CA2224816C - Ultrasonic cutting device - Google Patents

Abstract

An ultrasonic cutting device with an ultrasonic generator having a given natural frequency and being coupled to a cutting tool. The cutting tool is a revolving disc (5) and the ultrasonic generator (10, 11) is coupled to a central portion (4) of the disc (5) via a coupling means (30, 40), said central portion (4) being arranged on an amplitude antinode of the ultrasonic vibration generated by the ultrasonic generator (10, 11).

Description

ULTRASOUND CUTTING DEVICE
The present invention relates to a ultrasonic cutting device having a ultrasonic generator having a natural frequency given, coupled to a cutting tool.
The industrial division, particularly food products, can be achieved with the aid of a number of available techniques including traditional devices, such as guillotine cutting, or else devices that have been the subject of relatively recent developments, such as cutting food with a water jet supersonic. This last technique is done in.
particularly the object of an article by Jean-Luc BOUTONNIER, published in the ENIL Review (No. 163), pages 5 to 12.
Another known and relatively recent is that of the ultrasonic knife. In particular, a cutting unit which is described in the Application for Japanese Patent No. 4-75898, filed by NIGATA Company published on 10 March 1992, uses knives to ultrasounds that are animated by alternative movements, each knife being vibrated by a generator ultrasound that is simply coupled to one end of the blade of the knife so as to vibrate it.
A similar technique is described in the Application for Japanese Patent JP-122 2892, also of the Company NIGATA, published on 6 September 1989.
The technique of cutting with vibrating blades ultrasound allows to ensure a clean cut, but at the expense of speed, given that speed linear displacement of products and therefore the speed linear cutting is limited to a speed that does not hardly exceeds one meter per minute in practice.
The present invention relates to a ultrasonic cutting device not including the aforementioned drawback, and which in particular

two to achieve linear cutting speeds of several meters per minute, and up to 10 meters / minute.
Another object of the invention is a cutting device for cutting without removal of material.
Another object of the invention is a cutting device that can be used for products known to be difficult to cut, such as pastry, bread or even bread, found in the hot state at the exit of a baking oven.
Another object of the invention is a cutting device that can be easily cleaned, and which in particular can be cleaned in continuously, so as to allow division into high cleanliness conditions.
Another object of the invention is a cutting device having improved coupling between the ultrasound generator and the cutting tool.
The device according to the invention has a cutting tool that is a disk driven into rotation, and the ultrasound generator is coupled to a central region of the disc through a medium coupling, said central region being disposed on a amplitude belly of ultrasonic vibrations produced by the ultrasound generator according to a given mode.
The cutting device according to the invention therefore uses a conventional ultrasonic generator, and the coupling means according to the invention has the function of transform a movement directed along the axis of the disc into a movement that vibrates the surface of the disc perpendicular to this axis, either in a radial mode, preferably in a bending mode.
The coupling means comprises a bar whose the length is advantageously equal to half of the corresponding wavelength (; ~) for the material

3 dials the bar, at the natural frequency f of the generator ultrasound. Said bar has a coupled upstream end to the ultrasound generator, as well as a downstream end coupled to the disc, the bar having a non-section constant and decreasing from upstream to downstream. The bar preferably has an upstream region of length a./4, a downstream region of length X / 4, the region downstream having a constant section, less than that, also constant, from the upstream region.
The coupling means also comprises a coupling element of length λ / 2 which prolongs the bar. This coupling element may be a resonator cylindrical, the central region of the disc being then placed on a belly of longitudinal amplitude, to allow the preferred mode of excitation-disc by bending vibrations. According to a mode of preferred embodiment, the central region of the disk is advantageously arranged sandwiched between the end downstream of the bar and the upstream end of the coupling.
The invention also relates to a device characterized in that the cutting unit comprises a plurality of disks having at least one upstream disk coupled to the downstream end of the bar and a downstream disc coupled to the upstream end of said coupling element, the coupling element having a free downstream end, and in that the discs are spaced apart by intermediate coupling spacers so as to be arranged on bellies of vibrations inducing their displacement in bending mode.
The invention finally relates to a device characterized in that the cutting unit comprises a plurality of disks having at least one upstream disk coupled to the downstream end of the bar and a downstream disc coupled to the upstream end of said coupling element, the coupling element having a free downstream end, and

