Method for printing an image onto piece goods, and printing system used therefor

Abstract

The invention relates to a method for printing an image onto piece goods (101) by means of a printing system (1) which comprises a digital printing device (120) having at least one printhead (201), the printhead (201) having multiple individually controllable printing nozzles (202) in order to print multiple image dots onto at least one item of piece goods (101) passing by the printing nozzles. The invention also relates to the printing system (1) that can be used therefor, and to the use of the printing system (1).

Description

[0001] Method for printing an image onto individual items and printing system used for this purpose

[0002] Technical field of the invention

[0003] The present invention relates to a method for printing an image onto individual items and a printing system used for this purpose. In particular, the method and the printing system enable a character, graphic image, structure, code, etc. to be individually printed onto non-indexed items, such as lids, etc., using digital printing technology.

[0004] State of the art

[0005] In connection with the printing of objects, especially bulk goods, processing systems with a conveyor system are known, wherein the conveyor system is loaded with the objects to be processed in a device, processed in a printing unit, and the processed objects are subsequently unloaded. The processing system can include means for incoming inspection to monitor the spatial position of the objects required for processing as well as their required temporal sequence, which is established beforehand by positioning devices.

[0006] However, while a printing system for printing on individual items using non-indexing handling in digital printing technology is known in principle, it is not very widespread. Instead, it is more common to individually position the parts to be printed under a printhead using a holder.

[0007] Furthermore, it is known to print individual items, i.e., essentially identical or at least similar objects in large quantities, for example, injection-molded plastic closure lids, in an ordered single-row sequence, i.e., in a more or less defined position and spatial orientation, with an image, such as characters, structures, graphic images, 2D barcodes, or the like, on one side using digital printing technology. Such a single-lane printing system therefore comprises means for part recognition and / or part tracking and a digital printing device with one or more printheads, each comprising a plurality of individually controllable print nozzles or pixel generation units. The printing result can be checked by means of an optical inspection device, which can initiate the rejection of the object in the event of a printing defect.Such a printing system can produce customized printed products, with a current capacity of at least 1,500 individual items or objects per minute. This means that less than 40 ms are available per object for transport, printing, and potential rejection. With even higher production volumes, the available time is even less.

[0008] Increasing the capacity of a single-lane printing system to boost productivity by using multiple digital printing units connected side-by-side or in series and coordinated with each other can only be achieved with considerable effort, particularly in terms of tax costs, as well as double the pre-treatment and post-treatment sections and a significant increase in the cost of the printing system.

[0009] Therefore, there remains a need for a productive, flexible and cost-efficient method for printing an image onto at least one item and a printing system used for this purpose, whereby a sustainable compromise between production costs and print quality should be achieved.

[0010] Summary of the invention

[0011] The object of the present invention is therefore to provide a method for printing an image onto unit loads and a printing system used for this purpose, wherein the capacity is increased in a simple and cost-effective manner compared to previously known methods and printing systems.

[0012] In the following, the term "general cargo" shall be understood to mean both a plurality of objects and a single object. The problem is solved by the independent claims. Advantageous embodiments and further developments of the invention are described, among other things, in the dependent claims.

[0013] According to a first aspect of the invention, the method for printing an image onto individual items takes advantage of the fact that the items, comprising rotationally symmetrical or rotationally asymmetrical parts (also referred to below as items), are fed to a single digital printing device on at least one track without indexing and in any coordinated arrangement. The digital printing device has at least one printhead with a plurality of print nozzles to print a plurality of pixels onto conveyed and successive parts to generate an individual printed image. Digital printing technology allows for cost-effective, high-quality, and multi-color printing with any desired pattern and, with its dynamic image generation, enables inexpensive individual printing of objects. The image to be printed can be characters, graphic images, structures, or generally codes, such as...It could be a 2D barcode or something similar. The invention is not simply based on doubling the digital printing device, but on redesigning it.

[0014] The inventive method for printing an image onto a piece of goods by means of a printing system comprising a digital printing device with at least one printhead, wherein the printhead has a plurality of individually controllable print nozzles to print a plurality of pixels onto at least one passing part of the piece of goods, comprises the following steps:

[0015] - Conveying the unit load along at least one track, wherein the unit load is positioned on the at least one track in a singulated and / or oriented arrangement;

[0016] - Detecting at least a portion of the unit load on at least one track in the conveying direction upstream of the digital printing unit and determining at least one conveying parameter of the detected portion of the unit load; - Selecting a proportion of the printhead nozzles and determining a frequency at which the selected print nozzles are to be actuated to print pixels onto the at least one detected portion of the unit load within a print area; and

[0017] - Controlling the selected print nozzles depending on the print data of the image to be printed and / or the determined conveying parameter of the at least one detected part of the item and printing the at least one detected part of the item in the printing area of ​​the digital printing device.

