Transport device with reduced fluid consumption

Abstract

To reduce the fluid consumption, in particular the air consumption, during the transport of a sheet- or plate-shaped recording medium so as to increase the print quality of a printing device and / or the efficiency of a transport device.SOLUTION: A transport device is described, which is adapted to transport a recording medium (120) on a transport belt (130) through a printing unit (140). The conveyor belt (130) has a plurality of holes that have a first cross-sectional area towards the recording medium (120). Air is pumped out of the holes by means of a negative pressure unit in order to build up a negative pressure in the holes. In the process, the fluid is pumped over a second cross-sectional area that is smaller than the first cross-sectional area. As a result, relatively high holding forces on the recording medium (120) can be achieved with relatively low fluid consumption.SELECTED DRAWING: Figure 1a

Description

[Technical field]

[0001] The present invention relates to a transport device adapted to guide a recording medium in the form of a sheet or plate to be printed through a printing unit of a printing device, in particular an inkjet printing device. [Background technology]

[0002] An inkjet printing device typically comprises a printing unit having one or more print bars for different inks. The print bars may have one or more print heads, each having one or more nozzles. To print on the recording medium, the recording medium may be guided past the print heads by a transport device to print pixels of different lines of a print image incrementally on the recording medium.

[0003] The transport device may include a conveyor belt having a plurality of openings or holes through which a vacuum can be created to hold the recording medium on the conveyor belt. The vacuum may be created by a vacuum pump.

[0004] Directly adjacent recording media in the form of sheets or plates can be transported at a predetermined distance from each other on a conveyor belt, resulting in gaps between the recording media where holes in the conveyor belt are not covered by the recording media. A relatively high air flow can be created in these holes by a vacuum pump. Such air flow between adjacent recording media can result in deflection of the ink drops and therefore inaccuracies in the positioning of the pixels of the printed image on the recording media. Furthermore, such air flow increases the air consumption and therefore the energy consumption and the requirements for the vacuum pump. Summary of the Invention

[0005] The present document addresses the technical problem of reducing fluid consumption, in particular air consumption, during the transport of sheet- or plate-shaped recording media, in order to increase in particular 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 moving 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 rear side of the transport belt, and the recording medium is transported on the front side of the transport belt. The plurality of holes (as a whole) have a first cross-sectional area at the front part of the conveyor belt. The transport device further comprises a negative pressure unit adapted to create a negative pressure in the plurality of holes of the transport belt by pumping a fluid, in particular by pumping air, so that a holding force is created 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 smaller than the first cross-sectional area to build up a negative pressure. [Brief description of the drawings]

[0007] In the following, embodiments of the invention are explained in more detail with reference to schematic drawings. [Figure 1a] 1 shows a block diagram of an exemplary inkjet printing device. [Figure 1b] 1 shows a block diagram of an exemplary transport device for recording media. [Figure 1c] 1 shows a print situation with a covered hole. [Figure 1d] 1 shows a flow situation with an uncovered hole. [Figure 2a] , [Figure 2b] 1 illustrates an exemplary conveyor belt having variable cross-sectional area holes. [Figure 3a] , [Figure 3b] 3 illustrates another exemplary conveyor belt having variable cross-sectional area holes. [Figure 4a] , [Figure 4b] 1 illustrates a further exemplary conveyor belt having holes with variable cross-sectional areas. [Figure 5a] , [Figure 5b] 4 shows an exemplary positioning of the air inlets of the holes. [Figure 6] 1 shows a block diagram of an exemplary delivery device having an aperture. [Figure 7] 1 illustrates a further exemplary conveyor belt having variable cross-sectional area holes. [Figure 8a] , [Figure 8b] 1 illustrates a top view of a conveyor belt having two exemplary hole arrangements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The printing device 100 shown in Fig. 1a is designed for printing on a sheet- or plate-shaped recording medium 120. The recording medium 120 may be made of paper, cardboard, paperboard, metal, plastic, textile, combinations thereof, and / or other suitable printable materials. The recording medium 120 is guided by a transport belt 130 along a transport direction 1 (indicated by an arrow) through a printing unit 140 of the printing device 100. In this process, successive recording media 120 typically have a predetermined distance between them such that a gap 121 is formed between adjacent recording media 120.

[0009] In the illustrated example, the printing unit 140 of the printing device 100 includes two print bars 102, each of which may be used to print with a particular color ink (e.g., black, cyan, magenta, and / or yellow, and possibly MICR ink). Different print bars 102 may be used to print with different inks. Furthermore, the printing unit 140 may include at least one fusing unit 170 configured to fix a printed image printed on the recording medium 120. If necessary, the fusing unit 170 may be disposed after each print bar 102 to at least partially fix the printed image applied by the respective print bar 102. The fusing unit 170 may also be disposed external to the printing unit 140.

