WO2008135350A2

WO2008135350A2 - Piezoelectric drive

Info

Publication number: WO2008135350A2
Application number: PCT/EP2008/054532
Authority: WO
Inventors: Walter Haussecker; Jörg WALLASCHEK; Vincent Rieger; Jens Twiefel; Tobias Hemsel; Volker Rischmueller; Joerg Wallaschek; Dirk Guenther; Peter Froehlich
Original assignee: Robert Bosch Gmbh
Priority date: 2007-05-07
Filing date: 2008-04-15
Publication date: 2008-11-13
Also published as: WO2008135350A3; DE102007021338A1

Abstract

Piezoelectric drive (10) and method of operating same to move movable parts (11), in particular in a motor vehicle. The drive (10) has at least one piezoelectric motor (12) with at least one piezo-actuator (18). At least one friction element (30) of the piezoelectric motor (12) can generate a relative movement relative to a friction surface (14) opposite the friction element (30). The at least one piezo-actuator (18) is connected to an electronic unit (42) having an electric tuning circuit (46) that tunes the piezoelectric drive (10) to a resonance frequency (44).

Description

description

title

Piezoelectric drive device

State of the art

The invention is based on a piezoelectric drive device and a method for operating such according to the preamble of the independent claims.

With WO 00/28652 Al an ultrasonic motor has become known, in which a rotor shaft is rotated by means of ultrasonic vibrators in rotation. In this case, two ultrasonic vibrators are connected at right angles to each other, both vibrators are supplied with an AC voltage such that the two vibrators vibrate to each other with a phase difference. This vibration generates a movement of a plunger that rotates the rotor shaft. A disadvantage of this ultrasonic motor that due to the design and operation of the vibrators many ultrasonic vibrators are necessary to produce sufficient drive torque. Such a motor is therefore very expensive and requires a complex electronic control and a correspondingly large space for the superposition of the various excited vibrations.

Disclosure of the invention

Advantages of the invention

The piezoelectric drive device according to the invention, as well as the method for operating such a device with the features of the independent claims have the advantage that the piezoceramic is optimally utilized by the operation of the piezoelectric actuators in their resonance frequency. As a result, large displacement of the piezoactuator can be produced with relatively little use of material of the piezoceramic, which results in a large feed, or a large moment on the piezoelectric actuator corresponding friction surface can be transferred. By the resonance operation, the piezoceramic is operated at the point of their highest efficiency, whereby the electrical power loss is greatly reduced and thus heating of the piezoceramic is avoided. By exploiting the dielectric of the piezoceramic no disturbing electromagnetic fields are generated, nor is the operation of the piezoceramic significantly affected by external magnetic fields. When operating the piezoelectric actuator in resonant mode, the amplitude and the force transmission of the piezoelectric actuator can be adapted to the corresponding friction surface by the design of the piezoelectric actuator. Due to the high power density of the piezoelectric actuator, the use of materials of the relatively expensive piezoceramic can be reduced or the power of the piezoelectric drive can be increased. Particularly advantageously, the resonance operation of the piezoelectric actuator can be generated by means of an electrical tuning circuit which regulates the excitation frequency of the piezoelectric actuator to the resonance frequency of the piezoelectric motor. In this case, a load is advantageously avoided by the reactive power, whereby the electrical system is less burdened. Compared with conventional DC motors, no starting currents or blocking currents occur, so that a significantly higher efficiency of the piezo drive can be achieved.

The measures listed in the dependent claims advantageous refinements and improvements of the embodiments specified in the dependent claims are possible. By means of the tuning circuit of the electronics unit of the piezoelectric motor, or the entire drive device can be excited in its resonant frequency. By regulating the zero crossing of the phase characteristic of the drive system, the resonance frequency can be maintained very accurately, whereby the efficiency of the piezoelectric actuator can be significantly increased.

Conveniently, the piezo motor is operated at the frequency of the zero crossing of the phase characteristic of the impedance with positive slope, which can be controlled very easily by the tuning circuit according to the invention.

To maximize the mechanical oscillation amplitude of the piezoelectric actuator, it is advantageously driven in the region of the resonance frequency of the mechanical admittance or the mechanical impedance.

