Transport device with reduced fluid consumption

Abstract

A transport device (150) is described which is designed to transport a recording medium (120) on a transport belt (130) through a printing unit (140). The transport belt (130) has a plurality of holes (131, 331, 333) which have a first cross-sectional area towards the recording medium (120). By means of a vacuum unit (152), air is pumped out of the holes (131, 331, 333) in order to build up a vacuum (132) in the holes (131, 3331, 333). The fluid is pumped over a second cross-sectional area which is smaller than the first cross-sectional area. As a result, relatively high holding forces can be exerted on the recording medium (120) with relatively low fluid consumption.

Description

[0001] The invention relates to a transport device which is designed to guide a sheet-shaped, sheet-shaped or plate-shaped recording medium to be printed through a printing unit of a printing device, in particular an inkjet printing device.

[0002] An inkjet printing device typically comprises a printing unit with one or more printing bars for different inks. Each printing bar can have one or more print heads, each with one or more nozzles. To print on a recording medium, the recording medium can be guided past a print head by a transport device to successively print the pixels of different lines of a print image onto the recording medium.

[0003] The transport device may comprise a conveyor belt with a plurality of apertures or holes through which a negative pressure can be created to hold a recording medium to the conveyor belt. The negative pressure may be created by a vacuum pump.

[0004] Directly adjacent sheet-, leaf-, or plate-shaped recording media can be transported on the conveyor belt at a certain distance from one another, creating gaps between the recording media where the holes in the conveyor belt are not covered by a recording media. Relatively high air flows can be generated in these holes by the vacuum pump. Such an air flow between adjacent recording media can deflect ink droplets and thus lead to inaccuracies in the positioning of pixels of a printed image on the recording media. Furthermore, such air flows increase air consumption and thus energy consumption and the demands on a vacuum pump.

[0005] This document addresses the technical problem of reducing fluid consumption, in particular air consumption, during the transport of a sheet-, sheet-, or plate-shaped recording medium, in particular to increase the print quality of a printing device and / or the efficiency of a transport device. This problem is solved by the features of independent device claim 1.

[0006] According to one aspect of the invention, a transport device for transporting a recording medium through a printing unit of a printing device is described. The transport device comprises a transport belt and a movement unit configured to move the transport belt through the printing unit. The transport belt comprises a plurality of holes between a front side and a back side of the transport belt, wherein the recording medium is transported on the front side of the transport belt. The plurality of holes has a first cross-sectional area on the front side of the transport belt (as a whole). The transport device further comprises a vacuum unit configured to create a vacuum in the plurality of holes of the transport belt by pumping out a fluid, in particular by pumping out air, so that a holding force is exerted on the recording medium at the first cross-sectional area of ​​the plurality of holes.Furthermore, the transport device is designed such that the fluid is pumped through a second cross-sectional area which is smaller than the first cross-sectional area in order to build up the negative pressure.

[0007] In the following, exemplary embodiments of the invention are described in more detail with reference to the schematic drawings. In the drawings: Fig. 1a shows a block diagram of an exemplary inkjet printing device; Fig. 1b shows a block diagram of an exemplary transport device for a recording medium; Fig. 1c shows a printing situation with a covered hole; Fig. 1d shows a flow situation with an uncovered hole; Figs. 2a-2b show an exemplary transport belt with holes of variable cross-sectional area; Figs. 3a-3b show another exemplary transport belt with holes of variable cross-sectional area; Figs. 4a-4b show another exemplary transport belt with holes of variable cross-sectional area; Figs. 5a-5b show exemplary positions of an air inlet of a hole; Fig. 6 shows a block diagram of an exemplary transport device with a diaphragm; and Fig. 7 shows another exemplary transport belt with holes of variable cross-sectional area. Figs. 8a-8b show a top view of a transport belt with two exemplary hole arrangement geometries.

[0008] The Fig. 1aThe illustrated printing device 100 is designed for printing on a sheet-, sheet-, or plate-shaped recording medium 120. The recording medium 120 can be made of paper, cardboard, carton, metal, plastic, textiles, a combination thereof, and / or other suitable and printable materials. The marking medium 120 is guided by a conveyor belt 130 along the transport direction 1 (represented by an arrow) through the printing unit 140 of the printing device 100. Successive recording media 120 are typically spaced a certain distance apart, so that a gap 121 forms between adjacent recording media 120.

[0009] In the example shown, the printing unit 140 of the printing device 100 comprises two printing bars 102, wherein each printing bar 102 can be used for printing with ink of a specific color (e.g., black, cyan, magenta, and / or yellow, and optionally MICR ink). Different printing bars 102 can be used for printing with different inks. Furthermore, the printing unit 140 can comprise at least one fixing unit 170 configured to fix a print image printed on the recording medium 120. If necessary, a fixing unit 170 can be arranged downstream of each printing bar 102 in order to at least partially fix the print image applied by the respective printing bar 102. The fixing unit 170 can also be arranged outside of a printing unit 140.

