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(11) | EP 3 243 614 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A CUTTING UNIT FOR A LABELLING MACHINE |
| (57) There is described a cutting unit (1) for cutting labels (2) from a web (3) of labelling
material; the cutting unit (1) comprises a stationary blade (4), mounted on a stationary
support structure (5), a rotary drum (6), rotating, in use, about an axis (B) and
having a lateral surface (7) facing the stationary blade (4) and receiving the web
(3) of labelling material, and at least one rotary blade (8) borne by the lateral
surface (7) of the rotary drum (6) and cyclically passing, in use, by the stationary
blade (4) to define a cutting position, wherein the stationary blade (4) and the rotary
blade (8) cooperate, in use, with opposite sides of the web (3) of labelling material
so as to separate a label (2) from the web (3); the cutting unit (1) further comprises
sensor means (26), detecting, in use, a quantity (R) correlated to the distance or
interference between the stationary blade (4) and the rotary blade (8) at the cutting
position, and actuator means (27) configured to adjust the position of the stationary
blade (4) towards or away from the rotary drum (6) as a function of the quantity (R)
detected by the sensor means (26).
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TECHNICAL FIELD
[0001] The present invention relates to a cutting unit for labelling machines, particularly for the type of labelling machines comprising a reel from which a web of labelling material is cut into lengths (labels) of a predetermined size and applied on articles, namely on containers filled with a pourable product.
BACKGROUND ART
[0002] Known labelling machines of the above-mentioned type basically comprise a carousel for advancing the articles along an article path towards a labelling station, and a labelling unit fed with a web of labelling material, progressively advancing such web along a label path towards the labelling station as well as cutting the web itself into a plurality of labels to be applied onto the articles moving along the article path.
[0003] In detail, the labelling unit comprises:
- one or more motorized feeding rolls for moving the web of labelling material from a label reel towards the carousel;
- a cutting unit for cutting one label at any one time from the web; and
- a vacuum drum receiving the cut labels and transferring them to the articles in the carousel.
[0004] As each label is transferred from the cutting unit toward the labelling station, a layer of adhesive is typically applied on its surface for subsequently securing it to the surface of one respective article being fed to the labelling station.
[0005] As an alternative, in a sleeve-type labelling machine, the labels are transferred from the cutting unit in order to be wound about rotating mandrels carried by a carousel for forming tubular lengths of labelling material which shall subsequently be applied on the articles.
[0006] Known cutting units typically comprise:
- a stationary blade mounted on a stationary support structure;
- a rotary drum rotating, in use, about a vertical axis and having a lateral surface facing the stationary blade and receiving the web of labelling material; and
- a rotary blade borne by the lateral surface of the rotary drum and cyclically passing, in use, by the stationary blade to define a cutting position, wherein the stationary blade and the rotary blade cooperate, in use, with opposite sides of the web of labelling material so as to separate one label at any one time from the web itself.
[0008] In use, the web of labelling material is advanced between the stationary and the rotary blades of the cutting unit, the leading edge of the web being picked, by suction, by the vacuum drum.
[0009] In greater details, the vacuum drum is typically driven to rotate at a speed higher than the speed at which the web of labelling material is advanced along the label path, whereby the vacuum drum applies a pulling force on the leading edge of the web. When, upon rotation, the rotary blade becomes opposed to the stationary blade, the web is cut.
[0010] The applicant has observed that, in order to achieve a proper cut of the web of labelling material as well as to safeguard the life of the blades, it is preferable to maintain the stationary blade very close to the rotary blade at the cutting position without any interference between them; in other words, the minimum gap compatible with the performance of a proper cutting action on the web of labelling material should be established and maintained between the stationary blade and the rotary blade at the cutting position.
[0011] In practice, in use, the web of labelling material (generally a thin, polymeric film) is weakened along the cutting line and the label is "torn" off the rest of the web by means of the pulling force applied by the vacuum drum.