[0010] The printbar 102 may include one or more printheads 103, which may be arranged in adjacent rows, for printing pixels of different columns 31, 32 of the printed image on the recording medium 120. In the example shown in Figure 1a, the printbar 102 includes five printheads 103, each printhead 103 printing a group of pixels of columns 31, 32 of the printed image on the recording medium 120.

[0011] 1a, each printhead 103 of the printing unit 140 comprises a plurality of nozzles 21, 22, each nozzle 21, 22 arranged to fire or eject ink droplets onto the recording medium 120. For example, the printhead 103 of the printing unit 140 may comprise several thousand effectively utilized nozzles 21, 22 arranged along several rows transverse to the transport direction 1 of the recording medium 120. The nozzles 21, 22 of the printhead 103 of the printing unit 140 may cause pixels of a line of a printed image to be printed on the recording medium 120 transversely to the transport direction 1, i.e. along the width of the recording medium 120.

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

[0013] Thus, the printing unit 140 of the printing device 100 comprises at least one printbar 102 having K nozzles 21, 22, which can be controlled with a specific line cycle to print a line (transverse to the transport direction 1 of the recording medium 120) having K pixels or K columns 31, 32 of a printed image on the recording medium 120. In the example shown, the nozzles 21, 22 are stationary or fixed in the printing device 100 and the recording medium 120 is guided past the fixed nozzles 21, 22 at a specific transport speed.

[0014] In the printing device 100, the rigid plate-like recording medium 120 can be moved, in particular, by means of a conveyor belt 130. FIG. 1b shows an exemplary transport device 150 for such a recording medium 120. The transport device 150 has a moving unit 151 (e.g., one or more drive wheels or drive rollers) that can move the conveyor belt 130. The conveyor belt 130 has a number of holes (or openings) 131. A negative pressure unit (in particular, a negative pressure pump) 152 generates a negative pressure 132 on the second side (in particular, the lower or rear side) of the conveyor belt 130, which generates a force through the holes 131 on the recording medium 120 lying on the conveyor belt 130, so that the recording medium 120 is sucked onto the conveyor belt 130. To achieve a sufficiently large force, the conveyor belt 130 can have holes 131 with a relatively large cross section or diameter and / or a relatively large number of holes 131.

[0015] The conveyor belt 130 typically has a relatively large number of openings or holes 131 through which a fluid (particularly air) is sucked to build up a negative pressure 132 that draws the recording medium 120 into 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 the conveyor belt 130 typically have a diameter between 5 mm and 10 mm. Holes 131 with a relatively large diameter have the disadvantage that the recording medium 120 can bend relatively strongly over the holes 131. Holes 131 with a relatively small diameter have the disadvantage that only a relatively small force can be built up over a relatively small cross-sectional area to hold the recording medium 120. The force caused by a given negative pressure 132 increases with the cross-sectional area of ​​the holes 131. Thus, the conveyor belt 130 preferably has holes 131 with a cross-sectional area that represents a compromise between the force generated and the bending effect on the recording medium 120.

[0016] As long as the recording media 120 follow each other directly edge to edge without any gaps, the fluid (especially air) consumption of the transport device 150 is relatively low, since the recording media 120 cover the holes 131 of the conveyor belt 130 and therefore seal them. However, it may be advantageous or necessary to maintain a certain distance between directly successive record carriers 120 (e.g. to synchronize or circulate a machining process). As a result, gaps 121 may occur between different record carriers 120, where the holes 131 of the conveyor belt 130 are no longer covered and therefore a fluid flow (especially air flow) 133 occurs through the uncovered holes 131. The gaps may have a variable length (in the transport direction 1) between successive record carriers 120.

[0017] The generated fluid flow 133 may have a relatively high flow velocity along the printing direction (i.e. along the transport direction 1), which may reduce the positioning accuracy of the printing unit 140 (especially in the case of the inkjet printing device 100 by deflecting the ejected ink drops). Figure 1b shows an example of an ink drop 123 ejected by the print head 103 of the inkjet printing device 100. The ink drop 123 may be deflected by the fluid flow 133 and therefore may impact the recording medium 120 at an incorrect position.

[0018] Furthermore, the fluid flow 133 results in increased fluid consumption and therefore increased requirements for the vacuum unit 152 of the transport device 150 and increased energy consumption.