4 in that the discs are spaced apart by intermediate coupling spacers so as to be arranged with a pitch p substantially equal to a quarter of the wavelength and shifted one-eighth of a length wave compared to bellies of inducing vibrations their displacement in flexion mode.
It is particularly advantageous that the unit cutter has a central axis on which are mounted the spacers and the ultrasound generator and a clamping device cooperating with the axle to tighten the discs positioned between the spacers.
Discs may have recesses in ring retaining the symmetry of revolution of the discs. This allows to reduce the weight without altering the performance of the device.
The cutting unit may comprise a adjustment device, preferably individual, of the clamping force of the discs.
The device can be characterized in that that it has n said cutting units each having a plurality of discs spaced apart from each other by nxa and which are shifted relative to one another so as to produce cuts of equal thickness a.
Said given mode is preferably essentially free of flexing of the coupling elements, especially spacers.
According to a second variant relating to a excitation of the disk by radial vibrations, the coupling element is a profiled part whose diameter is preferably substantially equal to k / 2 and the central region of the disc is arranged on a belly of radial amplitude, that is to say on a node of longitudinal amplitude. In particular, the region central disk can be arranged between two regions of equal length of the profiled part, these so-called regions of equal length can then be symmetrical by compared to the disc, and present a diameter ranging decreasing as the distance to the disk increases.
The invention also relates to a use of the device as defined above, for cutting

5 products such as bread, bread, or bread.
pastry especially in the hot state, especially when leaving the oven of these products. The device according to the invention can also be used especially for the cutting of raw meat products or cooked, or cured products.
The frequency of the ultrasound generator is advantageously between 20 and 40 KHz and the speed rotation of the disc between 100 and 800 revolutions / minute.
The vibratory amplitude of the disc is advantageously between 15 and 25.
The linear speed of product displacement to be cut is advantageously between 2 and 10 meters / minute, which ensures industrial rates significantly improved compared to cutting tools at known ultrasounds, using a knife or a reciprocating saw.
The invention also relates to a method of ultrasonic cutting of a product, characterized in that that it implements a device as defined above.
above. According to a preferred embodiment, the cutting is carried out on a product coming out of the oven and in the state the cutting is followed by a conditioning of product, which makes it possible to obtain a very high quality of cleanliness. In particular, for products such as bread, we can avoid the step previously necessary cooling and bleeding that involves a long time during which the product is exposed in the open where microbial contamination, weight loss of the product, a mellow loss of this one, and the need to submit the product before

6 drying at a specific decontamination stage to ensure its subsequent conservation.
Other features and benefits of the invention will appear better on reading the description which will follow, given as an example not in the drawings annexed hereto, in which :
- Figure 1 shows schematically the process according to the invention applied to the manufacture of soft bread ;
FIGS. 2a and 2b represent respectively an ultrasound generator and the respective diagrams of stress and elongation;
- Figure 2c represents the generator of ultrasound of FIG. 2a to which is attached a bar amplifier for amplifying the amplitude of ultrasonic vibrations, this figure representing also the diagrams of the constraints and corresponding amplitudes;
FIGS. 3a, 3b and 3c represent respectively a preferred embodiment of cutting device according to the invention, flexion excitation of a disk, a mode of embodiment of the device according to the invention, a radial excitation of the disc, and finally the diagrams illustrating the longitudinal and radial along the aforementioned cutting device;
FIGS. 4a and 4b show two multilane cutting unit variants according to the invention, FIG. 5 represents a first mode of realization of a multi-blade cutting unit according to the invention, - and Figure 6 represents a mode of preferred embodiment of a multi-blade cutting unit according to the invention.

