Cutting unit comprising a rotating blade and an optical sensor

Abstract

Cutting unit (31) for equipment for working sheet-like material (32) with an unwind section (33) for a first material roller (36), a section (37) for cutting the material into strips (40), and a section (41) for rewinding the strips onto second rollers (42) having narrower transverse dimensions, the cutting unit comprising at least one rotating blade (34) supported by a spindle (35) by means of a support frame (43) and at least an optical sensor (6), paired with the rotating blade to detect a characteristic thereof. The optical sensor comprises a U-shaped support (8) with the respective rotating blade inserted between the ends thereof, a pair comprising an emitter (11) and a receiver (12) arranged in the U-shaped support to emit and receive light radiation, and a processing unit (45) connected to the receiver to receive a signal indicating the intensity of the light radiation received and to determine the characteristic of said rotating blade.

Description

[0001] DESCRIPTION

[0002] "CUTTING UNIT COMPRISING A ROTATING BLADE AND AN OPTICAL SENSOR"

[0003] TECHNICAL FIELD

[0004] The present invention relates to a cutting unit comprising a rotating blade and an optical sensor.

[0005] The present invention can be advantageously used roll-to-roll (R2R) equipment for working and cutting flexible sheet-like materials, such as metallized films.

[0006] The description below makes explicit reference to this example application, while remaining generally applicable.

[0007] BACKGROUND ART

[0008] Roll-to-roll working equipment, such as the equipment illustrated schematically in Figure 1, for working different types of flexible sheetlike material 32 (paper, plastic, metal films, technical fabrics, composites), comprises an unwind section 33 in which the sheet-like material 32 is unwound from a first roller 36 and fed through suitable rollers and other guide elements in a feed direction A towards a strips cutting section 37 where it is divided into strips 38 of appropriate width by a cutting unit 31. The cutting unit 31 typically comprises circular rotating blades 34 (two circular blades 34 are shown in the diagram in Figure 1) supported and connected, in predetermined positions (fixed or adjustable) depending on the desired width of the strips, to a spindle 35 with a shaft rotating about an axis T transverse to the feed direction A of the sheet-like material 32, and elements, for example support disks 38 (not shown in Figure 1) connected to a second rotating shaft 39 such that the sheet-like material 32 is between these supporting elements 38 and corresponding circular blades 34. The strips 40 of sheet-like material 32 thus obtained at the output of the cutting section 31 move on to a rewind section 41 where they are separately wound onto second rollers 42 having narrower transverse dimensions, ready for further working.

[0009] One of the main uses of the cutting machines is in the production of electrodes for batteries. Electrodes for batteries, such as lithium-ion batteries, are manufactured as continuous sheets on large rollers and, in an initial stage, the active material, such as lithium and graphite, is deposited on a conductive substrate, usually aluminium for the cathode and copper for the anode. These continuous sheets undergo coating and calendering processes to ensure a uniform thickness and the required optimum density. These sheets then undergo a cutting or "slitting" operation in a cutting unit such as the one described above, which transforms them into narrow strips, ready for use in the cells of the battery. The precision of the cut is critical, since the width of the strips must be perfectly uniform to ensure that they fit correctly within the form of the cells (cylindrical, prismatic, button, or pouch). Furthermore, it is essential that the cut is clean to prevent the formation of defects such as burrs, uneven edges or damage to the coating, which could at best adversely affect the performance of the battery for which the electrodes are intended. Metal burrs on the edges of a strip can easily cause short circuits in the battery between two adjacent electrodes (by puncturing the separator), which could even destroy the battery.

[0010] For this reason, it is extremely important to ensure that the blades are always in optimum condition and to stop them being used if not, for example if they are worn and / or chipped.

[0011] Known solutions for inspecting the condition of the blades include indirect inspection, checking the condition of the strips after cutting and intervening if irregular cutting or metal burrs are detected.