[0019] 1c shows the holes 131 of the conveyor belt 120 completely covered by the recording medium 120. Inside the printing unit 140, i.e., on the front side (commonly referred to as the first side, or alternatively the top side) of the conveyor belt 130, there is an environmental pressure p in There is an external pressure p applied to the rear side (commonly referred to as the second side or alternatively the bottom side) of the conveyor belt 130. out is generated by the vacuum unit 152. Thus, a pressure difference is created, and the recording medium 120 is pressed against the conveyor belt 130. The force acting on the recording medium 120 is determined by the cross-sectional area A of the air inlet of the hole 131 (facing the recording medium 120). in and the pressure difference (p in -p out ) depends on the cross-sectional area A in The larger the cross-sectional area A of the air inlet of the hole 131, the greater the force acting 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 the holes 131 of the conveyor belt 130 covered by the recording medium 120. in As the total force decreases, the number of holes 131, n, must be increased by the same amount to maintain the total force. The total force F acting on the recording medium 120 is calculated by multiplying the total cross-sectional area nA of the holes 131 acting on the recording medium 120 byin From the pressure difference, F=nA in (p in -p out ) is calculated as

[0020] FIG. 1d illustrates the situation where the air inlets of the n holes 131 are not covered by the recording medium 120. The holes 131 shown in FIG. 1d have the same cross-sectional area on both the air inlet side and the air outlet side, i.e., A in =A out The pressure difference (p in -p out ), the average velocity v 1 =v n The total air consumption dV / dt is dV / dt=nA out v n From this estimate, the cross-sectional area A out By reducing the number n of holes 131, and / or by reducing the pressure difference (p in -p out ) with a decrease in air velocity v n It can be seen that by reducing F, the air consumption can be reduced. However, this has a negative effect on the retention force F that can act on the recording medium 120.

[0021] In the following, a conveyor belt 130 for a transport device 150 is described in relation to Figures 2a to 7, which has openings or holes 131 with adapted geometry, in particular with a variable cross-sectional area. The holes 131 have a relatively large inlet cross-sectional area A 1 on the front side of the transport belt 130 facing the recording medium 120 in order to exert a relatively large holding force on the recording medium 120. in Further, the holes 131 may be formed such that a pre-chamber having a relatively small exit cross-sectional area A on the opposite back side of the conveyor belt 130 in order to reduce the air consumption caused by the holes 131. outThe conveyor belt 130 may be formed such that an air outlet having a cross-sectional area of ​​0.1 mm or less is formed. By geometrically dividing the holes 131 of the conveyor belt 130 into a pre-chamber area or an inlet area and an outlet area, the "retention force" and "air consumption" functions may be optimized separately. The inlet cross-sectional area of ​​the pre-chamber determines the resulting force applied to 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 ​​the air outlet.

[0022] 2a and 2b show a conveyor belt 130 having one or more conical openings or holes 131. The holes 131 are spaced apart from the cross-sectional exit area A of the air outlet. out Inlet cross-sectional area A is larger than in having an air inlet with in >A out Thus, the cross-sectional area of ​​the holes 131 is significantly smaller on the outside or rear side than on the inside or front side. The conical holes 131 have a diameter at the upper end 135 (see FIG. 2b) of 5-40 mm, more preferably 10-30 mm, even more preferably 15-25 mm, even more preferably 18-22 mm. Even more preferably, the diameter at the lower end 136 of the conical holes 131 is 3 / 8-5 / 8 of the diameter at the upper end 135 of the holes, in particular 2.5-20 mm, more preferably 5-15 mm, even more preferably 7.5-12.5 mm, even more preferably 9-11 mm. The above-mentioned diameter ranges have been found to be very advantageous for conveying media made of cardboard with a thickness of 1 mm-20 mm. For thinner conveying media, such as for example paper with a thickness of 300 μm, conveyor belts with smaller hole diameters are preferred so that the conveying media does not bend in the holes 131. This is because the conveyor belt 130 has an inlet cross-sectional area A in On the other hand, the exit cross-sectional area A of the rear side (i.e., the second side) of the conveyor belt 130 is out This determines the air consumption.