7 The subject of the invention is therefore a device for cutting that is usable under conditions of relatively difficult cutting, especially in the case of pastry or sandwich bread coming out hot from oven. We know that it is particularly difficult example, to cut thin slices into a bread of which has just been cooked. In practice, you have to let it rest, during a step called bleeding, up to 24 hours and during which the bread looses some of its moisture.
The bread is then cut and put in sachet.
This operation has the disadvantage, besides exposing the product in the open and contaminate it, to drive to a less mellow product than if it could have been cut off immediately and, although subject to specific decontamination step, the duration of which conservation is relatively limited. As we will show in the following description, the fact of cut the product in the hot state and bag it immediately afterwards, avoids all disadvantages mentioned above and leads to a product whose organoleptic qualities are improved and the duration conservation is significantly increased.
Cutting difficulties can be explained as follows.
When a blade enters a material with a certain speed and some mass, we can consider that there are essentially two types of phenomena that have been described by the authors DAURSKIJ
and MATCHIKHINE:
- establishment of a constraint that distorts the product, then causes it to break, - contact between two animated entities of opposite relative movements, hence the appearance of friction that tend to slow the entry of the tool in the product.

8 The cutting of a solid material is obtained at following three phenomena occurring successively, namely an elastic deformation, a deformation plastic and the propagation of a breaking line.
Three notions are therefore essential for describe the different deformation behaviors of solid materials.
- elastic deformation. the deformation is reversible, - plastic or viscous deformation. the deformation is irreversible and the material flows through sliding layers on each other. For the most of the solid materials, this phenomenon is reflected by a flow from a certain number of stress greater than the limit of their elastic phase, - break: if we continue to increase the strain or deformation of the material while it is in its plastic or viscous phase, the sliding of the layers relative to each other, and there comes a time when some layers do not touch more and where a crack appears. This crack whose propagation is done according to very strict laws complex leads to break through the entire thickness of the material.
Achieve controlled breaking of a material is the goal of cutting.
In the elastic phase, energy is stored and it is completely restored as soon as the constraint vanishes so that the material recovers its initial form.
In the viscous or plastic phase, energy is used to deform the material by sliding layers on each other and she is therefore consumed to overcome the frictional forces and the deformation persists when the stress or deformation ceases.

WO 97/0015

9 PCT / FR96 / 00932 In the breakup phase, energy is used to advance the crack and she is so completely consumed by creating new surfaces.
When making a cut, we apply to material, for a very short time, a constraint greater than its breaking strength. We do not take always consider the parameters characterizing the phase elastic because it is often negligible in front of the plastic phase and this especially as the deformations are fast. The most parameters important are those that characterize the phase flow of the material.
In practice, the three phases, elastic, plastic and rupture, always succeed one another when one performs the cutting of a solid material, but their manifestation is more or less visible depending on the nature of the material. For example, agar has essentially a elastic behavior, butter has essentially a plastic behavior and chocolate has basically a fracture propagation behavior.
In most materials, you often have a combination of these three typical behaviors.
When cutting, we want to remain master of the geometry of the cut line to get pieces of desired shape. Now, it happens that for a material given, one does not always control its deformation for a given level of constraint. This is all the more true for many food products characteristics evolve over time before reaching a state of equilibrium. In addition, the appearance of cracks within the material remains quite random. To avoid this is usually done by erosion or abrasion, that is, using a tool cutting edge whose best example is the saw. The cutting edge is machined perpendicular to the tool and one thus proceeds by surface deformation of small amounts of material, which is easier to mastering, but then there is cutting with removal of material.
5 With a sharp tool, we therefore apply very quickly to the material a stress greater than its breaking strength and it occurs at every point located on the cut line a succession of three phases of deformation, elastic, plastic and rupture,

