EP3225412A1

EP3225412A1 - Inkjet printer

Info

Publication number: EP3225412A1
Application number: EP17164115.2A
Authority: EP
Inventors: Gianpaolo Coin
Original assignee: Grafco Srl
Current assignee: Grafco Srl
Priority date: 2016-04-01
Filing date: 2017-03-31
Publication date: 2017-10-04
Anticipated expiration: 2037-03-31
Also published as: EP3225412B1; EP3225412B8

Abstract

Inkjet printer (10) for reproducing images, writing and/or designs on a printable surface of a substrate (12), comprising:
- a base (20) provided with first motor means (22) for moving a support device (24) for the substrate (12) on guiding means (27) arranged along a sliding axis (X);
- a printing unit (30) connected to the base (20) and comprising a casing (70) inside which an inkjet printing head (32) and driving means (36) are housed; the printing head (32) being slidably movable by means of the driving means (36) on guiding means (34) extending inside the casing (70) and arranged along a printing axis (Y) transverse to the sliding axis (X);
- a programmable control unit (40) operatively connected to the first motor means (22) and to the driving means (36) for the coordinated movement of the support device (24) and the printing head (32).

In accordance with the invention, the casing (70) of the printing unit (30) is provided with releasable connection means (50) by means of which the printing unit (30) is releasably connected to the base (20).

Description

The present invention relates to an inkjet printer.
Inkjet printers are normally used to reproduce images, writing and/or designs on a surface of a substrate.
For the purposes of the present invention the term "substrate" is understood as meaning any flat or three-dimensional object having at least one surface on which inkjet printing may be performed.
The substrate may be made of a rigid or flexible material.
Examples of a substrate printable using an inkjet printer are fabrics, sheets of glass or polymer material, objects made of plastic, metal, glass or wood and the like.
It is known that, for some time now, inkjet printing has replaced traditional printing methods because of the advantages which it is able to achieve in terms of speed and quality of the printed image on the substrate.
Inkjet printers are generally formed by a motorized base on which a gantry structure designed to support the printing head carriage is rigidly fixed.
The motorized base is provided with motor means suitable for moving a substrate support device along the printing path, while the printing carriage is moved along a direction transverse to the printing path by means of suitable driving means.
A printer control unit coordinates the movements of the support device with those of the printing carriage, ensuring that the substrate moves in a controlled manner along the printing path.
These inkjet printers, although regarded favourably, are not without drawbacks or problems.
The structure of the printer, in fact, composed of a printing unit rigidly fixed to the base, while, on the one hand, it ensures the necessary precision of the relative movements of substrate and printing head, on the other hand, gives rise to not insignificant maintenance problems.
In fact, even though during the course of the years the viscosity and density characteristics of the inks used in inkjet printing have improved, it not infrequently happens that during the printing process the inks may harden, blocking, even only partially, the nozzles of the printing head, thus adversely affecting the printing process.
If the obstruction of the nozzles cannot be removed by means of normal cleaning washing operations, the printing head must be replaced.
Replacement may be performed solely by stopping the machine and, even though it consists of a routine maintenance operation (since it may be repeated frequently during the period of activity, i.e. working life, of the printer) it inevitably results in a long downtime of the printer.
Similar problems are encountered whenever an operational problem occurs with the driving means of the printing head.
In this case also, in order to take remedial action and solve the problem, it is necessary to stop the inkjet printer for a certain period of time, which may also be fairly long, and replace or repair the components which are not working.
Finally, the fact that the printing unit is rigidly fixed to the motorized base means that there is a limit to the maximum possible dimensions of the substrate on which the image or the design must be printed.
It is evident, in fact, that the maximum dimensions of the substrates which may be loaded onto the printer depend on the centre-to-centre distance between the supports of the printing unit and the dimensions of the support device.
Consequently, in the case where a substrate having dimensions greater than the centre-to-centre distance of the supports of the printing unit must undergo printing, a second printer must be used, with an obvious increase in the equipment and labour costs.
The object of the present invention therefore is that of overcoming at least partially the drawbacks mentioned above with reference to the inkjet printers of the known type.
The task of the present invention is to provide an inkjet printer which is able to limit the downtime due to printing problems or malfunctions.
In addition, a task of the present invention is to provide an inkjet printer which is able to print an image or a design on substrates of different sizes or shapes.
Furthermore, a task of the present invention is to provide an inkjet printer which has a versatile structure and is able to ensure a high printing precision.
Finally, a task of the present invention is to provide an inkjet printer which may be easily modified or adapted to substrates which have a different width and/or height, without having to use specialized labour.
The object and tasks indicated above are achieved by an inkjet printer according to Claim 1.
The characteristic features and further advantages of the invention will become clear from the description, provided hereinbelow, of a number of examples of embodiment, provided by way of a non-limiting example, with reference to the attached drawings in which:

