Machine for cutting paper logs.

DESCRIPTION

The present invention relates to a machine for cutting logs of paper material.

More particularly, the present invention relates to the transverse cut of logs for the production of rolls of toilet paper, kitchen paper, etc. in various formats.

It is known that the production of logs of paper material, from which are obtained, for example, rolls of toilet paper or rolls of kitchen paper, implies the feeding of a web of paper, formed by one or more superimposed plyers, on a predetermined path along which various operations are performed before proceeding to the formation of the logs, including a transversal pre-incision of the web to form pre-cut lines which divide it into separable tear-off sheets. The formation of logs implies the use of cardboard tubes, commonly called "cores" on the surface of which a predetermined amount of glue is distributed to allow the paper web to be bonded onto the cores gradually introduced into the machine which produces the logs, machine commonly called "rewinder". The glue is distributed on the cores when they pass along a corresponding path comprising an end section commonly known as "cradle" due to its concave shape. The formation of the logs also implies the use of winding rollers located at the cradle, which impose on each core to rotate about its longitudinal axis thus determining the winding of the web on the same core. The process ends when a predetermined number of sheets is wound on the core, with the gluing of a flap of the last sheet on the underlying sheet of the roll thus formed (so-called "closing flap" operation). Upon reaching the predetermined number of sheets wound on the core, the last sheet of the log being completed is separated from the first sheet of the next log, for example by a jet of compressed air directed towards a corresponding pre-cutting line. At this point, the log is downloaded from the rewinder. The patent EP 1700805 describes a rewinding machine that operates according to the above operating scheme.

The logs thus produced are then conveyed to a buffer magazine which supplies one or more cutting-off machines through which the transverse cutting of the logs is carried out to obtain the rolls in the desired format. Notoriously, said cutting-off machines use blades that require a correct sharpening for the production of rolls that meet the quality standards required by the market

The present invention provides a cutting-off machine provided with a blade state control system based on the detection of the vibrations to which it is subjected the same blade during operation as further indicated in claim 1. Other features of the present invention are the described in the dependent claims.

The check carried out in accordance with the present invention allows to promptly detect any anomalies in the shape of the blade with respect to conditions deemed operationally acceptable, thus avoiding using the blade itself if the entity of said anomalies exceeds a predefined level.

These and further advantages and characteristics of the present invention will be more and more understood by any person skilled in the art, thanks to the following description and to the attached drawings, provided as an example but not to be considered in a limiting sense, in which:

Fig.l represents a schematic plan view from above of a cutting-off machines for the transverse cutting of logs of paper material which can be equipped with a control system according to the present invention;

Fig.2 is a schematic side view with parts in section of the blade and of the relative drive unit;

Fig.3 is a schematic front view of the group shown in Fig.2;

Figs. 4 and 5 illustrate some geometric characteristics of the blade;

Fig.6 is a simplified block diagram of the control system of a machine according to the invention.

A machine according to the present invention is of the type comprising a platform (1) on which one or more supply channels (10) are defined along which the logs (L) are moved. Said channels (10) are oriented along an advancing direction (AL) of the logs (L) which are moved by suitable pushers (2). It is understood, however, that the logs (L) moving members along the channels (10) can be of any type. The machine also comprises a cutting member formed by a circular blade (4) and one or more channels (11) for collecting the rolls (RO) obtained from the transversal cutting of the logs (L) by the blade (4). The channels (11) for collecting the rolls (RO) are downstream of the supply channels (10) and of the blade (4) with respect to the aforesaid direction (AL). Between the two groups of channels (10, 11) an empty space is formed (3) to allow the intervention of the blade (4). Fig.l shows the cutting plane (CP) of the blade (4), i.e. the plane in which the blade acts, blade which is not shown in this drawing. During the execution of the transversal cut, the logs (L) are normally held in position by clamp means (not visible in the drawings).

With reference to the example shown in Fig.2 and Fig.3, the blade (4) is mounted on an arm (41) which allows it to be moved to and from the logs (L) to be cut. Said arm (41) has a rear tubular appendix (42) which is connected to a respective electric motor (43) by means of a belt (44). Said motor (43) is constrained to a fixed structure (45) and determines the rotation of the arm (41) around a respective horizontal axis (x-x). The rotation of the blade (4) around its own axis (t-t) is determined by a second electric motor

(46) also connected to the fixed structure (45) and whose shaft (47) passes internally to the rear appendix (42) of the arm (41). The end of said shaft (47) projecting from the arm (41) is connected to the shaft (48) of the blade (4) by means of a corresponding belt (49). The shaft (48) of the blade (4) is inserted into the thickness of the arm (41) with interposition of bearings (C4). Similarly, the appendix (42) of the arm (4) is inserted into the fixed structure (45) by means of bearings (C42). Further bearings (C47) are interposed between the shaft (47) of the motor (46) and said tubular appendix (42). Therefore, according to a known operating scheme, the blade (4) rotates about its own axis (t-t) while the arm (41) rotates about the axis (x-x). The blade (4) has a cutting edge (40) which is worn with use.

According to the present invention, it is possible to determine the degree of wear of the blade (4), or its integrity, by detecting the vibrations produced by the blade during operation and comparing these vibrations with reference data used by a control unit (5) that is programmed to generate an alarm signal when the vibrations instantaneously detected correspond to a condition of excessive wear or non-integrity of the blade (4).

