The present invention relates to a printing device comprising electromechanical transport means for transporting a medium to be printed, as well as co-acting printing elements for printing the medium.

The invention further relates to a printing system comprising several printing systems arranged in succession for transporting and printing the medium, and to a method by which a medium to be printed is transported.

Such a printing device, printing system and method are generally known. In a printing process that is known as foil printing, the medium or the material to be printed is inserted in the form of a foil, for example from a roll, and subsequently subjected to a printing or die-cutting operation by a - usually vertically reciprocating - flat press. The electromechanical transport means that are used therewith exhibit a medium transporting accuracy such that the deviations resulting from said movement can easily be perceived with the naked eye, which makes them objectionable. This is in particular the case when several colours are superimposed with relatively large positioning deviations, causing the roughly overlapping, differently coloured printing images in question to exhibit distortions.

As a result of said distortion it becomes more difficult to realise qualitatively pure, so-called in register printing while using the various printing techniques that are possible.

The object of the present invention is to provide an improved printing device, printing system and printing method, which make it possible to realise a higher degree of accuracy, in particular in the case of high-quality multicolour printing.

In order to accomplish that object, the printing device according to the invention is characterized in that the electromechanical transport means comprise linear motors.

The advantage of the printing device according to the invention is that the use of linear motors makes it possible to achieve a much higher degree of accuracy in transporting and positioning the medium to be printed than is possible with other types of transport means. In the case of multicolour printing, it is thus possible to realise a very high degree of fineness and quality when printing a drawing, using printing inks composed of various colours. The use of the printing device according to the invention obviates the need to correct or obscure imprecise printing images, wherein a new but overlapping other colour image is superimposed over a preceding colour image, which leads to crude and untidy total images.

One embodiment of the device according to the invention is characterized in that the linear motors are arranged for transporting the medium to be printed with a degree of accuracy of at least 0.05 mm, preferably at least 0.02 mm, more preferably at least 0.01 mm. In-register printing with the present degree of accuracy by means of successive aligned printing presses, as in a printing system, makes it possible to achieve very high-quality printing results, in particular in the case of foil printing. High-quality precision printing can now also comprise the application of leaf metal, including leaf gold or leaf silver, and furthermore comprises the application of fine and usually closely spaced continuous metal tracks, for example on printed circuit boards.

Another embodiment of the device according to the invention is characterized in that the electromechanical transport means are arranged for carrying the medium to be printed along the printing means substantially without any mechanical tension. Mechanical tension, in particular such an alternating tension, leads to stretch in the medium to be printed, which stretch depends on the material in question and which is usually difficult to predict, if at all, as a result of which the degree of accuracy with which the medium is provided with successive differently coloured layers of ink, pigment or metal will gradually decrease, especially in the case of multicolour printing, in which the medium is transported from printing station to printing station. Such inaccuracies are prevented as a result of the medium being carried along the printing means without any mechanical tension, whilst at the same time a high throughput velocity can be achieved on the one hand, whilst on the other hand there is no need for the linear transport means to impose comparatively large forces for that purpose.

In another embodiment of the invention, the printincf device is advantageously provided with position-determining means, which are connected to linear motors arranged as controllable motors to enable the position-determining means to deliver medium position information to the motors. The position-determining means, which usually comprise measuring sensors and/or data input means in practice, make it possible to realise a - generally electronic - measuring and control system which makes it possible to achieve the required positioning accuracy at all times, irrespective of the type of material, the properties or the temperature thereof. One preferred embodiment of the printing device according to the invention is characterized in that the printing device is a foil-printing device. Foil printing involves heating of the plate and the foil, as a result of which expansion caused by said heat in addition to possible mechanical tension will be a source of positioning inaccuracies. The implementation of the above aspects, possibly in combination with each other, also leads to a higher printing quality when using a technique such as foil printing.

Accordingly, the printing system according to the invention is characterized in that each printing device has its own position-determining means, which are connected to individually controllable linear motors to enable said position-determining means to deliver medium position information that has been individually determined for each printing device to the respective linear motors. An advantageous aspect of this is that positioning errors do not accumulate in this manner but that they are minimised for each printing station each time so as to achieve a printing result exhibiting the desired degree of positioning accuracy.

The printing device according to the present invention will now be explained in more detail with reference to the figure below, which single figure is a schematic diagram of a preferred embodiment of a printing device according to the invention.

Figure 1 schematically shows a printing device comprising electromechanical transport means 3; 7, 8 for transporting a medium 1 to be printed, as well as stamps or printing elements 5 co-operating therewith for printing the medium 1 with a printing material, for example ink, a pigment or a metal. The medium 1 to be printed with ink is - 5 -

made of paper, cardboard or a plastic, for example, which may or may not be laminated, or of a metal, for example, such as tin. Said plastic may be a foil, such as PVC foil, to which the desired printing material is applied after the foil 1 has been positioned under the printing elements 5 by the transport means 3; 7, 8. The medium 1 to be printed is positioned under the printing elements 5 in sheets, or from a roll, for example, in order to be printed with printing material by means of vertically reciprocating printing elements 5, in this case configured as a flat press. The transporting accuracy will be very high if the electromechanical transport means are equipped with linear motors 3; 7, 8. Said linear motors are arranged for transporting the medium to be printed with a degree of accuracy of at least 0.05 mm, preferably at least 0.02 mm, more preferably at least 0.01 mm. When the linear motors 3 ; 7, 8 are used in multicolour printing, and several colour images are superimposed over each other, the colour images will superimposed over each other in accurately aligned relationship, without any deviation in the positions between the previously printed image and the subsequently printed image being detectable with the naked eye. Examples of the linear motors as referred to above are furthermore motors that derive their operation from a varying reluctance, so-called reluctance motors, or synchronous - linear - motors. The printing device may be embodied as a small hand press, but also as an automatic large-size press suitable for through-hole printing or (over)printing for producing a few thousand sheets per hour. A high degree of accuracy required for in-register printing, for example for printing foil material, can be realised by incorporating the linear motors in a feedback control circuit as known from the field of measuring and control engineering. Measuring means 6 (schematically indicated) or sensors 4 functioning as position-determining means are in that case connected to the linear motors, which are arranged as controllable motors 3; 7, 8, to enable the position- determining means 4, 6 to deliver accurately determined information as regards the position of the medium 1 to the controllable motors. Such a control circuit can be influenced, via generally programmed processor-controlled system control means, by operator-controlled input means, such as a keyboard, by means of which the required accuracy level can be input. In a special embodiment of the printing device, the electromechanical transport means are also adapted for carrying the medium to be printed to the reciprocating printing elements 5. This has been realised by having the material move in, for example, a freely suspended loop 2, as shown in the single figure, after which the material is moved in the direction of the stamps 5, in this case by a number of rollers mounted to the linear motors. In a printing system that is not shown, printed matter can be prepared in several printing devices arranged in succession. In order to prevent measuring and positioning errors accumulating, each printing device will have its own position-determining sensor or measuring means 4, 6 in that case, which are connected to individually controllable linear motors to enable said own position- determining means to deliver medium position information as individually determined for each printing device to the respective motors. As a result, any shrinkage and/or stretch that may occur in the medium between the stations caused by heating or cooling thereof during the printing process will not affect the final product of the printing process, which comprises several colours printed thereon.