Spindle with piezoelectric actuator

Abstract

A spindle (10) for performing non-ultrasonic axial oscillation-assisted machining, comprising a tool-holding shaft (12) and an exciter section for subjecting the shaft to a non-ultrasonic axial oscillation, particularly during rotation thereof, the exciter section comprising a first exciter stage comprising at least one piezoelectric actuator (24) and a second exciter stage comprising at least one piezoelectric actuator (22) having a non-zero axial overlap with the first exciter stage, wherein the actuators of the two stages are arranged to add up their respective actions.

Description

Technical Field

[0001] The present invention relates to a spindle for a machine tool or a robot.

Background Art

[0002] Machine tools, especially those said to be numerically controlled, have a movable support that holds an electric spindle and is movable in three directions in particular. The electric spindle is a spindle that includes a motor and a tool holder for rotationally driving it about its axis.

[0003] It has already been proposed to subject a rotationally driven tool to ultrasonic vibrations ("Ultrasonic Machining", i.e., UM) to increase the effectiveness of the tool and enable hard materials, such as glass, to be drilled. The ultrasonic vibrations make it possible to generate shear during cutting, but have no significant effect on the chip thickness and discharge.

[0004] U.S. Patent Application Publication No. 2011 / 0222975 describes a UM module that includes a transducer configured to receive a tool. This transducer is powered by a rotating electrical contact.

[0005] U.S. Patent No. 3561462 describes another example of a UM spindle that includes an ultrasound exciter operating at a frequency on the order of 16 - 20 kHz, which also requires a rotating contact.

[0006] U.S. Patent No. 8240396 discloses another UM spindle that includes a rotating piezoelectric element, where the excitation frequency ranges from 17 - 60 kHz.

[0007] Furthermore, it is a known practice to use a piezoelectric actuator within the spindle to generate a variable preload in order to compensate for the mechanical stress that appears in the rolling bearings during operation due to expansion caused by the rising temperature during operation.

[0008] Therefore, U.S. Patent No. 6,422,757 and European Patent Publication No. 1,004,783 disclose a spindle comprising a piezoelectric actuator for this purpose. European Patent Publication No. 1,004,783 teaches that the piezoelectric actuator is used in combination with a cylinder to increase the axial compensation movement of the preload.

[0009] Furthermore, it is a known practice to subject the tool to axial oscillation during drilling, with the frequency linked to the rotational frequency. Such axial oscillation is at a much lower frequency than in ultrasonic machining (UM) and is primarily intended to break down the chips generated by the tool during its rotation.

[0010] Conventionally, the frequency of these axial oscillations is between 5 Hz and 500 Hz, depending on the rotational speed.

[0011] In International Publication No. 2017 / 087377, it has already been proposed to generate such oscillations using a piezoelectric actuator. However, this application will only briefly touch upon its implementation.

[0012] U.S. Patent Application Publication No. 2016 / 0129505 describes a system that enables the automatic generation of a tool feed rate as a function of the rotation of the tool, comprising an electromechanical actuator which may be piezoelectric to superimpose an axial oscillation on the feed motion. The application does not mention any actual implementation of the piezoelectric actuator.

[0013] Currently, the use of piezoelectric elements to reliably generate axial oscillation to break down chips and to change the instantaneous trajectory of the tool presents many problems that must be solved in a way that is compatible with the industrial applications of spindles.

[0014] Firstly, the piezoelectric element is relatively brittle and must operate under load; therefore, a suitable load system must be provided.

[0015] Next, the elongation rate of a piezoelectric element when electrically excited is relatively low, on the order of 1 / 1000, while the amplitude of axial oscillation required to achieve chip fragmentation cannot be ignored. Therefore, it is necessary to find a means to obtain the required amplitude. Furthermore, piezoelectric actuators of large length are at risk of buckling under high axial strain.

[0016] Furthermore, the thermal energy dissipated by piezoelectric actuators at high frequencies cannot be ignored and must be eliminated.

[0017] Finally, the power supply to the piezoelectric element also presents challenges because it must be highly reliable over time and not present maintenance issues.

[0018] Apart from the issues related to the use of piezoelectric actuators, the spindle needs to remain small enough to be used in numerically controlled machine tools and to operate over the widest possible range of rotational speeds, preferably up to 15,000 or 18,000 rpm, to accommodate the maximum number of uses.

