Wrapping device with a circular track structure, and a film feeding device

A wrapping device having at least a circular track structure which forms a closed track, and a film feeding device which is arranged to circulate along the track and to feed a film around a piece to be wrapped, wherein the film feeding device is provided with a mechanism for fixing a film roll in the film feeding device in a rotating manner, feeding mechanism, through which the film is arranged to be fed at a predetermined film tension, and a drive mechanism which is arranged, if necessary, to rotate the film roll in a direction in which the film is rewound onto the film roll and which is arranged to receive its driving force by mechanical contact between the drive mechanism and the circular track structure. The film feeding device also has a mechanism which is arranged to disconnect and reconnect the contact, wherein the mechanism is controlled either on the basis of the film tension or on the basis of the location of the film feeding device on the track, or on the basis of them both.

FIELD OF THE INVENTION

The invention relates to a wrapping device. The invention also relates to a film feeding device for a wrapping device.

BACKGROUND OF THE INVENTION

For the wrapping of various pieces, for example coils, wrapping devices known as such are used to perform the wrapping by means of a wrapping film, preferably a thin and transparent stretch film made of plastic. The film roll is normally fitted in film feeding means, which are further placed in a carriage which moves along a circular structure and a track formed therein, either around the whole piece or passing via an opening in the central line of the piece.

However, such devices have the problem that the quantity of film to be supplied from the film roll at each moment varies at different locations on the circular tract, because the carriage is not continuously at the same distance from the piece. At some points, the distance is even reduced, having the result that the film between the piece and the carriage does not remain sufficiently stretched all the time, thereby leading to poor wrapping quality, causing tangling of the film or other problems.

One wrapping device is disclosed in EP 0 936 142 A2, or corresponding U.S. Pat. No. 6,192,653. The device comprises a roll device for guiding a film, having a roll placed against the film to maintain the tension of the film but being still allowed to rotate with the film in the feeding direction of the film. The roll is coupled by means of a moment limiter to a motor device which tends to rotate the roll in the opposite direction, but the tension of the film exceeds the set moment and the roll can thus not revolve in the opposite direction. If the film is slackened, the roll can revolve in the opposite direction and the film is re-wound on the film roll, wherein said problem is eliminated. However, problems may be involved in the synchronization of the operation of the guide roll and the film roll, because the film roll may also be provided with a moment limiter.

Another device is presented in EP 0 936 141 B1, in which the tension of the film is continuously monitored with sensor means and in which the film roll can be rotated by means of a motor. If the film is found to become slackened, the film roll is rotated backwards and the loose part is rewound onto the film roll. The device requires an auxiliary motor for the film roll, which is difficult to place in the carriage and which considerably increases the weight of the carriage.

One known device is presented in the publication EP 0 544 312 B1, or corresponding U.S. Pat. No. 5,282,347. The device comprises a roll device placed in a carriage and in which the loose film can be accumulated, if necessary. Some of the rolls are moved by spring force and controlled by changes in the tension of the film. The rolls require a lot of space and increase the weight of the carriage. An increase in the weight will make the moving of the carriage more difficult or will involve an increased power requirement and problems in the placement of the powerful motors.

SUMMARY OF THE INVENTION

It is an aim of the invention to provide a wrapping device as an alternative and an improvement to the disadvantages of prior art. By means of the invention, it is possible to rewind loose film without applying electrical sensors and auxiliary motors and to avoid such structures in the carriage which are coupled to the means for moving the carriage forward, wherein the structure becomes simpler and the design of the different parts can be kept separate.

By means of the invention, it is easier to design the carriage and to use alternative or even totally new types of structures, because the structures taking care of the loose film do not necessarily need to cooperate, for example, with the motor for moving the carriage or with the transmission mechanisms. Replaceability is increased and the maintenance and the replacement of parts become easier.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2show the principle of operation of the film feeding device1, and in this description, the device1will also be called a carriage and the feeding means10,12,13,14,15will also be called guide rolls. The carriage1and the guide rolls are shown in a reduced schematic view to illustrate the operation.FIG. 1shows a situation, in which the film9to be fed is suitably tensioned, wherein the tension of the film is predetermined or higher than that, and it is fed from a film roll8forward and further around a piece to be wrapped. The end of the film9is attached to the piece, wherein when the carriage1moves, the film9is simultaneously tightened by the effect of the guide rolls and is unwound from the film roll8.FIG. 2shows a situation in which the film9has been slackened and it is rewound around the film roll8.

