BACKGROUND ART The invention was developed for the protective wrapping and consolidation of stacks of sheet steel product and is described primarily with regard to that application hereinafter. It will be appreciated however that it is generally applicable to wrapping other goods of various natures. Indeed, an object of the invention is to provide a more versatile wrapping apparatus in terms of the variety of target objects that the one apparatus may wrap.

The broad term "wrapping apparatus" covers many types of machines comprising dispensing means able to support a roll of pliable wrapping medium, for example, so called stretch wrap plastics film, and allow a web of the medium to be drawn from the roll and applied to a target object to be wrapped.

Such apparatus range from simple hand held devices, to complex special purpose machines.

Hand held apparatus are versatile, but their use is labourious and time consuming, making them unsuitable for wrapping large target objects, especially in the context of a production line.

This type of apparatus is only suited to "one offs", small target objects and, at best, short packaging runs.

Another class of known apparatus comprises a turntable (carousel) or the like on which the target object may be supported. As the turntable is rotated the target object rotates with it.

A dispenser supporting a roll of wrapping medium is located adjacent to the turntable and an end of a web of the medium is attached to the target object. As the target is rotated by the turntable the wrapping medium is drawn from the roll and applied to the target. The dispensing means may be moved in the axial direction of the roll during rotation of the target object so that successive layers of the medium are applied to the target object to provide an uninterrupted envelope of its side faces. A disadvantage of this class of apparatus is the limitation on the mass and physical dimensions of the target objects that may be wrapped.

Another class of known wrapping apparatus which alleviates some of the disadvantages of the previously described equipment comprises a rotatable frame which supports the dispensing means. In this instance, instead of a web being drawn from the roll and applied to the target object by virtue of its rotation, the wrapping is applied as a result of the dispensing means orbiting the stationary target object. Orbital wrapping apparatus overcome the problems associated with rotating large unbalanced masses. However, problems do arise due to sudden, and sometimes large, variations in the length of the web extending from the roll to the target object, with corresponding variations in the tension applied to the web of wrapping media, as a result of discrepancies between the shape of the track taken by the dispensing means and the envelope of the target object. This results in a lack of versatility, rendering orbital wrapping apparatus ill suited to wrapping irregularly shaped target objects or for wrapping a succession oftarget objects when there is variation, from object to object in the shape or size of the objects.

Yet another class of known apparatus particularly suited to wrapping elongate articles comprises a circular structure which carries a dispenser for wrapping medium. The structure is caused to rotate about its axis, which is horizontal, to produce orbital movement of the dispenser about that axis. The article to be wrapped is passed by appropriate conveyors through the structure along the axis. This class of machine is commonly called a spiral wrapper or ring wrapper and essentially, an elongate article or bundles of elongate articles may be conveyed through the circular structure and receive an application of stretch film around its radial extremities in a helically overlapped style. The disadvantages with this style of apparatus are that

the ends ofthe package are not always sealed over with plastic film depending upon the physical size of the article/s and it is often difficult to convey articles of certain dimensions and shape through the structure.

Australian Patent No. 653255 (John Lysaght (Australia) Limited et al), describes a wrapping apparatus adapted to apply stretch wrapping film to all surfaces of annular, cylindrical articles. This is a specialised, orbital, wrapping apparatus developed for special purpose wrapping applications.

DISCLOSURE OF THE INVENTION An aim of the present invention is to provide a wrapping apparatus which is more adaptable and better able to wrap differing target objects.

The invention attains that aim by providing apparatus wherein the dispensing means may be caused to follow any path of pre-selected shape or size, within the size range of the apparatus, including paths requiring abrupt changes in direction or corners.

Accordingly, this invention consists in a wrapping apparatus to apply a pliable wrapping medium to the surface of a target article, said apparatus comprising dispensing means to support a roll of said pliable wrapping medium and permit a web of said medium to be drawn from the roll, carriage means mounting said dispensing means for movement in a plane generally perpendicular to the plane of said web of wrapping medium, control means operable in response to input characterising the shape of the target article to operate said carriage means to move said dispensing means along a path adjacent the surface of said target article to at least partly circumnavigate the target without the path substantially diverging from the surface of the article.

