Packaging machine for the continuous packaging of products having a variable size

Abstract: A packaging machine suitable for the continuous packaging of products, or of groups of products (12) having a different shape and size in height, wherein, thanks to a particular combined movement of the transversal welding unit (18), both of sinking down towards the product, and of accompanying of the same product during the welding step, relatively to a car for its essentially horizontal shift, a quick and correct packaging of the products is obtained, even very different as regards the length in the direction of advancement of the packaging film, besides as regards the height, with the consumption of the packaging material being minimized to the strictly necessary amount, and the continuous packaging after each other being made possible of products or of product groups, having mutually different dimensions.

Description: The present invention relates to a packaging machine for continuously wrapping products having a variable size. A packaging machine as defined in the preamble of claim 1 is described in GB-A-2 024 760. Packaging of products or groups of products in packaging machines which are provided with a lower conveyor unit, on which the products to be packaged are fed towards a transversal welding unit, are known. Under said welding unit, the product, once that the conveyor belt is stopped, is welded inside the packaging film, after which the again started conveyor unit carries out the final discharge of the package towards a heat-shrinking oven, or towards a side longitudinal welding unit before the possible heat-shrinking operation suitable for individuating a correctly done package. It clearly appears that this type of packaging causes a time wasting operation owing to the stop, with the consequent loss of production and limited packaging speed. A first solution of the problem had been proposed by causing the products to continuously advance on a closed-loop conveyor belt constituted by a silicone-treated material, above which the upper welding element acted, with a vertical motion being supplied to the same upper welding element by means of a pneumatic piston. In this way, the same belt, besides acting as a conveyor means, performs the function of the counter-welding element, or lower welding element. Thus, packaging is carried out in a nearly continuous way, however causing the serious problem of the considerably large consumption of wrapping material, which increased, above all, when the product to be packaged had a rather considerable size, e.g., when it is a parcel of the height of a bottle, or when it even is a group of bottles. A different solution was given by proposing lower conveyor means provided with counter-welding elements positioned at a constant pitch from each other, on which a welding element sinks, by being pushed by a pneumatic piston. In both above-mentioned solutions, there was hence a downward movement time and an upwards return movement time, which was strictly a function of the speed of the pneumatic device which drove the welding element, and a non-constant welding time, because it had to match the different speeds, and the descent of the welding element and the same welding step had to be correlated to the products continuously fed after each other. All said systems known from the prior art, by being a combination of mechanical movements and of pneumatic movements, require continuous adjustment when the speeds are changed, as well as when the product to be packaged is changed, and inasmuch as the mutual enslaving of the various operating units is very complex, misadjustments are very likely to occur. A further solution to the problem was given, but unfortunately for packaging machines for low-thickness products only, by using transversal welding units installed on board of a carriage, and vertically movable, so as to be supplied with a movement of elliptical type, which enable a certain saving in packaging material to be achieved, but does not reach a valid solution of the initial technical problem, which is that of minimizing the amount of wrapping thermoplastic material needed in order to wrap the products to be packaged, independently from their size, above all, from their height. The purpose of the present invention is on the contrary the solution of said problems in a continuous packaging machine, in such a way as to reduce to zero the stop times necessary for the transversal welding, or even for a possibly necessary and carried out longitudinal welding, with the productivity and the packaging rate thus being increased. This purpose according to the present invention is achieved by providing a packaging machine with the features as defined in the characterizing portion of claim 1. The structural and functional characteristics and the