ES2957903B2 - CARDBOARD SHEET TRANSPORT SYSTEM IN DIGITAL PRINTER - Google Patents

Description

DESCRIPTION

CARDBOARD SHEET TRANSPORT SYSTEM IN DIGITAL PRINTER

The invention, as its name indicates, refers to a system that transports a series of cardboard sheets in optimal conditions as they pass through a digital printing process.

Said system comprises at least one perforated band and a vacuum table that optimizes the suction process in flow and pressure on different types of cardboard sheets with different thicknesses, maintaining said optimization even with the first and last sheet of a production batch, with the table enabling the passage of the flow as the first sheet enters, adapting to its dimensions and disabling the passage of the flow once the last sheet enters.

The technical sector to which it belongs is printing.

BACKGROUND OF THE INVENTION

Digital printers currently print at a distance of between 1 and 4 mm from the plate, forming a tiny drop that falls on the plate to be printed. If the distance increases, the quality of the print is affected and degraded, since these drops risk being deviated by the passage of air at that distance.

In order to solve this problem, digital printers must ensure that the cardboard sheets are as flat as possible when going through the printing process, so that the printing distance is as homogeneous and constant as possible at all times and across the entire surface of the sheet to be printed.

Currently, digital printers offer expensive and complex solutions when it comes to transporting plates in a printing process, and the best-performing versions have the disadvantage of not being able to efficiently transport plates that only partially occupy the conveyor belt.

One of the most commonly used systems is the vacuum system. For this, the inside of the table has a negative pressure zone with respect to the outside, with the inside and outside connected. The positive pressure exerted on the cardboard sheet keeps it flat and on the table. This system includes a suction system, such as a turbine, which generates a vacuum inside the table. To optimize the vacuum effect, mechanisms are used that regulate the width of the vacuum table according to the size of the sheet. The objective is to minimize the open area while the turbines are working, since otherwise all the suction power is lost.

EP1097821A2 relates to a plate transport apparatus providing air suction to adhere the plate to a belt while said plate is being transported, in which the belt may have an optimised surface roughness and the adjacent suction holes provided thereon may be separated by an optimised distance. This type of embodiment is intended for thin paper plates so this solution is not suitable for handling thick cardboards.

Patent ES2837072 refers to a vacuum system for holding the pieces to be printed, which comprises a drawer connected to a suction system and provided with a perforated wall in relation to the surface of the printing table, where the drawer has side panels that vertically close the interior of the drawer, which are movable to adjust the separation between them in relation to the width of the pieces to be printed. Said drawer has individual chambers that have different degrees of suction, being greater at the inlet of the plates and decreasing as it advances towards the outlet.

US2011292145 relates to a vacuum system that creates a vacuum pressure that keeps the printable medium on the transport surface, the vacuum system has at least one adjustable deflector configured to move in a transverse direction of the process and change a dimension of the vacuum system based on a dimension of the printable medium. This patent seeks to incorporate some vacuum in the printing zone, making a system that adjusts to the edges by giving up having a vacuum in the printing zone.

US2021/0213759 relates to a vacuum transport system including a vacuum chamber lid having a first surface and a second surface opposite the first surface, as well as a plurality of openings through the lid from the first surface to the second surface. A plurality of seals are provided to match the location of the openings. Each seal extends along the length of the vacuum chamber lid and is operable to open or close an opening region. A vacuum chamber beneath the second surface of the vacuum chamber lid is configured to apply vacuum to the medium through one or more of the openings that are open.

This type of execution requires oversizing the turbines that generate the vacuum, causing high energy consumption. In addition, in most cases, it is not possible to keep the first or last plate completely flat as it passes through the printing process, generating unproductive stops with the consequent plate jams. Each stop generates a lot of waste, since all the plates that have come out of the feeder have to be discarded.

DESCRIPTION OF THE INVENTION

To solve the problems described above, the invention relates to a system for transporting cardboard sheets in a digital printing process that has a vacuum table which minimizes its open area, adapting to the dimensions of the cardboard sheets in a digital printing process.

