FR2707081A1 - A method of controlling the operation of a rotary jaw closure unit for a packaging machine. - Google Patents

Abstract

During an interval (-alpha1; alpha2) during which the active elements (4) of the rotating jaws (2) interact with a packaging (W) so that products (A) are packaged by pressing, welding and possibly cutting said packaging, the orbital speed of the jaws (2) is regulated so as to be constant (omega0).

Description

METHOD FOR CONTROLLING OPERATION OF A UNIT OF

  CLOSURE WITH ROTARY JAWS FOR PACKAGING MACHINE

  The present invention relates to a method for controlling the operation of a rotary jaw closure unit for a packaging machine, having the features indicated in the preamble of claim 1. Closure units of the type specified above are commonly used. in the art, as described for example in US patents

  number US-A-4,862,673, US-A-4,914,889 or US-

  A-4.955.184, all issued to the holder of this application. In more recent configurations, the closure unit comprises two superimposed rotary jaws together defining a space or gap through which a tubular package passes within which articles or groups of articles to be packaged are disposed with a regular spacing. Each jaw generally comprises a driven shaft on which are mounted one or more active elements which, because of the rotation of the shaft on its axis, describe an orbital movement, generally

circular, around this axis.

  The synchronized movement of the jaws results in the fact that an active element of the jaw mounted to a higher position is lowered while an active element of the lower jaw is lifted so that the two elements in question compress the jaw between them. packaging and then close it to form a transversely sealed zone (generally by thermal welding of the material constituting the package). This sealed zone is then cut to separate the packaging thus formed, either by means of the jaws which formed the closure of the package or, in other configurations, by means of another unit to

  jaws against rotary downstream.

  It is also known and used in the art that jaw motion is not controlled with a uniform angular velocity, but rather, a technique of imparting to the jaws a generally "oscillating" motion which can be generally expressed by a type relation: O (0) = (o + Op (o0) op (0) generally expresses a pendulum function, according to which the angular velocity o (O) of the jaws passes through a minimal value in the region

  (0_0) o The jaws interact with the package.

  In order to obtain said pendulum function, epicyclic or other mechanisms are generally used, about which the patent can be usefully consulted.

  from US-A-4,914,889 previously cited.

  The use of these mechanisms always leads to a certain compromise of operation. The pendulum function mentioned above means that as it gets closer to the region of interaction with the package, the jaw slows its orbital motion to a minimum speed (so that it can somehow "accompany" the packaging) when the active element which acts at this time on the packaging is perfectly aligned in the vertical direction with the active element of the complementary jaw, then accelerates after compression, welding and possibly cutting the package, when the active elements of the jaws are removed from the package and released therefrom. What is mentioned above is strictly accurate for conventional mechanical type packaging machines, in which the movements of the various active units of the packaging machine are controlled by a single main motor via

  transmission mechanisms and springs.

  However, even in newer packaging machines of the so-called "electronic" type in which the various active units (which comprise the closing unit) are activated by respective motorized units (such as electronically controlled electric motors), said mechanism

  intervention remained virtually unchanged.

  In any case, this device can not be considered optimal. In fact, it does not make it possible to eliminate all the stresses (in particular those which are exerted in a direction of longitudinal traction) resulting from the interaction between the jaws and

packaging.

  The present invention proposes to provide a method for controlling a closing unit of the type specified above, in which these disadvantages are

completely eliminated.

  In accordance with the present invention, this object is achieved by a method having the features specified in claim 1. Advantageous developments of the invention constitute the subject of the invention.

Claims 2 to 8.

  The invention is described below by way of example, with reference to the accompanying drawings, in which: FIG. 1 generally illustrates in schematic form the structure of a closure unit that can be actuated using the method of the invention; 'invention; Figure 2 is a timing diagram illustrating the speed of rotation of the jaws in a unit operating in accordance with the invention; and FIG. 3 illustrates, in the form of a flowchart, the possible modes of operation of a

  control method of the invention.

  In FIG. 1, reference numeral 1 globally designates a rotary jaw closure unit of the type currently used in horizontal continuous-motion packaging machines of the type currently known as "circulating packages" or "shaping-filling-sealing" (or

  "FFS" (form-fill-seal) for short).

