This application claims priority under 35 U.S.C. ยง119 from German Patent Application No. DE 10 2011 006 929.1, filed Apr. 7, 2011, the entire disclosure of which is herein expressly incorporated by reference.
The invention relates to a method for printing at least one printing substrate on a printing support, more particularly a printing table, by way of a digital printing unit. The invention also relates to a device for printing at least one printing substrate, which device includes a printing table for the accommodation of a printing substrate and a digital printing unit for producing a print image on the printing substrate, and a control unit for controlling the digital printing unit.
In prior methods employed for printing substrates by use of a digital printing unit or with prior devices having a digital printing unit, a printing substrate to be printed, for example a sheet of paper, is laid on the printing table and secured in a required position on the printing table by use of stop members. In the case of large printing tables, it is usually possible to apply a negative pressure to the surface of the printing table in order to fix the position of the printing substrate on the printing table, thus rendering it immovable during the printing operation. The register, that is to say, the exact required position of the print image on the printing substrate, is ensured by aligning the printing substrate at a defined position and printing at the defined position of the printing substrate.
Alignment of the printing substrate is carried out manually or mechanically. The material to be printed is caused to approach so-called locating pins, which are raised at this point and which mechanically stop the movement of the material to be printed. A vacuum is then applied to the surface of the printing table and the material to be printed is retained in its position against the locating pins. This manual or mechanical alignment of the printing substrate is time-consuming and results in positioning errors of the print image on the printing substrate when the alignment is not carried out with sufficient precision.
When modern digital printers are used in commercial companies, it is desirable to utilize the entire surface of the printing table during each printing operation. This increases productivity and also makes it possible to print different motifs in different quantities and in different formats in one operation cycle. The requirement to position a plurality of printing substrates and accordingly the requirement to align each individual printing substrate exactly demands precision and, in the case of manual alignment of the printing substrate, the concentration of the operator. On the one hand, this aligning procedure constitutes a source of error and, on the other hand, will always consume time for positioning and aligning the printing substrates. In the case of very large printing tables, the dimensions of the printing table are beyond the reach of the operator for the purpose of positioning the printing substrates so that the aligning operation is further complicated.
The object of the invention is to improve a method and a device for printing at least one printing substrate by way of a digital printing unit.
According to the invention, there is provided for this purpose a method for printing at least one printing substrate on a printing support, more particularly a printing table, by way of a digital printing unit, which method provides for the transport of the printing substrate onto the printing support, the detection of a position of the printing substrate on the printing support, and the alignment of a print image produced by the digital printing unit in accordance with the detected position of the printing substrate.
By means of the invention, it is possible to position the printing substrate arbitrarily on the printing support. In the method of the invention, it is of no consequence when the printing substrate is not located at its exact predefined position on the printing support, since the position of the printing substrate on the printing support will be first detected and then the print image produced by the digital printing unit will be aligned with the detected position of the printing substrate. This ensures that at all times the print image will be in register with the printing substrate. Thus, apart from reducing the time taken to position the printing substrates on the printing support, it is possible to eliminate sources of error, since exact alignment is not required. It may also be possible to economize on constructive positioning aids such as locating pins. For example, a printing table or alternatively a conveyor belt can be used as the printing support. For example, printing tables may be designed to be movable such that printing substrates can be positioned at a first position of the printing table and the printing table then moved to a second position below the printing unit. The position of the printing substrate is then detected by a camera or a scanner during the movement of the printing table. The invention can also be used in stationary digital printing units in which the printing table is moved relative to the printing unit or printing units during the printing operation. Finally, positions for the printing substrate or for a plurality of printing substrates on the printing table need not be predetermined exactly, according to the invention, as a result of which there is increased flexibility of the method with respect to formats, sizes, and shapes of media to be printed. Thus, the product range can be expanded while achieving the highest possible productivity.
According to the invention, the printing substrates require no, or only rough, alignment on the printing support. In order to ensure that the print image is in register with the printing substrate, use is made of devices for detecting the position, shape, size, and/or location of the printing substrates, for example by use of image processing, for transferring the acquired information to a control unit for the printing unit and for printing the print image on the printing substrate by use of the printing unit in accordance with the detected position of the printing substrate.
In a development of the invention, the position of the at least one printing substrate on the printing support is acquired by optical detection.
Optical detection is readily achieved, for example, by use of a camera and suitable image processing software. It is also possible, for example, to provide optical sensors in the surface of the printing support to detect the presence of a printing substrate.
In a development of the invention, provision is made for detecting the format of the at least one printing substrate.