[0012] This indirect inspection, in addition to requiring parts on which the sub- optimal cut is detected to be discarded, cannot always detect abnormal blade conditions in a timely manner, and requires systems that are somewhat complex and expensive to check all the cut edges. Also for this reason, it is often preferred to replace the blades at set intervals, after a certain quantity of material has been worked (measured in kilometres) or after a certain number of cycles. This approach involves intervening regardless of the actual condition of the blade, and adequately ensuring against sudden failures or malfunctions potentially compromising the quality of the cut and stopping production for unacceptable periods of times in consideration of desired throughput rates very often involves replacing blades that could actually still work perfectly.

[0013] DISCLOSURE OF THE INVENTION

[0014] The purpose of the present invention is to provide a cutting unit for high-precision cutting in which a characteristic of a rotating blade can be reliably and promptly checked.

[0015] According to the present invention, a cutting unit comprising a rotating blade and an optical sensor according to the attached claims is provided.

[0016] The claims describe preferred embodiments of the present invention and are an integral part of the present description.

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is described below with reference to the attached drawings, which show some non-limiting example embodiments of the invention, in which:

[0019] • Figure 1 is a schematic perspective view of a roll-to-roll equipment comprising a cutting unit according to the present invention;

[0020] • Figure 2 is a schematic view of an optical sensor from Figure 1;

[0021] • Figure 3 is a schematic view of a different embodiment of an optical sensor from Figure 1;

[0022] • Figure 4 is a graph showing the measurements of an array of photodiodes of an optical sensor from Figure 1;

[0023] • Figures 5, 6 and 7 are schematic representations of the readings from an array of photodiodes of an optical sensor from Figure 1;

[0024] • Figures 8, 9 and 10 are graphs showing the evolution of the measurements of an optical sensor from Figure 1, with no problems, with a partial breakage of a rotating blade, and with an eccentricity in the rotating blade, respectively;

[0025] • Figure 11 is a side view of a cutting unit of Figure 1 where, for clarity and simplicity reasons, some components are shown very schematically with different proportions compared with Figure 1; and

[0026] • Figure 12 is a front view of the cutting unit in Figure 11.

[0027] BEST MODES FOR CARRYING OUT THE INVENTION

[0028] A cutting unit 31 according to the present invention is shown in Figure 1, in the roll-to-roll working equipment as partially described above.

[0029] Figures 11 and 12 schematically show an enlarged part of the cutting unit 31 of Figure 1. In particular, the cutting unit 31 comprises, in addition to the rotating blades 34 (the front view in Figure 12 shows two, but there may be just one or a different number, for example six) connected to the spindle 35 and corresponding support disks 38 connected to the rotating shaft 39, optical sensors 6, each of which is connected to the spindle 35 by means of a suitable support frame 43 and is paired with one of the rotating blades 34. Typically, there are a plurality of rotating blades 34 and a plurality of optical sensors 6, and the number of optical sensors 6 is equal to the number of rotating blades 34, as in the example illustrated. However, there may be a single optical sensor 6 paired with a single rotating blade 34 of the plurality, or fewer optical sensors 6 than rotating blades 34, in which case the optical sensors 6 are paired with only some of the rotating blades 34 of the respective plurality. Typically, the support frame 43 is integral with the spindle 35, and, where a plurality of optical sensors 6 is present, all the optical sensors 6 are supported by the support frame 43.

[0030] Each optical sensor 6 is used to measure wear (breakage, chipping, etc.) of the rotating blade 34 (i.e. to detect irregularities and missing parts in the edge of the rotating blade 4).

[0031] Figures 2 and 3 schematically illustrate two different embodiments of the optical sensor 6 (identical parts in the two embodiments are indicated using identical reference numbers).

[0032] The optical sensor 6 comprises a U-shaped support 8 (i.e. forkshaped with two separate prongs 9 and 10) that is preferably made of stainless steel. The support 8 comprises the two opposing prongs 9 and 10, between which, i.e. between the opposed ends defined by the U- shaped support (or "opposed ends of the U-shape"), the rotating blade 34 can be inserted when in use. In other words, when in use, the U- shaped support 8 and the spindle 5 are arranged so that the rotating blade 34 is between the two opposing prongs 9 and 10, between the opposed ends of the U-shape.

