BALANCING SYSTEM FOR MICRO SAW

Description

Technical field of the invention

[0001] The present invention relates to the field of micro-saws intended for dental or surgical applications, i.e. handpieces provided with cutting tools. It relates more specifically to a balancing module intended for such a micro-saw. State of the art

[0002] Motorized handpieces are known that have an integrated motor that generates a linear reciprocating saw motion; the Stryker "Core Reciprocating Saw" product is an example of such a micro-saw with a cutting tool that performs reciprocating movements with a stroke of approximately 3 mm and a frequency of between 10,000 and 30,000 revolutions per minute depending on the motor speed. This product was also the subject of a US patent US4036236, which has now expired.

[0003] According to this solution, the rotary movement of the motor is transformed into reciprocal linear movement of a blade holder via a finger mounted on ball bearings oriented off-axis relative to the transmission axis.

[0004] A disadvantage of this solution is the generation of a high level of vibrations that are transmitted directly to the practitioner's hand due to the significant and periodic displacement of the center of mass in the handpiece. In addition, vibrations limit cutting efficiency, which levels off with increasing speed and power applied to the motor; in fact, due to the increase in vibrations, efficiency decreases with increasing power. Cutting precision and speed are therefore limited by the displacement of the center of mass of the transmission shaft-clamp-blade system.

[0005] In the surgical field, for cutting bones, saws are also known, for example from patent US5725530, which operate in the manner of a chainsaw, i.e. based on one or more flexible strips provided with abrasive teeth, and which are rotated, for example in pairs in opposite directions around rigid fixed guide parts. This solution is however not suitable for high-precision operations involving reduced dimensions, and the configuration of the cutting tool also greatly reduces the maneuverability of the tool.

[0006] Still in the surgical field, solutions are also known using several blades driven in antagonistic movements in order to compensate for vibrations, such as the solution described in international application WO97 / 10765. This solution is however relatively complex to implement and is quite cumbersome in terms of the working area of ​​the tool.

[0007] Patent document US2015 / 066032 also describes a cutting tool to which both a low-frequency reciprocating movement and very high-frequency ultrasonic vibrations are imparted. A conversion element provided with oblique grooves in which drive pins are positioned makes it possible to impart a reciprocating movement respectively to a blade drive cylinder and together with a countermass cylinder. A disadvantage of this type of tool, however, is that the integrated balancing device does not allow any decoupling between the motor part and the blade drive part.

[0008] The solution disclosed in the much older document US3642002 concerns a surgical tool provided with a connecting rod system connected to the rotor secured to a motor shaft, and in which the rotor is provided with a counterweight. A disadvantage of such a solution is that the counterweight is integrated directly into the motor part, which affects its performance and again prevents any modular configuration of the balancing device. There is therefore a need for a solution free from these known limitations. Summary of the invention

[0009] An aim of the present invention is to propose a new micro-saw for dental or surgical use, the balancing of which is carried out in a simple and efficient manner, and also allowing decoupling of the motor part from the handpiece.

[0010] Another aim of the present invention is to propose a new micro-saw for dental or surgical use with minimal bulk, and requiring the minimum of adaptations compared to existing solutions.

[0011] According to the invention, these aims are achieved by means of a cutting device for surgical or dental use comprising a motor and a handpiece equipped with a transmission module for a cutting tool, the motor being connected to the handpiece, and the transmission module comprising: a motor coupling part arranged to be driven in rotation by the motor; a kinematic chain transforming the rotary movement of the motor into a first linear reciprocating movement of a blade holder via a rotary transmission shaft provided with an eccentric.

[0012] The transmission module is characterized in that it further comprises a countermass arranged so as to move according to a second linear reciprocating movement synchronized with the first linear reciprocating movement of the blade holder, and in the opposite direction to the latter.

[0013] An advantage of the proposed solution is to reduce the level of vibrations without requiring the implementation of a complex solution, nor generating significant additional space requirements either at the level of the handpiece or the working area of ​​the cutting tool.

[0014] Another advantage of the proposed solution is to offer a modular construction of a transmission-conversion system guaranteeing both sufficient connection strength between the handpiece and the motor at the operational level, but also easy disassembly to use the motor part in combination with other surgical tools.

[0015] According to a preferred embodiment, the first kinematic chain of the transmission module comprises a first drive finger for the blade holder mounted on a first part of the eccentric, as well as a second drive finger for the countermass mounted on a second part of the eccentric.

