The present invention relates to an apparatus for measuring in an offset printing press the radial distance between plate or master, alternatively, on a plate cylinder or rubber web on a rubber cylinder according to the preamble of the following claim 1.

It is generally known, that a measuring of this type has to be carried out with a high degree of accuracy in order to obtain perfect offset prints.

A measuring body is used, which is provided with contact edges, sometimes provided with wheels, for manually operating the body to get in contact with the plate cylinder or rubber cylinder with a proper pressure to avoid misindication by a gauge that is attached to an arm provided with friction joints and protruding out from an end portion of the measuring body. Further, applying of the measuring body has to be carried out very carefully to prevent a contact edge of the body or an edge of one of the wheels, if present, from damaging the support surface. There is a risk of causing scores on a plate consisting of aluminium or master consisting of polyester foil when using presently available measuring devices. Hence, a protecting sheet of paper is usually placed on the plate or master. This is a cumbersome method that is leading to risk of erroneous measuring. The surface of the rubber web is rough, and measuring edges or wheels have a tendency of making an incision into the surface of the rubber web, once again with the risk of erroneous measuring.

The object of the invention is to provide an apparatus in which said inconveniences are completely or mainly eliminated.

This is achieved according to the invention in that the apparatus is characterized as set forth in claim 1. Instead of applying the two edge lines of the V-shaped measuring body directly against the normally easily damaged surface of the cylinder, or permitting the wheels of a U-shaped measuring body to contact the cylinder surface, is according to the invention at least one elongated roll, preferably made of plastics, attached to each edge portion. By using one single, thick shaft for journalling one or two elongated rolls along each edge portion it has become easy to put the rolls in position exactly in parallel with the back edge and, accordingly, at the use, also exactly in parallel with the centre axis of the plate cylinder or rubber cylinder. Moreover, elongated rolls do not cause notches or impressions in the cylinder surface, which easily will be the case when using fixed edge lines or usual wheels.

Different types of offset printing presses demand measuring apparatuses having measuring devices protruding different distances. For that purpose known measuring devices are provided with pivoted arms connected by friction joints for movable attachment of the measuring device on the measuring body. Moreover, said arms are sometimes attached to a slide axially movable on the measuring body. This means that the measuring device becomes rather unstable when attached to the measuring body. Another drawback is that the user of the apparatus has to be observant of the distance between the measuring device at the reference surface and the measuring body not becomes too small in a specific type of offset printing presses. If that distance becomes too small the measuring body will be positioned to close to especially the end portion of the rubber cylinder where the rubber web is without the impression that normally is formed during the printing process, and the measuring becomes erroneous. This risk is eliminated with the apparatus according to the invention in that the apparatus may be characterized in accordance with any of claims 2,3 or 4.

It is important, that the handling of the apparatus by hand involves a natural feeling resulting in a balanced applying of the apparatus against the surface of the plate cylinder or rubber cylinder without oblique pressure to any of the rolls. To achieve this a preferred embodiment of the invention is characterized as set forth in claim 5. This embodiment easily permits an axial displacement of the handle on the measuring body for balancing the measuring body with respect to a longer or shorter support plate attached to the measuring body.

The invention is described more in detail below with reference to the attached drawings, which schematically show an example of an embodiment of an apparatus according to the invention, wherein Figure 1 is an end view of the apparatus, Figure 2 is a side view of the same apparatus, Figure 3 is a top view of two supporting plates, and Figures 4 and 5 are side views of the apparatus positioned on two rubber webs belonging to different offset printing presses.

As illustrated in Figs. 1 and 2 a measuring body 1 is formed by a V-shaped profile section, suitably aluminium, and provided with two legs 2,3 starting from a back edge 4. Each leg 2,3 is provided with two recesses 7,8, which with a small play accommodate two rolls 5,6 journalled on a common, thick shaft 9 with ends that are beveled and screwed to the belonging leg 2,3 by fastening screws 10. Moreover, a handle 11 with a V-shaped ridge 12 is attached with the ridge facing the back edge 4. A fastening screw 13 extends diametrically through the handle 11 and through a slit 14 through the back edge between the legs 2,3 to a securing member 15. The slit 14 permits displacement a bit of the handle 11 in the longitudinal direction of the measuring body.

