Patent Application
20130286126
This application claims priority under 35 U.S.C. §119 to German Patent Application No. 10 2012 103 712.4 filed 27 Apr. 2012, the entire contents of which are incorporated herein by reference.
The invention relates to a device for serial printing of print media and to a method for serial printing of print media.
A method is known from US 2011/0074844 A1 for printing print media in which the media to be printed are supplied by means of a transport device to a print head. The transport device comprises several conveyor belts articulated to one another and arranged in series in the transport direction, wherein a central conveyor belt is located underneath the print head and is height-adjustable relative to the print head in order to adjust a suitable distance between the print medium to be printed and the print head when the print medium is situated underneath the print head. The central conveyor belt has an articulated connection to the adjacent conveyor belts, wherein the upstream conveyor belt in the transport direction forms a supply ramp and the downstream conveyor belt in the transport direction forms a discharge ramp for the print media.
In order to bring the print medium to be printed to the print head with a suitable spacing between the surface to be printed on the print medium and a printing face of the print head, the thickness of the print medium is first detected while the print medium is being transported by the transport device. When a print medium to be printed is situated on the central conveyor belt underneath the print head, the central conveyor belt is shifted to a suitable height relative to the print head in order to adjust a distance suitable for printing between the surface of the print medium to be printed and the printing face of the print head, taking the detected thickness of the print medium into account. As soon as the print medium is a suitable distance from the print head and is located underneath the print head, the printing process is started, wherein the print medium is moved in the transport direction at a speed suitable for printing. After printing, the printed print medium is transferred from the central conveyor belt to the conveyor belt downstream in the transport direction and is transported away.
This known arrangement for serial printing of print media proves disadvantageous especially if the print head is a print head that has a certain longitudinal elongation in the transport direction of the media to be printed. This is the case for inkjet print heads, for example, in which a number of inkjet nozzles (possibly for different inks) are arranged one after the other and separated from one another in the longitudinal direction of the print head (and thus in the transport direction of the print media to be printed). Other print heads as well, such as laser print heads, have a certain longitudinal elongation in the longitudinal direction of the print head. The result of this is that the height-variable transport device with which the print media to be printed are serially fed to the print head cannot be varied in height relative to the print head during the printing of a print medium that has been brought on the central conveyor belt to the print head, because the print medium located on the central conveyor belt must be kept a suitable distance away from the print head during printing. For this reason, subsequent print media cannot be transferred to the central conveyor belt and brought thereby to a suitable distance from the print head until the preceding print medium is finished with printing and transferred to the downstream conveyor belt. This causes a reduction of the possible transport speed of the transport device for feeding and discharging the print medium, and reduces the throughput of the printing device.
Starting from this point, certain embodiments of the invention address the problem of specifying a device and a method for serial printing of print media with which a faster feeding and removal of the print media is made possible. In particular, the throughput of printed print media in the printing device is to be increased.
The device according to the invention is particularly suitable for printing mailpieces such as envelopes on which, for example, the recipient and sender addresses and/or a postage imprint and/or promotional imprints are to be printed. The device according to the invention for serial printing of print media comprises a print head extending in a longitudinal direction with a planar printing face and a printing area extending in the longitudinal direction. The device according to the invention further comprises a transport device for feeding the print media to be printed to the print head, wherein the transport device comprises at least one first transport unit and a second transport unit, which can be moved independently of one another in a transport direction and in an orthogonal direction relative to the printing face of the print head in order to feed a print medium guided on the transport units to the printing face of the print head and to bring the surface of the print medium that is to be printed to a suitable distance from the printing face. According to the invention, the transport device comprises a transfer area located in the printing area of the printing face, so that a print medium can be transferred from the first transport unit to the second transport unit in the transfer area and thus inside the printing area of the printing face. Several transfer areas arranged one after another in the longitudinal direction inside the printing area can also be provided.
This arrangement of one or more transfer areas in the printing area of the print head allows a print medium to be transferred from the first transport unit to the second transport unit before or during printing, or at the latest directly after termination of the printing. Thereby the positioning of the upstream transport unit as viewed in the transport direction relative to the printing face can already be adjusted to the next print medium, which is to be printed after the print medium that is currently in the printing area. This next print medium can possibly have a different thickness than the print medium that is currently in the printing area. The position of the upstream transport unit relative to the printing face can thus be adapted if necessary, even during the printing of the print medium that is currently in the printing area, or immediately after the printing process is finished. There is therefore a faster adjustment of the positioning of the upstream transport unit with respect to the printing face, taking into account the thickness of the subsequent print medium as viewed in the transport direction. Thereby the transport device can be run at a higher feeding and discharge speed. In addition, a smaller distance between successive print media being serially fed with the transport device to the print head can be selected. An increased throughput of the printing device can be achieved with both measures.