[0010] A printing bar 102 may comprise one or more print heads 103, which may be arranged in several rows next to one another, in order to print the pixels of different columns 31, 32 of a print image onto the recording medium 120. In the Fig. 1a In the example shown, a printing bar 102 comprises five print heads 103, each print head 103 printing the pixels of a group of columns 31, 32 of a print image onto the recording medium 120.

[0011] Each print head 103 of the printing unit 140 comprises in the Fig. 1aIn the embodiment shown, a plurality of nozzles 21, 22, each nozzle 21, 22 being configured to fire or impinge ink drops onto the recording medium 120. A print head 103 of the printing unit 140 can, for example, comprise several thousand effectively used nozzles 21, 22 arranged along several rows transversely to the transport direction 1 of the recording medium 120. By means of the nozzles 21, 22 of a print head 103 of the printing unit 140, pixels of a line of a print image can be printed onto the recording medium 120 transversely to the transport direction 1, ie, along the width of the recording medium 120.

[0012] The printing device 100 further comprises a control unit 101 (e.g., a control hardware and / or a controller) which is configured to control the actuators of the individual nozzles 21, 22 of the individual print heads 103 of the printing unit 140 in order to apply the print image to the recording medium 120 as a function of print data.

[0013] The printing unit 140 of the printing device 100 thus comprises at least one printing bar 102 with K nozzles 21, 22, which can be controlled with a specific line clock in order to print a line (transverse to the transport direction 1 of the recording medium 120) with K pixels or K columns 31, 32 of a print image onto the recording medium 120. In the example shown, the nozzles 21, 22 are immovably or permanently installed in the printing device 100, and the recording medium 120 is guided past the stationary nozzles 21, 22 at a specific transport speed.

[0014] In a printing device 100, rigid, plate-shaped recording media 120 can be moved by means of a conveyor belt 130. Fig. 1bshows an exemplary transport device 150 for such a recording medium 120. The transport device 150 has a movement unit 151 (e.g. one or more drive wheels or drive rollers) through which the transport belt 130 can be moved. The transport belt 130 has a plurality of holes (or openings) 131. By means of a vacuum unit (in particular a vacuum pump) 152, a vacuum 132 is created on a second side (in particular the underside or back side) of the transport belt 130, which vacuum exerts a force on a recording medium 120 lying on the transport belt 130 via the holes 131, so that the recording medium 120 is sucked onto the transport belt 130. In order to achieve sufficiently high forces, the transport belt 130 can have holes 131 with relatively large cross-sections or diameters and / or a relatively high number of holes 131.

[0015] A conveyor belt 130 typically has a relatively large number of openings or holes 131 through which a fluid (in particular air) is sucked out in order to build up the negative pressure 132 that draws a recording medium 120 onto the conveyor belt 130. The negative pressure 132 is typically between 10 mbar and 25 mbar and typically depends on the material of the recording medium 120. The holes 131 in a conveyor belt 130 typically have a diameter of 5 mm to 10 mm. Holes 131 with relatively large diameters have the disadvantage that the recording medium 120 can bend relatively significantly over the holes 131. Holes 131 with relatively small diameters have the disadvantage that only a relatively small force for holding the recording medium 120 can be built up over the relatively small cross-sectional area. The force caused by a certain negative pressure 132 increases with the cross-sectional area of ​​a hole 131.Conveyor belts 130 therefore preferably have holes 131 with a cross-sectional area that represents a compromise between the force exerted and the bending effect on the recording medium 120.

[0016] As long as recording media 120 follow one another directly edge to edge without any gap, the fluid (in particular air) consumption of a transport device 150 is relatively low because the recording media 120 cover and thus seal the holes 131 of the transport belt 130. However, it may be advantageous or necessary to maintain a certain distance between directly consecutive recording media 120 (e.g., in order to synchronize or time a machining process). As a result, gaps 121 may arise between different recording media 120 in which the holes 131 of the transport belt 130 are no longer covered, thus causing a fluid flow (in particular an air flow) 133 through the uncovered holes 131. The gaps between successive recording media 120 may have a variable length (in the transport direction 1).

[0017] The resulting fluid flow 133 may have a relatively high flow velocity along the printing direction (i.e., along the transport direction 1), whereby the positioning accuracy of a printing unit 140 (particularly in an inkjet printing device 100 due to deflection of the ejected ink drops) may be reduced. Fig. 1b shows, by way of example, an ink droplet 123 ejected by a print head 103 of an inkjet printing device 100. The ink droplet 123 may be deflected by the fluid stream 133 and thus impinge on the recording medium 120 at an incorrect position.

[0018] Furthermore, the fluid flow 133 leads to increased fluid consumption and thus to increased requirements and increased energy consumption of the vacuum unit 152 of a transport device 150.

