CN112874173A

CN112874173A - Printing assembly for digital printing on continuous metal strip

Info

Publication number: CN112874173A
Application number: CN201911202912.6A
Authority: CN
Inventors: 贾科莫·普蒂尼
Original assignee: Globus Ltd
Current assignee: Globus Ltd
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2021-06-01
Anticipated expiration: 2039-11-29
Also published as: CN112874173B

Abstract

Printing assembly for digital printing on a continuous metal strip (S), comprising: a digital printing unit (12) having a printing area (15) and a conveyor belt (16) arranged to advance the continuous metal strip (S) in a longitudinal direction (A) through the printing area (15); an inlet guide unit (28) located upstream of the printing unit (12) and configured to guide the continuous metal strip (S) along a path comprising at least one first movable fold (B1) freely movable in the longitudinal direction (A), and an outlet guide unit (46) located downstream of the digital printing unit (12) and configured to guide the continuous metal strip (S) along a path comprising at least one second movable fold (B2) freely movable in the longitudinal direction (A).

Description

Printing assembly for digital printing on continuous metal strip

Technical Field

The present invention generally relates to a system for the surface treatment of a continuous metal strip, for example of steel or aluminium.

More specifically, the present invention relates to a printing assembly for digital printing on a continuous metal strip.

Background

Digital printing by means of ink jet printers is becoming increasingly popular in many technical fields. The increasing popularity of digital printers stems primarily from the fact that: they allow high-definition multi-color printing on various types of objects without any restrictions on the print pattern, and they allow the print pattern to be changed in real time without the need to operate to retool the machine.

Digital printers typically include a plurality of print bars, each having a respective color. The product to be printed is advanced through the print zone and the print bar extends in a direction transverse to the direction of movement of the product to be printed.

One of the problems with digital printing is ensuring accurate positioning of the workpiece to be printed relative to the print head while the product is fed through the digital printer. The clarity of the printed image can be compromised if the product to be printed does not remain centered in the lateral direction during its movement. In general, in order to obtain good print definition, the positioning tolerance in the transverse direction of the workpiece must be less than 0.02mm during its movement through the print zone.

Currently, there are various types of systems for digital printing on individual workpieces (such as, for example, ceramic tiles, and rigid or semi-rigid sheets such as plastic, wood, metal, etc.).

When the workpiece to be printed is of a defined size, there is generally no problem in ensuring the centering of the workpiece during its movement through the digital printer.

Machines for digital printing on continuous strips are also known. However, in the current state of the art, digital printing can only be performed on continuous strips made of very flexible materials, such as, for example, fabrics or films of plastic material. In fact, the current solutions can only ensure the necessary sharpness of the printing on the continuous strip if it can be maintained with high precision while advancing in the longitudinal direction, without tensions that could compromise the positioning precision.

Currently in the prior art, solutions for digital printing on continuous metal strips, for example with a thickness from 0.05mm up to 1mm and above, are not available. In fact, during its movement in the longitudinal direction, the continuous metal strip is subjected to transverse forces which tend to cause displacements in the transverse direction of the entity greater than the tolerance (0.02mm) required to obtain good print definition. Even with a centering device, the accuracy required for quality printing cannot be ensured.

Disclosure of Invention

It is an object of the present invention to provide a printing assembly for digital printing on a continuous metal strip having a thickness of 0.05mm up to 1mm and above, for example a continuous metal strip of aluminium or steel.

According to the invention, this object is achieved by a digital printing assembly having the features that form the subject matter of claim 1.

The claims form an integral part of the disclosure provided herein in relation to the invention.

Drawings

The invention will now be described in detail with reference to the accompanying drawings, given by way of non-limiting example only, in which:

figure 1 is a schematic side view of a digital printing assembly according to the invention,

FIG. 2 is a schematic plan view of the digital printing assembly of FIG. 1, and

figures 3 and 4 are schematic side views on an enlarged scale of the part represented by the arrows III and IV shown in figure 1.

