GB2103189A

GB2103189A - Controlling tension in paper strip fed to rotary printing press

Info

Publication number: GB2103189A
Application number: GB08220642A
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: 1983-02-16
Also published as: IT8168038A0; IT1144435B; JPS5890961A; FR2510038A1; GB2103189B; DE3227662A1; BR8204321A

Abstract

The tension in paper strips (7) being fed to a rotary printing press is controlled by varying the extent of the surface of contact between the strip (7) and a tensioner roller (9) which is driven to be rotatable with a peripheral speed the same as or greater than the speed of advance of the strip (7). Variation in tension in a strip (7) is detected eg by sensor (15) and by the associated control unit (8) which is operable to advance or retard a presser roller (13) which changes the length of the arc of contact of the strip on the tensioner roller (9). The control unit (8) includes a reference signal generator (17) which is compared at comparator (16) with the signal from sensor (5) and motor (16) is controlled to equalise the signals. <IMAGE>

Description

SPECIFICATION A device for driving strips of sheet material, particularly strips of paper, in a rotary printing press The present invention relates to a device for advancing strips of sheet material, particularly, but not exclusively, strips of paper in rotary printing presses.

Rotary printing presses are normally fed with webs of paper wound on reels and of a width equal to the length of the printing cylinders of the machines themselves. These paper webs, after having been printed, are normally cut into strips each of which carries one page repeatedly printed along its length. To obtain the finished printed matter the various strips are first deflected from a position alongside one another to a superimposed position and then cut transversely into sections the length of which is equal to the height of the page in the finished printed matter.

The advancement of the strips is normally obtained by means of a traction unit comprising two counterposed and contra-rotating rollers which act on the superimposed strips by imparting to them a traction or advancement tension. The application of the above mentioned traction or drive tension can cause disadvantages mainly due to the fact that the elongation under tension of the strips normally varies from strip to strip. Consequently it can happen that after the application of the traction tension one or more of the strips is too taut whilst others are completely untensioned.

The object of the present invention is that of providing a feed device which will be able to apply a uniform tension of determined value to the strips, eliminating the risk that some of the strips should break due to excess tension and other strips break due to being completely untensioned, that is to say as a result of stresses due, among other things, to flapping movements.

The said object is achieved by the present invention in that it relates to a strip feed device for sheet material, particularly strips of paper in rotary printing presses, including a traction unit operable to cooperate with the said strips to make them advance at a predetermined velocity along a given path, characterised by the fact that it further includes, for each said strip, a tension control unit for controlling the tension of the strip itself; the said control unit being located along the path of the associated strip upstream of the said traction unit and including a driven tensioner roller rotatable in contact with the said strip at a peripheral velocity greater than the said speed of advance and in the same direction thereas, and actuator means operable to cooperate with the said strip to vary the surface contact between this latter and the said tensioner roller.

Further characteristics and advantages of the present invention will become apparent from the following description with reference to the single Figure of the attached drawings, which is a schematic diagram illustrating a non limitative embodiment.

In the attached drawings there is illustrated an advancement or traction device 1 for a rotary printing press generally indicated 2. The device 1 includes a traction unit 3 constituted by a pair of counterposed and contra-rotating rollers 4 and 5 which are driven in opposite senses with a peripheral velocity determined by a drive device 6.

Between the rollers 4 and 5 there are located a plurality of strips of paper 7 superimposed in a stack, each of which is caused to advance by the rollers 4 and 5 at a speed substantially identical to their peripheral velocity by means of an associated control unit 8 the function of which is that of permitting an optimum tension to be imparted to the associated strip 7, the-value of which tension should be such as not to involve any risk of breakage of the strip 7 in any circumstances whilst at the same time preventing flapping movements thereof which are dangerous for their structural stability.

Each control unit 8 includes a tensioner roller 9 a part of the outer surface of which is located in contact with the associated strip 7. The tensioner roll 9 is driven- to rotate by a drive device 10 which imparts to it a peripheral velocity in the same directional sense as the advancement of the strip 7 but slightly greater than that of the rollers 4 and 5 and therefore of the strip 7.

In consequence of what has been described above, the outer surface of the tensioner roller 9 slides continuously with respect to the associated strip 7, applying a driving tension by friction to this latter, the value of which tension varies in a manner which is directionally proportional to the extent of the surface contact between the tensioner roller 9 and the strip 7.

The extent of the above mentioned surface contact is controlled by an actuator device 1 ova which in the illustrated example is constituted by an electric actuator including a stepping motor 11 operable to control the axial position of an output shaft 1 2 carrying a presser roller 1 3 at its end.

The presser roller 1 3 is freely rotatable and its axis is parallel to that of the tensioner roller 9 and located upstream of this latter in the direction of advance of the strip 7 and downstream of a further, reaction roller 14 which is also freely rotatable. The rollers 9 and 14 are in contact with the same surface of the strip 7 whilst the roller 13 is in contact with the other surface of the strip 7.

The actuator device 1 Oa could be manually operated by an operator capable of evaluating by eye, or else by means of a tension indicator or sensor 1 5, the tension of the strip 7, and of introducing suitable corrections when necessary.

As an alternative to manual control there can be utilised a servo system comprising a comparator 1 6 which receives a current signal emitted by the sensor 1 5 and proportional to the tension of the strip 7, compares this signal with a reference signal emitted by a calibrated signal generator 17, and operates the motor 11 in such a way as to nullify any possible difference between these two signals.

Added to what has been described above it is appropriate to confirm that the variations in the tension in the strip 7 are not imparted, as could apparently seem, directly by the roller 13, but solely by the tensioner roller 9 since the only function of the actuator device is that of increasing or reducing the contact surface between the strip 7 and the roller 9 in response to a reduction or increase respectively in the tension in the strip 7 with respect to a predetermined optimum value.

Naturally, the principle of the invention remaining the same, it would be possible to introduce a number of variations to the advancement or traction device 1 described purely by way of non limitative example, without by this departing from the scope of the present invention.

Claims

1. A device for driving strips (7) of sheet material, particularly strips of paper in a rotary printing press (2), comprising a traction unit (3) operable to cooperate with the said strips (7) to make them advance at a predetermined speed along a given path, characterised by the fact that it further includes, for each said strip (7), a control unit (8) for controlling the tension in the strip itself; the said control unit (8) being located along the path of the associated strip (7) upstream of the said traction unit (3) and including a driven tensioner roller (9) driven to rotate in contact with the said strip (7) at a peripheral velocity greater than the said speed of advance and in the same direction thereas, and actuator means (1 0a) operable to cooperate with the said strip (7) to vary the surface of contact of this latter with the said tensioner roller (9).

2. A device according to Claim 1, characterised by the fact that the said actuator means (1 0a) include a presser roller (13) located adjacent the said tensioner roller (9), and actuator means (11, 12) for transversely displacing the said presser roller ( 13) with respect to the said tensioner roller (9); the said presser roller (13) being located in contact with a surface of the said strip (7) opposite that in contact with the said tensioner roller (9) and being disposed between this latter and a fixed reaction element (14).

3. A device according to Claim 2, characterised by the fact that the said fixed reaction element includes a freely rotatable roller (14) in contact with the same surface of the said strip (7) as is in contact with the said tensioner roller (9).

4. A device according to Claim 2 or Claim 3, characterised by the fact that the said actuator means (1 1, 12) are responsive to a sensor (15) for detecting the tension in the said strip (7).

5. A device for advancing strips of sheet material, particularly strips of paper in a rotary printing press, substantially as described with reference to the attached drawings.