[0019] Fig. 1cshows a hole 131 of a conveyor belt 120 which is completely covered by a recording medium 120. In the interior of the printing unit 140, i.e. at the front side (generally also referred to as the first side or alternatively as the top side) of the conveyor belt 130, the ambient pressure p in is present. The external pressure p out , which is applied to the back side (generally also referred to as the second side or alternatively as the underside) of the conveyor belt 130, is generated by the vacuum unit 152. This creates a pressure difference which causes the recording medium 120 to be pressed against the conveyor belt 130. The force acting on the recording medium 120 depends on the cross-sectional area A in of the air inlet of the hole 131 (facing the recording medium 120) and on the pressure difference (p in -p out ). The larger the cross-sectional area A in , the greater the force exerted on the recording medium 120 at the air inlet of the hole 131.The total force acting on the recording medium 120 corresponds to the sum of the forces of all holes 131 of the conveyor belt 130 covered by the recording medium 120. If the cross-sectional area A in of the air inlet of the holes 131 is reduced, the total force also decreases. To maintain the total force, the number n of holes 131 would have to be increased by the same amount. The total force F acting on the recording medium 120 is calculated from the total cross-sectional area n A in of the holes 131 acting on the recording medium 120 and the pressure difference as F = n A in (p in - p out ).

[0020] Fig. 1d illustrates the situation where the air inlet of the n holes 131 is not covered by a recording medium 120. The Fig. 1dThe holes 131 shown have the same cross-sectional area on both the air inlet side and the air outlet side, ie A in = A out . Due to the pressure difference (p in -p out ), an air flow 133 with the average speed v 1 =vn is created at each hole 131. The total air consumption dV / dt is calculated as dV / dt = n A out V n . From this estimate it can be seen that the air consumption can be reduced by reducing the cross-sectional area A out , by reducing the number n of holes 131 and / or by reducing the air speed vn (which is accompanied by a reduction in the pressure difference (p in -p out )). However, this has a negative effect on the holding force F that can be exerted on a recording medium 120.

[0021] In the following, in connection with the Figures 2a to 7Conveyor belts 130 for a transport device 150 are described, which have openings or holes 131 with adapted geometry, in particular with variable cross-sectional areas. A hole 131 can be designed such that a pre-chamber with a relatively large inlet cross-sectional area A in is created on the front side of a conveyor belt 130 facing a recording medium 120, in order to effect relatively large holding forces on a recording medium 120. Furthermore, a hole 131 can be designed such that an air outlet with a relatively small outlet cross-sectional area A out is created on the opposite rear side of a conveyor belt 130, in order to reduce the air consumption caused by the hole 131. By geometrically dividing the holes 131 of a conveyor belt 130 into pre-chamber or inlet areas and outlet areas, the functions of "holding force" and "air consumption" can be optimized separately.The inlet cross-sectional area of ​​a prechamber determines the resulting force exerted on the recording medium 120 at a given negative pressure 132. On the other hand, the maximum air flow rate is determined by the outlet cross-sectional area of ​​an air outlet.

[0022] Figures 2a and 2b show a conveyor belt 130 with one or more conical openings or holes or bores 131. A hole 131 has an air inlet with an inlet cross-sectional area A in that is larger than the outlet cross-sectional area A out of the air outlet, ie A in > A out . Thus, the cross-sectional area of ​​the hole 131 on the outside or rear side is significantly smaller than on the inside or front side. The conical hole 131 comprises at the upper end 135 (relative to Fig. 2b) a diameter between 5 and 40 mm, more preferably between 10 and 30 mm, even more preferably between 15 and 25 mm, even more preferably between 18 and 22 mm. Furthermore, a diameter at the lower end 136 of the conical hole 131 is preferably between 3 / 8 and 5 / 8 of the diameter at the upper end 135 of the hole, in particular between 2.5 and 20 mm, more preferably between 5 and 15 mm, even more preferably between 7.5 and 12.5 mm, even more preferably between 9 and 11 mm. The stated diameter ranges have proven to be very advantageous for transport media made of corrugated cardboard with thicknesses between 1 mm and 20 mm. For thinner transport media such as 300 µm thick paper, conveyor belts with smaller hole diameters should preferably be selected so that the transport medium does not bend in the holes 131. This creates a pre-chamber with an inlet cross-sectional area A in at the front (ieon the top side) of the conveyor belt 130, which can achieve a relatively high holding force. On the other hand, the air consumption is determined by the outlet cross-sectional area A out at the rear side (i.e., on the second side) of the conveyor belt 130.

[0023] With cylindrical holes 131, it may happen that the initially empty conveyor belt cannot build up sufficient differential pressure to fix a recording medium on the conveyor belt because the cylindrical shape of the holes 131 allows for a high air flow. Therefore, it is advantageous to design the holes 131 conical, as shown in Fig. 2a and 2bshown in order to limit the air flow accordingly. The air consumption can be significantly reduced due to the relatively small outlet cross-sectional area. For example, depending on the transport speed of a recording medium 120, the air consumption can be reduced to 1 / 16 or less (compared to the case where A in = A out ). The outlet cross-sectional area is preferably dimensioned in such a way that it is dependent on the transport speed that sufficient pressure equalization can still take place in the pre-chamber via the reduced running outlet in order to quickly build up an unchanged high holding force A in ·(p in -p out ) on the recording medium 120 following a gap 121. The smallest sensible hole diameter of the outlet cross-sectional area is determined by the expected degree of contamination. A lot of dust can accumulate in holes 131 with a small diameter, which then blocks the flow.