[0018] The individual item to be printed, i.e., the part of the item, can be rotationally symmetrical. For example, the item could be a multitude of molded parts or closure lids, which have the form of a cylindrical hollow body closed at one end with a shell surface and a lid surface and can be manufactured in large quantities as injection-molded parts. Preferably, in the process, the print image is printed onto the lid surface. However, the invention is not limited to such rotationally symmetrical items, nor to the printing location, and nevertheless relates to many other printable objects, including rotationally asymmetrical parts.

[0019] Advantageously, the conveying of the unit load takes place along at least two parallel tracks, wherein one or more parts of the unit load can be positioned on each of the parallel tracks in a singulated and / or oriented arrangement, and the detection of at least one part of the unit load on one of the parallel tracks in the conveying direction takes place in front of the digital printing device and at least one conveying parameter of the at least one detected part of the unit load is determined.

[0020] Furthermore, the method preferably comprises the step of distributing the unit load, which is loaded into the printing system, onto several parallel tracks, preferably two parallel tracks, of the digital printing device. This distribution can be carried out by means of at least one sorting device onto the at least two parallel tracks. The unit load can therefore be distributed onto the tracks after a loading device by means of a sorting device adapted to the number of tracks, or a track sorter, or by means of a sorting device assigned to each track.

[0021] In one embodiment of the method, it is provided that the image to be printed on the item in the printing area can be checked and, in the event of a misprint, the corresponding part of the item is sorted out.

[0022] The individual components are transported by the printing system along parallel tracks in the conveying direction, each with its corresponding orientation, by means of a conveying device. This conveying device comprises one or more conveying elements, as described below. The positioning and orientation of the components on the conveying element of the conveying device also depends on the position and / or orientation of the printing surface of the component to be printed. In the case of a closure, the closure opening is therefore oriented downwards, meaning that the lid surface, as the printing surface, faces the printhead within the printing area.

[0023] The unit load can be loaded onto the conveyor system either manually or by a suitable loading device. The loading device(s) are designed to be adaptable to the conveyor system and / or the number of tracks, and in particular, to be expandable. Alternatively, depending on the number of tracks, several conveyor devices can be provided; for example, in the case of two parallel tracks, two conveyor devices are arranged appropriately. The unit load can be conveyed per track, starting from a buffer zone, via an infeed section, and along a conveying path in a single-row arrangement and / or in a largely defined position through the pressure system.

[0024] Furthermore, the individual components can be separated and conveyed to the printing area in a defined orientation. For this purpose, devices are provided that separate the components and / or position them in a suitable position and orientation for printing. To separate the components, separation devices adapted to the number of parallel tracks are provided. A separation device is known per se and could be designed as a star wheel, two counter-rotating wheels, or as rocker-like, pivoting locking elements that are actively or passively movable, or the like. The arrangement of the components in each of the parallel tracks is independent of the arrangement of at least one adjacent track, so that the components are transported largely asynchronously or synchronously.Accordingly, the individual components of the goods can be conveyed separately and sequentially offset from one another using a conveyor system. In this case, the overall width of the conveyor system, i.e., a conveyor belt, is smaller compared to that of two independent conveyor belts.

[0025] The conveying device can be designed as one or more conveyor belts with one or more drive means, for example, a motor, to convey the workpieces, preferably arranged with a gap between successive objects, in parallel tracks into and through the printing area or printing section of the digital printing device. The conveying device can include conveyor belts, appropriately dimensioned counter-rotating star wheels, or supports that hold and guide the workpieces. Furthermore, lateral guides can be provided to achieve suitable positioning of the workpieces within the printing area, i.e., under the printhead.

[0026] Preferably, the conveying device comprises a conveying element designed as a vacuum belt for each lane, which has a plurality of vacuum holes in its center to position and / or orient the workpiece by means of an applied vacuum. However, it is also conceivable that the conveying device comprises a single conveying element designed as a vacuum belt in which vacuum holes are arranged in parallel rows, or that the conveying device comprises at least two belts arranged essentially parallel to each other but spaced apart, the gap between the belts forming a longitudinal gap to position and / or orient the workpiece by means of an applied vacuum. In the case of a vacuum belt conveyor, the positioning and / or orientation can preferably be achieved or supported by means of the vacuum, whereby the respective object can be positioned centrally over the vacuum holes.Such a vacuum conveyor increases the contact pressure of the workpiece on the surface of the conveying medium and stabilizes the position of the conveyed parts. It is also advantageous if the conveying medium is made of metal, as the frictional conditions are particularly suitable for transport.