[0012] In the known solutions, the condition of non-interference cannot be ensured during the initial transitory time following the start-up of the cutting unit; as a matter of fact, during that time, the temperatures of the blades are lower than the target ones and this typically generates interference between the blades, with a consequent undesired wear thereof.
[0013] In addition, possible problems of non-uniform wear or degradation of the stationary blade may occur when webs of different heights are subsequently used on the same cutting unit. In particular, a working cycle with a first type of web only engaging a portion of the height of the stationary blade may produce different levels of wear on different zones of the blade itself (the working zone may be subjected to a higher wear than the non-working zone); in a subsequent working cycle with a higher web engaging the whole height of the stationary blade, the cutting action may be negatively affected by the non-uniform wear of the stationary blade itself.
[0014] Furthermore, the gap between the stationary blade and the rotary blade can change during the operation, due to the inevitable wear of the blades. An increase or decrease in such gap of one or two micrometres may result in a big difference in the quality of the cutting.
DISCLOSURE OF INVENTION
[0015] It is therefore an object of the present invention to provide a cutting unit for cutting labels from a web of labelling material, which allows to overcome, in a straightforward and low-cost manner, the drawbacks associated with the cutting units of known type.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Two preferred embodiments are hereinafter disclosed for a better understanding of the present invention, by mere way of non-limitative examples and with reference to the accompanying drawings, in which:
Figure 1 shows a side view of a cutting unit according to the present invention, with parts removed for clarity;
Figure 2 shows a smaller-scale section along line II-II in Figure 1, in a different configuration of the cutting unit and with the additional representation of a web of labelling material cut by the cutting unit into a plurality of labels;
Figure 3 shows a schematic smaller-scale side view of the cutting unit of Figure 1 with additional diagrammatic details of a control system of the cutting unit itself;
Figures 4 to 6 diagrammatically show different possible operating conditions of the cutting unit of Figures 1 to 3;
Figures 7 shows an enlarged section view of a detail of the cutting unit of Figure 2 in one possible operating condition and without the web of labelling material, the proportions of the parts being overemphasized for illustrative purposes and clarity reasons;
Figure 8 is analogous to Figure 7 and shows the cutting unit cooperating with the web of labelling material;
Figure 9 is analogous to Figure 7 and shows the same detail of the Figure 7 itself in a different condition and without the web of labelling material;
Figure 10 is analogous to Figure 9 and shows the cutting unit cooperating with the web of labelling material;
Figure 11 is analogous to Figures 7 and 9 and shows the same detail of these latter Figures in a further different condition and without the web of labelling material;
Figure 12 is analogous to Figure 2 and shows a different embodiment of the cutting unit according to the present invention, with parts removed for clarity; and
Figure 13 is analogous to Figure 3 and shows the cutting unit of Figure 12 with additional diagrammatic details of a control system of the cutting unit itself.
BEST MODE FOR CARRYING OUT THE INVENTION
[0018] Number 1 in Figures 1 to 3 indicates as a whole a cutting unit according to the present invention for cutting material from a web, in particular labels 2 from a web 3 of labelling material.
[0019] Cutting unit 1 is adapted to be incorporated into a labelling machine (known per se and not shown), especially into a roll-fed labelling machine for applying labels 2 to relative articles, in particular containers (known per se and not shown) filled with a pourable product.
[0020] In detail, the roll-fed labelling machine substantially comprises:
- a label reel from which web 3 is unwound along a path A from a motorized roll;
- a carousel for advancing the articles to be labelled along an additional curved path; and
- a labelling unit for applying labels 2 onto respective articles which are advanced by the carousel.
[0021] In a known manner, the labelling unit comprises:
- a web feeding device C including one or more motorized feeding rolls (known per se and not shown) for moving web 3 from the label reel towards the carousel;
- cutting unit 1 for cutting one label 2 at any one time from web 3; and
- a vacuum drum D (only partially shown in Figure 2) receiving the cut labels 2 and transferring them to the articles in the carousel.