The carriage1comprises a frame structure2in which the functional parts are coupled. The presented carriage1is shown without a motor or means by whose force effect the carriage1is moved along the track structure3and following a desired path. The motors, or the means26moving the carriage forward, can be implemented by means known as such, wherein the frame2is provided, for example, with an electrical motor to rotate, for example, a cogged wheel which is placed against a cogging on the track3. By means of the cogged wheel, the carriage1is driven forward, and simultaneously the necessary electrification is provided by means of sliding connections, wherein the carriage1is provided with contacts and the track3is provided with an electrified conductor track, along which the contacts of the carriage slide. The track3is a circular track forming an endless path along which the carriage1travels. The track3has, for example, such a shape that it comprises two horizontal track parts which are on top of each other and which are connected by means of vertical arch-like track parts, wherein during a cycle, the carriage1rotates around a direction which is horizontal and transverse to the plane in which the carriage1moves. The carriage1is supported to the track3by means of upper wheels4and5and lower wheels6and7, carrying the carriage1in its different positions. The wheels are placed on opposite sides of the track structure3. The track3is, for example, a flat plate structure supported or connected to the frame.

The carriage1is provided with a film roll8from which the film9is fed and guided by guiding rolls off the carriage1and further around the piece to be wrapped, which is placed inside the circular track or through which the carriage1and the track3are placed to pass. In this case, particularly coils made of a metal band, having a large inner opening, are feasible. If necessary, the track is provided with a port which can be opened or a movable part to insert the track3in the piece and to form a continuous track for the carriage1. Furthermore, a rotating device is placed under the track structure3to rotate the coils during the wrapping, wherein each part of the coil can be wrapped. The rotating axis of the coil is its longitudinal axis which is placed in parallel with the track.

The guide rolls are used to keep the film9suitably tensioned by braking and to take care of the pre-tensioning and guiding of the film. In the shown embodiment, the guide rolls also comprise a cam roll10whose position depends on the tension of the film9. Thus, the cam roll10is a means which detects the tension of the film and whose position is dependent on the tension. The cam roll10is coupled to a rotatable lever11whose other end is connected to the rotation axis of the roll12or in another fixed position. The roll12is freely rotatable. The guide rolls also comprise a free roll15which guides the film9unwound from the film roll8. Rolls13and14are provided between the rolls12and15. The roll13cooperates with the braking roll14, because they are coupled to each other by a transmission, wherein they rotate in synchronization with each other. The transmission is preferably implemented by means of cogged wheels placed at the ends of the rolls, around the shaft. The locations of the rolls12,13,14and15, as well as of the film roll are fixed in relation to each other.

The carriage1also comprises a drive roll16which is not in contact with the track3when the film9is tensioned. The drive roll16and the film roll8are coupled to each other by means of a fixed transmission17,18,19, wherein they rotate in synchronization and in the same direction. The gearing of the transmission is preferably implemented by means of a cogged belt17and cogged belt pulleys18and19. In this case, the transmission is fixed, wherein the drive mechanism is also arranged to rotate with the film roll8in the direction in which the film is fed from the film roll8when the tension of the film is predetermined or higher than that. In the situation ofFIG. 1, the force effect rotating the roll16is obtained from the film roll8which, in turn, is rotated by the tensioned film9being unwound. The tensioned film9keeps, by means of its force effect, the drive roll16off the track3, which is implemented by means of a lever20in such a way that also the drive roll16is coupled to the lever20. The lever20, in turn, is coupled to the lever11or the cam roll10in such a way that a movement of the the cam roll10will also affect the position of the lever20. The drive roll16is coupled to the film roll8in such a way that the drive roll16can be turned in relation to the film roll8and away from the track3when the lever20tends to move the drive roll16. The rotation is made possible by means of a lever21which is coupled between the shafts of the drive roll16and the film roll8. The cam roll10and the levers11and20constitute a mechanism which controls the drive roll16and thereby the connection and disconnection of the drive mechanism to the source of the driving force.