[0019] Currently, in the case of chip evacuation, the frequency of the axial oscillation is linked to and increases with the rotation frequency. However, at high frequencies, the inertia of the moving parts causes a significant increase in the power required to generate the axial oscillation.

[0020] As a result, there is a need for a spindle that can generate axial oscillation using a piezoelectric element to address such various constraints. [Overview of the Initiative] [Problems that the invention aims to solve]

[0021] Accordingly, the present invention aims to generate non-ultrasonic axial oscillations within a spindle (preferably an electric spindle) using a piezoelectric element in order to improve machining performance and, in particular, to improve chip evacuation. [Means for solving the problem]

[0022] The present invention aims to address this need, and the subject matter according to its first aspect is a spindle for performing machining supported by non-ultrasonic axial oscillation, Tool holding shaft, and The shaft is equipped with an exciter section for subjecting it to non-ultrasonic axial oscillation, particularly during its rotation. The exciter unit is, A first exciter stage comprising at least one piezoelectric actuator, A second exciter stage comprising at least one piezoelectric actuator having a non-zero axial overlap with the first exciter stage. It is equipped with, Here, the two stages of the actuator are arranged in such a way that their respective actions are added together, and this is the spindle described above.

[0023] The two stages can be connected by a link member on which the actuator of each stage rests at one end, so that the actuator of one stage is fixed at one end on this link member to the end of the actuator of the other stage, and so that the extension of the actuator of the first stage is added to the extension of the actuator of the second stage by resting on this link member.

[0024] In a preferred implementation of the present invention, the spindle has a body, a front bearing that is at least partially axially movable relative to the body, and a rear bearing that is at least partially axially movable relative to the body and a tool holding shaft that is axially movable relative to the body, wherein at least partial axial displacement of the plurality of bearings is accompanied by axial displacement of the tool holding shaft. a first exciter stage, preferably stationary, operating between the intermediate link member and the body, a second exciter stage, preferably stationary, operating between one of the plurality of bearings and the intermediate link member and is provided with.

[0025] "Stationary" should be understood to mean not rotating relative to the body, in contrast to the tool rotating relative to the body. Thus, "stationary" is synonymous with "non-rotating" in this specification.

[0026] "Non-ultrasonic" means that the frequency of the axial oscillation is well below the frequency of ultrasound-assisted machining ("Ultrasonic Machining"), and thus well below 16 kHz. The effect of the axial oscillation is, in the present invention, to change the instantaneous trajectory of the tool in order to subdivide the chips.

[0027] "Front bearing" refers to the bearing closest to the tool. "Bearing" should be understood to mean one or more parts that ensure the function of guiding the rotation of the shaft. Thus, the bearing can comprise rolling bearings and supports for the rolling bearings for holding them relative to the body of the spindle.

[0028] "Non-zero axial overlap" should be understood to mean that the piezoelectric actuators occupy at least one common set of transverse coordinates along the longitudinal axis of the spindle.

[0029] The two stages of the actuator can have their respective actions added together when electrically excited, because the extension of one stage of the actuator can be added to the extension of the other stage of the actuator.

[0030] The second stage actuator may be interposed axially between one of the bearings and the intermediate link member. The first actuator may be interposed axially between the intermediate link member and the main body.

[0031] The present invention enables a particularly sophisticated and effective solution to many of the problems described above that arise from the use of piezoelectric elements within a spindle.

[0032] Firstly, the axial overlap between the exciter stages allows the majority of the spindle's longitudinal direction to be kept in a state compatible with use in numerically controlled machinery, while at the same time having sufficient piezoelectric actuator length to obtain the amplitude required for the axial oscillation.

[0033] Furthermore, the presence of these two stages allows only one to be excited at a high rotational frequency in order to reduce the number of moving parts and their corresponding inertia, and therefore the energy required. This makes it possible to generate axial oscillation at a higher frequency for a given power.

[0034] Furthermore, the limited longitudinal bulk of the exciter section according to the present invention also makes it possible to easily incorporate an electric motor into the spindle in order to make the spindle an electric spindle.

[0035] The body of the spindle can be formed by one or more parts that are assembled together.

[0036] Preferably, each stage of the exciter section comprises several piezoelectric actuators, for example, two to four, and especially three. These actuators are advantageously identical and have longitudinal axes parallel to each other and to the axis of rotation.