[0023] With reference to Figures 1 to 3, cutting unit 1 substantially comprises:
- a stationary blade 4 mounted on a stationary support structure 5;
- a rotary drum 6 rotating, in use, about a vertical axis B and having a lateral surface 7 facing stationary blade 4 and receiving web 3; and
- at least one rotary blade 8 borne by lateral surface 7 of rotary drum 6 and cyclically passing, in use, by stationary blade 4 to define a cutting position, wherein the stationary blade 4 and the rotary blade 8 cooperate, in use, with opposite sides of the web 3 so as to separate a label 2 from the web 3 itself.
[0024] Axis B of rotary drum 6 is parallel to the axis of vacuum drum D; rotary drum 6 and vacuum drum D are substantially arranged tangential to one another to allow transfer of the cut labels 2 from the rotary drum 6 to the vacuum drum D.
[0025] In detail, rotary drum 6 comprises a central shaft 9 supported in a rotating manner about its axis B by a fixed frame 10 through a pair of bearings 11, in particular rolling bearings, and a cylindrical annular main body 12, coaxially coupled onto shaft 9 and delimited by lateral surface 7.
[0026] As clearly shown in Figure 2, rotary blade 8 outwardly protrudes slightly from lateral surface 7 of rotary drum 6 and is provided with a cutting edge 15 (Figures 7 to 11) extending parallel to axis B.
[0027] As a possible alternative not shown, rotary drum 6 may also comprise two or more rotary blades 8 equally spaced angularly about axis B.
[0028] In the particular example shown in Figure 2, axis of rotary drum 6 extends orthogonally to path A followed by web 3 at the cutting position.
[0029] With reference to Figures 1 and 2, support structure 5 comprises a vertical prismatic block 16 arranged in a position facing lateral surface 7 of rotary drum 6 and carrying stationary blade 4 on one of its sides.
[0030] In particular, stationary blade 4 is defined by a plate having two opposite and parallel flat lateral faces 17, 18, one of which rests, in use, on a relative side of block 16; stationary blade 4 also includes a front wedge-shaped cutting portion 19, protruding from block 16 towards rotary drum 6, and a flat back surface 20 opposite the cutting edge 19. In the particular example shown, back surface 20 abuts against a flange 21 outwardly protruding from the side of block 16 on which stationary blade 4 is arranged.
[0031] Cutting portion 19 of stationary blade 4 has a linear and vertical cutting edge 22 (see in particular Figures 7 to 11) extending parallel to axis B of rotary drum 6 and to cutting edge 15 of rotary blade 8.
[0032] As visible in the specific embodiment shown in Figure 2, which has no limiting effect, block 16 has an internal cavity 23, which opens at a side of the block 16 itself, opposite the rotary drum 6, and is closed by a cover plate 24 secured to said block 16. This specific arrangement permits to amplify, in use, the vibrations generated on stationary blade 4 by rotation of the rotary drum 6; the aim of this amplification will be clarified later on.
[0033] Stationary blade 4 and lateral surface 7 of rotary drum 6 define a passage 25 for web 3; at cutting position, i.e. where rotary blade 8 faces stationary blade 4, the passage 25 reaches a minimum value set to allow a cutting action on the web 3.
[0034] With reference to Figures 1 to 3, cutting unit 1 further comprises:
- sensor means 26 detecting, in use, a quantity R correlated to the distance or interference between stationary blade 4 and rotary blade 6 at the cutting position; and
- actuator means 27 configured to adjust the position of stationary blade 4 towards or away from rotary drum 6 as a function of the quantity R detected by sensor means 26.
[0035] In particular, actuator means 27 are configured to produce micrometric displacements of stationary blade 4 towards or away from rotary drum 6.
[0036] Cutting unit also comprises (Figure 3) a control unit 28 connected to sensor means 26 and to actuator means 27 and configured to control activation of the actuator means 27 so as to maintain the detected quantity R within a given threshold range Ro corresponding to a given air gap range between cutting edge 22 of stationary blade 4 and cutting edge 15 of rotary blade 8 at the cutting position (see in particular Figures 7 and 8).