[0033] The optical sensor 6 comprises an emitter 11 and a receiver 12, arranged in the U-shaped support 8 and configured to emit and receive light radiation transmitted between the opposed ends of the U-shape. In particular, in the embodiment in Figure 2, the emitter 11 (for example provided with an LED or a laser) is arranged on the prong 9 and is configured to emit light radiation directed towards the prong 10, and the receiver 12 is arranged on the prong 10 and is configured to receive the light radiation and to measure an intensity of the received light radiation, that is to provide a signal indicative of the intensity of the received light radiation. In Figures 2 and 3, the receiver 12 of a preferred embodiment of an optical sensor used in the cutting unit according to the present invention is shown very schematically, highlighting particularly important features. However, components such as lenses / optical assemblies, which may generally be provided to improve the optical quality of the shadow received, are not represented. The emitter 11 comprises a dedicated control circuit 13 which controls the emission of the light radiation. The receiver 12 comprises a dedicated control circuit 14 which processes the measurement of the received light radiation, preferably by converting the analogue signal into a digital signal. For example, the lightradiation intensity measurement is converted by a compact microcontroller using its integrated analogue-to-digital converters (ADCs), although external converters outside the microcontroller can also be used.

[0034] According to a preferred embodiment illustrated in the attached figures, the control circuit 13 of the emitter 11 and the control circuit 14 of the receiver 12 are housed inside the support 8 of the optical sensor 6 or 7.

[0035] Each optical sensor 6 comprises a dedicated processing unit 45 (i.e. a control board) which can be arranged outside or inside the U- shaped support 8 of the sensor (as shown schematically in Figure 1), and is electrically connected to the emitter 11 and the receiver 12, more specifically to the control circuits 13 and 14 of the emitter 11 and the receiver 12 of the sensor 6, by an electrical cable, that is a cable carrying an electrical signal which is preferably digital but may also be analogue. The processing unit 45 of each optical sensor 6 processes the intensity measurement of the light radiation received by the receiver 12 in order to extract the desired information, in particular to detect wear (breakage, chipping, etc.) of the rotating blade 34. In the embodiment according to which the processing unit 45 of each optical sensor 6 is arranged inside the support 8, all the components of the optical sensor 6 are contained in the support 8

[0036] According to an alternative embodiment, there is a single processing unit 45 which is connected to several optical sensors 6 (to both optical sensors 6 in the embodiment illustrated) and which processes the measurements from the optical sensors 6, alternately or simultaneously.

[0037] As illustrated in Figures 2 and 3, the receiver 12 (according to this preferred embodiment of the optical probe) comprises an array (row) of light radiation sensitive elements, e.g. photodiodes 17, typically more than sixteen photodiodes, for example thirty-two photodiodes, that are aligned in a radial direction with respect to the rotating blade 34 (i.e. a direction perpendicular to an axis of rotation of the rotating blade 34). In other words, the array of photodiodes 17 has a single row of photodiodes 17 arranged on a given line oriented radially with respect to the rotating blade 34. Each photodiode 17 is configured to measure the intensity of the light radiation received by the photodiode 17, independently of the other photodiodes 17, i.e. to provide, on a scale (for example between 0 and 100), a measurement of the intensity of the light radiation received. The receiver 12 therefore outputs a number of measurements of light intensity equal to the number of photodiodes 17 (for example thirty-two). According to other entirely equivalent embodiments, the number of photodiodes 17 that make up the array may be different (i.e. there may be fewer photodiodes 17 or more photodiodes 17) and the minimum number of photodiodes 17 that make up the array is two (although there are usually at least ten photodiodes 17).

[0038] In general, the receiver 12 comprises an array (row) of at least two photodiodes 17 and, according to other embodiments (not illustrated), comprises a matrix of photodiodes 17 made up of at least two arrays (rows) of photodiodes 17 arranged side by side. In essence, the receiver 12 is a sensor formed by a line or grid (matrix) of semiconductor elements (photodiodes 17) that can accumulate an electrical charge proportional to the intensity of the electromagnetic radiation incident thereon. It may be a charge-coupled device (CCD) circuit or use a different technology, such as CMOS sensor technology. By sending a timed sequence of pulses to the receiver 12, an electrical signal is output and it is possible to reconstruct the matrix of the pixels that make up the projected image on the surface of the receiver 12.