advantages of a packaging machine according to the present invention will be better understood from the following description referring to the drawings, wherein: Figure 1 shows a side elevation view of a packaging machine, wherein the film path with the relevant unwinding units, and the drive mechanisms driving the conveyor belts are shown; Figure 2 shows an enlarged longitudinal sectional view of the machine of Figure 1 in its welding position; Figure 3 shows an enlarged longitudinal sectional view equivalent to that of Figure 1, in a different operating position; and Figure 4 is a chart showing the combined motion of the welding unit and of the carriage. Referring to the drawings, a continuous packaging machine according to the present invention comprises a framework, generally indicated by the reference numeral 11, on which a plurality of operating units - the transversal welding unit, the product conveyor units, the drive units, the unwinding units for unwinding the continuous wrapping material, and so on - are installed. Individual products, or groups of products to be packaged are indicated by the reference numeral 12. They have sizes, both in height and in length dimensions, which may vary from one another. These products are fed towards the welding station according to a whatever order, such as books, newpapers, magazines, bottles, containers, parcels, and the like. As depicted in the figures, a wrapping or packaging material 13, such as, a continuous heat-shrinking plastic film, is fed by a couple of bobbins 14 respectively positioned on an upper unwinding unit 15 and on a lower unwinding unit 16, fitted with compensating means 17, such as so-said "dancer rolls", which enable said same film 13 to be constantly, continuously and parallelly fed to a transversal welding unit, generally indicated by the reference number 18, which constrains said film around the product 12, cutting it and welding it in correspondence of the leading edge of the downstream and the trailing edge of the upstream product 12 (Figure 1). The product 12 is fed by a conveyor belt (not shown in the figures) onto a first conveyor belt 19 installed upstream said transversal welding unit 18 and is subsequently advanced by a second conveyor belt 20 installed downstream of said transversal welding unit 18. Both said conveyor belts 19, 20 run along a closed-loop path and are caused to revolve by a couple of drive rolls 21, linked with each other by a chain transmission 22, and driven by a transmission 23, also of chain-transmission type, driven by a main centralized motor-speed variator unit 24, which is suitable for supplying the drive to all the operating units of the packaging machine. The conveyor belts 19 and 20 each constitute an essentially trapezoidal closed loop path wherein the mutually opposite sides of both paths show a "C"-shaped recess which is individuated by a stationary return roll 25 fastened to the framework 11. At the ends of said sides of said "C"-shaped recess, two further rolls 26 and 27 are positioned, which are horizontally movable relatively to the framework 11. In fact, the upper roll 26 is integrally rotatable relatively to a central carriage 28, on which said transversal welding unit 18 is mounted, whilst the lower roll 27 is integrally rotatable relatively to a belt length compensating device 29, so designed as to link both said lower rolls 27 of both conveyor belts 19 and 20 (Figure 2). Such a compensating device 29 connects the lower end of two chain portions 30 which, after running around two sprocket wheels 31 coaxially positioned relatively to the stationary rolls 25, are constrained to the central carriage 28, at the top thereof, next to the corresponding upper roll 26. A plurality of supports 32, constrained to the chain portions 30, bear an equal number of rolls 33 constituting a roller apron on which upper portions of both conveyor belts 19 and 20 slide in the area wherein the product 12 are fed. The chain portions 30 slide on a flat guide 34 which is integral with the framework 11; also integral with the framework 11 is a further flat guide 35 on which the compensating device 29 is guided by means of rolls 36 integral with it. The framework 11 furthermore supports further flat guides 37 on which support rolls 38 slide, which are integral, at the bottom, with the central carriage 28, so that also said central carriage 28 can horizontally translatable. The central carriage 28, which is horizontally reciprocable, is provided with shoulder portions 39, which extend upwards and through which slots 40 are provided, inside which support rolls 41 slide, which support the opposite ends of an upper welding bar 42 vertically movable inside said slots, which, together with a lower welding bar 43, stationary relatively to the central carriage 28, constitutes the above-said