Vibration-assisted machining

Abstract

A method for generating a gear-shaped workpiece (23) by generating, in particular continuous generating grinding, is disclosed, in which the gear-shaped workpiece rotates about a workpiece axis (C) in generating mesh with a generating tool. During processing, the gear-shaped workpiece undergoes an oscillatory movement that is superimposed on the rotation of the gear-shaped workpiece. Also disclosed is a clamping device (22) configured to carry out the method, as well as a system including such a clamping device and a control device (50). Furthermore, a generating machine including a clamping device of the aforementioned type is also disclosed.

Description

[Technical field]

[0001] The present invention relates to a method for machining a gear-shaped workpiece by a generating process, in particular continuous generating grinding, a clamping device configured for carrying out this method, a system for generating a vibration movement of a gear-shaped workpiece during machining by a generating process, and a generating grinding machine in which the clamping device is used. [Background technology]

[0002] Final hardening in gear manufacturing is one of the most important machining steps in determining the quality of the gear. During this process, the geometry that will later become the teeth meshing is produced. Continuous generating grinding is a commonly used method for hardening. In continuous generating grinding, the gear-shaped workpiece is machined by rolling meshing with a grinding tool in the form of a grinding wheel with a worm-shaped tooth profile (grinding worm). Generating gear grinding is a very demanding machining process, which requires a large number of independent movements to be performed precisely and synchronously with each other and is subject to many boundary conditions. Basic information on continuous generating grinding is provided, for example, in reference [1].

[0003] FIG. 1 shows an example of the meshing of a generating tool as a grinding worm 16 with a helical gear 23 during continuous generating grinding. The grinding worm 16 rotates about the tool axis B, and the gear 23 rotates about the workpiece axis C. The grinding worm 16 and the gear 23 mesh in this case in a worm drive (so-called roll coupling or generating coupling) manner. During the grinding stroke, the axial feed movement of the grinding worm 16 relative to the gear 23 is performed along a feed axis Z running parallel to the workpiece axis C. At the same time, the grinding worm 16 is continuously translated along the Y direction running parallel to the tool axis B (so-called shift movement) in order to continuously mesh new worm material with the gear 23. Along the feed axis X, the grinding worm 16 is radially fed relative to the gear 23.

[0004] As a result of the complex cutting movement between the grinding worm 16 and the gear 23, a regular wavy structure is formed on the tooth flank along the tooth flank line (so-called grinding grooves), which may generate undesirable noise during use of the gear.

[0005] In the prior art, various approaches have been proposed to post-remove such regular structures, for example by adding an abrasive grinding or honing process following a continuous generating grinding process, but such additional processes often entail undesirable additional costs.

[0006] The prior art also proposes taking measures to avoid the formation of such regular structures from the very beginning. For example, in the so-called Low Noise Shifting (LNS), the rotation angles of the grinding worm and the dressing wheel are coupled during dressing. By means of deliberately adapted shifting movements during grinding, periodic variations in the grinding pattern are deliberately provided in order to achieve a more favorable noise behavior of the gear (see reference [2]). However, due to the increasing complexity of the processes, this method does not cover all applications where the effects of noise are important.

[0007] In reference

[30] , it is proposed to generate a specific waviness during continuous generating grinding by utilizing a specific imbalance of the tool.

[0008] Other generating processes can also produce undesirable regular structures, such as skiving in gears. Summary of the Invention

[0009] In a first aspect, it is an object of the present invention to provide a method for generating machining, in particular continuous generating grinding, of gear-shaped workpieces, which makes it possible to reduce undesirable regular structures on the tooth flanks of the machined workpiece.

[0010] This object is achieved by a method according to claim 1. Further embodiments are defined in the dependent claims.

[0011] The invention proposes a method for machining a gear-shaped workpiece, in particular its tooth flanks, by a generating process, in particular continuous generating grinding. During machining, the gear-shaped workpiece rotates about the workpiece axis in generating mesh with a generating tool, in particular a grinding tool with a worm-shaped tooth profile, which rotates about the tool axis. The method is characterized in that the gear-shaped workpiece undergoes an oscillatory movement during machining, which is superimposed on the rotation of the gear-shaped workpiece. This results in a modification of the meshing of the workpiece with the tool, such that the surface structure of the workpiece produced is improved. In particular, regular structures such as grinding grooves can be avoided or prevented.

[0012] The oscillatory movement of the gear-shaped workpiece is preferably Axial direction along the workpiece axis, Radial to the workpiece axis, and The motion includes a component along at least one of the directions of motion, including a direction of twisting about the workpiece axis.

[0013] In particular, the oscillatory motion may correspond to a superposition of components along these motion directions.

[0014] In some embodiments, the vibratory motion has a fundamental frequency greater than 15 kHz. In other words, in such embodiments, the vibratory motion is in the ultrasonic range. As will be described in further detail below, such motion can be generated particularly efficiently by resonant excitation of a clamping device to which the workpiece is clamped. In other embodiments, the fundamental frequency is lower than 15 kHz. The term "fundamental frequency" refers to the spectral component of the vibration that has the lowest frequency.

