GB2103810A

GB2103810A - Detecting tension and breakage in sheet material

Info

Publication number: GB2103810A
Application number: GB08220639A
Authority: GB
Inventors: Bruno Molinatto
Original assignee: Componenti Grafici SRL
Current assignee: Componenti Grafici SRL
Priority date: 1981-07-24
Filing date: 1982-07-16
Publication date: 1983-02-23
Also published as: IT8168037A0; JPS5895059A; BR8204319A; DE3227641A1; GB2103810B; IT1144434B; FR2510039A1

Abstract

A tension and breakage detection system for strips of sheet material, particularly for rotary printing presses, comprises at least on sensor (11) which constantly senses the deflection of an associated pin (4) projecting from a fixed support (14) and rotatably supporting a cylinder (3) about which the said strip passes. In operation, the pin (4) is normally deflected by the tension in the strip and the sensor (11) maintains a driving motor in operation. If the strip breaks the deflection of the pin (4) is reduced and the sensor (11) operates to stop the motor. <IMAGE>

Description

SPECIFICATION A tension and breakage detector system for strips of sheet material, particularly for rotary printing presses.

The present invention relates to a tension and breakage detection system for strips of sheet material, particularly for rotary printing presses.

In rotary printing presses it is known to utilise detection systems comprising a series of sensors, normally constituted by photo cells or other similar devices, spaced along the path of the strip of paper to be printed and operable to detect the tension and possible breakage thereof in the quickest possible manner.

The number of said tension sensors employed on rotary printing presses has been continuously increasing with the increase in productivity of these. In fact, the continuous increase of productivity carries with it a corresponding ever increasing necessity to reduce the working dead times to a minimum. In the case of breakage of a strip of paper to be printed such dead time is normally proportional to the time interval elapsing between breakage of the strip and stopping of the printing machine.

By using the above-described known detector system it has not been possible to reduce the said time interval below a certain limit. In fact such a result could only have been obtained by using a number of sensors so great as to reduce the reliability of the associated detection system to an unacceptably low level.

The object of the present invention is that of providing a tension detection system which will not only be relatively simple and economic but will be able to detect breakage of a strip of paper in an extremely reduced time independently of the position in which the breakage itself takes place along the path which the paper follows.

The said object is achieved by the present invention in that it relates to a tension and breakage detection system for strips of sheet material, particularly for rotary printing presses, characterised by the fact that it includes at least one support pin projecting from a support; a cylinder mounted on the said support pin to rotate about the axis of this latter, the said strip passing around the said cylinder; and detection means mounted on the said support and sensitive to the elastic deformations imparted to the said pin by the said strip; this latter cooperating with actuator means operable to impart a determined driving tension.

Further objects and advantages of the present invention will become apparent from the following description with reference to the attached drawings, which illustrate a non limitative embodiment thereof, and in which: Figure 1 is a block schematic diagram illustrating an automatic tension and breakage detection system formed according to the principles of the present invention; and Figure 2 is a partially sectioned view of a preferred embodiment of a detail of Figure 1.

In Figure 1 an automatic tension and breakage detection system for a strip 2 of sheet material, in particular paper, is generaliy indicated with the reference numeral 1. The strip 2 is caused to advance along a determined path (not illustrated) along which the strip 2 is wound over at least one cylinder 3, in particular a deflector cylinder of a rotary printing press (not illustreted).

The cylinder 3 is rotatably supported cantilever fashion by an axial pin 4 and rotates with a peripheral speed which is substantially ident;cal to the speed of advance imparted to the strip 2 by a driving unit 5 comprising two counter rotating rollers 6 and 7 carried by a transmission box 8 the input shaft of which is connected to the output shaft of an electric motor 9.

The actuation of the rollers 6 and 7 by the motor 9 involves the application to the strip 2 of an axial driving force schematically represented by the arrow 10, which is transmitted to the cylinder 3 and the pin 4. This latter behaves as a bracket subjected to a distributed load and deflects in a manner which is substantially proportional to the force 10.

The free end of the pin 4 cooperates with a sensor 11 which is a sensor r responding proportionally to the load so as to generate a zero signal upon breakage in the paper, which sensor is disposed in the supply circuit feeding the motor 9 and is operable to interrupt this latter when the deflection of the pin 4 falls below a predetermined minimum value.