Detailed Description

With reference to the accompanying drawings, numeral 10 indicates a printing assembly for digital printing on a continuous metal strip S. The continuous metal strip S may be any metal material, such as, for example, steel or aluminum, and may have a thickness of from 0.05mm up to 1mm or more, and may have a width of about 300 mm and 1800 mm. The continuous metal strip S has an indefinite length along its longitudinal axis. The continuous metal strip S may come from a reel or an in-line work station (e.g. a painting station).

Printing assembly 10 includes a digital printing unit 12 that includes a plurality of print bars 14 that define a print zone 15. The digital printing unit 12 comprises a conveyor belt 16 arranged to support and advance a continuous metal strip S in a longitudinal direction a through a printing area 15 of the digital printing unit 12. The conveyor belt 16 may have an upper horizontal branch 16a connected to a suction source for holding the continuous metal strip S by means of suction during its passage through the digital printing unit 12.

Downstream of the digital printing unit 12, a section may be arranged to dry the printed ink according to the properties of the ink itself. After this, the surface treatment unit may be arranged to apply a protective layer, for example on the printed surface of the continuous metal strip S. The ink treatment section 18 may have a respective conveyor belt 20 to support and advance the continuous metal strip S in the longitudinal direction.

Printing assembly 10 may include an entrance traction constraint 22 arranged to feed continuous metal strip S towards digital printing unit 12. The inlet traction constraint 22 may include two rollers 24 rotatable about respective parallel axes. At least one of the rollers 24 of the inlet traction constraint 22 may be driven in rotation by an electric motor 26. The continuous metal strip S may be wound according to a substantially S-shaped path onto the roller 24 of the inlet traction constraint 22. Motor 26 of inlet traction constraint 22 may regulate the feed rate of continuous metal strip S in the inlet section of printing assembly 10.

The inlet guide unit 28 is located downstream of the inlet traction constraint 22. The inlet guide unit 28 guides the continuous metal strip S between the inlet traction constriction 22 and the inlet section of the conveyor belt 16. The inlet guide unit 28 guides the continuous metal strip S along a path comprising at least one first movable fold B1, which is freely movable in the longitudinal direction a. The continuous metal strip S is bent along a semicircular track of substantially U-shape. In one possible embodiment, the inlet guide unit 28 can guide the continuous metal strip S along a substantially S-shaped path comprising: a first movable bent portion B1 that is freely movable in the longitudinal direction a; and a first fixed fold B1' fixed in the longitudinal direction a. The first movable bent part B1 and the first fixed bent part B1' may have recesses opposite to each other.

In one possible embodiment, the inlet guide unit 28 may have a first sliding plane 30, a second sliding plane 32 and a third sliding plane 34, which are parallel to each other and spaced apart in the vertical direction, and along which the continuous metal strip S may move in a path running from the inlet traction constraint 22 to the digital printing unit 12. The

sliding surfaces

30, 32, 34 may be provided with idler rollers that support the continuous metal strip S in an S-shaped path. One or more of the

sliding surfaces

30, 32, 34, for example, the upper sliding plane 30, may be a pneumatic support plane configured to support the corresponding section of the continuous metal strip S on an air cushion. The upper sliding plane 30 of the inlet guide unit 28 may be aligned with the upper horizontal branch 16a of the conveyor belt 16.

The upper sliding plane 30 of the inlet guide unit 28 may be provided with centering means 35 which guide the lateral edges of the continuous metal strip S and perform the centering of the continuous metal strip S in the transverse direction with respect to the digital printing unit 12.

A first distance sensor 38 may be provided to measure the distance D1 between the first movable fold B1 of the continuous metal strip S in the longitudinal direction a relative to a fixed reference point. The distance sensor 38 may be a non-contact sensor, such as a laser distance sensor, an ultrasonic distance sensor, or the like.

The inlet guide unit 28 may be provided with a curved guide section 36 to guide the continuous metal strip S between the second 32 and third 34 sliding planes and to apply a first fixed bend B1 to the continuous metal strip S.