[0015] The vibratory motion can be generated in particular as follows: the gear-shaped workpiece is clamped in a clamping device during the generating grinding operation, while the clamping device is arranged on the workpiece spindle. The workpiece spindle drives the gear-shaped workpiece clamped in the clamping device in rotation about the workpiece axis. The clamping device has a clamping part that is in direct contact with the workpiece clamped in the clamping device. The vibratory motion of the gear-shaped workpiece is then preferably generated by exciting a vibration of the clamping part of the rotating clamping device. This excitation is preferably resonant, so that the vibrations are natural modes of the clamping device to which the gear-shaped workpiece is clamped. This allows high-amplitude, controlled excitation. The corresponding natural frequencies are usually in the ultrasonic range. In order to reduce the unwanted transmission of vibrations to the workpiece spindle, the natural modes are preferably selected in such a way that the vibration nodes of the natural modes are located in the mounting area of ​​the clamping device in contact with the workpiece spindle.

[0016] To excite the vibrations, the clamping device may have a vibration generator integrated therein. The vibration generator converts an electrical excitation signal in the form of an alternating voltage of a suitable frequency into vibrations of the clamping device on which the gear-shaped workpiece is clamped. To monitor the vibrations caused by the excitation signal, an electrical sensor signal characterizing the vibrations may be determined. The sensor signal may then be used to control the excitation signal such that the excitation of the vibrations is resonant, as explained above. In particular, the sensor signal may characterize the amplitude of the generated vibrations and / or the phase position of the generated vibrations relative to the excitation signal. Based on such sensor signals, a control of the excitation signal (in particular its frequency) may be performed such that the vibration system consisting of the clamping device and the gear-shaped workpiece clamped thereon is excited resonantly as desired. Suitable control algorithms are generally known for controlling the excitation of a vibration system such that the system vibrates resonantly.

[0017] Preferably, the excitation signal and the sensor signal are transmitted contactlessly between the rotating clamping device and the fixed control device. The control device may in particular comprise a frequency generator for generating the excitation signal and a controller for controlling said excitation signal. Devices suitable for contactless transmission of energy and signals are known per se. For example, inductive transmission is possible by means of two coils arranged concentrically around the workpiece axis, one of the coils being arranged on the clamping device and the other coil being arranged on the fixed mechanical element.

[0018] In a second aspect, the present invention provides a clamping device for clamping a gear-shaped workpiece on a workpiece spindle of a gear cutting machine, in particular a generating grinding machine, configured for carrying out the above-mentioned method according to the first aspect of the invention, characterized in that the clamping device comprises a vibration generator for generating vibrations of the clamping device in the clamped state of the gear-shaped workpiece.

[0019] In particular, the vibration generator Axial direction along the workpiece axis, Radial to the workpiece axis, and The workpiece may be configured to generate vibration excitation along at least one of the directions of motion, including a torsional direction about the workpiece axis.

[0020] In a preferred embodiment, the vibration generator comprises or is designed as a piezoelectric actuator. In particular, the vibration generator of the vibration generator may have at least one piezoelectric actuator element in the shape of a disk ring or in the shape of a ring segment, the ring axis of the piezoelectric actuator element corresponding to the workpiece axis.

[0021] The vibration generator may be arranged in the clamping device as follows: the clamping device defines a proximal end and a distal end, the proximal end being configured to be connected to the workpiece spindle; the clamping device includes a clamping part configured for direct contact with the gear-shaped workpiece; the clamping part may be configured in a manner known per se, for example as a hydraulically actuated expanding sleeve or as a mechanically actuated split clamp bush; the vibration generator may be arranged between the proximal end and the clamping part, or may be arranged distally from the clamping part.

[0022] The clamping device may further include a vibration sensor that determines at least one sensor signal characterizing vibrations of the clamping device with the gear-shaped workpiece clamped thereon.

[0023] The vibration sensor in particular comprises or is configured as a piezoelectric sensor. The vibration sensor can be configured similarly to the vibration generator and comprises at least one piezoelectric sensor element in the shape of a disk-ring or a ring segment, the ring axis of the piezoelectric sensor element corresponding to the workpiece axis. The vibration generator and the vibration sensor together can form a vibration transducer comprising a stack of a disk-ring or a ring segment shaped piezoelectric element, a disk-ring shaped electrode and a disk-ring shaped insulating disk.

[0024] In a third aspect, the present invention provides a system for generating a vibratory movement of a gear-shaped workpiece during machining by a gear machining process, in particular continuous generating grinding. On the one hand, the system comprises a clamping device according to the second aspect of the invention. On the other hand, the system comprises a frequency generator generating an excitation signal for the vibration generator to cause vibration of the clamping device to which the gear-shaped workpiece is clamped. The system may comprise a controller configured to receive a sensor signal and to control the excitation signal based on the sensor signal such that the vibration excitation occurs sympathetically.

[0025] As already mentioned above in the context of the method, the system may further comprise a transmission device for contactlessly transmitting the excitation signal and the sensor signal between the rotating clamping device and the fixed control device.