[0016] An advantage of this solution is that it can be easily integrated into existing solutions, simply by doubling the fingers, and without having to create parallel transmission mechanisms for the counter-mass, which could be the source of parasitic vibrations that do not effectively reduce vibrations, but are likely to increase them.

[0017] According to an even more preferred embodiment, the eccentric is arranged symmetrically in a “V” shape, the first drive finger of the blade holder is mounted on a first series of bearings around the first part of the eccentric and the second drive finger of the blade holder is mounted on a second series of bearings around the second part of the eccentric.

[0018] An advantage of this solution is that it is possible to use a conventional form of eccentric in the transmission kinematic chain and only requires the addition of a second finger mounted symmetrically on a series of bearings to generate the reverse synchronized movement of the countermass. This makes the integration of the countermass actuation system particularly simple on the same kinematic chain and with minimal bulk.

[0019] According to another preferred embodiment, the geometric shape of the counterweight is adapted to that of the cutting tool and the blade holder, which provides maximum flexibility in the design of the balancing system. Preferably, the counterweight will thus be cylindrical to correspond to a blade holder in the form of a shaft which is also cylindrical.

[0020] According to another preferred embodiment, the countermass is guided axially along a transmission axis corresponding vectorially to the direction of longitudinal movement of the blade holder and the cutting tool by at least one axial guide element inserted into at least one guide orifice made in the countermass.

[0021] A technical advantage of this solution is that it can best compensate for the vibrations generated by the back-and-forth movements of the cutting tool driven by the blade holder, which is generally also guided in this direction. The vibrations are thus confined to a single direction, and the self-balancing operation is easier without having to control unwanted movements.

[0022] According to an even more preferred variant corresponding to this embodiment, the axial guide element is formed by a first axial guide rail and a second axial guide rail connecting in parallel a first part of the chassis connected to the motor to a second part of the chassis supporting and axially guiding the blade holder of the transmission module, the first axial guide rail and the second axial guide rail being inserted into respective guide holes of the counterweight.

[0023] The additional technical advantage of this variant is that it can maximize the guiding properties of the countermass, on the one hand, and on the other hand, free up space in the center to accommodate a coupling shoe for the blade holder. Furthermore, the fact that the rails act both as guide pins for the countermass and as a connecting element for the transmission module frame makes it possible to reduce the number of parts required for its production, and therefore to reduce manufacturing costs.

[0024] According to yet another preferred embodiment, the cutting device for surgical or dental use according to the invention is characterized in that the transmission module further comprises a cooling device for the counter-mass.

[0025] An advantage of this solution is that it can optimize the balancing of the device obtained via the countermass by minimizing the undesirable effect of heating resulting from friction when the kinetic energy of the overall system increases.

[0026] According to an even more preferred embodiment for producing such a cooling device, the first axial guide rail comprises a first integrated cooling duct and / or the second axial guide rail comprises a second integrated cooling duct.

[0027] An advantage of this solution is that it can directly combine the cooling mechanism into the guide elements, which minimizes the overall size of the system, which thus does not require any dedicated parts to perform this additional technical cooling function, which is carried out by elements directly integrated into the chassis and which thus allow other functions to be performed simultaneously.

[0028] According to yet another preferred embodiment, the transmission module is removably connected to the motor, and the weight of the counterweight is determined to be greater than a defined minimum value relative to the combined weight of the blade holder and the cutting tool as a function of the disconnection force of the transmission module from the motor, the stroke of the cutting tool, and the oscillation frequency of the reciprocating movement of the cutting tool.

[0029] According to another preferred embodiment, the weight of the countermass is determined so as to be less than a predefined value determined by a thermal balance.

[0030] An advantage of each of these two solutions is that they allow the definition of counter-masses whose weight is not necessarily equal, but preferably less than the assembly formed by the cutting tool and the blade holder. It is thus possible to reduce the dimensions of this counter-mass and minimize the overall size of such a self-balancing system, while maximizing the design level of the system according to the needs, depending on whether one prioritizes, for example, the reliability of the motor coupling compared to the level of heating during use depending on the operations to be carried out.

[0031] Thus, according to yet another particularly preferred embodiment, the weight of the counterweight is simply between 25% and 50% of the combined weight of the assembly formed by the blade holder and the cutting tool, which constitutes an optimum in terms of coupling reliability and heating during use.

[0032] According to yet another preferred embodiment, the density of the counter-mass is greater than 7000 kg per cubic meter, which makes it possible to further reduce its volume and therefore its size for a given weight, and consequently to minimize the level of friction and heating generated during use.