The difference in pressure between the inside of the table and the area occupied by the cardboard sheets to be printed will keep them flat and attached to the transport table.

The cardboard sheets enter the digital printing process in a row on a mobile belt, which we will call a transport belt, preferably perforated, which allows suction on the sheets. This transport belt supports and transports the cardboard sheets from a feeder, passing through the printing area, to finally the area where they are stacked.

In order for the cardboard sheets to remain sufficiently flat and close to the transport belt throughout the transport process so that when they pass under the printing heads they maintain this same position, the transport system must be able to generate a pressure difference between the outside and the inside of the table. To do this, it is necessary to equip it with a suction system coordinated with a system for opening and closing certain areas of the transport table. The efficiency of the system will depend on whether there is communication between the inside and outside of the table only in the areas occupied by the cardboard sheets to be printed, since if air is sucked in from the outside in areas not occupied by the cardboard sheets, this will mean a loss of suction force and, therefore, a waste of energy.

Controlling the areas where suction occurs is an objective of the present invention.

The objective is then to open suction zones that coincide with the area that the cardboard sheets to be printed occupy at any given time, from the first to the last sheet.

For this purpose, the transport system comprises a vacuum system which in turn comprises a vacuum table, suction elements and control means.

The vacuum table comprises a set of superimposed layers, which can be made of different materials, configurations and functions, interrelated and which close the upper part or the inner chamber of the vacuum table. The relative positions of each of the layers allow the chamber to communicate or disconnect from the outside of the vacuum table.

The chamber is connected on one side to suction elements, such as one or more turbines, and on the other, as has been said, to the layers that allow or prevent communication with the outside.

The set of superimposed layers comprises:

A first, outer layer, or conveyor belt, preferably perforated, although it could be meshed. In a preferred embodiment, this belt is an endless belt. This belt is supported by at least two rollers, one of which is preferably the traction roller.

A second layer, which we will call the attached layer, on which, preferably, the transport belt runs, which has a series of holes that, in a possible execution and in a specific relative position with respect to the transport belt, are aligned with the perforations of said transport belt.

A third layer, which we will call the dynamic layer, which comprises holes that cross its surface where said surface is divided into sub-areas with independent movement that follow a limited path transversally to the advance of the cardboard sheets. In this limited movement, the holes of this layer are aligned or misaligned with respect to the holes of the adjacent layer, and where appropriate with the perforations of the transport belt, enabling or not the passage of air through the layers. In this way, the fraction of longitudinal area that will support the difference in pressure between the inside and outside of the vacuum table is defined and that, therefore, will have a suction effect on the cardboard sheets to be printed deposited on the transport belt. Said fraction of longitudinal area increases as the first cardboard sheet enters the printing process and decreases as the last cardboard sheet exits in its movement on the transport belt.

In another order of things, for the adjustment of the transversal area of suction action, the transport system also comprises a control system for opening or closing the longitudinal width. This system controls at least two facing gates arranged in the chambers of the vacuum table longitudinally to the transport belt, moving closer to and further away from each other, where said gates adjust to the width of the cardboard sheets defining the transversal area of suction in the transport belt. In a preferred execution, the gates adapt to the width of the cardboard sheets by means of a reduction motor and a screw longitudinally limiting the range of vacuum action.

The combination of the aforementioned layers, the longitudinal gates and the suction turbine, allow to delimit an area of the transport table in which a suction effect will be created, keeping the cardboard sheets flat and secure, while the rest of the surface of the transport table is closed and without communication between the outside and the inside.

The chambers preferably arranged at the bottom of the vacuum table comprise a series of windows that have means to communicate with at least one turbine located, preferably, on the sides of the vacuum table.

The turbine works at high flow and pressure levels, which translates into a high suction force, and by being located as close to the vacuum table as possible, it minimises the pressure losses generated by using longer pipes.

