Background art A machine and a method according to the present invention can for example be utilized in thermoforming plants destined to produce hollow articles, such as cups, plates, trays or other such disposable products.

These articles are produced from one or more thermoformable materials, such as polystyrene, polypropylene, polyethylene or the like, which are extruded in the form of a continuous sheet. The articles formed and separated from the rest of the sheet are collected in stacks and transferred to subsequent processing phases, for example edging for cups or packaging in the case of other articles.

Prior art machines generally include a movable mould (or half- mould), that is a matrix containing the cavities of the articles to be formed, which is movable between at least one position to form the articles and at least one position to eject the formed articles. Movement generally consists of components of translation and components of rotation.

An example of a machine of this type is for example described in the German patent DE 3346628, wherein the movements of the movable mould are produced by cams, keyed onto a common motor shaft, which act on a complex series of articulated levers. In addition to being particularly complex, with this solution there is a considerable amount of unbalance in the structure and the machine as a whole is particularly cumbersome.

In more recent prior art machines attempts have been made to

overcome these drawbacks by producing a machine wherein the movement mechanisms are simplified by using two separate motors, one dedicated to rotating the mould around its axis and the other dedicated to moving the mould in translation. Synchronism between the movements, and therefore control of the two motors, is implemented electronically.

It is nonetheless very difficult to vary, when necessary, synchronism between the two movements. In fact, during use of the machine, it may be necessary to vary for example the dwell times of the mould during the forming cycle as a function of the characteristics of the thermoformable material used. By varying the law of time of the translatory movement (during which forming is implemented in each cycle) the law of time of the rotational movement to which the mould is subjected must also be varied to maintain synchronism between the two motors. Adjustment of these machines is therefore extremely difficult.

Summary of the invention An object of the present invention is therefore to provide a machine and a method to produce articles by means of thermoforming wherein the drawbacks of prior art can be overcome.

Another object of the present invention is to provide a'machine and a method of the aforesaid type wherein synchronism between the translatory movement and the rotational movement of the mould can remain unchanged, notwithstanding the law of time for the movement of the same plane.

A further object of the present invention is to provide a machine and a method of the aforesaid type wherein high production efficiency can be obtained.

These objects are obtained by a machine according to claim 1 and a method according to claim 15. Further characteristics are specified in

the respective dependent claims.

According to a first aspect of the present invention, a machine is provided to produce articles by means of thermoforming, including at least one supporting plane for a portion of a thermoforming mould, wherein the supporting plane is movable between at least one position to form the articles and at least one position to eject the articles from the mould, an wherein means are provided to move the supporting plane between the at least two positions with components of rotational movement with respect to an axis of the plane and components of translatory movement along a rectilinear trajectory, characterized in that the means to move the plane include a single motor connected by a rigid kinematic chain to the axis of rotation of the plane.

The rigid kinematic chain allows synchronism between the translatory movements and the rotational movements to remain unchanged, irrespective of the law of time that is set by means of an electronic control unit that controls the single motor.

The rigid kinematic chain connected to the single motor is provided with an oscillating device and an intermitting device that respectively impart the rotational movements and the translatory movements according to a pre-established synchronization by their internal mechanisms. This means that synchronization of the movements of the plane can be calculated a priori and accurately maintained in a simply way.

According to a particular aspect of the present invention, the rigid kinematic chain includes means to transmit the components of rotational movement around the axis of rotation of the plane, according to a pre- established law of time, irrespective of the position of the plane along the rectilinear trajectory. In other words, it is possible in the design phase to choose the points in which to start, stop and invert rotation of the

plane. to optimize the stresses to which the various movable elements of the machine are subjected, and the overall dimensions of the actual machine as a function of the positions adopted by the mould during its travel in each cycle.

Thanks to this characteristic, during the design phase it has also been found that it is possible to establish laws of times of translation and rotation that allow each forming cycle to be implemented without ever stopping movement of the plane. Besides the forming position, in which the plane remains at a standstill for a few seconds, it is possible, for example, to transfer the formed articles without stopping the plane during the cycle.

In the ejection position, the mould can if necessary be stopped for a brief moment to allow ejection of the articles from the movable portion of the mould, as occurs in prior art machines, or it can be maintained in movement if ejection is to be produced by a condition of vacuum pressure according to a method according to another pending patent application by the same Applicant and the content of which is considered incorporated herein by reference. In this way the overall time of each operating cycle of the machine can be optimized, with noteworthy advantages also from the viewpoint of productivity.