If the piezoelectric actuator is operated in the region of the resonance of the electrical admittance, the reactive power can advantageously be minimized, whereby the efficiency of the piezo- is optimized. Alternatively, the piezo drive can also be operated in the electrical antiresonance (maximum of the impedance).

The piezoelectric actuator is expediently simulated an electrical resonant circuit which is operated to control the resonance frequency in the zero crossing of the phase characteristic of the piezoelectric actuator resonant circuit.

In resonance mode, the piezoceramic, the electronics unit and the voltage source is not charged with a reactive power, whereby the electronics can be performed more easily and can be dispensed with, for example, additional switches and filter elements.

The control of a zero crossing of a phase curve is particularly simple by means of a phase locked loop (PLL), which provides a voltage controlled oscillator (VCO) as a manipulated variable an excitation frequency for the piezoelectric element.

To simplify the control effort, a range of variance around the resonant frequency can be defined, within which the excitation frequency is constantly being scanned.

Since the resonance frequency of the piezoelectric actuators can change due to external influences, the excitation frequency or the variance range of the variable resonance frequency is readjusted.

By using a higher-level control unit, it can also optimally coordinate with one another as an operator a larger number of piezoactuators and / or piezomotors. By inputting a plurality of status signals to control the operator by the operator, the operator can also display error or maintenance information of the drive system.

Preferably, the piezoelectric actuator is only offset in longitudinal vibrations, so that only vibration components are excited along the longitudinal direction with the largest dimension of the piezoelectric actuator. For this purpose, the piezoceramic and the design of the housing of the piezoelectric actuator are optimized accordingly.

If, in the rest state, the longitudinal direction of the piezoelectric actuator is oriented substantially perpendicular to the corresponding friction surface of the drive element, then the longitudinal - A - vibration of a single piezoelectric actuator can be effectively implemented in both opposite directions of movement of the relative movement relative to the friction surface.

To generate a large oscillation amplitude of the piezoelectric actuator in the longitudinal direction, the piezoceramic is biased in the piezoelectric housing in such a way that no tensile forces arise in the piezoelectric ceramic during oscillation operation. This makes it possible to achieve a vibration system with a high rigidity in the longitudinal direction.

Due to the micro-pushing movement of the friction element relative to the corresponding friction surface, a relative movement can be generated without additional inert masses having to be set in motion. By a suitable choice of the friction partner between the friction element and the corresponding friction surface, the vibration of the piezoelectric actuator can be converted very low loss in a linear movement or rotational movement of a drive element. To support the power transmission, in addition to the frictional engagement, a form-fitting connection - for example a micro-toothing - can be formed between the friction element and the friction surface.

Due to the arrangement of the friction element relative to the piezoelectric actuator, the longitudinal vibration of the piezoelectric actuator can be converted into a linear, an elliptical or a circular movement of the friction element, in particular its end facing the friction surface. An elliptical movement of the friction element can be transmitted very harmoniously to the drive element, whereby the direction of the relative movement can be reversed by reversing the direction of rotation.

The drive element with the friction surface can be advantageously designed as a linear drive rail or as a rotor shaft. By the holding force with which the friction element is pressed against the linear rail or the rotating body, the tangential movement component of the friction element is transmitted to the drive element.

It is particularly advantageous to fix the piezomotor to the movable part, so that it moves away from a stationary friction surface with the movable part. For example, the piezomotor can be fastened to a window pane and repel along a rubbing surface of a body-fixed guide rail. Alternatively, the piezoelectric motor can be arranged stationary and Accordingly, the friction surface move, which is arranged on a linear rail of the part to be adjusted.

If the piezoceramic is formed in several layers, between which electrons are connected, a larger oscillation amplitude can be generated with a predetermined voltage. If the layers are arranged transversely to the longitudinal direction of the piezoactuator, the longitudinal oscillation in the longitudinal direction is thereby maximized.

