POSITIONING DEVICE AND METHOD FOR OPERATING SUCH A POSITIONING DEVICE

Description

[0001] The invention relates to a positioning device according to claim 1 and a method for operating such a positioning device according to claim 9.

[0002] A piezoelectrically driven positioning device is known from EP 1 752 642 A1. Piezoelectrically driven positioning devices enable fine positioning in ranges from a few tenths of picometers to several centimeters. Piezoelectric multilayer actuators are used as actuators in these mechanical systems. Piezoelectric actuators are electromechanical energy converters whose operating principle is based on the deformation of certain crystals under the influence of an electric field. The actuators consist of piezoelectric single crystals, piezoelectric monocrystalline ceramics, or piezoelectric polymer composites.

[0003] Piezoelectrically driven positioning devices are used, among other things, in highly complex and therefore expensive systems, such as lithography machines or optical telescopes. Although the multi-layered actuators operate predominantly quasi-statically, i.e., far below the system's lowest resonance, they, as well as the solid-state joints typically used in such positioning devices—through which the movement of the driven element is achieved via elastic deformation—are nevertheless subject to constant mechanical stress. The contraction and expansion of the actuator, or the bending of the solid-state joints, can occur up to 20,000 times per second during operation.With increasing operating time, microcracks, short circuits, delaminations, or other defects can occur in the actuators, guides, joints, or other components of the micropositioning device. These defects can negatively impact the device's operation, potentially leading to total failure. A sudden failure of the positioning device typically results in high costs.

[0004] Most of the aforementioned defects do not typically appear suddenly, but rather develop over time, starting with a minor initial defect and then propagating. Every mechanical system exhibits a specific resonance pattern, which depends on the shape, geometric dimensions, material properties, etc., of individual system components. Defects cause a change in a system's resonance pattern. The emergence of resonances that were not previously present, or a change or elimination of resonances previously present in the system, indicates the development of defects.

[0005] US Patent 3,720,098 discloses a method for the non-destructive measurement of material properties of an object using ultrasound waves. For this purpose, ultrasound waves are induced into the object under investigation using a transmitter, and their propagation time is measured using a receiver. By analyzing the ultrasound wave propagation within the object, conclusions can be drawn about its material properties.

[0006] The scientific article 'Rapid Nondestructive Testing of Ceramic Multilayer Capacitors' by O. Boser, P. Kellawon, and R. Geyer, published in IEEE Transactions on Components, Hybrids and Manufacturing Technology, Vol. 12, No. 1, 1989, describes a method for the non-destructive detection of cracks, delaminations, or other defects in a multilayer piezoceramic capacitor. The method is based on the excitation of standing ultrasonic waves within the capacitor. The capacitor's impedance is recorded using an HP Model 4192A laboratory impedance analyzer. It is shown that a change in the impedance profile of a multilayer capacitor is evidence of an internal defect.

[0007] From the scientific article 'Impedance Spectroscopy of Piezoelectric Actuators' by CR Bowen, M. Lopez-Prieto, S. Mahon, and F. Lowrie in: Scripta mater, 42 (2000), 813-818, a method for the non-destructive detection of cracks, delaminations, or other defects in a multilayer piezoelectric actuator is known. This method examines the change in the actuator's resonance pattern due to internal defects. For this purpose, an impedance spectrum of the actuator is compared with direct measurements using an optical and a scanner electron microscope. The impedance is recorded using a laboratory impedance analyzer (Solartron 1260) from below to above the actuator resonance. It is confirmed that by examining the impedance of the multilayer piezoelectric actuator, it is possible to detect defects within the actuator quickly and non-destructively.

[0008] US Patent 2010 / 0013352 A1 describes a system for analyzing and suppressing unwanted vibrations in various machines, such as turbines, motors, or robots. The system includes a number of piezoelectric vibration sensors, actuators for generating vibrations, and a controller connected to the sensors and actuators. The measured vibrations are transmitted to the controller via feedback, which then dynamically modifies the control signal for the actuators. To suppress the unwanted vibrations, the controller controls the actuators according to a vibration suppression algorithm.

[0009] From EP 1 735 586 B1, a device for the non-destructive detection of structural damage is known. The device comprises a piezoelectric sensor and an actuator. The actuator generates acoustic waves in the structure under investigation. The sensor receives the waves reflected by the structure. An evaluation of the sensor signal allows conclusions to be drawn about the presence of structural damage.