[0037] Preferably, the piezoelectric actuators in one stage are alternated with those in the other stage, with their angular distribution being equally distributed around the longitudinal axis of the spindle. This allows for good load distribution.

[0038] Preferably, the spindle is equipped with an axial preloading system for stressing the tool-holding shaft with an axial displacement that is the opposite of the axial displacement caused by the excitation of the actuator. This makes it possible to keep the piezoelectric element compressed.

[0039] This preload system can be interposed axially between the main body and one of the bearings, preferably the front bearing. In a modified example, it can be interposed between the main body and the rear bearing.

[0040] The preloading system may include at least one elastic return member that acts by compression, for example, a set of elastic washers disposed in a recess in a portion of the spindle that is fixed relative to the body. Each set may rest at one end on the bottom of the recess. The preloading system may include at least one tie rod that is connected at one end to one of the bearings, preferably the front bearing, and rests at the other end on the set of washers on the side of the opening of the recess. Thus, the set of elastic washers acts by compression to apply stress to the bearing in the direction of compression of the piezoelectric actuator.

[0041] In a modified example, the preload system includes a spring that acts by tension. These springs are, for example, attached at one end to a point fixed relative to the body and at the other end to one of the bearings, preferably the front bearing, so as to stress the bearing and cause it to rest on the piezoelectric actuator, thereby subjecting the latter to an axial compressive force.

[0042] The intermediate link member preferably has a plurality of recesses that alternately open toward one end of the spindle in the axial direction and toward the opposite end, where the plurality of piezoelectric actuators are to be received in the plurality of recesses. The link member may be a single piece or may be formed by an assembly of several parts. In each recess, the corresponding piezoelectric actuator may be axially mounted on a portion provided with a centering O-ring seal located at the bottom of the recess.

[0043] Preferably, at least one of the bearings, more preferably each bearing, comprises at least one rolling bearing held by a flexible support that can bend under the action of a force generated by the piezoelectric actuator to allow axial displacement of the shaft, while the radial position of the rolling bearing is kept constant relative to the body.

[0044] The use of such a support is advantageous because it reduces the inertia of the part that moves axially to generate the axial oscillation, thereby limiting the use of rolling bearings or other guide means.

[0045] The flexible support advantageously has a layered structure comprising small plates oriented, particularly perpendicular to the axis of rotation of the shaft. These plates are introduced advantageously by cutting sheet metal. Their thickness is, for example, in the range of 0.1 to 1 mm, and their number is 10 to 50 per support.

[0046] The support can be given various forms, particularly to increase flexibility and / or to allow the passage of tie rods, cables, or cooling airflow. Furthermore, holes can be fabricated within the support to provide greater flexibility.

[0047] If necessary, a centering screw can be provided on the support in order to refine the centering of the support.

[0048] Each support can be fixed to the main body at a fixed point on one side, and fixed to the rolling bearing housing at a location angularly offset from the fixed point with respect to the axis of rotation of the shaft on the other side.

[0049] For example, the support has a generally triangular shape when viewed from the front, allowing the body of the spindle to be fixed at the vertices of the triangle and the rolling bearing housing of the bearing to be fixed midway along each side of the triangle. In a modified example, the support has a corrugated shape in the circumferential direction.

[0050] Preferably, each bearing comprises two flexible supports disposed on either side of the one or more rolling bearings.

[0051] Each bearing preferably comprises two ball bearings arranged side by side.

[0052] Each stage of the piezoelectric actuator preferably comprises 2 to 4 actuators, more preferably 3 actuators.

[0053] Each piezoelectric actuator can transmit its thrust via a flexible transmission section, which at least one of its axial ends is, for example, T-shaped with a widened portion in cross-section, on which the piezoelectric actuator rests. The elongated portion of the transmission section, by its flexibility, allows for rotation. As a variation, a transmission system with a spherical reach is used. The advantage of the T-shaped transmission section is its simplicity of machining compared to a spherical reach. Both ends of the actuator can be received within a centering piece, which is provided with an O-ring seal that presses against the outer surface of the actuator, as mentioned above.

[0054] Preferably, the piezoelectric actuator is cooled by the circulation of compressed air.