[0039] The emitter 11 illustrated in Figure 2 has a small size and can be housed in the prong 9 of the support 8. In addition, preferably, the emitter 11 has high directivity, i.e. the scattering angle of the rays of the light radiation is reduced in order to cast a sharp shadow on the receiver 12.

[0040] In the embodiments illustrated in Figures 2 and 3, the emitter 11 comprises a light source 18 which is housed in the support 8 and preferably comprises an LED of very small mechanical dimensions.

[0041] In the embodiment illustrated in Figure 2, the light source 18 (for example an LED) of the emitter 11 directly emits the light radiation perpendicular to the prong 9 and directed towards the prong 10. The advantage of this embodiment is the simplicity of implementation but, on the other hand, it requires a light source 18 with a small emitting area and polar emission large enough to cover the entire field of the receiver 12, while also being of suitably small mechanical dimensions in the emission direction.

[0042] In the embodiment illustrated in Figure 3, the light source 18 of the emitter 11 emits the light radiation parallel to the prong 9, i.e. along a direction substantially radial with respect to the rotating blade 34, towards one of the two opposed ends of the U-shaped support 8, where there is an optical deflecting element 19 (for example a prism with a reflective surface 19', or a mirror) that reflects the light radiation emitted by the light source 18 perpendicular to the prong 9 and directed towards the prong 10, i.e. towards the other of the two opposed ends of the U-shaped support 8. Figure 3 shows the components very schematically to illustrate as clearly as possible (and in the space available) important aspects of the present invention, disregarding functional coherence in some cases. This applies in particular to the optical deflecting element 19 which is shown in Figure 3 with a reflective surface 19' inclined with respect to the prong 9 and the emission direction of the light source 18 by an angle that is clearly not 45°, whereas this angle must be (and is) 45° to properly reflect (as shown graphically in Figure 3) the light radiation perpendicular to the prong 9. This embodiment, while structurally more complex, has the advantage of better defining the shadow cast because it enables sources with smaller emission areas and narrow polar emission (i.e. highly directed) to be used, since there is enough space for the beam to widen enough to cover the entire array of photodiodes 17. In this embodiment, mechanically larger sources can be used, thus providing a wider selection of available light sources 18 (for example LEDs) with high directivity. In addition, this embodiment enables a lens to be inserted in the optical path to collimate the light radiation.

[0043] Figure 4 is a graph illustrating the measurements of an array of thirty-two photodiodes 17 of a receiver 12. As shown, the first fourteen photodiodes 17 are substantially in shadow (i.e. the light from the emitter 11 directed towards the first fourteen photodiodes 17 is blocked by the rotating blade 34), the last fifteen photodiodes are in full light (i.e. the light from the emitter 11 directed towards the last fifteen photodiodes 17 is in not blocked at all by the rotating blade 34) and the three photodiodes 17 in the middle are partially illuminated (i.e. the light from the emitter 11 directed towards the three photodiodes 17 in the middle is partially blocked by the rotating blade 34).

[0044] According to a possible embodiment illustrated schematically in Figures 5, 6 and 7, the processing unit 45 is configured to detect the desired characteristic of the rotating blade 34 considering only the light-radiation intensity measurements provided by a group G made up of a limited number of the photodiodes 17 (in the most limited case, by a single photodiode 17), that are located around an edge of the rotating blade 34 (i.e. straddling the shadow zone in which the rotating blade 34 blocks the passage of light radiation and the light zone in which the rotating blade 34 does not block the passage of light radiation). In this embodiment, the processing unit 45 sums the lightradiation intensity measurements provided by the group G made up of a limited number of the photodiodes 17 (or by the single photodiode 17) that are located around an edge of the rotating blade 34 (i.e. straddling the shadow zone and the light zone), compares this measurement with a predetermined intensity measurement, preferably with the total intensity measurement of the group G of photodiodes 17 (or of the single photodiode 17) previously taken when the photodiodes 17 in the group G (or the single photodiode 17) were all illuminated and, on the basis of a predetermined threshold, identifies the position of the rotating blade 34. In particular, given that the position of the photodiodes 17 is known, the position of the edge (corresponding to the external radius) of the rotating blade 34 is determined by identifying the last photodiode 17 that is not obscured (or the first photodiode 17 that is obscured) on the basis of a predetermined threshold. Then the lightradiation intensity measurements provided by the photodiodes 17 adjacent to said last / first photodiode 17 that are located around the edge of the rotating blade 34 being measured are added together and the percentage of intensity of the obscured light radiation, and therefore the measurement of a position of the edge of the rotating blade 34, is obtained.