[0010] The object of the invention is to provide a positioning device that enables the prediction or detection of defects occurring within the positioning unit, and to provide a method for operating such a positioning device in order to predict or detect defects within the positioning unit. This particularly enables the timely replacement of relevant components of the positioning unit before, in the worst case, its total failure occurs.

[0011] The positioning device according to the invention comprises a positioning unit and a controller. The positioning unit, in turn, comprises at least one piezoelectric and preferably multilayer actuator, which serves to move a drive element, wherein the movement of the drive element is caused by targeted mechanical deformations of the at least one actuator, and the movement of the drive element is provided for driving or positioning an element to be positioned. The positioning device has: a positioning unit comprising a piezoelectric actuator, a drive element movable by the actuator and provided for coupling with an element to be positioned, and a controller, wherein the positioning device has a defect analysis device for detecting defects in the positioning unit, wherein in the case ofthat the positioning unit has a single actuator, which comprises a generator and a receiver of acoustic ultrasonic waves, and in the case that the positioning unit has multiple actuators, at least one of the actuators comprises at least one generator of acoustic ultrasonic waves and at least one other of the actuators comprises at least one receiver of acoustic ultrasonic waves, and the defect analysis device has a measurement signal generator for generating a measurement signal in the form of an alternating electrical voltage for exciting the generator(s), wherein the defect analysis device has a resonance analyzer for analyzing an electrical signal generated by the receiver(s), wherein the resonance analyzer is configured to predict or detect defects in the positioning unit,that this, by comparing a resonance pattern of the positioning unit before normal operation with a resonance pattern of the positioning unit during normal operation, detects and analyzes the emergence of new resonances or the disappearance or change of previously existing resonances, wherein the resonance analyzer is configured to perform the comparison of the resonance pattern before normal operation with a resonance pattern during normal operation according to one of the following alternatives (A), (B), (C), (D), (E): (A) the measurement signal generator is configured such that, in order to determine the resonances that were previously present and have now disappeared or changed, it generates an electrical sinusoidal voltage whose frequency changes periodically from an initial to an final value; (B) the measurement signal generator is configured such that the frequency value of the measurement signal is equal to a measurable resonance frequency value of an actuator,wherein the resonant frequency belongs to the various types of acoustic ultrasonic waves and wherein, after a brief excitation of a generator at the resonant frequency, the decay of the positioning unit is recorded via a receiver and, in order to detect a change in resonance, the recorded decay curve is compared with a decay curve recorded at an earlier time; (C) the measurement signal generator is configured such that the frequency value of the measurement signal is equal to a measurable resonant frequency value of the positioning unit, wherein, after a brief excitation of a generator, the decay behavior of the positioning unit is recorded in order to detect a change in resonance and is compared with a decay behavior recorded at an earlier time; (D) the measurement signal generator is configured such that the frequency value of the measurement signal is equal to at least one measurable resonant frequency value of the positioning unit,(E) the measurement signal generator is configured such that the frequency value of the measurement signal is substantially equal to a measurable resonance frequency value of the positioning unit, and the reflected pulse is received by a receiver during or after a brief excitation of a generator, and parameters of the reflected pulse are recorded for the purpose of detecting a resonance change and compared with parameters received at an earlier time.

[0012] To transmit the movement of the drive element to the element to be positioned, a coupling between the drive element and the element to be positioned is provided. This coupling can, for example, be a rigid mechanical connection, resulting in a direct conversion of the drive element's movement to the element to be positioned. However, the coupling can also be implemented as a friction contact, and in particular as an intermittent friction contact between the drive element and the element to be positioned. In this case, a frictional contact exists between the drive element and the element to be positioned only temporarily, i.e., during a drive step, and a mechanical coupling via a frictional contact is present during this period.Each drive step is then followed by a phase in which the drive element returns to a starting position, thus preparing the next drive step.

[0013] If the positioning unit has a single actuator, this actuator is designed and configured, in addition to its drive function, to act as both a generator and a receiver of ultrasonic acoustic waves. If the positioning unit has multiple actuators, i.e., at least two, at least one of the actuators is designed and configured to act as a generator of ultrasonic acoustic waves, and at least one other actuator is designed and configured to act as a receiver of ultrasonic acoustic waves.