[0024] The Figures 3a and 3bshow a conveyor belt 130 with multiple layers 330, 332. A first layer 330 (facing the recording medium 120) has holes 331 with a relatively large inlet cross-sectional area A in . A second layer 332 (facing away from the recording medium 120) can have holes 333 with a relatively small outlet cross-sectional area A out at corresponding locations. The two layers 330, 332 can be glued together. The holes 333 through the second layer 332 can be produced (drilled or punched) after the two layers 330, 332 have been connected to one another. This ensures that corresponding holes 331, 333 lie directly above one another. A manufacturing process is also possible in which each layer 330, 332 is first structured separately using suitable tools and in which the layers 330, 332 are then connected to one another. Here, too, the diameter of the hole 331 in the first layer (relative to Fig. 3b) preferably between 10 and 30 mm, more preferably between 15 and 25 mm, even more preferably between 18 and 22 mm. Furthermore, a diameter of the hole 333 in the second layer 333 is preferably between 3 / 8 and 5 / 8 of the diameter of the hole 331 in the first layer, in particular between 5 and 15 mm, even more preferably between 7.5 and 12.5 mm, even more preferably between 9 and 11 mm.

[0025] The Figures 4a and 4bshow a conveyor belt 130 in which an air-permeable fabric (e.g., a plastic fleece, a plastic or metal mesh, etc.) or a porous film is used as the second layer 332. The degree of air permeability of the material of the second layer 332 can be selected such that, for an inlet cross-sectional area A in of a hole 331 in the first layer 330, an air permeability through the second layer 332 results that corresponds to a reduced outlet cross-sectional area A out . With such fabrics or porous films, it must be taken into account that the diameters of the holes can be smaller here than in the other embodiments and that possible contamination by dust or dust-ink adhesions can become more relevant here. Therefore, advantageous hole diameters in the fabric or film are preferably not smaller than 0.5 mm, even more preferably not smaller than 0.7 mm.The ratio between the opening area and the cover area is between 10 and 70% for advantageous fabrics or porous films. To reduce contamination, cleaning methods such as sweeping, vacuuming, or blowing are particularly effective. Furthermore, a clogged fabric or porous film can be cleared using positive pressure instead of negative pressure. Service calls involving manual cleaning are also conceivable.

[0026] The Figures 5a and 5bshow exemplary arrangements of the holes 333 of the second layer 332 relative to the corresponding holes 331 of the first layer 330 of a multi-layer conveyor belt 130. When using a relatively large inlet cross-sectional area A in for a hole 331 of the first layer 330, a substantial bending of a concealing recording medium 120 can occur. This can lead to the underlying hole 333 of the second layer 332 (with the reduced outlet cross-sectional area A out ) being closed by the bent recording medium 120 (see Fig. 5a ). As a result, the holding force on the recording medium 120 could be reduced. For this reason, a hole 333 of the second layer 332 can be positioned relatively close to the edge of the corresponding hole 331 of the first layer 330 (see Fig. 5b ). In this way, a closure of the hole 333 of the second layer 332 by a bent recording medium 120 can be reliably avoided.

[0027] For typical conveyor belt thicknesses between 1.5 mm and 3.0 mm and negative pressures between 15 and 30 mbar, no measurable deflection could be detected with a 3D profile scanner for hole diameters between 15 and 25 mm for transport media made of corrugated cardboard with a thickness between 1 and 20 mm.

[0028] Fig. 7shows a conveyor belt 130 with a plurality of holes 131 having a variable cross-sectional area. In particular, a hole 131 of the conveyor belt 130 at the front of the conveyor belt 130 has the inlet cross-sectional area A in . Furthermore, a hole 131 of the conveyor belt 130 has a reduced outlet cross-sectional area A out at at least one point along the route from the front to the back of the conveyor belt 130. The hole 131 of a conveyor belt 130 can thus have a variable cross-sectional area along the route from the front of the conveyor belt 130 to the back of the conveyor belt 130, wherein the hole 131 has an outlet cross-sectional area at at least one point along the route that is reduced compared to the inlet cross-sectional area at the front of the conveyor belt 130. The reduced outlet cross-sectional area does not necessarily have to be at the rear of the conveyor belt 130.Thus, it can be achieved that the fluid flow 133 is only effected through a reduced outlet cross-sectional area, while the holding force continues to be effected via a relatively large inlet cross-sectional area. The shape of the wall of the hole 131 can be conical (see . Fig. 2b ) or have the shape of a diabolo spinning top (see Fig. 7 ).

