The prior art The invention relates to a vacuum holding device for the lifting and/or transport of sheet-shaped objects, such as sheets of cardboard, plywood sheets and the like, said device comprising a roller or a cylinder whose outer side, shell, is perforated for the passage of air, which is sucked from the interior of the roller to generate a vacuum for holding the object by en¬ gagement and contact with it.

The use of vacuum for holding sheet-shaped objects is generally known and is used everywhere where there is a need for the handling of individual sheets in connection with the production and transport of these from a posi¬ tion, such as a stack, to a working or deposit position.

Various forms of vacuum rollers or cylinders are known. Particularly in con¬ nection with the printing industry where it is common to use vacuum lifting devices for lifting the uppermost sheet from a stack by means of a vacuum device.

DE 2754370 A1 discloses such a device in the form of a cylinder with openings distributed evenly everywhere in the shell. To ensure that there is only passage through the openings which are present at the object, valve bodies are mounted in all the openings. This is a very vulnerable and un- certain way of limiting the vacuum loss, since the many valve bodies easily become leaky, which reduces the vacuum and thereby the holding force.

The object of the invention The object of the invention is to improve vacuum holding devices such that a great lifting force is achieved at the lowest possible vacuum consumption, and this is achieved according to the invention in that the suction through the shell is restricted to the area which forms the contact face between the roller, the cylinder and the object.

The vacuum is utilized optimally in this simple manner, and a safe and stable holding force is ensured with the lowest possible consumption of en¬ ergy.

When, as stated in claim 2, a suction channel, a vacuum channel, is pro¬ vided, which terminates at the contact point, and when this is provided with a valve, a single valve will be able to control the vacuum flow through the shell. This ensures that vacuum is consumed only when there is contact with a surface of an object to generate the holding effect.

When, as stated in claim 3, the valve is provided with a movable valve body, this will be sucked against the cooperating valve seat and shut off the atmospheric air.

When, as stated in claim 4, the valve is provided with a minor leak, there will be a restricted air passage through the valve when closed to ensure that vacuum is created instantaneously at contact with a surface of an ob¬ ject.

When, as stated in claim 5, the valve body is controlled by means of a closed resilient container, a passage will be opened or closed depending on the surrounding air pressure of the container by affecting the valve body.

When, as stated in claim 6, the shell is provided with a resilient porous coating, a good contact with the object will be achieved, even if this might have an irregular surface.

Finally, as stated in claim 7, it is expedient to provide the coating with pro- truding resilient ribs of the same height, as this ensures a good contact with the object.

The drawing Examples of the device according to the invention will be described more fully below with reference to the drawing, in which

fig. 1 shows an example of the lifting of objects from a stack,

fig. 2 shows the stack and a vacuum cylinder, seen from the end,

fig. 3 shows a sectional view of a vacuum cylinder with two examples of valves in the vacuum channel,

fig. 4 shows an example of the surface with ribs and air gaps,

fig. 4A shows the profile shape of a rib, and

fig. 5 shows a sectional view of a cylinder with two further examples of valves.

Description of the exemplary embodiments The invention will be described below in connection with the use for the raising of sheets, such as plywood sheets and the like from a stack.

Fig. 1 schematically shows a stack of sheet-shaped objects 1 which are stacked on a pallet placed on a lifting device such that the stack may be raised to engage a plurality of vacuum cylinders 3 disposed above the stack, as shown.

These cylinders 3 are connected with a vacuum source such that the up- permost sheet will be sucked firmly to the cylinders 3 by engagement with these.

If it is a matter of feeding a system with sheets one by one, all the cylinders above the stack may be moved away optionally to a deposit position (not shown) via a support of a number of brush cylinders 4.

Such a transport of a sheet may take place by depositing on a roller con¬ veyor with rotatable cylinders 4.

Fig. 2 shows the stack with the sheet stack 1 and a vacuum cylinder 3 seen from the side.

It is observed that the cylinder 3 is mounted in pins 4 in the sides of a hy- draulic or pneumatic pad or hose 5, such that there is a certain vertical movability for the individual cylinders 3, allowing their position to be adapted to the object.

Fig. 3 shows a sectional view of a cylinder 3.

The interior of the cylinder accommodates a tubular diaphragm 14 which controls the inlet of air through the exterior of the cylinder.

An opening 15 is shown, in which passage may be regulated by turning the diaphragm 14, just as the pipe is provided with cooperating partitions to form sections which may operate individually. The vacuum cylinder may hereby be adapted to the width of the objects.

A channel 10 leads from the suction channel through the pipe 14 to a valve comprising a seat 12 with small passages 13 as a safeguard against lock¬ ing of the valve body 11 to the seat, so that this may be moved from the seat 12 more easily.

The channel 10 terminates at the openings 6A in the shell 14 which is dis¬ posed at the engagement area for the object 1 when the parts are in con- tact with each other.

Fig. 3 shows an embodiment at the bottom where the valve body 11 has the shape of a ball so that this may engage the seat 12 with passages 13.

Other shapes of valve bodies are conceivable, the purpose of the valve being that the body is activated, moved, at an increased air flow when the contact with the surface of the underlying object is not existing. This saves unnecessary consumption of vacuum.

The valve body 11 is sucked to engage the seat 12 when no object 1 is present at the openings 6A, and the valve body is therefore sucked for blocking such that the air passage through the channel 10 is interrupted partially.

Fig. 3, at the top, shows a flat valve body 11 , while it has a spherical shape at the bottom.

Fig. 5 shows an alternative embodiment of the valve structure. Here, the moving device is formed by closed flexible chambers 16 which control the valve body 11 in response to the surrounding air pressure.

When an object 1 blocks the air passage, the pressure drops and the con¬ tainers 16 expand such that the valve body 11 is lifted free of the seat 12.

In the lowermost example in fig. 5, the valve body is formed by a tilting body 17 which opens and closes a passage 15 to the vacuum source. In all the shown examples of valve devices, small passages 13 are pro¬ vided in the valve seat 12, and, in the tiltable valve body 17 shown in fig. 5, a channel 18 through the body, all of said passages ensuring that the valve body is not locked firmly to the seat, but may be moved when contact with an object is created, and the vacuum passage is to be established.

As indicated in fig. 3, the cylinder shell 14 is provided with openings 6A in the entire extent of the shell, said openings providing passage for the vac¬ uum.

In the example shown, the surface is coated with a layer of cellular rubber 15, whose structure is such that the air may pass from the outside and through the layer via air paths 6 and further through the shell 14 to the vac¬ uum channel 10.

To ensure the best possible contact with the object 1 , a rib pattern, as indi¬ cated in fig. 4, may additionally be provided, said pattern being configured as an outermost layer 7. This rib pattern may be adapted to the extent of the objects, and where there is a division into sections, connecting transi- tions may not be present in the pattern. Other patterns are conceivable, such as a herringbone pattern or similar, obliquely extending patterns.

Openings 8 for the inlet of air are present between the ribs 9, whose profile is indicated in fig. 4A.

This rib pattern ensures that non-plane surfaces of the object can adhere to the cylinder, as the ribs will be able to conform to the surface of the object 1 by their flexible configuration.

The device according to the invention hereby ensures that unnecessary consumption of vacuum does not take place, and the operational reliability is great because the device is simple and sturdy.