[0023] With cylindrical holes 131, it may happen that the initially empty conveyor belt cannot build up enough pressure difference to fix the recording medium on the conveyor belt, because the cylindrical shape of the holes 131 allows for high airflow. Therefore, it is advantageous to design the holes 131 in a conical shape, as shown in Figures 2a and 2b, to appropriately restrict the airflow. A relatively small exit cross-sectional area can significantly reduce air consumption. For example, depending on the conveying speed of the recording medium 120, the air consumption can be reduced by 100%. in =A out 121), the air consumption can be reduced by a factor of 16 or more. The exit cross-sectional area is preferably such that a constant high coercive force A on the recording medium 120 following the gap 121 is in (p in -p out The diameter of the outlet cross section is dimensioned according to the conveying speed so that sufficient pressure equilibration still occurs in the prechamber through the reduced barrel outlet to build up the flow rate (131) quickly enough. The minimum practical hole size of the outlet cross section is determined by the expected degree of contamination. A hole 131 with a small diameter can accumulate a lot of dust, which blocks the flow.

[0024] 3a and 3b show a conveyor belt 130 having several layers 330, 332. The first layer 330 (facing the recording medium 120) has a relatively large inlet cross-sectional area A in The second layer 332 (facing away from the recording medium 120) has a hole 331 with a relatively small exit cross-sectional area A outThe two layers 330, 332 may be bonded together. The holes 333 through the second layer 332 may be made (drilled or punched) after the two layers 330, 332 are bonded together. This may ensure that the corresponding holes 331, 333 are directly above each other. A manufacturing process is also possible in which each layer 330, 332 is first structured separately using a suitable tool and then the layers 330, 332 are bonded together. Again, the diameter of the holes 331 in the first layer (see FIG. 3b) is preferably 10-30 mm, more preferably 15-25 mm, even more preferably 18-22 mm. Even more preferably, the diameter of the holes 333 in the second layer 333 is 3 / 8-5 / 8 of the diameter of the holes 331 in the first layer, in particular 5-15 mm, even more preferably 7.5-12.5 mm, even more preferably 9-11 mm.

[0025] 4a and 4b show a conveyor belt 130 in which an air permeable fabric (e.g., plastic fleece, plastic or metal mesh, etc.) or a porous film is used as the second layer 332. The degree of breathability of the material of the second layer 332 is determined by the inlet cross-sectional area A of the holes 331 of the first layer 330. in For the reduced exit cross-sectional area A out The thickness of the second layer 332 may be selected so that a breathability through the second layer 332 corresponding to the thickness of the second layer 332 is obtained. It must be taken into account that in the case of such a fabric or porous film, the diameter of the holes may be smaller here than in other embodiments, and possible soiling due to dust or dust-ink adhesion may be more relevant here. For this reason, the pore diameter of the fabric or film is preferably 0.5 mm or more, even more preferably 0.7 mm or more. The ratio of the open area to the covered area is 10 to 70% for advantageous fabrics or porous films. To reduce soiling, cleaning methods such as sweeping, suction or blowing are especially used. Furthermore, clogged fabrics or porous films can be blown free again using positive pressure instead of negative pressure. Service operations in which manual cleaning is performed are also conceivable.

[0026] 5a and 5b show an example arrangement of holes 333 in a second layer 332 relative to corresponding holes 331 in a first layer 330 of a multi-layer conveyor belt 130. in When using the second layer 332, substantial bending of the covering recording medium 120 may occur. This is because the bending recording medium 120 causes the second layer 332 to bend due to the (reduced exit cross-sectional area A out 5a), which may result in the lower holes 333 (having a bent hole 331) being closed. As a result, the retention of the recording medium 120 may be reduced. For this reason, the holes 333 in the second layer 332 may be arranged relatively close to the edges of the corresponding holes 331 in the first layer 330 (see FIG. 5b). This may reliably prevent the holes 333 in the second layer 332 from being blocked by the bent recording medium 120.

[0027] With standard conveyor belt thicknesses of 1.5 mm to 3.0 mm and negative pressures of 15 to 30 mbar, no measurable deflection could be detected with a 3D profile scanner with a hole diameter of 15 to 25 mm for cardboard conveying media with thicknesses of 1 to 20 mm.

[0028] 7 shows a conveyor belt 130 having a number of holes 131 with variable cross-sectional areas. In particular, at the front of the conveyor belt 130, the holes 131 in the conveyor belt 130 have an inlet cross-sectional area A in Additionally, the holes 131 in the conveyor belt 130 have a reduced exit cross-sectional area A at at least one point along the front-to-back section of the conveyor belt 130. outThus, the holes 131 of the conveyor belt 130 can have a variable cross-sectional area along the section from the front side of the conveyor belt 130 to the rear side of the conveyor belt 130, the holes 131 having at least one point along said section an outlet cross-sectional area which is reduced compared to the inlet cross-sectional area at the front side of the conveyor belt 130. The reduced outlet cross-sectional area does not necessarily have to be present at the rear of the conveyor belt 130. Thus, it can be achieved that the fluid flow 133 is only provided by the reduced outlet cross-sectional area, while the retention force continues to be provided via the relatively large inlet cross-sectional area. The path of the walls of the holes 131 can be conical (see FIG. 2b) or have a diabolo gyroscope shape (see FIG. 7).