In a preferred embodiment of the invention, the piezoelectric motor has exactly two piezoelectric actuators. These can be favorably operated such that in each case a piezoelectric actuator is excited for a direction of movement of the relative movement. This has the advantage that only exactly one piezoelectric actuator is vibrated by means of the electronic unit, and the second piezoelectric actuator resonates only as an inertial mass. As a result, a complicated superposition of the two simultaneously excited piezoactuator oscillations is prevented. Alternatively, a plurality of piezoelectric actuators can also be controlled simultaneously by means of an identical or by means of different excitation signals. Supply signals.

For example, the Peizomotor for a power window drive in the motor vehicle can be attached to a window pane. By directly generating a linear

Motion is a very fast response time with high dynamics possible. Due to the micro-shock principle, an extremely precise positioning of the part to be adjusted can be achieved with low noise emission.

The resonant frequency of the piezoelectric actuators can be changed very inexpensively by means of positive or negative balancing, in order for example to be able to operate a plurality of piezoactuators with exactly one excitation frequency. For this purpose, housing material can be removed at a corresponding point, or material can be added.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. Show it

1 is a piezoelectric drive device according to the invention,

2 shows a further embodiment for a rotary drive, FIG. 3 shows a piezo element for installation in the piezoelectric actuator according to FIG. 1, FIG.

4 shows a schematic illustration for operating the drive device,

Fig. 5 is a resonance curve of the piezo motor and 6 shows an impedance curve for the piezoelectric drive system FIG. 7 a, b shows a course of the mechanical admittance with a corresponding phase curve,

8 schematically shows the regulation of the excitation signal of the piezoactuator, and FIG. 9 shows a schematic illustration of a phase locked loop of the piezoelectric drive device.

In Fig. 1, a piezoelectric drive device 10 is shown, in which a piezoelectric motor 12 performs a relative movement relative to a corresponding friction surface 14. The friction surface 14 is in this case formed as a linear rail 16, which is fastened, for example, to a body part 17. The piezomotor 12 has at least one piezoelectric actuator 18, which in turn contains a piezoelectric element 20. For this purpose, the piezoelectric actuator 18 has an actuator housing 22 which accommodates the piezoelectric element 20. The actuator housing 22 is formed, for example, sleeve-shaped. In the illustrated embodiments, the piezoelectric element 20 is enclosed by the actuator housing 22. Of the

Piezo actuator 18 has a longitudinal direction 19, in the direction of which the expansions of the piezoelectric actuator 18 is greater than in a transverse direction 24 thereto. The piezoelectric element 20 is preferably biased in the actuator housing 22 in the longitudinal direction 19, such that upon excitation of a longitudinal vibration 26 of the piezoelectric element 20 in this no tensile forces occur. Due to the vibration of the piezoelectric element 20, the entire

Piezoelectric actuator 18 in longitudinal vibration 26 is offset and transmits a vibration amplitude 45 via a bridging web 28 on a friction element 30 which is in frictional contact with the friction surface 14. By the longitudinal vibration 26 of the piezoelectric actuator 18, the bridge web 28 is set in a tilting movement or a bending movement, so that the friction surface 14 facing the end 31 of the friction element 30 a

Performs micro-momentum motion. The interaction between the friction element 30 and the friction surface 14 is shown in the enlarged section, in which it can be seen that the bridging web 28, which is arranged in the rest position approximately parallel to the friction surface 14, tilted with respect to the friction surface 14 at the excited vibration of the piezoelectric actuator 18. In this case, the end 31 of the friction element 30 performs, for example, an elliptical movement 32 or circular movement, by means of which the piezomotor 12 abuts along the linear rail 16. The piezomotor 12 is mounted in the region of vibration nodes 34 of the piezoactuators 18 and connected, for example, to a part 11 to be moved. At the same time, the piezomotor 12 is pressed against the rubbing surface 14 via a bearing 36 with a normal force 37. As a result, the end 31 of the friction element 30 now executes an elliptical movement 32 which, in addition to the normal force 37, has a tangential force component 38 which controls the advance of the Piezo motor 12 relative to the rubbing surface 14 causes. In an alternative embodiment, the friction element 30 performs only a linear pushing movement at a certain angle to the normal force 37. This also leads to a relative movement by means of micro-collisions.

