WO2022229778A1

WO2022229778A1 - Product printing method, device and software program

Info

Publication number: WO2022229778A1
Application number: PCT/IB2022/053564
Authority: WO
Inventors: Filip Feyaerts; Laurent DEVOLDER
Original assignee: Printing International Nv
Priority date: 2021-04-28
Filing date: 2022-04-15
Publication date: 2022-11-03
Also published as: BE1029347A1; EP4330046A1; BE1029347B1

Abstract

A method is described for setting a pad print of a product. A printing plate (10) which comprises an engraving of a print image and an identifying mark (11) is provided as well as a pad (53) and the product (55) or a product holder (54) for holding product (55). A camera image of the identifying mark (11) is captured (56), in which the identifying mark (11) is recognised. In a processing unit (59) a projection is identified between printing plate (10) and product (55) and a point of the print image formed by the engraving and a target position are compared to correspondingly control adjusting actuators (57).

Description

PRODUCT PRINTING METHOD, DEVICE AND SOFTWARE PROGRAM

The present invention relates to the art of printing, more specifically pad printing. This pad printing technique is particularly suitable for printing all kinds of products, such as articles with a (possibly) curved and/or complex shape. More specifically, the invention relates to a method, device and software product for setting a pad print of a product, and a printing plate for use in the method.

In the pad printing technique a desired image is applied to a product using one or several pad printing devices. Every device hereby provides a colour component of the image to be made. The eventually obtained image can thus consist of a simple monochrome or halftone image that was applied in a single pad printing step, or a composite image that is formed by combining several printing steps, e.g. a combination of several basic colours, such as cyan, magenta, yellow and black (limited to these colours).

In a prior printing technical development, a combination of possible doctor blade systems, printing plates, types of ink and pads is composed to obtain the desired result, e.g. with the desired positioning of the print on the product and the required capacity in terms of the number of printed pieces per unit of time in mind. Other factors can also be taken into consideration, e.g. environment parameters such as temperature, atmospheric humidity etc., to arrive at a suitable combination of applicable elements and techniques. To implement the developed process practically for the production floor, the printing plate(s), pad(s) and the product on which the pad print is applied must be aligned, or configured, relative to each other. The printing of the products requires a precise adjustment and setting of the used system. A precise positioning of a print on an article can be particularly complicated due to a complicated and/or curved shape of the article, due to possible small tolerance margins on the acceptable placement of the print on the article, and/or due to the number of colours used in the print.

The machines used in said printing processes are typically adapted to save and apply a certain combination of product and print to be applied, after the configuration process. This is referred to as the (product and print) recipe. An exemplary recipe describes, in a structured way, the set values for the components, such as positioning coordinates relative to a calibration point according to predefined and/or fixed movement axes, a desired temperature and a desired waiting period between the doctor blade movement and the lifting of the image. Typically, the recipe may also comprise measured values regarding the components, such as a measured position of a component, e.g. read via a micrometer measurement system and/or a setting of a component that can be set in a number of discrete positions.

When a product is printed with a certain machine, a corresponding machine setting is applied, as specified by the recipe. However, to print said product on another machine, said machine needs to be reconfigured. The available recipe for the previous machine cannot be simply transferred, in view of the fact that, for example, the coordinates system and/or the calibration point do not correspond.

A method, as known in the art, for configuring pad printing systems can, for example, be as follows. In a typical manual adjustment, the image is positioned on the product in a number of steps.

The printing plate or cliche, as designed and manufactured to transfer the desired image information (or one colour component thereof in any case), comprises an engraving in a typically flat plate, on which ink is applied in a first step. A doctor blade system is used hereby to, in a relative movement between the doctor blade and the printing plate, remove excess ink from the plate, such that the grooves of the engraving are well coated with ink without ink residue outside the margins of the provided engraving.

In this step, the printing plate is located in a holder. Alignment characteristics are applied in the printing plate, which are aligned in the printing process relative to the holder to position the printing plate relative to the holder. Said (mechanical) alignment characteristics are usually provided in the form of perforations in the plate, e.g. reference holes, which are subject to strict tolerance criteria. Said holes correspond with dowels that are applied in/on the holder.

A magnet plate can also be used for this as an intermediate support of the dowels, which, for reasons of user- friendliness, can be removed from the printing system. In turn, the magnet plate can be exactly positioned in the holder via corresponding reference points between the magnet plate and the holder. For example, the magnet plate can be provided with cut reference sides, which are positioned relative to reference points on the holder.

In a second step, the image is lifted from the inked printing plate by the pad. Said pad, or stamp, is made of an elastic material, such that it can mould itself to the product upon transferring the image on the product. Moreover, preferably the pad is smooth and ink-repellent to transfer the ink optimally to the product, such as for example a pad made from silicone rubber.

Printing technical parameters such as depth of the engraving, lineature and grid percentage, but also e.g. the shape and hardness of the pad, determine how much ink is lifted from the engraving by the pad. The properties of the pad (e.g. shape, hardness) jointly determine the distortion of the image upon transferring to the product, whereby obviously the shape of the product is an important factor. To consistently and properly reproduce the lifting of the image by the pad, the image is always applied on the pad in the same place, to thus systematically retain one and the same distortion of the image upon transferring to the product.

Thus a second adjustment step is needed to guarantee that the image is lifted on the desired location of the pad. This may be the centre of the pad, but printing technical considerations may also indicate another position on the pad as the most suitable choice.

To this end, the pad is positioned with a configuration according to two orthogonal axes parallel to the (flat) surface of the printing plate. Often a rotation around an axis perpendicular to the plane of the printing plate may be set, such that the position and orientation of the pad in a plane parallel with the printing plate are completely defined. However, said additional orientation definition is not strictly required, e.g. in case of a circle-symmetrical pad.

It needs to be noted hereby that the engraving in the printing plate may not be exactly positioned relative to the references in the printing plate (e.g. dowel holes). This can be the case, for example, due to deviations and/or error margins upon applying the engraving. The tolerance on the placement of the image on the product may be stricter hereby than the tolerance with which the engraving is positioned on the printing plate. Consequently, it is possible that, when a printing plate is placed on the printing system, the aforementioned steps need to be repeated. The importance of such iterative adjustment process becomes greater as the tolerance of the printing on the product becomes stricter. In case of multi-colour printing, this effect, due to an accumulation of positioning errors in the different colour layers, will also be greater. In a third step, the image lifted by the pad is positioned on the product. This requires shifting the printing system relative to the product, or vice versa.

To this end, similarly to the alignment of the transfer from plate to pad, a two-dimensional translation system could be used in combination with a rotation angle in the translation plane. However, in practice, due to cost considerations typically only adjustment options according to the mutually perpendicular translation axes will be provided. Therefore, this also means that, if the orientation of the image on the product does not correspond with the desired result, the previous steps must be repeated to adjust the orientation of the printing plate and/or the pad.