[0027] Along the conveying path of the unit load, individual sections of the conveying system can also be designed differently, so that, for example, the inlet area and the pressure area differ with regard to the conveying medium. For instance, compressed air conveying can be provided in the inlet area or the accumulation section.

[0028] The conveying element(s) are guided around a drive roller (a first roller) and a second roller, the two of which define the conveying path. The conveying element(s) can also include toothed pulleys and a toothed belt, and this conveying element is characterized by low slippage. Along the conveying path, the unit load is transported in parallel tracks in an asynchronous or synchronous arrangement. High conveying speeds, preferably approximately 50 m / min or more, for example approximately 75 to 90 m / min, can be easily achieved with each circulating conveyor belt.

[0029] To execute the process, particularly to control the printing system, at least one conveying parameter is recorded, for example, by means of a measuring and control system. The conveying parameter can be, for example, the rotational frequency of the drive roller's motor, a torque, a diameter, the wrap of the respective roller, the trigger point of an optional trigger light barrier, and / or a coefficient of friction between the conveying medium and the drive element. Based on well-known relationships between conveying parameters and conveying speed, this speed can be determined at the first and second rollers of the conveying device, as well as at one or more points between the two rollers. Based on this, the relevant conveying speed of the portion of the workpiece below the at least one printhead can also be determined.

[0030] The method according to the invention preferably utilizes digital printing technology, although the application of other printing techniques, such as hot stamping, or engraving techniques, such as laser engraving, is also conceivable. With digital printing technology, the print image can be transferred directly from a processor to the digital printing device in the form of print data. A key advantage is that digital printing technology is flexible and can be used very quickly and with high quality as a rapid prototyping method. The method requires data to control the printing system, which is acquired by an integrated measuring and control system and used to control the digital printing device with at least one printhead with a plurality of print nozzles.The printhead, or in another embodiment several controllable printheads, for example corresponding to the number of colors to be printed, can be designed, for instance, as a piezoelectric inkjet printhead. Here, the multitude of print nozzles, also referred to as pixel generation units, can be individually controlled by the measuring and control system to print an image according to a template onto parts of the workpiece. The term "print nozzle" also includes an ejection opening and an associated fluid channel, as well as means for generating the ink ejection from the print nozzle.

[0031] The number of printhead nozzles depends, among other things, on the maximum resolution of the printed image, i.e., the density of the printable dots, specified in "dots per inch." Equally relevant to the resolution is the minimum amount of ink that can be dispensed by the printhead in one cycle, or during one period at the selected frequency; for high quality, the output amounts are reduced.

[0032] The print data contains the image to be printed, for example, as a machine-readable print data set, which is translated from a graphic template using a printer driver. The print data set is created based on the maximum resolution of the printhead and transmitted to the digital printing device or the measurement and control system. Based on the print data, in particular the maximum resolution and the frequency at which the respective print nozzle ejects ink, a feed rate of at least a portion of the workpiece can be determined, at which the part to be printed is to be conveyed under the printhead. Or, preferably, the feed rate is measured and the frequency of the printhead is adjusted or varied accordingly to achieve the desired print result.

[0033] According to one embodiment, the at least one printhead of the digital printing device comprises a plurality of individually controllable print nozzles arranged within the printing area. The printing area has a width transverse to the conveying direction that corresponds at most to the sum of the widths of the parallel tracks. In the case of two parallel tracks, the dimension of one printhead transverse to the conveying direction corresponds at least to the sum of the part diameters or part dimensions transverse to the conveying direction, including any distance between the parts guided in the tracks. Alternatively, several printheads per ink station can be provided transverse to the conveying direction and offset from one another, e.g., in a cascaded configuration. The printing width of the printhead is divided into sections according to the number of parallel tracks.The virtual division of the printhead can be done via a program, so that familiar printheads can be used for this task unchanged and aligned to each other as usual.

[0034] The printhead can be considered a print module whose width is adapted to the area to be printed. Furthermore, the printhead can be designed as an arrangement of several print modules, which are virtually combined into a single unit and, for the purposes of the invention, are considered separate print modules. This has the advantage that, with a variable relative positioning of the print modules, objects of different sizes can be printed better and more flexibly than with a single print module. The inventive method allows the generation of individual printed images on parts of the workpiece guided asynchronously or synchronously along parallel tracks, whereby the controllable print sections, or the number and position of the print nozzles of the at least one printhead, are always individual. Thus, the workpiece can be printed with a character, a structure, etc.They can also be printed with an individual image, for example a 2D code, such as a matrix code, from which further information about the item can be determined, for example for the purpose of traceability ("track and trace"). The control of the at least one print head is adaptable for each of the parallel tracks, since the item conveyed in one of the parallel tracks is never, or if at all, only randomly aligned with the adjacent track, and the printed images are therefore unique for each track.