The drive roll16, the spring22, and the parts17,18and19of the gearing constitute the drive mechanism which rotates the film roll8and receives its driving force via a mechanical contact26. In this case, the contact is the contact of the rolling driving roll16along the stationary track3, wherein frictional forces rotate the drive roll16which is pushed by the spring22against the surface of the track3. If the force effect of the tension of the film is greater, it will overcome the effect of the spring22, and the drive roll is pulled off the track, wherein the contact is disengaged. In this case, it should be noted that the driving force is only generated when the carriage1is in motion, wherein the source of the driving force is the movement between the carriage1and the circular track structure3. Alternatively, the mechanical contact26can also be formed by a circular crawler track placed against the track3. Furthermore, the track3may be provided with pins or other protrusions placed at regular intervals, which hit corresponding means in the drive mechanism of the carriage1and thereby move or rotate the drive mechanism and the film roll backwards, for example stepwise. The tensioned film9moves the drive mechanism in such a way that it will no longer hit the protrusions but the slack film9will allow the contact. InFIG. 2, the contact is continuous, but it may also be sectional or periodical, as presented above in connection with the protrusions. The aim is to rotate the film roll8backwards.

The force effect of the slack film9is not sufficient to resist the force effect of the spring22, wherein the spring22presses the drive roll16against the track3, as shown in FIG.2. Instead of the spring22, it is also possible to apply gas springs or other means which provide a suitable counterforce and which are preferably adjustable. Furthermore, the slack film9must be rewound onto the film roll8, which is implemented by providing the force effect to rotate the film roll8from the drive roll16, which is now pressed against the track3and tends to roll along it. The carriage1is driven along the track3, which also causes the rotation of the roll16. In comparison with the situation ofFIG. 1, the rotating direction of the drive roll16is reversed, wherein the rotating direction of the film roll8is simultaneously reversed and the loose film9is now rewound onto the film roll8.

The surface of the drive roll16or the track3or them both can be roughened or provided with a suitable embossing to prevent the sliding or slipping of the drive roll16. Thus, the track3can also be equipped with a cogging, against which the corresponding cogging of the drive roll16is placed. The track3or the drive roll16may also be coated with a suitable material, such as rubber, to achieve higher friction in the contact26.

The film roll8is mounted on its rotation axis preferably in such a way that the film roll which has become empty can be easily replaced with a new, full film roll. The distance between the rolls13and14can be preferably set to enable controllability. The spring22or the corresponding gas spring can also be installed in such a way that they tend to push the lever21or the drive roll16towards the track3. InFIG. 1, the spring22is coupled in such a way that it tends to pull the lever21and the drive roll16towards the track3. In one embodiment, the frame2comprises two parallel plates between which the guide rolls12,13,14and15are mounted on bearings at each end. Between the plates, there may be connecting structures to support and reinforce the structure. Thus, when looking atFIG. 1, the front plate is removed and only the back plate is exposed. The lever20is preferably placed outside the front plate, and the front plate is provided with a groove in which the shaft of the roll16can move. The shaft supporting the film roll8is, in turn, mounted on bearings in only one of the plates, wherein the opposite plate is provided with an opening, through which the film roll8can be replaced. Consequently, the carriage1is provided with means which enable the fixing of the film roll8in the carriage in a replaceable and rotatable manner. The length of the rolls10,12,13,14, and15corresponds to the width of the film9or is greater than that. The drive roll16is narrow, and only one end of its shaft journal25, shown inFIG. 3, is mounted on bearings in the lever21.

In one embodiment, the number of upper and lower wheels totals eight, wherein they are placed close to each edge of the track3and on opposite sides of the track3. In the presented embodiment, the width of the track3corresponds substantially to the width of the carriage1. Each plate is provided with four wheels, and the lower wheels are connected to the frame2by means of such structures which extend around the edges of the track3. The mounting of the rolls and wheels on bearings and their installation are implemented by utilizing mechanical components which are known as such and whose application in the principle of the carriage1ofFIGS. 1,2and3will be obvious on the basis of this description for a person skilled in the art. The adjustment of the force effect of the spring22and the other functions can be easily implemented and may also be based on pure experimentation and the selection of a suitable component.