Obviously it is ultimately important that the products on which the pad print is applied, in a production series, always need to be positioned in the same way and with a high repetition precision. To this end, products are generally, e.g. already in the design phase, provided with reference points and/or planes to allow a precise positioning in all directions.

The method according to the state of the art described above is largely based, on adjusting the (obtained) print, often in an iterative and possibly long-winded process. This principle can be summarised concisely as 'print-and- correct'. Setting the machine(s) to obtain a monochrome or halftone image in the desired position on the product can be a particularly time-consuming process according to said 'print-and-correct principle, which can be the case to an even greater extent for multiple colour images made up of several monochrome or halftone images.

It is an object of embodiments of the present invention to provide good, precise, efficient and/or simple printing of an article.

In particular, embodiments of the present invention can solve problems and challenges in a method according to the state of the art, as described above for example.

It is an advantage of embodiments of the present invention that an automatic, or substantially automatic (e.g. requiring only a limited participation of an operator), approach is provided for adjusting a print image on a product.

It is an advantage of embodiments of the present invention that the time for adjusting a printing machine can be limited, e.g. greatly reduced relative to an alternative method as known in the art.

By limiting the time required for setting and adjusting, a high efficiency of the printing process can be obtained, e.g. resulting in a high net capacity of the process (resp. the use of the device) according to embodiments of the present invention, which can also have a positive impact on the cost per print.

In particular, loss of time can be reduced or prevented when switching print images, when switching the product (and print image), and when adjusting the process for a new print image for a certain product. Quick conversion times when switching sets may moreover be important in realising just-in-time printing. These advantages may result in sectors being helped which so far have been rather reluctant to apply tampography due to the setting work, and the time, the required expertise and/or associated costs.

These advantages can be explicitly evident in situations whereby a big number of colours to be printed is combined and/or whereby images need to be printed in different positions on the product. Examples include multi-colour printing (e.g. CMYK printing), e.g. at high quality, such as photo quality. Tampography can in such situations, according to the state of the art, often signify too great an investment in light of the required knowledge and setting time. In addition to multi-colour printing, embodiments may also be particularly advantageous in situations with fewer colours to print, but where the set and/or product need to be switched very regularly.

It is an advantage of embodiments of the present invention that a print can be set and adjusted without, or with only very limited, material waste, such as ink and/or copies of the product which could be used for the experimental testing and readjustment of the alignment of the printing in an alternative approach. Loss of products due to wrong printing applied during the configuration of the machine, according to the 'first-time right' principle, can thus be substantially avoided or strongly limited in any case. It is an advantage of embodiments of the present invention that several (e.g. uniform) products can be printed successively (e.g. quickly), whereby differences in the positioning and/or orientation of said products (e.g. substantially instantly) can be detected, such that the alignment of the printing machine can be readjusted per product (e.g. automatically) to compensate said differences. This also allows a pad printing technique to be applied in situations where a precise alignment of individual articles cannot be guaranteed, or can only be obtained with difficulty (e.g. at a high cost). Moreover, (small) deviations in terms of shape and dimensions of the products can be simply compensated.

It is an advantage of embodiments of the present invention that the method (resp. software product, device) described here can be applied/operated by an operator without the operator needing extensive training and/or specific expertise to this end. It may suffice, for example, that an operator provides the required printing plates, ink containers and pad, without any manual alignment and/or adjustment being required.

For example the use of an inked image for the adjustment process, according to a process as known in the art, requires in-depth knowledge and proficiency in the control of printing technical parameters. In addition, the (human) evaluation of the image in fine-tuning the readjustment process creates a subjective dependence. Because this process is not completely objective according to the state of the art, the obtained results between different operators may vary, even if they all, in essence, possess the necessary experience and expertise.

By limiting the required time, trained manpower and complexity in the setting process, the costs for printing on the products can also be limited, which can be particularly advantageous for printing limited runs. In this way the start-up cost of small production series and small batches of e.g. prototypes or test products in particular can be kept advantageously low. This therefore also benefits a wide applicability of the described technique. Embodiments of the present invention can be exceptionally suitable for series production with a small batch size, or if need be even for a batch size of one. This means that for every product to be printed, the printing machine can be set separately based on information on product and print image.

The Overall Equipment Effectiveness (OEE) is determined as the combined effect of availability, performance and quality. By reducing the conversion time of the machine, a substantially higher 'availability' coefficient can be obtained. The 'quality' parameter can also be improved by a better, and more consistent setting of the machine. Ongoing monitoring also allows the setting to be readjusted if necessary, which can also have an effect on the quality. A higher Overall Equipment Effectiveness (OEE) results in a higher net capacity of the machine and thus a lower cost per print for the same cost.

In addition to the aforementioned practical inconveniences, e.g. in view of the printing technical requirements and human evaluation in an approach according to the state of the art, an important aspect of the problems that occur in configuring a pad printing process is that engravings are applied in a printing plate with limited precision relative to references in the plate, e.g. due to inevitable technical limitations and/or in light of the profitability which is reasonably justifiable, e.g. in terms of the rising costs, time, means and/or required processing machines to make the engraving with a possibly even higher precision.

A practical limitation of said precision arises because a common reference system uses dowel holes in the printing plate to mount printing plates using dowels on the holder. This requires, for obvious reasons, that the dowel hole is at least as big as the dowel, and preferably slightly bigger with a minimum margin. Inevitably, when placing the engraving this already gives rise to a small inaccuracy, thus a tolerance. Said tolerance plays a role when the printing plate is placed on the holder. This gives rise to deviations in the positioning of the image on the product, both according to the mutually perpendicular translation axes and the rotation angle in the image plane.

A device, printing plate, software product and/or method in accordance with embodiments of the present invention realises the aforementioned objective, e.g. by providing a solution for an aforementioned challenge.

In a first aspect, the present invention relates to a method for setting a pad print of a product. The method comprises obtaining a printing plate which comprises an engraving, in accordance with a print image, and a first identifying mark. The method comprises obtaining a pad to transfer the print image in ink or other transferable material from the engraving to the product, and obtaining the product or a product holder for the product. The method further comprises capturing a camera image with a camera system such that the first identifying mark is shown in the camera image, and recognising at least the first identifying mark in the camera image. In this way the corresponding position, or position and orientation, of the first identifying mark is identified in the camera coordinates. The method comprises identifying a projection, from the printing plate to the product or vice versa, by applying a transformation indicative of the printing process based on the identified position, or position and orientation, of the first identifying mark. At least one point of the print image formed by the engraving and a predefined target position on the product are compared using the projection, and one or several actuators are controlled to reposition and/or to reorientate the printing plate, the pad and/or the product or product holder such that the projection of the point of the engraving on the product is brought closer to the target position.