[0035] For a high-quality print image, the control of the printhead, or the selected and controlled print nozzles, and the conveying of the part of the workpiece to be printed must be correctly coordinated. In one embodiment, the measuring and control system is configured to provide control signals for controlling the printhead to eject printing ink and / or for controlling the conveying device to transport the part of the workpiece in accordance with print data, position and / or orientation data, and at least one conveying parameter of the part to be printed.

[0036] The measuring and control system includes measuring devices that detect parameters of the conveyed part of the unit load relevant for controlling the printing of the image. To detect the presence and determine the position data of the unit load conveyed in parallel tracks, the printing system preferably includes an optoelectronic measuring device that detects the parts conveyed in each track. In one embodiment, an optoelectronic switch, for example a trigger light barrier, is provided on each side of the conveying device and thus assigned to each of the parallel tracks. These switches are designed as optoelectronic measuring devices and are arranged transversely to the conveying direction. Using the trigger light barriers, the conveyed part of the unit load can be detected independently on each of the parallel tracks, and a generated signal can be used to activate a printing process.

[0037] Conventional photoelectric sensors consist of a transmitter and receiver. Depending on the type, the transmitter and receiver are located at opposite ends of a monitoring path or at the same end, with the latter type also having a reflector at the opposite end. In a trigger photoelectric sensor, an evaluation circuit is connected downstream of the receiver. This circuit is activated when the transmitted light pulse from the transmitter is interrupted by a part entering the beam path. Based on the generated signal, the part of the item passing through the trigger photoelectric sensor on one of the parallel tracks triggers an individual printing process when the detected part of the item is within the print area of ​​the printhead.

[0038] In one embodiment, the measuring and control system can include an encoder for tracking the parts. This encoder is located on each track and uses the current conveying speed of the part being transported on each track as a conveying parameter. Accordingly, the digital printing unit can operate autonomously using a signal generated by the trigger light barrier as a start signal and the conveying speed determined by the encoder. This creates a printing system that, with knowledge of the geometric data of the part and using the position feedback from the motor via the integrated encoder, can individually trigger and control the printing process. Thus, based on the determined print position of the part, it can be printed sequentially in all available color stations during multicolor printing.

[0039] In a preferred embodiment, a receiving unit is further provided upstream of the digital printing unit in the conveying direction to detect the position and / or location, and optionally a dimension, such as length, of the conveyed portion of the item per lane. A digital image sensor or camera unit can be provided to capture an image of the portion of the item in the conveying direction upstream of the printing area and, by means of an integrated evaluation unit, determine position data and / or other data of the detected portion, which can be transmitted to the digital printing unit or the control unit. The position data contains information about the orientation of the portion on the conveying device. Depending on the orientation, which can be represented as an angular measurement or in the form of coordinates, the digital printing unit can be controlled such that the image to be printed is virtually adjusted.The control of the print nozzles is adjusted accordingly. This is particularly important for rotationally asymmetrical shapes of the part being printed. However, even with rotationally symmetrical shapes, an improved print image can be achieved by adjusting the nozzle position.

[0040] The control system for the digital printing device provided according to the invention, based on determinable position data, length information and / or trigger activation, can also be used in a single-track system.

[0041] In one embodiment, the measurement and control system further comprises a control unit with both hardware features, such as a computer or processor, and software features, such as implementable programs, functions, routines, program code, algorithms for machine learning or for automating intelligent behavior ("artificial intelligence"), etc. The control unit is configured to control the printing system based on the transmitted and evaluated data, i.e., the recorded conveying parameter or conveying speed, parameters of the part of the workpiece to be printed, parameters of the printhead, and / or print data. In particular, the measurement and control system may, for this purpose, include programmable logic gate arrays (FPGAs) and / or microprocessors.

[0042] According to one embodiment of the invention, the workpieces are conveyed asynchronously in parallel tracks into and through the printing area of ​​the digital printing device. To achieve high print quality, the components of the workpieces and their conveying parameters are individually determined for each track. The data thus determined forms the basis for the dynamic control of the individually controllable print nozzles, which are virtually assigned to each track. The measuring and control system is preferably configured for dynamic control in order to be variable with regard to workpieces being transported in a non-constant sequence on the respective track. The dynamic control allows for individual selection and adjustment of the frequency at which the respective print nozzles are actuated.

[0043] To print a multi-colored image, the digital printing system comprises several printheads, preferably arranged sequentially in the direction of material flow. The printing medium ejected from the print nozzles can be available in different colors, for example, white, black, blue, magenta, and / or yellow, etc., and is stored in the ink tanks assigned to the print nozzles. Furthermore, the printing medium can also be a varnish, primer, or similar substance. Preferably, a separate printhead is provided for each printing color and / or material to be printed.