[0029] The conveying device 150 typically has guiding means which allow the conveyor belt 130 to be stably guided in a predefined and reproducible manner through the printing units 140. Figure 6 shows the conveying device 150, in which an opening 632 is used as a guiding means for guiding the conveyor belt 130 through the printing units 140. The conveyor belt 130 rests on the cover 632 and is therefore moved by the moving unit 151 through the printing units 140 in a defined manner. The opening 632 has a relatively small cross-sectional area A out 30 and thus assumes the function of the second layer 332 of the conveyor belt 130. Thus, a reduction in air consumption can be achieved by fixed openings 632 with relatively small holes (in particular bores) 333. The holes 333 in the guide openings 632 can be arranged partially (only in one printing unit 140) or all over (along the entire transport device 150) below the conveyor belt 130. The spacing of the holes 333 in the openings 632 is determined by the cross-sectional area A of the holes 131 of the conveyor belt 130. in In particular, the holes 333 of the fixed diaphragm 632 may be adapted to provide a substantially constant effective cross-sectional area A at any point in time under the holes 131 of the conveyor belt 130 (in particular under all the holes 131). out In ​The diaphragm 632 may be designed and positioned so that there is an effective aperture of the diaphragm 632 having a constant adhesion and airflow 133.

[0030] Thus, this document describes a transport device 150 for transporting the recording media 120 through the printing units 140 of the printing device 100. In particular, sheet-like or plate-like recording media 120 can be transported. In particular, the transport device 150 may be set up to transport several successive record carriers 120, whereby directly successive record carriers 120 may have gaps 121 between them. The transport device 150 may be part of the (inkjet) printing device 100.

[0031] The recording medium 120 on the front side of the conveyor belt 130 (also called substrate side or front side). The conveyor belt 130 may have a width that corresponds at least to the width of the recording medium 120. The conveyor belt 130 may be designed as an endless belt guided via rollers or rollers from the output of the conveying device 150 back to the input of the conveying device 150. The conveying device 150 comprises at least one moving unit 151 (e.g. a drive roller), which is set up to move the conveyor belt 130 (on which the recording medium 120 is arranged) through the printing unit 140. Then, the print image can be printed stepwise (e.g. line by line) on the recording medium 120. The conveyor belt may move at a given conveying speed. The conveying speed typically depends on the line cycle in which the printing unit 140 prints the lines of the print image on the recording medium 120. In particular, the conveying speed increases as the line cycle increases.

[0032] The conveyor belt 130 includes a number of holes 131, 331, 333 between the front and rear sides of the conveyor belt 130. The cross-sectional area of ​​the holes 131, 331, 333 may depend on the flexibility of the recording medium 120 being conveyed. Typically, a larger cross-sectional area may be selected as the flexibility of the recording medium 120 decreases. A typical cross-sectional area is 20 mm 2 ~100mm 2The holes 131, 331, 333 may have a circular cross section. Typically, the conveyor belt 130 has hundreds or thousands of 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 a 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 ​​the holes 131, 331, 333 at the front of the conveyor belt 130 is also referred to herein as the inlet cross-sectional area.

[0034] The transport device 150 comprises a negative pressure unit 152 (in particular a negative pressure pump) set up to generate a negative pressure 132 in the plurality of holes 131, 331, 333 of the conveyor belt 130 by pumping out a fluid. In particular, a negative pressure 132 can be made to exist in the plurality of holes 131, 331, 333 of the conveyor belt 130 (for example in the pre-chambers of the holes 131, 331, 333) against a pressure (in the present document also called pin) of the record carrier 120 facing away from the conveyor belt 130 (in the present document also called pout). As a result, a retention force on the record carrier 120 can be exerted on a 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 retention force is a total force F=nA in (p in -p out ), where n is the number of holes 131, 331, 333 in the conveyor belt 130 acting on the conveyor belt 120.

[0035] The conveying device 150 is designed such that the fluid for building up the negative pressure 132 is pumped through a second cross-sectional area smaller than the first cross-sectional area. The second cross-sectional area may correspond to the total cross-sectional area through which the fluid (particularly air) is pumped. The second cross-sectional area may depend on the conveying speed of the conveying device 150, in particular increasing with increasing conveying speed or decreasing with decreasing conveying speed.