In a preferred implementation, the windows are arranged along the lower central part of the chamber.

In a possible execution, the windows are arranged on the sides of the vacuum table and connected to the turbines by means of pipes suitable for helping to pass the current generated from the turbine.

The air flow generated by the turbine moves from the chamber to the turbine through these windows.

In one possible implementation, the dynamic layer is located under the top of the transport belt and between it and the attached layer.

In one possible implementation, the dynamic layer is a motorized blind that closes or opens in the direction of advance of the cardboard sheets, blocking or not the passage of the air current.

In another possible implementation, the dynamic layer comprises a series of plates that, when activated from the sides of the transport table, move transversely to enable or disable communication between the inside and outside of the table.

In another possible execution, the dynamic layer comprises a series of slats in contact with each other on their larger sides and with independent movement, this being a path transversal to the direction of advance of the cardboard sheets, where said slats have a series of slots that when aligned with the, where applicable, perforations of the transport belt and with the holes of the attached layer enable the passage of the air current towards the turbine.

The dynamic layer's stroke is limited by a mechanism that moves said surface totally or partially transversally and by a stop that it encounters.

The mechanism that pushes and moves all or part of the dynamic layer is preferably at least one pneumatic piston that is activated and moves said surface, aligning its holes with those of the adjacent layer and, where appropriate, the perforations of the transport belt as the cardboard sheets move during the printing process.

The transverse movement of the dynamic layer generates at least two positions, open and closed, which condition the passage of the air flow. In the open position, a series of holes in the dynamic layer are aligned with the holes in the adjacent layer and, where appropriate, with the perforations in the transport belt, thus allowing the turbine to draw air from outside the table. In the closed position, the dynamic layer moves, causing the holes previously aligned with the holes in the adjacent layer to become misaligned, thus blocking the passage of the air flow. It will be common, except at the time of closing at the end of printing, that at the same time as a series of holes become misaligned, others become aligned.

In a preferred embodiment, there may be intermediate positions between open and closed, which may present a partial alignment, which may be progressive, of its holes with the perforations of the transport belt and with the holes of the attached layer, thus controlling the degree of vacuum force on the transport belt on the cardboard sheets.

The transport system has a mechanical and dynamic control that acts on the vacuum system, allowing sections or stretches to be opened as the transport system detects the proximity of the first plates and closing the air flow when the last plates progressively leave the transport belt.

This dynamic control refers to:

- That the vacuum system is enabled a certain time (t1) before the first plate enters the transport belt.

- That the vacuum system is disabled for a certain time (t2) after the last cardboard sheet leaves the printing process.

- Both (tx) and (t2) can be manually adjusted by the user or can be automatic.

In one possible implementation, the dynamic control is cancelled allowing the air current flow to always be enabled and constant.

In another possible implementation, the dynamic control can disable sections of vacuum action along the transport band leaving a series of sub-areas of the dynamic layer fixed.

Automatic adjustment allows a small area to be always left open, preferably the area closest to the entry of the cardboard sheets, to make it easier to reach the optimum vacuum regime before the sheets enter the transport table.

In one possible implementation, the vacuum system in the inlet area of the transport table is open without closing mechanisms.

The air stream usually has a hard time reaching optimum suction levels, which is why the vacuum takes a few seconds to reach the proper operating level. The opening and closing mechanism is controlled in such a way that there is a control of the time lag between the opening of the air stream and the entry of the first cardboard sheet onto the transport belt, leaving the sheet firmly attached to the belt from the outset.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows an exploded view of the different elements of the transport table, where the transport belt (2) driven by the rollers (6) can be seen, the chambers (4) that house the facing gates (10) that longitudinally delimit the vacuum action and the windows (11) that connect the interior of the chambers with the turbines (3).

Fig. 2 shows an exploded section of the vacuum table with the different superimposed layers where the transport belt (2), the dynamic layer (9), which has the sub-areas (7), and the attached layer (8) can be seen, and the chambers (4) can also be seen.