[0044] According to another aspect of the invention, after printing by the digital printing unit of the printing system, the print result is checked using an optical inspection device. The optical inspection device can be a digital image sensor, such as a camera, e.g., a CCD camera, which captures image data of the printed components conveyed in parallel tracks. It is conceivable to use a single camera, which can be set up and controlled to capture the components conveyed in parallel tracks. However, it is preferred to provide one camera for each of the parallel tracks, as this simplifies image capture. The captured image data can be compared with stored images, and a printing defect will result in a deviation from the print template. In particular, artificial intelligence can be used for this purpose, for example, to provide a self-learning system for evaluating the printed image.An image captured by the image sensor can be processed by a processor to derive indications of a defect. The self-learning system can be trained using objects with both error-free and error-prone print images. For example, a discrepancy in size and / or position between the printed image on the object and the stored images can indicate an incorrectly set conveyor speed, which can then be corrected at the conveyor's drive mechanism. The color saturation and intensity of the printed image can also be compared with a template and / or the stored images to potentially adjust the amount of ink output from the print nozzles.

[0045] Furthermore, it may be possible to automatically sort out defective parts. For this purpose, a sorting module is preferably arranged for each lane in the conveying direction downstream of the optical inspection device, which removes the defective parts from the conveying system. This sorting can be carried out, for example, by a short, targeted burst of compressed air using a laterally arranged compressed air valve, whereby the defectively printed or otherwise faulty part of the item is blown away from the conveying system and collected and / or recycled in a suitable manner. It is also possible to provide other types of sorting modules by which defectively printed or generally faulty parts can be sorted out. For this, the requirements regarding speed, safety, and efficiency must be met.The portion of the item that passes the inspection is transported further by the conveyor system and leaves the printing system. Devices may be provided at the system's output to transport the printed and inspected items further.

[0046] Another aspect of the invention relates to a printing system for a method of printing an image onto a piece of goods, comprising a digital printing device with at least one printhead having a plurality of print nozzles which can be individually controlled to print a plurality of pixels onto at least a part of the piece of goods as it passes through a printing area.The printing system comprises a conveying device with at least one track of a conveying means for transporting the unit load between a drive roller and a second roller, a loading device for placing the unit load parts in a singulated, positioned, and oriented arrangement on the at least one track, wherein the unit load parts are arranged asynchronously or synchronously on the at least one track, and a measuring and control system with an optoelectronic measuring device for detecting at least a portion of the unit load on the at least one track, an encoder for determining a conveying parameter for the detected portion of the unit load, and a control device for operating the printing system. Preferably, the optoelectronic measuring device comprises a trigger light barrier.

[0047] According to one embodiment, the conveying device comprises a conveying means for conveying unit loads along at least two parallel tracks.

[0048] To load the parts of the package into the printing system and / or to distribute them in a predetermined arrangement onto at least one track or several tracks, at least one loading device and / or at least one sorting device is provided.

[0049] Furthermore, as described above, a recording unit can be provided in the conveying direction in front of the digital printing device, which takes a picture of the item and extracts position data of the recorded item by means of an evaluation unit, which can be transmitted to the digital printing device.

[0050] In one embodiment of the printing system, at least one optical inspection device for monitoring the quality of the printed image and at least one sorting module are provided in the conveying direction after the digital printing device, which removes a defective item from the conveying device.

[0051] Another aspect of the invention relates to the use of the pressure system in the inventive method.

[0052] Further details of the invention will become apparent from the following description of the preferred embodiment, which is illustrated by way of example in the accompanying drawings. The description will also reveal the further advantages of the present invention, as well as suggestions and proposals on how the subject matter of the invention can be modified or further developed within the scope of the claim.

[0053] Brief description of the drawings

[0054] The embodiments of the invention are explained in more detail below with reference to the drawing. The drawing shows:

[0055] Figure 1 shows a schematic block diagram of an embodiment of a method for operating a pressure system,

[0056] Figure 2 shows a schematic top view of an embodiment of a printing system, and

[0057] Figure 3 shows a second schematic view of an embodiment of a printing system.

[0058] Preferred embodiments of the invention

[0059] In the figures, identical or functionally equivalent elements are designated with the same reference symbols, unless otherwise specified.

[0060] Figure 1 shows a schematic block diagram of an embodiment of a method for operating a pressure system 100, as shown in Figure 2.