In the exemplary embodiment according to FIG. 1, the piezomotor 12 has exactly two piezoactuators 18, which are both arranged approximately parallel to their longitudinal direction 19. In this case, the bridge web 28 is arranged transversely to the longitudinal direction 19 and connects the two piezo actuators 18 at their end faces 27. The bridging web 28 is formed for example as a flat plate 29, in the middle of the friction element 30 is arranged. In a preferred mode of operation of the piezoelectric drive device 10, only one of the two piezoactuators 18 is excited for a relative movement in a first direction 13. In this case, the second, non-excited piezoactuator 18 acts via the bridging web 28 as an oscillating mass, due to which the bridging web 28 is tilted or bent with the friction element 30 with respect to the longitudinal direction 19. According to the

Stiffness of the structure of the piezoelectric motor 12 thus the longitudinal vibration 26 of the piezoelectric element 20 is converted into a micro-shock movement with a tangential force component 38. The electrical excitation of the piezoelectric element 20 via electrodes 40, which are connected to an electronic unit 42. For a movement of the piezo motor 12 in the opposite directions 15 is accordingly the

Piezo element 20 of the other piezoelectric actuator 18 excited by means of the electronic unit 42. In this mode of operation, only one piezoelectric element 20 of the piezoelectric motor 12 is always excited, so that there can be no superimposition of two oscillatory excitations of the two piezoelectric actuators 18.

According to the invention, the piezoelectric drive device is operated at its resonance frequency 44. For this purpose, the electronic unit 42 has a tuning circuit 46, which controls the corresponding piezoelectric element 20 in such a way that the entire system oscillates in resonance. The electronic unit 42 may be arranged, for example, at least partially within the actuator housing 18 or the bearing 36. In Fig. 1, the amplitudes 45 of the resonance frequency 44 of the longitudinal vibration 26 are shown in the two piezoelectric actuators 18, wherein the two piezoelectric actuators 18 are not excited simultaneously in this mode of operation.

FIG. 2 shows a variation of the drive device 10, in which the piezomotor 12 is mounted in a body part 17. By contrast, the friction surface 14 is formed as a circumferential surface of a rotary body 48, so that through the Plunger movement of the friction element 30 of the rotary body 48 is rotated. According to the mode of operation described with reference to FIG. 1, the direction of rotation 49 of the rotary body 48 can in turn be predetermined by the activation of only one piezoelectric element 20 on one of the two piezoactuators 18. Such a drive device 10 generates a rotation as a drive movement and can thus be used in place of an electric motor with a downstream transmission.

In Fig. 3, a piezoelectric element 20 is shown enlarged, as it can be used for example in the piezoelectric motor 12 of FIG. 1 or 2. The piezoelectric element 20 has a plurality of separate layers 50, between which the respective

Electrodes 40 are arranged. If a voltage 43 is applied to the electrodes 40 via the electronic unit 42, the piezoelectric element 20 expands in the longitudinal direction 19. The expansion and the contraction of the individual layers 50 add up, so that the total amplitude 45 of the piezoelectric element 20 in the longitudinal direction 19 can be predetermined by the number of layers 50. The layers 20 are transverse to

Longitudinal direction 19 arranged in the actuator housing 22, so that the entire piezoelectric actuator 18 is offset by the piezoelectric element 20 in longitudinal vibration 26. The piezoelectric element 20 is preferably designed so that very large amplitudes 45 can be generated during resonance operation of the piezoelectric element 20.

FIG. 4 shows a model of the piezoelectric drive device 10 which serves as the basis for adjusting the resonance frequency 44. In this case, in the form of an electrical equivalent circuit 51 of the piezoelectric actuator 18 is shown as a resonant circuit 52 in which an inductance 53 with a first capacitor 54 and a resistive load 55 are connected in series. For this purpose, a second capacitance 56 is connected in parallel. At this oscillation circuit 52, a voltage 43 is applied by means of the electronic unit 42. By converting the longitudinal vibration 26 of the piezoelectric actuator 18 in the plunger movement of the friction element 30, the resonance frequency 44 of the piezoelectric actuator 18 is influenced. Furthermore, the resonance frequency 44 of the entire drive device 10 depends on the load 58, which is determined for example by the weight of the part 11 to be adjusted. Furthermore, the resonance frequency depends on the coupling of the power transmission 57, which is essentially determined by the friction condition between the friction element 30 and the friction surface 14.

