Mandrel for digital printing

ES 2 298 951 T3

DESCRIPTION

Chuck for digital printing.

A method and a clamping pin are proposed for the exact fixation of hollow bodies for the realization of precise controlled movements. In this way it should be possible to precisely control the position of the hollow body, so that a fingerprint of the outer wall of the hollow body with high precision is possible. Digital printing replaces the coloring and decoration of the outer wall of the hollow body applied up to now by means of a procedure.

The invention relates to the chuck for a hollow body of symmetrical rotation, especially for cans configured in one piece with body and bottom, in most cases with a bottom curved inwardly in the shape of a herringbone.

It is already known that for a treatment, especially for printing or decorating the outer surface of hollow bodies of this type, a precisely controlled movement or rotation of the hollow body, almost always step by step, is very important in order to achieve the accuracy and reliability of the exterior surface treatment, compare US-A 6,769,357 (Joe Finan).

From US-A 3,960,073 (Rush) a printing device operating with rollers is known, compare abstract, abstract drawing, work station 19A with the corresponding roller for printing the can on the mandrel 13B. In the extensive description of the operation of the clamping pins used in said document, reference is made to Figures 6 to 10 which are explained in detail in column 10, from line 22 to line 60. Depression and overpressure controlled attraction and repulsion of a beverage can to or from the chuck is envisaged, compare column 10, pages 23 to 27. However, the can itself is not only held axially because of the depression, but also, according to Figures 7 and 8 of the document, by means of a radial positioning of several clamping segments distributed around the perimeter, with the reference 91. These clamping segments are coupled, through bolts and springs, to a cylindrical sliding piece (reference 97), which by means of slanted surfaces, achieves a disconnection and connection. The springs cause the control of the clamping force, compare column 10, lines 52 to 60 of the document. The air pressure used through the channel 89 is not used again for the modification of the radial position of the clamping segments 91, nor the depression through the same channel 89 is used for the purpose of clamping the clamping segment 91 . This is also not necessary, since, according to figure 1 of the document and, for example, also according to figure 3, the printing is carried out with the contact pressure transmission station 19a and with the rollers that do not require high pressure. precision, such as that here presupposed. Depression and overpressure are also used by other documents for the aspiration and repulsion of the cans to be treated (treatment in the sense of a print), for example US-A 3,548,745 (Enn Sirvet) with the description in the column 2, lines 28 to 33 and the pressure cylinder 7 connected according to figure 1, or US-A 3,356,019 (Albert Zurick) according to column 2, lines 59 to 64, which, however, also works with a method of printing blanket, Compare column 1, the first three paragraphs, and reference 15 as "impression blanket" in figure 2.

The aim of the invention is to make possible a precisely controlled movement or rotation and, in most cases step by step, of the hollow body by clamping from the inside and at a high speed of digital printing and / or a change of hollow body.

This objective is fulfilled thanks to a clamping pin with the characteristics of claim 1, alternatively with the method according to claim 12.

Clamping forces occur synchronously and uniformly inside the hollow body, especially as a can or beverage can. In this way, with the corresponding radial pressure, the mandrel and the can can be brought together in a movement unit whose movements can be controlled with maximum precision. Any risk of permanent deformation of the hollow body is excluded, as can happen in the case of clamping from the outside or only from the front faces.

The components and devices for the controlled movement of the clamping elements are located inside the clamping mandrel.

The depression and the coupling in the hollow body (claim 1) are especially advantageous with regard to simplicity, time saving and efficiency. On the one hand, the application and control of the depression (claim 1) or the overpressure (claim 2) are possible inside the clamping mandrel without great effort, with great accuracy and at high speed. On the other hand, the positioning and repulsion of the hollow body on the clamping mandrel or the clamping mandrel is achieved at the same time without additional means (claim 13).

The bottom of the hollow body is used in conjunction with the free front face of the clamping mandrel as a valve element that automatically ensures that during the positioning of the hollow body on the clamping mandrel by means of depression, the bottom adjusts to the front face. of the mandrel, the depression coming into action in order to move the clamping segments radially outwards, thereby conforming under pressure to the inner wall of the hollow body.

ES 2 298 951 T3

The procedure claimed for the exact positioning and for the controlled precision movement, preferably step by step, of the hollow bodies of symmetrical rotation, formed by a body and a bottom "in one piece" (seamless in the bottom area) , in particular cans for drinks, also with the bottom curved inwards, it is made possible thanks to the exact clamping that is achieved. It is an exact fixation without risk of damaging or deforming the hollow body.

The accuracy of the clamping can be described in such a way that an equivalent precision of the transmission of motion is thus also achieved in a direction that can be termed "suitable for digital printing".

A rest position of the clamping device is achieved by a return force (claims 11 and 14). This withdraws the force transmission device to a rest position. This in any case is also suitable for compensating for varying diameters of the hollow bodies which can be fitted to the clamping mandrel with varying diameters.