  More specifically, the unit 1 comprises two superimposed rotary jaws 2 intended to act on a tubular package W containing articles or groups

  Regularly spaced items to be packaged.

  Packing W advances between the two jaws 2 in a horizontal direction along a line indicated at T and from left to right in FIG.

  Vt speed which is normally constant.

  Each jaw 2 consists of a shaft 3 having a horizontal axis X3 on which one or more active elements 4 (two, angularly spaced 180 in the illustrated embodiment) constituting the jaws themselves, are mounted and provided with surfaces end 5 located at a distance R from respective axes of rotation X3. In use, as the axes 3 rotate (in opposite directions, for example counterclockwise and clockwise respectively for the two jaws 2 shown in Figure 1), the active elements 4 act on the package W by the ends 5 to produce a compression of the package W, a welding of the parts in contact so as to form a junction zone and possibly by cutting of this junction zone so as to produce a separation of the

separate packages thus formed.

  The welding of the packaging is generally carried out by thermal welding of the material constituting the packaging W itself: for this purpose, on the end surfaces 5 of the active elements 4 are heating elements, generally of the electric thermoresistive type ( not shown), intended to cause local thermal fusion of the W packaging material.

during a contact with it.

  With regard to the cutting of the welding regions, this can be done at the same time as the welding, by means of scissors 6 arranged on the end surfaces 5, or by means of a similar structural unit located downstream (also not illustrated). As previously mentioned in the introduction to this specification, the general criteria and construction details of the closure unit of the specified type are well known in the art and therefore do not require

no detailed description here.

  It is known in particular to link the rotary movements of the two shafts 3 to each other so as to obtain a perfect coordination of the movement of the active elements 4. As mentioned above, the result that one wishes to obtain is to make sure that whereas while an active element 4 of the upper jaw (which is located above the line T) is lowered towards the package W, while advancing with it, an active element 4 of the lower jaw (c ') that is to say, that which is located under line T) rises, also following the packaging in a perfectly symmetrical way

  with the active element of the upper jaw.

  In this way, with reference to the position illustrated in solid outline in FIG. 1, when the active element 4 of the upper jaw 2 is oriented vertically and therefore perpendicular to the path T of the package W, the lower element corresponding 4 is also located at an angularly identical position, under the line T. This result, and the synchronization of the movements of the two shafts 3, can be obtained for example in the manner illustrated in the arrangement shown in Figure 1 of the accompanying drawings, by connecting the shaft 3 of one of the jaws (for example the lower jaw) to a gearbox motor 7 driven by an electric motor 8 and transmitting the movement of the shaft 3 of the upper jaw by through a mechanical transmission for example consisting of two bevel gears, the output wheel of the first bevel gear (whose input wheel is driven by by the geared motor 7) driving the input wheel of the second bevel gear via a transmission shaft. This mechanical transmission is not explicitly illustrated in the accompanying drawings. It is clear that it is also possible to envisage a doubling of the motorization of the two jaws (upper and lower) by associating with each of them a respective electric motor which drives the shaft around which the respective active elements move. and synchronizing the movement of the two motors by means of a device known as

"electric shaft".

  As already known, the adoption of two rotary jaws that are not mutually symmetrical is not essential. It is known in particular in the art (reference will be made, for example, to US Pat. No. 4,862,673), closure units in which the upper jaw comprises a number of active elements different from the number of active elements of the invention. lower jaw (for example two active elements on the upper jaw and three

  active elements on the lower jaw).

  It is clear that in this case, the synchronization of the movement of the two shafts 3 must be carried out so as to take into account the different numbers of active elements. It is the same in the case where, for specific operating reasons, it is desired to use two jaws in which the orbital path radii described by the ends 5 of the active elements 4, are different from each other (it is necessary to

  in this respect will again refer to US-A-

  4.862.673, which also describes the possibility of giving the assembly 1 of the closure unit a generally pendulum movement back and forth). Whatever the construction details of the unit 1, it is sufficient to recall, to better understand the invention, that in general the speed of movement of the motor 8 (or motors if separate motors are used for both jaws) is controlled by taking into account the number of active elements on each jaw, the radius of the respective orbital path, etc., so as to obtain a synchronization of the approach (closing) movement and the movement of the jaw. separating (opening) the two active elements (one located on the upper jaw, the other on the lower jaw) relative to the package that advances along the path T to be compressed, welded and

possibly cut.