Preferably, the path is a closed path circumnavigating the target. In one form of the invention the path consists of a plurality of substantially linear segments. Preferably, the angles between the linear segments are acute or obtuse angles toward said target. The linear

segments of the path can be joined by relatively short curved segments defining rounded corners between the linear segments.

In one preferred form the wrapping apparatus further comprises a hollow frame to enclose the target article and having a first axis, a second axis intersecting said first axis, and a third axis perpendicular to said first and second axes and wherein said carriage means includes primary carriage means mounted on said frame in a manner enabling its displacement relative to the frame in the direction of said first axis, a secondary carriage means external to said station mounted on said primary carriage means in a manner enabling its displacement relative to the primary carriage means in the direction of said second axis, said dispensing means being mounted on said second carriage means in a manner enabling it to move transnationally therewith and rotate about an axis of rotation that is fixed relative to the secondary carriage means and extends substantially in the direction of said third axis, primary drive means to displace said primary carriage means as aforesaid and secondary drive means to displace said secondary carriage means as aforesaid.

In preferred embodiments said first and second axes intersect at right angles, so that said first, second and third axes then become orthogonal axes, and for the sake of simplicity may then be referred to as the X. Y and Z axes respectively.

Those or other preferred embodiments preferably further comprise tertiary drive means, also controlled by said control means, effective to displace the dispensing means relative to the secondary carriage means in the direction of the third or Z axis so that the dispensing means may be positioned at any point within the envelope of operation.

In most instances the defined path will be endless and such that the dispensing means circumnavigates the target object, however this is not essential and the position of the dispensing means at the end of a wrapping operation may differ from its position at the start of the operation, if the nature of the wrap so requires.

The input data essentially informs the control means of the shape, size and position of the

target object, and the control means convert that data into instructions to the drive means which ensure that the dispensing means follow a path slightly larger than, but conforming generally in shape to, the envelope of the object. The term "envelope" in this context is the figure arrived at by joining the salient points of the article, as seen when viewed in the third or Z axis direction, by straight lines. The actual path of the dispensing means is not only a little larger than the envelope of the object but also will usually have rounded corners rather than sharp angular corners.

According to one class of embodiments of the invention, the external frame is fixed and the target object is introduced into the wrapping station and, after it is wrapped, removed from the station, by hand, conveyor means or other transporter devices. According to an alternative class of embodiments, the external frame is mobile and may be advanced so as take in the target object for wrapping, and then retracted to release the wrapped object from the station.

In either of those classes, the versatility of the apparatus may be still further enhanced by the provision of support means for the target object enabling it to be re-positioned or re-oriented within the wrapping station during a wrapping operation, or between stages of a multi-stage wrapping operation. In this event, input data may be derived at two or more orientations of the target object to cause the circumnavigating path of the dispensing means to be adjusted to the envelope of the object as seen in each orientation.

The three axis of motion may be effected by any one or more of a number of conventional linear motion systems such as hydraulic, pneumatic, or electrically operated actuators. One embodiment utilises electrical drives over mechanical systems to achieve its three axis movement, the complete system being fully programmable by a computerised, P. L. C. (Programmable Logic Control) system. The control system may be linked with another master control system and may be an open or closed loop control circuit.

It will be apparent that combinations of three axes of motion may be applied by the control system to produce movements of the film dispenser such as rectangular, circular or polygon form paths all with or without vertical movement. That is, sinesoidal circular, helical

and an infinite number of rotary and non rotary wave form paths can be followed depending upon the settings of the control system programmable to suit the size, shape and nature of the article being stretch wrapped.

As a result the invention provides for the efficient wrapping of articles such as palletised sheet parks, coil and cylindrical product, non-rectangular articles such as trapezoids, parallelograms, rhomboids elongate articles and small articles.

It has particularly been found that the use of an apparatus in which the dispenser path closely conforms to the target article shape without substantial divergence allows the use of a much lower lay on tension in the wrap than in previous devices. This is of particular advantage in wrapping articles with shape edges or protrusions.

The invention also provides for the wrapping of long than articles which was impractical using previous orbital wrapping apparatus.