In tampography, commonly an ink layer, structured by the engraving, is transferred via a pad to the product on which the pad print is applied. However, embodiments are not limited to only ink printing. For example, another transferable material, such as a varnish, a glue, a metal, a conductor, an insulator, etc., can be applied to the product in a substantially similar way by tampography, to thus reproduce the shape or the pattern defined by the engraving.

Where a camera system, in connection with both this first aspect and in the further (2^nd, 3^rd, 4^th) aspects of the invention as described below is referred to, it must be noted that the camera system may comprise a single camera or multiple cameras.

Where a (first; second; third) identifying mark in connection with the first and further (2^nd, 3^rd, 4^th) aspects of the present invention is referred to, it must be noted that this may comprise a combination of several (first, second, third) identifying marks.

In a method according to embodiments of the present invention, the first identifying mark can be engraved together with the engraving in the printing plate.

In a method according to embodiments of the present invention, the identifying mark can be spatially separated from the print image in the engraving, whereby the identifying mark is located in a peripheral area of the printing plate relative to the engraving in a central area.

In a method according to embodiments of the present invention, the first identifying mark may comprise a registration mark, line segments at mutually different angles and/or one or several circular characteristics. In a method according to embodiments of the present invention, the first identifying mark may comprise an optically legible code, whereby said optically legible code encodes digital information.

This digital information may comprise information relating to the position of the point of the print image formed by the engraving relative to the first identifying mark and/or the predefined target position of said point on the product (without limitation). This digital information may also, additionally or alternatively, comprise a reference code which allows said position of the point of the print image in the engraving relative to the identifying mark and/or the target position on the product to be retrieved from a database. The digital information may, for example, consist of a serial number (or comprise the serial number, together with further digital information), whereby said serial number uniquely identifies the printing plate such that the associated (position) information can be obtained by querying the database.

In a method according to embodiments of the present invention, the optically legible code may comprise a QR code or bar code.

In a method according to embodiments of the present invention, the pad may comprise a second identifying mark and/or the product or the product holder may comprise a third identifying mark. In a method according to embodiments of the present invention, recognising may further comprise recognising the second and/or third identifying mark in the camera image, and the corresponding position, or position and orientation, of the second and/or third identifying mark may also be identified in the camera coordinates.

In a method according to embodiments of the present invention, the projection can be identified based on the identified position, or position and orientation, of the first identifying mark and of the second and/or third identifying mark.

In a method according to embodiments of the present invention, the camera system may be fixedly arranged, and configured such that the first identifying mark, the pad and the product or the product holder are simultaneously detected in the camera image or a combination of camera images.

In a method according to embodiments of the present invention, the camera system may be movably arranged, such that the camera system possesses a fixed and predefined position and orientation relative to the (movable - e.g. using the actuators) product or the product holder or relative to the (movable - e.g. with the actuators) pad.

A method according to embodiments of the present invention may comprise a camera calibration, whereby an image is captured with the camera system of a test card to determine a correspondence between camera image coordinates and actual two- or three-dimensional coordinates. A method according to embodiments of the present invention can be repeated for configuring several printing plates and pads to print multiple print images on one and the same product such that a composed or composite image is formed.

In a second aspect the present invention relates to a device for setting a pad print of a product. The device comprises:

- a holder for receiving a printing plate which comprises an engraving, in accordance with a print image, and a first identifying mark,

- a holder for receiving a pad to transfer the print image in ink or another transferable material from the engraving to the product, and

- a holder for receiving the product on which the pad print is to be applied or an intermediary holder adapted to the product.

The device further comprises a camera system to capture a camera image, whereby the camera system is configured such that the first identifying mark falls in the angle of view of the camera system when the printing plate is placed in the corresponding holder. The device comprises one or several actuators to move the printing plate, the pad and/or the product (e.g. by moving the corresponding holders) when placed in the corresponding holder(s).

The device comprises a processing unit adapted for:

- recognising the first identifying mark in the camera image captured by the camera system and identifying the corresponding position, or position and orientation, of the first identifying mark in camera coordinates, - identifying a projection, from the printing plate to the product or vice versa, by applying a transformation indicative of the printing process based on the detected position, or position and orientation, of the first identifying mark,

- comparing at least one point of the print image formed by the engraving with a predefined target position on the product using the identified projection, and

- controlling the actuator or actuators to reposition and/or reorientate the printing plate, the pad and/or the product or product holder such that the projection of the point of the engraving on the product is brought closer to the target position.

In a third aspect the invention relates to a software product to, when performed by a processing unit, perform a method according to embodiments of the first aspect of the present invention.

In a fourth aspect, the invention relates to a printing plate for use in pad printing of a product. The printing plate comprises an engraving, in accordance with an image to be printed on the product, and an identifying mark that can be optically recognised by a camera system.

In a printing plate according to embodiments of the present invention the identifying mark may be engraved in the printing plate together with the engraving.

In a printing plate according to embodiments of the present invention, the identifying mark may comprise a registration mark, line segments at mutually different angles and/or one or several circular characteristics.

In a printing plate according to embodiments of the present invention, the identifying mark may comprise an optically legible code, whereby said optically legible code encodes digital information. The digital information may comprise information relating to the position of at least one point of the print image formed by the engraving relative to the first identifying mark and/or a predefined target position of said point on the product, and/or may comprise a reference code, such as a serial number of the printing plate.

In a printing plate according to embodiments of the present invention the optically legible code may comprise a QR code or bar code.

The independent and dependent claims describe specific and preferred characteristics of the invention. Characteristics of the dependent claims can be combined with characteristics of the independent claims and with characteristics of other dependent claims as appropriate and not necessarily only as indicated in the claims.

FIG. 1 shows an exemplary method 100 according to embodiments of the present invention.

FIG. 2 shows an exemplary printing plate, with an identifying mark provided therein, according to embodiments of the present invention. FIG. 3 shows an exemplary drive system for a pad plate, as applicable in accordance with embodiments of the present invention.

FIG. 4 schematically shows an example of a device according to embodiments of the present invention.

The figures are schematic and not limiting. Elements in the figures are not necessarily shown to scale. The present invention is not limited to the possible specific embodiments according to the present invention as shown in the figures.

Regardless of the exemplary embodiments described below, the present invention is only restricted by the enclosed claims. The enclosed claims are hereby explicitly included in this detailed description, whereby every independent claim forms a separate embodiment of the present invention.

The term "comprises", as used in the claims, is not restricted to the characteristics, elements or steps described thereinafter and does not exclude additional characteristics, elements or steps. This therefore specifies the presence of the specified characteristics, without excluding a further presence or addition of one or more characteristics .

In the detailed description below numerous specific details are put forward. Embodiments of the present invention can be realised without these specific details. In addition, well- known characteristics, elements and/or steps may not be described in detail in the interest of clarity and conciseness .

In a first aspect the present invention provides for a method for setting a pad print on a product.