[0045] The embodiment described above with reference to figures 5 to 7 is particularly useful in situations where it is not possible to move the optical sensor 6 in relation to the rotating blade 34, and provides a measurement with a higher resolution than the measurement that would be obtained by adding together the measurements of all the photodiodes 17 of the array, as well as a measuring range as large as the size of the array, since the length of the measurement area can be selected by simply adding the intensity measured by the limited number of photodiodes 17 (or, at the extreme, the single photodiode 17) of the group G and ignoring photodiodes that do not provide any information for the measurement because they are very far away from the dark / light transition zone.

[0046] Figures 5, 6, and 7 show three examples where the group G is made up of a limited number of photodiodes 17 that straddle the edge of the rotating blade 34 (i.e. that straddle the shadow zone and the light zone). In the example embodiment illustrated in Figures 5, 6 and 7, the limited number of photodiodes 17 that make up the group G is three, but this number may be different (typically between one and five).

[0047] According to an alternative embodiment, the optical sensor 6 comprises a first array of photodiodes 17 and a second array of photodiodes 17. The last obscured photodiode 17 is identified in the first array of photodiodes 17, and the first obscured photodiode 17 is identified in the second array of photodiodes 17, or vice-versa, thereby providing two different types of detection that can be averaged to increase the precision and confidence level of the measurement.

[0048] According to a possible embodiment, due to the high resolution for receiving the light radiation, the optical sensor 6 can also be used to detect a variation of the position of the edge of the rotating blade, more specifically to take measurements of the position of the rotating blade 34 in relation to a predefined reference position of the spindle 35.

[0049] The processing unit 45 of the optical sensor 6 is configured to create a digital image (illustrated by way of example in Figures 8, 9 and 10) of the development of the edge of the rotating blade 34 using estimates of the position of the edge of the rotating blade 34 for at least a full rotation of the rotating blade 34 (i.e. for a 360° rotation of the rotating blade 34). Then, the processing unit 45 of the optical sensor 6 analyses (uses) the digital image of the development of the edge of the rotating blade 34 to detect at least one characteristic of the rotating blade 34, such as eccentricity, run-out, or the like, in a known manner.

[0050] In this regard, it should be noted that the angular position of the rotating blade 34 can be detected by an angle encoder paired with the rotating blade 34 and therefore be known with high precision and good resolution. In other words, the digital image of the development of the edge of the rotating blade 34 is obtained from the estimates of the position of the edge of the rotating blade 34 over a period of time in which the rotating blade 34 makes at least a full rotation. Where high precision is not required, it is still possible, even without an encoder, to obtain the digital image of the development of the edge of the rotating blade 34 by indirect correlation, for example by identifying a period of rotation of the rotating blade 34 from an analysis of the trend of the acquired signal over time.

[0051] Figure 8 illustrates an example of a digital image of the development of the edge of a problem-free rotating blade 34. As shown, the position of the edge of the rotating blade 34 is (substantially) constant throughout the rotation of the rotating blade 34.

[0052] Figure 9 illustrates an example of a digital image of the development of the edge of the rotating blade 34 that has a break (i.e. a missing part). As shown, the position of the edge of the rotating blade 34 has a "hole" indicating a break (i.e. a missing part). The angular width of the "hole" is proportional to the circumferential dimension of the break, while the depth of the "hole" is proportional to the radial dimension of the break.

[0053] Figure 10 illustrates an example of a digital image of the development of the edge of the rotating blade 34 with an eccentricity (for example due to uneven wear). As shown, the position of the edge of the rotating blade 34 is not constant but varies in an approximately sinusoidal pattern. That is, in the case of eccentricity of the rotating blade 34, the position of the edge of the rotating blade 4 appears as a curve and not as a straight line.