[0061] In a first step 10, parts of the unit load 101 (see Fig. 2) are conveyed in a singulated, positioned, and oriented arrangement along at least two parallel tracks 102, 102', wherein the parts of the unit load 101 are arranged asynchronously to one another on the parallel tracks 102, 102'. However, the conveying of the parts of the unit load along parallel tracks 102, 102' can also be synchronous. The singulated, positioned, and oriented arrangement here means, for example, that the unit load 101, or parts of the unit load 101, are arranged in a successive row at a defined position of a conveying means 121 of a conveying device 120 (see Fig. 2) without abutting each other, such that a surface of the unit load 101 to be printed is directed towards a printhead 201.

[0062] In a second step 20, at least a portion of the unit load 101 is detected on one of the parallel tracks 102, 102' in the conveying direction upstream of a digital printing device 200 by a detection device described in more detail below, e.g., an optoelectronic measuring device 310. Here, both the portion of the unit load 101 itself and its dimensions and / or its position, orientation, etc., can be verified. Furthermore, in step 20, a conveying parameter of the detected portion of the unit load 101 is determined. The conveying parameter can, for example, be a conveying speed v, in particular a conveying speed v of the detected portion of the unit load 101 in the area of ​​the at least one printhead 201 of the digital printing device 200.

[0063] In a third step 30, a proportion of print nozzles 202 of the printhead 201 is selected, which define a print area for the detected part of the item 101 located in one of the parallel tracks 102, 102'. Furthermore, a frequency F is determined at which the selected print nozzles 202 of the printhead 201 are controlled to dispense printing ink 203 in order to generate a printed image on the detected part of the item 101. The frequency F can be predetermined by the printhead 201 or alternatively derived from boundary conditions.

[0064] In step 40, the selected print nozzles 202 of the printhead 201 are controlled with a specific frequency F and print data D. The print data D comprises the motif to be printed, for example, as a machine-readable data set, where the motif to be printed, as a digital image data set, represents a template that can be transferred into the print data taking into account a maximum resolution. Based on the print data and a known frequency, i.e., the frequency with which the printing ink is to be or can be dispensed from the respective controlled print nozzle 202, the conveying speed v can be determined at which the part of the unit load 101 is to be conveyed under the printhead 201.

[0065] The printing system 1 is controlled via a measuring and control system (not shown). The measuring and control system comprises a control unit configured to input the print data D via input means and to select, via determination means, those print nozzles 202 which are to be activated to print the design onto the detected part of the item 101 at a set or predetermined frequency F to dispense a defined quantity of ink. Furthermore, the control unit includes control means to activate the print head 201 accordingly after reading the print data. The selected print nozzles 202 of the print head 201 are activated so that, during one period of frequency F, each selected print nozzle 202 dispenses a specific quantity of ink, thus creating a pixel on the part of the item 101.

[0066] This method can be used to operate a printing system 1, the at least one printhead 201 of which can be variably controlled depending on the detected conveying speed v of a piece item 101 conveyed in one of the parallel tracks 102, 102'. The variable control includes both the number of print nozzles 202 and the frequency F.

[0067] Figure 2 schematically shows an embodiment of a printing system 1. The printing system 1 comprises the conveying device 120 with the conveying medium 122, which is preferably designed as a vacuum belt with vacuum holes 123. Accordingly, the portion of the unit load 101 conveyed by the conveying device 120 on the conveying medium 122 is conveyed by the printing system 1 by means of vacuum along parallel tracks 102, 102' in the conveying direction 124. The unit load 101 can be distributed onto the parallel tracks 102, 102', in particular by means of a loading and singulating device (not shown), so that portions of the unit load 101 are conveyed in a non-adjacent or adjoining arrangement, preferably centrally over the vacuum holes 123 and with the surface 130 to be printed facing the print head 201.In the illustrated embodiment, the parts of the unit item 101 are closure lids in a rotationally symmetrical shape with a lateral surface and a lid surface, which represents the surface 130 to be printed.

[0068] The conveying device 120 further comprises a first roller 125, e.g., a drive roller, and a second roller 126, around which the conveying means 122 is arranged. A printing area 204 of the digital printing device 200 is located between the first roller 125 and the second roller 126. One or both of the first roller 125 and the second roller 126 are driven by a drive means (not shown), preferably a motor. This motor is, in particular, an electric motor that directly drives one of the rollers 125, 126, so that precise control of the conveying speed of the unit load 101 can be achieved.

[0069] In the printing system 1, as shown in Fig. 2, an optoelectronic measuring device 310, designed as a trigger light barrier, is arranged upstream of the digital printing unit 200 in the conveying direction 124 for piece detection. Each of the parallel tracks 102, 102' is assigned a light barrier transmitter 311, 31T. A light barrier receiver 312, 312' is arranged opposite each of the light barrier transmitters 311, 31T across a monitoring path. In the illustrated embodiment, the light barrier receivers 312, 312' are therefore located between the parallel tracks 102, 102'. An evaluation circuit (not shown) is connected downstream of the light barrier receivers 312, 312'.