More specifically, this method can, relate to a computer- implemented method, or at least partially computer- implemented method. In this way the steps of the method can be autonomously, or semi-autonomously, e.g. under supervision and/or limited control by a user, performed by a computer system. However, some embodiments may require steps that may (possibly) require specific hardware, such as a communication bus interface, network connection, camera (or connection), and the like (as ensues logically from the description below).

FIG. 1 shows an exemplary method 100 according to embodiments of the present invention. This method provides an automatic (or semi-automatic) adjustment of print images on a product by means of pad printing based on references on each of the relevant components used, more specifically the printing plate (plates), pad(s) and the product on which the pad print is applied. A camera system is used to detect said references, and movement of one or several of said relevant components according to one or several movement axes is controlled. This allows the printing (or at least the preparation of printing) of products in one or several colours in an advantageous short setting time of the used machine (s) and accessories. A major advantage is that said method permits the (largely) automated configuration of the printing machine(s) for applying a print on a product. By automating, the time to configure the machine will be strongly reduced.

Due to conceptual changes to the method according to embodiments of the present invention relative to a 'print- and-correct' approach according to the state of the art, the required printing technical knowledge of an operator is strongly reduced or even unnecessary. The described method according to embodiments can, by analogy with the 'print- and-correct' principle, be summarised as a 'measure-and- correct' approach.

In this method according to embodiments, configuring is no longer done using the print image as such, i.e. with a test print as it were, but using references applied on the different relevant components: the printing plate, the pad and/or the product or a (base)holder for placing the product. To this end visual references are used, the positions of which are identified using a camera system.

Said references are thus visually recognisable identifying marks and/or characteristics that are applied on the aforementioned relevant components. The reference(s) on the printing plate can be applied with high placement precision relative to the image (the engraving). Preferably, said reference (s) can be part of the engraving in the printing plate to guarantee a precise placement relative to the engraving components to be inked . Said reference(s) can for example be applied in a location on the printing plate whereby they fall outside the reach of the area on which, in the printing process, ink (or another material) is applied, and/or a location where, in use, no contact is made with the pad, such that no image of said reference(s) is transferred to the pad.

In a first step, the method 100 thus provides for obtaining 101 a printing plate which comprises an engraving, according to a print image (on its own, or a colour component of a multi-colour image to be formed) and a preset (first) identifying mark or identifying marks. This identifying mark can be part of the engraving, in other words can be applied in the same engraving process as used for the engraving. The printing plate may also comprise several predefined identifying marks. Said identifying mark or identifying marks can be located in a peripheral area of the printing plate, whereby the engraving to form the image is located in a central area of the printing plate, such that, as aforementioned, transfer of an image formed by the identifying mark on the pad can be avoided.

Referring to FIG. 2, an exemplary printing plate 10 may thus comprise an engraving 12 which is spatially separated from a peripheral zone in which the identifying mark 11 is applied. The identifying mark may also be engraved in the plate. The identifying mark may, for example, comprise a cross, such as a (form of a) reticle or registration mark. This may, for example, comprise two orthogonal line segments (the cross) and optionally one or more circular forms. Other variants may, for example, also comprise a recognition point, such as a central point, surrounded by a circle and one or several line characteristics, for example line segments which intersect the circle at 0°, 90°, 180° and 270° to indicate the quadrants. Where the example shown in FIG. 2 is symmetrical relative to two orthogonal reflections (and/or a point reflection relative to the centre), this is not strictly necessary. By way of an example, one of the line characteristics may be longer to avoid confusion of the reference axes. However, it needs to be noted that applying the identifying mark in a clearly defined corner can be sufficient to avoid such confusion.

In application of a method according to embodiments it is no longer required to precisely position the engraving relating to conventional references, such as dowel holes for receiving dowels. In some applications it is currently difficult or not possible to apply the engraving within the strict tolerances of such conventional references. By integrating a new identifying mark in the engraving, an alternative and very strict tolerance can be added and used. Obviously, said identifying mark is preferably applied outside the print image of the engraving in itself, such that it is not transferred to the product. When one or several references are applied in the engraving, the exact position of the actual image to be printed is precisely defined relative to said reference(s). This applies to both the positioning according to two mutually perpendicular axes which are parallel with the plane of the printing plate and to the angle around an axis perpendicular to this same plane (rotation of the print). Said position information can moreover be included as information on the printing plate. Different embodiments are possible for this, such as for example encoding in a barcode or a QR code.

In a method according to embodiments of the invention, said reference (s) is used to position the useful engraving (the actual image to be printed) relative to the product.

Optical detection of the identifying mark allows the position, preferably the position and orientation, to be identified with great precision. For example, the position and orientation of a registration mark can be simply identified (recognised) by means of the intersection and the orientation of the mutually perpendicular lines. In a combination of registration lines and circle (s), the orientation can be identified by the orientation of one or several mutually perpendicular lines, and the position through the centre of the circle(s), if relevant in combination with intersection (s) of the line(s). It is an advantage that a circular form also provides additional support in detecting and compensating optical distortion (visual deviation from the perfect circular form), e.g. by lens effects. As described in more detail below, the identifying mark may also comprise a QR (or similar) code. A QR code contains, apart from encoded information, three typical squares in a clearly defined pattern which unambiguously determine the position and orientation of the code pattern. Said reference squares may thus also be used in this as the basis for determining the positioning (e.g. preferably determining of the position and orientation). The step of obtaining 101 said printing plate may also comprise the production of the printing plate, such as by controlling an engraving machine to apply the engraving and optionally the identifying mark. However, in many practical applications this will already be provided separately. Preferably, the identifying mark is engraved in the plate, but strictly speaking this is not necessary. Alternatively, the identifying mark can be applied using another technique, such as a print or 3D print, in so far that a precise placement relative to the engraving can be guaranteed within acceptable tolerance limits.

As already mentioned, printing machines are typically designed such that for a specific combination of product and print to be positioned, the machine settings can be saved in the so-called recipe. According to embodiments of the invention a recipe can be composed such that it is transferable to other machines which are adapted to work with the same (or compatible) method for the automatic configuration according to embodiments.

In this way, for example, instead of directly saving coordinates relative to the movement axes in the recipe, the (lifting) position of the image on the printing plate relative to the reference(s) can be saved. Every time the machine is (automatically) configured, the required coordinates for the movement axes can be automatically identified.

In very advantageous embodiments, this information can be applied directly on the printing plate. Consequently, even this information need not be saved in the recipe. To this end, said information can for example be processed in a QR (or the QR code or similar encoding on the printing plate may allow this information to be simply retrieved from a database, e.g. via a serial number). In an embodiment of the present invention, the identifying mark or the identifying marks may thus comprise an optically legible code, such as a bar code or QR code, which encodes information relating to the printing process, such as a position and/or orientation of the engraving relative to the identifying mark or one or several of the identifying marks on the printing plate. In an example, the identifying mark may thus substantially consist of an optically legible code (computer-legible code, such as e.g. a QR code). Indeed, such QR code can already provide sufficient information in itself to deduce a precise positioning from camera images (and to read the saved information) . It needs to be noted that a QR code possesses a specific formatting, which can be replaced, however, by many conceivable and substantially equivalent alternatives, e.g. an encoding of digital information (possibly with redundancy, checksums, etc.) in an equivalent way to point, line and/or plane characteristics, e.g. a specific encoding designed for said application.