[0026] In a fourth aspect, the present invention provides a generating machine, in particular a generating grinding machine, configured to carry out a method according to the first aspect of the invention. The creation processing machine is A tool spindle that drives a generating tool, particularly a grinding tool having a worm-shaped tooth profile, so as to rotate around a tool axis; a workpiece spindle for driving a gear-shaped workpiece to rotate about a workpiece axis; and a machine controller configured to control the tool spindle and the workpiece spindle such that a roll coupling is established between a rotation of the tool produced by the tool spindle and a rotation of the workpiece produced by the workpiece spindle.

[0027] The generating machine is characterized in that a clamping device is attached to the workpiece spindle according to the second aspect of the present invention. Of course, the generating machine may further comprise a frequency generator, a controller and / or a transmission device as shown in the third aspect of the present invention.

[0028] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to the drawings, which are for the purpose of illustrating the present invention only and should not be construed as limiting. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a sketch illustrating the mechanism of continuous generating grinding. [Diagram 2] FIG. 2 shows a schematic diagram of a generating grinding machine. [Diagram 3] FIG. 3 is a schematic sketch showing exemplary vibration types and shapes of a clamping device with a clamped gear. [Figure 4] FIG. 4 is a schematic diagram of a clamping device in which a gear is clamped and a vibration transducer is placed above the gear to generate and measure the torsional motion of the gear, along with associated controls and example vibration modes. [Diagram 5] FIG. 5 is a schematic exploded view showing a vibration transducer as a vibration generator on the one hand and a vibration sensor on the other hand. [Figure 6] FIG. 6 is a schematic diagram of a clamping device with a gear mounted thereon and a vibration transducer positioned below the gear for generating and measuring the vibratory torsional motion of the gear, along with example vibration modes. [Figure 7] FIG. 7 is a schematic diagram of a clamping device with a gear mounted thereon and a vibration transducer positioned above the gear for generating and measuring longitudinal vibration motion of the gear, along with example vibration modes. [Figure 8] FIG. 8 is a schematic diagram of a clamping device with a gear mounted thereon and a vibration transducer positioned below the gear for generating and measuring longitudinal vibration motion of the gear, along with example vibration modes. [Figure 9] FIG. 9 is a schematic diagram of a clamping device with a gear mounted thereon and a vibration transducer positioned above the gear for generating and measuring radial vibratory motion of the gear, along with example vibration modes. [Figure 10] FIG. 10 is a schematic diagram of a clamping device with a gear mounted thereon and a vibration transducer positioned below the gear for generating and measuring radial vibratory motion of the gear, along with example vibration modes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Example of a generating grinding machine configuration FIG. 2 shows an example of a generating grinding machine 1 known from the prior art. The grinding machine has a machine bed 11 on which a tool carrier 12 is displaceably guided along a feed direction X. The tool carrier 12 carries an axial slide 13 which is displaceably guided along an axial direction Z relative to the tool carrier 12. A grinding head 14 is mounted on the axial slide 13 and can be swiveled about a pivot axis (so-called axis A) running parallel to the X axis in order to adapt to the helix angle of the gear to be machined. The grinding head 14 in turn carries a shift slide on which a tool spindle 15 can be shifted along a shift axis Y relative to the grinding head 14. A grinding worm 16 is clamped to the tool spindle 15. The grinding worm 16 is driven by the tool spindle 15 and rotates about a tool axis B.

[0031] The machine bed 11 further supports a swivellable workpiece carrier 20 in the form of a rotating turret, which is swivellable about an axis C3 between at least two positions. Two identical workpiece spindles 21 are mounted diametrically opposite each other on the workpiece carrier 20, only one of which is shown in FIG. 1. A clamping device 22 for clamping a workpiece 23 is mounted on each workpiece spindle. The workpiece spindle shown in FIG. 1 is in a processing position in which a workpiece 23 clamped on the clamping device 22 can be processed by a grinding wheel 16. The other workpiece spindle, offset by 180° and not shown in FIG. 1, is in a workpiece exchange position in which a workpiece that has been completely processed can be removed from the clamping device on this spindle and a new unmachined part can be clamped. Each workpiece spindle 21 drives a clamping device 22 mounted with a clamped workpiece 23 to rotate about the workpiece axis C.

[0032] All driven axes of the generating grinding machine 1 are digitally controlled by a machine controller 30. The machine controller 30 receives sensor signals from a number of sensors of the generating grinding machine 1 and outputs control signals to actuators of the generating grinding machine 1 in response to these sensor signals. In particular, the machine controller 30 includes a number of axis modules (NC modules) 32, which provide control signals at their respective outputs for respective machine axes (i.e., at least one actuator, such as a servo motor, used to drive each machine axis). The machine control system 30 further includes an operation panel 33 and a control computer 31 that interacts with the operation panel 33 and the axis modules 32. The control computer 31 receives operation commands and sensor signals from the control panel 33 and calculates control commands to the axis modules 32 based thereon. The control computer 31 further outputs operation parameters to the control panel 33 for display based on the sensor signals.