[0033] According to yet another preferred embodiment, the motor coupling part of the transmission module consists of a grooved orifice, which cooperates with a standard coupling nose of said motor comprising a series of grooves in which O-rings are inserted.

[0034] Such a configuration of the transmission module allows coupling with any standard dental or surgical micromotor, without requiring any adaptations of the latter. Thus, the proposed solution resolves any problems of incompatibility that may have arisen.

[0035] Furthermore, since precisely the transmission module is compatible with any type of usual micromotor, and since a handpiece comprising such a transmission module can therefore be sold independently of the “motor” parts to which they can be easily coupled and decoupled, the present invention also relates to such handpieces provided with such transmission modules taken independently of the motor. Brief description of the drawings

[0036] Other advantageous characteristics will emerge more clearly from the following description of a particular embodiment of the invention given by way of non-limiting example and represented by the appended drawings, in which: there figure 1 illustrates a side view of the functional parts of a surgical or dental cutting tool according to the present invention, namely the micromotor and the handpiece / micro-saw; the Figures 2A and 2B respectively illustrate a three-dimensional profile view of a standard micromotor intended for dental or surgical applications and a sagittal sectional view of its coupling nose; the figure 3 is a perspective view of a cutting tool for surgical or dental use according to a preferred embodiment of the invention, provided with a transmission module balanced by a short counter-mass; the figure 4is a perspective view of a transmission module for a cutting tool for surgical or dental use according to another preferred embodiment of the invention, in which the counterweight is long; the Figure 5 is an exploded perspective view of the transmission module for a cutting tool for surgical or dental use according to the preferred embodiment of the figure 3 ; there figure 6 is a sagittal sectional view of the transmission module illustrated in the figures 3 And 4 ; THE Figures 7A and 7B are respectively a top view and a sagittal section of the transmission shaft, the eccentric and the fingers for activating respectively the blade holder and the counterweight according to the preferred embodiment described with the aid of the preceding figures; figure 8is a three-dimensional profile view of a transmission module for a cutting tool for surgical or dental use according to a preferred embodiment with a long counterweight, and which is also provided with an integrated cooling mechanism. Detailed description

[0037] There figure 1 shows a side view of the functional parts of a surgical or dental cutting tool according to the present invention, and comprises, as for a conventional dental handpiece, a first part containing the motor and another constituting the handpiece itself, that is to say the part which is manipulated by the dental surgeon.

[0038] So on the figure 1we can distinguish, on the right of the figure, the micromotor 10, as well as its coupling nose 11 conventionally comprising a series of grooves in which O-rings are arranged for the transmission of a rotary movement materialized by the arrow R in this same figure. Figure 2A represents such a micromotor 10 in perspective, and which resembles in all respects a usual micromotor 10 for handpiece with a short coupling nose 11 on which are arranged O-rings 111 housed in the series of grooves 110 visible on the Figure 2B which shows the detail of the coupling nose in sagittal section.

[0039] On the left of the figure 1, we can distinguish the casing of the handpiece 4, that is to say its outer casing, enclosing the transmission module 2 described later. This transmission module 2 makes it possible to transform the rotary movement imposed at the inlet of the handpiece 4 into a back-and-forth movement M1 of a cutting tool, not shown in this figure, and which will be referred to in what follows as the “first” back-and-forth movement M1 as corresponding to that of the blade holder 27, that is to say the element carrying the cutting tool 3. These two elements are shown later on the figure 3 showing an overview of the transmission and self-balancing mechanism according to a preferred embodiment for the present invention.

[0040] At the left end of the handpiece 4 is shown a clamping device 6 for the cutting tool 3, which is provided with a fin corresponding to an integrated irrigation channel 61 intended to supply the surgically treated area 61 with physiological liquid, so as to minimize heating on this area. The solution of coupling a cutting tool to a transmission mechanism as described for example in the European patent EP2316356 of the applicant may for example be very suitable for mounting the cutting tool 3 within the scope of the present invention, and for this reason, no further details will be provided in the following concerning these aspects of fixing the cutting tool 3 to the transmission module 2 of the handpiece 4.

