EP0220712A1

EP0220712A1 - Process and apparatus for wrapping loads in stretchable film

Info

Publication number: EP0220712A1
Application number: EP86114945A
Authority: EP
Inventors: Sauro Pieri; Rino Pieri
Original assignee: Pieri Srl
Current assignee: Pieri Srl
Priority date: 1985-10-30
Filing date: 1986-10-28
Publication date: 1987-05-06
Also published as: IT1188054B; IT8512593A0

Abstract

Apparatus for wrapping loads in stretchable film comprising a pre-stretching unit (7) which is translated in a circular path around the periphery of a load (10) to be wrapped, whilst being reciprocated with respect to the height of said load (10). The said said unit (7) comprises a supply reel (18) for the stretchable film, a first pair of nipple rollers (21-22) positively driven at a first peripheral speed by a suitable motor, and a second pair of nipple rollers (35-36) driven at a second peripheral speed greater than the said first peripheral speed, by the said driving motor, through a suitable transmission. The film from said supply reel is passed through the said two pairs of nipple rollers (21,22-35,36) for being pre-stretched before being wound around the said load (10). The output from the said motor is transmitted through a reducer (37) directly to one pair of the said nipple rollers, and is transmitted to the other pair of nipple rollers from said reducer (37) through a suitable speed change gear (26).

Description

This invention relates to a process and an apparatus for wrapping loads in a pre-stretched film of subsequently shrinkable material, of the kind of the plastics "with a memory", which are elastic but require a certain time interval between stretching and contraction.
From GB-A- 2083.002 it is known a process and apparatus for wrapping loads in stretch film comprising a roller assembly having two interconnected rollers rotatable by the web as it is drawn off a film supply upon being wrapped around a load on a turntable, according to which the said rollers are interconnected so that an upstream one of which rotates slower than the other to produce film elongation between the rollers, and in which the force on the film between the roller assembly and the load is relieved by the action of a positive constant torque device driving the rollers, so that the elongation between the roller assembly and the load is equal to or less than the elongation incurred between the rollers.
According to the above prior art device, the load must be supported on a turntable, with the film feeding and pre-stretching device being fixed. This is a serious drawback, particularly whenever wrapping loads formed by a stacks of single articles, as for instance bricks or the like. Moreover, in order to wrap loads of different peripheral extension, with a film having a given pre-stretch, it is necessary to vary the speed at which the turntable is rotated, or to change the transmission ratio between the two film-stretching rollers, which later operation may not be performed easily and quickly with the said prior art device.
Apparatuses are known, as for instance the apparatus described and shown in the Italian Utility Model Application 15283 B/83, according to which the load is supported on a fixed platform, and the film feeding and stretching device is carried by a rotatable arm, which is displaced all around the load to be wrapped. Although by this apparatus the problems depending from the rotation of the load are solved, nevertheless the other problems mentioned, viz easy and quick change of the load-wrapping speed and change of the pre-stretch amount of the film, are still unsolved.
Moreover, with such a device it is difficult to overcome the problems arising at the very beginning of the wrapping operation, whenever the fast rotating pre-stretched film is engaged with the stationary load, which may result in tearing of the said film.
From U.S.-A 3.589.091 it is known a method and apparatus for wrapping a package, according to which (Figure 14 and column 8, lines 28 to 64) a film of the kind referred to is fed between two pairs of rollers in which the leading rollers pair is rotated at a faster rate than the trailing rollers pair so as to stretch the film section between said two roller pairs, and the thus pre-stretched film is thereafter fed beneath a stream of articles to be wrapped ad is formed by means of a plow-like device into a tube-shaped configuration loosely fitting around the articles.
The above prior art apparatus is intended to wrap loads which are displaced, and not rotated, with respect to the stationary film stretching device (or devices), and it is fully unsuited for wrapping heavy or bulky loads. Moreover, also according to the said prior art device no provision is made to quickly and easily vary the amount of stretch imposed to the film, as a function of the kind and of the dimensions of the load to be wrapped.
A still further problem in all the prior art load wrapping devices of the kind above referred derives from the fact that, generally, the loads to be wrapped have a polygonal outline, so that the tension imposed to the pre-stretched film leaving the pre-stretching device during the load wrapping operation is not uniform, and varies continuously from one edge of the load to the adjacent ones.
It is therefore main object of the present invention to provide a process and apparatus for wrapping loads in a stretchable film, according to which the amount of pre-stretching imposed to the film may be varied at will within the limits admitted by the film itself, as a function of the type, of the peripheral extension, and of the outline of the load to be wrapped.
According to the invention, this object is attained, in a pre-stretching unit which is translated in a circular path around the periphery of a load to be wrapped, whilst being reciprocated with respect to the height of said load, and comprising a first pair of nipple rollers positively driven at a first peripheral speed by a suitable motor-reducer, and a second pair of nipple rollers positively driven at a second peripheral speed, greater than the said first peripheral speed, by the said motor-reducer through a suitable transmission, for pre-stretching a continuous strip of stretchable film unwound from a supply-reel carried by the said pre-stretching unit which is continuously feed through said first and second nipple-rollers pairs, by providing the improvement according to which in the transmission from the said motor-reducer to said one pair of nipple rollers, and preferably to said first pair of nipple rollers, a suitable speed change gear is interposed.
According to another feature of the invention, means are provided in the said pre-stretching unit downstream of the said second pair of nipple rollers, in the form for instance of dandy rollers, cooperating with suitable sensors disposed along the path of said dandy rollers, the said sensors being electrically connected to means, such as for instance a frequency variator connected to the electric motor, and for instance an electric asynchronous motor, of the said motor-reducer, so as to automatically and instantaneously change the speed of rotation of the motor of said motor-reducer as a function of the variations in the tension imposed to the pre-stretched film leaving the pre-stretching device by differences in the dimensions and in the outline of the loads being wrapped.
According to another feature of the invention, means are provided for positively driving the supply roller of stretchable film at the same peripheral speed of the said first roller pair, so as to control the unwinding speed of the film from the said supply roller.
Further objects and advantages of the present invention will be apparent from the following description made with reference to the accompanying drawings showing by way of non limiting example one preferred embodiment of the invention, in which:

Figure 1 is a front elevational view of an appartus according to the invention, for wrapping loads with a stretchable film.
Figure 2 is a diagrammatical plan view of the apparatus of Figure 1, with the portal like frame omitted.
igure 3 is a perspective view of the reciprocable carriage carrying the pre-stretching unit according to the invention.
Figure 4 is a diagrammatical plan view of the pre-stretching unit assembled on the reciprocable carriage shown in Figure 3, and
Figure 5 is a diagrammatical plan view showing the means for controlling the pre-stretching unit according to the invention.

With reference to the drawings, and with particular reference to Figures 1 and 2, the machine shown comprises a fixed portal-like frame comprising two side uprights 1, connected together by a crosspiece 2. An electrical motor 3 is mounted on the middle region of the crosspiece 2, with its shaft 4 downwardly extending from said crosspiece 2. To the shaft 4 the shorter horizontal leg 5 of an L shaped supporting structure is secured by one end. To the other end of leg 5 the vertical depending leg 6 of the said L shaped structure is secured. The leg 6 extends downwardly up to in proximity of the bottom of the machine. Reference 7 denotes a carriage which is slidably supported along leg 6. The said carriage 7 may be reciprocated along leg 6 by the motor 8 carried by the leg 5, through a suitable transmission. Carriage 7 houses the pre-stretching unit, to be described later. Below the portal-like frame 1,2 a roller conveyer 9 is disposed, supporting the load 10. Sidewise of the load 10, a gripper 11 is mounted to which the leading edge of the wrapping film 118 is fastened, before starting the load-wrapping operation, that is before that the carriage 7, housing the pre-stretching device, is translated together with the leg 6 under the control of the operating motor 3, all around the load 10 along the path of arrow F of Figure 2.
With reference to Figures 3 and 4, the carriage 7 will be now described. The said carriage 7 comprises a box-like base member 12, which is secured at one side to the slide 13 which is slidably guided in the guide 14 formed in the leg 6. During the wrapping operation, the slide 13 is reciprocated along the guide 14 by the motor 8 through suitable transmission means, and for instance through a transmission cable (not shown). Numeral 15 denotes a lever- like member, housed inside of base member 12, and fulcrumed at one end to the pin 16. To the other end of the lever 15 the expanding mandrel 17 is idly secured. The said mandrel 17 projects downwardly outside of the base member 12 through a circular slot 19 formed in the bottom of the said base member 12. The jaws of the expanding mandrel 17 are operated through the handwheel 120 secured to the shaft 121 which in turn is connected to the mandrel 17, in a manner per se known. To the said expanding mandrel 17 the stretchable film supply reel 18 is fastened. Reference numeral 20 denotes a downwardly extending idle roller rotatably supported by the base member 12, with its axis parallel to the axis of the mandrel 17. With numerals 21 and 22 the first nipple rollers pair is shown. The roller 21 of said nipple rollers pair is idly supported for rotation about ist axis by the base member 12. To the shaft of said roller 21 a gear 23 is keyed, in mesh with a gear 24 which in turn is keyed to the output shaft 25 of a speed change gear housed in gear box 26. The shaft 29 of the second roller 22 of the said nipple rollers pair 21-22 is idly rotatably secured to the free end of a lever arm 27, fulcrumed at its other end to the pin 28 carried by the base member 12. The said shaft 29 extends downwardly through a circular slot 30 formed in the bottom wall of the base member 12. The lever arms 27 and 15 are urged together by means of the helical spring 31. The nipple roller 22 is constantly urged in the direction of the roller 21 by means the helical spring 32 connected at one end to the lever 27 and at its opposite end to the fixed base member 12. A cam-like member 33 is pivotably secured to the base member 12. The said cam-like member 33 may be brought in contact with the shaft 29 of the nipple roller 22, by means of the operating lever 34, thus causing said nipple roller 22 to be spaced from roller 21, against the action of spring 32. By reference numerals 35 and 36 the second pair of nipple rollers is shown. The nipple roller 35 is rotatably supported by the base member 12, and its shaft is connected to the output shaft of the motor-reducer 37 carried by the base member 12. To the same output shaft of the motor reducer 37 a gear wheel 38 is keyed, which in turn is connected through a toothed belt 39 to the gear wheel 40 keyed on the input shaft of the speed change gear housed in box 26. The nipple roller 36 is fitted on the shaft 41 extending downwardly through the slot 49 in the bottom of base member 12. The shaft 41 is in turn rotatably idly secured to one end of the lever arm 42 of a bell crank lever, pivoted to the pin 43 secured to the base member 12. To the other arm 43 of said bell crank lever, one end of a helical spring 44 is secured, said spring 44 being connected at its other end to the base member 12. The said bell crank lever is also provided with a third lever arm 45 cooperating with a cam like element 46 pivoted at 47 to the base member 12, and operable through a lever 48 so as to shift the nipple roller 36 away from nipple roller 35, against the action of spring 44.