Fig. 3 shows a section of the set of different layers where, in a possible execution, the image on the left shows the open system where the holes of the attached layer (8) are aligned with the holes of the dynamic layer (9) and the perforations of the transport belt (2). The image on the right shows another section of the set of layers with the closed system where the holes of the dynamic layer (9) are misaligned with respect to the perforations of the transport belt (2) and the holes of the attached layer (8).

Fig. 4 shows the arrangement of the gates (10) inside the chambers where the movement made by said gates across the width of the transport table can be seen.

DESCRIPTION OF A FORM OF EXECUTION OF THE INVENTION

The invention relates to a system for transporting cardboard plates in a digital printing process which comprises a vacuum system that allows a vacuum table (1) to adapt to the dimensions of the plates, minimising their open area, which allows the plates to remain firmly attached to the transport belt (2), allowing digital printing to be carried out without generating waste.

The cardboard plates enter the digital printing process in a row supported on a perforated transport belt (2), which transports the plates from a feeder through the printing area to the stacking area.

The transport system comprises a vacuum system which in turn comprises a vacuum table (1), a series of suction turbines (3) and control means.

The vacuum table (1) comprises three interrelated superimposed layers that close the upper part of the inner chamber (4) of the vacuum table (1).

Said chamber (4) communicates on one side with the suction turbines (3) and on the other side with the layers that allow or prevent communication with the outside.

The set of superimposed layers comprises:

An endless perforated conveyor belt (2) supported by a free roller (6) and a traction roller.

An attached layer (8), on which the transport belt (2) runs, which has a series of holes that in a specific position with respect to the transport belt (2) are aligned with the perforations of said transport belt.

A dynamic layer (9) comprising holes that pass through its surface where said layer is divided into sub-areas (7) with independent movement that perform a limited displacement. In said displacement the holes are aligned or misaligned with respect to the holes of the adjacent layer (8) and with the perforations of the transport belt (2) enabling or disabling the passage of air through the three layers. In this way, the fraction of longitudinal area that supports the difference in pressure between the interior and the exterior of the vacuum table is defined, causing the air suction effect between the cardboard sheets and the transport belt.

This fraction of longitudinal area increases as the first cardboard sheet enters the printing process and decreases as the last cardboard sheets exit on their movement along the transport belt (2).

As regards the adjustment of the transversal area of action of the suction on the transport belt (2), the transport system has a control system for opening or closing two facing gates (10) arranged in the chamber (4) of the vacuum table (1) longitudinally to the transport belt (2), moving closer to and further away from each other by means of a reduction motor and a spindle adjusting to the width of the cardboard sheets, thus defining the transversal area of suction on the transport belt (2).

By combining the action of the layers, gates and turbines, a limited area of the transport table is generated based on the dimensions of the cardboard sheets, in which the suction effect is produced, helping to keep said sheets flat and secure, while the rest of the surface of the transport table is without communication between the inside and the outside, favouring the minimum energy consumption necessary for the proper functioning of the vacuum system.

The chambers (4) arranged in the lower part of the vacuum table (1) comprise a series of windows (11) connected by means of pipes to the turbines (3) located on the sides of the vacuum table (1) where said windows (11) are arranged along the lower central part of the chamber (4).

The dynamic layer (9) performs a movement transversal to the movement of the transport belt (2) where said movement is limited on one side by a pneumatic piston that activates the movement and on the other side by a stop (not shown) that defines the limit of the displacement.

The transverse displacement of the mobile surface generates at least two positions conditioning the passage of the air flow, open and closed.

In the open position the holes in the dynamic layer (9) align with the holes in the attached layer (8) and with the perforations in the transport belt (2) allowing the turbines (3) to draw air from outside the transport table.

In the closed position, the dynamic layer (9) performs a movement in which the holes, previously aligned, are misaligned with the holes of the attached layer (8), blocking the passage of air flow.