In accordance with this circuit diagram, when the adjusting device 10 is excited by means of the electronic unit 42, a frequency response occurs, as shown in FIG. 5. Here, the power 59 is plotted against the frequency 69. At zero-crossing 61 of the shown reactive power 62 results in a maximum 63 of the active power 64. The maximum 63 of the active power 64 occurs at the resonance frequency 44, to which the piezoelectric drive device 10 is controlled by means of the tuning circuit 46. The resonance frequency 44 is for example in the range between 30 and 80 kHz, preferably between 30 and 50 kHz.

FIG. 6 shows the associated impedance behavior of the piezo motor 12 via the frequency response. The phase characteristic 60 of the impedance of the adjusting device 10 represented by the oscillatory circuit 52 according to FIG. 4 has a first positive-slope zero-crossing 65 and a second negative-zero zero crossing 66 corresponding to the series resonance and the parallel resonance of the oscillating circuit 52 , The phase angle 68 is shown on the Y-axis on the right side of the diagram. In order to keep the drive device 10 in resonance mode - for example, even with a variable load 58 - the tuning circuit 46 controls the frequency 69, for example, on the zero-crossing 65 with a positive slope, which electronically relatively easily by means of a phase locked loop 47 (Phase Locked Loop, PLL). is feasible. The left Y-axis 74 represents the magnitude 70 of the impedance, wherein the impedance curve 70 over the frequency 69 is a minimum 71 (antiresonance, corresponds to the maximum of the electrical admittance) at the first zero crossing 65 and a maximum 72 at the second zero crossing 66 has.

In Fig. 7a, the course of the mechanical admittance 76 is shown, as it results from the quotient of the mechanical vibration speed of the piezoelectric actuator 18 by the electrical supply voltage 43. The mechanical admittance 76 represents the reciprocal of the mechanical impedance (not shown), which results from the quotient of the supply voltage 43 by the mechanical oscillation speed of the piezoelectric actuator 18. The mechanical admittance 76 is shown over the frequency range 69 and forms a maximum at a resonance frequency 44 and a minimum at an anti-resonance frequency 77.

In FIG. 7b, a phase curve 60 of the mechanical phase angle 68 between the mechanical oscillation speed and the electrical supply voltage 43 is recorded accordingly. In the region of the resonance 44 of the mechanical admittance 76, the phase curve 60 has a zero slope 66 with a negative slope, and with the anti-resonance frequency 77 a corresponding zero passage 65 with a positive slope. The tuning circuit 46 controls the excitation frequency 93 of the piezoelectric actuator 18, for example, to the resonance frequency 44th the mechanical admittance 76, being used as a controlled variable of the zero-crossing 66 with a negative slope of the corresponding phase curve 60.

The reciprocal of the mechanical admittance 76 forms the mechanical impedance (not shown), which then has a very similar course as the electrical impedance curve 70 according to FIG. 6. The phase characteristic (not shown) corresponding to the mechanical impedance is likewise given by the reciprocal value 7b and thus has a very similar course as the phase characteristic 60 of the electrical impedance of Fig. 6. In the electrical impedance curve 70 of FIG. 6 can also by the formation of the

Inverse, the electrical impedance can be formed with a corresponding phase curve. The resonant frequencies 44 and the anti-resonant frequencies 77 may differ between the mechanical admittance 76 and the electrical admittance. Therefore, according to the requirements of the piezoelectric driving device 10, the piezoactuator 18 can be controlled to the resonance frequency 44 or the anti-resonant frequency 76 of the electrical or mechanical impedance.