[0041] The modular construction thus proposed, with a handpiece 4 carrying the cutting tool 3 to form a micro-saw removable from the micromotor 10, therefore offers on the one hand the possibility of using the same surgical micromotor 10 not only in combination with the handpiece 4, but also with any other mechanical handpiece available in a hospital or medical practice (for example implantology contra-angles); on the other hand, it makes it possible to ensure a more efficient cleaning, decontamination and sterilization process of all the elements of the handpiece 4, in particular the components in contact with the irrigation liquid, therefore in indirect contact with the patient. In fact, the possibility of disconnecting the handpiece 4 from the motor makes it possible to better clean the handpiece 4 manually or to use dedicated positions when cleaning in a washing machine or in a thermo-disinfector.

[0042] There figure 3illustrates in more detail the transmission mechanism according to a preferred embodiment for the invention, in which the countermass 5 used is a short countermass 5B, the objective of which is thus to minimize friction and the generation of excessive heating to achieve self-balancing. It consists of a three-dimensional perspective view of a complete assembly composed on the micromotor 10, assembled to a handpiece 4 whose casing has been removed to see the interior and in particular the transmission module 2, circled in dotted lines, which is intended to transmit the movement of the motor to the cutting tool 3 according to a first back-and-forth movement M1 according to a predetermined stroke D.

[0043] The cutting tool 3 is driven in a back-and-forth translational movement by a blade holder 27, and is fixed to the latter by means of a clamping device 6 provided with an integrated irrigation channel 61 supplying the surgical treatment area with physiological liquid. The transformation of the rotational movement of the motor into a translational movement of the blade holder 27 is carried out via a first finger 241, the structure of which will be detailed in particular using the Figures 7a and 7b , and which is inserted into a first insertion orifice 272 of a coupling shoe 271 provided for this purpose. The connecting part of the blade holder 27 between the coupling shoe 271 and the clamping device is constituted by a cylindrical body 270.

[0044] As can be seen on the figure 3, the transmission module comprises a chassis 20 formed by a first part 201 for connection with the micromotor 10, and a second part 202 in the shape of a U and constituting the support of the blade holder 27. The first part 201 and the second part 202 are connected to each other using respectively two cylindrical rods, forming in parallel a first axial guide rail 261 and a second axial guide rail 262, constituting an axial guide element 26 for the countermass 5 (here the short countermass 5B). In this way, the chassis 20 can perform a guiding function for the countermass 5 without requiring the addition of a dedicated part. The short countermass 5B is driven according to a second reciprocating movement M2, opposite to that of the first reciprocating movement M1 of the cutting tool, via a second finger 242 which is inserted into a second orifice 51 of the countermass 5.

[0045] Thus, compared to a solution of the prior art, self-balancing was achieved simply by doubling the fingers, without however having to substantially modify the structure of the chassis, the drive mechanism, and in particular the eccentric 23 illustrated in particular on the figures 6 And 7a / 7b This eccentric, rotating around the same axis as that of the transmission shaft 22, generates a back-and-forth translational movement of the end of the fingers while causing a movement of approaching and respectively moving away from their lower end due to the non-constant spacing with respect to the axis of rotation along the entire length of the eccentric.

[0046] There figure 4 illustrates an enlargement of a transmission module 2 according to another preferred embodiment for the invention, this time using a long countermass 5A instead of the short countermass 5B illustrated in the figure 3previous. The other parts illustrated in this figure are in all respects identical to those of the figure 3 and will not be described in detail again. The transmission and balancing mechanism remains identical to that of the previous embodiment by making it possible to generate the first reciprocating movement M1 of the blade holder 27 from the rotary movement R supplied as input via the micromotor 10, and to generate in parallel a second reciprocating movement M2 of the long countermass 5A. The second reciprocating movement M2 of the countermass is synchronized in phase opposition with respect to the first reciprocating movement M1; these two movements M1 and M2 are always generated via respectively a first finger 241 and a second finger 242, of which only the ends are visible, the rest being hidden under the long countermass 5A. The direction of movement of the first finger S1 is always opposite to that of movement of the second finger S2.

[0047] There Figure 5 constitutes an exploded perspective view of the transmission module 2 for a cutting tool for surgical or dental use according to the preferred embodiment of the figure 4previous, that is to say having a long counter-mass 5B. We can now see the body of each of the drive fingers, that is to say the first finger 241 for driving the blade holder 27, and the second finger 242 for driving the counter-mass 5A, which also has two longitudinal guide orifices 52 allowing the respective insertion of each of the axial guide rails oriented parallel to the axis of movement of the blade holder 27, of which we can see the cylindrical body 270 and the coupling shoe 271. In this figure, only the first axial guide rail 261 is visible.This figure also highlights the grooved coupling orifice 21 of the transmission module 2 which is intended to cooperate with the coupling nose 11 of the motor to impart the rotational movement to a transmission shaft, illustrated in the following figures, and thus constitutes a preferred structural variant for the production of the motor coupling part of the transmission module 2.