The coupling of the force in the suctioned and clamped hollow bodies, for example a hollow body with a thin wall, is preferably improved, so that the clamping mandrel has a front surface which at least in the area of ​​the exit of the perforation axial is adapted to the shape of the bottom of the can. An inward herringbone bend (in the hollow body) is an inward herringbone bend (in the chuck) in the axial direction.

The invention is described in more detail below by means of schematic drawings in various embodiments. The different figures show:

Fig. 1 shows in a perspective view, a clamping pin according to a first example of the invention,

Fig. 2 schematically shows a side view of the chuck on a larger scale,

Fig. 3 shows a schematic longitudinal section through the clamping mandrel.

The clamping surface of the clamping mandrel 1 itself is formed by a number of clamping segments 2a, 2b, 2c, etc. (abbreviated: 2), preferably identically configured, respectively having a partially cylindrical outer surface and therefore together forming a cylindrical clamping surface. They extend over the entire length of the mandrel 1 and are guided in the mandrel base body movably in the radial direction.

The base body is made up of a central axis 3 that extends over the entire length of the mandrel and beyond one of its front ends; on said axis are fixed at a corresponding axial distance, two front wall elements 6 and 7 between which the clamping elements 2 are understood. The front wall element 7 at the free front end of the mandrel 1 has a cylindrical wall 11 which it extends axially for a length into the mandrel.

The shaft 3 has a continuous axial bore 4 which ends flush with the free end 5 of the shaft 3 and the outer surface 7a of the front wall element. At an axial distance from this end 5 and in the region of the cylindrical wall 11, the shaft 3 has radial perforations 21 which are in contact with the axial perforation 4. A little more axially towards the inside of the mandrel, a disc-like wall component 10 is arranged which can be axially displaced on axis 3 and which is guided through a ring component 12 in a waterproofing and sliding manner in cylindrical wall 11.

A rotationally symmetrical activation or control element is firmly attached to the disc-shaped wall component 10. While the front wall element 7 forms with the cylindrical wall 11 and the disk-shaped wall component 10, a pressure chamber 9, the control element 13 lies axially outside the pressure chamber 9, although together it forms with the disc-shaped wall component 10, a force transmission device as immediately explained in more detail. The control element 13 has an axial bore 13 whose diameter is clearly greater than the outer diameter of the shaft 3. By means of interposed support sleeves 20, the control element 13 is guided in an axially displaceable manner on the shaft, thus being able to carry and guiding the disk-shaped drive element 10 itself.

The control element has an outer surface 19 which develops slightly conically in the axial direction.

As can be seen in figure 3, the clamping segments 2 have on their inner face, a corresponding surface 17, that is to say, a conical surface parallel to the surface 19. As shown, this can also be provided in separate elements, although firmly attached to the clamping segments.

In the conical intermediate zone between the opposite surfaces 17 and 19, corresponding support and force transmission elements 18 are arranged, which are firmly connected to one of the two components 2 or 13.

The radial movement of the clamping segments 2 is caused by the depression for clamping and the overpressure for loosening the clamping. Both pressures are produced through axial bore 4 of shaft 3.

ES 2 298 951 T3

The two pressures are used to place a can, which consists of a bottom and body in one piece, axially on the mandrel and to push it off the mandrel. In this process, the bottom of the can, together with the outer surface of the front wall element 7, is used to automatically activate the clamping movement of the clamping segments 2 only when the can is axially positioned in the mandrel in the proper way. and to start the ejection process only when the clamping segments have properly unlocked the can.

The outer surface 7a, 7b of the front wall element 7 is configured in such a way that, together with the tightly fitted can bottom, it presents an annular surface contact that stops a suction of air from the outside through the adjacent depression, so that now the The depression acts, through the radial perforations 21 and the chamber 9, on the disk-shaped wall component 10 and moves it to the left together with the control element 13 in figure 3. In this case, the clamping segments 2 move radially outward through the conical surfaces that act in combination.

Good coupling is achieved when the shape of the herringbone bottom of the hollow body, which is not shown but is generally known, corresponds to the shape of the front face of the clamping mandrel. A concave / convex fit is appropriate.

If it is convenient to release the can, compressed air is led into the chamber 9 through the axial bore 4. This moves the elements 10 and 13 and loosens the clamping force of the clamping segments 2. When this clamping force ceases, the compressed air acts on the bottom of the can through the end of the perforation 4, thus repelling the can from the mandrel.

The return movement of the positioning device can be achieved by means of a spring 40. This is arranged between the control element 13 and the front wall element (6). By this movement it is achieved that the control element 13 assumes a rest position after a discharge from the hollow body, the so-called zero position, and remains in an indefinite axial position. In this way it is possible to correctly position the next hollow body and compensate for variations in diameter of the hollow body caused by tolerance.

The structure has a very simple construction, however, it works in an extremely fast and precise way. The clamping segments clamp the hollow bodies from the inside over a large area and safely, but at the same time carefully. The necessary paths of movement of the moving components of the chuck are small. Control by means of depression and overpressure is simple and reliable.

In the clamping position, the can and the mandrel form a functional unit that can be reliably moved by controlled movement of the axis 3 in any direction, with any pitch width and at any pitch speed.