[0037] Cutting unit 1 also comprises a temperature sensor 29 arranged on stationary blade 4 and connected to control unit 28.
[0038] According to the preferred embodiment shown in Figures 1 to 3, sensor means 26 comprise two sensors 30 detecting the quantity R at distinct zones 22a, 22b of cutting edge 22 of stationary blade 4 to give distinct measures of the distances between cutting edge 15 of rotary blade 8 and the zones 22a, 22b of the cutting edge 22 itself.
[0039] In particular, zones 22a, 22b are defined by the opposite end portions of cutting edge 22 stationary blade 4.
[0040] As a possible alternative not shown, sensor means 26 may even comprise more than two sensors 30.
[0041] In the example shown, quantity R is the acceleration of the vibrations transmitted by stationary blade 4 to block 16 during rotation of rotary drum 4. Hence, sensors 30 are accelerometers mounted on portions 31 of block 16 adjacent to zones 22a, 22b of cutting edge 22 of stationary blade 4. In particular, in this case, each sensor 30 detects the acceleration of the vibrations transmitted by the corresponding zone 22a, 22b of cutting edge 22 of stationary blade 4 to block 16 during rotation of rotary drum 6; such accelerations reach respective peaks at cutting position (see for example the diagrams of Figures 4 to 6).
[0042] The applicant has noted that when the peaks detected by each sensor 30 are comprised within the threshold range R0, corresponding to a given threshold air gap between cutting edge 15 of rotary blade 8 and the respective zone 22a, 22b of cutting edge 22 of stationary blade 4, the cutting operation is performed in the desired or optimal conditions.
[0043] The diagram of Figure 4 shows the desired condition, wherein the peaks of acceleration are contained within the prescribed threshold range R0.
[0044] The diagram of Figure 5 shows a condition, wherein, at a certain point, the peaks of acceleration start to be out of the prescribed threshold range R0, i.e. they start to exceed the upper limit of such range. Activation of actuator means 27 by control unit 28 permits to restore the correct condition.
[0045] The diagram of Figure 6 shows a further condition, wherein some of the peaks are within the threshold range Ro and others are out of such range; there is no repeatability of the values detected. The applicant has noted that this condition corresponds to a failure of bearings 11, which should be replaced. In this specific case, control unit 28 generates a warning signal and the cutting unit 1 has to be stopped to permit replacement of bearings 11.
[0046] In practice, control unit 28 is configured to generate a warning signal as the quantity R detected by one of the sensors 30 shows no repeatability in a given time interval corresponding to a given plurality of turns of rotary drum 6.
[0047] Figures 7 and 8 show an example of correct air gap between cutting edge 15 of rotary blade 8 and cutting edge 22 of stationary blade 4 at cutting position; the applicant has observed that such gap has to be comprised between 0 and 2 micrometers.
[0048] Figures 9 and 10 show an example wherein there is interference of some micrometers between cutting edge 15 of rotary blade 8 and cutting edge 22 of stationary blade 4 at cutting position; this situation should be corrected to avoid excessive wear of stationary blade 4 and subsequently a non-correct cutting action on the web 3 of labelling material.
[0049] Figure 11 shows a typical situation of failure of bearings 11; the air gap between cutting edge 15 of rotary blade 8 and cutting edge 22 of stationary blade 4 at cutting position continuously varies.
[0050] With reference to Figures 1 to 3, actuator means 27 preferably comprise a plurality of independent actuator members 31 configured to produce independent micrometric displacements of respective areas 22c of cutting edge 22 of stationary blade 4.
[0051] It is pointed out that areas 22c may be distinct from zones 22a, 22b and/or even coincide with the latter.
[0052] Actuator members 31 are configured to adjust the position of the respective areas 22c of cutting edge 22 of stationary blade 4 by direct deformation of the stationary blade 4 itself and/or by deformation of corresponding portions of flange 21 of block 16 directly contacting the stationary blade 4.
