GB2257127A

GB2257127A - Sheet feeder for machines printing on cardboard sheets.

Info

Publication number: GB2257127A
Application number: GB9210990A
Authority: GB
Inventors: Bertold Gruetzmacher
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 1991-06-28
Filing date: 1992-05-22
Publication date: 1993-01-06
Also published as: FR2678254A1; JPH05246577A; GB9210990D0

Abstract

The sheet feeder has a pneumatically acting device for detection of thickness enlargements 14 in the cardboard sheets 1. The device comprises an array of blowtubes 3 (only two shown) which extends transversely across the width of the cardboard sheet. An enlargement causes increase of pressure in a tube 9 and corresponding generation of a signal at 12. The signal stops the sheet drive. <IMAGE>

Description

Sheet feeder for machines for the printing of cardboard sheets The invention relates to sheet feeders for machines for the printing of cardboard sheets, sheets of thick paper or similar.

As a result of mechanical loading or through errors in production, it is possible for cardboard sheets to exhibit enlargements, for example folded-over corners, detached and/or pushed-together top layers, pushedtogether and thus wrinkled areas. If such defective cardboard sheets enter the printing press, particularly a printing unit of an offset printing press, there may be damage to the printing units, above all damage to the rubber-covered cylinders. There are no known sheet feeders with devices for preventing damage in the printing press as a result of the entry into the printing press of defective cardboard sheets.

Conversely, devices for the contactless measurement of the thickness of banknotes are known from DE-OS 33 26 720, in which at least two measuring instruments are disposed opposite one another, with the banknote being passed between said measuring instruments. Known also therefrom are pneumatically acting measuring instruments for thickness measurement. However, such a device measures the thickness of the banknote only at one point or on a straight line which results when the banknote is moved between the two measuring instruments. Such a device is not suitable for the detection of irregularities at any point in the thickness of a sheet.

DE-GM 71 42 249 describes a pneumatic device for checking the position of the sheet at the front lays of a sheet feeder, in which blow-nozzles are provided above a feed table and receptor nozzles are provided below said feed table. Such devices simply register whether the sheet has impacted correctly against the front lays, but not the satisfactory condition of the sheet.

Known from DE-OS 22 03 731 is a device for multiple- and imperfect-sheet monitoring, in which the thickness of the transported material is sensed by mechanical means and, in the event of overthickness (multiple sheet) or underthickness (no sheet), the measured value obtained is converted into a switching pulse for switching off the drive of the feeder.

The object of the invention is to design a sheet feeder for machines for the printing of cardboard sheets or similar, particularly a sheet feeder for sheet-fed offset rotary printing presses, such that irregular enlargements in the cardboard sheets are detected already in the feeder and the drive of the feeder as well as of the printing press is switched off before such a sheet enters the printing units.

The object of the invention is achieved by a sheet feeder having the features described in claim 1.

The advantage of the features according to the invention lies above all in the fact that irregular enlargements in the cardboard sheet are detected by the sensor irrespective of their position and the measuring result from the sensor is converted into a switching pulse, said switching pulse being used instantaneously to switch off the drive of the sheet feeder and of the downline printing units. This makes it possible to remove the defective cardboard sheet and thus prevents damage to the printing unit or any further disruptions in printing.

In a preferred embodiment of the invention, the device consists of blow-tubes, said blow-tubes being juxtaposed in the feeder transversely to the direction of sheet travel and the mouths of said blow-tubes being directed approximately perpendicularly onto the cardboard sheet as the latter is transported across a feed table in the feeder - and being disposed at a slight distance from said cardboard sheet, with the blow-tubes being advantageously energized with a low air pressure and being connected to a dynamic-pressure sensor, said dynamic-pressure sensor converting changes in dynamic pressure into an electrical switching pulse, said electrical switching pulse being used to switch off the drive of the feeder. Such a device can be manufactured at low cost and operates very reliably in order to achieve the purpose pursued by the invention.

Preferred design features of such a device are contained in claims 3 to 6.