[0055] The spindle may include a spacer-forming sleeve surrounding the piezoelectric actuator, where the front bearing rests axially on the sleeve. This simplifies the mounting of the bearing. The sleeve may have longitudinal grooves on its radially outer surface, into which power supply cables connected to the actuator and / or sensors are engaged. If the sleeve is made of metal, it can provide additional shielding from electromagnetic radiation generated by the piezoelectric actuator, particularly to cables connected, for example, to sensors, through the grooves.

[0056] The spindle may be equipped with a release system for acting on the clamping of the tool holder, where this release system is preferably disposed between the motor and the piezoelectric actuator. The release system may be pneumatic and may have several consecutive pressure chambers, for example three, to obtain a greater operating force for a given pressure. This allows for a reduction in the radial bulk of the release system and facilitates its installation between the exciter stage and the motor. The rearward placement of the motor with such a release system simplifies the manufacture of the motor, where the shaft can be rigid except for the cutting fluid intake channel, which can also be manufactured more easily.

[0057] Another subject matter of the invention according to another aspect of the present invention is a method of drilling or shaping, wherein a tool is rotationally driven using the spindle according to the present invention, and the tool is subjected to non-ultrasonic axial oscillation simultaneously with its rotation by periodically exciting the piezoelectric actuator.

[0058] The two stages of the actuator can be excited simultaneously. This allows for the maximum amplitude of axial oscillation, and the extensions of each actuator are aggregated.

[0059] Preferably, the actuator is excited by a sinusoidal voltage. The frequency of the axial oscillation can be 0 to 350 Hz.

[0060] Each stage of the actuator can be powered by its own power stage.

[0061] Furthermore, a single stage of the actuator, particularly one operating between the front bearing and the link member, can also be excited. This allows it to operate at a higher excitation frequency for a given power by reducing the inertia of the axially moved portion during such oscillation.

[0062] In this case, the non-oscillating actuator stage may be deprived of power or powered by a fixed voltage selected to provide more precise compensation for rotor displacement.

[0063] The spindle may be mounted on a numerically controlled machine or effector.

[0064] The spindle is conventionally displaced axially during drilling or shaping, where the feed rate per revolution of the spindle and the peak-to-peak amplitude of the axial oscillation are of the same order (i.e., the difference between them is at most 10 times).

[0065] The method may be a method for drilling metals, particularly aluminum or titanium, or other metals or materials, supported by vibration-free vibration, in which the vibration parameters (amplitude and frequency) can be adjusted.

[0066] The method may also be shape machining, particularly countersinking or counterboring. In this case, the axial oscillation can be stopped before the end of the tool feed.

[0067] Furthermore, it is also possible to generate a non-rotational axial oscillation, for example, to perform amplitude measurement on the tool or to assist in its removal.

[0068] The present invention can be better understood by reading the following description of non-limiting examples of its implementation and by considering the accompanying drawings. [Brief explanation of the drawing]

[0069] [Figure 1] Figure 1 is a mechanical diagram of an example of a spindle according to the present invention. [Figure 2] Figure 2 shows a schematic perspective view of an example of a spindle according to the present invention. [Figure 3] Figure 3 is a diagram similar to Figure 2, but with a partial crop. [Figure 4] Figure 4 is a similar diagram to Figure 3, but showing a different cross-section. [Figure 5] Figure 5 shows a longitudinal cross-section of the spindle. [Figure 6] Figure 6 is a similar diagram to Figure 5, but with a cross-section perpendicular to that of Figure 5. [Figure 7] Figure 7 shows one of the support structures of the rolling bearing separated and in a front view. [Figure 8] Figure 8 shows a portion of the spindle frame separated from the rest of the frame. [Figure 9] Figure 9 shows perspective, schematic, and partial views of a modified embodiment of the spindle. [Figure 10] Figure 10 is a diagram similar to Figure 9, but with a partial crop. [Figure 11] Figure 11 shows a separated cross-sectional view of the link member between the two stages of the piezoelectric actuator in the axial direction. [Figure 12] Figure 12 is a diagram similar to Figure 7 showing a deformed embodiment of the bearing support. [Modes for carrying out the invention]

[0070] Next, an example of the spindle 10 according to the present invention will be described with reference to Figure 1.

[0071] The spindle 10 is an electric spindle because, as described herein, it incorporates an electric motor 11, for example, a synchronous motor having permanent magnets.