transversal welding unit 18. Inside said shoulder portions 39 and said same carriage 28, the film 13 runs (Figure 1), according to a vertical direction parallel to the direction of movement of the welding bar of the transversal welding unit 18. Said film is continuous, in that the film coming from the upper bobbin, and the film coming from the lower bobbin have been previously made integral with each other by means of a transversal welding. More precisely, the film 13 coming from the upper bobbin 14, once that it has left the upper unwinding unit 15, is guided by a return roll 75 between the shoulder portions 39 of the carriage 28 towards a calender 76 which drives the film being unwound from the lower bobbin 14 made revolve by the lower unwinding unit 16 and positioned under the upper rolls 26, and it too on board of the central carriage 28, and made revolve by a transmission 78 integral with the upper roller 26 of the second conveyor belt 20. The above said calender 76 acts as a means for guiding, driving and unwinding the film 13, which comes from the lower unwinding unit 16 and is deviated towards it by return rolls 77 integral with the framework 11 of the machine (Figure 1), and is engaged on said film by actuator means 79 constituted by a cylinder and controlled by suitable sensor means. The lower welding bar 43, which is positioned in the gap between the two conveyor belts 19, 20, has its upper surface approximately at the same level as said belts, such that a continuous film curtain is provided in said gap. The horizontal reciprocating movement of the central carriage 28, as well as the vertical movement of the upper welding bar 42 are determined in a purely mechanical way according to a certain law deriving from the particular structure given to a cam-crank and slotted link unit coupled with corresponding levers which transmit the motion to the upper welding bar, and to the welding unit supporting carriage, which furthermore enables the upper, inner, mutually-opposite ends of both conveyor belts to be shifted. In fact, exiting from said centralized motor-speed variator unit 24 (Figure 1), a toothed belt 44 transmits the movement to a reduction gear 45, with the interposition of a brake-clutch unit 46. Furthermore, a small transmission 47, e.g., a chain-type transmission, drives a main intermediate shaft 48 to revolve, from the ends of said main intermediate shaft 48 the revolutionary motion being taken, which drives a cam 49 which controls the movement of the upper welding bar 42 and respectively the movement of a swinging crank and slotted link 50 for the horizontal reciprocating movement of the central carriage 28 (Figure 2). The main intermediate shaft 48 is integral, at an end, with the center of a disk-cam 49, which is provided with an eccentrically-positioned groove 51; and at its other end, said main intermediate shaft 48 is integral with an eccentric lever, i.e., a crank 52; with a pin 54, which drives the swinging lever, i.e., the crank and slotted link, 50, being suitable for being radially positioned inside a groove 53 provided in said crank 52. The position of said pin 54 inside the groove 53 is adjustable relatively to said main intermediate shaft 48. Now, examining at first the drive of the upper welding bar 42, one can observe that inside the eccentric groove 51 of the disk-cam 49 an idle roll 55 is inserted, which protrudes from an intermediate portion of a swinging lever 56, which is hinged, at its corresponding lower end, 57, and at its other end bears an articulated, adjustable lever 58. Said articulated lever 58 is linked in its turn to a drive lever 59 keyed on a reciprocating shaft 60 which bears, at its opposite ends, a couple of levers 61 which drive the movement of the upper welding bar 42, and are linked to said upper welding bar 42 by means of respective tie-rods 62, each of which incorporates a shock-absorber mechanism, not shown in the figures, in order to optimize the transversal welding of the wrapping film 13. The crank 52, installed at the other end of the intermediate shaft 48, by causing the pin 54 to rotate, causes the crank and slotted link 50 to swing; with such crank and slotted link 50 the central carriage 28 is articulatedly linked by means of an adjustable tie-rod 63. Said central carriage 28 is thus caused to reciprocate. The crank and slotted link 50 is provided with a groove 80, inside which a runner or pad element 81, positioned on the end of said pin 54, can slide. The pin 54 can be shifted in an adjustable way inside the groove 53, e.g., by means of an adjustment screw 64, so that the length of the stroke of the central carriage 28, or, better, the amplitude of its reciprocating movement, can be changed as desired, with varying lengths of the product to be packaged. In this way, by adequately adjusting the