[0029] The transport device 150 typically has guide means that enable the transport belt 130 to be guided through a printing unit 140 in a stable and defined, reproducible manner. Fig. 6shows a transport device 150 in which a baffle 632 is used as a guide means to guide the transport belt 130 through a printing unit 140. The transport belt 130 rests on the baffle 632 and is thus moved in a defined manner through a printing unit 140 by means of the movement unit 151. The baffle 632 can have holes 333 with relatively small cross-sectional areas A out , and thus assume the function of a second layer 332 of the transport belt 130. The reduction in air consumption can thus be achieved by a fixed baffle 632 with relatively small holes (in particular bores) 333. The holes 333 in the guide baffle 632 can be arranged partially (only in a printing unit 140) or over the entire surface (along the entire transport device 150) under a transport belt 130. The spacing of the holes 333 in the aperture 632 can be adapted to the cross-sectional area A in the holes 131 of the conveyor belt 130.In particular, the holes 333 in the fixed aperture 632 can be designed and arranged such that at any time below a hole 131 (in particular below all holes 131) of the conveyor belt 130, an effective hole in the aperture 632 with a substantially constant effective cross-sectional area A out < A in results. Thus, constant adhesive forces and air flows 133 can be achieved.

[0030] This document thus describes a transport device 150 for transporting a recording medium 120 through a printing unit 140 of a printing device 100. In particular, a sheet-, sheet-, or plate-shaped recording medium 120 can be transported. In particular, the transport device 150 can be configured to transport a plurality of consecutive recording media 120, wherein directly consecutive recording media 120 can have gaps 121 between them. The transport device 150 can be part of an (inkjet) printing device 100.

[0031] The transport device 150 comprises a transport belt 130, which is configured to carry a recording medium 120 on a front side of the transport belt 130 (also referred to as the substrate side or the front side). The transport belt 130 can have a width that corresponds at least to the width of the recording medium 120. The transport belt 130 can be designed as an endless belt that is guided via rollers or cylinders from an output of the transport device 150 back to an input of the transport device 150. The transport device 150 comprises at least one movement unit 151 (e.g., a drive roller), which is configured to move the transport belt 130 (with the recording medium 120 arranged thereon) through the printing unit 140. A print image can then be printed gradually (e.g., line by line) onto the recording medium 120. The transport belt can move at a specific transport speed.The transport speed typically depends on a line clock rate with which the printing unit 140 prints lines of a print image onto the recording medium 120. In particular, the transport speed increases with an increase in the line clock rate.

[0032] The conveyor belt 130 comprises a plurality of holes 131, 331, 333 between the front and a rear side of the conveyor belt 130. The cross-sectional area of ​​a hole 131, 331, 333 can depend on the flexibility of the recording medium 120 to be transported. Typically, a larger cross-sectional area can be selected as the flexibility of the recording medium 120 decreases. Typical cross-sectional areas are in the range from 20 mm 2 to 100 mm 2 . The holes 131, 331, 333 can have a circular cross-section. Typically, a conveyor belt 130 has several hundred or several thousand holes 131, 331, 333.

[0033] The plurality of holes 131, 331, 333 may have a first cross-sectional area at the front of the conveyor belt 130. The first cross-sectional area may be the sum of the cross-sectional areas of the individual holes 131, 331, 333 of the plurality of holes 131, 331, 333. The cross-sectional area of ​​a hole 131, 331, 333 at the front of the conveyor belt 130 is also referred to in this document as the inlet cross-sectional area.

[0034] The transport device 150 comprises a vacuum unit 152 (in particular a vacuum pump) which is configured to create a vacuum 132 in the plurality of holes 131, 331, 333 of the transport belt 130 by pumping out a fluid. In particular, a vacuum 132 (also referred to as p out in this document) can be created in the plurality of holes 131, 331, 333 of the transport belt 130 (e.g., in prechambers of the holes 131, 331, 333) compared to the pressure on the side of the recording medium 120 facing away from the transport belt 130 (also referred to as p in in this document). As a result, a holding force can be exerted on the recording medium 120 at the first cross-sectional area of ​​the plurality of holes 131, 331, 333.If the first cross-sectional area corresponds to the sum of the inlet cross-sectional areas of the holes 131, 331, 333, the holding force can correspond to the total force F=n·A in ·(p in -p out ), where n is the number of holes 131, 331, 333 of the conveyor belt 130 acting on the recording medium 120.

[0035] The transport device 150 is configured such that the fluid is pumped through a second cross-sectional area, which is smaller than the first cross-sectional area, to build up the negative pressure 132. The second cross-sectional area can correspond to the total cross-sectional area through which fluid (in particular air) is pumped. The second cross-sectional area can depend on the transport speed of the transport device 150 and, in particular, can increase with increasing transport speed or decrease with decreasing transport speed.

[0036] Thus, a transport device 150 is described which has a transport belt 130 with holes 131, 331, 333 in order to exert a relatively large holding force on a recording medium 120 with a relatively large first cross-sectional area at the front of the transport belt 130. On the other hand, by pumping fluid through a relatively small second cross-sectional area to build up the negative pressure 132 for the holding force, the fluid consumption can be reduced.

