Device for sharpening blades.

DESCRIPTION

The present invention relates to a device for sharpening blades that can be used, in particular, for the production of paper rolls.

It is known that paper rolls, such as rolls of toilette paper and rolls of kitchen paper, are made by subdividing a paper log to obtain a plurality of shorter rolls by means of so-called "cutting-off machines".

The transverse cut of the logs is particularly critical. In fact, the cutting of the logs along planes that are not perfectly orthogonal to the axis of the same involves the formation of defective rolls, in which the side bases are oblique. This drawback is even more serious when the rolls are intended to be used in automatic dispensers which require, in fact, rolls with the side bases perfectly orthogonal to the axis of the rolls themselves, otherwise the rolls tend to get jammed in the dispenser.

The main object of the present invention is to provide a device that allows the elimination, or at least a great reduction, of the above-mentioned drawbacks .

This result is achieved, according to the present invention, by adopting the idea of realizing a device having the features indicated in claim 1 Other features of the invention are the subject of the dependent claims.

Thanks to the present invention, it is possible to always ensure a correct orthogonality of the bases of the rolls relative to the axis of the logs from which they are obtained, allowing a drastic reduction of scraps and the production of paper rolls especially, though not exclusively, usable in automatic dispensers. Furthermore, a device in accordance with the present invention is relatively simple and can be easily configured according to the specific production requirements.

These and other advantages and features of the present invention will be best understood by anyone skilled in the art from the following description and with the help of the accompanying figures, given as a practical exemplification of the invention, but not to be considered in a limitative sense, in which:

- Fig.l is a schematic side view of a portion of the blade of a cutting machine on whose bevel two grinding wheels act from opposite sides;

- Fig.2 is a schematic front view of the whole of Fig.l, in which the blade bevel is perfectly symmetrical;

- Fig.3 and Fig.4 schematically show two blades with an asymmetric bevel;

- Fig.5 is a schematic side view of another portion of the blade of Fig.l in which is shown a sensor of a control device in accordance with the present invention; Figs.6A, 6B and 6C represent a schematic front view of the whole of Fig.4, in which the bevel of the blade is symmetrical (Fig.6a) or asymmetric (Figs. 6BE 6C) ;

- Fig.7 is a simplified block diagram of a control device in accordance with the present invention.

Reduced to its basic structure, a device in accordance with the present invention is a device for sharpening blades used in the so-called cutting-off machines. The device includes a grinding wheel (1) acting on each of the two sides of a blade (2) of a cutting-off machine. The structure and operation of the grinding wheels (1), the blade (2) and of the cutting-off machine (T) are known per se to those skilled in the art and, therefore, are not described in greater detail. Examples of cutting machines for the production of paper rolls are provided, for example, in EP2097231 and EP2145742. A device for sharpening the blade of a cutting-off machine is disclosed in GB1301988. According to the example shown in the figures 5-6C, a control device in accordance with the present invention comprises a capacitive or inductive sensor (3) positioned on one side of the blade (2) at a predetermined distance from the same, and more precisely in a predetermined lateral position with respect to the cutting edge (20) of the blade itself. In the example, the blade (2) is a band blade.

The sensor (3) can be positioned, for example, downstream of the grinding wheels (1) with respect to the advancement direction of the blade (2) . In general, there are three cases.

With reference to the diagrams of Figs 2, 3 and 4 and respectively Figs. 6A, 6B and 6C the three cases are the following:

(a) n>p

(b) n*p

(c) n<p

wherein n and p are the length of the left side and the length of the right side of the edge (20) . These lengths (n, p) are detected in a plane transverse to the blade (2) . Cases (a) and (c) are related to a condition of asymmetry of the cutting edge (20) and then of possible execution of improper cutting of the logs by the blade (2) .

Case (b) is related to a condition of symmetry of the cutting edge (20) and then of correct execution of the cut of the logs by the blade (2) .

The sensor (3) detects the length (n, p) of the left and right sides of the cutting edge (20) . Therefore, it can be detected an error, equal to the difference (d = n-p) of these lengths.

A programmable electronic unit (4) receives signals from the sensor (3). The unit (4) acts on the wheels (2) - as further described in the following in function of the value assumed by the difference "d".

More particularly, the unit (4) acts on the grinding wheels (1) if the absolute value of "d" is greater than a predetermined reference amount. For example, the unit (4) acts on wheels (1) if the absolute value of "d" is greater than 1 mm.

The unit (4) does not intervene if the absolute value of "d" is less than the predetermined reference amount. For example, the unit (4) does not act on grinding wheels (1) if the absolute value of "d" is less than 1 mm.

For example, if the grinding wheels (1) are motorized grinding wheels, that is, each grinding wheels is driven by a rotary actuator (5), the unit (4) acts on the actuators (5) by adjusting the rotation speed of the grinding wheels (1) as long as the absolute value of "d" is greater than the predetermined reference amount.

Or, for example, if the grinding wheels (1) are each connected to a respective motorized slide (6), the unit (4) acts on the motorized slides (6) by adjusting the pressure exerted by the grinding wheels (1) on the cutting edge (20) as long as the absolute value of "d" is greater than the preset reference quantity as schematically indicated by the arrows "F" in Fig.7.

The actuators (5) and the slides (6) are represented in the diagram of Fig.7, in which, for simplification, to the unit (4) are connected both the actuators (5) and the slides (6), although, in general, it is preferred to connect both grinding wheels to rotary actuators only or to motorized slides only.

The unit (4) acts on the right grinding wheel (1) or on the left grinding wheel (1) depending on the sign, positive or negative, of the difference d = n-p.

Thanks to this device it is possible, therefore, control the condition of symmetry of the cutting edge (20) of a blade (2) and automatically intervene to restore the symmetry when the cutting edge (20) will wear asymmetrically.

The unit (4) can emit a light signal and/or an acoustic alarm when the absolute value of "d" is greater than the predetermined reference amount. The unit (4) can also be programmed to emit the said audible alarm and /or light signal in the case of detection of the condition of asymmetry of the cutting edge (20) without operating any automatic intervention on the grinding wheels (1) . In this case, an operator will sharpen the blade (2) by acting manually on the grinding wheels (1) when the unit (4) will emit the acoustic and/or light signal.

In accordance to what has been disclosed above, the unit (4) intervenes when the difference (d=n-p) exceeds, in absolute value, a predetermined limit, the intervention being selectively operated on the grinding wheel that is on the right of the blade or on the left of the blade in function of the sign, positive or negative, of this difference.

The sensor (3) can be, for example, of the inductive or capacitive type.

In practice, the details of execution may vary in any equivalent way as in the shape, dimensions, elements disposition, nature of the materials used, without leaving the scope of the adopted solution and thus remaining within the limits of the protection granted by this patent.