[0048] There figure 6 , which constitutes a sagittal sectional view of the transmission module which can be used within the framework of the preferred embodiments of the transmission modules illustrated in the figures 3 And 4, materializes a first longitudinal axis AA for moving the cutting tool 3 via the blade holder 27. The rotary movement R of the micromotor 10 is transmitted to a rotary transmission shaft 22, which extends along a second longitudinal axis BB parallel to the first longitudinal axis AA. This second longitudinal axis is not illustrated in this figure for reasons of readability, but is visible in particular on the Figures 7a and 7bdescribed in the following. The transmission shaft 22 is rotatably mounted between input bearings 28 and output bearings 29, secured respectively to the first part 201 and the second part 202 of the chassis 20 of the transmission module 2. Furthermore, an eccentric 23 configured symmetrically in the shape of a “V” is mounted on this rotatable transmission shaft 22. The eccentric 23 comprises a first part 231 on which the first finger 241 is mounted, the reciprocating movement of which drives the blade holder 27, and consequently, the cutting tool 3, and a second part 232 on which the second finger 242 has been mounted, provided for driving the counterweight 5 in order to achieve self-balancing of the system. In this figure, the second insertion orifice 51 arranged in the counterweight 5 for the second finger 242 can be clearly seen.In order to enable the rotational movement of the eccentric 23 to be transformed into a back-and-forth movement of the fingers, the body of each of these fingers is also provided with a series of bearings, namely a first series of bearings 251 for the first finger 241, and correspondingly, a second series of bearings 252 for the second finger.

[0049] The transmission mechanism, or more precisely the conversion of the rotary motion applied as input into back-and-forth translational motion, is explained in detail using the Figures 7a and 7b , which shows respectively a sagittal and top sectional view of the transmission shaft 22 provided with the eccentric and the fingers mounted thereon.

[0050] As can be seen on the Figure 7a, the transmission shaft 22 rotates around its axis, i.e. the second longitudinal axis BB. It is rotatably mounted relative to the chassis 20 via the input bearings 28 with respect to the first part of the chassis 201 and the output bearings 29 with respect to the second part 202 of the chassis 20 of the transmission module 2. During its rotation, it drives the eccentric 23, the first part 231 of which, on which the first finger 241 is mounted via the first series of bearings 251, will generate a first back-and-forth movement M1 in a first direction S1, while the second part, on which the second finger 242 is mounted via the second series of bearings 252, will generate a second back-and-forth movement M2 of identical amplitude, but of simply opposite direction (i.e. in the second direction S2). Figure 7bhighlights the fingers seen from above; apart from the bearings which are no longer visible inside them, all the elements illustrated are identical to those of the Figure 7a This view makes it easy to represent the translational movement of each of these fingers along the second longitudinal axis BB and makes it possible to explain why it is more advantageous to couple the cutting tool 3, via the blade holder 27, by means of the first finger 241 and to carry out the balancing using the counter-mass 5 via the second finger 242. Indeed, given that the cutting tool 3 is arranged at the end of the cutting tool, it is more natural to arrange the coupling shoe at this same end, i.e. as far to the right as possible in these figures.

[0051] There figure 8illustrates a particularly preferred variant of a transmission module 2 for the embodiment of the present invention, the chassis 20 of which is provided with an integrated cooling mechanism 7 for the countermass 5. According to this illustrated embodiment using a long countermass 5B, which aims to achieve the most efficient possible balancing of the proposed cutting device in operation, and to best guarantee the coupling of the micromotor - not shown in this figure but whose rotational movement R shown here on the right of the figure 8- with respect to the handpiece 4 via the coupling orifice 21. According to the preferred variant illustrated, the integrated cooling device 7 advantageously uses the longitudinal connecting elements between the first part of the frame 201 and the second part of the frame 202, i.e. the cylindrical beams which form parallel axial guide elements 26, by incorporating integrated cooling ducts therein. Thus, as can be seen represented in dotted lines on the figure 8, the first axial guide rail 261 is provided with a first integrated cooling duct 2610 and similarly the second axial guide rail 262 is provided with a second integrated cooling duct 2620. A fluid supply duct 71 can thus be directly arranged at the end of the chassis close to the micromotor, and be used directly for a supply of physiological liquid, replacing for example the irrigation channel 61 visible in particular on the figure 3 . Although according to the preferred embodiment in this figure two channels are used for the cooling ducts, it will be understood that such a configuration is only sufficient, but not necessary for the implementation of the present invention, and that it would also be conceivable to use only a single cooling duct integrated in an axial guide element 26 which would only comprise a single guide rail.