[0036] Thus, a transport device 150 is described having a transport belt 130 with holes 131, 331, 333 to provide a relatively large retention force on the recording medium 120 at a relatively large first cross-sectional area at the front of the transport belt 130. Meanwhile, fluid consumption may be reduced by pumping the fluid across a relatively smaller second cross-sectional area to build up a negative pressure 132 for the retention force.

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

[0038] The fluid may be pumped through the N corresponding holes 131, 331, 333 to generate a 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 pumping occurs may each have an exit cross-sectional area. The corresponding holes 131, 331, 333 may be holes 131, 331, 333 in the conveyor belt 130 or in the opening 632 of the conveying device 130. The second cross-sectional area may be the sum of the exit cross-sectional areas of the N corresponding holes 131, 331, 333. Here, the exit cross-sectional areas of the different corresponding holes 131, 331, 333 may be at least partially different. Alternatively, the corresponding holes 131, 331, 333 may have substantially the same exit cross-sectional area. The exit cross-sectional area of ​​the holes 131, 331, 333 may correspond to the cross-sectional area of ​​the holes 131, 331, 333 through which fluid is pumped to create the vacuum 132 in the holes 131, 331, 333. To this end, the holes 131, 331, 333 may have a reduced exit cross-sectional area at a location between the front and rear of the conveyor belt 130 (but not directly in front of the conveyor belt 130).

[0039] Thus, a conveying device 150 is described, adapted to convey the recording medium 120 on the conveyor belt 130 through the printing unit 140. The conveyor belt 130 has a number of holes 131, 331, 333 with a first cross-sectional area (in total) towards the recording medium 120. A negative pressure unit 152 pumps fluid (particularly air) from and / or through the holes 131, 331, 333 to build up a negative pressure 132 in the holes 131, 3331, 333 of the conveyor belt 130. In this process, the fluid is pumped through a second cross-sectional area, which is reduced compared to the first cross-sectional area. As a result, a relatively high holding force on the recording medium 120 can be achieved with a relatively low fluid consumption. Preferably, for each individual hole 131, 331, 333, the exit cross-sectional area used to expel air from 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 of the plurality of holes 131, 331, 333 (particularly each hole 131, 331, 333) may have an inlet cross-sectional area at a front side of the conveyor belt 130. Furthermore, at least one hole 131, 331, 333 of the plurality of holes 131, 331, 333 (particularly each hole 131, 331, 333) may have an outlet cross-sectional area at at least one location on a path between the front side and the rear side of the conveyor belt 130, the inlet cross-sectional area of ​​the hole 131, 331, 333 being greater than the outlet cross-sectional area of ​​the hole 131, 331, 333, respectively. In particular, the hole 131, 331, 333 may have a reduced outlet cross-sectional area directly at the rear side of the conveyor belt 130.

[0041] For example, the holes 131, 331, 333 may extend at least partially conically from the front to the rear of the conveyor belt 130. Additionally or alternatively, the cross-sectional area of ​​the holes 131, 331, 333 may decrease in one or more steps along the front-to-rear axis of the conveyor belt 130, or may decrease 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 retention force on the one hand and a relatively low fluid consumption on the other hand may be achieved in a reliable and efficient manner.

[0042] The conveyor belt 130 may be multi-layered. In particular, the conveyor belt 130 may have a first layer 330 arranged relatively close to the front and a second layer 332 arranged relatively close to the rear, which may be rigidly connected to each other. By using a multi-layer conveyor belt 130, different (effective) inlet and outlet cross-sectional areas for the holes 131, 331, 333 may be achieved in an efficient manner.

[0043] In particular, a first layer 330 and a second layer 332 may have corresponding (overlapping) holes 331, 333, respectively. One hole 331 in the first layer 330 may have an inlet cross-sectional area, while the corresponding hole 333 in the second layer 332 may have a smaller outlet cross-sectional area.

[0044] As mentioned above, the recording medium 120 may have a certain flexibility and may therefore be drawn into the holes 331 of the first layer 330 due to the negative pressure 132. Thus, the holes 331 of the first layer 330 may have a center surrounded by the edges of the holes 331 of the first layer 330. The corresponding holes 333 of the second layer 332 may then be arranged between the edges and the center of the holes 331 of the first layer 330. In particular, the corresponding holes 333 of the second layer 332 may be arranged such that they extend through the center of the holes 331 of the first layer 330 and do not surround an axis standing vertically on the conveyor belt 130. In this way, it can be reliably avoided that the recording medium 120 closes the holes 333 of the second layer 332. Thus, a reliable transport of the recording medium 120 can be achieved.