Embodiments of the present invention are not focused on finding suitable printing technical parameters, such as ink, engraving parameters, pad parameters (shape, hardness, etc.), and the like. Sufficient methods are known in the art to determine said parameters. However, identifying the position parameters for the printing process can be substantially simplified and/or accelerated according to embodiments. Other parameters, identified according to a method known in the art, can, as specified, be saved in a file (the recipe, or part thereof), or wholly or partly encoded in the identifying mark (e.g. the specified QR code).

The printing plate can be obtained 101 in a holder, and/or an operator can place the printing plate in a holder according to a commonly used method. The printing plate can, for example, be put in the holder using dowels in corresponding dowel holes of the plate.

The method 100 also comprises obtaining 102 a pad. The pad can, as known, consist of (or at least comprise) a smooth, preferably ink-repellent, and elastic material, such as silicone rubber. The pad can be applied on a suitable holder, such as a pad plate, in an unambiguous and clearly defined way (position/orientation). For practical purposes, 'the pad', as referred to hereinafter, may also comprise such holder and/or other supporting tools for the manipulation of the pad.

The pad may comprise a second identifying mark or identifying marks which, similar to the description above for the printing plate, is optically recognisable and/or detectable. It needs to be noted that the identifying mark is not necessarily applied on the elastic stamp material (although it is a possibility), but can also be applied, for example, on the pad holder, e.g. the pad plate. The identifying mark can be similarly formed, e.g. a reticle, QR code, registration lines, and/or the like. A reference, or references, can thus be applied on the pad, e.g. on the plate on which the pad is attached unambiguously and in a precise position/orientation. However, this does not exclude that a further plate is used, e.g. not directly applied on the pad plate itself, but on a plate on which said pad plate is in turn unambiguously and precisely attached. This can for example allow an existing pad to be adapted in a simple manner (by addition of the further plate) for use in a method according to embodiments.

If the pad possesses a clearly recognisable shape, the position and/or orientation (e.g. not necessary for a circle- symmetrical pad) can also be recognised based on a spatial characteristic of the pad itself, e.g. a centre point. In other words, an (explicit) identifying mark may be applied on the pad (e.g. on a pad plate bearing the pad) or an (implicit) identifying mark can be detected, such as characteristics of the edge of the pad, the centre point or the like.

The position of the references (or inherently detectable characteristics) applied on the pad can be calibrated relating to the relevant movement axis or axes in transferring the image lifted by means of the pad to the product, as explained below. In an example the centre point of the pad can be used as reference, and all parameters are further referred to relative to said centre point. The base surface of the pad (e.g. of the base plate of the pad) can be provided with explicit or virtual coordinates axes with a known orientation relative to further reference points. The method also comprises obtaining 103 a product or product holder. The product or the product holder may comprise a third identifying mark or identifying marks. A marking can, for example, be provided on the product, or on a product holder which is adapted to unambiguously hold the product, e.g. in a clearly defined position and orientation relative to the holder. Similarly (with first and/or second identifying mark) said third identifying mark or identifying marks may comprise a registration mark, QR code, registration line(s), reference point (s), circle (s) and/or similarly recognisable characteristics. Alternatively, the product or the product holder may be adapted to recognise a clear point and/or orientation based on implicit characteristics, such as recognisable points, edges, planes, etc. As described above, for example, the centre of the product or the product holder can be identified (or of a specific plane of the product or the product holder).

The position of a basic holder for the product can thus either be inherently known, or be unambiguously identified from camera observation of one or several identifying marks. The position of the basic holder can subsequently serve as the basis for determining the position of the product. A combination of a general basic holder, in which or on which a specific product holder fits, can be used. A specific product holder can keep the product on the basic holder using dowels or other means, in an unambiguous and precise positioning. Using an identifying mark on the basic holder, avoids having to adapt the specific product holder or the product itself by applying identifying marks, insofar as the relative position of the product, specific holder and basic holder relative to each other, together with the desired position of the print on the product, is identified once and unambiguously .

The method 100 comprises the capture 104 of one or several camera images with a camera system in which the first identifying mark is shown. The camera system can be arranged in a fixed position, in a calibrated configuration, and can be configured such (e.g. arranged) that, additionally to the first identifying mark, the pad (e.g. the second identifying mark) and the product and/or product holder (e.g. the third identifying mark) are also shown in the camera image (or in the several camera images). Alternatively, the camera system can be movably arranged in a fixed relationship (position and orientation) with the pad, such that the pad is always located in a known position and orientation relative to the image coordinates. Alternatively, the camera system can be movably arranged in a fixed relationship (position and orientation) relative to the product or the product holder, such that the product (directly or when placed in an unambiguous position/orientation relative to the holder) is always located in a known position and orientation relative to the image coordinates. In other words, the method 100 comprises capturing 104 one or several camera images with a camera system in which the first identifying mark is shown and whereby the pad and the product or product holder are also shown in the camera image (or in the several camera images) or assume a clearly defined position and orientation relative to the camera system. A camera system with a sufficiently high resolution can be used hereby, such that the optics and the image resolution are dimensioned such that the position of the first identifying mark, the pad (e.g. the second identifying mark) and the product and/or product holder (e.g. the third identifying mark) can be identified, e.g. in a single image.

A suitable dimensioning and placement of a single camera can be sufficient hereby to show said three elements simultaneously and with sufficient resolution, but embodiments whereby multiple cameras are used are not excluded, e.g. such that at least one of said elements is visible in the image frame of at least one camera (and the three elements are covered by the combination of camera images) . It can suffice hereby that a clearly defined spatial relationship is identified between the optical characteristics of the separate cameras, e.g. taking into account position, orientation and angle of view (in addition to possible other parameters, such as focal length and the like) of every camera in spatial (3D) coordinates. It must also be noted that for reasons of simplicity and cost efficiency a single camera can offer advantages, but that the use of multiple cameras can also be advantageous, e.g. by improving the precision of the detected elements. For example, one and the same characteristic (or each of several characteristics) can thus be detected in several images, from different views, to determine, in combination, an even more precise position/orientation thereof

A single camera can be placed and oriented such that all references of all relevant elements can be shown without having to move the camera. With a static arrangement, deviations as a result of movements can be excluded, which can thus improve the precision.