Said alarm signal can be used to activate an automatic procedure for deactivating the cutting system, that is, a procedure for stopping the machine, and / or for producing a visual or luminous alarm. For this purpose, the control unit (5) is connected to the actuators (43, 46) which operate the blade (4) during the cutting of the logs.

The inventor observed that it is possible to make use of the blade vibrations as a means of determining whether the blade itself is worn to such an extent as to compromise the quality of the cut.

In accordance with the present invention, a transducer (6) is used to produce instantaneous electric signals having amplitude and/or frequency related to the vibrations detected by the same transducer and said signals are compared with reference data contained in a database (DB). The transducer (6) is connected to the control unit (5).

For example, the reference data used to perform the aforementioned comparison can be divided into a first set of data, representative of acceptable wear conditions of the blade (4), and a second set of data, representative of unacceptable wear conditions. The first and second data sets can be obtained in an acquisition step carried out using a cutting-off machine equipped with a non-worn blade. The latter is subsequently replaced by blades that are differently worn, i.e. blades whose degree of wear is different from a blade to another, and using logs offering different resistance to be cut (logs formed using paper material of various structure and composition and with different winding density, said density being intended as a number of paper sheets of homogeneous thickness wrapped on a given diameter of the logs; higher density values determine a greater resistance of the log to be cut and, therefore, more difficult working conditions for the blade that performs the cut).

The first data set will consist of representative values of amplitude and / or frequency considered acceptable as produced by the transducer (6) using blades characterized by acceptable wear. Vice versa, the second database dataset (DB) will consist of representative values of amplitude and / or frequency considered unacceptable as produced by the transducer (6) using blades characterized by wear considered unacceptable.

For example, the degree of wear of the blades used in the aforesaid data acquisition phase can be determined on the basis of an evaluation criterion which takes into account geometric differences found between a new blade and a worn blade.

For example, with reference to the diagram of Fig.4, the vibrations corresponding to the values of the second data set are due to chipping and / or discontinuity (S4) on the cutting edge of the blade (4) which make the blade profile not circular, that is geometrically different from a nominal circular profile.

For example, with reference to the diagram of Fig.5, it can be established that the blade (4) has an acceptable degree of wear if al-a3<3° (where al is the opening angle of the bevel on the left side of the blade and a2 is the bevel opening angle on the right side) and an unacceptable degree of wear if al-a2> 3°. In this case, therefore, the evaluation criterion of the degree of wear of the blade takes into account a possible excessive asymmetry of the cutting edge (40).

Alternatively, only the first data set can be acquired and used. In this case, using the terminology used in the previous example, the second data set will consist of any value not belonging to the first set.

According to the present invention, the amplitude and/or frequency data of the signals instantaneously detected by the transducer (6) during the operational use of the cutting- off machine are continuously compared by the control unit (5) with the database data (DB). The control unit (5) is programmed to generate an alarm signal if at least one given amplitude and / or frequency of the signal produced by the transducer (6) coincides with a datum of the second set mentioned above, i.e. it does not belong to the range of variability defined by the minimum and maximum values of the amplitude and/or frequency data of the first set. Said alarm signal can be used, for example, to activate a procedure of acoustic or light signaling of the detected anomaly and/or to activate the stop of the cutting-off machine by acting on the motors (43) and (46). The control unit (5) can also be programmed to activate the stopping procedure of the cut-off and / or acoustic or light signal if the transducer (6) detects a predetermined number of abnormal vibrations in a predetermined time lapse.

For example, the transducer (6) may consist of a microphone or an accelerometer of the type commonly available on the market positioned on the fixed structure (45) externally of the aforementioned appendix (42) of the arm (41) as shown in Fig.2. In this position, the transducer (6) detects the vibrations to which the blade (4) is subjected in correspondence with each "stroke", that is whenever the blade (4) performs the transversal cutting of a log, vibrations transmitted along the appendix (42) and the structure (45).

As previously stated, according to the present invention, a correlation is established between the blade vibrating mode (4) at each cut and the actual geometry of the blade itself. In other words, according to the present invention a correlation is established between the blade vibrating mode (4) at each cut and the current blade shape. When the current shape of the blade (4) differs from the nominal shape, whereby the amplitude and/or frequency values of the signals generated by the transducer (6) exceed corresponding pre-established amplitude and/or frequency limits, the control unit (5 ) generates the alarm signal that triggers the acoustic or luminous signal of the detected anomaly and/or the stopping procedure of the cutting-off machine.

The transducer (6) can be connected to a converter (A/D) in such a way that the control unit (5) receives data in digital format. Alternatively, the transducer (6) can be connected to an analog input of the control unit (5) which will be provided with an internal A/D converter. The database (DB) can be stored in an internal memory section of the control unit (5) or even in an external server.

The aforesaid transducer (6) will also be able to detect the possible deformations of the blade due to other causes, for example excessive heat generated during cut.

In accordance with a further method of use of the present invention, an intensification of the sharpening cycles of the blade can be provided in relation to a transducer alarm, in order to restore the conditions of good operation of the blade, or the geometric conformation considered correct of the same blade. If the alarm signal continues after a pre-set number of sharpening cycles, the machine is then stopped.

In practice, the details of execution may in any case vary in an equivalent manner as regards the individual elements described and illustrated and their mutual arrangement without departing from the scope of the solution idea adopted and therefore remaining within the limits of the protection conferred by the present patent.