[0052] The creation of one or more supply pipes inside the guide rails of the countermass 5, which therefore become irrigation tubes, presents two particularly interesting advantages at the operational level: the irrigation liquid allows the friction zone of the countermass 5 to be locally cooled, thus allowing the use of heavier countermasses - such as for example the long countermass illustrated in the figure 8 - and therefore longer and heavier surgical blades; irrigation of the cutting tool via an internal mechanism makes it possible to avoid having to connect an irrigation line to the blade holder, as is usually the case, a connection of the irrigation line which is therefore carried out both closer to the surgeon's fingers, and closer to the working area, which also implies a risk of accidental disconnection of the line.

[0053] Thus, this solution provides a significant improvement in surgeon ergonomics and patient safety, while providing increased flexibility in calibrating the tool according to needs.

[0054] Still according to a preferred embodiment for carrying out the present invention, the weight of the counter-mass 5 is between a minimum value, dependent on the motor-handpiece disconnection force, the maximum reciprocating frequency of the cutting tool 3, the stroke D of the cutting tool illustrated for example on the figure 3 , and the mass of the cutting tool 3 - blade holder 27 assembly and a maximum value, depending on the cooling power of the micro-saw / handpiece 4 and the gripping diameter of the cutting tool. Thus, the weight of the countermass is not necessarily equal to the weight of the assembly secured to the cutting tool and which is driven in a reciprocating movement.

[0055] These constraints are formulated in the following equation 1, which takes up the fundamental equation of dynamics following a modeling in accordance with a system materialized according to physical laws relating to point mechanics. More particularly, the mass M c of the counter-mass 5 must be greater than a limit value defined by the following equation (1): x = δ 2 cos 2 πft → d 2 x dt 2 = δ 2 2 πf 2 cos 2 πft a max = 2 δπ 2 f 2 F d > M s + M p a max − M c a max M c > M s + M p − F d / 2 δπ 2 f 2 where M s is the mass of the cutting tool 3, M p that of the blade holder 27, i.e. the cylindrical body 270 and the coupling shoe 271, F d the disconnection force, δ the stroke D of the cutting tool 3, and f the maximum frequency of the reciprocating movement.

[0056] Equation (1) above ensures that the cutting tool 3 is not accidentally disconnected from the motor module, i.e. the part corresponding to the micromotor 10, during the various working situations. For this, the maximum acceleration of the system is calculated and deduced from the equation indicating that the sum of the forces applied to the system is equal to the mass multiplied by the acceleration.

[0057] The modeling of the blade holder system 27 and cutting tool 3 on the one hand, and countermass 5 on the other hand as material points is justified by the assumption that the solid components are subjected to vibrations of very low amplitude, and at high frequency, and consequently their low-frequency dynamic behavior is essentially given by the movement of their center of gravity. Since the only active degree of freedom consists of the longitudinal movement along the axial guide element 26 (preferably formed by the two axial guide rails 261, 262), there is no rotational drive effect that would require taking into account the position of the center of gravity relative to a possible pivot center.

[0058] The mass of the counter-mass 5 must thus be less than a limit defined by the thermal balance of the micro-saw, without requiring the configuration of a self-balancing system where equality (2) M c = M s + M p is strictly respected.

[0059] The thermal power generated by the reciprocating movement of the countermass 5 on the guide element 26 (such as the first guide rail 261 and the second guide rail 262 parallel to the transmission axis, i.e. the second longitudinal axis BB) is linked in particular to the following factors: (i) the external surface and the material of the cap of the micro-saw (the cooling essentially depending on the convection around the handpiece 4); (ii) the diameter of the handle of the micro-saw, which imposes the maximum diameter of the counter-mass 5 and therefore the lever arm between the center of gravity of the counter-mass 5 and the first finger 241 for transmitting the reciprocating movement; (iii) the frequency f and the stroke D of the reciprocating movement; (iv) the distance of the axis of the guide rails 261, 262 of the counter-mass 5 and the axis of transmission of the reciprocating movement, such as the second longitudinal axis BB of the transmission shaft 22.