To the shaft of the nipple roller 35 the collar 50 is idly pivoted. To the said collar 5O a first, radially outwardly extending lever arm 51 is secured. To the free end of said lever arm 51 one end of a helical spring 52 is secured, the other end of which is secured to a bushing 57 which in turn is secured in rotatable but not slidable manner to one end of a screw-threaded spindle 53, which is in screw-engagement by its other end with a nut 54 rotatably supported in the tubular support 55 fastened to the base member 12. The nut 54 is connected to the operating handwheel 56. A link 58 is pivotably connected at one end to the bushing 57, the other end of said link 58 being pivotably connected to a slider 59 slidably guided in a slot 60 of the base member 12. The slider 59 is provided with a pointer cooperating with an indexed scale formed on the base member 12. To the collar 50 a second radially outwardly projecting lever arm 61 is secured, provided at its free end with a pivot pin 62 extending through a curved slot 63 formed in the bottom of the base member 12. To the pivot pin 62 the bell-crank lever 64 is pivotably secured. To the free ends of said lever 64 the dandy rollers 65 and 66 are idly pivoted. Reference numeral 67 indicates an abutment member secured to pin 62, for abutment against sensors 69′ and 69", and 68 is a second abutment member secured to pin 62 for abutment against sensor 69. The sensors 69, 69′ and 69" are electrically connected to the control panel 70 (Figure 3) of the machine, and whenever activated, each of them may control through a frequency variator (not shown) a different speed of rotation of the asynchronous motor of the motor-reducer 37. The speed change gear 26 may be controlled either manually or, as shown in Figure 3, it may be controlled by means of a remote control comprising an auxilary motor-reducer 71, the otput shaft of which is connected to the input of the speed change gear 26 through the belt 72 and pulleys 73,74 transmission. The output shaft of the auxiliary motor-reducer 71 is further connected, through a reduction gear train 75, 76 to the rotating element of a potentiometer 77, electrically connected to a proportional control circuit 78 housed in control panel 70, through which it is possible to set the desired output speed of the speed change gear 26.
The operation of the described device will be now evident.
A new bobbin 18 is inserted on the expandible mandrel 17, and fastened thereto by expanding the mandel jaws through the handweel 120. The periphery of the bobbin 18 is mantained in contact with the periphery of the roller 21 by the action of the spring 31. The continuous film web 118 from the bobbin 18 is guided around roller 20, then between the first nipple rollers pair 21,22. In order to introduce it easily between the said rollers, the roller 22 is moved away from roller 21 by acting through lever 34 on the cam member 33. Thereafter the film web 118 is passed between the second nipple roller pairs 35, 36. Again, during this step the roller 36 is moved away from roller 35 by acting through lever 48 on cam member 46. Thereafter, the film web is guided around rollers 65 and 66 and its free end is gripped to the gripper 11, as best shown in Figure 2. The degree of pre-stretching of the film passing between the two nipple rollers pairs 21,22 and 35,36 is controlled by controlling the output speed of the speed change gear 26. Due to the fact that, generally, the load 10 is formed by a polygonal body, the film 118 is subjected during the wrapping operation of said load to changing strains. The said changes in the strains applied to the stretched film are transferred to the the dandy rollers 65, 66. Wenever said strains exceeds the load value imposed to said rollers 65,66 by the adjustable tension of spring 52, the pivot 62 is caused to move along slot 63, thus striking with its abutment member the sensors 69′ and 69", whilst abutment 68 is relieved from sensor 69. The energization of the sensors 69′ (or 69") and the de-energization of sensor 69 causes automatically an increase of the speed of the motor of the motor-reducer 37, under control of the frequency variator 79. This increased speed, whilst not affecting the pre-stretching degree of the wrapping film, caused an increase in the feeding rate of the pre-stretched film to the load being wrapped. Thanks to the above feature, loads having different peripheral extension, or different outlines, are wrapped with an uniform tension on the wrapping film.