[0070] Furthermore, in the exemplary embodiment of the printing system 1, an encoder 320, 320' is assigned to each track 102, 102' for part tracking. The encoders 320, 320' are configured to precisely determine the conveying speed v of at least one part of the unit load 101 by means of displacement measurement on the respective track 102, 102', particularly in the printing area 204.

[0071] Also in the conveying direction 124 upstream of the digital printing device 200, a recording unit 400, for example a CCD camera, is provided in the illustrated embodiment. This unit is configured to capture an image from which the position and / or orientation of the portion of the unit 101 conveyed per track 102, 102' can be extracted. Particularly in the case of rotationally asymmetrical parts 101, this information must be transmitted to the digital printing device 200 so that the image to be printed can be positioned and printed precisely without having to rotate or reposition the portion of the unit 101.

[0072] The digital printing device 200 comprises at least one printhead 201, preferably several printheads 201, each having a plurality of individually controllable print nozzles 202 for ejecting different printing inks. For this purpose, the print nozzles 202 of each of the printheads 201 are individually controlled by means of the measuring and control system, the ejection of the printing ink being dynamic and dependent on the conveying speed v of the portion of the unit load 101 detected by the optoelectronic measuring device 310 per track 102, 102'. The printhead 201 is divided into virtual areas, the width of which each corresponds at least to the dimension of the portion of the unit load 101 transverse to the conveying direction 124.

[0073] In the conveying direction 124 downstream of the digital printing unit 200, each of the tracks 102, 102' is assigned an optical inspection unit 500 to capture the printed motif printed by the digital printing unit 200 on each part of the unit 101 using appropriately arranged cameras and, in particular, to convert it into image data. The image data can be compared with the print data by the measuring and control system to verify any deviations in the printing results and, if necessary, to make adjustments to the printing system 1. The adjustments can be made via a correction unit and may relate to the conveying speed v, the selection of the print nozzles 202, the frequency of ink output, and / or the output quantity of ink.

[0074] In the illustrated embodiment, if a defective print image is detected, a sorting module 600 is arranged downstream of the optical inspection device 500. This module removes the defective part of the item 101 from the conveying medium 121, for example, by means of a compressed air pulse. The printing system 1 can therefore comprise separate components for each of the parallel tracks 102, 102', such as a loading and singulation device (not shown), a conveying medium 124, an optoelectronic measuring device 310 (e.g., a trigger light barrier), a receiving unit 400, an optical inspection device 500, and / or a sorting module 600. Likewise, the printing system 1 can comprise a separate digital printing device 200 for each of the parallel tracks or only a single digital printing device 200, which includes at least one printhead 201 and virtually divided print nozzles 202 arranged therein.

[0075] Figure 3 shows a first part 101a of the unit 101 and a second part 101b of the unit 101, which are rotationally asymmetric. Both parts 101a and 101b of the unit 101 are held on the vacuum belt 122 by the vacuum applied to the vacuum holes 123. The position of the first part 101a and / or the second part 101b of the unit 101 can be detected by the receiving unit 400, and the detected position and / or orientation data can be transmitted to a control unit of the printing system 1 in order to adjust the printing process on parts 101a or 101b of the unit 101 based on this data.In the illustrated case, the position of the first part 101 a corresponds to a desired position and the second part 101 b is rotated by 90° relative to the desired position, so that the print nozzles 202 of the print head 201 must be controlled in such a way that the image printed on the second part 101 b is also rotated by 90° relative to the image printed on the first part 101 a.

Claims

22 Patent claims 1. A method for printing an image onto a piece of goods (101) using a printing system (1) comprising a digital printing device (200) with at least one printhead (201), wherein the printhead (201) has a plurality of individually controllable print nozzles (202) to print a plurality of pixels onto at least one part of the piece of goods passing through it. (101 ) to print, comprising the following steps: - Conveying (10) the general cargo (101) along at least one track (102) wherein the packaged goods (101) can be positioned on the at least one track (102) in a singulated and / or oriented arrangement; - Detecting (20) at least one part of the unit load (101) on the at least one track (102) in the conveying direction (124) in front of the digital printing device (200) and determining at least one conveying parameter of the at least one detected part of the unit load (101); - Selections (30) of a proportion of the print nozzles (202) of the printhead (201) and determining a frequency (F) at which the selected print nozzles (202) to print pixels onto the at least one captured part of the item (101) in a print area (204); and - Controlling (40) the selected print nozzles (202) depending on print data (D) of the image to be printed and / or the determined conveying parameter of the at least one detected part of the unit item (101) and printing the at least one detected part of the unit item (101) in the print area (204) of the digital printing device (200) in one printing operation.