In an alternative embodiment the camera can be attached on the movement axes of the pad (plate), such that the camera moves together and parallel with the pad. The relative positioning of the pad can be calibrated by mechanical and/or optical measurement, such that the position (and orientation) of the pad is clearly defined relative to the camera image. After said calibration, the method is reduced to identifying references on the printing plate and product or product holder/(basic) holder as further described. Subsequently, a desired position can be set for the printing process by controlling the movement axes of the pad (plate) to lift the image off the printing plate and transfer it to the right position on the product.

In yet another alternative embodiment, the camera is attached on the product or the product holder, or in a fixed relationship therewith. Similarly, the camera system can be calibrated, such that the position and/or orientation of the product, in the printing process, is clearly defined. Consequently, the method is reduced to determining references on the printing plate and pad (plate) via the camera system, as further described. From here the desired positions can be identified for controlling the movement axes of the pad (plate) to lift the image off the printing plate and transfer it to the correct position on the product. The method comprises recognising 105 at least the first identifying mark or identifying marks on the printing plate in the camera image(s). If the position and/or orientation of the pad relative to the camera system is not known a priori, this recognition may also comprise recognising at least the position of the pad (e.g. using the second identifying mark or identifying marks or a recognisable characteristic of the pad) . If the position and/or orientation of the pad relative to the camera system is not known a priori, this recognition may also comprise recognising at least the position of the product or the product holder (e.g. using the third identifying mark or identifying marks or a recognisable characteristic of the holder or the product).

This results in a reference position in the coordinates system (image coordinates, e.g. row and column index) of the image (or of the images) of each of the aforementioned elements, as a result of the recognition or by a priori knowledge as a result of the characteristics of the camera system (e.g. with associated calibration information). Optionally, an orientation of one or several of the elements can be identified (e.g. an angle of a registration mark as identifying mark).

A camera calibration can be taken into account to transform the coordinates system of the image (image coordinates, e.g. row and column) to actual coordinates. In this way a transformation can be performed, for example, to compensate lens effects and/or optical geometry. The method may comprise a calibration of the camera system, prior to the procedure, or a calibration can be read from a file where said information was saved in advance. The (world) coordinates can be fully three-dimensionally defined coordinates, or coordinates in one or more reference planes, such as a translation plane of the printing plate, of the pad (plate) and/or the product. If several reference planes are used, at least a transformation of the image in the printing process between said planes can be clearly defined, e.g. by specifications of the printing machine. The camera calibration can thus be applied to eliminate the influence of the intrinsic parameters of the camera system, such as focal length, skew, distortion and image centre. By way of an example, for said calibration, an image can be captured, with the camera system in the same configuration as applied in the method as specified, of a test card, such as a checkerboard pattern. Said test card can for example be placed in a reference plane in which the coordinates of detected characteristics (e.g. identifying marks) need to be identified when in use. The test card, e.g. a checkerboard pattern, can for example be placed in the plane of the printing plate to subsequently precisely identify the position of the first marker based on a corrective transformation which is determined to restore the linear and aligned character of the pattern (or more generally, to restore the faithful representation of the test card after the determined transformation to its natural units of measurement) .

By recognising several identifying marks on one and the same component, the detected position and/or orientation can be identified even more precisely, if required or desirable. By, optionally, recognising the same identifying mark or recognition point in several (e.g. substantially simultaneously) captured images, the precision can also be improved .

Various image recognition methods are known in the state of the art, such as recognising lines (e.g. radon transformation), edges (e.g. Sobel filter, Laplace filter and many variants), points, circles, patterns, centre of an aligned area and the like. Based on the choice of recognition points (e.g. specific identifying marks), the person skilled in the art is able to determine an algorithm to obtain a corresponding recognition in the image. In this way, algorithms are available to obtain a high-quality recognition of many possible identifying marks, such as, for example, for automatically recognising and reading a QR code (including determining the image position, or position and orientation, of the code).

The order in which references of the relevant elements are analysed and processed according to the procedure is not essential, and they can even, possibly, be identified simultaneously by using a suitable algorithm (and/or hardware, such as a multicore central processing unit and/or graphic processing unit).

After image capture of the reference(s) on the printing plate (the first identifying mark or identifying marks), and recognition thereof, the position and the orientation of said reference(s) is obtained. Coordinates and orientation of said reference(s) are consequently identified in the coordinates system of the camera and by calibrating, said information can also be expressed in a more general system, such as 2D or 3D world coordinates (in other words an absolute frame of reference).

After image capture of the reference(s) on the pad (plate), e.g. the second identifying mark or an implicit characteristic of the pad (plate) such as the centre, the position and the orientation of said reference(s) is obtained. Coordinates and orientation of said reference(s) are hereby thus also specified in the coordinates system of the camera. This information can also be expressed in a more general system, e.g. by calibration, e.g. the same 2D or 3D word coordinates system as aforementioned, or a similar system with known dependence (e.g. resp. an XY system bound to the printing plate and an XY system bound to the pad plate with a known spatial relationship between the two). If the camera is arranged such that it moves with the pad (plate), said coordinates and orientation are already implicitly known.

As already mentioned, it is not necessary in all situations to explicitly identify the orientation of one or several of the relevant components to supplement the position (regardless of the described situations in which a component is fixed relative to the camera system and thus the position and orientation are implicitly known). For example, the product, the pad and/or the image to be transferred may possess a point symmetry, such that orientation plays little to no role. When the camera is attached fixedly relative to a component, such as the pad, the position information is already inherently known (or identified through separate calibration), such that the position and/or orientation of the relevant component does not have to be identified from image information.

After image capture of the reference(s) on the product or the product holder, e.g. the third identifying mark or an implicit characteristic of the product/the product holder, the position, or position and orientation, of said third reference (s) is also obtained. Coordinates and orientation of references are hereby identified in the coordinates system of the camera, but can also be translated again to a suitable frame of reference (2D or 3D world coordinates). If the camera is arranged such that it moves with the product (or holder), said coordinates and orientation are already implicitly known.

The method further comprises identifying 106 a projection of at least a point of the image formed by the engraving on the printing plate via the pad to the product, or a product when placed in the product holder, by applying a transformation indicative of the printing process based on the identified position, or position and orientation, of the first identifying mark and the known or identified positions and/or orientations of the pad and the product (or product holder), and comparing the projection of the point (or the points) on the product with a predefined target position on the product. Alternatively, in an entirely equivalent way, a target position on the product can be projected via such transformation (more specifically the inverse of the aforementioned transformation) to the plane of the printing plate and compared with a reference point in the image formed by the engraving. It needs to be noted that in the latter case it is possible to work substantially within camera coordinates (upon detection of the plane of the printing plate), subject to corrections for distortions of the image by the optics and camera properties.

The method may comprise reading a position of the point of the image (or several points of the image) formed by the engraving relative to the first identifying mark(s). This can be received from a user, read from a file, and/or read as information encoded in the first identifying mark(s), e.g. in the form of a QR code. This point of the image may concern a point of the information to be printed, such as a centre of the engraving, several reference points, or directly, substantially, the image information of the engraving, such as a bitmap or other digital representation of the image.