10 but during the duration of the division, these three phases coexist throughout the thickness of the material.
If we stick to the case of sandwich bread out of the oven, we see that this product is difficult to be sliced thin because of the fact that tends to become sticky and cause fractures irregular by blocks.
The interest of the cutting technique ultrasound according to the invention as described below is to change this behavior and allow, thanks to the implementation of a tool, circular preferably, devoid of teeth, and put into vibration, to arrive at a regular spacing of the cutting material and a free cutting of the product preferably without removal of matter. The cutting is performed by a disc which is always rotating avoids the disadvantages of ultrasonic knives which, given that they are subject to a reciprocating movement, have a proper speed which vanishes with each reversal of the direction of movement, this which constitutes a major disadvantage in the case of products "sticky" that tend to quickly foul the blade of the knife, which can not be cleaned without interrupt the cutting.
In accordance with Figure 1, products such that breads, designated by general reference 1, are cooked in an oven 2 then are brought on a advance device 3, such as a treadmill, is

11 moving longitudinally in the direction of arrow F1 to a cutting installation with one or several discs 5 rotated in the direction of the arrow F2 around their central part 4.
The installation may include a device for guillotine cut 6 actuated in the direction of the arrow F3 and intended to perform a transverse slicing in upstream or, as shown, downstream of the disk 5.
product cut in the hot state is then placed on a second feeding device 7 to an installation bagging 9 during which products 1 are packaged in sachets 8.
The rotary disk 5 is subjected to ultrasonic vibrations generated by a device that will be described below and which makes it possible to reach high linear speeds of the transport device 3, while allowing a slice of thin slices in bread rolls coming out of the oven.
It will also be noted that the disk being in contact with the product to be cut only on a part of its circumference, it can be cleaned and / or permanently disinfected by a device 50 known in itself.
Figure 2a shows a transmitter ultrasound known per se, designated by the general reference 10. It consists of a ceramic sandwich piezoelectric 11, consisting for example of two disks, prestressing between two metal masses, namely a roof 12 and a counter-mass 14. The whole vibrates in mechanical resonance with electrical excitation supplied by generator 11. For this purpose, ceramics an alternating voltage dV to which corresponds an alternative variation of electric field dE, resulting in an alternative thickness variation ceramics dT. With each variation of thickness dT
corresponds then a pressure variation dP.

12 The application of an alternating voltage dV to the terminals of the transmitter thus formed induces pressure waves which, from the two ceramic discs, reflect at the ends 16 and 18 of the transmitter.
If we size the length of a bar to a value such as the frequency of vibrations longitudinal lines of it exactly correspond to the frequency f of electrical excitation, the bar becomes the stationary wave seat and vibrates in resonance with electrical excitation. This condition is obtained for a bar 10 whose total length, between end faces 16 and 18, is equal to ~, / 2, k designating the wavelength in the bar corresponding to the frequency f. Ceramics 11 are arranged in the center and the flag 12 and the counter-mass 13 are arranged symmetrically on both sides of ceramics 11.
Like the vibrations of the transmitter 11 that one can get in practice are in the range of 10 to 14 crest to peak depending on the type of generator used, it amplification of these vibrations for obtain sufficient amplitudes.
For this purpose and as shown in FIG.
2c, we attach to the transmitter a metal bar of length k / 2 tuned to the natural frequency of the transmitter for example 20KHz. The bar 20 comprises a first section 22 of length X / 4 having a section constant S1 which is more important than the section also constant S2 of the second section 24, also of length k / 4. The face 26 of the section 22 is contiguous to the face 18 of the counter-mass 14. The diagram of amplitudes and constraints is shown in the figure 2c, on which the movement of the face 16 is represented by the curve x0, the movement of the faces 18 and 26 by the curve x1 and the movement of the face 28 of the section 24 by the curve x2.