In the preferred embodiment of the system 1 illustrated in Figure 2, the pin 4 projects from a foot 12 provided with a mounting flange 13 by which it is mounted to a wall 14 of the rotary printing press (not illustrated), and is connected to the wall 14 by means of a through bolt 15. The cylinder 3 is rotatably mounted on the pin 4 by means of a pair of radial bearings of which the first, located nearest the foot 12, is not illustrated, whilst the second is indicated with the reference numeral 1 6 and mounted on a cylindrical projection 17 extending axially from the free end of the pin 4.The outer ring of the bearing 16 is fitted into a cup-shape body 18 a lateral wall 19 of which is coupled for rotation with the inner surface of the cylinder 3, and a bottom wall 20 of which has a central hole rotatably engaged by the projection 1 7.

To the wall 14 there is connected, by means of an attachment foot 21, a tubular sleeve 22 the axis of which is substantially parallel to that of the cylinder 3. Within the tubular sleeve 22 there is fixed, by means of screws 23, one end of a tubular shaft 24 the other end of which projects beyond the free end of the cylinder 3 and engages a through hole 25 formed axially along a projection 26 extending from a bottom wall 27 of a cupshape body 28. This latter has an axis substantially parallel to that of the shaft 24 and is closed by a cover 29 fixed to a lateral wall 30 of the cup-shape body 28 by means of screws 31.

On the projection 26 there are formed, by means of transverse and axial cuts, two curving arms 32 provided with terminal flanges joined together by means of screws 33 to clamp the cup-shape body 28 onto the end of the shaft 24. Within the cupshape body 28 a bracket 34, rigidly connected to the bottom wall 27, supports a proximity switch which constitutes the sensor 11 and is operable, when not actuated, to interrupt a supply line 35 for the motor 9, which extends through the tubular shaft 24 from which it extends through a radial hole 36 coaxial with a further hole 37 formed in the sleeve 22.

The sensor 11 includes the movable element 38 located elastically in contact with the lateral surface of a shaft 39 a first end of which penetrates into the interior of the cup-shape body 28 through a hole 40 formed in the wall 27, with the interposition of a resilient seal, and a second end of which extends into the cylinder 3 and is rigidly connected to the free end of the pin 4 by means of an axial threaded pin 41 engaged within an axial threaded hole 42 of the pin 4.

In use, a predetermined tension, and a breakage of the strip 2 along any point along its path causes a sudden drop in the driving tension of the strip itself. Obviously, such a drop in the driving tension corresponds to an immediate reduction in the deflection of the pin 4 to below a predetermined minimum in correspondence with which the sensor 11 causes closure of the supply circuit for the motor 9 and immediate stopping thereof.

In a case where the path followed by the strip 2 through the rotary printing press is, as normally happens, particularly tortuous, it will obviously be advisable to utilise two or more sensors 11 cooperating with respective pins 4 conveniently spaced from one another.

Naturally, the principle of the invention remaining the same, numerous variations could be introduced to the detection system described without by this departing from the scope of the present invention.

Claims

1. A tension and breakage detection system for strips of sheet material, particularly for rotary printing presses, characterised by the fact that it includes at least one support pin (4) projecting from a support (14); a cylinder (3) mounted on the said support pin (4) to rotate about the axis of this latter, the said strip (2) passing around the said cylinder (3); and detection means (11) mounted on the said support (14) and sensitive to the elastic deformations imparted to the said pin (4) by the said strip (2); this latter cooperating with actuator means (5) operable to impart a predetermined driving tension to it.

2. A system according to Claim 1, characterised by the fact that the said detection means (11) are operable to detect a drop of tension in the said strip (2) caused by a breakage thereof to indicate that breakage has occurred.

3. A system according to Claim 1 or Claim 2, characterised by the fact that the said detection means (11) are connected to a supply line for the said actuator means (5) and are operable to interrupt this when the elastic deformation imparted to the said pin (4) falls below a predetermined value.

4. A system acording to Claim 3, characterised by the fact that the said detection means (11) include a proportional sensor.

5. A system according to any of the preceding Claims, characterised by the fact that it includes a shaft (24) extending from the said support (14) parallel to the said cylinder (3) and carrying the said detection means (11) connected to its end.

6. A system according to any of the preceding Claims, characterised by the fact that the said detection means (11) include a movable element (38) located elastically in contact with the lateral surface of the shaft (39) extending axially from the free end of the said pin (4) and rigidly connected thereto.

7. A system for detecting the breakage of strips of sheet material, particularly for rotary printing presses, substantially as described with reference to the Figures of the attached drawings.