The number of positions may be greater since the transverse displacement of the dynamic layer (9) may present a partially progressive alignment of the holes of said surface with the perforations of the transport belt (2) and the holes of the attached layer (8) thus controlling the degree of vacuum force desired in the transport belt (2) on the cardboard sheets.

The transport system has a mechanical and dynamic control that acts on the vacuum system, allowing sections or stretches to be opened as the transport system detects the proximity of the first plates and closing the air flow when the last plates progressively leave the transport belt (2).

The operation of dynamic control refers to:

- That the vacuum system is enabled a certain time (tt) before the first plate enters the transport belt (2).

- That the vacuum system is disabled for a certain time (t2) after the last cardboard sheet leaves the printing process.

- Both (tx) and (t2) can be manually adjusted by the user or can be automatic.

The automatic adjustment functionality includes a parameter that allows leaving an area always open to the air flow, the closest to the plate inlet, where this constant air flow allows maintaining an optimal vacuum regime prior to the cardboard plates entering the printing process.

Claims (7)

1. CARDBOARD PLATE TRANSPORT SYSTEM IN A DIGITAL PRINTER comprising a transport table with an endless perforated transport belt (2) and at least one traction roller that transmits the movement to the transport belt (2) which supports and transports the cardboard plates in the digital printing process, characterised in that the transport system has a mechanical and dynamic control that acts on the vacuum system which in turn comprises a vacuum table (1) comprising: - A series of chambers (4) arranged inside the vacuum table (1) where said chambers house at least two gates (10) facing each other and arranged longitudinally to the transport table (2). - A set of superimposed layers that close the chambers (4) from above, where the set of superimposed layers comprise: - An endless perforated conveyor belt (2). - An attached layer (8) having a series of holes. - A dynamic layer (9) that has holes and is divided into sub-aerial areas (7) with independent movement. - Control means on the vacuum table (1) - Suction elements connected to the chambers (4). Where the sub-areas (7) of the dynamic layer (9) make a limited path transversally to the direction of advance generating at least two positions, open and closed: - In the open position, a series of holes in at least one sub-area (7) of the dynamic layer (9) are aligned with the holes in the attached layer (8) and, where applicable, with the perforations in the transport belt (2), defining the longitudinal vacuum area enabled. - In the closed position, at least one sub-area (7) of the dynamic layer (9) moves, causing the holes previously aligned with the holes of the attached layer (8) to become misaligned, thus blocking the passage of air flow. Where the gates (10), which move closer and further away from each other thanks to an opening and closing control system, are adjusted to the width of the cardboard sheets, defining the cross-sectional area of vacuum action on the surface of the transport belt. And where the dynamic control enables the vacuum system a certain time (tt) before the first plate enters the transport belt (2) and disables it a certain time (t2) after the last cardboard plate leaves the printing process, thus generating vacuum action sections on the transport belt (2). 2. CARDBOARD PLATE TRANSPORT SYSTEM IN A DIGITAL PRINTER according to claim 1, characterized in that the transverse path of the dynamic layer (9) is limited by a stop. 3. CARDBOARD PLATE TRANSPORT SYSTEM IN A DIGITAL PRINTER according to claim 1, characterized in that the movement of the dynamic layer (9) is governed by at least one pneumatic piston. 4. CARDBOARD PLATE TRANSPORT SYSTEM IN A DIGITAL PRINTER according to claim 1, characterized in that the suction element is a turbine (3). 5. CARDBOARD PLATE TRANSPORT SYSTEM IN A DIGITAL PRINTER according to claim 1, characterized in that the chambers comprise a series of windows (11) that have means to communicate with the turbines (3). 6. CARDBOARD PLATE TRANSPORT SYSTEM IN A DIGITAL PRINTER according to claim 1, characterized in that the dynamic control is cancelled and the air flow is constant. 7. CARDBOARD SHEET TRANSPORT SYSTEM IN A DIGITAL PRINTER according to claim 1, characterized in that the input area of the transport table is open without a closing mechanism.