2. The method according to claim 1, characterized in that - the conveying (10) of the unit load (101) takes place along at least two parallel tracks (102, 102'), whereby one or more parts of the general cargo (101) can be positioned on each of the parallel tracks (102, 102') in a single and / or oriented arrangement, and - the detection (20) of at least one part of the unit load (101) on one of the parallel tracks (102, 102') in the conveying direction (124) in front of the digital printing device (200) and the determination of at least one conveying parameter of the at least one detected part of the unit load (101).

3. The method according to claim 2, characterized in that the method comprises the step of distributing the unit load (101) by means of at least one sorting device onto the at least one track (102) or the at least two parallel tracks (102, 102') for further conveyance by the pressure system (1).

4. The method according to one or more of the preceding claims, characterized in that the unit load (101) comprises rotationally symmetric parts or rotationally asymmetric parts which are separated and conveyed in a defined orientation along the at least one track (102) or the at least two parallel tracks (102, 102') through the pressure system (1).

5. The method according to one or more of the preceding claims, characterized in that the part of the package (101) is a closure lid in the form of a cylindrical hollow body closed at one end with a shell surface and a lid surface.

6. The method according to one or more of the preceding claims, characterized in that the printing process for the unit load (101) on the track (102) or each of the at least two parallel tracks (102, 102') is triggered by actuating the selected printing nozzles (202) when at least a part of the unit load (101) is located in the printing area (204), wherein this printing process can be determined by means of a signal generated by an optoelectronic measuring device (310) and based on a conveying speed (v) determined as a conveying parameter.

7. The method according to one or more of the preceding claims, characterized in that at least one layer of the at least one part of the unit load (101) is optically detected on each track (102, 102') and position and / or location data are extracted in order to adapt the printing process to the at least one part of the unit load (101) on the basis thereof.

8. The method according to one or more of the preceding claims, characterized in that the printed image to be printed is multicolored and / or individualizable for each part of the unit item (101).

9. The method according to one or more of the preceding claims, in that the printed image printed on the unit item (101) is inspected and, if a defect in the printed image is detected, the part of the unit item (101) is sorted out and / or an adjustment of the printing system (1) is made.

10. The method according to claim 9, characterized in that a self-learning system is used to assess the print image, which is trained using faulty and / or faultless print images.

11. A printing system (1 ) for a method for printing an image onto unit load (101 ) according to one or more of claims 1 to 10, comprising: - a digital printing device (200) with at least one printhead (201) having a plurality of individually controllable print nozzles (202) to print a plurality of pixels onto at least one item (101) as it passes through a print area (204) during a printing process; - a conveying device (120) with a conveying means (121) for conveying unit loads (101) along at least one track (102); and - a measuring and control system (300) with an optoelectronic measuring device (310) to measure at least one track (102) on which at least one track (102) 25 positioned unit items (101 ) to detect, with an encoder (320) to determine a conveying parameter for the at least one detected unit item (101 ), preferably a conveying speed (v) and with a control unit to operate the printing system (1 ).

12. Printing system (1 ) according to claim 11 , characterized in that the conveying device (120) comprises a conveying means (121 ) for conveying unit loads (101 ) along at least two parallel tracks (102, 102').

13. Printing system (1 ) according to claim 11 or 12, characterized in that at least one loading device and / or at least one sorting device is included to position the unit load (101 ) in a singulated and / or oriented arrangement on the at least one track (102) or the parallel tracks (102, 102').

14. The pressure system (1 ) according to claim 11 , 12 or 13, characterized in that the conveying device (120) is designed as a vacuum belt conveyor with at least one vacuum belt to which a vacuum can be applied.

15. The printing system (1 ) according to one or more of claims 11 to 14, characterized in that the optoelectronic measuring device (310) for the at least one track (102) or each of the parallel tracks (102, 102') comprises a trigger light barrier.

16. The printing system (1 ) according to one or more of claims 11 to 15, characterized in that it further comprises a receiving unit (400) which receives an image of the at least one unit item (101 ) in the conveying direction (124) in front of the digital printing device (120) and determines position and / or location data of the at least one recorded unit item (101 ) by means of an included evaluation unit, which can be transmitted to the control unit.

17. The pressure system (1) according to one or more of the preceding claims 11 to 16, characterized in that in the conveying direction (124) at least one optical inspection device (500) is provided after the digital printing device (120) to verify the quality of the printed image and at least one sorting module (600) to remove defective items (101) from the conveying device (120).

18. Use of a printing system (1) according to one or more of claims 11 to 17 in a method according to one or more of claims 1 to 10.

Images