[0060] A heavier countermass, such as for example the long countermass 5A, therefore makes it possible to better ensure the holding of the micromotor module 10 with the handpiece 4, comprising the transmission module 2. This, however, causes a greater lever arm between its center of gravity and the second transmission finger 242; consequently, to minimize the length of the handpiece 4, it is preferable for the countermass 5 to occupy all the free space inside the handle, that is to say the outer envelope thereof which is grasped by the dental surgeon. This explains the particular shape of the short countermass 5B of the figure 3 and that of the long counter-mass 5A of the figure 4, the section of which corresponds substantially to a truncated cylindrical ring if the guide holes are disregarded. Thus, the longer the countermass 5, the closer its center of gravity is to the central axis of the handle; on the contrary, the end of the second transmission finger 242 driving the countermass 5 is preferably spaced as far as possible from the center of the handpiece 4 to maximize the stroke of the back-and-forth movement imposed on the countermass 5.

[0061] International standards set the maximum temperature that can be reached by the micro-saw (currently 55°C during normal use), which therefore makes it possible to deduce the maximum thermal power that can be generated by the presence of the counter-mass 5, which will preferably be made of a metallic material such as bronze, copper, steel or even a noble and heavy metal so as to have a density greater than 7000 kg per cubic meter, and thus make it possible to obtain a sufficient mass without having to require a volume that is too large and cumbersome compared to the rest of the transmission module, and in particular the kinematic chain driving the cutting tool 3 itself.

[0062] The fact of having, according to the preferred embodiments described with the aid of the preceding figures, counter-masses guided by at least 2 guide rails makes it possible to reduce friction and heating.

[0063] According to a particularly advantageous embodiment, the mass of the counter-mass 5 according to the invention is between 25% and 50% of the total mass of the cutting tool 3 / blade holder 27 assembly, which makes it possible to further minimize any additional heating due to self-balancing. Even more preferably, the mass of the counter-mass 5 according to the invention is between 2.5 g and 6 g, while the mass of the cutting tool is between 1 and 3 grams.

[0064] Thus, according to the invention, an effective means is proposed for counterbalancing the displacement of the center of mass of a cutting tool using a countermass which: is independent of the working speed minimizes the dependence on the mass and shape of the constituent elements of the micro-saw to be balanced minimizes the impact on the average efficiency (rotary movement-reciprocating movement conversion) of the handpiece minimizes the impact on the wear rate of the bearings does not generate overheating of the handpiece allows a modular type physical separation between the mechanical handpiece 4 (the module forming the micro-saw, which does not need a power supply), as illustrated in the figure 1 , and the feed motor, such as the micro-motor 10 also illustrated in the figure 1 , ensuring that the connection-disconnection of the surgical cutting tool to the motor is simple and quick, thanks to a disconnection force of around 30 N (3 kg).

[0065] According to the preferred embodiments described, the presence of the countermass and a 'symmetrical' transmission system of the rotary movement to the countermass and to the blade makes it possible to reduce vibrations. Since the countermass moves in perfect phase with the blade, the reduction of vibrations is ensured independently of the rotation speed of the motor. Furthermore, the guidance of the countermass makes it possible to avoid the heating and wear potentially caused by the addition of an additional heavy component to the transmission chain. The doubling of the ball bearings for each transmission finger makes it possible to reduce their wear. It is also possible to reduce the inverse dependence of the efficiency on the power applied to the motor (the efficiency decreases with the increase in power for an unbalanced system) by making it possible to increase the cutting efficiency.

[0066] Although only a few embodiments have been described by way of example in the foregoing, it will be understood that these are not intended to exhaustively set out all possible embodiments. Those skilled in the art will understand that it is possible to replace a means described by an equivalent means without departing from the scope of the present invention.

[0067] Furthermore, it would also be possible, without departing from the scope of the present invention, to modify the shape of the countermass according to the geometry of the cutting tool and the blade holder used, via an electronic or electromagnetic device. A preferred embodiment for implementing such a solution would be, for example, to secure two parts of the countermass via an electromagnetic device (of the electromagnet type) positioned on one of the two parts of the countermass and a magnet positioned on the second part of the countermass. Changing the polarity of the electromagnet therefore makes it possible either to secure (magnetic attraction) or to separate (magnetic repulsion) the two parts of the countermass.If a heavier cutting tool is used, the user can impose the two parts to be joined together ('heavy' countermass), whereas if a lighter cutting tool is used, the user can impose repulsion between the two parts of the countermass, and therefore use a lighter countermass.