13 We have seen previously that the transmitter-amplifier produces ultrasonic vibrations longitudinal. The disc 5 can not be excited unless from its center 4, that is to say from its axis of rotation, it is imperative to transform the movement axial axis in radial motion oriented in the plane of disk.
According to the invention, two embodiments are envisaged.
According to Figure 3_ci, disk 5 is sandwiched between the face 28 of the section 24 and the face 32 of a resonator 30 which is a cylindrical bar of length k / 2 which ends with an end face.
34. The bar 30 acts as a resonator and its role is to ensure the return of waves under the conditions mechanical resonance of the whole. The transformation of movement is ensured by the fact that the disc 5 is located, as shown by the amplitude al curve longitudinal, on a belly of longitudinal amplitude vl. It vibrates according to a bending mode regardless of its diameter. In practice, its thickness remains between 2 and 4 mm in order to stay as close as possible to theoretical point of belly of longitudinal amplitude Vl and to allow maximum deformation in flexion. We have represented in box the enlarged profile of the edge of the disc 5. In the vicinity of the edge of the disc, the thickness decreases as you get closer to the edge of the disc, it being understood that for cutting without removal of material, the profile is smooth and devoid of teeth.
The embodiment of FIG.
implement an element 40 intended to ensure the transformation axial movement in radial motion. It is fixed at neighborhood of a belly of radial amplitude Vr corresponding to a node of axial amplitude. The element 40 is generally cylindrical in shape and has a upstream section 46 whose face 42 is contiguous to the face 28

14 of the section 24 and a downstream section 48 having a face 44. The disk 5 is arranged in the center of the element 40 between two crown regions 45 and 47 in diameter larger than that of regions 46 and 48 to which they are connected by rounded profiles 41 and 43.
Regions 46 and 48 are larger in diameter than region 24, and in the example shown, substantially equal to that of region 22. The length of the element 40, between these faces 42 and 44 is equal to X / 2 and the disc 5 is therefore disposed at a distance A / 4 from the 28. In these circumstances, it is fixed in the neighborhood a belly of radial amplitude Vr, as shown in curve ar of Figure 3c. In practice; a conical profile should be adopted for a thickness at the base of the order of 10 mm. Regions 45 and 47 of element 40 have a diameter close to X / 2, which creates radially resonance conditions. That is what makes it possible to obtain a sufficient radial amplitude for excite the disc 5.
With regard to materials, parts 12, 14, 20 and 30 can be advantageously realized made of titanium alloy TA6V which presents excellent elastic properties and which, being biocompatible, is therefore chemically inert with respect to products cut. In addition, this alloy is stainless, easily machinable and affordable for applications to consider.
With regard to disc 5, the alloy mentioned above can of course be advocated but, it is better to use for this wear part which is likely to be replaced, a less expensive alloy such as a stainless steel alloy of the type used to classic cutting tools, especially the Z200C13 alloy that combines all the qualities sought to know. chemical inertness, machinability, high hardness and acceptable cost. Its properties elastics are lower than those of the alloy of titanium but are sufficient for the application to consider.
As an indication, it will be recalled that the speed 5 of the sound in TA6V alloy is 4900 meters / second then that it is 5200 meters / second in stainless steel Z200C13.
The tests carried out show that the systems which operate in the flexion mode (Figure 3a) have 10 a resonant frequency set imposed by the terminal resonator 30. As a result, the diameter of the disk 5 has little influence on the overall frequency. Its thickness should be taken into account as it is integral part of the axial stack, transmitter,. 10

Amplifier 20 and resonator 30.
In bending mode, a cutting disc of diameter 600 mm can cut a product of 280 mm height. It is possible to cut products even higher, to the detriment of cutting finesse, since in this case, it is necessary to increase the thickness of the blade.
In contrast to the flexural assembly, the assembly radial mode, shown in FIG. 3b, presents a resonance frequency that depends on the diameter of the disc 5. For example, the resonant diameter at 40KHz is around 200 mm.
Figures 4a and 4b show two machine variants allowing more particularly slicing bread products or Viennese pastries, for example for slicing a sandwich bread whose height is approximately 120 mm, the thickness has slices to achieve being 12 mm 1 mm.
In practice, it takes about twenty blades.
This configuration is however difficult to implement because a 300 mm diameter blade and 2mm thick has a mass of about one kilogram