length of the stroke of the carriage 28 which bears the welding unit 18, the speed thereof can properly match the speed of the conveyor belts with varying product lengths. The upper unwinding unit 15 is driven by a kinematic transmission which draws the motion directly from the out let end of the centralized motor-speed variator unit 24, with a speed reduction gear 65 and a brake-cluth unit 66 being interposed (Figure 1). On the contrary, the lower unwinding unit 16 draws its motion from a sprocket wheel 67, which interacts with the chain transmission 22 which drives the driving rolls 21 of the conveyor belt 19 and of the conveyor belt 20. Said sprocket wheel 67 drives a chain 68 which, with the interposition of a coupling 69, causes an unwinding roll 70 to revolve in order to unwind the lower bobbin 14, whenever necessary. Together with these devices of essentially mechanical type, suitable sensor elements are provided in the machine, which control and correlate the various movements of the packaging machine, so as to cause it to perfectly and correctly operate, in particular acting on the movement of the main carriage, and on the movement of the upper welding bar, in order to achieve the purpose of the invention. For example, at the inlet side of the machine, a first set of photocells 71, vertically positioned on the framework 11, is provided (Figure 1), which detect the arrival of the product, or of the products 12, defining the size in height thereof, and consequently presetting a time corresponding to a "low", to a "medium" or to a "high" product), for the actuation of the upper unwinding unit 15. The welding cycle is then started by a second photocell 72, which is preferably positioned on the same plane as of the first conveyor belt 19. In fact, said first conveyor belt is preferably composed by two conveyor belts placed side-by-side and spaced apart from each other wherein, in the gap between their adjacent sides, an upwards-facing receiver element (not shown in the figures) for said photocell 72 is positioned. A third photocell 73 is also positioned in the area between said two side-by-side belts of the first conveyor belt 19, next to its end outlet portion and, once that it detects the arrival of the leading edge of the product, starts by means of the cylinder 79, the engagement of the drive calender 76 on the film 13, thus enabling the plastic film 13 to wrap on both the upper and lower sides of the product and to advance it by the conveyor belts 19 and 20 and possibly, with the drive calender 76 being disengaged only when the trailing edge of the product is detected. Of course, the lower unwinding unit 16 determines the unwinding of the film from the lower bobbin 14 when the compensator means 17 command the coupling 69 to engage, so as to make the unwinding roll 70 revolve. Finally, a fourth photocell 74 can be and optionally provided, which is positioned beyond the gap between the two conveyor belts 19, 20, or better, at the inlet end of the second belt 20 and above it on the framework 11, which, by detecting the trailing edge of the passed and packaged product, controls the perfect prosecution of machine's operation and allows sich prosecution. The provision of said sensor elements or photocells allows the operation of the packaging machine according to the present invention to be easily understood. In fact, as hereinabove said, a conveyor means feeds the products towards the packaging machine and said feed is initialy detected by the first set of photocells 71 at the inlet end of the first conveyor belt 19. Thereafter, the product continues to advance on board of the conveyor belt 19, until the passage thereof in correspondence of the second photocell 72 confirms the feed, and the third photocell 73 commands the drive calender 76 to reach its engagement position, with the lower unwinding unit 16 being started, if necessary, thus enabling the film 13 to wrap the product both at the top and at the bottom, in that the film coming from the upper bobbin of the upper unwinding unit 15 is bonded to the film coming from the upper unwinding unit, by means of a transversal welding previously carried out. When the second photocell 72 detects the trailing end of the product 12, said detection starts the cycle of welding-central carriage shifting by means of the brake-clutch unit 46 which, by getting engaged, enables the motion to be transmitted. Of course, when also the third photocell 73, detects the trailing edge of the product 12, it disengages the drive calender 76 and causes the lower unwinding unit 16 to stop, so that, after that the welding and the cutting of the film have been simultaneously carried out, said film positions again itself in a nearly vertical position inside the carriage 28, nearly parallel to the direction of movement of the welding unit, ready