WO2004000652A1

WO2004000652A1 - Device for automatically setting the presser in a stretch film packaging machine

Info

Publication number: WO2004000652A1
Application number: PCT/EP2003/006248
Authority: WO
Inventors: Renato Rimondi
Original assignee: A.W.A.X. Progettazione E Ricerca S.R.L.
Priority date: 2002-06-19
Filing date: 2003-06-13
Publication date: 2003-12-31
Also published as: DE60302439D1; ES2249734T3; AU2003246426A1; EP1474330A1; EP1474330B1; ITGE20020054A0; ITGE20020054A1; DE60302439T2; ATE310674T1

Abstract

A servocontrol (13-25) is provided for automatically and proportionately setting the elevation of the presser (1, 2) as the height and/or other characteristics of the product to be packaged vary. The presser presses on the product with its own weight, optionally balanced by suitable means (9). The said servocontrol positions the presser at a suitable elevation below the height of the product, determined by, among other things, its characteristics, and when the product is raised it acts on the lower flexible contrast means (1) of the presser, deforming them and further raising the presser, in opposition to the action of a friction brake means (26, 126) which is such that, when the product is removed from the packaging station, the presser returns by gravity to the previous elevation in which it had been positioned by the said servocontrol, unless this position is to be modified because of modified characteristics of the next product to be packaged.

Description

DEVICE FOR AUTOMATICALLY SETTING THE PRESSER IN A STRETCH

FILM PACKAGING MACHINE

TITLE: "Device for automatically setting the action of the contrast presser in stretch film packaging machines"

DESCRIPTION

The invention refers to packaging machines used for packaging products in stretch film and having a presser which, by its own, usually flexible and revolving lower opposing means, contacts the top of the product during the packaging phase, to keep it correctly positioned relative to the means which are folding the edges of the packaging film underneath the product and which at the end of the cycle remove the product from the workstation of the packaging machine. In the prior art the presser is a completely passive means, its elevation being fixed and predetermined in relation to the minimum height of the products to be packaged, and it acts on the product by its own weight or by the action of elastic means or ballast means. These pressers have been found to be inefficient at coping with the increased work speeds of present-day packaging machines and acting selectively on sometimes very delicate products.

It is an object of the invention to obviate these and other disadvantages of the prior art, with the following proposed solution. It provides a servocontrol for automatically setting the elevation of the presser as the height and/or characteristics of the product to be packaged vary. The presser presses on the product with its own weight, and with the optional action of balance means. The presser is positioned at a suitable elevation below the height of the product, determined by, among other things, its characteristics, and when the product is raised it acts on the lower flexible contrast means of the presser, deforming them and further raising the presser, in opposition to the action of a friction brake means which is such that, when the packaged product is removed from the packaging station, the presser returns by gravity to the previous elevation in which it had been positioned by the said servocontrol, unless this position is to be modified because of modified characteristics of the next product to be packaged. Other features of the invention, and the advantages it provides, will be made more evident by the following description of a preferred embodiment thereof, illustrated purely by way of non-restrictive example, in the figures of the attached sheets of drawings, in which: - Fig. 1 is a side view with parts in section of the device during operation;

Fig. 2 illustrates the device in a top plan view with parts in section; and Fig. 3 illustrates other details of the device taken on the section lines marked Ill-Ill in Figures 1 and 2.

In Figure 1 , S indicates the lifter that carries the product P to be packaged and that is here illustrated in the position of raising the product against the packaging film F held around the edges by suitable means partly indicated by Z, while B is a general reference for the pusher and the rear folder, which intervene at the end of the packaging cycle to complete the packaging and unload the product from the workstation of the packaging machine. When the product is raised into the workstation of the packaging machine, as illustrated in Figure 1 in solid lines, the product interferes with the flexible and usually revolving contrast means 1 of the presser, which in the example discussed here are formed by a plurality of spiral- spoked idle wheels made of elastomeric material projecting below the body 2 of the presser, which is attached to an articulated support structure 5. In Figure 1 the presser assembly is illustrated in dashed lines in the lowest position and in chain lines in the highest position. The structure 5, as also illustrated in the details in Figures 2 and 3, consists of a parallel-motion mechanism which comprises pairs of levers 105, 105' hinged sideways at 6, 6' to the part 205 of the same structure as that to which the body 2 of the presser is fixed, and hinged at the other end to strengthening plates 305, 305' fixed to the side walls of a boxlike support structure 8 mounted to the packaging machine frame. The plates 305, 305' form the fixed vertical sides of the parallel-motion mechanism, to which the aforementioned part 205 is parallel, so that the operational parts 1 , 2 of the presser can modify their elevation while always maintaining their horizontal disposition. Opposing cylindrical helical springs 9 are fitted between the levers 105 and 105', becoming loaded, for example, as the structure 5 rises.