16 for 20 blades you have to vibrate 20 kg that go spread over the diameter.
Two possibilities are envisaged as example of the invention:
- have several blade systems (61 to 64) equipped with as many ultrasonic generators (65 to 68) with an inter-blade gap of 12 mm (Figure 4a), - have n blade systems (71 to 75) equipped with as many ultrasonic generators (76 to 80) with an inter-blade gap of nx 12 mm (Figure 4b where n = 5).
In the first case (Figure 4a), there is no offset the cutting edge between each slice. This solution, however, presents a problem of implementation ultrasound because the inter-blade distance of 12 + 1 mm is in direct relation with the frequency of the excitation of the system. This brings this inter-axis of 12 mm to a frequency above 100 kHz, frequency too high to ensure a vibratory power transfer effective on blades that are disks 5.
In the preferred case (Figure 4b), the blades (discs 5) being staggered, the cutting edge is no longer parallel and may pose difficulties when the commitment of the product. However, the gap between the discs 5 allows to use a lower frequency more compatible with the dimensions of the disks 5.
Difficulties that may arise during the commitment of bread are not important. Attempts on the single-disc prototype showed a penetration of the blade in the bread significantly improved by the presence of ultrasound. For systems with sufficient nested, the bread does not separate untimely. Of Moreover, ultrasound greatly reduces the coefficient of apparent friction of the material on the discs vibration so a priori the disks 5 have no tendency to remember the bread during its passage.

17 In the case of Figure 4a, as well as FIG. 4b, the set of disks 5 of each unit of cutting is coupled to the same axis set in vibration by an ultrasound generator. The discs 5 are positioned at a belly of longitudinal vibrations (or near a belly of vibrations). It is necessary to regulate clamping force of the discs 5 so as to ensure a good ultrasound coupling and in particular a homogeneous displacement amplitude on all disks, which can be advantageously obtained by a setting individual tightening of the disks 5, for example the flanges 92 are threaded and can be tightened on the centering region 98 itself threaded.
As shown in Figure 5, the disks are mounted on an axis 97 via spacers 90 that slide along axis 97 and that come take the discs 5 sandwich, a tightening of the assembly being provided by means of a plug 99 so as to get a good hold of the discs 5 and a surface of increased transmission in contact with disks 5.
There are several modes to do work the discs 5 in bending. For a distance inter-blades 60 mm, a first mode is around 30kHz and allows from a good displacement in translation to level of the spacers 90 to induce a movement of bending of disks 5.
The second mode, which is around 36 kHz, in contrast, the bending of the spacers 90 in contact with the discs 5.
From experience, it can be seen that when the ultrasound transmission is via bending interfaces, the transmission is lower quality. Indeed, as the link is not perfect, the different parts are not intimately linked.

18 So the mode around 30 kHz is essentially devoid of bending of the interface 90 which is preferred.
It is found that identical spacer, the mode operated for a 2- to 4-blade system remains unchanged almost at the same frequency. We can observe that system designed for even (or odd) number of blades remains usable for a higher or lower number of blades as soon as this number remains even (or odd).
The shape of the blade has some influence on the frequency: the more it is light and more importantly elastic, the lower the frequency is appreciable.
The diameter of the blade being fixed at 300 mm, one can lighten the disc 5 by regularly evading next rings 101 (see box in Figure 5). The blade in disc shape remains symmetrical of revolution.
The blade thickness of 2.5 mm at the beginning, is set at 2 mm for mass reasons to vibrate and improved elasticity.
Regarding the influence of distance inter-blades, we observe the following points:
- with the envisaged blades (0 300 -thickness 2 mm), we can work without much problem with an interlam distance of 48 mm (a step of 50 mm) - the smaller the inter-blade distance, more dissymmetry of the spacer is to take in account. both ends of the spacer move closer to each other and it is harder to place a node (equilibrium) equidistant from these past, - the smaller the inter-blade distance, the number of blades to be used per system is important. Depreciation and losses not taken in account in the calculations can become preponderant and