to receive a new product. The engagement of the brake-clutch unit 46 makes the disk-cam 49 revolve, in order to actuate the upper welding bar 42, and makes the crank and slotted link 50 start to swing, which causes the central carriage 28 to reciprocate. From Figure 4, one can observe that the (A) step of approaching of the welding bar towards its position of engagement with the material to be packaged, the (C) step of removal, and the (D) step of car return are rather fast, whilst the (B) step of accompanying during the welding step is slower. By the "O" character, the stand-by position at which the welding cycle starts is indicated, and in dottes lines the film-wrapped product is indicated, wherein the minimizing in wrapping film consumption can be observed. It should be observed that the (A) step, and the (C) step, respectively of approaching and of removal of the welding bar, take place on a nearly vertical direction, with the welding unit travelling in the same direction of advancement as of the conveyor belts, still in order to minimize the consumption of the packaging film. According to a generic and exemplifying formulation, the whole cycle could be subdivided, as regards the total revolution angle, into three angles of approximately 100° each, for the first three (A), (C) and (D) steps, and an angle of 60° as regards the last (B) step, of accompanying during the welding step. The combination of the movements of said cam and of said swinging crank and slotted link enables a combined movement to be obtained, which is determined in a completely mechanical way, essentially comprising a step of approaching of the welding bar towards said products wrapped inside said packaging material, an accompanying step during the welding step, a removal step, and a step of quick return to the stand-by position, and representable by means of an upside-down isosceles trapezium with inclined, curved sides. The important point is that during the (B) step of accompanying during the welding step, the central carriage 28 horizontally moves in such a way that its motion, causing a change in length of both portions of conveyor belts 19 and 20 in correspondence of the rollers 33 which constitute the so-said roller apron, enables the movement of the belts 19, 20 to be equated, so that the transversal welding unit 18 remains closed for the necessary time for a correct welding of the wrapping film to be obtained. This is the so-said "slow step" of the welding cycle. The movement of the conveyor belts 19 and 20 in order that the upper portions thereof facing towards the product may vary relatively to each other, and consequently the underlying roller aprons which support them may vary as well. This is possible because the upper rolls 26 translate together with the carriage 28, by being integral with it, whilst the lower rollers 27 are made integral with a conveyor belt compensating and tightening device 29 and with the chain portions 30, and exactly move in the opposite direction to the direction of displacement of the upper roll 26 positioned on the same side, and next to the end of said chain portion 30. In fact, one could consider that the two chain portions 30, the tightening device 29 and the lower body of the central carriage 28 constitute a closed loop which can move around both idle coaxial sprocket wheels 31, free of rotating relatively to the stationary rolls 25, revolutionary and integral with the framework 11. In this way, inasmuch as the upper, movable welding bar 42, positioned in a nearly bridge-fashion on the upwardly extending shoulder portions 39, is driven by a cam, and inasmuch as with this movement the movement is combined with that of the carriage 28 which supports the welding unit, which is driven by a swinging crank and slotted link. Thus, a combined movement of sinking of the welding bar, and of accompanying of the product with the carriage during the welding step, derives which, by realizing the transversal welding precisely next to the product, enables a saving in the amount of the plastic material used for the packaging to be obtained, with an as small amount thereof as possible being consumed. Precisely the arrangement of the welding bar in a bridge-position, the possibility of actuating the cycle of welding at the trailing edge of the product, and the detection of the height of the product being packed enables the optimization in packaging film consumption to be achieved, independently from the height of the product, or of the products to be packaged, with any stop times being got rid of. Advantageously, it should be observed that in a machine according to the present invention, inasmuch as the transversal welding unit 18 can be turned on at the end of the same product 12 by means of the intervention of the photocell 72, products of any lengths can be packaged.