[0072] The motor 11 rotates the shaft 12 via a link 14, the link 14 allowing a constant axial clearance between itself and the shaft, sufficient to allow the shaft to swing axially with a required amplitude along its longitudinal axis.

[0073] The shaft 12 drives a tool holder 13 at the end opposite the motor 11, and the tool holder 13 can accept any type of tool, for example, a drill bit or any other tool for shape machining, as schematically shown in Figure 1.

[0074] The interface between the tool holder and the tool may be of the clamp type and may be manufactured according to various standardized or custom-developed standards, such as ER or D type in particular.

[0075] The tool can also be held in the tool holder by means of hydraulic clamping, thermal shrinkage, mechanical shrinkage, or by means of a barrier, among other things, of the Weldon or Wissonnotch type.

[0076] The interface between the tool holder and the spindle may also be determined by a proprietary standard or specification, such as HSK, BIG, CAPTO, BT, or ISO(SK40) type, or a Morse taper may be used, and this list is not limiting.

[0077] The interface between the spindle and the numerically controlled machine can be made by clamping or any other preferred method.

[0078] The front bearing 15 and the rear bearing 16 guide the rotating shaft 12 while allowing axial movement.

[0079] These bearings 15 and 16 are axially movable at least on the shaft 12 relative to the body 19 of the spindle 10.

[0080] The latter comprises a first exciter stage 21 having several piezoelectric actuators 22 operating in parallel between the main body 19 and a link member 18 that is movable relative to the main body 19, and a second exciter stage 23 having several piezoelectric actuators 24 operating between the link member 18 and one of the bearings, the front bearing 15 in the example considered in this particular case.

[0081] An elastic preloading system 30 is axially interposed between the body 19 and one of the bearings, in this particular case the front bearing 15, to maintain the piezoelectric actuators 22 and 24 with the required prestress.

[0082] As can be seen in Figure 1, the link member 18 is positioned to allow a certain degree of axial overlap between the piezoelectric actuators along the longitudinal axis X of the spindle 10.

[0083] The actuators 22 and 24 do not rotate relative to the body 19, which simplifies their power supply and avoids the use of rotating slip rings.

[0084] They are connected to a control system, which outputs a variable voltage to oscillate them in conjunction with the rotation of the shaft 12 so that the tool has a sufficiently precise trajectory according to the required application.

[0085] The actuators 22 and 24 are powered, for example, by two separate amplifiers.

[0086] At low rotational frequencies, the actuators 22 and 24 are fully powered, and their extensions are combined, which allows for the maximum amplitude of the axial oscillation of the tool to be obtained. The actuators 22 and 24 are preferably excited by a sinusoidal voltage of a frequency and phase selected as a function of the rotational frequency and angular phase of the tool.

[0087] At a high rotational frequency, only the second stage 23 closest to the front bearing is excited to reduce the inertia of the movable part, and the link member 18 becomes immovable in the axial direction.

[0088] The spindle 10 according to the present invention preferably satisfies the following relationship. The frequency of the axial rocking generated by the piezoelectric actuator: 0 to 500 Hz, more preferably 0 to 350 Hz, The rotational frequency ω of the tool rotation : 0 to 18000 rpm, The peak-to-peak amplitude of the axial rocking: 0 to 0.25 mm, more preferably 0.02 to 0.25 mm, Frequency ω axial oscillation / ω rotation The ratio of is preferably a non-integer, for example 1 / 2, 3 / 2, 5 / 2, or 7 / 2. When f represents the feed per revolution, that is, the axial displacement of the entire spindle with respect to a 360° rotation of the tool, preferably 1 / 10f < a < 10f, where a refers to the peak-to-peak amplitude of the axial rocking. f is preferably 0.01 to 0.5 mm.

[0089] The control system of the piezoelectric actuator can be configured to enable the start of the axial rocking over the entire machining phase or, as a variant, only over a part thereof, according to the method which is the subject of the applicant's European Patent No. 2790860, and the rocking is stopped at the end of the machining.

[0090] In the figure shown in FIG. 1, the bearings 15 and 16 are axially movable relative to the body 19. The bearings 15 and 16 can be manufactured to have deformable parts that allow axial displacement of the shaft while accurately guiding the rotating shaft as will be described later.