19 risk of causing a significant malfunction of the extreme blades.
It will be possible in practice to use spacers 90 having straight tubular shapes, provided with their ends of complementary collars 91 and 92 centering on each other and also centering the discs 5 (Figure 5). The blades 5 shaped discs are regularly spaced so as to be within bellies of vibrations, corresponding to a vibration of the disks 5 in bending mode.
It is particularly advantageous to mechanically decouple the ultrasound generator (11, 12, 14) and the tool carrier (97, 90, 5) of the maintaining and rotating part of the cutting, for example by coupling the device of maintaining and rotating in the housing of the ultrasonic generation transducer. In this way, the part put in excitement is much shorter, the ultrasound excitation is more direct, which allows to minimize the loss of ultrasound in the media (such bearings and belts) between the device exciter and disks 5, and further disassembly is easy for both cleaning and repair.
The case of an odd number (5 blades) implies dimensional changes on the first 94 and the last 95 spacers that are, anyway, geometrically different from others by their support ultrasonic generator side (14, 11, 12) and plug side 99 (end of the tool).
The exciter + tool set is composed an ultrasonic motor (14, 11, 12, cf.
Fig.3a) - a mechanical adaptation part (amplifier) 24, - an axis 97 which is fixed in the amplifier 24, - 5 disc-shaped blades 5, a spacer 94 on the generator side ultrasound, - 4 spacers 90 ensuring spacing 5 blades of 48 mm edge to edge (50 mm center to center), a plug-side spacer 95 which can be integrated in the plug 99, this spacer being dimensioned to ensure the return of wave, - a plug 99 which is on the axis 97 10 allowing the clamping of the assembly.
The nominal operating frequency is 32.2 kHz.
On all these parts are provided elements centering, surface finishes and tolerances 15 rigorous in order to allow the best quality of assembly and assembly.
The identification of a nodal plane 21 in the 22 amplifier part allows to come fix if needed is, a stainless steel plate that will isolate the area of

20 slicing for ultra-cleanliness issues.
We can consider working for example with units of 7 blades of outer diameter 210 mm with an inter-blade distance of 36 mm or even with units of 11 blades of outside diameter equal to 150 mm with an inter-blade distance of 24 mm, the frequencies being in both cases for example included between 35 and 40 kHz for a pitch of the blades substantially equal to half a wavelength.
An embodiment for lowering the operating frequency consists of arranging the blades or discs 5 with a constant pitch p substantially equal to a quarter of a wavelength, these being at this longitudinally offset effect of about one-eighth of wavelength (X / 8) compared to the bellies of longitudinal vibrations (see Fig. 6). With a step

21 50 mm, the frequency is of the order of 22 kHz, for the example shown in FIG.
To determine a multi-blade unit, one chooses the diameter of the blades, their pitch and the geometric characteristics of the parts that compose it (spacers, etc ...). A calculation for example by the finite element method, allows to determine the value of the wavelength X corresponding to the structure. This wavelength ~ depends on the parts configuration, that is to say that in its determination occurs a form factor. In in particular, the cutting unit shown in FIG.
uses tubular struts 90 and a rod 97 tightened by a plug 99, this situation affecting the value of the wavelength.

Claims (19)