[0033] Machining of workpiece lots The unmachined workpiece (unmachined part) is machined by clamping it on the clamping device of the workpiece spindle in the workpiece exchange position by the automatic workpiece changer. The workpiece change is performed in parallel with the machining of another workpiece on the other workpiece spindle in the machining position. Once the new workpiece to be machined has been clamped and the machining of the other workpiece has been completed, the workpiece carrier 20 is swiveled 180° about the C3 axis and the spindle with the new workpiece to be machined is moved to the machining position. Before and / or during the turning process, a meshing operation is performed using a meshing probe. For this purpose, the workpiece spindle 21 is rotated and the position of the tooth space of the workpiece 23 is measured by means of the meshing probe. The rolling angle is determined on this basis.

[0034] When the workpiece spindle carrying the workpiece 23 to be machined reaches the machining position, the tool carrier 12 moves along the X-axis, so that the workpiece 23 comes into mesh with the grinding wheel 16 without colliding with it. The workpiece 23 is then machined in a generating mesh state by the grinding wheel 16. Meanwhile, in order to continuously use unused areas of the grinding wheel 16 for machining, the tool spindle 15 moves slowly and continuously along the shift axis Y (so-called shift movement).

[0035] Concurrently with the machining of the workpiece, the finished workpiece is removed from the other workpiece spindle and another blank is clamped onto this spindle.

[0036] Introducing vibration during continuous generating grinding. In the process proposed here, an externally excited oscillatory motion is introduced into the generating grinding process. By proper selection of the amplitude, frequency and phase position of the oscillatory motion, favorable effects on the structure of the workpiece surface can be obtained.

[0037] In cylindrical and surface grinding, ultrasonic vibrations have been used in various situations to reduce grinding forces, minimize tool wear and optimize the workpiece surface in terms of structure and roughness parameters (see references [3]-

[24] ). The superposition of ultrasonic vibrations discontinuously changes the continuous contact between the tool and the workpiece and / or modifies the trajectory of the abrasive grains, resulting in advantages in terms of productivity and quality. However, the knowledge gained in surface and cylindrical grinding cannot be transferred to continuous generating grinding, since the mechanics and meshing conditions are completely different in continuous generating grinding.

[0038] In the process proposed here, the process mechanics of generating grinding are superimposed in an appropriate manner with vibration movements in the ultrasonic range (above 15 kHz) or in the low-frequency range (below 15 kHz). The aim is to reduce the waviness of the ground tooth flank surface and to avoid or prevent regular grinding grooves. Other aims are to reduce the machining forces and the tool wear. This allows the subsequent grinding process to be more intense (e.g. by increasing the axial feed and shortening the grinding time) since the grinding forces are reduced due to the smaller stress on the individual abrasive grains. The superimposition of vibration movements with frequencies below the ultrasonic range may suppress the chatter frequencies.

[0039] Within the framework of the proposed procedure, a vibration movement is generated in the workpiece. For this purpose, the clamping device for the workpiece (hereinafter also called clamping set) can be equipped with an actuator system for generating the vibrations.

[0040] Vibration direction There are three main possible directions for the alignment of the oscillatory motion with respect to the conventional grinding direction in continuous generating grinding. Table 1 shows these three main directions for the example of machining a spur gear. [Table 1]

[0041] Combinations of these three principal directions are possible and useful, and to some extent unavoidable in practical systems. This is especially true for helical gears.

[0042] Vibration Frequency In terms of frequency range, a distinction can be made between low-frequency vibrations (below 15 kHz) and high-frequency vibrations in the ultrasonic range (above 15 kHz). Their impact on processes is very similar and the same objectives can be pursued. However, there are variations in practical implementations regarding the generation of vibrations for the different frequency ranges.

[0043] For the generation of ultrasonic vibrations, it is proposed to exploit the natural structural dynamics of the structure to be excited, consisting of a gear and a clamping set. Typically, the available eigenmodes are in the ultrasonic frequency range due to the distribution of mass and stiffness of such a structure, which can also be optimized and adapted by design measures. Advantages of resonance excitation are, for example, the spatial separation possibility of the actuator for excitation from the active point of the process, the preservation of a relatively high stiffness of the structure, and the high efficiency in generating vibration amplitudes at the active point of the process. An example of integrating a vibration transducer into a clamping set to achieve these goals is described in more detail below.

[0044] To generate low frequency vibrations, resonant excitation is usually not possible. Due to the structural dynamics of the clamping set and the gears, resonant excitation in the low frequency range is usually not possible or the stiffness of both would have to be reduced to such an extent that they cannot be used in the process. Therefore, non-resonant excitation is proposed to generate low frequency vibrations. With the right actuator arrangement and a linkage system for translating and transmitting the deflections, it is also possible to generate low frequency vibrations of the gears without using resonance.

[0045] Eigenmodes of ultrasonic vibration In some embodiments, in order to specifically couple the ultrasonic vibrations to the active points of the process, it is intended to excite natural eigenmodes at resonance, thereby exciting standing waves (resonant excitation). The eigenmodes in this case are characterized by areas of maximum deflection and simultaneously minimum strain, so-called antinodes. In contrast, areas of minimum mechanical deflection and maximum mechanical strain are called nodes.

[0046] The workpiece (gear) and the workpiece clamping device (clamping set) are preferably excited as a common vibration structure in the appropriate natural mode. In this case, the natural mode that leads to a highly uniform deflection around the circumference of the gear is preferably used. In other cases, such as in the case of bending vibrations of the workpiece and clamping set about axis C, where the alignment of the vibration modes is random, the vibrations generated at the active points will be subject to randomness and the reliability of the process cannot be guaranteed.