[0054] In other words, the array of photodiodes 17 of the receiver 12 enables the position of the edge of the blade 34 to be determined punctually and the position of the edge of the blade 34 in space and time can be processed to obtain a two-dimensional digital image (illustrated by way of example in Figures 8, 9 and 10) of the edge of the rotating blade 34.

[0055] The digital image has high spatial and temporal resolution, and can be advantageously used to carry out advance filtering processes allowing to get reliable information from the acquired measurement signals even where the working environment involves hard operating conditions. In some cases, for instance, not negligible numeric noise can be present in the working environment and it might not be easy to distinguish such numeric noise from the useful signal corresponding to breakages / irregularities of the rotating blades 34. The processing unit 45 can store and manage a high number of measurement signals provided by the array(s) of photodiodes 17 in a time interval corresponding to at least one full rotation of the rotating blades 34. The presence of a number of photodiodes 17 guarantees a high spatial resolution and allows to identify different spatial evolution lines. For instance, it is consequently possible to identify the trend of a signal corresponding to numeric noise that is present in the working environment and to distinguish it from the measurement signal corresponding to breakages / irregularities of the rotating blades 34, since the two events have each a specific spatial and temporal fingerprint that can be identified by the processing unit 45. Moreover, when the acquisition time interval allows the rotating blades 34 to perform more full rotations, detecting the periodic occurrence of events that are not correlated with the noise allows to tune the filtering with the rotation speed of the rotating blades 34 so improving the identification of the proper measurement signals. In other words, the analysis of the digital image can include the application of filtering processes allowing, for example, to identify the proper measurement signals relating to the characteristics of the rotating blades 34 and distinguish it from numeric noise.

[0056] The processing units 45 are connected to a processing and control unit 50 of the equipment receiving the results of the measurements, performs appropriate processing to evaluate the condition of the rotating blades 34 and indicates anomalies that require the working to be stopped and the rotating blade or blades 34 to be replaced.

[0057] The optical sensors 6 enable an advantageous real-time evaluation of the actual condition of the rotating blades 34, timely detection of breakage or wear affecting optimal cutting of the sheetlike material 32, and replacement when needed, without the delay inherent in known indirect inspection systems that involve checking the cut material, and without the possibility of early replacement inherent in methods involving periodic replacement without knowing the actual condition of the rotating blades 34. This improves the operational efficiency of the working while reducing costs associated with unnecessary replacements, resulting in a longer life cycle of the rotating blades 34 and avoiding sudden machine stoppages that are not strictly necessary.

[0058] Cutting units according to the present invention can include optical sensors of a different kind, e.g. where the receiver 12 has a single photodiode. However, cutting units including optical sensor 6 as described above with reference to figures 2 to 10 have further important advantages.

[0059] In particular, each of the optical sensors 6 described above has a higher resolution in detecting the received light radiation due to the fact that the receiver 12 comprises an array of photodiodes 17 (i.e. a plurality of photodiodes 17 arranged in a straight line). Among other things, using more photodiodes 17 (sensitive elements) enables the application of new, more flexible, more advanced processing algorithms, both for detecting alert thresholds and for taking actual dimensional measurements.

[0060] An additional advantage granted by the use of the optical sensor 6 described above is the flexibility of use and the possibility to install and, in case, replace it by very simple operations thanks to its extreme miniaturization, which is also achieved by integrating the control circuits into the support 8.

[0061] Finally, the sensor 6 described above is simple and inexpensive because it involves the use of components that are easily available on the market at low cost.

[0062] The cutting unit according to the present invention as described above is particularly advantageous when used in apparatuses for the production of electrodes for batteries, where the sheet-like material includes a conductive substrate (usually aluminium for the cathode and copper for the anode) on which active material such as lithium and graphite is deposited. However, cutting units according to the present invention can be used in apparatuses for working different types of flexible sheet-like materials, such as for instance other types of metal films, paper, plastic, technical fabrics.