In accordance with a second aspect of the present invention, a method is provided for the production of articles by means of thermoforming, wherein at least one portion of the thermoforming mould is mounted on a supporting plane movable between at least one position to form the articles and at least one position to eject the articles from the mould, and wherein the supporting plane is moved between the at least two positions with components of rotational movement with respect to an axis of the plane and components of translatory movement along a rectilinear trajectory, characterized in that it includes

movement of the plane by means of a single motor connected to the axis of rotation of the plane by a rigid kinematic chain.

During each cycle, the method according to the present invention may also include separation by cutting of the articles from the plate or sheet of material subjected to thermoforming, and also ejection of the articles from the respective cavities in the thermoforming mould.

Brief description of the drawings Further characteristics and advantages of the present invention shall become clearer from the description hereunder, provided with reference to the accompanying drawings, wherein: - Figure 1 is an elevation view of a machine for producing articles by thermoforming according to a possible embodiment of the present invention; - Figures 2A and 2B are schematic views showing the translatory movement of the movable portion of mould in a machine according to the present invention ; - Figures 3A and 3B are schematic views showing rotational movement of the movable portion of the mould in a machine according to the present invention; - Figure 4 is a schematic illustration of a coupling used in the machine according to the present invention; and - Figure 5 is a cross sectional view according to the plane ll-ll of the same machine in Figure 1.

Modes for carrying out the invention Figure 1 shows a machine for producing articles by thermoforming, to which a sheet 1 of thermoformable material is fed continuously.

The machine includes at least one supporting plane 10, in which a movable portion of mould 20 is housed, which moves cyclically up to a closing position, or the forming position, against a fixed portion of mould

25.

Movement of the plane 10 is assisted by guide systems along the vertical direction. The guide systems of the supporting plane 10 include in particular centering guides that employ, for example, eccentric bearings 35 to guarantee correct alignment of the supporting plane 10 when the movable portion of mould 20 is in proximity to the fixed portion of mould 25. This allows any clearances in the movable system to be taken up and thus guarantees in each cycle correct alignment between the two portions of the mould during the closing (or forming) phase.

The machine is provided with a single motor (or geared motor) 70, controlled by an electronic control unit (not shown) that establishes the law of time of operation. The motor 70 is connected to an intermitting device 40 and to an oscillating device 60 by a rigid kinematic chain to be described in greater detail hereunder.

Reference will now be made also to Figures 2A and 2B, which schematically represent the translatory movement of the supporting plane 10 and the associated movable half-mould 20 with respect to the fixed half-mould 25 along the rectilinear trajectory T.

The transmission of alternate movement along the trajectory T is produced by means of a toggle mechanism 30, connected to the supporting plane 10 by means of a pair of connecting rods 31 pivotally attached to the bearing journals 32 of the supporting plane 10. The bearing journals 32 are coaxial to the axis of rotation of the supporting plane 10.

On the other side, the toggle mechanism 30 is operatively connected to the intermitting device 40 (Figure 2A) to impart alternate lifting and lowering movement of the supporting plane 10 along the trajectory T.

The rotational movement of the output shaft by the intermitting device 40 is transformed into rectilinear alternate movement by the toggle

mechanism 30, but with the law of time established by the internal mechanisms of intermitting device 40.

In Figure 2A the movable portion of mould 20 is closed on the fixed mould portion 25, that is in the forming position. In this position the hot sheet 1 of thermoformable material is shaped according to the cavities in the mould 20, for example by compressed air, to impress in the sheet the forms of the articles desired, for examples cups, plates, trays or the like.

The articles thus formed can be removed by cutting them from the sheet 1 at the end of the forming phase, that is while the mould is in the position represented in Figure 2A. For example, it is possible to impart additional upward travel to the supporting plane 10 until the sheet 1 comes into contact with a shaped cutting matrix inserted in any one of the two mould portions 20 and 25.

Once the forming and cutting phase of the articles has been performed, the supporting plane 10 is carried towards the position to eject the formed articles following the rectilinear trajectory T; as represented in Figure 2B.

At the same time, the supporting plane 10 can be rotated with respect to the axis passing through the journals 32, according to a pre- established law of time, in the most suitable position of the plane 10 along the trajectory T.

Figures 3A and 3B schematically show the rotational movement of the supporting plane 10. Transmission of the components of rotation of the supporting plane 10 is produced by means of a particular type of coupling 50 formed of two articulated parallelograms connected rigidly to each other at two adjacent sides.

The coupling 50 is keyed on one side onto at least one of the bearing journals 32 of the supporting plane 10, while on the other side it is keyed

onto the output shaft 62 of the oscillating device 60. This device transmits to the coupling 50, and therefore to the supporting plane 10, alternate rotational movement, for a certain pre-established angle, first in one direction and then in the other, according to the preset law of motion in said oscillating device.