Printing assembly 10 may comprise an outlet traction constraint 40 located at the outlet of printing assembly 10 and arranged to advance continuous metal strip S from the outlet of printing assembly 10 towards a downstream device, which may be a winding reel for collecting continuous metal strip S in a spool, or a device for performing further processing on continuous metal strip S. The exit traction constraint 40 may comprise two rollers 42 rotatable about respective axes parallel to each other, and the continuous metal strip S may be wound around the rollers 42 according to a substantially S-shaped path. At least one of the rollers 42 of the outlet traction constraint 40 can be rotated by means of a respective electric motor 44. In the example shown, the two rollers 42 are driven in rotation by respective electric motors 44.

Printing assembly 10 includes an exit guide unit 46 located downstream of digital printing unit 12 and upstream of exit drag constraint 14. Similar to the inlet guide unit 28, the outlet guide unit 46 guides the continuous metal strip S along a path comprising at least one second movable fold B2, which is freely movable in the longitudinal direction a. The outlet guide unit 46 can guide the continuous metal strip S along a substantially S-shaped path comprising: a second movable bent portion B2 that is freely movable in the longitudinal direction a; and a second fixed fold B2' fixed in the longitudinal direction a. The second movable bent part B2 and the second fixed bent part B2' may have recesses opposite to each other.

The outlet guide unit 46 may include a first slide plane 48, a second slide plane 50, and a third slide plane 52 that are parallel to each other and spaced apart in a vertical direction. The third bent part B3 extends between the first sliding plane 48 and the second sliding plane 50, and the fourth bent part B4 extends between the second sliding plane 50 and the third sliding plane 52. The sliding surfaces 48, 50, 52 may be provided with idler rollers. One or more of the sliding

surfaces

48, 50, 52 (e.g., the upper sliding surface 48) may be an air cushion plane. The upper slide surface 48 may be aligned with the conveyor belt 20 of the ink treatment section 18.

The printing assembly 10 may comprise a second distance sensor 54 arranged to detect a distance D2 in the longitudinal direction a of the second movable fold B2 relative to a fixed reference point. The second distance sensor 54 may be a non-contact sensor, such as a laser distance sensor, an ultrasonic distance sensor, or the like

The printing assembly 10 may include an electronic control system 56 programmed to receive information from the

distance sensors

38 and 54 and control the inlet and

outlet traction constraints

22 and 40 to maintain a distance D1 of the first movable fold B1 and a distance D2 of the second movable fold B2 within a predetermined range. The electronic control system 56 may include a first PLC58 associated with the first distance sensor 38 and the inlet traction constraint 22, and a second PLC60 associated with the second distance sensor 54 and the outlet traction constraint 40. The electronic control system 56 may also receive information regarding the speed of the conveyor belt 16 of the digital printing unit 12 and possibly the speed of the conveyor belt 20 of the ink handling section 18.

When the distance D1 of the first movable bend B1 approaches a predetermined minimum value, the electronic control system 56 controls the motor 26 of the first constraint 22 and increases the speed of the continuous metal strip S upstream of the inlet guide unit 28 by means of the first PLC 58. When the distance D1 of the first movable fold B1 approaches a predetermined maximum, the electronic control system 56 controls the motor 26 of the entrance traction constraint 22 to slow the feed speed of the continuous metal strip S upstream of the entrance guide unit 28.

Accordingly, when the distance D2 of the second movable bend B2 approaches the predetermined minimum value, the electronic control system 56 controls the motor 44 of the outlet traction constraint 40 by means of the second PLC60 to reduce the feeding speed of the continuous metal strip S downstream of the outlet guide unit 46. When the distance D2 of the second movable fold B2 approaches a predetermined maximum value, the electronic control system 56 controls the motor 44 of the outlet traction constraint 40 to increase the feeding speed of the continuous metal strip S downstream of the outlet guide unit 46.

During operation, the straight section of continuous metal strip S between the first movable fold B1 and the second movable fold B2 advances in the longitudinal direction a through the digital printing unit 12 with substantially zero tension in the longitudinal direction. In fact, the first fold B1 and the second fold B2, which are freely movable in the longitudinal direction a, eliminate longitudinal tension on the section of the continuous metal strip S comprised between the movable folds B1, B2. Eliminating the longitudinal tension on the continuous metal strip S during its advancement through the digital printing unit 12 ensures a high degree of precision in the positioning of the continuous metal strip S with respect to the digital printing unit 12 and ensures a high quality of print definition.