  For this purpose, the unit 2 for driving the jaws (in what follows, for simplicity, reference will be made to a single motor such as the motor 8 of FIG. 1) is controlled by means of a card respective control boards 9 (such boards are generally arranged on electric motors adopted for the most recent generations of packaging machines) used for electronic control, from a programmable unit 10 (it

  this is usually a PLC or "AP").

  In addition, a position sensor 11 (generally known as the encoder, preferably of the optical type) associated with the output shaft of the motor 8 or, in general, with one of the movable elements of the unit 1 is used. , to provide the programmable unit 10 with a signal representative of the angular position of the elements

  active 4 jaws of unit 1.

  Referring more particularly to the example of the embodiment illustrated in FIG. 1, it will be assumed in the present specification that the two jaws 2 each have two active elements 4 mounted diametrically opposite each other. (and therefore angularly spaced 180) and following the same orbital path as the active ends 5 with a radius R about the respective axis of rotation X3 of the

trees 3.

  It will further be assumed, depending on the dimensions of the articles A to be packaged and the packagings to be obtained (assuming furthermore that the angular position of the two elements 4 is defined by a general angle 0, where 0 0 = 0 when each element is oriented vertically), the active elements 4 come into contact with the package W which advances in the horizontal direction (trajectory T) when they form a cal angle with respect to the vertical and then separate from the compressed, welded and possibly cut after having traveled an angle x2 with respect to the

vertical alignment direction.

  These angles are generally related to the median plane of the active elements, which generally have a symmetrical shape. In all cases, even if one uses active elements 4 of non-symmetrical profile, these angles col and a.2 are always definable as being angular positions of rotation of the respective shaft 3. In the vast majority of situations of normal use, it can further be assumed that the two angles cx1 and a2 are equal to each other (interval 1; o2 symmetrical with respect to the state 0 = 0:

  element 4 orthogonal to the package W).

  The method of the invention is essentially based on the fact that, for a so-called electronic packaging (and in general in all situations in which it is possible to selectively and independently control the drive of the unit rotary jaw closure), it is possible to obtain (for example by electronic control of the card 9 by means of the control device 10 by a general feedback system from the angular position signal supplied by the encoder 11 ), a point-by-point adjustment of the rotational speed of the unit, in particular of the speed of rotation of the shafts 3 and consequently of the instantaneous speed at which the active elements 4 and in particular their peripheral ends 5, describe their movements

Orbital.

  More particularly, the present invention is based on the fact that this type of drive control is easy to obtain a regular orbital movement of the active elements so that during the entire time interval and over the entire distance during which the ends of the active elements 4 remain in contact with the package T, these ends move at a constant speed equal to the moving speed Vt of the package in the direction T. It is therefore possible to performing the condition that for the entire interval (-c2; + l1) during which the active elements 4 act on the package W,

  these active elements also follow the packaging itself.

even without variations of speed.

  More particularly, the electronic control of the speed of rotation of the motors 8 makes it possible to obtain the following result: (0) = θ = Vt / R for -a2 <e <cal (1) oo (O) represents the angular velocity of the trees 3 and R is the radius of the orbital trajectory described by the

  extremes 5 of the active elements 4.

  Obtaining the condition that the jaws 2 follow the packaging exactly and with

  Precision has several advantages.

- 10 -

  First and foremost, during the initial phase of the interaction between the jaws and the package, it is possible to avoid a relative slip phenomenon. More particularly, if the welding of the packaging to be closed is performed by thermal welding, this allows an optimization of the heat transfer between the jaws and the packaging

to be thermally welded.