According to the invention, one of the pivot pins 7 or 7', specifically the upper pin 7' in the present example, is formed by a shaft which is fixed firmly by its ends to the levers 105, passes through the boxlike structure 8 and is supported rotatably, in bearings 10, by the fixed plates 305, 305'. A downward-oriented lever 13, keyed to this shaft by means of the key 11 and fixed for example by screws 12, and having its lower end forked, supports a rotatable roller 14 whose axis is parallel to the said shaft 7'. The side of the roller 14 furthest from the active members 1 , 2 of the presser is acted upon by the upward projection 115 of a slide 15 which is in a parallel arrangement with the longitudinal axis of the said active members 1 , 2, and integral with a nut 16 engaging with a screw 17 supported rotatably at either end by supports 18, 18' fixed to the structure 8, one end of the screw 17 being keyed to the shaft of a small electric motor 19 designed for electronic control of speed and phase. The other end of the screw is connected to an encoder 20 for detecting the speed of rotation and the angular position of this screw 17. The slide 15 has a grooved flank engaging with a straight guide 21 parallel to the screw 17 and fixed to a flank of the support structure 8. On the unguided flank, the slide 15 carries a projection 22 which, when the slide is in the position of maximum retraction, with the presser fully down, engages with a start-of-stroke sensor 23 which, together with the encoder 20, is connected to a processor-based logic circuit 24 with interface 124 for controlling the motor 19 and having an input 25 which sends to the processor 24 the information about the height and/or other characteristics of the products P to be packaged. The information about the products' characteristics may be generated manually by the operator on selectors provided for that purpose, while information about the height of the products is obtainable from the optoelectronic means usually provided in packaging machines for adapting the unwinding and treatment of the wrapping film in the workstation of such machines.

At the start of each working cycle, the slide 15 is in the retracted position, in which the sensor 23 is activated, and the presser is down. When the signal with the information about the height of the product P placed in the machine for packaging is received via the input 25, the processor 24, with the help of the encoder 20 and of the starting sensor 23, starts the motor 19 in such a way as to move the slide 15 and raise the presser 1 , 2 by a suitable predetermined amount that is less than the height of the product, in such a way that in the final part of the lifting stroke, the product itself interferes with the flexible wheels 1 of the presser, deforming them and itself raising the presser assembly. To improve the operation of the presser, especially at the high working speeds of the packaging machine, it has been found to be useful for the last part of the stroke in which the presser is lifted by the product to also be opposed by the action of friction brake means, such as to absorb the kinetic energy transmitted to the presser by the product during rapid lifting and also such that when the product is removed from the workstation of the machine and from the presser, the latter returns slowly under gravity to the down position in which the roller 14 meets the projection 115 of the slide 15, which latter will remain in the set position if the next product to be packaged has the same height as the previous product, whereas it will vary its position if the height of the next product is different. Although the impact of the roller 14 on the projection 115 is deadened by the action of the friction means 26, the same roller 14 can usefully be made of hard rubber or the surface of the said projection intended to contact the roller may be coated with some suitable material for deadening the impact between the parts.

As can be seen in Figure 3, to achieve the braking purposes stated above, a friction disc 26 is keyed to the shaft T and is pushed axially by any suitable means to engage with a suitable friction means with a complementary body 126 fixed to the adjacent flank of the structure 8. This engagement between the parts 26, 126 can be brought about by the action of an electromagnet, a permanent magnet, elastic means, or by the action of other suitable means.

Claims

1. Device for controlling the contrast presser of a machine for packaging products in stretch film, characterized in that it comprises servocontrolled means for automatically and proportionally setting the elevation of the said presser as the height and/or other characteristics of the products to be packaged vary.

2. Device according to Claim 1 , characterized in that it comprises means such that, by means of the said automatic setting of the elevation of the presser, the product comes into contact with the said presser only in the final part, which is of predetermined amplitude, of the stroke in which it is raised by the lifter (S) of the packaging machine.

3. Device according to Claim 2, characterized in that it comprises friction brake means in order suitably to brake the stroke in which the presser is raised by the product to be packaged, in order to dissipate the kinetic energy transmitted by the lifter (S) of the packaging machine.

4. Device according to Claim 3, in which the said friction means are such as also to be active in the reverse or downward stroke of the presser to the position it had before contact with the product, when the said product is unloaded from the packaging station of the packaging machine.

5. Device according to Claim 1 , with the presser supported by the mobile vertical end (205) of a parallel-motion structure (5), characterized in that one of the pins (7, T) by which the said parallel-motion structure pivots on the fixed support structure (8) is formed by a shaft mounted to the corresponding side levers (105) of the said parallel-motion structure and that supports a keyed lever (13) which via an interposed roller (14) is acted upon by the projection (115) of a slide (15) guided by suitable means (21) perpendicular to the said fulcrum axis of the lever (13) and that carries an integral nut (16) parallel to the said guide means and engaging with a screw (17) supported rotatably by the support structure (8) of the device and connected to an electric motor (19) with electronic control of speed and phase, controlled by means for automatically modifying the angular position of the said lever and hence the elevation of the presser, by an amount that is directly proportional to the height of the products to be packaged, leaving the presser free to rise above whichever position it is placed in.

6. Device according to Claim 5, in which the said roller (14) and/or the said projection (115) of the slide (15) are made from or coated with a suitable elastomeric material.

7. Device according to Claim 5, in which the electric motor (19) for driving the screw (17) is controlled via a suitable interface (124), by a processor (24) that has an input (25) enabled to receive the information about the characteristics and/or height of the products to be packaged and that is connected to an encoder (20) for detecting the speed of rotation of the screw and to a sensor (23) for detecting the rest position of the said slide (15), relative for example to the fully down position of the presser, these means being such as to enable the device to function as claimed in Claim 2.

8. Device according to claim 5, in which there is keyed to the same pin (7') as that to which the presser elevation varying lever (13) is keyed, the axially mobile part (26) of a brake unit, which engages with sliding friction and with the correct degree of friction with a complementary part (126) fixed to the support structure (8) of the presser, against which the said mobile part (26) is pushed by means of any suitable type, such as electromagnetic, permanent magnet, mechanical, fluid-pressure or other means.

9. Device according to claim 5, in which the longitudinal levers (105, 105') of the parallel-motion structure (5) supporting the presser (1 , 2) are connected together by elastic means (9) that become loaded and absorb energy as the presser rises.