According to the invention, the first transport unit and the second transport unit in the device for serial printing of print media can be moved in the orthogonal direction relative to the printing face independently of one another in order to adjust suitable distances between the transport surfaces of the first and the second transport units with respect to the printing face. Both the first transport unit and the second transport unit are advantageously coupled to a drive unit for this purpose. The drive unit can be a servomotor or a linear motor, for example. Each drive unit expediently comprises a counterweight to compensate for mass forces.
A thickness measuring device arranged upstream of the print head in the transport direction is expediently provided for detecting the thickness of the print media that are to be printed and are being serially transported to the print head by means of the transport device. The thickness measurement device can be a rotary encoder, for example. An optical sensor that detects the thickness of the print media by means of a triangulation process is preferred for detecting the thickness of the print media. The thickness of each print medium detected by the thickness measuring device is taken into account in adjusting the positions of the first and/or the second transport units relative to the printing face of the print head in order to guarantee that the surfaces of the print media to be printed, possibly having different thicknesses, arrive at a suitable distance from the printing face during the printing process.
In a preferred embodiment, the transport device of the device according to the invention has a first conveyor belt and a second conveyor belt, each conveyor belt being guided at its upstream end and at its downstream end via a roller. At least one of the rollers of each conveyor belt is driven by a motor.
The conveyor belts of the first transport unit and the second transport unit are each preferably constructed as suction belts, which attract the print medium on the transport surface by means of negative pressure.
In one embodiment of the device according to the invention, the transfer area of the transport device is formed by an overlap area in which the two transport devices overlap in the longitudinal direction. For this purpose, the two transport units are expediently arranged laterally offset one alongside the other. The extension of the overlap area in the longitudinal direction expediently also substantially corresponds to the longitudinal extension of the printing area of the print head.
To achieve a secure transfer of a print medium from the first transport unit to the second transport unit, the transport surfaces of the two transport units are expediently at the same level during the transfer of the print medium.
In a preferred embodiment of the device according to the invention, the first transport unit and/or the second transport unit can be pivoted with respect to the printing face. This allows an inclination of the transport surfaces of the transport unit relative to the printing face. The inclination of the transport surfaces expediently runs in the direction perpendicular to the transport direction. This embodiment of the device according to the invention is suitable for serial printing of print media with a thicknesses that vary over their width or length. An inclination of the transport surfaces for the transport unit can guarantee that the surfaces of the print media to be printed lying on the transport surfaces of the transport units can be brought into a plane parallel to the printing face.
These and further advantages of the invention follow from the embodiment described below with reference to the accompanying drawings. The drawings show:
The print head 2, which can be an inkjet print head, has a housing and several printing nozzles 2a, 2b, 2c, 2d arranged separated from one another in the longitudinal direction. The printing nozzles are inkjet printing nozzles, for example. The exit faces of the printing nozzles form a planar printing face 3, which extends in the longitudinal direction (i.e. in the transport direction R of the transport device) across a printing area 3a, which extends from the front printing nozzle 2a to the rear printing nozzle 2d. The printing face 3 is expediently in a horizontal plane; a different arrangement of the print head is also possible. As an alternative to an inkjet print head, a laser print head can also be used, which similarly has a flat printing face 3 and a printing area 3a extending in the longitudinal direction.
In the embodiment of
Transport supports 17 and 18 are arranged transverse to the transport direction R on either side of the conveyor belts 15 and 16. The transport supports 17 and 18 are respectively used for guiding the print medium on the transport surfaces 5c and 6c during transport in the first transport unit 5 and the second transport unit 6.
Both the first transport unit 5 and the second transport unit 6 can be moved vertically relative to the transport direction R, with respect to the stationary print head 2. For this purpose, a drive 8 is provided on the first transport unit 5 and a drive 9 is provided on the second transport unit 6. The drives 8, 9 can be servomotors or a linear motors. The two transport units 5 and 6 can be moved independently of one another by the drives 8 and 9 in a direction perpendicular to the transport direction R and relative to the print head 2. Thereby the first transport unit 5 can be positioned independently of the second transport unit 6 in such a manner with respect to the stationary print head 2 that the distance between the transport surface 5c and the printing face 3 of the print head 2 can be adjusted continuously within predetermined limits. The distance between the transport surface 6c of the second transport unit 6 and the printing face 3 of the print head 2 can be correspondingly adjusted continuously within predetermined limits and independently of the positioning of the first transport unit 5.