  Secondly, when, due to thermal welding of the package, the ends of the jaws establish some adhesive contact with the package material W which deforms under the effect of thermal welding (and under the effect of of a possible shaping of the surface such as grooves, etc., which is normally produced by the ends 5 of the active elements 4 of the jaws), the exact synchronization of the speeds prevents the application of longitudinal stresses to the packaging W by the jaws. These longitudinal stresses can damage the packaging, especially in the region of the weld that has just been formed, or in extreme cases,

  also cause a tear in the packaging itself

  even. The device of the invention, however, allows a significant improvement over the devices known in the art, whether mechanical devices or others, in that, as a pendulum action of the speed of rotation is ensured in the contact interval with the package W, in order to produce a forward movement of the active elements 4 as close as possible to the speed of movement of the package, the actual speeds of displacement are identical only in a very short time interval, which generally only corresponds to the vertical alignment position (O = 0) of the two jaws. The diagram of Figure 2 schematically illustrates a speed control law indicating

- 11 -

  the rotational speed of the rotary jaw unit,

  obtainable according to the invention.

  In particular, the diagram of FIG. 2 illustrates the variation of the speed o (O) imparted to the shafts 3 by the motor 8 as a function of the angle which describes the angle of inclination of the active elements 4 by

  relative to the vertical alignment plane of the two axes X3.

  As shown in the illustration, the interval (-xl; a2) during which the speed of rotation is maintained at the constant value wo is defined by the relation (1)

previously indicated.

  Outside this interval (which corresponds to the interval during which the active elements 4 are in contact with the package T), the speed of rotation

jaws vary.

  In particular, when approaching the package (O <a2), the speed of rotation is brought to gradually decrease from a maximum value omax up to the value oO in accordance with a relationship of the type O (0 ) = 0 + al '(0 + E1) o the function ol (0 + al) is a decreasing function substantially identical to a rectilinear ramp having end connection areas

(function sin2 or of this type).

  Likewise, after the active elements 4 have moved away from the package (0> + a2), the rotation speed o (0) is progressively reduced from the value oO to the omax value in accordance with a function of the type: o (0) = oo + ol (O - c2) o 2 (0 - c2) is a rectilinear acceleration ramp (here also with an end connection region corresponding for example to a function

  sin2), which reduces the speed (0) to the omax value.

  This last value is reached for an angular value 02 which also expresses the period of the

diagram of Figure 2.

  The value of 02 equals 180 in the case of rotary jaw units with a single element

- 12 -

  4. In this case, between two successive actions of the element 4 on the package, the shaft 3 on which the active element is mounted must rotate

  angular equal to 360 (2 x 02 with 02 = 180).

  In the embodiment illustrated by way of example herein, in which there is mounted on each shaft 3 two active elements 4, 02 is equal to 90 for the presence of two active elements. In this case, between two successive actions on the package, the shaft 3 must rotate by an angle equal to 180, that is to say 2 x 02

with 02 = 90.

  In the same way, if the jaws had to comprise three elements (with an action on the packaging every 120 of rotation of the tree), 02

should be equal to 60.

  It is clear that if the two jaws had to have rotational radii R of the active elements different from each other, the relations expressed by the formula 1 and by the figure 2 would be determined

  independently for each jaw.

  In general, o (O) = 2 (-0), that is, the deceleration ramp and the acceleration ramp are

  usually controlled in a symmetrical manner.

  The diagram of FIG. 3 illustrates, in the form of a flowchart, the possible implementation of a control program controlling the motor card 9 via the PLC 10 in accordance with FIGS.

criteria previously described.

  At predetermined intervals, the controller 10 reads (phase 100) the signal supplied by the encoder 11 and representative of the current position (angle θ) of the active elements 4. For conceptual simplicity, it is assumed here that the rotary jaws are

identical to each other.

  The control device 10 then compares (comparisons made at the phases 101, 102, 103) the signal representing the position of the active element with the three threshold values -a2, a1 and 02, to identify

- 13 -

  if the current value is in one of three

different beaches.

  More particularly, if the angle θ has a value lower than -al (comparison phase 101 with a negative result), the controller 10 acts on the card 9 to control (phase 104) a gradual decrease in the angular velocity so to cause a progressive change from omax value to 0 (phase 104, with return to phase 100). This result can be obtained for example using a look-up table which, for each value of 0, provides a value

  corresponding function 2 (O).

  If the current value of 0 is between -al and + a2 (positive result of the comparison during the phase 101, negative result of the comparison during the phase 102), the automaton 10 imposes on the card 9 a speed of constant rotation oo = Vt / R (phase 105 with return to the

reading phase 100).