A recess 16 is made at one end of the measuring body 1 from the back edge 4 down to two securing surfaces 17. A support plate 18 is attached to said securing surfaces by two fastening screws 19. The support plate 18 has a protruding end portion provided with a hole 20 for attaching a micrometer measuring gauge 21 of a well-known type provided with a measuring point 22 made of plastics. The length of the support plate 18 is adapted such that the measuring gauge 21 extends a smallest, by the type of offset printing press permitted distance from the nearest ends of the rolls 5, as shown in Figs. 4 and 5.

Figs. 4 and 5 show the measuring body 1 positioned on a rubber cylinder 25. This cylinder has one or more layers 26 of under packing material wrapped on the cylinder 25 and a rubber web 27 wrapped on the layers 26. On a plate cylinder the rubber web is replaced by a printing plate made of aluminium with a thickness of 0.15 to 0.6 mm or a master made of polyester foil with a thickness of 0.2 mm.

The requirements necessary for a good printing result are, as is well known, that all rollers and cylinders come into contact with exactly the prescribed contact force. A rubber web of good quality having a thickness of 1.95 mm may be laminated by 4 layers of fabric and 5 layers of rubber.

When the web is stretched around the cylinder it becomes between 0.03 to 0.06 mm thinner. After 10-15,000 printing operations the web has to be stretched again and it becomes further 0.03 to 0.06 thinner. The rubber web is stretched at regular intervals and becomes up to 0.25 mm thinner throughout its useful life. A certain portion of the rubber web becomes further thinner depending on the size of the sheets and on which part of the rubber web the sheets are passing.

Under packing sheets 26 have very high accuracy of dimension and are available with a thickness between 0.05 to 1.00 mm. These sheets have the same width as the rubber web or plate and are used for obtaining the exact height of web or plate in relation to a cylindrical reference surface 28 that is positioned at the end portions of each cylinder and is stipulated by the manufacturer of the printing device.

As shown in Fig. 4, the measuring is carried out by placing the measuring body 1 on the surface of the rubber web 27 with the measuring gauge in contact with the reference surface 28. It is important to adjust the measuring body carefully by hand such that the contact force against the rolls 5,6 becomes equal and, thus, the longitudinal axis of the measuring body 1 defined by the back edge 4 becomes directed in parallel to the centre axis of the cylinder 25. Further, it is important that the measuring body 1 is placed on the part of the rubber web 27 where the thickness is reduced due to frequent printing operations. This part extends to the dashed line 30 on the drawing. Due to the fact that the measuring body 1 is delivered with a support plate 18, that secures a distance a between the fastening hole 20 of the measuring gauge and the adjacent ends of the rolls 5, which distance is such that said ends are prevented from reaching the line 30 when the measuring point of the measuring gauge is positioned on the reference surface 28. For adaption to other types of cylinders or for measuring further back on the rubber web 27 one or more support plates may be delivered, like the support plate indicated by a dashed line 31, which in that case should be clearly marked indicating to which types of cylinders the support plates are intended. By using longer support plates the centre of gravity is displaced towards the end of the measuring body to which the support plate is attached. In order to balance this displacement it is possible to move the handle 11 in the same direction such that the apparatus becomes well balanced when the handle is gripped with one hand. The cylindrical shape of the handle in combination with the V-shape of the measuring body brings about a very pleasant grip of the measuring apparatus that facilitates a balanced applying of the measuring apparatus against any of the cylinder surfaces.

The invention is of course not limited to the embodiment shown and described here but may be modified in various ways within the scope of the invention defined by the patent claims. Hence, a single, long roll may be arranged at each leg, or, as an alternative, a single, long roll at one leg and a short roll at the other leg.