1. Ultrasonic cutting device comprising at least one cutting unit comprising a ultrasonic generator having a natural frequency given, coupled to at least one cutting tool, unit of cutting in which the cutting tool is a disk (5) driven in rotation, and in that the generator ultrasound (10, 11) is coupled to a central region (4) of the disc (5) via a coupling means (30, 40), said central region (4) being disposed on an ultrasonic vibration amplitude belly produced by the ultrasonic generator (10, 11), according to a given mode or in the vicinity of said belly, characterized in that the coupling means comprises a bar (20) whose length (.lambda./2) is equal to half of the wavelength (M corresponding to the natural frequency F
of the ultrasonic generator (10, 11), and having a upstream end (26) coupled to the ultrasonic generator (10, 11) and a downstream end (28) coupled to the disc (5), the bar (20) having a non-constant section and decreasing from upstream to downstream and in that the means coupling also comprises a coupling element (30, 40, 95) of length .lambda./2 which extends the bar of so as to ensure the return of waves. 2. Device according to claim 1, characterized in that the bar (20) has a region upstream (22) of length .lambda./4 and a downstream region (24) of length .lambda./4, the downstream region (24) having a section constant less than that, also constant, of the upstream region (22). 3. Device according to one of claims 1 or 2, characterized in that the coupling element (30) is a cylindrical resonator and in that the region center (4) of the disc (5) is arranged on a belly of longitudinal amplitude, sandwiched between the end downstream (28) of the bar (20) and the upstream end of the coupling element (30). 4. Device according to claim 3, characterized in that the cutting unit comprises a plurality of discs (5) comprising at least one disc upstream coupled to the downstream end (28) of the bar (20) and a downstream disc coupled to the upstream end of said element coupling element (95), the coupling element (30) having a free downstream end, and in that the discs are spaced apart by coupling spacers intermediaries (90) so as to be arranged on antinodes of vibrations inducing their displacement in mode bending. 5. Device according to claim 3, characterized in that the cutting unit comprises a plurality of discs (5) comprising at least one disc upstream coupled to the downstream end (28) of the bar (20) and a downstream disc coupled to the upstream end of said element coupling element (95), the coupling element (30) having a free downstream end, and in that the discs are spaced apart by coupling spacers intermediaries (90) so as to be arranged with a pitch p substantially equal to a quarter wavelength and shifted by substantially one eighth of a wavelength compared to antinodes of vibrations inducing their displacement in flexion mode. 6. Device according to one of claims 4 or 5, characterized in that the cutting unit comprises a central axis (97) on which are mounted the spacers (90) and the ultrasonic generator (11, 12, 14) and a clamping device (99) cooperating with the axis (97) to clamp the discs (5) positioned between the spacers (90). 7. Device according to one of claims 4 to 6, characterized in that the discs (5) have ring recesses retaining rotational symmetry some discs. 8. Device according to one of claims 4 to 7, characterized in that it comprises a device (99) adjustment, preferably individual, of the strength of tightening the discs (5). 9. Device according to one of claims 4 to 8, characterized in that it comprises n said units of blank each having a plurality of spaced discs between them of nxa and which are staggered one with respect to the other so as to produce cutouts of equal thickness a. 10. Device according to one of claims 4 to 9, characterized in that said given mode is essentially devoid of bending of the coupling elements. 11. Device according to claim 1, characterized in that the coupling element is a part profile (40) extending radially and in that the central region (4) of the disc (5) is arranged on a belly of radial amplitude and in that the region center (4) of the disc (5) is arranged between two regions of equal length of the shaped piece (40). 12. Device according to claim 11, characterized in that said two regions of equal length are symmetrical with respect to the disc (5) and have a diameter that decreases when the distance to the disc increases. 13. Device according to one of claims 11 or 12, characterized in that the profiled part (40) has a diameter substantially equal to .lambda./2. 14. Use of the device according to one of the preceding claims, characterized in that the product to be cut is bread, sandwich bread, or pastry, especially when hot. 15. Use of the device according to one of the preceding claims, characterized in that the product to be cut is a raw or cooked meat product, or quite a curing product. 16. Use according to one of the claims 14 or 15, characterized in that the frequency of the ultrasound generator (10, 11) is between 20 and 40KHz, and in that the disk rotation speed is between 100 and 800 rpm. 17. Use according to claim 16, characterized in that the vibratory amplitude of the disk (5) is between 15 and 25 microns. 18. Use according to one of the claims 16 or 17, characterized in that the linear speed of movement of the product to be cut (1) is between 2 and 10 m/min. 19. Ultrasonic cutting process of a product, characterized in that it implements a device according to one of claims 1 to 13, and in that that the cutting is carried out on a product leaving the oven and in the hot state and in that the cutting is followed by packaging of the product before its cooling.