[0037] The conveyor belt 130 can have N holes 131, 331, 333, which can be used at a specific time during the operation of the transport device 150 to exert a holding force on a recording medium 120. For example, the conveyor belt 130 can be designed such that the conveyor belt 130 has N holes 131, 331, 333 at any time or on average, which can be covered by a recording medium 120. A circulating endless conveyor belt 130 can have approximately 2N holes 131, 331, 333 for this purpose. Furthermore, n can be the number of holes 131, 331, 333 that are actually covered by a recording medium 120 during the operation of the transport device 150. Nn holes 131, 331, 333 can thus be located at a gap 121 between recording media 120, thereby causing a fluid flow 133. The first cross-sectional area can be the sum of the inlet cross-sectional areas of the N holes 131, 331, 333.The inlet cross-sectional areas for different holes 131, 331, 333 can be at least partially different. Alternatively, the holes 131, 331, 333 can have substantially the same inlet cross-sectional area.

[0038] The fluid can be pumped through N corresponding holes 131, 331, 333 to create the negative pressure 132 in the N holes 131, 331, 333 of the conveyor belt 130. The N corresponding holes 131, 331, 333 through which the fluid is pumped can each have an outlet cross-sectional area. A corresponding hole 131, 331, 333 can be a hole 131, 331, 333 in the conveyor belt 130 or in a baffle 632 of the transport device 130. The second cross-sectional area can be the sum of the outlet cross-sectional areas of the N corresponding holes 131, 331, 333. The outlet cross-sectional areas for different corresponding holes 131, 331, 333 can be at least partially different. Alternatively, the corresponding holes 131, 331, 333 may have substantially the same outlet cross-sectional area.The outlet cross-sectional area of ​​a hole 131, 331, 333 may correspond to the cross-sectional area of ​​the hole 131, 331, 333 through which fluid is pumped to create a negative pressure 132 in the hole 131, 331, 333. For this purpose, the hole 131, 331, 333 may have the reduced outlet cross-sectional area at a location between the front and rear of the conveyor belt 130 (but not directly at the front of the conveyor belt 130).

[0039] A transport device 150 is thus described which is configured to transport a recording medium 120 on a transport belt 130 through a printing unit 140. The transport belt 130 has a plurality of holes 131, 331, 333 which (in total) have a first cross-sectional area towards the recording medium 120. By means of a vacuum unit 152, fluid (in particular air) is pumped out of the holes 131, 331, 333 and / or through the holes 131, 331, 333 in order to build up a vacuum 132 in the holes 131, 331, 333 of the transport belt 130. The fluid is pumped out via a second cross-sectional area which is smaller than the first cross-sectional area. As a result, relatively high holding forces can be exerted on the recording medium 120 with relatively low fluid consumption.Preferably, for each individual hole 131, 331, 333, the outlet cross-sectional area used to pump the air out of the hole 131, 331, 333 is smaller than the inlet cross-sectional area of ​​the hole 131, 331, 333 facing the recording medium 120. In this way, a homogeneous force distribution and a further reduction in air consumption can be achieved.

[0040] At least one hole 131, 331, 333 (in particular each hole 131, 331, 333) of the plurality of holes 131, 331, 333 can have an inlet cross-sectional area at the front side of the conveyor belt 130. Furthermore, at least one hole 131, 331, 333 (in particular each hole 131, 331, 333) of the plurality of holes 131, 331, 333 can have an outlet cross-sectional area at at least one location on the path between the front side and the back side of the conveyor belt 130, wherein the inlet cross-sectional area of ​​a hole 131, 331, 333 is in each case larger than the outlet cross-sectional area of ​​the hole 131, 331, 333. A hole 131, 331, 333 can have the reduced outlet cross-sectional area, in particular directly on the back of the conveyor belt 130.

[0041] For example, a hole 131, 331, 333 can extend at least partially conically from the front to the back of the conveyor belt 130. Alternatively or additionally, the cross-sectional area of ​​the hole 131, 331, 333 can decrease along an axis from the front to the back of the conveyor belt 130 in one or more stages or continuously from the inlet cross-sectional area to the outlet cross-sectional area. By providing holes 131, 331, 333 with different inlet and outlet cross-sectional areas, a high holding force and a relatively low fluid consumption can be achieved in a reliable and efficient manner.

[0042] The conveyor belt 130 can be multi-layered. In particular, the conveyor belt 130 can have a first layer 330 arranged relatively close to the front side and a second layer 332 arranged relatively close to the rear side, which can be firmly connected to one another. By using a multi-layer conveyor belt 130, different (effective) inlet and outlet cross-sectional areas for the holes 131, 331, 333 can be efficiently achieved.

[0043] In particular, the first layer 330 and the second layer 332 can each have corresponding (overlapping) holes 331, 333. A hole 331 of the first layer 330 can have the inlet cross-sectional area. On the other hand, the corresponding hole 333 of the second layer 332 can have the smaller outlet cross-sectional area.