[0091] Figures 2 to 6 represent examples of spindles 10 manufactured according to the present invention.

[0092] The spindle 10 is an electric spindle, and its motor 11 is housed in a housing equipped with separate fluid connections (liquid and / or gas) 70 and electrical connections 71, which ensure cooling of the spindle, power supply to the motor and the piezoelectric actuator, control of the tool holder, and signal exchange with various sensors. In particular, in the example considered, the spindle is equipped with engine coolant intake and outlet connections and a compressed air intake for cooling the piezoelectric actuator.

[0093] In this example, the front bearing 15 comprises two ball bearings 80 and 81, which abut axially against the shoulder 82 of the shaft 12 at one end and abut axially against the housing 83 at the other end. The latter are fixed by screws 86 to two supports 84 arranged on both sides of the housing 83.

[0094] Each support 84 is formed by the superposition of metal sheets having a substantially triangular shape, for example, as shown in Figure 7, exhibiting high rigidity in the thickness direction and a certain degree of flexibility in the direction perpendicular to the surface of the metal sheets. The screw 86 passes through an opening 90 located midway along each side of the support 84.

[0095] Furthermore, as can be seen in Figure 7, the support 84 is also fixed by screws 88 to an element 92 that forms part of the body 19 of the spindle 10 through an opening 93 located at its apex.

[0096] The flexibility of the support 84 allows for the axial clearance of the housing 83 necessary to enable the axial swing of the shaft 12, while keeping the housing 83 centered relative to the body 19 of the spindle 10.

[0097] The rear bearing 16 has a similar structure, with ball bearings 95 and 96 resting on the shoulder of the shaft 12 at one end and on the housing 97 at the opposite end.

[0098] Two identical supports 84 to those of the front bearing are fixed to the housing 97 through the opening 90. The supports 84 of the rear bearing are immobilized on the spindle body elements 101 by screws 102 engaged with the opening 93 of the supports 84.

[0099] With respect to the front bearing, the flexibility of the metal sheet of the support 84 allows for the axial clearance of the rear bearing in the rolling bearings 95 and 96, while also ensuring its centering.

[0100] The piezoelectric actuator 24 is mounted via a transmission section 107 having a T-shaped cross-section in the axial direction, enabling load distribution across the entire front surface of the actuator and compensation for any misalignment of the front bearing relative to the housing 83.

[0101] The actuator 24 of one of the stages is mounted on the link member 18 at the rear via a portion 110. The portion 110 may include a seal 111 for centering the actuator, as shown in the figure.

[0102] In particular, as can be seen in Figure 5, the mounting of the actuator 22 on the other stage is similar, where the latter rests at the rear on a bearing portion 113 that forms part of the spindle body 19 via the transmission portion 107, and at the front on the link member 18. The bearing portion 113 is hollow and houses a preload system 30 consisting of a stack of Belleville washers through which each tie rod 120 passes.

[0103] Each stack of elastic washers 230 is compressed between the nut 121 engaged with the tie rod 120 and the bottom 122 of the recess in the bearing portion 113 that receives it, as can be seen in particular in Figure 4.

[0104] Each tie rod 120 rests on the front of the housing 83 via a nut 123, thereby exerting tension on it in a backward direction.

[0105] Each tie rod passes freely through the support 84 through openings manufactured in the support between the openings that serve as passages for the fixing screws mentioned above.

[0106] Therefore, the elastic washer 230 ensures the necessary preload for the piezoelectric actuator.

[0107] A sleeve-shaped metal part 130 that forms a spacer is arranged around the link member 18, with one end resting axially on the bearing part 113 and the other end resting on the fixing element 92.

[0108] As shown in Figure 8, the spacer forming portion 130 may be provided with a longitudinal groove 133 on its radially outer surface for passing the power supply cable of the piezoelectric actuator and / or a cable connected to the sensor.

[0109] These grooves 133 can also facilitate the circulation of cooling air within the spindle 10.

[0110] The shaft 12 is hollow, and the operating rod 140 of the tool holder, which is mounted on the spindle 10, passes through it longitudinally. The rod 140 is also hollow to allow cutting fluid to be delivered to the tool.

[0111] The rod 140 is held in a locked position by the stacking of elastic washers 142 and rests axially on the shoulder portion 143 of the shaft 12.