By detecting the format of the printing substrate, it is possible to check, for example, whether a print image to be produced is suitable for the printing substrate. It is also possible, for example, to select and carry out one of several pending print jobs in accordance with the detected format of the printing substrate. In this way, the format of the printing substrates disposed on the printing support can be recognized by way of software, and pending print jobs can then be assigned to these printing substrates until the current print jobs have been completed. It is likewise possible to scale the print image produced by the digital printing unit to match the detected format of the printing substrate.
In a development of the invention, provision is made for detecting the format, at least one side length, the shape, the location of the center of the printing substrate and/or the alignment of the printing substrate on the printing table.
The detection of such parameters contributes toward an additional improvement of the method of the invention. For example, substrates of arbitrary shape such as a polygon shape or a free shape such as a Christmas tree shape or alternatively a piece of furniture can be printed on the printing substrates such that the print image is in exact register therewith.
In a development of the invention, provision is made for controlling the devices for generating a negative pressure on the surface of the printing support in accordance with the detected position and/or the detected format of the printing substrate.
In this way, a negative pressure can be applied only to those regions of the surface of the printing support in which the printing substrate is actually located. This measure conserves energy, since it is only necessary to generate the negative pressure in those regions in which the printing substrate needs to be retained.
In a development of the invention, provision is made for projecting marks onto the printing support at least during the feed-in of the at least one printing substrate.
In this way, a manual feed of printing substrates can also be facilitated without the provision of mechanical locating devices such as locating pins. For example, laser lines or even print images can be projected onto the surface of the printing support in order to facilitate approximate alignment of the printing substrates when they are fed onto the printing support.
The object of the invention can also be achieved by a device for printing at least one printing substrate, which device comprises a printing support, more particularly a printing table, for accommodating a flat printing substrate, and a digital printing unit for producing a print image on the printing substrate, and also a control unit for controlling the digital printing unit, which control unit comprises at least one detector for the purpose of detecting the position of the printing substrate on the printing support, and said control unit also comprises an alignment device that aligns the print image produced by the printing unit in accordance with the detected position of the printing substrate.
In a development of the invention, at least one camera is provided for the purpose of detecting the position of the printing substrate on the printing support.
In a further development of the invention, there are provided at least one device for generating a negative pressure on the surface of the printing support and a controller for controlling the device(s) in accordance with the detected position, in accordance with the detected format, in accordance with at least one detected side length, in accordance with the detected shape, in accordance with the detected location of the center of the printing substrate and/or in accordance with the detected alignment of the printing substrate on the printing support.
In a still further development of the invention, devices are provided for projecting marks onto the printing support.
Additional features and advantages of the invention are revealed in the claims and the following description of preferred embodiments of the invention with reference to the drawings. Individual features of the various embodiments shown can be combined in an arbitrary manner without going beyond the scope of the invention.
The illustration shown in
According to an embodiment of the invention, there is provided a camera 24, which is shown purely diagrammatically in
For the purposes of the invention it is merely essential for the position of each printing substrate 11 to 22 relative to the printing table 10 to be made known, in order to make it possible to align a print image to be produced on the printing substrates 11 to 22 in accordance with the position detected and to ensure that the print image is in register with the printing substrate. However, the parameters by which this position of the printing substrates 11 to 22 relative to the printing table 10 is detected, for example, the corner points of each printing substrate 11 to 22, the side lengths and the location of the centers of the printing substrates 11 to 22 or the like, are insignificant.
The illustration shown in
The illustration shown in
The printing device 30 further comprises a camera 42 that makes it possible to detect the surface of the printing table 10 on which the substrate to be printed is to be placed. A printing substrate positioned on the surface of the printing table 10 is indicated purely diagrammatically by the reference numeral 44 by means of dash lines in the illustration shown in
The surface of the printing table 10 is provided with numerous orifices 46 through which a negative pressure can be applied by way of a pump 48. The generation of a negative pressure in the region of the orifices 46 serves to fix the position of a printing substrate, for example the printing substrate 44 positioned on the surface of the printing table 10, during a printing operation. The pump 48 and devices (not shown in the figure) disposed inside the printing table 10 for controlling the individual orifices 46 are likewise controlled by the control unit 40. The control unit 40 ensures that negative pressure is applied to only those orifices 46 that are located beneath a printing substrate 44 as detected by the camera 42. In the illustration shown in
In order to facilitate the rough alignment of the printing substrate 44 when it is manually positioned on the printing table, there is provided a laser 50 that is controlled by the control unit 40. Laser lines 52 indicating a required position of the printing substrate 44 can be projected onto the surface of the printing table 10 by use of the laser 50. The laser lines 52 are indicated by dot-dash lines in
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
Number | Date | Country | Kind |
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10 2011 006 929.1 | Apr 2011 | DE | national |