BRIEF DESCRIPTION OF THE DRAWING By way of example, an embodiment of the above described invention is described in more detail hereinafter with reference to the accompanying drawing, being a diagrammatic perspective view of a wrapping apparatus according to the invention BEST MODE FOR CARRYING OUT THE INVENTION The illustrated embodiment comprises a fabricated steel, stationary, hollow frame 1 comprising four comer posts 2 supporting two longitudinal beams 3 and two transverse beams 4. The frame 1 encompasses or surrounds a wrapping station, being substantially all of the rectangular prismatic space defined by the corner posts 2 lying below the beams 3 and 4.

Primary carriage means 5 comprise a fabricated steel, rectangular frame furnished with supporting rollers 6 adapted to run on rails (not shown) extending along the inner side faces of the beams 3.

The primary carriage means 5 is able to be displaced longitudinally of the frame 1, that is to say in the direction of the X axis of the wrapping station, as indicated by the arrow X-X, by primary drive means comprising a speed controllable, reversible, gear motor 7 driving a head shaft 8, two capstan pulleys 9 fixed on the head shaft, and two flexible wire ropes 10 each extending from respective ends of one side of the carriage means 5 about the capstan pulleys 9, to and about tail pulleys 11 and then to the ends of the opposite side of the carriage means 5.

The ropes 10 are wrapped about the capstan pulleys 9 a sufficient number of times to ensure that the drive between the capstan pulleys and the ropes is free of appreciable slip. For preference the rope anchorages on one side of the primary carriage means 5 incorporate take up springs (not shown) to ensure that the ropes 10 remain taut. Also for preference the tail pulleys 11 are able to slide freely along their supporting axles so that they may remain in alignment with the flights of the ropes as they wind upon and unwind from the capstan pulleys.

The motor 7 is preferably a synchronous motor and is fed from a variable frequency power source at a frequency dictated by the control means of the apparatus. Also the motor revolutions are monitored by means of conventional digital transducers producing electric pulses indicative of the angular travel of the motor. Those pulses are an input to a conventional, programmable, numerical control device included in the control means, whereby the precise position of the primary carriage means 5 is known to those control means. Thus the exact position of the primary carriage means 5 at each instant is input to the control means, and its speed of displacement and the magnitude of the displacement from a reference position is within' the control of the control means at all times.

At times, the displacement of the primary carriage means 5 may require to be abruptly stopped at a pre-selected point. To that end the primary drive means may include a brake under the control of the control means. Conveniently, to that end, the motor 7 is preferably of the kind that may function as an electro-magnetic brake upon the injection of a DC current into its field circuit, and the control means may also control the supply of such a DC current.

Secondary carriage means 12 comprise a generally square chassis mounted for

displacement from end to end of the primary carriage means 5, that is to say in the direction of the wrapping station's Y axis. indicated by the arrows Y-Y.

The secondary carriage means 12 are displaced by secondary drive means comprising, a gear motor 13 carried by the secondary carriage means similar to the motor 7 and under the same type of control. The motor 13 has an output shaft carrying a toothed pulley 14 engaging a pliable, but substantially inextensible toothed belt 15 extending along a horizontal flange on the side member of the primary drive means and passing under wheels 16 on the secondary carriage means. It will be apparent, therefore, that the speed and magnitude of the displacement of the secondary carriage means 12 in the Y axis direction is as effectively controlled as is the displacement of the primary carriage means in the X axis direction.

It must be emphasised that the above described primary and secondary drive means are purely exemplificative, and may be replaced by other drive devices providing controlled or controllable displacement of the respective carriage means. For preference, the respective drive means are such that the magnitudes of the carriage means displacements are steplessly variable, as are the drive means described above.

However in other. less versatile, embodiments of the invention, one or both of the drive means may comprise a multi-stroke linear actuator or other means providing for a plurality of fixed starting and stopping points for the individual displacements. In such instances the number of predetermined paths available for the dispensing means would be multitudinous but not infinite.

Dispensing means 16 are mounted on the secondary carriage means 12. The dispensing means 16 may be a conventional dispensing device, carrying a roll 17 of stretch wrap film or other pliable wrapping medium, mounted for rotation with or upon a cantilever shaft extending downwardly from the secondary carriage means 12, in the direction of the Z axis indicated by the arrow Z.