Claims

1) An apparatus for wrapping loads in stretchable film comprising a pre-stretching unit (7) which is translated in a circular path around the periphery of a load (10) to be wrapped, whilst being reciprocated with respect to the height of said load (10), said unit comprising a supply reel (18) for the stretchable film, a first pair of nipple rollers (21-22) positively driven at a first peripheral speed by a suitable motor, and a second pair of nipple rollers (35-36) driven at a second peripheral speed greater than the said first peripheral speed, by the said driving motor, through a suitable transmission, and in which the said film from said supply reel is passed through the said two pairs of nipple rollers (21,22-35,36) for being pre-stretched before being wound around the said load (10), characterized by the fact that the output from the said motor is transmitted through a reducer (37) to one pair of the said nipple rollers, and is transmitted to the other pair of nipple rollers from said reducer (37) through a suitable speed change gear (26).

2) Apparatus according to claim 1, characterized by the fact that the said speed change gear (26) is disposed in the transmission line between the motor-reducer (37) and said first pair of nipple rollers (21,22).

3) Apparatus according to claim 1, characterized by the fact that means (65-66) are provided which are responsive to the tension imposed to the pre-stretched web (118) being delivered to the load (10) to be wrapped, the said tension-responsive means (65,66) acting on control means (69, 69′, 69") electrically connected to a circuit (79) which is apt to control the rotational speed of the said nipple-rollers (21,22-35,36) driving motor (37).

4) Apparatus according to claim 3, in which the said tension responsive means are in the form of dandy rollers (65,66), the said dandy rollers having associated therewith abutment means (67,68) cooperating with two or more sensors (69, 69′,69") electrically connected to the said motor speed-control circuit (79).

5) Apparatus according to any one of the preceding claims, characterized by the fact that the said stretchable film supply reel (18) is positively driven at the same peripheral speed of the said first nipple-rollers pair (21, 22), by frictional contact with one (21) of the said nipple rollers of said first nipple rollers pair.

6) Apparatus according to claims 2 or 3, in which means (51,52,53,55,56) are provided for adjusting the tension value to which the said tension-responsive means (65,66) are responsive.