Claims: Packaging machine for continuously wrapping products (12) having a variable size, said packaging machine comprising a framework (11), which supports conveyor means (19,20) running along a closed loop path for conveying said products (12) to be wrapped through a sealing station and a transversal welding unit (18) to perform the transversal welding operation in a wrapping material (13) in a gap provided in said conveyor means, said wrapping material passing said conveyor means and forming a curtain into which said products (12) to be wrapped are fed, said wrapping material (13) being fed by a pair of bobbins (14) respectively positioned on an upper (15) and a lower unwinding unit (16), a horizontally reciprocable carriage (28), said carriage (28) carrying a conveyor length compensating device (29), said welding unit (18) which is composed of a vertically reciprocable upper (42) and a stationary lower welding bar (43), the latter being positioned at the same level as the carrying surface of said conveyor means, and a product pressing device (83), said product pressing device being vertically reciprocable above said products, and sensor means (72,73,74) for monitoring the position of said products (12) on said conveyor means, said sensor means (72, 73,74) activating motor means (24) and actuator means (23, 44) for the drive transmission means, characterised in that said conveyor means are composed of a first (19) and a second conveyor belt (20), each of them running along a closed loop path defining therebetween said gap, and in that said curtain passes in a vertical direction through said gap between said first and said second conveyor belt. Packaging machine according to claim 1, characterised in that said first conveyor belt (19) and said second conveyor belt (20) each constitute an essentially trapezoidal closed loop path, wherein mutually opposite sides of said two paths define a "C"-shaped recess which is constituted by a stationary roll (25) fastened to said framework (11), and by an upper roll (26) and a lower roll (27) which are positioned at the respective ends of said sides, with said upper roll (26) being said return roll constrained to said carriage (28) and said lower roll (27) being are return roll positioned at the corresponding lateral ends of said conveyor length compensating device (29). Packaging machine according to claim 2, characterised in that the ends of said compensating device (29) are fastened to chain portions (30), which run around sprocket wheels (31) coaxial with said stationary rolls (25), and at their other end are fastened to said carriage (28), next to the corresponding upper rolls (26). Packaging machine according to claim 3, characterised in that a plurality of supports (32) are provided on said chain portions (30), said supports bearing rolls (33) defining a roller apron on which portions of said first conveyor belt (19) and second conveyor belt (20) slide. Packaging machine according to claim 1, characterised in that said motor means (24) drives with the interposition of a first brake clutch unit (36), selectively actuated by said sensor means (72,73,74), an intermediate shaft (48) to revolve in order to actuate a cam (49) for the vertical movement of said upper welding bar (42) and for actuating a crank and slotted link (50) for transmitting the horizontal reciprocating motion to said carriage (28). Packaging machine according to claim 5, characterised in that said cam (49) for the vertical movement of said upper welding bar (42) comprises a disk, integral with said intermediate shaft (49), provided with an eccentric groove (51) inside which an idle roll (55) is guided, which extends from a swinging lever (56), hinged relatively to said framework (11) at one of its ends, and articulatedly linked at its other end to an articulated lever (58) for said vertical movement of said upper welding bar (42). Packaging machine according to claim 5, characterised in that said swinging crank and slotted link (50) comprises a crank (52), installed at an end of said intermediate shaft (48), said crank (52) being provided with a groove (53) inside which a pin (54) is radially positionable in an adjustable way relatively to said intermediate shaft (48), said pin (54) rotatably supporting a slider or pad element (81) which enters inside a further groove (80) provided in a crank and slotted link lever (50) which is articulated at one of its ends in a swinging way relatively to said framework (11), and which drives, by means of a tie-rod (63), said carriage (28) in a horizontally reciprocating motion. Packaging machine according to claim 1, characterised in that said unwinding units (15,16) are operatively linked to said motor means (24) by means of transmissions with the interposition of a second brake-clutch assembly (65,66) relating to the upper unwinding unit (15), and with a drive calender (76) which through a coupling (69) can be brought into its position of engagement with said film (16) by means of an actuator means (79), relative to the lower unwinding unit (16).

Inventors: BALLESTRAZZI ARIS, TASSI LAMBERTO, BALLESTRAZZI, ARIS, TASSI, LAMBERTO
Applicants: SITMA SPA, SITMA S.P.A.
Application year: 1988
Main classification: B65B25
IPC codes: B65B59, B65G21, B65B11, B65B9