In Fig. 8, the control process of a piezo motor 12 is shown, which is controlled by means of a tuning circuit 46 having the electronic unit 42. As a manipulated variable 80, for example, the excitation frequency 93 of the supply voltage 43 is used, but also the amplitude or other parameters of the excitation signal 94 can be specified. For example, as an excitation signal 94, a rectangular, triangular, sinusoidal or trapezoidal voltage can be applied to the piezoelectric actuator 18 whose frequency and / or its amplitude is regulated. As a setpoint 83, for example, a specific resonance frequency 44, or a certain

Variance range 82 given around the resonant frequency 44, which controls the tuning circuit 46. Furthermore, additional signals 91 can be supplied to the electronic unit 42, which, for example, reflect environmental influences or input instructions. The piezomotor 12, which has one or more piezo actuators 18, effects a mechanical oscillation 99, which causes a relative movement between the piezomotor 12 and the rubbing surface 14 at a specific frequency. As a controlled variable 79, the actual values 84 of the piezomotor 12 or of the adjusting device 10, for example the actual oscillation frequency, are returned to the tuning circuit 46.

In Fig. 9, a phase-locked loop 47 (Phased Locked Loop, PLL) is shown, which is particularly adapted to a zero-crossing 65, 66 of the phase curve 60, 78 as Rule size 79 to use. A phase detector 85 identifies the frequency 69 of the zero crossing 65, 66 and supplies the signal to a filter 86. The actual signal 84 is fed to a voltage controlled oscillator (VCO) 87, which provides a voltage signal 43 with a specific frequency as the manipulated variable 80. The output signal of the VCO 87 is correspondingly amplified by means of an amplifier 88 and supplied to the piezoelectric actuator 18, which converts this voltage signal 43 into a corresponding mechanical oscillation of the piezoelectric element 20. For the control of the resonance frequency 44, both the mechanical vibration signal of the piezoelectric actuator 18 can be used, or directly the electrical excitation signal, so that the phase detector 85, the zero crossing 65, 66 of the mechanical admittance or electrical admittance, or the electrical or mechanical impedance detected.

When using a plurality of piezo motors 12 as a drive of a window (Part 11), the piezo motors 12 must be coordinated to ensure the synchronization of the part 11. The networking of the individual piezoelectric actuators 18 is intended to provide an accumulation of the driving forces at the same feed rate. The control should tune the operation behavior of the respective piezo motors 12 with each other automatically during operation. The required synchronization of the piezo motors 12 is ensured via the electronic unit 42. When using two rails 16, each with one or more piezo motors 18 per rail 16, the piezomotor positions can optionally be detected by suitable sensors. The control of a single piezo motor 12 involves a real-time measurement of its actual electro-mechanical state, which is influenced by external parameters such as aging, load, wear or temperature. Depending on the requirements of the quality of the drive 10 different strategies are possible: each piezo motor 12 is controlled by a separate control unit 42, or in more demanding drive devices 10, the following method can be used. As soon as several piezo motors 12 work together, the information processing of the mechatronics is superimposed on self-optimized information processing. This expansion of the overall drive system in the form of a higher-level component decides which piezo motors 12 will be operated, what parameters and setpoints need to be adjusted, and will make fault diagnoses and maintenance decisions. This superordinate unit or so-called operator 90 includes a mathematical modeling of the overall drive system 10, consisting of electrical drive, the piezoelectric material behavior, the mechanical vibration system and a friction element / friction surface contact model. By capturing and returning all necessary quantities into this overall model, it is possible to draw conclusions about the overall behavior and to configure a process control for the entire system. The operator 90 receives information from the individual motor controls and from the driven part 11 on the one hand and receives state signals from the outside on the other hand (user input,

Environmental influences, ...). The operator 90 provides the separate electronics units 42 with changed parameters and setpoints, and provides the user with system information, such as information. Drive status or due maintenance, back. In the event of a failure of the operator 90, the individual piezomotors 90 are still able to move the part 11. By integrating further intelligence into the drive system (embedded systems), further important functions can be realized, such as In an alternative, simplified embodiment, all the piezo actuators 18 of the drive device 10 are operated at a fixed frequency, which is in the resonance range of all piezoelectric actuators 18 or in the immediate vicinity of the piezoactuators. In a further embodiment, the excitation frequency 93 is varied continuously over the variance region 82.