[0047] FIG. 3 shows three example vibration modes optimized and plotted for a spur gear 23 to achieve different directional oscillatory motion of the gear 23 in the three main directions mentioned above in Table 1.

[0048] In the superposition of the cutting direction (view a in FIG. 3), the clamping set 22 together with the gear 23 is excited in natural modes with longitudinal vibrations in the direction of the gear axis (workpiece axis C). The order of the modes is selected and the structure is designed in such a way that the vibration antinodes of the longitudinal vibrations are formed in the area of ​​the gear 23. This means that the maximum amplitude in the axial direction of the gear 23 acts on the active point of the process and therefore in the cutting direction.

[0049] In geometrically restricted configurations, longitudinal vibrations are always accompanied by transverse vibrations (thickness vibrations) due to transverse contraction. This is called "quasi-longitudinal" vibration. In this case, the maximum transverse deflection occurs at the point of maximum longitudinal strain. This means that the actual longitudinal vibration nodes do not show longitudinal displacements, but transverse ones. This behavior can be exploited when performing overlap generating grinding on the cutting surface transverse to the cutting direction. This form of vibration excitation is sketched in Fig. 3, view b and is characterized by a longitudinal vibration node in the region of the gear 23.

[0050] Due to the overlap in the cutting depth direction, the rotationally symmetrical structure consisting of the gear 23 and the clamping set 22 can be excited in torsional mode about the workpiece axis C by a torsional vibration antinode in the area of ​​the gear 23. This vibration morphology is sketched in Fig. 3, view c.

[0051] Depending on the type of vibration generator (thickness or shear transducer), its positioning, the shape of the end mass and the choice of eigenmode (by excitation frequency), superpositions and combinations of various types of vibrations can be achieved. The so-called operational vibration modes always represent a combination of different directional components of the vibration directions, more or less idealized, as occurs in real structures.

[0052] Integration of vibration generators into clamping devices To generate the vibrations, a vibration generator is preferably integrated into the clamping set. The vibration generator preferably comprises one or more piezoelectric actuators that convert an electrical control corresponding to the operating frequency into mechanical vibrations. The arrangement and orientation of the vibration generator determine the vibration parameters achieved on the surface of the tooth flank to be machined and can be configured according to the type of vibration superposition intended.

[0053] For effective vibration excitation, the actuator is preferably placed close to the vibration node of the eigenmode to be excited. In this case, the mechanical action direction of the actuator is the direction of the strain of the vibration mode at the actuator's location. Preferably, multiple thin actuators are used as stacked actuators with alternately polarized electrodes for voltage supply. This setup provides the required electric field strength at a relatively low voltage.

[0054] In order to protect the machine parts connected to the clamping set and to avoid unwanted vibration transmission to other structures of the generating grinding machine, it is considered to isolate the vibrations of the clamping set with gears from the rest of the machine. For this, a vibration mode is preferably selected which has a vibration node in the area where the clamping set is connected to the workpiece spindle. Vibration transmission can be further reduced by giving the clamping set a high mass in the mounting area and / or by providing a geometry for reducing vibration transmission.

[0055] A frequency generator can be used to supply the actuator with an excitation signal in the form of an alternating voltage of the desired excitation frequency. The generated excitation frequency corresponds to the resonant frequency of the natural mode to be excited. The resonant frequency depends, within certain limits, on influences such as temperature and the acting machining forces. To ensure a high efficiency excitation always in a good operating range, it is desirable to control the frequency of the frequency generator by a controller. The frequency generator and the controller can be integrated in one control device. This allows the output excitation frequency to be adapted to the variable resonant frequency of the system. Furthermore, the ultrasonic force is preferably adjusted so that the desired amplitude can be introduced into the process independently of the load.

[0056] The actual vibration of the gear can be recorded as frequency, phase position and / or amplitude in order to control the vibration amplitude and adjust the excitation frequency. The vibration motion of the tooth flank in the process cannot be detected directly, but can be measured indirectly, allowing conclusions about the gear vibration. With one sensor it is possible to obtain an actual measurement of the vibration of the tooth flank, assuming that the correct natural modes are excited. The determination of whether the excitation is actually in the desired mode is only possible to a certain extent with a single sensor. By the arrangement of several sensors at characteristic points, the phase position of the sensor signals and a comparison of the measured amplitudes, it is also possible to determine the excited three-dimensional vibration mode. This allows vibration excitation in the desired natural modes, which increases the process stability in controlled vibration operation. Piezoelectric elements from which a voltage signal can be extracted can also be provided as sensors.

[0057] Both the electrical supply for the actuators and the sensor signals are transmitted between the rotating clamping set with the gears and the fixed control device. For this purpose, for example, a contactless rotary transducer with inductive power transmission may be provided.

[0058] Example 1 Generation of torsional vibration by a vibration generator on the upper part of the gear Next, a specific example of the implementation of the above-described principles will be described with reference to FIG.