[0112] When the tool (not shown) is unlocked, a forward thrust is applied to the rod 140 by a pneumatic unlocking system 150, which comprises three chambers 151, 152, and 153, which aggregate their effects on the transmission section 154.

[0113] In the illustrated example, the unlocking system 150 is axially positioned between the exciter unit, which is located in front of the spindle and equipped with the piezoelectric actuator, and the motor 11.

[0114] The latter comprises a rotor 141 having permanent magnets and a stator 142, and is cooled by liquid.

[0115] The shaft of the rotor 141 is connected to the shaft 12 of the spindle 12 by an elastic coupling system 155, which allows for torque transmission and axial clearance between the two shafts. The system 155 comprises two metal parts having teeth that interlock with each other in a claw-like manner, with an elastomer cushion between the teeth.

[0116] The motor 11 is equipped with a coder 156 at its rear, which allows for precise determination of the angular position of the shaft. The piezoelectric actuator is advantageously driven in accordance with the information provided by this coder.

[0117] The spindle 10 comprises a cylindrical housing 160 divided into several parts, which is closed at the front by a front flange 161 and at the rear by a rear flange 157 that houses the codder 156.

[0118] As is evident, numerous modifications can be made to the spindle 10 without departing from the framework of the present invention.

[0119] A modified spindle 10 in which the preload of the piezoelectric actuator is guaranteed in a manner different from that described above will now be described with reference to Figures 9 to 12.

[0120] In this example, the preload system 30 comprises a coil spring 180 which acts by tension between a ring 181 that is axially displaced together with the rolling bearings 80, 81 of the front bearing and a tie rod 183 that is fixed relative to the body of the spindle 10.

[0121] The actuator 24 is mounted on the front bearing at the front via a transmission with the spherical reach 184, and on the link member 18 at the rear.

[0122] The latter is shown separately in Figure 11.

[0123] In this specification, it takes the form of a single piece portion comprising a recess 200 opening toward the rear for receiving the piezoelectric actuator 22 and a recess 202 opening toward the front for receiving the actuator 24. A groove 203 is formed on the outside of the portion for receiving the spring 180.

[0124] The front and rear bearings have support members 84 whose shape differs from that of the support member 84 in the previously described example, as shown in Figure 12.

[0125] The support 84 has a corrugated shape and includes an opening 210 that allows a screw for axially immobilizing the spindle 10 to pass through, and an opening 211 for passing a fixing screw for the rolling bearing housing.

[0126] The recess formed between the opening 210 and the opening 211 allows electrical cables to be passed through if necessary.

[0127] In this example, the motor 11 (not shown) is located immediately behind the rear bearing, and the tool holder release system is located behind the motor 11 and immediately behind the spindle 10.

[0128] Other modifications can be made to the spindle without departing from the framework of the present invention.

[0129] For example, the spindle does not have a motor, but is driven by a pulley and a motor located remotely from the machine.

[0130] The spindle can be used on a robotic arm rather than a numerically controlled machine.

[0131] The ball bearing can be replaced by a roller bearing.

Claims

1. A spindle (10) for performing non-ultrasonic axial oscillation assisted machining, comprising: A tool holder shaft (12), and an exciter section for subjecting the tool holder shaft (12) to a non-ultrasonic axial oscillation; It is equipped with The exciter section, a first exciter stage comprising at least one piezoelectric actuator (22); a second exciter stage comprising at least one piezoelectric actuator (24) having a non-zero axial overlap with the first exciter stage; It is equipped with The spindle, wherein the piezoelectric actuator (22) of the first exciter stage and the piezoelectric actuator (24) of the second exciter stage are arranged to add up their respective effects.

2. The spindle, A main body (19), a front bearing (15) at least partially axially movable relative to said body (19); a rear bearing (16) at least partially axially movable relative to said body (19); the tool holder shaft (12) being axially movable relative to the body (19), where at least partial axial displacement of the bearings is accompanied by axial displacement of the tool holder shaft (12). the first exciter stage being disposed between an intermediate link member (18) and the body (19) and moving non-rotatably therebetween, wherein the intermediate link member (18) and the body (19) are in abutment with the first exciter stage; the second exciter stage disposed between one of the plurality of bearings and the intermediate link member (18) and non-rotatably moving therebetween, wherein the one of the plurality of bearings and the intermediate link member (18) are in abutment with the second exciter stage; The spindle of claim 1 , comprising:

3. 3. The spindle according to claim 1 or 2, wherein the piezoelectric actuators of one of the first and second exciter stages alternate with the piezoelectric actuators of the other of the first and second exciter stages in an angularly equidistant manner about a longitudinal axis (X) of the spindle.