Figure 1 shows in schematic form a perspective view of a first embodiment of the inkjet printer according to the invention;
Figure 2 shows in schematic form a front view of the inkjet printer according to Figure 1;
Figure 2A shows a schematic view, similar to that of Figure 2, in which the printing unit is separated from the base;
Figures 3 shows in schematic form a side view, on a larger scale, of the detail indicated by A in Figure 1;
Figure 3A shows a schematic view, similar to that of Figure 3, in which the printing unit is separated from the base;
Figure 4 shows in schematic form a front view of the base of an inkjet printer according to the invention;
Figure 5 shows a view similar to that of Figure 4, but in a different operating configuration;
Figure 6 shows in schematic form a simplified side view of the base of the inkjet printer according to Figure 4;
Figure 7 shows in schematic form a top plan view of the base of the inkjet printer according to Figure 6;
Figure 8 shows a schematic cross-sectional view along the plane indicated by VIII-VIII in Figure 6;
Figure 9 shows a schematic cross-sectional view along the plane indicated by IX-IX in Figure 6;
Figure 10 shows a schematic cross-sectional view along the plane indicated by X-X in Figure 6;
Figure 11 shows in schematic form a simplified view of an inkjet printer according to the invention, in a disassembled configuration;
Figure 12 shows in schematic form a view similar to that of Figure 11, in which the inkjet printer is in the assembled configuration;
Figure 13 shows a simplified view similar to that of Figure 11;
Figure 14 shows a front view of the printer according to Figure 13, in an assembled configuration;
Figure 15 shows a schematic perspective view of the base of a printer according to the invention, in a first operating configuration;
Figure 16 shows a schematic front view of the base of the inkjet printer according to Figure 15;
Figure 17 shows a view similar to that of Figure 15, but in a different operating configuration;
Figure 18 shows a schematic front view of the base according to Figure 17;
Figure 19 shows a schematic front view of an inkjet printer according to the invention, in a further operating configuration;
Figure 20 shows a view similar to that of Figure 19 in which the base of the printer is connected to a second printing unit.