In the recipe for the printing machine/the printing process, e.g. per image to be transferred or per print via one printing system, reference can be made to the position of the image on the product relative to the basic holder. Alternatively, the position of the product (e.g. via an intermediate specific product holder) can be defined relative to the basic holder, and, per image to be transferred, the position of the image can be defined relative to the product. In a third exemplary option, first the position of the product (e.g. on the specific product holder) is specified relative to the basic holder, and the position of the image relative to the product. Per image to be transferred (e.g. per colour) reference can be made to the position of said image component relative to the print position on the product. Where the latter would be unnecessary in an ideal situation, it may still be useful, e.g. based on the print image, the shape of the pad and the shape of the product, to shift the centre point of the pad, for example, to lift off the image next to the top of the pad and transfer it to the product. This also allows simply shifting one or several colours relative to each other without having to take into account the absolute positioning on the product.

The method comprises controlling 107 one or several actuators to reposition and/or reorientate the printing plate, the pad and/or the product or product holder to bring the projection of the point of the engraving on the product closer to the target position, or, vice versa, the point of the engraving closer to the projection of the target position (projection from the product to the printing plate). This may also comprise comparing an intermediary projection of the point on the pad with a target position on the pad, and controlling the actuators so they coincide (or are at least closer to the target position).

The lifting position of the image off the printing plate on the pad is determined by the definition of the point or the points of the image in the engraving relative to the first identifying mark, and the detected position of the first identifying mark, in combination with the position information of the pad, which can be detected or fixedly defined by configuration of the camera system. This allows a clearly defined part (e.g. point) of the image to be reproducibly lifted on a clearly defined part of the pad by relative repositioning and/or reorientation of the printing plate and the pad by controlling the actuators. Similarly, the transfer position of the image on the pad to a predefined position on the product is clearly defined by knowledge of the relative position of the pad and the product, e.g. by image recognition and/or the known (spatial) configuration of the camera system.

To lift the image off the printing plate by means of the pad, said actuators of the printing plate and/or the pad are controlled to obtain the correct position of the image on the pad. Considering that for every position on the printing plate (or at least for the specified point) the coordinates are known in image coordinates via the reference in the printing plate (first identifying mark), and considering that for every position in image coordinates the converted necessary shift is known of actuators of the printing plate and/or pad (plate), for every offered, and a priori undefined, position of the printing plate, the driving axes of the printing plate and/or the pad can be controlled to lift the image in the correct position on the pad.

The coordinate axes defined by the reference(s) on the printing plate, e.g. the coordinate axes identified by the first identifying mark or identifying marks, typically relate via a rotation angle and a shift position (in two orthogonal directions) to the system of the movement axes provided by the actuators. A scale factor may play a role hereby, which is possibly not the same for different coordinate components. However, through known characteristics of the system and possible calibration measurements, it is possible to express the shift to be performed in terms of the shifts (and/or rotations) of the movement axes of the printing plate and/or pad. Where a shift is theoretically subdivided according to two mutually perpendicular axes, in practice the shift will be subdivided into shifts according to mutually imperfect perpendicular axes.

By moving the printing plate by means of the provided drives of the printing system (for example doctor blade movement, rotational movement and/or configuration in orthogonal translation directions of a plane) shifts in image coordinates can be obtained which are unambiguously correlated to the movements performed by said drives. This relationship is a priori known through the characteristics of the system and/or a static camera calibration, or can be simply measured by the effect of translation steps (and/or other drive steps) to be detected in the camera image. Based on said movements the position of a random point on the printing plate can be simply recalculated in camera coordinates, and vice versa.

By moving the pad (plate) by means of the provided drives (for example movement in the basic plane and/or movement according to the axis of the pad) shifts in image coordinates are obtained which are unambiguously correlated to the shifts performed by said drive shafts. If a single camera is used to simultaneously observe the printing plate and the pad, the depth of field of the image may play a role, but this can be compensated or the effect can be kept to a minimum by limiting movements in the pad plane to small corrections. Considering that typically the system can possess more degrees of freedom than is strictly necessary (but nevertheless useful to be able to precisely check every step of the transfer), it may be possible in many cases to give preference to broader shifts of the printing plate with smaller corrections of the pad (relatively speaking). Based on said movements a random position to which the pad (plate) needs to be shifted can be simply recalculated in camera coordinates, and/or vice versa. The relationship between the movement steps of the pad and the image coordinates can again be known through the characteristics of the system or can be determined with a simple calibration based on reference steps of the actuators.

For instance, FIG. 3 shows an exemplary drive system 20 for the pad, in which two stepper motors 21, 22, or similar actuators, provided a free translation movement in a basic plane.

Similarly, the system can be provided with actuators to shift (and/or to reorientate) the product or the product holder, for example translation movement in a basic plane and/or rotational movement around an axis perpendicular thereto. The relationship between said movements and the captured images can again be a priori known or determined by calibration. Such that again this relationship can be applied in transformations between camera coordinates and the degrees of freedom of the drive(s).

For transfer of the image from the pad to the product, the aforementioned axes to position the pad (plate) and/or the product to the correct position can be controlled. Considering that for every position of a random point on the product or product holder the coordinates are determined in image coordinates (e.g. using an identifying mark on the product holder or the product if necessary), and considering that for every position in image coordinates the converted necessary shift of the pad (plate) and/or the product is known, the relative position between pad and product, for every offered, and a priori unknown, position of the product (or the holder), can be adapted as necessary, to correctly transfer the image from the pad to the product.

A method 100 as described above can be repeated 108 for several printing plates and pads for printing on one and the same product, e.g. to print the product in several places and/or with several aligned colours relative to each other. Images of several printing systems with different printing plates can thus be transferred to the product via pads to obtain a composite and/or multi-colour print. It goes without saying that the same system can also be used to transfer different colours (or other images) to the same product in several steps, after intermediate reconfiguration. It is thus also an advantage that, by the simple adjustment, it is possible to work with only one system to obtain a multi colour printing, without demanding a heavy toll in terms of setting time and/or with a high-quality alignment of the different applied image components.

Another possible embodiment may provide multi-colour printing by switching a product between different processing positions, in accordance with the different colour or print components, whereby the shift between said positions can be precisely provided, e.g. using a highly precise conveyor. In this way the product can be placed and offered in a product holder at exactly defined positions, whereby in every position a printing system was configured according to a method as described above to obtain an efficient and high- quality composite print.

This allows a method according to embodiments to set a printing system automatically such that the image or the superposition of several images (resulting in a multi-colour image and/or a composite print) can be applied in the desired position (s) on the product.

In a second aspect the present invention provides a device for setting a pad print of a product.

FIG. 4 schematically shows a device 50 for setting a pad print of a product according to embodiments of the present invention .