The dispensing means 16 may be freely rotatable about the axis ofthe shaft to enable

those means to align themselves as required with a web 18 being drawn from the roll 17, and wrapped upon a target object 19, as the dispensing means are caused to circumnavigate that object in consequence of the controlled operation of the respective primary and secondary drive means.

Alteratively, and preferably, an electro-magnetic coupling or other energy absorbing device (not shown) may be incorporated in the shaft mounting arrangements to damp the rotary movement of the dispensing means 16 relative to the secondary carriage means 12.

In the illustrated embodiment the target object 19 may be a rectangular stack of steel sheet work pieces, and the wrapping may be applied only to the vertical faces of the stack to protect those faces and consolidate the stack. In such an instance the target object may be introduced and removed by a simple endless conveyor, indicated diagrammatically at 20.

In other embodiments of the invention, the mounting means for the dispensing means include tertiary carriage means, mounted on the secondary carriage means 12, supporting the dispensing means 16 and being displaceable to and fro in the Z axis direction. In such other embodiments the displacement of the tertiary carriage means (and the dispensing means carried thereby) is effected by tertiary drive means under the control of the control means in a manner analogous to that described above with reference to the primary or secondary carriage means.

In some instances the input data may be entered to the control means by hand using a conventional computer keyboard or the like. This may require the user to measure the target object and convert the measurements into appropriate input data defining the appropriate envelope. In other instances the target objects may be more standardised, with each object conforming to one of a limited number of possibilities. In that event, the input data for each possible object may be stored in a computer memory, and selected by a corresponding pre-determined call up signal or name.

In preferred embodiments the input data is automatically determined by the apparatus when the target object is introduced to the wrapping station, either by sensors determining the

various target object envelopes or, where appropriate, recognising the object as one of a class of which the envelope data has been memorised beforehand.

For example, the illustrated apparatus may be provided with a row of spaced apart intrusion sensors at the object input end of the wrapping station. Each of those sensors may comprise a radiation beam emitter and detector on the beam 4 at that end of the station and a corresponding reflector at or near the plane of the conveyor surface, or vice versa. In such instances the conveyor 20 may require to be a multiple chain conveyor or the like to provide for the stationary positioning of the reflector, or the radiating unit as the case may be, between the respective chains. The arrangement is such that if the detector receives a reflected radiation beam it produces a first signal output, if not it produces a second different signal output. Thus, if an established radiation beam is broken the sensor provides an indication of that event to the control means. Likewise when the broken beam is re-established the sensor provides an indication of that event to the control means. Provided the instantaneous position of the conveyor is also known to the control means, for example by means of a digital transducer associated with the conveyor drive, the control means is thus made aware of input data enabling those means to calculate the instantaneous widths and position of the object in the Y axis direction and the instantaneous lengths and position of the object in the X axis direction.

Such intrusion sensors are well known and need not be described in detail herein.

Frequently the radiation is a laser beam, and the reflector is a prismatic device ensuring a predetermined polarisation of the reflected beam. The detector is filtered by a polarising medium and only responds to a correctly polarised return beam. This prevents spurious operation due to reflection from the object itself.

In other embodiments the size, shape and position ofthe target object may be determined by a frame grabber and fixedly positioned video) camera. preferable a CCD camera enabling simple pixel by pixel signals to be produced for processing by the control means.

In other embodiments of the invention, the conveyor 20 may be replaced by other supporting devices for other types of target objects, for example, a rotary turntable or a series

of driven rollers both of which arrangements can be used to re-orient the target article during the wrapping process.

In other applications a rotary table turning counter to the movement direction of the dispenser can be used to increase wrapping speed.

The rigid structure described above may also be constructed as a mobile unit so as to move between two or more work stations (or wrapping stations). The structure in this case would be supported moveably on one of the known types of rail system readily available either floor mounted or overhead.

In an alternative embodiment, the rigid structure may be stationary and fixed to the floor with one or other of the above described supporting devices being conveyed into its envelope, for example, on rails.

The foregoing describes only some embodiments of this and modifications can be made without departing from the scope of the invention