[0044] As already explained above, a recording medium 120 can have a certain degree of flexibility and can thus be drawn into a hole 331 in the first layer 330 due to the negative pressure 132. A hole 331 in the first layer 330 can have a center point that is surrounded by the edge of the hole 331 in the first layer 330. The corresponding hole 333 in the second layer 332 can then be arranged between the edge and the center point of the hole 331 in the first layer 330. In particular, the corresponding hole 333 in the second layer 332 can be arranged such that the hole 333 in the second layer 332 does not enclose an axis running through the center point of the hole 331 in the first layer 330 and perpendicular to the conveyor belt 130. This reliably prevents the recording medium 120 from closing the hole 333 in the second layer 332. Thus, a reliable transport of a recording medium 120 can be achieved.

[0045] Alternatively or additionally, the second layer 332 can consist of a fluid-permeable material, in particular of a mesh and / or a porous material. The fluid-permeable material can be designed such that a fluid flow 133 through a hole 331 in the first layer 330 is throttled by the second layer 332. In particular, the fluid-permeable material and / or the thickness of the second layer 332 can be designed such that the region of the second layer 332 that covers a hole 331 in the first layer 331 throttles the fluid flow 133 in the same way as a corresponding hole 333 in the second layer 332 with a reduced outlet cross-sectional area. Thus, a reduction in fluid consumption can be effectively achieved by means of a second layer 332 made of a fluid-permeable material.

[0046] The transport device 150 can have a fixed aperture 632 arranged on the rear side of the conveyor belt 130. The aperture 632 can be configured to guide the conveyor belt 130 in a stable manner. The movement unit 151 can be configured to move the conveyor belt 130 over the aperture 632. The aperture 632 can have a plurality of holes 333, and the vacuum unit 152 can be configured to pump fluid through the plurality of holes 333 of the aperture 632 to generate the vacuum 132 in the plurality of holes 131 of the conveyor belt 130.

[0047] The aperture 632 can be configured such that the aperture 632 at least partially covers the plurality of holes 131 of the conveyor belt 130, resulting in the reduced second cross-sectional area through which fluid is pumped to generate the negative pressure 132. By using the guide aperture 632 of the transport device 150, a reduction in fluid consumption can be achieved in a particularly efficient manner.

[0048] The plurality of holes 333 in the aperture 632 and the plurality of holes 131 in the conveyor belt 130 are preferably configured such that the second cross-sectional area remains substantially constant during operation of the transport device 150 (in particular during any relative movement between the conveyor belt 130 and the aperture 632). This allows constant holding forces on different recording media 120 and constant fluid flows 133 in gaps 121 between recording media 120 to be achieved, thereby increasing the print quality of a printing device 100.

[0049] The plurality of holes 333 of the aperture 632 can be arranged such that, at any time during operation of the transport device 100 (in particular during any relative movement between the conveyor belt 130 and the aperture 632), a hole 131 of the conveyor belt 130, in particular each hole 131 of the plurality of holes 131 of the conveyor belt 130, overlaps with at least one hole 333 of the aperture 632 and / or is partially concealed by the aperture 632. The reduction in the cross-sectional area can thus be distributed among the plurality of holes 131 of the conveyor belt 130, so that a homogeneous distribution of holding forces and air flows can be achieved.

[0050] At least one hole 333 (in particular each hole 333) of the aperture 632 may have a larger cross-sectional area on a side facing the rear side of the conveyor belt 130 than on a side facing away from the rear side of the conveyor belt 130.

[0051] For example, a hole 333 of the aperture 632 can be conical. This can accelerate the buildup of negative pressure during operation of the transport device 150, thus improving the adhesion of a recording medium 120. Alternatively or additionally, a further reduction of the second cross-sectional area and thus of fluid consumption can be achieved.

[0052] The Figures 8a and 8b show a plan view of a conveyor belt with two conceivable spacing geometries of the holes 131, 331. A distance 132 between the center point 133a of a first hole 131a and the center point 133b of a second hole is preferably, in particular for transport media made of corrugated cardboard with thicknesses between 1 mm and 20 mm, between 25 and 80 mm, more preferably between 50 and 70 mm, even more preferably between 54 and 64 mm. As in Fig. 8aAs shown, the holes 131a, 131b are arranged in a square spacing geometry. However, triangular geometries as in Fig. 8b or other arrangements are possible. The holes 131, 331 are arranged here in the shape of isosceles triangles.