To further improve the print quality, a smoothing unit may be provided, located upstream of the printing assembly 10 to eliminate the undulations of the continuous metal strip S. Eliminating the undulation of the continuous metal strip upstream of the printing assembly allows reducing the distance between the print head and the surface of the continuous metal strip (which should ideally be less than 2 mm).

In the figures, the inlet and outlet movable folds are shown in horizontal position, but it is understood that within the scope of the invention there are alternative solutions that can bring the movable folds in a vertical or inclined position.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to those described and illustrated, without thereby departing from the scope of the present invention as defined by the annexed claims.

Claims

1. Printing assembly for digital printing on a continuous metal strip (S), comprising:

-a digital printing unit (12) having a printing area (15) and a conveyor belt (16) arranged for advancing the continuous metal strip (S) in a longitudinal direction (A) through the printing area (15),

-an inlet guide unit (28) located upstream of the printing unit (12) and configured to guide the continuous metal strip (S) along a path comprising at least one first movable fold (B1) freely movable in the longitudinal direction (a); and

-an outlet guide unit (46) located downstream of the digital printing unit (12) and configured to guide the continuous metal strip (S) along a path comprising at least one second movable fold (B2) freely movable in the longitudinal direction (a).

2. The printing assembly of claim 1, comprising: an entry traction constraint (22) configured to advance the continuous metal strip (S) upstream of the entry guide unit (28); and an outlet traction constraint (40) configured to advance the continuous metal strip (S) downstream of the outlet guide unit (46).

3. The printing assembly of claim 2, comprising:

-a first distance sensor (38) arranged to measure a distance (D1) in the longitudinal direction (a) of the first movable fold (B1) relative to a fixed reference point; and a second distance sensor (54) arranged to measure a distance (D2) of the second movable fold (B2) in the longitudinal direction (A) relative to a fixed reference point, and

-an electronic control system (56) programmed to receive information from the distance sensors (38, 54) and to control the inlet traction constraint (22) and the outlet traction constraint (40) so as to keep the distance (D1) of the first movable fold (B1) and the distance (D2) of the second movable fold (B2) within a predetermined range.

4. Printing assembly according to any one of the preceding claims, wherein at least one of the inlet guide unit (28) and the outlet guide unit (46) is configured to guide the continuous metal strip (S) along a substantially S-shaped path comprising a movable fold (B1, B2) and a fixed fold (B1', B2').

5. Printing assembly according to any one of the preceding claims, wherein at least one of the inlet guide unit (28) and the outlet guide unit (46) comprises a first sliding plane (38, 48), a second sliding plane (32, 50) and a third sliding plane (34, 52) parallel to each other and spaced apart from each other in a vertical direction.

6. Printing assembly according to claim 5, wherein said first sliding plane (38, 48) is aligned with an upper horizontal branch (16a) of said conveyor belt (16) of said digital printing unit (12).

7. Printing assembly according to claim 6, wherein the inlet guide unit (28) comprises a centering device (35) associated with the first sliding plane (38).

8. A method for digital printing on a continuous metal strip (S), comprising:

-feeding a continuous metal strip (S) in a longitudinal direction (A) through a digital printing unit (12),

-upstream of the digital printing unit (12), guiding the continuous metal strip (S) along a path comprising at least one first movable fold (B1) freely movable in the longitudinal direction (a) and movable in the longitudinal direction (a)

-downstream of the digital printing unit (12), guiding the continuous metal strip (S) along a path comprising at least one second movable fold (B2) freely movable in the longitudinal direction (a).

9. The method according to claim 8, comprising measuring a distance (D1) of the first movable fold (B1) in the longitudinal direction (A) relative to a fixed reference point, relative to the first movable fold (B1), and controlling a feed speed of the continuous metal strip (S) upstream of the first movable fold (B1) so as to keep the distance (D1) in a predetermined range.

10. Method according to claim 8 or claim 9, comprising measuring the distance (D2) of the second movable bend (B2) in the longitudinal direction (a) with respect to a fixed reference point, and controlling the feed speed of the continuous metal strip (S) downstream of the second movable bend (B2) so as to keep the distance (D2) in a predetermined range.