Claims

CLAIMS1. Cutting unit (31) for an apparatus for working a sheet-like material (32) including an unwind section (33) of a first roller (36) of material, a strips (40) cutting section (37) of the sheet-like material (32) and a rewind section (41) of the strips (40) in second rollers (42) having narrower transversal dimensions, the cutting unit (31) comprising:- at least one rotating blade (34); and- a spindle (35) configured for supporting said at least one rotating blade (34); characterized in that it comprises an optical sensor (6) coupled to said at least one rotating blade (34) by means of a support frame (43) for detecting a characteristic of said at least one rotating blade (34), said optical sensor (6) comprising: a U-shaped support (8) defining two opposed ends between which said at least one rotating blade (34) is inserted; an emitter (11) and a receiver (12) arranged in the U-shaped support (8) and configured to emit and to receive a light radiation that is transmitted between the opposed ends of the U-shaped support (8); and a processing unit (45) connected to the receiver (12) to receive a signal indicative of the intensity of the received light radiation and detect the characteristic of said at least one rotating blade (34).

2. Cutting unit (31) according to claim 1, wherein said support frame (43) is integral with the spindle (35).

3. Cutting unit (31) according to claim 1 or claim 2, wherein the optical sensor (6) includes a control circuit (13) of the emitter (11) and a control circuit (14) of the receiver (12), both being housed in the U-shaped support (8) and electrically connected to the processing unit (45).

4. Cutting unit (31) according to any one of claims 1 to 3, wherein the receiver (12) of said optical sensor (6) includes at least an array of light radiation sensitive elements (17) which are aligned in a radial direction with respect to said at least one rotating blade (34).

5. Cutting unit (31) according to claim 4, wherein each sensitive element (17) of the receiver (12) of said optical sensor (6) is configured to measure an intensity of the light radiation received by the sensitive element (17) independently of the other sensitive elements (17).

6. Cutting unit (31) according claim 4 or claim 5, wherein the processing unit (45) of the optical sensor (6) is configured to determine the feature of the rotating blade (34) by taking into account only intensity values of the light radiation provided by a group (G) made up of a limited number of sensitive elements (17) of the receiver (12) that are located between a shadow zone in which the rotating blade (34) blocks the passage of the light radiation and a light zone in which the rotating blade (34) does not block the passage of the light radiation.

7. Cutting unit (31) according to any one of claims 4 to 6, wherein the receiver (12) of the optical sensor (6) includes a matrix of light radiation sensitive elements (17) made up of at least two side by side arrays of light radiation sensitive elements (17).

8. Cutting unit (31) according to any one of the preceding claims, wherein the emitter (11) of said optical sensor (6) includes a light source (18) arranged in the U-shaped support (8).

9. Cutting unit (31) according claim 8, wherein the light source (18) emits the light radiation along a direction substantially radial with respect to said at least one rotating blade (34) towards one of the two opposed ends of the U-shaped support (8), the emitter (11) includingan optical deflecting element (19) which reflects the light radiation emitted by the light source (18) towards the other of the two opposed ends of the U-shaped support (8).

10. Cutting unit (31) according to any one of the preceding claims, wherein the processing unit (45) of the optical sensor (6) is configured to create a digital image of the edge development of the at least one rotating blade (34) by considering estimates of the position of the edge of the at least one rotating blade (34) for at least a full rotation of said at least one rotating blade (34); and analyse the digital image of the edge development of the at least one rotating blade (34) in order to detect characteristics of the at least one rotating blade (34).

11. Cutting unit (31) according claim 10, wherein the processing unit (45) of the optical sensor (6) is configured to analyse said digital image by carrying out filtering processes allowing to identify a proper measurement signal relating to the characteristics of the at least one rotating blade (34) and to distinguish it from numeric noise.

12. Cutting unit according to any one of the preceding claims, comprising a plurality or rotating blades (34) and a plurality of optical sensors (6) having the features of said optical sensor (6), each optical sensor (6) being coupled to one rotating blade (34).

13. Cutting unit according to claim 12, comprising an equal number of rotating blades (34) and optical sensors (6).

14. Cutting unit according to claim 12 or claim 13, wherein the optical sensors are supported by said support frame (43).

15. Cutting unit according to any one of the preceding claims, for an apparatus for working a sheet-like material (32) used for the production of electrodes for batteries.

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