4. The spindle of any one of claims 1 to 3, comprising an axial preload system (30) for stressing the tool holder shaft (12) with an axial displacement that is the inverse of the axial displacement caused by excitation of the piezoelectric actuators (24, 22).

5. The spindle of claim 4 , wherein the axial preload system operates in compression.

6. A spindle as claimed in claim 2 or any one of claims 3 to 5 which rely on claim 2, wherein the intermediate link member (18) has a plurality of recesses which open alternately towards one axial end of the spindle and towards the opposite axial end, and wherein the piezoelectric actuators (24, 22) are received in the plurality of recesses.

7. A spindle according to claim 2 or any one of claims 3 to 5 which depend on claim 2, wherein at least one of the or each bearing comprises a rolling bearing carried by a flexible support which is capable of yielding under the action of forces generated by the piezoelectric actuators (24, 22) to allow an axial displacement of the tool holder shaft (12), while the radial position of the rolling bearing remains unchanged relative to the body (19).

8. 8. The spindle according to claim 7, wherein the flexible support has a plate-like structure oriented perpendicular to the axis of rotation of the tool-holding shaft (12).

9. 9. A spindle according to claim 7 or 8, wherein each of the flexible supports is fixed on the one hand to the body (19) at a fixed point and on the other hand to a rolling bearing housing at a location angularly offset from said fixed point around the rotation axis of the tool holder shaft (12).

10. Spindle according to any one of claims 7 to 9, wherein each bearing comprises two of said flexible supports arranged on either side of said rolling bearing or rolling bearings.

11. The spindle of any one of claims 1 to 10, wherein each of the first and second exciter stages comprises between 2 and 4 piezoelectric actuators.

12. The spindle according to any one of claims 1 to 11, wherein each of the piezoelectric actuators (24, 22) transmits its thrust force via a flexible transmission at at least one of its axial ends, and wherein each of the piezoelectric actuators (24, 22) abuts on the flexible transmission against the front bearing (15) and the body, respectively.

13. Spindle according to any one of the preceding claims, wherein the piezoelectric actuators (24, 22) are cooled by circulation of compressed air.

14. A spindle according to claim 2 or any one of claims 3 to 5 which is dependent on claim 2, comprising a spacer-forming sleeve (130) surrounding the piezoelectric actuators (24, 22), wherein the front bearing (15) rests axially on the spacer-forming sleeve.

15. 15. The spindle according to claim 14, wherein the spacer-forming sleeve (130) has a longitudinal groove (133) on its radially outer surface, in which a power supply cable for the piezoelectric actuators (24, 22) and / or connected to a sensor is engaged.

16. The spindle according to any one of the preceding claims, comprising a motor for driving the tool holding shaft (12), a tool holder driven by the tool holding shaft (12), and a release system for affecting the clamping of the tool holder, wherein the release system is arranged between the motor and the piezoelectric actuator (24, 22).

17. 17. Spindle according to claim 16, wherein the release system is pneumatic and comprises several successive pressure chambers (151, 152, 153).

18. A method for drilling or profile machining, in which a tool is rotationally driven using a spindle (10) according to any one of claims 1 to 17, in which the tool is subjected to a non-ultrasonic axial oscillation simultaneously with its rotation by periodically exciting the piezoelectric actuators (24, 22).

19. The method of claim 18 , wherein the first exciter stage and the second exciter stage are excited simultaneously.

20. 20. The method of claim 18, wherein only one of the first exciter stage and the second exciter stage is excited.

21. A method according to any one of claims 18 to 20, wherein the spindle is mounted on a numerically controlled machine or effector.

22. 22. The method of any one of claims 18 to 21, wherein the frequency of the axial oscillation is from 0 to 350 Hz.

23. 23. A method according to any one of claims 18 to 22, wherein the spindle is displaced axially during the drilling or shape machining, and wherein the feed per revolution of the spindle and the peak-to-peak amplitude of the axial oscillation are of the same order of magnitude (mm).

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