With reference to the figures, Figure 1 shows a first inkjet printer - indicated overall by 10 - which is provided in accordance with the principles of the present invention.
The inkjet printer 10 is designed to reproduce images, writing and/or designs on a printable surface of a substrate 12.
The printer 10 is preferably a printer of the industrial type, i.e. is suitable for reproducing images, writing and/or designs also on heavy and large-size substrates 12.
The term "substrate" is understood as meaning, as already mentioned above, any article which is made of rigid or flexible material and on which an inkjet printing operation may be performed.
As schematically shown in Figure 1, the printer 10 comprises a base 20 and a printing unit 30 which are connected together.
The base 20 is provided with first motor means 22 for moving a support device 24 for the substrate 12 on guiding means 27 arranged along a sliding axis X (see Figures 8 and 10).
As shown in the attached figures, the base 20 has preferably a hollow box-like structure composed of four vertical walls 21 and two horizontal surfaces 23 connected together by means of mechanical support elements 31.
As shown schematically in Figure 1, in which the support device 24 is shown partially cross-sectioned, the support device 24 is designed to slide backwards and forwards, in the direction of the sliding axis X, above the upper surface 23 of the base 20.
With reference to Figures 8-13, 15 and 17, in which for greater clarity the vertical walls 21 and the horizontal surfaces 23 of the base 20 have been removed, in one embodiment the support device 24 is moved by means of a slide 25 situated underneath the upper surface 23 of the base 20.
The connection between support device 24 and slide 25 may be performed by means of lateral support elements which are designed to slidably engage corresponding through-slits 127 provided in the upper surface 23 of the base 20.
The slide/support device assembly is moved by the first motor means 22 which may consist of one or more linear actuators operated by one or more electric motors. The linear actuator may consist for example of a worm screw actuator 27 which has, keyed thereon, a support, for example of the recirculating ball bearing type 29, intended to be connected to the slide 25.
Different types of transmission systems, for example a belt transmission, may be used in order to satisfy other particular requirements.
Advantageously, the support device 24 may be provided with heating means for ensuring quicker drying of the ink deposited on the substrate 12.
Moreover, the support device 24 may also be provided with suction means for retaining small-thickness substrates, such as a sheet of paper, on the support device 24 during the various printing movements.
Furthermore, as will become clear from the description below, the support device 24 may be provided with raised surfaces for loading articles of clothing, such as T-shirts, shirts and trousers, and removable surfaces of various sizes.
In a known manner, the support device 24 may also consist of a driving belt intended to travel between a front roller and a rear roller which are arranged in the base. This solution, since it is well-known to the person skilled in the art, is not shown in the attached figures.
The printing unit 30 comprises a casing 70 inside which the printing head 32 and driving means 36 are housed.
The printing head 32 is movable slidably by means of driving means 36 on guiding means 34 extending inside the casing 70 and arranged along a printing axis Y transverse to the sliding axis X.
The printing head 32 and the driving means 36 are of the known type and will not be described in detail in the description below.
The system for supplying the inks of the printing head 32 is also advantageously housed inside the casing 70. This supply system, since it is well-known to the person skilled in the art, is not shown in the attached figures.
Preferably the guiding means 34 consist of one or more guide bars 34 (see Figures 1 and 2A).
The printer 10 also comprises a programmable control unit 40. The control unit may be programmable in a known manner via a keyboard or via a touch screen device.
This control unit 40 is operatively connected to the first motor means 22 of the base 20 and to the driving means 36 of the printing unit 30.
The function performed by the control unit 40 is to coordinate the movements of the support device 24 and the printing head 32.
In a known manner, the printer 10 may comprise a signal generator, for example an encoder, able to supply to the control unit 40 of the printer the exact position of the support device 24 along the guides 27. Depending on the position detected, the control unit 40 will perform movements of the printing head 32 along the printing axis Y.
At the same time, after each passing movement of the printing head 32 along the axis Y, the control unit will perform a movement of the support device 24 along the sliding axis X.
In accordance with the invention and as is clearly shown in Figures 2A and 3A, the casing 70 of the printing unit 30 is provided with releasable connection means 50 by means of which the printing unit 30 is releasably connected to the base 20.
In other words, the entire printing unit 30, owing to the provision of these releasable connection means 50, may be easily separated from the base 20, with the advantages which will be described in detail below.
As shown in Figures 2A, 3 and 3A, preferably the connection means 50 comprise at least one electrical connector 52, for electrically connecting the printing unit 30 to the base 20, and at least one releasable fixing element 54, for mechanically fixing, in a removable manner, the printing unit 30 to the base 20.
The releasable connection means 50 are designed to engage corresponding fixing seats 62, 64 provided on a mounting plate 60 of the base 20.
As shown schematically in the figures, the electrical connector 52 may be a male bayonet connector designed to engage inside a corresponding female connector 62 provided in the plate 60.
Alternatively, the electrical connector 52 may be a female bayonet connector designed to engage with a corresponding male connector provided in the plate 60.
By means of the electrical connector 52 it is therefore possible to connect electrically in a removable manner the printing head 32 and the driving means 36 to the base 20. In this way it is also possible to connect the printing unit 30 to the control unit 40. The electrical connection between printing unit and base, finally, allows the same power supply means used for the base to power also the driving means of the printing unit and any other electrical components provided in the printing unit.