The two transport units 5 and 6 are arranged one after another in the longitudinal direction and are aligned with one another. The downstream end 5b of the first transport unit 5 adjoins the upstream end 6a of the second transport unit 6. The downstream end 5b of the first transport unit 5 and the upstream end 6a of the second transport unit 6 form a transfer area 7. A print medium can be transferred from the first transport unit 5 to the second transport unit 6 in this transfer area 7. The exact length of the transfer area 7 in the longitudinal direction depends on the dimensions of the print media to be transported. The transfer area 7 is defined by the area in the longitudinal direction in which a secure transfer of a print medium from the first transport unit 5 to the second transport unit 6 can take place.
As can be seen particularly from the side view of
The exact positioning of the first transport unit 5 relative to the print head 2 results from the suitable distance between the surface 1a of the print medium 1 and the thickness of the print medium. To detect the thickness of the print medium, a thickness measurement device, not shown here, is therefore provided, and is arranged upstream of the print head 2 in the transport direction R. The thickness measurement device can be a rotary encoder, for example. However, an optical sensor is preferably used for detecting the thickness of the print media 1. An optical sensor that determines the thickness of the print media 1 by means of an optical triangulation method has proved particularly suitable in this regard.
The thickness as detected by the thickness measurement device for each print medium 1 being fed by the transport device 4 to the print head 2 is transferred to a control unit (not shown here), and the control unit determines the position of the transport unit 5 that is to be set with respect to the print head 2, taking into account the suitable printing distance between the surface 1a of the print media 1 and the printing face 3 of the print head 3. The thus-determined optimal position of the first transport unit 5 is then adjusted via the drive 8, and the print medium 1 to be printed is brought in this position to the print medium 2 by the first transport unit 5. When the front edge of the print medium 1 is at the upstream start of the printing area 3 as viewed in the transport direction R, the printing process begins. During printing, the print medium is moved farther in the transport direction R by the first transport unit 5, until the rear edge of the print medium 1 has reached the rear edge of the printing area 3 and the printing is finished. After the end of the printing process, the finished print medium 1 is transferred from the first transport unit 5 to the second transport unit 6. In the embodiment shown in
In an alternative process design, the print medium 1 is transferred from the first transport unit 5 to the second transport unit 6 already during printing, i.e. while the print medium 1 is in the printing area 3a of the print head 2. It is also possible with the device according to the invention to transfer the print medium 1 to be printed from the first transport unit 5 to the second transport unit 6 even before the beginning of the printing process. The print medium 1 is always transferred in the transfer region 7, which is situated in the printing area 3a of the printing face 3. In the embodiment shown in
The serial feeding of print media 1 to the print head 2 and the discharge therefrom after printing are shown in
The invention is not limited to the example shown in
In another embodiment, not shown in the drawings, the first transport unit 5 and the second transport unit 6 comprise conveyor rollers arranged sequentially in the longitudinal direction rather than conveyor belts. The conveyor rollers can be separately driven by a motor associated with each conveyor roller. It is also possible to provide only a single motor for driving the conveyor rollers and to couple the rollers to one another via a drive belt. Several transfer areas 7 arranged one after another longitudinally and inside the printing area 3a can also be provided.
In a preferred embodiment of the device according to the invention, a single motor 13 is provided for driving the two transport units 5 and 6 in the transport direction R. The first transport unit 5 is driven directly with this motor. The second transport unit 6 is connected to the motor via a coupling. In this embodiment variant, it is possible to adjust a different transport speed of the first transport unit 5 relative to the second transport unit 6. This makes it possible, for instance, to adjust a faster discharging of the already finished print medium with the second transport unit 6 in comparison to the feeding transport of the still unprinted print media to the print head 2 by the first transport unit 5.
In a preferred embodiment of the device according the invention, the control unit for the device is to be programmed in such a manner that a print medium situated on the first transport unit 5 is transferred to the second transport unit 6 and transported farther in the transport direction R thereby as soon as the print medium is in the transfer area 7.
In order to compensate the flywheel mass, it is further provided in an embodiment (not shown) that the two drives 8, 9 are each provided with a counterweight for compensating the mass forces. This allows a vibration-free approach of the transport units 5, 6 to the print head 2.
The transport surfaces 5c, 6c are expediently inclined by pivoting the first transport unit 5 or the second transport unit 6 relative to the print head 2. In the embodiment illustrated in
In the embodiment shown in
All references cited herein are expressly incorporated by reference in their entirety. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. There are many different features to the present invention and it is contemplated that these features may be used together or separately. Thus, the invention should not be limited to any particular combination of features or to a particular application of the invention. Further, it should be understood that variations and modifications within the spirit and scope of the invention might occur to those skilled in the art to which the invention pertains. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as further embodiments of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102012103712.4 | Apr 2012 | DE | national |