[0053] In the specific example shown in Figures 1 to 3, actuator members 31 are linear actuators, in particular screw actuators, externally supported by block 16 and each having an output element 32 directly cooperating with a side of flange 21 opposite the one contacting back surface 20 of stationary blade 4. In this case, the micrometric displacements of each area 22c of stationary blade 4 are obtained as a result of corresponding deformations produced by the respective actuator member 31 on the portion of flange 21 adjacent to said area 22c.
[0054] The operation of cutting unit 1 is described starting from a configuration, in which cutting edge 15 of rotary blade 8 is in the cutting area.
[0056] Web 3 is taken up at its end by suction by vacuum drum D, and advanced within passage 25 which is defined, on its opposite sides, by cutting edge 22 of stationary blade 4 and lateral surface 7 of rotary drum 6.
[0057] Due to the rotation of rotary drum 6 about axis B, at a certain time, rotary blade 8 faces cutting edge 22 of stationary blade 4 reaching the cutting position (Figures 2, 7 and 8), in which rotary blade 4 closes passage 25 so as to leave a minimum air gap.
[0058] In the cutting position, one label 2 is cut from the remaining part of web 3 by the actions of cutting edges 15, 22 of rotary and stationary blades 8, 4.
[0059] Sensors 30 continuously detect quantity R, in the example shown the acceleration of the vibrations produced on block 16 by stationary blade 4 during rotation of rotary drum 6; when the peaks of the detected quantity R by one of sensors 30 exceeds the threshold range Ro (as for instance in the conditions of Figures 5, 9 and 10), control unit 28 activates one or more actuator members 31 to produce given displacements of stationary blade 4 at the areas 22c of cutting edge 22 involved in such detection.
[0060] During the initial transitory time following the start-up of cutting unit 1, as a result of the temperature detected by temperature sensor 29 along with the quantity R detected by sensors 30, control unit 28 activates the actuator members 31 to maintain the air gap between cutting edge 15 of rotary blade 8 and cutting edge 22 of stationary blade 4 within the desired threshold range.
[0061] If the detected quantity R results in a plurality of peaks having different and not repeatable values, such as shown in the diagram of Figure 6, control unit 28 generates a warning signal indicating a possible failure of bearings 11, which have to be replaced.
[0062] Each cut label 2 is conveyed by the suction action of vacuum drum D towards the carrousel where it is applied onto a relative article by the labelling group.
[0063] With reference to Figures 12 and 13, number 1' indicates as a whole a different embodiment of a cutting unit according to the present invention; as cutting unit 1' is similar to cutting unit 1, the following description is limited to the differences between them, by using the same references, where possible, for identical or corresponding parts.
[0064] In particular, cutting unit 1' basically differs from cutting unit 1 by using piezoelectric actuator members 31' instead of linear actuator member 31.
[0065] In this case, piezoelectric actuator members 31' directly act on back surface 20 - which preferably has an arcuate profile - of stationary blade 4. As a possible alternative not shown, piezoelectric actuator members 31' may also act on a portion of support structure 5 directly contacting the stationary blade 4.
[0066] Each piezoelectric actuator member 31' can be selectively deformed under a control voltage signal CVS generated by control unit 28 and selectively transmits its deformations to stationary blade 4 so as to produce corresponding displacements of the respective area 22c of cutting edge 22 of the stationary blade 4 itself towards or away from rotary drum 6.
[0067] Each piezoelectric actuator member 31' is advantageously used as "sensor means" since it selectively transforms impacts of stationary and rotary blades 4, 8 on web 3 into corresponding detected-voltage values DVV correlated to the distance or interference between the stationary and rotary blades 4, 8 themselves at both the cutting position and the respective area 22c of cutting edge 22 on which said piezoelectric actuator member 31' operates.
[0068] The detected-voltage values DVV are transmitted from each piezoelectric actuator member 31' to control unit 28 as a detected-voltage signal DVS; control unit 28 generates a respective control voltage signal CVS for each piezoelectric actuator member 31' as a function of the detected-voltage signal DVS generated in use by the same piezoelectric actuator member 31'.