  If the current value of 0 is greater than a2 and less than 02 (positive result of the comparisons during the phases 101 and 102, a negative result of the comparison during the phase 103), the automaton 10 acts on the card 9 so as to progressively increase the motor speed from 0 to omax (phase 106, followed by a return to read phase 100). In this case too, it is possible to use a look-up table, in particular the one mentioned above, to exploit the characteristics of

  symmetry of the functions o1 (0) and 2 (0).

  Finally, if the comparison made in step 103 indicates that the current value of 0 has exceeded the value 02, the AP makes it (step 107) to skip this current value of 0 during the value of the period of time. Figure 2, that is to say, to increase it twice to 02, by starting again the program from the entry of the comparison to the

phase 101.

- 14 -

  It follows from the foregoing that the device of the invention lends itself to an automatic adaptation depending on the geometry of the unit 1 and / or the characteristics of the articles A and the package W (quantities Vt, cal, a2, R, etc.). It is in particular possible to consider a preconfiguration of the programmable logic controller 10 (for example by acting on the memory unit or on memory units associated therewith) so that, during a variation of the operating characteristics ( so-called "shape variations"), the programmable automation 10, when it receives information (for example from a keyboard during a simple action of an operator that does not even need to be particularly specialized) concerning dimensions of the articles A, the characteristics of the packaging to be made, and (optionally) other parameters, selects the quantities mentioned above fully automatically and, just as automatically, adapts its operation to said characteristics.

- 15 -

Claims (8)

  A method of controlling the operation of a rotary jaw closure unit (1) for a packaging machine, said unit comprising at least one active element (4) which, in use, can interact with a package ( W) in an orbital path movement about an axis (X3), said at least one active element being associated with a controllable motor means (8) (9, 10) so as to selectively vary the speed of said motion orbital, characterized in that it comprises the steps of: - determining the interval (-al; x2) of the orbital trajectory during which said at least one active element (4) must interact with said package (W), and - controlling said respective orbital path within said range at a constant speed (O 0) 2. Method according to claim 1, applied to a closing unit (1), wherein said orbital trajectory of said at least one active element (4) takes place within at least said interval (-al; c2 ), with a given radius (R), and wherein the movement of said package (W) is effected at a given constant speed (Vt) characterized in that, within said interval (-cal; a2), the angular velocity (o (0)) of said orbital path is controlled to be equal to a constant value 0 given by Vt / R where Vt is said given constant speed and R is said given radius.   3. Method according to claim 1 or claim 2, characterized in that, within the intervals respectively upstream (-02; -al) and downstream (a2; 02) of the interval (- 51; a2) during which it interacts with the package (W), the speed of - 16 -   said orbital path is controlled so as to   respectively decrease and grow.   4. Method according to claim 3, characterized in that in said upstream interval (-02; -cl) and in said downstream interval (+ a2; 02), the speed of said orbital movement is modified in accordance with a substantially linear law.   5. Process according to any one of   Claims 1 to 4, characterized in that   orbital trajectory is controlled with a cyclic variation, each cycle (-02; 02) of said motion comprising an initial interval (-02; al) during which the velocity of said orbital trajectory decreases, an intermediate interval (- a2; said interval of interaction with said package (W) at a constant speed (aO), and a terminal interval (c2; 02) in which said speed of the orbital trajectory is growing.   6. Process according to any one of   preceding claims, characterized in that said   interaction interval (-a2; a1) with the package (W) is substantially symmetrical with respect to the central reference position (0 = O) at which said at least one active element (4) is substantially orthogonal by relative to the package (W).   7. Process according to any one of   preceding claims, characterized in that   comprises the step of associating with said at least one active element (4), at least one respective motor (8), and using a corresponding electronic means (9, 10) for selectively controlling the speed of   rotation of said at least one motor (8). - 17 -   8. Method according to claim 7, characterized in that it comprises the operation of associating with said at least one active element (4) an angular detection element (11) capable of supplying said electronic means (9; 10) with via a general feedback device, a signal representative of the instantaneous position reached by said at least one active element (4).