The releasable fixing element 54 may consist for example of a tap bolt or a stud bolt intended to engage a through-hole provided in the printing unit 30 and to be screwed inside a corresponding female thread 64 provided in the plate 60.
The connection between the screws 54 and the corresponding female threads 64 ensures, once connection has been performed, the necessary solidity of the base/printing unit assembly. On the other hand, it also ensures the correct relative positioning of the printing unit 30 and the base 20.
Furthermore, the provision of a threaded connection between printing unit 30 and base 20 allows the printing unit 30 to be easily disassembled from the base 20.
Different types of electrical connectors which may comprise, by way of a non-limiting example, also wireless connection technologies such as Bluetooth and WiFi transmission protocols, and different types of releasable fixing systems may be used in order to satisfy other specific requirements.
Advantageously the provision of connection means 50 suitable for removably connecting the printing unit 30 to the base 20 allows a same base 20 to be used in combination with two or more printing units 30 which are identical to each other.
In the event of a fault, for example should the printing head 32 become blocked up with ink, it is merely required to loosen the screws 54 and disconnect the electrical connector 52 in order to separate the entire printing unit 30 from the underlying base 20, so as to be able to replace it with a functioning unit.
The repair or maintenance of the damaged component may therefore be carried out after disconnecting the printing unit 30 from the base 20, without therefore resulting in stoppage of the printer (except for the minimum time needed to replace the printing unit).
In the printers of the known type, on the other hand, the repair or the replacement of the individual components of the printing unit must be performed with the printer stopped, since the printing unit is rigidly connected to the base and the replacement of its single components necessarily results in stoppage of the entire printer.
Advantageously the base 20 may be used also in combination with two different printing units 30, provided that they are equipped with connection means 50 compatible with the corresponding seats provided in the base 20.
These printing units may for example be designed to support the printing head 32 at different heights with respect to the support device 24.
In this way it is therefore possible to use the same base 20 in combination with different printing units 30 in order to carry out printing on substrates of varying thickness depending on the needs.
As shown in the attached figures, the casing 70 of the printing unit 30 consists preferably of a hollow gantry structure.
This structure comprises two support columns 71 connected by a cross member 72, inside which the printing head 32 is slidably movable.
Advantageously, the ink supplying device may also be housed inside the cross member 72 or the support columns 71.
With reference to Figures 2 and 2A, advantageously, the releasable fixing means 50 are provided at the end where the support columns 71 rest on the base 20.
Gripping means 74 designed to facilitate removal of the printing unit 30 from the base 20, once the connection means 50 have been released, may also be provided on the support columns 71.
These gripping means 74 may consist of two handles, or other gripping systems, provided on the sides of each of the support columns 71.
Advantageously, the printing unit 30 comprises a stiffening frame 80, preferably made of steel. The stiffening frame 80 is preferably inserted inside the casing 70 of the printing unit 30.
This stiffening frame 80 may comprise two lateral supports 81, suitable for being fixed to the support columns 71, and a cross bar 82, suitable for being fixed to the cross member 72 of the printing unit 30.
Advantageously, the guides 34 of the printing head 32 and the driving means 36 may also be fixed to the stiffening frame 80.
The function performed by the stiffening frame 80 is to brace the entire structure of the printing unit 30, preventing the precision of the printing process from being adversely affected by any flexing of the guides 34 or misalignment between cross member and lateral supports of the printing unit.
Moreover, the provision of this frame 80 allows removal and, if necessary, replacement of the printing unit to be performed safely, ensuring correct alignment of the support columns 71 and the cross member 72 of the printing unit 30.
Advantageously, the end of each lateral support 81 intended to be arranged facing the base 20 may be provided with a support foot 84, also made of metallic material and intended to be connected to the mounting plate 60 of the base 20.
Advantageously, the connection means 50 may be arranged on these support feet 84.
As shown in the attached figures, the base 20 may comprise two symmetrical support elements 90, where the printing unit 30 may be connected to the base 20.
The support elements 90 are located on the sides of the base 20 and are aligned along a transverse axis W which is arranged orthogonal to the sliding axis X.
The mounting plate 60 is preferably arranged on the upper end of each of the two support elements 90.
Advantageously, as shown in detail in Figures 13-18, the base 20 may comprise second motor means 26 for moving the support elements 90 along the transverse axis W, so as to allow the distance W1, W2 between said support elements 90 to be varied.
The distance between the support elements 90 is understood as meaning the length, perpendicular to the sliding axis X, which joins together the outermost surfaces of each support element 90.
The second motor means 26 are controlled by the control unit 40 of the printer 10.
The movement of the two support elements may be performed advantageously independently of each other.
Advantageously, the machine may be provided with a laser projector system for projecting points or lines orthogonal to each other, inserted on the sliding guides of the axis X and the transverse axis W.
This system advantageously helps an operator, where necessary, to check that the support elements 90 remain fixed orthogonally relative to this axis X, when they are moved or positioned on the sides of the base 20.