At the end of the forming and cutting phase, during lowering of the supporting plane 10 along the rectilinear trajectory T, the plane 10 can be rotated with respect to its axis until reaching the position indicated in Figure 3B, that is the transfer position of the articles formed and separated from the sheet of thermoformable material.

At or in proximity to this position, the articles formed and cut are ejected slightly from the movable portion of mould 20 by activating suitable ejection means. An example of ejection means that can be activated pneumatically to eject thermoformed cups from the mound-ils indicated with reference 28 in Figure 1.

The articles are thus transferred towards a pick-up station 100, producing for example a condition of vacuum pressure between the movable portion of mould 20 and the pick-up station 100 as established in a pending patent application by the same Applicant. In this way the transfer phase of the articles can also take place without stopping the movement of the supporting plane 10.

From the position represented in Figure. 3B, the supporting plane 10 is rotated in the opposite direction and brought back in alignment with the fixed half-mould portion 25 during simultaneous translatory movement along the trajectory T until returning to the position indicated in Figure 3A or 2A.

Figure 4 schematically represents in greater detail a coupling 50 of the type utilized in the machine according to the present invention.

The coupling 50 is formed essentially of two articulated

parallelograms 51 and 52, connected rigidly to each other at two adjacent sides by means of a common plate 53 in the form of a quadrilateral.

In particular, a first parallelogram articulation 51 includes a pair of connecting rods 54 joined to a first pair of opposed vertices 55 of the plate 53 in the form of quadrilateral. The connecting rods 54 are also joined to a flange 56 forming the remaining side of the parallelogram articulation 51 and keyed, for example, onto the output shaft 62 of the oscillating device 60.

A second parallelogram articulation 52 includes a pair of connecting rods 57, joined to the remaining pair of opposed vertices 58 of the quadrilateral plate 53. At opposed ends, the connecting rods 57 are joined to a flange 59, forming the remaining side of the parallelogram articulation 52 and in turn keyed onto the bearing journal 32 of the movable plane 10.

Connection of the connecting rods 54 and 57 to the diametrally opposed vertices of the quadrilateral (or parallelogram) shaped plate 53 allows a torque to be transmitted between the shaft 62 and the journal 32 irrespective of the distance between their centres along the trajectory T. Moreover, the translatory movement to move the journal 32 and the shaft 62 towards and away from each other does not transmit any torque to the ends of the coupling connected to the journal 32 and the shaft 62.

During operation, a driving torque supplied by the shaft 62 to the flange 56 is decomposed into two forces with null resultant and transmitted to the plate 53 through the connecting rods 54. The plate is therefore also subject to a torque transmitted in the form of two forces, also with null resultant, to the flange 59 through the connecting rods 57, and therefore to the bearing journal 32. In this way, the coupling is perfectly homocinetic.

Figure 5 shows a sectional view of the machine which illustrates in greater detail the diagram of movement of the supporting plane 10 through a rigid kinematic chain connected to a single motor 70.

In fact, movement of the movable plane 10 in its components of translation and rotation is imparted by a single motor 70 connected to a unit 71 to distribute movement to a single shaft including output portions 74 and 76 on the opposed sides of the distribution unit 71.

The portion of shaft 74 exiting on the right side is connected at the input to the intermitting device 40 which controls translatory movement of the movable plane 10 through the toggle mechanism 30.

The portion of shaft 76 exiting on the left side is connected to a shaft 78 through a timing coupling 75. This shaft is connected at the input to a right angle transmission 77 that in turn transmits movement to the oscillating device 60. The timing coupling 75 allows the movements of the rigid kinematic chain to be phased. The oscillating device 60 is thus also controlled by the single motor 70 to produce rotational movement of the movable plane 10 through the coupling 50.

As already mentioned hereinbefore, the laws of translatory and rotational movement of the movable plane 10 are determined by the internal mechanisms of the intermitting device 40 and of the oscillating device 60 respectively. These are mechanisms essentially including cam systems with profiles that are studied in the design phase to determine the laws that control movement of the plane 10.

Synchronism between the laws of movement thus determined, that is between the various components of movement, is instead obtained in a particularly simple way by the rigid kinematic chain connecting the single motor 70 to both the devices 40 and 60. By studying these and their synchronism in the design phase, the typical dwell times of prior art machines can be limited or even eliminated, to switch from situations of transtatory movement to those of rotational movement, and vice versa, as can those required for transfer of the articles produced.