[0059] In FIG. 4 the clamping set 22 is shown in a highly schematic manner for rigid coupling to the rotation axis of the workpiece spindle. The end of the clamping set for connection to the spindle axis is hereinafter referred to as the proximal end 221, the opposite end 222 as the distal end. In FIG. 4 the proximal end is at the bottom and the distal end is at the top. The clamping set 22 has a clamping part 223 in the form of a radially expandable expansion sleeve or a split clamping bush, on which the gear-shaped workpiece 23 is clamped. Above the workpiece 23 (between the clamping part 223 and the distal end 222 in the axial direction) the vibration transducer 40 is integrated in the clamping set. Above the vibration transducer 40 (distal from the vibration transducer 40), the clamping set 22 has an exchangeable end piece 224 as a preload nut. This end piece 224 fixes the vibration transducer 40 to the clamping set 22 and at the same time compresses it axially along the workpiece axis C.

[0060] As will be described in more detail below, the vibration transducer 40, on the one hand, generates a high frequency excitation signal V to excite a torsional vibration 41 in the workpiece 23. A On the other hand, the vibration transducer 40 includes a vibration sensor 420 for measuring characteristics of the generated vibration. The vibration sensor 420 outputs one or more sensor signals V S Output.

[0061] The control device 50 is used to read out the vibration sensor 420 and control the vibration generator 410 based thereon. The control device 50, on the other hand, controls the excitation signal V A On the other hand, the control device 50 includes a frequency generator 51 for generating the sensor signal V S and based on this sensor signal, generates an excitation signal V AThe controller 50 includes a controller 52 that controls the frequency f and amplitude A of the vibration transducer 40. The electrical output and input signals of the vibration transducer 40 are transmitted through electrical connections inside the clamping set 22. The excitation signal V A For the contactless transmission of the sensor signal V, an inductive transmission device 53 is used, which is only shown diagrammatically. A further transmission device 54 is also provided for transmitting the sensor signal V S from the clamping set 22 to the control device 50. For example, inductive transmission is possible by means of two coils arranged concentrically around the workpiece axis, one of the coils being arranged in the clamping device and the other coil being arranged in the fixed mechanical element. In particular, configurations such as those known from references

[31] and

[32] can also be used in different contexts.

[0062] In this embodiment, the vibration generator 410 generates a torsional vibration about the workpiece axis C. The frequency of this torsional vibration is controlled by the controller 52 so that the unit consisting of the clamping set 22 and the workpiece 23 is resonantly excited. In the simplest case, the controller 52 controls the excitation frequency f so that the amplitude A measured by the vibration sensor 420 is maximized.

[0063] Along the workpiece axis C, a standing wave is formed with vibration nodes (i.e., points where the amplitude of the torsional vibration is minimal) and vibration antinodes (i.e., points where the amplitude of the torsional vibration is locally maximal). The amplitude distribution of this standing wave along the workpiece axis is shown in the left part of FIG. 4 as an amplitude distribution 61 with a non-zero radius R. The clamping set 22 is configured such that the standing wave has vibration antinodes in the area of ​​the workpiece 23, while the vibration generator 410 is located near the vibration node. In this embodiment, the vibration generator 410 is located near the first vibration node above the gear 23, thereby contributing to a particularly large amplitude of the torsional vibration occurring at the vibration antinode. In order to minimize the transmission of the torsional vibration to the workpiece spindle, the clamping set 22 is configured such that the vibration node is located at its proximal end 221, i.e., at the position where the clamping set 22 is connected to the spindle shaft.

[0064] The design of the clamping set 22 geometry and the positioning of the vibration generator 410 to generate resonant excitation and to locate the vibration antinodes and nodes at the desired points can be easily achieved by using known vibration behavior simulation methods, in particular FEM simulation. Since the workpiece 23 forms part of the resonant vibrating structure, the design of the clamping set 22 and the positioning of the vibration generator 410 are in principle workpiece specific. However, once the clamping set 22 has been designed, it can be used within a certain range for different workpieces 23 by adapting the excitation frequency f to the workpiece so that resonant excitation occurs.

[0065] Vibration Transducer Structure The structure of a suitable vibration transducer 40 is illustrated in Figure 5. The vibration transducer 40 is made up of a stack of flat disk-ring shaped elements. The stack has two regions. A first lower region forms the vibration generator 410 and a second upper region forms the vibration sensor 420.

[0066] In this embodiment, the vibration generator 410 includes two annular piezoelectric shear actuators 411, one axially above the other, with a central annular electrode 412 disposed between them. An outer annular electrode 412 is disposed at each of the two axial ends of the vibration generator 410, above the upper shear actuator and below the lower shear actuator. The two outer electrodes are electrically connected to each other. Both shear actuators are of identical construction, but are disposed in mirror images of each other with respect to a horizontal plane passing through the central electrode 412.

[0067] Shear actuators are known per se in the prior art. For many piezoelectric materials, shear actuators have a piezoelectric shear deformation coefficient d 15 is not zero. In this example, the shear actuators 411 are configured to generate shear deformations in the circumferential direction under the action of an electric field extending along the workpiece axis C. The direction of action of each actuator with respect to its respective axis C can be achieved by a special polarization process, where a closed ring is polarized circumferentially segment by segment. Actuators for generating shear deformations in the circumferential direction are described, for example, in references

[33] -

[36] .