Claims

1. A cutting device for surgical or dental use (1) comprising a motor (10) and a handpiece (4) equipped with a transmission module (2) for a cutting tool (3), said motor (10) being detachably connected to said handpiece (4), said transmission module (2) comprising: - a motor coupling part arranged to be rotated by said motor (10); - a kinematic chain transforming said rotary movement of said motor (10) into a first linear reciprocating movement (M1) of a blade holder (27) via a rotary transmission shaft (22) provided with an eccentric (23), said transmission module (2) being characterized in that it further comprises a counter-mass (5) arranged so as to be displaced according to a second linear reciprocating movement (M2) synchronized with said first linear reciprocating movement (M1) of said blade holder (27), and in the opposite direction to the latter.

2. The cutting device for surgical or dental use (1) according to Claim 1, characterized in that the first kinematic chain comprises a first drive finger (241) of said blade holder (27) mounted on a first part (231) of said eccentric (23), as well as a second drive finger (242) of said counter-mass (5) mounted on a second part (232) of said eccentric (23).

3. The cutting device for surgical or dental use (1) according to Claim 2, said eccentric (23) being symmetrically arranged in a "V" shape, said first drive finger (241) of said blade holder (27) being mounted on a first series of bearings (251) around said first part (231) of said eccentric (23) and said second drive finger (242) of said counter-mass (5) being mounted on a second series of bearings (252) around said second part (232) of said eccentric (23).

4. The cutting device for surgical or dental use (1) according to any one of the preceding claims, wherein the geometric shape of said counter-mass (5) is adapted to that of said cutting tool (3) and of said blade holder (27).

5. The cutting device for surgical or dental use (1) according to any one of the preceding claims, wherein said counter-mass (5) is guided axially along a first transmission axis (A-A) corresponding vectorially to the direction of longitudinal displacement of said blade holder (27) and of said cutting tool (3) by at least one axial guide element (26) inserted into at least one guide hole (52) made in said counter-mass (5).

6. The cutting device for surgical or dental use (1) according to Claim 5, wherein said axial guide element (26) is formed by a first axial guide rail (261) and a second axial guide rail (262) connecting, in parallel, a first piece (201) of the frame (20) connected to said motor (10) to a second piece (202) of the frame (20) supporting and axially guiding said blade holder (27) of said transmission module (2), said first axial guide rail (261) and said second axial guide rail (262) being inserted into respective guide holes (52) of said counter-mass (5).

7. The cutting device for surgical or dental use (1) according to any one of the preceding claims, characterized in that said transmission module (2) further comprises a cooling device (7) for the counter-mass (5).

8. The cutting device for surgical or dental use (1) according to Claim 7, when it is dependent on Claim 6, characterized in that the first axial guide rail (261) comprises a first integrated cooling duct (2610) and / or in that said second axial guide rail (262) comprises a second integrated cooling duct (2620).

9. The cutting device for surgical or dental use (1) according to any one of the preceding claims, characterized in that said transmission module (2) is detachably connected to said motor (10), and in that the weight of said counter-mass (5) is determined so as to be greater than a minimum value defined with respect to the combined weight of the assembly formed by the blade holder (27) and of said cutting tool (3) as a function of the disconnection force (Fd) of said transmission module (2) to said motor (10), of the course (D) of said cutting tool (3), and of the frequency (f) of oscillation of the reciprocating movement of said cutting tool (3).

10. The cutting device for surgical or dental use (1) according to any one of the preceding claims, characterized in that the weight of said counter-mass (5) is determined so as to be less than a predefined value determined by a heat balance.

11. The cutting device for surgical or dental use (1) according to any one of Claims 8 to 10, when they are dependent on Claim 7, characterized in that the weight of said counter-mass (5) is between 25% and 50% of the combined weight of the assembly formed by said blade holder (27) and said cutting tool (3).

12. The cutting device for surgical or dental use (1) according to any one of the preceding Claims 7 to 11, characterized in that the density of said counter-mass (5) is greater than 7000 kg per cubic meter.

13. The cutting device for surgical or dental use (1) according to any one of the preceding claims, characterized in that the motor coupling part of said transmission module (2) consists of a fluted coupling hole (21) which cooperates with a standard coupling nose (11) of said motor (10) having a series of grooves (110) into which O-rings (111) are inserted.

14. A handpiece (4) comprising a transmission module (2) for the cutting device for surgical or dental use (1) according to any one of the preceding Claims 1 to 13.