FIG. 3shows, in a detail, the drive roll16and the guide roll23alone when they are pushed towards the track3in a location where the track3is also provided with an elevation24. In this case, the elevation3forms a guide profile along which the guide roll23rolls and forces the drive roll16off the track3. In this way, the guide roll23disconnects the contact26shown in FIG.2and forces the drive roll16to move. In the figure, the rolls16and23are seen from the direction of the track3and the movement of the carriage1, in other words seen from the right when compared withFIG. 1or2.

The drive roll16can now be forced off the track3, which makes it possible to guide and time the rewinding in a more precise manner. For this purpose, a freely rotating roll23is placed on the same shaft as the drive roll16, wherein if its diameter corresponds to that of the drive roll16, it will also roll along the track3, or is smaller, wherein it will not be placed against the flat track3. The drive mechanism does not receive its driving force via the guide roll23. Now, the track3can be provided, at a desired location, with a guide profile24by the guide roll23, wherein the guide roll23can be used to force the drive roll16off the track by raising it, wherein the film roll8is not rotated backwards. This situation corresponds to the situation ofFIG. 1, but it can now be provided by active measures, with the help of the elevation24, by using forced control. The guide roll23connected to the shaft25constitutes a mechanism which guides the drive roll16and thereby the connection and disconnection of the drive mechanism to the source of the driving force. The guide roll23may also be coupled to the lever21, wherein the lever21, in turn, moves the drive roll16. If the geometry and the force effect of the guide roll23are directed in a suitable way, the guide roll23may also be coupled to the lever20which lifts the drive roll16off the track3. The drive roll16can also be placed underneath the track3, wherein the directions of motion of the levers must be arranged to correspond to this situation. Similarly, the guide roll23can be on opposite side of the track3, wherein the guide roll23must be arranged to move the drive roll16in a corresponding manner. The elevation24can also be constructed as a separate track structure which is parallel to the track3and which is followed by the guide roll23. Said track may be continuous or may be placed only in a section of the track3, which is also typical with the elevation, because forced guidance is only needed at desired points. Preferably, the location of the guide profile24is adjustable or its length can be changed by means of, for example, extension pieces.

If the behaviour of the film9is well known in advance, or if pieces of very constant shapes are wrapped, the slackening of the film can be estimated already beforehand and thereby those points of the track in which rewinding will be needed are known in advance. In a simple embodiment of the invention, the drive mechanism receives its control from the guide profile24alone, wherein the movement of the cam roll10or the lever20are unnecessary. In the embodiment shown inFIGS. 1,2and3, both the guide profile24and the moving cam roll10are used. The guide profile24will not be compulsory, if forced guidance is not necessary or if the operation of the cam roll10is sufficiently accurate.

The position of the drive roll16can also be set by means of a mechanism formed by electrical actuators, wherein the actuators, controlled by the movement of the cam roll10, pull the drive roll16off the track3, if necessary. The position of the cam roll10is used as a tension indicator and couples the actuator to operation in a rotating or linear movement. For this purpose, the frame2must be equipped with actuators and it must be provided with electrification for sensors and/or actuators. In this case, sliding contacts, known as such, are applied, which slide along a guide mounted on the track3. The tension indicator may also be the guide profile24alone, which guides the actuator by means of the guide roll23and the sensor. In these embodiments, the carriage1must be equipped with electrification, wherein all the advantages of a simple, purely mechanical system will not be achieved. A more complex system is also represented by an embodiment of the invention, in which sensors are used in the carriage1to find out its location on the track3, and the position of the drive roll16is controlled according to the location. For example, the sensor detects mechanically, optically or electrically marks which are fixed on the track3and are preferably movable to cause the release or return of the drive roll16in an alternating manner.

The invention is not limited solely to the advantageous embodiment presented above, but it may vary within the scope of the appended claims. For example, the upper and lower wheels are connected, for example, to a separate frame structure, in which the frame2is arranged to be connected for maintenance and quick replacement of broken parts. The separate frame is provided, for example, with a different set of wheels or a different motor, wherein the selection of the motor alternative for a different track is easy and quick and wherein it is possible to form various replaceable module structures.