Therefore, it is clear from a comparison of Figures 14, 16 and 18 that, by means of the motor means 26, not only is it possible to vary the distance W1, W2 between the support elements 90, but it is also possible, while keeping this distance W2 unchanged, to vary the position of the support elements 90 with respect to the base 20, maintaining a perfectly orthogonal position relative to the axis X.
These second motor means may consist of a linear actuator 28 operated by an electric motor 26.
The actuator 28 may be of the worm screw/nut type or may be an actuator of the hydraulic/pneumatic type.
As shown schematically in Figures 16 and 18, the rods of the actuators 28 may be protected by protective panels 128 integral with the support elements 90 and designed to be extracted from or retracted inside the base 20.
Detection means, of the encoder type, may be connected to the linear actuator, so as to transmit to the control unit 40 the exact position of the two support elements 90.
With reference to Figures 19 and 20, advantageously the provision of releasable connection means 50 between base 20 and printing unit 30, together with the provision of support elements 90 movable along the axis W, allows two or more different printing units 30 to be used with a single base 20, provided that that they are equipped with connection means compatible with the fixing seats 62, 64 formed in the base 20.
Advantageously, in the event of faults or malfunctioning of the printing unit, the faulty printing unit 30 may be replaced rapidly with an identical perfectly functioning unit.
Moreover, it is also possible to replace the printing unit 30 with a similar, but differently sized unit.
For example, the same base 20 may be advantageously used in combination with a printing unit 30 having a distance between the support columns 71 equal to Y3 (see Figure 19) and with a printing unit 130 having a distance between the support columns 71 equal to Y4 (see Figure 20).
Replacement of the printing units 30 and 130 may be performed very rapidly, after varying the distance W3, W4 between the support elements 90 of the base 20.
It is clear how, as a result of this characteristic feature, it is possible to use the printer 10 in order to reproduce images and designs on substrates with different dimensions. In fact, the support device 24 may be equipped with support surfaces which are removable or replaceable depending on the printing requirements and also have dimensions greater than that of the support device 24, provided that they remain within the centre-to-centre distance of the two support columns 71 of the printing unit.
These removable surfaces may also have an asymmetrical form.
With reference to Figures 4, 5 and 11, advantageously each support element 90 may comprise a movable appendage 91.
Said movable appendage 91 is preferably arranged on the upper surface of the support element 90 and is designed to slide along vertical guides 93 formed in the support element 90.
Advantageously, the mounting plate 60 of the base 20 may be fixed to the movable appendage 91 so that the printing unit 30 is in turn joined together with the movable appendage 91, once the connection between base and printing unit has been performed.
The base 20 may comprise third motor means 92 suitable for moving the movable appendages 91 along an elevation axis Z perpendicular to the sliding axis X and to the printing axis Y.
The third motor means 92, as schematically shown in Figures 11, 12, 13 and 15, may be advantageously provided on each support element 90.
Advantageously the motor means 92 may consist of a linear actuator 94 operated by an electric motor.
The linear actuator 94 may be of the worm screw/nut type or may be an actuator of the hydraulic/pneumatic type (see for example Figures 11 and 12).
In a similar manner to that described above with reference to the first and second motor means, the support elements 90 may be provided with detection means able to indicate to the control unit 40 the exact height of the movable appendages 91, so as to control the movement thereof.
Advantageously, owing to the provision of these movable appendages 91, the printing unit 30 may be raised from the base 20, moving the printing head 32 away from or towards the support device 24.
In this way it is therefore possible to use the same printer 10 in order to reproduce images and designs on substrates which have different thicknesses.
Advantageously, the provision of an appendage 91 movable along the elevation axis Z may be combined with the provision of support elements 90 movable along the transverse axis W.
In this way, a same printer 10 may be used to perform printing on substrates which have dimensions and forms which are very different from each other, without adversely affecting the printing precision.
The inkjet printer 10 according to the invention may be used as a stand-alone machine controlled by an operator responsible for programming the control unit 40 and loading the various substrates to be printed.
Alternatively, the inkjet printer 10 may be configured as an automatic printing station along a production line. Such a production line will be preferably complete with an automatic system for loading the substrate and an automatic system for unloading the printed substrate.
At this point it is clear how the predefined objects have been achieved.
Firstly, with an inkjet printer according to the present invention the machine downtime due to malfunctioning of the printing unit may be reduced.
Should these problems arise, the printing unit 30 may be replaced with a new unit provided that it is equipped with connection means 50 compatible with the base 20.
Secondly an inkjet printer according to the invention is versatile and able to be used with different substrates.
The possibility of moving the support elements 90 along an axis W transverse to the sliding axis X and the possibility of varying the height of the support elements 90 along an elevation axis Z allows the same base to be used, if necessary combining it with different printing units 30, in order to perform printing on substrates varying in shape and size from each other.
Thirdly, owing to the provision of the stiffening frame 80 in the printing unit 30 and the provision of high-precision linear actuators it is possible to ensure a high degree of printing precision.
Finally, the provision of the releasable connection elements such as those described facilitates greatly the replacement of the printing unit, avoiding the need to use specialized labour.
Obviously the description above of an embodiment applying the innovative principles of the present invention is provided by way of example of these innovative principles and must therefore not be regarded as limiting the scope of the rights claimed herein.