The device comprises a holder 51 for receiving a printing plate 10 which comprises an engraving 12, in accordance with a print image, and a first identifying mark 11. The device comprises a holder 52 for receiving a pad 53 to transfer the print image in ink (or another transferable material) from the engraving to the product.

The device comprises a holder 54 for receiving the product on which the pad print is to be applied 55, or, indirectly, for receiving an intermediary holder adapted to the product.

The device comprises a camera system 56 to capture a camera image, whereby the camera system is configured such that the first identifying mark(s) 11 falls in the angle of view of the camera system when the printing plate 10 is placed in the corresponding holder 51.

The device further comprises one or several actuators 57 to move the printing plate 10, the pad 53 and/or the product 55, when they are placed in the provided holders 51,52,54.

The device comprises a processing unit 59, such as e.g. a computer, an application-specific integrated circuit (ASIC), a processor, or similar (digital) processing and/or control device.

The processing unit is adapted to recognise the first identifying mark(s) 11 in the camera image captured by the camera system 56 and to identify the corresponding position, or position and orientation, of the first identifying mark in the camera coordinates.

The processing unit is adapted to identify a projection, from the printing plate to the product or vice versa, by applying a transformation indicative of the printing process based on the identified position, or position and orientation, of the first identifying mark(s) 11.

The processing unit is adapted to compare at least one point of the print image formed by the engraving with a predefined target position on the product using the identified projection, in other words after transformation to one and the same coordinates system (e.g. in a plane of the product, the printing plate or the pad).

Finally, the processing unit is adapted to control the one or several actuators 57 to reposition and/or reorientate the printing plate, the pad and/or the product or product holder such that the projection of the point of the engraving on the product is brought closer to the target position, preferably substantially coincides.

In a third aspect the present invention provides a software product for setting a pad print of a product. The software product is adapted, when performed by a processing unit, e.g. a computer, to perform a method according to embodiments of the present invention, or at least the processing steps of capturing 104 the camera image, recognising 105 the identifying mark and determining the corresponding position, identifying 106 the projection and comparing at least the point of the print image and the target position on the product, and controlling 107 the actuator(s).

Further optional characteristics of a device, respectively a software product, according to embodiments of the present invention are apparent from the above description relating to the first aspect of the present invention. Moreover, further details of the aforementioned device and software product have also been described in more detail based on a method according to said first aspect.

In a fourth aspect, the present invention relates to a printing plate, as described above in the scope of a method according to embodiments of the present invention.

The present invention is by no means limited to the embodiments of the device, methods, software and printing plates described as an example and shown in the drawings, but a method, device, software and printing plate according to the invention as defined by the claims can be realised in all kinds of variants without departing from the scope of the invention.

Claims

1.A method (100) for setting a pad print of a product, the method comprising:

- obtaining (101) a printing plate (10) which comprises an engraving (12), in accordance with a print image, and a first identifying mark (11),

- obtaining (102) a pad to transfer the print image in ink or another transferable material from the engraving to the product,

- obtaining (103) the product or a product holder for the product,

- capturing (104) a camera image with a camera system such that the first identifying mark is shown in the camera image,

- recognising (105) at least the first identifying mark in the camera image and identifying the corresponding position, or position and orientation, of the first identifying mark in the camera coordinates,

- identifying (106) a projection, from the printing plate to the product or vice versa, by applying a transformation indicative of the printing process based on the identified position, or position and orientation, of the first identifying mark, and comparing at least one point of the print image formed by the engraving and a predefined target position on the product using the projection, and

- controlling (107) one or several actuators to reposition and/or reorientate the printing plate, the pad and/or the product or product holder such that the projection of the point of the engraving on the product is brought closer to the target position.

2. The method according to claim 1, whereby the first identifying mark is engraved together with the engraving in the printing plate.

3. The method according to any one of the previous claims whereby the identifying mark is spatially separated from the print image in the engraving, the identifying mark being located in a peripheral area of the printing plate relative to the engraving in a central area.

4. The method according to any one of the previous claims, whereby the first identifying mark comprises a registration mark, line segments at mutually different angles and/or one or several circular characteristics.

5. The method according to any one of the previous claims, whereby the first identifying mark is an optically legible code, whereby said optically legible code encodes digital information.

6. The method according to claim 5, whereby the optically legible code comprises a QR code or bar code.

7. The method according to any one of the previous claims, whereby the pad comprises a second identifying mark and/or the product or the product holder comprises a third identifying mark.

8. The method according to claim 7 whereby the recognition (105) further comprises recognising the second and/or third identifying mark in the camera image, and identifying the corresponding position, or position and orientation, of the second and/or third identifying mark in the camera coordinates

9. The method according to claim 8, whereby the projection is identified (106) based on the identified position, or position and orientation, of the first identifying mark and of the second and/or third identifying mark.

10. The method according to any one of the previous claims, whereby the camera system is fixedly arranged, and configured such that the first identifying mark, the pad and the product or the product holder are simultaneously detected in the camera image or a combination of camera images.

11. The method according to any one of the claims 1 to 9, whereby the camera system is movably arranged, such that the camera system possesses a fixed and predefined position and orientation relative to the product or the product holder or relative to the pad.

12. The method according to any one of the previous claims, comprising a camera calibration, whereby an image of a test card is captured with the camera system to determine a correspondence between camera image coordinates and actual two- or three-dimensional coordinates.

13. The method according to any one of the previous claims, whereby said method (100) is repeated for setting several printing plates and pads for printing several print images on one and the same product such that a composed or composite image is formed.

14. A device (50) for setting a pad print of a product, the device comprising:

- a holder (51) for receiving a printing plate (10) which comprises an engraving (12), in accordance with a print image, and a first identifying mark (11), - a holder (52) for receiving a pad (53) to transfer the print image in ink or another transferable material from the engraving to the product,

- a holder (54) for receiving the product on which the pad print is to be applied (55) or an intermediary holder adapted to the product,

- a camera system (56) to capture a camera image, whereby the camera system is configured such that the first identifying mark (11) falls in the angle of view of the camera system when the printing plate (10) is placed in the corresponding holder (51),

- one or several actuators (57) to move the printing plate (10), the pad (53) and/or the product (55) when placed in the corresponding holder (51,52,54), and

- a processing unit (59) adapted for: o recognising the first identifying mark (11) in the camera image captured by the camera system (56) and identifying the corresponding position, or position and orientation, of the first identifying mark in the camera coordinates, o identifying a projection, from the printing plate to the product or vice versa, by applying a transformation indicative of the printing process based on the identified position, or position and orientation, of the first identifying mark (11), o comparing at least one point of the print image formed by the engraving with a predefined target position on the product using the identified projection, and o controlling the one or several actuators (57) to reposition and/or reorientate the printing plate, the pad and/or the product or product holder such that the projection of the point of the engraving on the product is brought closer to the target position .

15. A software product to, when performed by a processing unit, perform a method of one of the claims 1 to 13.