[0045] Alternatively or additionally, the second layer 332 may comprise a fluid-permeable material, in particular a mesh and / or a porous material. The fluid-permeable material may be designed such that the fluid flow 133 through the holes 331 of the first layer 330 is throttled by the second layer 332. In particular, the thickness of the fluid-permeable material and / or the second layer 332 may be formed such that the area of ​​the second layer 332 covering the holes 331 of the first layer 331 throttles the fluid flow 133 in the same way as the corresponding holes 333 of the second layer 332 with a reduced exit cross-sectional area. Thus, a second layer 332 made of a fluid-permeable material may be used to effectively reduce fluid consumption.

[0046] The transport device 150 may have a fixed cover 632 arranged on the rear side of the conveyor belt 130. The cover 632 may be designed to stably guide the conveyor belt 130. The moving unit 151 may be arranged to move the conveyor belt 130 over the opening 632. The opening 632 may have a plurality of holes 333, and the vacuum unit 152 may be configured to pump a fluid through the plurality of holes 333 of the opening 632 to create a vacuum 132 in the plurality of holes 131 of the conveyor belt 130.

[0047] The orifice 632 may be configured such that the orifice 632 at least partially covers the plurality of holes 131 in the conveyor belt 130, thereby providing a reduced second cross-sectional area through which the fluid is pumped to create the vacuum 132. The use of the guide orifice 632 in the conveying device 150 may reduce fluid consumption in a particularly efficient manner.

[0048] The plurality of holes 333 of the opening 632 and the plurality of holes 131 of the transport belt 130 are preferably formed such that the second cross-sectional area remains substantially constant during operation of the transport device 150 (particularly during any relative movement between the transport belt 130 and the opening 632). In this way, a constant retention force on the different recording media 120 and a constant fluid flow 133 in the gaps 121 between the recording media 120 are provided, which may improve the print quality of the printing device 100.

[0049] The plurality of holes 333 of the opening 632 may be arranged such that at any point during operation of the transport device 100 (particularly during any relative movement between the conveyor belt 130 and the opening 632), the holes 131 of the conveyor belt 130, and 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 opening 632 and / or is partially covered by the opening 632. Thus, the reduction in cross-sectional area is distributed over the plurality of holes 131 of the conveyor belt 130, and as a result, a uniform distribution of retention force and airflow may be achieved.

[0050] At least one hole 333 of the opening 632 (in particular each hole 333) may have a larger cross-sectional area on the side facing the rear side of the conveyor belt 130 than on the side facing away from the rear side of the conveyor belt 130. For example, the hole 333 of the opening 632 may be conical. In this way, an accelerated build-up of negative pressure during operation of the conveying device 150 and therefore an improved adhesion of the recording medium 120 may be achieved. Alternatively or additionally, in this way, a further reduction in the second cross-sectional area and therefore a further reduction in fluid consumption may be achieved.

[0051] Figures 8a and 8b show top views of a conveyor belt with two possible spacing geometries of holes 131, 331. The distance 132 between the center 133a of the first hole 131a and the center 133b of the second hole is preferably 25-80 mm, more preferably 50-70 mm, even more preferably 54-64 mm, in particular for a conveying medium made of corrugated board with a thickness of 1 mm-20 mm. As shown in Figure 8a, the holes 131a, 131b are arranged in particular with a square spacing geometry. However, a triangular geometry as in Figure 8b or other arrangements are also possible. The holes 131, 331 are arranged here in the form of an isosceles triangle.

[0052] Further described herein is a printing device 100, which includes a transport device 150 as described herein.

[0053] Reference List 1 Conveying direction 21, 22 Nozzle 31, 32 (printed image) gap 100 Printing Devices 101 Control unit 102 Print Bar 103 Print Head 120 Recording media 121 Gap or gap (between recording media) 123 Ink Drops 130 Conveyor Belt 131 holes (conveyor belt) 131a hole (conveyor belt) 131b hole (conveyor belt) 132 distance 133a Center point (hole) 133b Center point (hole) 135 Top 136 Bottom end 140 printing units 150 Transport Device 151 Mobile Unit 152 Vacuum Unit 170 Fixing unit 330 1st layer (conveyor belt) 331 holes (first layer) 332 Second layer (conveyor belt) 333 Hole (2nd layer, cover) 632 Aperture

Claims

1. A transport device (150) for transporting a recording medium (120) through a printing unit (140) of a printing device (100), comprising: said transport device (150) comprises a transport belt (130) and a movement unit (151) adapted to move said transport belt through said printing unit (140); - said conveyor belt (130) comprises a number of holes (131, 331, 333); - said conveyor belt (130) is arranged to transport said recording medium (120) in front of said conveyor belt (130); the holes (131, 331, 333) on the front side of the conveyor belt (130) have a first cross-sectional area; the transport device (150) comprises a negative pressure unit (152) arranged to generate a negative pressure (132) in the plurality of holes (131, 331, 333) of the transport belt (130) by pumping a fluid, resulting in a holding force on the recording medium (120) in the first cross-sectional area of ​​the plurality of holes (131, 331, 333), the conveying device (150) is designed such that the fluid for building up the negative pressure (132) is forced through a second cross-sectional area smaller than the first cross-sectional area.