At the resonance frequency 44, the piezoelectric drive 10 reaches its greatest efficiency. The resonant frequency 44 of the piezoelectric actuator 18 depends on the structure of the piezoelectric motor 12, the materials used and the external influences, such as temperature, aging and the load by the movable member 11 from. Further, the piezoelectric actuators 18 may have different resonance frequencies 44, even if the piezoelectric actuators 18 were made identical. To drive a plurality of piezoelectric actuators 18 with a single resonance frequency 44, and thereby simplify the tuning circuit 46, the piezo actuators 18 can be mechanically manipulated to shift their resonance frequency 44. In this case, for example, material 95 is removed from the actuator housing 22 (see FIG. 2). For this purpose, material 95 on the piezoelectric actuator 18 can be reduced at attractive locations of the piezoelectric housing 22 by means of milling, drilling, eroding or grinding. As a further option, additional material 96 may be attached to the piezoactuator 18 at another piezoelectric actuator 18, for example by means of bonding, welding, coating. This positive or negative balancing can be realized at all accessible locations of the piezoactuator 18 to shift the resonant frequency 44 in the desired direction.

It should be noted that with regard to the embodiments shown in the figures and in the description of diverse combination options of the individual Characteristics are possible with each other. Thus, for example, the specific design of the piezoelectric actuators 18, the actuator housing 22, the piezoelectric elements 20 (monobloc, stack or multilayer), the bridging web 28 and the friction element 30 can be varied according to the application. In this case, the plunger movement may be formed as a pure pushing movement or as a substantially elliptical trajectory, wherein according to the transverse component of the power transmission, the friction pairing between the friction element 30 and the friction surface 14 has a higher or lower coefficient of friction. As a limiting case, training with a pure form-fitting, for example by means of a micro-toothing is possible in which the friction element 30 engages without friction in corresponding recesses of the drive element, for example, the linear guide rail 16 or the rotary body 48. In a further variation of the piezoelectric actuator 18 may also be operated with a bending vibration, which overlaps, for example, with the longitudinal vibration 26. Likewise, the corresponding vibrations of a plurality of piezoelectric actuators 18 of a piezoelectric motor 12 can be excited simultaneously (single-phase or multi-phase), whereby a superposition of these vibrations a

Causes plunger movement, which sets the drive element in motion. Preferably, the drive unit 10 according to the invention is used for adjusting movable parts 11 in the motor vehicle, but is not limited to such an application.

Claims

claims

1. A method for operating a piezoelectric drive device (10) for adjusting moving parts (11), in particular in the motor vehicle, with at least one piezomotor (12) having at least one piezoelectric actuator (18), wherein by means of at least one friction element (30) of the Piezo motor (12) has a relative movement with respect to a friction element (30) opposite

Friction surface (14) is generated, characterized in that the at least one piezoelectric actuator (18) is connected to an electronic unit (42) having an electrical tuning circuit (46) which controls the piezoelectric drive device (10) to a resonant frequency (44) ,

2. The method according to claim 1, characterized in that the tuning circuit (46) controls an excitation frequency (93) for maintaining the resonance frequency (44) to a zero crossing (65, 66) of a phase characteristic (60) of a controlled variable (79).

3. The method according to any one of claims 1 or 2, characterized in that the tuning circuit (46) identifies the zero crossing (65, 66) of the phase characteristic (60) with a positive slope and / or negative slope.

4. The method according to any one of the preceding claims, characterized in that the tuning circuit (46) the piezoelectric drive device (10) in the region of the resonance frequency (44) of the mechanical admittance (vibration over voltage) or the mechanical impedance (reciprocal) operates.

5. The method according to any one of the preceding claims, characterized in that the tuning circuit (46), the piezoelectric drive device (10) in the region of the resonance frequency (44) of the electrical admittance or the electrical impedance operates.

6. The method according to any one of the preceding claims, characterized in that the tuning circuit (46) an excitation signal (94) to a maximum or a Minimum of an electrical or mechanical admittance or impedance curve controls.

7. The method according to any one of the preceding claims, characterized in that the piezoelectric drive device (10) is designed such that their

Equivalent circuit (51) is simulated by an inductor (53), a capacitor (54) and an ohmic resistor (55) which are connected in series with each other, wherein a further capacitor (56) is connected in parallel thereto, and the tuning circuit (46 ) controls the excitation frequency (93) to maintain the electrical resonance frequency (44) on the zero crossing (65, 66) of the phase characteristic (60) of the equivalent circuit (51).