[0053] Furthermore, this document describes a printing device 100 which includes the transport device 150 described in this document. List of reference symbols

[0054] 1Transport direction 21, 22Nozzle 31, 32Gap (of the print image) 100Printing device 101Control unit 102Printing bar 103Print head 120Recording medium 121Gap or gap (between recording media) 123Ink drop 130Transport belt 131Hole (transport belt) 131aHole (transport belt) 131bHole (transport belt) 132Distance 133aCenter point (hole) 133bCenter point (hole) 135Upper end 136Lower end 140Printing unit 150Transport device 151Moving unit 152Vacuum unit 170Fusing unit 330First layer (transport belt) 331Hole (first layer) 332Second layer (transport belt) 333Hole (second Position, aperture) 632 aperture

Claims

1. Transport device (150) for transporting a recording medium (120) through a printing unit (140) of a printing device (100); wherein - the transport device (150) comprises a transport belt (130) and a movement unit (151) which is configured to move the transport belt (130) through the printing unit (140); - the transport belt (130) comprises a plurality of holes (131, 331, 333); - the transport belt (130) is configured to transport the recording medium (120) on a front side of the transport belt (130); - the plurality of holes (131, 331, 333) on the front side of the transport belt (130) have a first cross-sectional area;- the transport device (150) comprises a vacuum unit (152) which is configured to create a vacuum (132) in the plurality of holes (131, 331, 333) of the transport belt (130) by pumping out a fluid, so that a holding force is exerted on the recording medium (120) at the first cross-sectional area of ​​the plurality of holes (131, 331, 333); and - the transport device (150) is configured such that the fluid is pumped out through a second cross-sectional area, which is smaller than the first cross-sectional area, to build up the vacuum (132); 2. Transport device (150) according to claim 1, wherein - at least one hole (131, 331, 333) of the plurality of holes (131, 331, 333) at the front side of the conveyor belt (130) has an inlet cross-sectional area; - the at least one hole (131, 331, 333) has an outlet cross-sectional area at at least one location between the front side and an opposite rear side of the conveyor belt (130); and - the inlet cross-sectional area is larger than the outlet cross-sectional area.

3. Transport device (150) according to claim 2, wherein - the hole (131, 331, 333) extends conically at least along a partial path from the front to the back of the conveyor belt (130); or - the cross-sectional area of ​​the hole (131, 331, 333) reduces along an axis from the front to the back of the conveyor belt (130) in one or more steps or continuously from the inlet cross-sectional area to the outlet cross-sectional area.

4. Transport device (150) according to one of the preceding claims, wherein - the conveyor belt (130) has a first layer (330) arranged relatively close to the front side and a second layer (332) arranged relatively close to an opposite rear side, which are firmly connected to one another; - the first layer (330) and the second layer (332) each have corresponding holes (331, 333); and - a hole (331) of the first layer (330) has an inlet cross-sectional area that is larger than an outlet cross-sectional area of ​​a corresponding hole (333) of the second layer (330).

5. Transport device (150) according to claim 4, wherein - a hole (331) of the first layer (330) has a center point which is surrounded by an edge of the hole (331) of the first layer (330); - a corresponding hole (333) of the second layer (332) extends between the edge and the center point of the hole (331) of the first layer (330); and / or - the corresponding hole (333) of the second layer (332) does not enclose an axis running through the center point of the hole (331) of the first layer (330) and perpendicular to the conveyor belt (130).

6. Transport device (150) according to one of the preceding claims, wherein - the transport belt (130) has a first layer (330) arranged relatively close to the front side and a second layer (332) arranged relatively close to an opposite rear side, which are firmly connected to one another; - the first layer (330) has a plurality of holes (331); - the second layer (332) consists of a fluid-permeable material, in particular of a mesh and / or a porous material; and - the fluid-permeable material is designed such that a fluid flow (133) through a hole (331) in the first layer (330) is throttled by the second layer (332).

7. Transport device (150) according to one of the preceding claims, wherein - the transport device (150) has a fixed aperture (632) arranged on a rear side of the conveyor belt (130); - the holes (131) of the conveyor belt (130) each extend from the front to the rear of the conveyor belt (130); - the movement unit (151) is configured to move the conveyor belt (130) along the aperture (632); - the aperture (632) has a plurality of holes (333); - the vacuum unit (152) is configured to pump fluid through the plurality of holes (333) of the aperture (632) in order to generate the vacuum (132) in the plurality of holes (131) of the conveyor belt (130);and - the aperture (632) is designed such that the aperture (632) at least partially covers the plurality of holes (131) of the conveyor belt (130), so that the reduced second cross-sectional area is obtained through which fluid is pumped out in order to generate the negative pressure (132); 8. Transport device (150) according to claim 7, wherein the plurality of holes (333) of the aperture (632) and the plurality of holes (131) of the conveyor belt (130) are formed such that the second cross-sectional area remains substantially constant during a relative movement between the conveyor belt (130) and the aperture (632).

9. Transport device (150) according to one of claims 7 to 8, wherein the plurality of holes (333) of the panel (632) are arranged such that during a relative movement between the conveyor belt (130) and the panel (632), at any time a hole (131) of the conveyor belt (130), in particular each hole (131) of the plurality of holes (131) of the conveyor belt (130), - overlaps with at least one hole (333) of the panel (632); and - is partially covered by the panel (632).

10. Transport device (150) according to one of claims 7 to 9, wherein a hole (333) of the aperture (632) has a larger cross-sectional area on a side facing the rear side of the transport belt (130) than on a side facing away from the rear side of the transport belt (130).

Images