2. 2. The transport device (150) of claim 1, at least one hole (131, 331, 333) of the plurality of holes (131, 331, 333) on the front side of the conveyor belt (130) has an inlet cross-sectional area, said at least one hole (131, 331, 333) has an exit cross-sectional area at at least one point between said front side and the opposite rear side of said conveyor belt (130); - a conveying device (150), said inlet cross-sectional area being larger than said outlet cross-sectional area.

3. 3. A transport device (150) according to claim 2, comprising: - said holes (131, 331, 333) extend in the shape of a cone at least along the section from the front to the rear of said conveyor belt (130); or a conveying device (150) in which the cross-sectional area of ​​the holes (131, 331, 333) decreases in one or more steps along the axis from the front to the rear of the conveyor belt (130) or decreases continuously from the inlet cross-sectional area to the outlet cross-sectional area.

4. A conveying device (150) according to any one of claims 1 to 3, comprising: 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 the opposite rear side, which are rigidly connected to each other; - said first layer (330) and said second layer (332) each have corresponding holes (331, 333); - a conveying device (150) in which the holes (331) of said first layer (330) have an inlet cross-sectional area greater than the outlet cross-sectional area of ​​the corresponding holes (333) of said second layer (330).

5. 5. A transport device (150) according to claim 4, comprising: - the hole (331) of said first layer (330) has a center surrounded by the edge of said hole (331) of said first layer (330); the corresponding hole (333) of said second layer (332) extends between the edge and the center of said hole (331) of said first layer (330); and / or - a conveying device (150) in which the corresponding hole (333) of the second layer (332) does not surround an axis extending perpendicular to the conveyor belt (130) through the center of the hole (331) of the first layer (330).

6. A conveying device (150) according to any one of claims 1 to 5, comprising: 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 the opposite rear side, which are rigidly connected to each other; - said first layer (330) comprises a plurality of holes (331); said second layer (332) consists of a fluid-permeable material, in particular a braided and / or porous material; - said fluid permeable material is designed such that the fluid flow (133) through the holes (331) of said first layer (330) is throttled by said second layer (332), said transport device (150).

7. A conveying device (150) according to any one of claims 1 to 6, comprising: - said conveying device (150) has a fixed opening (632) arranged on the rear side of said conveyor belt (130); - each of the holes (131) of the conveyor belt (130) extends from the front side to the rear side of the conveyor belt (130); - said moving unit (151) is set up to move said conveyor belt (130) along said opening (632); said opening (632) comprises a plurality of holes (333); - said negative pressure unit (152) is arranged to pump a fluid through said plurality of holes (333) of said opening (632) to create said negative pressure (132) in said plurality of holes (131) of said conveyor belt (130); - a conveying device (150), wherein the opening (632) is configured to at least partially cover the plurality of holes (131) of the conveyor belt (130) so as to provide the reduced second cross-sectional area through which fluid is pumped to create the vacuum (132).

8. 8. A conveying device (150) as described in claim 7, wherein the plurality of holes (333) of the opening (632) and the plurality of holes (131) of the conveying belt (130) are formed such that the second cross-sectional area remains substantially constant during relative movement between the conveying belt (130) and the opening (632).

9. 9. A conveying device (150) according to claim 7 or 8, characterized in that the holes (333) of the opening (632) are arranged in such a way that at any instant during the relative movement between the conveyor belt (130) and the opening (632), a hole (131) of the conveyor belt (130), in particular each hole (131) of the holes (131) of the conveyor belt (130), is drilled through the opening (333) of the opening (632), - said opening (632) overlaps with at least one hole (333); - a conveying device (150) partially covered by said cover (632).

10. 10. A conveying device (150) as claimed in any one of claims 7 to 9, wherein the holes (333) of the openings (632) have a larger cross-sectional area on a side facing the rear side of the conveyor belt (130) than on a side facing the opposite side to the rear side of the conveyor belt (130).

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