20) essentially comprises a cross member (22) slidingly guided by guide studs (21) and driven by a screw-nut screw coupling (23,24), said cross member (22) bearing rotatable link elements (26,27) linking said linkages (29,33,39; 28,32,38) to said oscillating motion supplying drive means (15,16). Device according to claim 1, characterised in that said first adjustment unit (20) and second adjustment unit (44) comprise at least one indicating pointer (51,52) and a respective fractional scale (53,54).

Inventors: BALLESTRAZZI, ARIS, TASSI, LAMBERTO
Applicants: SITMA S.P.A.
Application year: 1988
Main classification: B65B51
IPC codes: B65B51, B29C65