[0069] This permits to detect the distance or interference between the stationary and rotary blades 4, 8 at any area 22c of cutting edge 22, without using corresponding sensors, which may complicate the general structure.
[0070] Analogously to cutting unit 1, control unit 28 of cutting unit 1' is configured to generate a warning signal as the detected-voltage values DVV associated to one or more specific piezoelectric actuator members 31' show no repeatability in a given time interval corresponding to a given plurality of turns of rotary drum 6.
[0071] Finally, it should be noted that, in this specific embodiment, support structure 5 has no internal cavity to amplify vibrations generated on stationary blade 4 by rotation of the rotary drum 6, as piezoelectric actuator members 31' do not detect accelerations of vibrations.
[0072] The advantages of cutting units 1, 1' according to the present invention will be clear from the foregoing description.
[0073] In particular, thanks to the continuous detection of the distance between cutting edge 15 of rotary blade 8 and cutting edge 22 of stationary blade 4 at the cutting position as well as the consequent adjustment of the position of the stationary blade 4, it is possible to avoid any possible interference between such cutting edges 15, 22 during operation, so increasing the lives of the blades themselves. At the same time, it is possible to ensure a high quality of the cutting during the entire operation of the cutting unit 1.
[0074] This kind of control also applies during the initial transitory time following the start-up of the cutting unit 1, wherein the temperatures of the stationary and rotary blades 4, 8 are lower than the target ones; in this way, any interference between the blades 4, 8 and any consequent undesired wear thereof during this step are avoided.
[0075] The proposed solution also permits to avoid possible problems of non-uniform wear or degradation of the stationary blade 4 due to the use of webs 3 of different heights. As a matter of fact, by monitoring the behaviour of the stationary blade 4 at different zones of its cutting edge 22 permits the control unit 28 to detect whether a web 3 extending along only part of the entire height of the cutting edge 22 is used and to control the actuator members 31, 31' in such a way to take into account of this.
[0076] Furthermore, as previously explained, the proposed solution permits to detect possible failures of bearings 11.
[0077] Finally, the solution of Figures 12 and 13 permits to avoid to install additional sensors on the stationary blade 4 or on support structure 5, since piezoelectric actuator members 31' can be also used as "sensor means".
1. A cutting unit (1, 1') for cutting material (2) from a web (3) , said cutting unit
(1, 1') comprising:
- a stationary blade (4) mounted on a stationary support structure (5);
- a rotary drum (6) rotating, in use, about an axis (B) and having a lateral surface (7) facing the stationary blade (4) and receiving the web (3); and
- at least one rotary blade (8) borne by the lateral surface (7) of the rotary drum (6) and cyclically passing, in use, by the stationary blade (4) to define a cutting position, wherein the stationary blade (4) and the rotary blade (8) cooperate, in use, with opposite sides of the web (3) so as to separate material (2) from said web (3);
characterized by further comprising actuator means (27) configured to adjust the position of the stationary blade (4) towards or away from the rotary drum (6) as a function of the detected distance or interference between said stationary blade (4) and said rotary blade (8) at the cutting position.2. The cutting unit as claimed in claim 1, wherein said actuator means (27) are configured
to produce micrometric displacements of the stationary blade (4) towards or away from
the rotary drum (6).
3. The cutting unit as claimed in any one of the foregoing claims, wherein said stationary
blade (4) and said rotary blade (8) have respective cutting edges (22, 15) cooperating
in use with opposite sides of the web (3) .
4. The cutting unit as claimed in claim 3, wherein said cutting edges (22, 15) of said
stationary and rotary blades (4, 8) extend substantially parallel to the axis (B)
of the rotary drum (6).