A specimen embodiment of the invention is represented schematically in the drawing.

The diagram in the drawing shows a section transverse to the transport direction of the cardboard sheet 1 across the feed table 2 of a sheet feeder (sheet feeder otherwise not shown for reasons of improved clarity).

The sensor for detection of enlargements in the cardboard sheet 1 consists of closely juxtaposed blowtubes 3, distributed transversely over the width of the sheet 1, with the mouths 4 of said blow-tubes 3 being directed, at the lower ends, approximately perpendicularly onto the surface of the sheet 1 as the latter is transported across the feed table 2. The distance of said mouths 4 from the surface of the sheet 1 may be controllable. The drawing shows only two blow-tubes 3 on a distorted scale, but, in reality, the blow-tubes 3 are distributed, as closely juxtaposed as possible, over the entire width of the sheet 1.The arrangement may be such that the blow-tubes are disposed in one or more transverse rows or also staggered in relation to one another, with the latter arrangement having the advantage that mutual influencing of the pressure in the blow-tubes can more easily be prevented and that blow-tubes may be disposed in mutually overlapping manner in the transport direction of the sheet 1 in order to achieve improved accuracy of measurement. All blow-tubes 3 are connected, through the intermediary of a common connecting line 5, to a blower 6 or to another compressed-air source, with the pressure being controllable by means of a butterfly valve 7, which simultaneously permits a zero adjustment, in which the air supplied from the blower 6 is able to escape via the annular gap 8 resulting at the mouths 4 of the blow-tubes 3.All blow-tubes 3 are connected, through the intermediary of a branch tube 9, to a common measuring space 10 in a tube 11 extending over the width of the sheet 1. Connected to the measuring space 10 is the pressure sensor 12, the measured value from which is converted into a switching pulse for switching off the drive of the feeder or of the downline printing units. The branch tubes 9 of the blow-tubes 3 join into the measuring space 10 with a non-return valve 13, with said non-return valve 13 being in the form of a non-return flap which opens when there is an increase in pressure in the branch tube 9. All blowtubes 3 are thus connected, through the intermediary of their branch tubes 9, to a common pressure sensor, with only those changes in pressure being detected which are detected by a blow-tube 3 as a result of an enlargement 14 in the cardboard 1.

It will be appreciated that the invention has been described above by way of example only and that changes may be made without departing from the scope of the invention.

Claims

1. Sheet feeder for machines for the printing of cardboard sheets, comprising a pneumatically acting device with a sensor for detection of enlargements in the sheets supplied and for conversion of the measured value obtained from the sensor into a switching pulse, in which the switching pulse acts on the drive and the sensor extends across the entire width of the sheet.

2. Device according to claim 1, in which the device consists of blow-tubes juxtaposed in the feeder transversely to the direction of sheet travel, mouths of said blow-tubes being directed approximately perpendicularly onto the cardboard sheet as the latter is transported across a feed table by the feeder and being disposed at a slight distance from said cardboard sheet and in which the blow-tubes are energizable by controllable blow-air and are connected to a dynamic-pressure sensor, said dynamic-pressure sensor converting changes in dynamic pressure into electrical switching pulses which switch off the drive of the feeder.

3. Device according to claim 2, in which the blow-tubes or groups of blow-tubes are connected to a common dynamicpressure sensor.

4. Device according to claim 2 or claim 3, in which the blow-tubes are distributed, juxtaposed, across the entire width of the cardboard sheet as the latter is transported in the feeder.

5. Device according to any one of claims 2 to 4, in which branch tubes of the blow-tubes join into a common measuring space and are closed by separate non-return valves, which open when there is a rise in dynamic pressure in the associated blow-tube, and in which the measuring space comprises a pressure sensor, the measured values from said pressure sensor being able to be converted into electrical switching pulses for switching off the drive.

6. Device according to any one of claims 2 to 5, in which the distance of the mouths of the blow-tubes from the surface of the cardboard sheet is controllable as the latter is transported across a feed table in the feeder.

7. Device substantially as described, with reference to the drawings.