[0068] When a voltage is applied between the outer and central electrodes, the two shear actuators 411 generate a shear force in the same direction along the circumferential direction. Overall, this generates a torque between the upper and lower ends of the vibration generator 410. By driving the shear actuators with an AC voltage, torsional vibrations can be generated.

[0069] The vibration sensor 420 is essentially constructed in a very similar manner: in this embodiment, the vibration sensor 420 comprises only a single annular piezoelectric element that generates an output voltage under the action of a shear deformation between its lower and upper surfaces acting in the circumferential direction.

[0070] The vibration generator 410 and the vibration sensor 420 are electrically insulated from each other by an insulating washer 430. A compressive force F is applied along the axial direction to the stack of disk-ring shaped elements via the end piece 224 configured as a preload nut. C can be added.

[0071] Other vibration directions and configurations 6 shows another configuration for exciting torsional vibrations. The vibration transducer 40 is arranged axially between the proximal end 221 of the clamping set 22 and the clamping part 223 of the workpiece 23. As in the previous example, the vibration transducer 40 is arranged in the region of a vibration node. By means of a suitable preload device, in this embodiment it is also possible to generate an axial preload on the vibration transducer 40.

[0072] The configuration of FIG. 7 is similar to that of FIG. 4, and in this respect reference is made to the above description. However, unlike FIG. 4, the vibration transducer 40 is arranged to generate mainly longitudinal vibrations 42 of the workpiece 23. Here too, a resonant excitation occurs. On the left side of FIG. 7, the amplitude distribution of the resulting longitudinal vibration component 62 is sketched in the C-axis direction of the workpiece and the clamping set. As in the embodiments of FIGS. 4 and 6, the vibration transducer 40 is arranged in the region of the vibration nodes (here in the longitudinal direction). In this embodiment, the piezoelectric longitudinal deformation coefficient d 33 By utilizing this, the annular thickness actuator can be used as a piezoelectric actuator.

[0073] 8 also excites longitudinal vibration of the workpiece 23. In this embodiment, the vibration transducer 40 is positioned below the workpiece 23 in the region of a longitudinal vibration node between the proximal end of the clamping set 22 and the clamping portion of the workpiece.

[0074] In the embodiment of FIG. 9, transverse (radial) vibrations 63 of the gear 23 are excited, the amplitude of which is always the same over the entire circumference of the gear. Since longitudinal vibrations are always accompanied by transverse contractions, a longitudinally acting vibration transducer can be used to induce radial vibrations 63 in the area of ​​the workpiece 23, as already described above in the context of FIG. 3. On the left side of FIG. 9, the longitudinal amplitude distribution 62 and the transverse amplitude distribution 63 are sketched diagrammatically for a non-zero radius R. The vibration transducer 40 is located in the area of ​​a longitudinal node. The workpiece 23 is located in the area of ​​the adjacent longitudinal node, i.e. in the area of ​​the antinode of the transverse vibration.

[0075] 10, the excitation of radial vibrations 63 of the gear 23 is also performed by a longitudinally acting vibration transducer 40. In this embodiment, the vibration transducer 40 is located near a longitudinal vibration node between the proximal end of the clamping set 22 and the clamping point of the workpiece 23.

[0076] Variations Although the present invention has been described above with reference to the embodiments, the present invention is not limited to these embodiments, and various modifications are possible without departing from the scope of the present invention.

[0077] For example, other types of vibration generators than those described above can be used. Also, multiple vibration generators can be used per clamping set. Similarly, the vibration generators can include a number of actuators other than two. For example, multiple vibration generators can be located at different axial positions to selectively generate specific vibration shapes. The generated vibration shapes can be more complex than the examples described above and can include, for example, a superposition of longitudinal, radial, and torsional vibrations.

[0078] The same is true for the vibration sensors: as explained above, several vibration sensors may be provided at different axial positions in order to characterize more precisely the type of vibration and its amplitude distribution.

[0079] Where the vibration generator and / or vibration sensor comprises a flat disc-ring shaped piezoelectric element, as in the previous examples, a number of such elements may be stacked on top of each other with electrodes interposed between them.

[0080] Instead of the disk-ring shaped piezoelectric elements, other shapes of piezoelectric elements may be used, in particular elements in the form of ring segments arranged as a whole to form a ring, or elements of other shapes evenly distributed around the circumference of the clamping set.

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Claims

1. A method for machining a gear-shaped workpiece (23) by a generating process, in particular continuous generating grinding, comprising: The gear-shaped workpiece (23) rotates about the workpiece axis (C) in generating mesh with a generating tool (16), in particular a grinding tool with a worm-shaped tooth profile, 10. A method according to claim 9, wherein said gear-shaped workpiece (23) is specifically excited during machining so as to perform a vibrational movement which is superimposed on said rotation of said gear-shaped workpiece (23).

2. 10. The method of claim 1, The oscillatory motion is an axial direction along the workpiece axis (C); radially relative to the workpiece axis (C), and a twisting direction about the workpiece axis (C); A method including a component along at least one of the directions of motion including

3. 3. The method of claim 1 or 2, The method wherein the vibratory motion has a fundamental frequency greater than 15 kHz.