Claims

Inkjet printer (10) for reproducing images, writing and/or designs on a printable surface of a substrate (12), comprising:
- a base (20) provided with first motor means (22) adapted to move a support device (24) for the substrate (12) on guiding means (27) arranged along a sliding axis (X);

- a printing unit (30) connected to the base (20) and comprising a casing (70) inside which an inkjet printing head (32) and driving means (36) are housed; the printing head (32) being slidably movable by means of the driving means (36) on guiding means (34) extending inside the casing (70) and arranged along a printing axis (Y) which is transverse to the sliding axis (X);

- a programmable control unit (40) operatively connected to the first motor means (22) and to the driving means (36) for the coordinated movement of the support device (24) and the printing head (32);
characterized in that
the casing (70) of the printing unit (30) is provided with releasable connection means (50) by means of which the printing unit (30) is releasably connected to the base (20).
Inkjet printer (10) according to claim 1, characterized in that said releasable connection means (50) comprise at least one electrical connector (52) for electrically connecting the printing unit (30) to the base (20) and at least one releasable fixing element (54) for fixing the printing unit (30) in a predetermined position relative to the base (20).
Inkjet printer (10) according to claim 1, characterized in that said releasable connection means (50) are suitable for engaging corresponding fixing seats (62, 64) arranged on a mounting plate (60) of the base (20).
Inkjet printer (10) according to claim 1, characterized in that the casing (70) of the printing unit (30) is a gantry structure which comprises two support columns (71) connected by a cross member (72) inside which the printing head (32) is slidably movable; the releasable connection means (50) being arranged at the ends of said support columns (71).
Inkjet printer (10) according to claim 4, characterized in that the casing (70) of the printing unit (30) comprises a stiffening frame (80); said stiffening frame (80) comprising two lateral supports (81), suitable for being fixed to the support columns (71), and a cross bar (82), suitable for being fixed to the cross member (72).
Inkjet printer (10) according to any one of the preceding claims, characterized in that the base (20) comprises at least two support elements (90) where the printing unit (30) is releasably connected to the base (20); said support elements (90) being aligned along a transverse axis (W) which is situated orthogonal to the sliding axis (X).
Inkjet printer (10) according to claim 6, characterized in that at least one mounting plate (60) is arranged on the upper end of each support element (90).
Inkjet printer (10) according to claim 6, characterized in that the base (20) comprises second motor means (26) suitable for moving the support elements (90) along the transverse axis (W) so as to vary the distance (W1, W2) between said support elements (90).
Inkjet printer (10) according to claim 6, characterized in that each support element (90) comprises a movable appendage (91); the base (20) comprising third motor means (92) suitable for moving said movable appendage (91) along an elevation axis (Z) perpendicular to the sliding axis (X) and to the printing axis (Y).
Inkjet printer (10) according to claim 4, characterized in that it comprises at least two printing units (30) identical to one another and suitable for being interchangeably connected to the base (20).
Inkjet printer (10) according to claim 8, characterized in that it comprises at least two printing units (30, 130) suitable for being interchangeably connected to the base (20); a first printing unit (30) having a first distance (Y3) between the support columns (71) and a second printing unit (130) having a second distance (Y4) between the support columns (71) different from the first distance (Y3).
Inkjet printer (10) according to claim 6, characterized in that it comprises a laser projector system for projecting points or lines orthogonal to each other, the system being inserted on the guiding means (27) of the sliding axis (X) and the transverse axis (W) along which the support elements (90) are movable; said projector system being suitable for indicating correct positioning of the support elements (90) relative to the base (20).