5. The cutting unit as claimed in claim 3 or 4, wherein said actuator means (27) comprise
at least one actuator member (31, 31') configured to adjust the position of the cutting
edge (22) of the stationary blade (4) towards or away from the rotary drum (6) by
deformation of the stationary blade (4) itself and/or by deformation of a portion
(21) of the support structure (5) directly contacting the stationary blade (4).
6. The cutting unit as claimed in claim 5, further comprising a control unit (28) connected
to said actuator member (31, 31') and configured to control activation of said actuator
member (31, 31') so as to maintain a given air gap range between the cutting edge
(22) of the stationary blade (4) and the cutting edge (15) of the rotary blade (8)
at the cutting position.
7. The cutting unit as claimed in claim 6, wherein said actuator member is a piezoelectric
actuator member (31') selectively deformed under a control voltage signal (CVS) generated
by said control unit (28) and selectively transmitting its deformations to the stationary
blade (4) so as to produce corresponding displacements of the cutting edge (22) of
the stationary blade (4) itself towards or away from the rotary drum (6).
8. The cutting unit as claimed in claim 7, wherein said piezoelectric actuator member
(31') selectively transforms impacts of the stationary and rotary blades (4, 8) on
the web (3) into corresponding detected-voltage values (DVV) correlated to the distance
or interference between the stationary and rotary blades (4, 8) themselves at the
cutting position.
9. The cutting unit as claimed in claim 8, wherein said detected-voltage values (DVV)
are transmitted from said piezoelectric actuator member (31') to said control unit
(28) as a detected-voltage signal (DVS), and wherein said control unit (28) generates
said control voltage signal (CVS) for said piezoelectric actuator member (31') as
a function of said detected-voltage signal (DVS).
10. The cutting unit as claimed in claim 8 or 9, wherein said control unit (28) is configured
to generate a warning signal as the detected-voltage values (DVV) show no repeatability
in a given time interval corresponding to a given plurality of turns of said rotary
drum (6).
11. The cutting unit as claimed in claim 6, further comprising sensor means (26) connected
to said control unit (28) and detecting, in use, a quantity (R) correlated to the
distance or interference between the stationary blade (4) and the rotary blade (8)
at the cutting position; said actuator member being a linear actuator member (31)
configured to adjust the position of the cutting edge (22) of the stationary blade
(4) towards or away from the rotary drum (6) as a function of the quantity (R) detected
by the sensor means (26).
12. The cutting unit as claimed in claim 11, wherein the sensor means (26) comprise at
least two sensors (30) detecting said quantity (R) at distinct zones (22a, 22b) of
the cutting edge (22) of the stationary blade (4) to give distinct measures of the
distances between the cutting edge (15) of the rotary blade (8) and said distinct
zones (22a, 22b) of the cutting edge (22) of the stationary blade (4).
13. The cutting unit as claimed in claim 12, wherein said distinct zones are defined by
the opposite end zones (22a, 22b) of the cutting edge (22) of the stationary blade
(4).
14. The cutting unit as claimed in any one of claims 11 to 13, wherein said quantity (R)
is the acceleration of the vibrations transmitted by the stationary blade (4) to the
support structure (5) during rotation of the rotary drum (6).
15. The cutting unit as claimed in claim 14, wherein said sensors (30) are accelerometers
mounted on portions of the support structure (5) adjacent to said distinct zones (22a,
22b) of the cutting edge (22) of the stationary blade (4).
16. The cutting unit as claimed in any one of claims 11 to 15, wherein said control unit
(28) is configured to generate a warning signal as the quantity (R) detected by said
sensor means (26) shows no repeatability in a given time interval corresponding to
a given plurality of turns of said rotary drum (6).
17. The cutting unit as claimed in any one of claims 5 to 16, wherein said actuator means
(27) comprise a plurality of said actuator members (31, 31') configured to produce
independent micrometric displacements of respective areas (22c) of the cutting edge
(22) of the stationary blade (4).
18. The cutting unit as claimed in any one of claims 6 to 17, further comprising a temperature
sensor (29) arranged on the stationary blade (4) and connected to the control unit
(28).