4. 3. The method of claim 1 or 2, The gear-shaped workpiece (23) is clamped in a clamping device (22) during the generating process; The clamping device (22) is arranged on the workpiece spindle (21), The clamping device (22) has a clamping portion (223) where the clamping device (22) contacts the gear-shaped workpiece (23), The workpiece spindle (21) drives the gear-shaped workpiece (23) clamped in the clamping device (22) to rotate about the workpiece axis (C); The method wherein the vibratory motion of the gear-shaped workpiece (23) is generated by exciting vibrations of the clamping part (223) while the gear-shaped workpiece (23) is in contact with it.

5. 5. The method of claim 4, The excitation of the vibrations is a resonance in which the vibrations are at an eigenmode of the clamping device (22) to which the gear-shaped workpiece (23) is clamped, the eigenmode preferably having a vibration node in the region where the clamping device (22) is connected to the workpiece spindle (21).

6. 5. The method of claim 4, The method wherein said clamping device (22) comprises a vibration generator (410) for exciting said vibrations.

7. 7. The method of claim 6, Electrical excitation signal (V A ) is supplied to the vibration generator (410), The excitation signal (V A at least one electrical sensor signal (V) characterizing the vibration caused by S ) is determined, The excitation signal (V A ) is adjusted to the sensor signal (V S ) controlled method.

8. 8. The method of claim 7, The excitation signal (V A ) and the sensor signal (V S ) is transmitted contactlessly between the rotating clamping device (22) and a fixed control device (50).

9. A clamping device (22) for clamping a gear-shaped workpiece (23) onto a workpiece spindle (21) of a generating machine, in particular a generating grinding machine, and for driving the gear-shaped workpiece (23) in rotation about a workpiece axis (C), comprising: The clamping device (22) has a clamping portion (223) where the clamping device (22) contacts the gear-shaped workpiece (23), The clamping device (22) is characterized in that it comprises a vibration generator (410) for generating vibrations in the clamping part (223) when the gear-shaped workpiece (23) is in contact with the clamping part (223).

10. 10. A clamping device (22) according to claim 9, The vibration generator (410) an axial direction along the workpiece axis (C); radially relative to the workpiece axis (C), and a twisting direction about the workpiece axis (C); a clamping device (22) configured to generate vibrational excitation along at least one of the directions of motion including

11. 10. A clamping device (22) according to claim 9, The vibration generator (410) is a clamping device (22) that includes at least one piezoelectric actuator.

12. 12. A clamping device (22) according to claim 11, The vibration generator (410) includes at least one piezoelectric actuator element (411) in the shape of a disk ring or a ring segment, the ring axis of the piezoelectric actuator element (411) corresponding to the workpiece axis (C).

13. 10. A clamping device (22) according to claim 9, The clamping device (22) defines a proximal end and a distal end; the proximal end is configured to be connected to the workpiece spindle (21); The vibration generator (410) is disposed between the proximal end and the clamping portion (223) or distally from the clamping portion (223) of the clamping device (22).

14. 10. A clamping device (22) according to claim 9, At least one sensor signal (V) characterizing the vibrations of the clamping device (22) on which the gear-shaped workpiece (23) is clamped. S The clamping device (22) further includes a vibration sensor (420) for determining the vibration of the clamping device (22).

15. 15. A clamping device (22) according to claim 14, The clamping device (22) wherein the vibration sensor (420) comprises a piezoelectric sensor.

16. 16. A clamping device (22) according to claim 15, The vibration sensor (420) comprises at least one piezoelectric sensor element (421) in the shape of a disc ring or a ring segment, the ring axis of the piezoelectric sensor element (421) corresponding to the workpiece axis (C).

17. 1. A system for generating oscillatory motion of a gear-shaped workpiece (23) during machining by continuous generating grinding, comprising: A clamping device (22) according to any one of claims 9 to 16, An excitation signal (V) for the vibration generator (410) to induce the vibration of the clamping device (22) on which the gear-shaped workpiece (23) is clamped. A a frequency generator (51) for generating a Optionally, a controller (52), wherein the controller (52) is configured to receive the sensor signal (V S ) and receives the sensor signal (V S ) so that the excitation of the vibration occurs at a predetermined amplitude in resonance. A ).

18. 18. The system of claim 17, The excitation signal (V A ) and optionally the sensor signal (V S The system further includes a transmission device (53, 54) for contactlessly transmitting the signal to the sensor.

19. A generating machine, in particular a generating grinding machine, comprising: a tool spindle (15) for driving a generating tool (16), in particular a grinding tool having a worm-shaped tooth profile, to rotate about a tool axis (B); a workpiece spindle (21) for driving the gear-shaped workpiece (23) to rotate about the workpiece axis (C); a machine controller configured to control the tool spindle (15) and the workpiece spindle (21) such that a roll coupling is established between the rotation of the generating tool (16) generated by the tool spindle and the rotation of the workpiece (23) generated by the workpiece spindle; A generating machine, characterized in that a clamping device (22) according to any one of claims 9 to 16 is attached to the workpiece spindle (21).

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