8. The method according to any one of the preceding claims, characterized in that the tuning circuit (46) controls the piezoelectric drive device (10) to the resonant frequency (44), such that approximately no reactive power occurs.

9. The method according to any one of the preceding claims, characterized in that the tuning circuit (46) comprises a phase locked loop 47 (phase locked loop, PLL), by means of a VCO 87 (Voltage Controlled Oscillator) the

Excitation frequency (93) for the piezoelectric actuator (18) as the manipulated variable (80).

10. The method according to any one of the preceding claims, characterized in that the amplitude of the excitation voltage (43) as an excitation signal (94) can be specified, in particular as a cascade control together with a further excitation signal (94).

11. The method according to any one of the preceding claims, characterized in that the tuning circuit (46) continuously varies the excitation frequency (93) over a variance region (82) about the resonance frequency (44) of a piezoactuator (18), and in particular the variance region (82). in case of deviations of the individual resonance frequencies (44) of different piezo actuators (18) all resonance frequencies (44).

12. The method according to any one of the preceding claims, characterized in that the tuning circuit (46) tracks the excitation frequency (93), or its variance region (82) under varying operating conditions.

13. The method according to any one of the preceding claims, characterized in that for driving a plurality of piezo motors (12) an operator (90) by means of a mathematical modeling under supply of state signals of the individual piezo actuators (18), and / or environmental influences and / or of

User inputs and / or error diagnoses the manipulated variables (80) of the excitation signal (94) of the individual piezo actuators (18) pretends.

14. The method according to any one of the preceding claims, characterized in that the piezoelectric actuator (18) has a longitudinal direction (19), along which the

Piezoelectric actuator (18) has a greater extent than in a transverse direction (24) thereto, and the piezoelectric actuator (18) by means of the electronic unit (42) in longitudinal vibration (26) - in particular only in the longitudinal direction (19) without transverse components - is added.

15. The method according to any one of the preceding claims, characterized in that the friction element (30) performs a dynamic micro-shock motion and repels by means of frictional engagement and / or positive engagement of the friction surface (14).

16. The method according to any one of the preceding claims, characterized in that the friction element (30) is geometrically arranged on the piezomotor (12) that the longitudinal vibration (26) of the piezoelectric actuator (18) in an elliptical path movement (32) or linear thrust movement of Friction element (30) is converted.

17. The method according to any one of the preceding claims, characterized in that only a first piezoelectric actuator (18) and for the opposite direction of movement (15) only a second piezoelectric actuator (18) is actuated for a first movement direction (13) of the relative movement, and the piezo actuators (18) in particular are subjected to an identical excitation signal (94).

18. The method according to any one of the preceding claims, characterized in that the piezoelectric drive device (10) has an electronic unit (42) which always drives two or more piezo actuators (18) of the piezo motor (12) with a single-phase excitation signal (94).

19. Piezoelectric drive device (10) for applying the method according to one of the preceding claims, characterized in that the longitudinal direction (19) of the piezoelectric actuator (18) extends approximately perpendicular to the friction surface (14).

20. Piezoelectric drive device (10) according to any one of the preceding claims, characterized in that the piezoelectric actuator (18) has an actuator housing (22) in which a piezoceramic (21) is arranged, wherein the piezoceramic (21) in the actuator housing (22). is biased in the longitudinal direction (19).

21. Piezoelectric drive device (10) according to any one of the preceding claims, characterized in that by means of the biasing of the piezoelectric element (20) whose damping and thus the resonance frequency (44) of the piezoelectric actuator (18) is adjustable.

22. Piezoelectric drive device (10) according to one of the preceding claims, characterized in that the resonance frequency (44) of the piezoelectric actuator (18) by means of a targeted material compensation on the piezoelectric body (22) is adjustable, in particular to the resonance frequencies (44) of different piezoelectric actuators (18 ) to match.

23. Piezoelectric drive device (10) according to any one of the preceding claims, characterized in that the targeted material compensation by application of material or removal of material on the actuator housing (22) can be realized.

24. Piezoelectric drive device (10) according to any one of the preceding claims, characterized in that the piezomotor (12) on the movable part (11) is arranged, and the friction surface (14) is designed karossieriefest.