[0014] In other words, the positioning device according to the invention, or its positioning unit, comprises either only one piezoelectric and preferably multilayer actuator, which then, in addition to its function of moving the drive element, simultaneously acts as a generator and receiver of acoustic ultrasonic waves, thus combining the functions of drive, generator, and receiver, or several, i.e., at least two, piezoelectric and preferably multilayer actuators, of which either only one, or several, or all simultaneously act as generators and receivers of acoustic ultrasonic waves in addition to moving the drive element. Furthermore, it is possible that, in the case that the positioning device or the positioning unit comprises several actuators, one or more of the actuators, in addition to their drive function, act only as generators of acoustic ultrasonic waves.function, and another actuator or several other actuators function only as receivers of acoustic ultrasonic waves in addition to the drive function, so that the functions drive plus generator and drive plus receiver are divided among at least two different and spatially separated actuators.

[0015] When subsequent parts of the description or the claims refer to "an actuator" or "the actuator" (i.e., singular), this is not to be understood as referring to a single actuator. Rather, the use of the singular in connection with the term "actuator" (i.e., "an actuator" or "the actuator") is to be understood or interpreted as meaning that the features relating to the actuator either apply only to the single actuator, or, in the case of multiple actuators, to all or only some of them, or only one of them. For example, if an arrangement of an actuator is described, then this arrangement description refers either, i.e., in the case of a single actuator, to that single actuator, or, i.e., in the case of multiple actuators, to one of the actuators, to all of the actuators, or only to some of the actuators, or only to one of the actuators.The foregoing applies identically to the use of the terms 'a generator' and 'a receiver' herein.

[0016] The term 'or' used herein is to be understood – unless explicitly stated otherwise – as an inclusive or, i.e., as a non-exclusive disjunction. In this context, for example, the phrase 'the actuator has the function of a generator or a receiver' is to be understood as meaning that the actuator has the function of a generator or the function of a receiver, or alternatively, that the actuator has the function of both a generator and a receiver.

[0017] The actuator(s) perform the function of the mechanical control element in the positioning unit, with the number of actuators used being primarily determined by the application. In addition to its control function, a single actuator also functions as both a generator and a receiver of ultrasonic waves. In this case, i.e., with a single actuator, it incorporates both the generator and the receiver of ultrasonic waves. The generator's function is to produce ultrasonic waves, while the receiver's function is to receive them.

[0018] The actuator is, for example, arranged between solid joints and connected or coupled to the drive element via these joints. The movement or deformation of the actuator is transmitted to the drive element through elastic deformation of the solid joints.

[0019] In the case of a multilayer actuator, it is constructed from several layers, each consisting of two electrodes and a polarized piezoelectric material positioned between the electrodes. This is also referred to as a multilayer actuator.

[0020] The controller comprises a control controller for the actuator or positioning unit, a defect analysis device that excites the acoustic ultrasound wave generator and records and analyzes the signal from the acoustic ultrasound wave receiver, and optionally a commutator. The optional commutator switches between actuator operation (i.e., generating movement or deformation) and sensor operation as either a generator or a receiver. The controller can also include an interface to a computer with a screen, allowing for visual defect analysis by a person.

[0021] The control controller includes a power output stage for the actuator, a trajectory and signal generator, a position controller for regulating the position and optionally the speed or acceleration of the positioning unit.

[0022] The defect analysis device has the functions of controlling and / or regulating the actuator or positioning unit, exciting the generator(s) of acoustic ultrasound waves with a measurement signal, and processing the signal coming from the receiver(s) of the acoustic ultrasound waves. The defect analysis device comprises at least one measurement signal generator for generating an electrical sinusoidal voltage and a resonance analyzer for analyzing a signal generated by an actuator acting as a receiver.

[0023] The piezoelectric material for the actuator can be a monocrystalline piezoelectric material, a polycrystalline piezoelectric ceramic, a piezoelectric polymer material, or another piezoelectric or electrostrictive material. The positioning unit can include one or more actuators, preferably multilayer actuators. If solid-state joints are used in the positioning unit, these can be designed as bending or torsional joints.

[0024] The actuator is connected to the controller to excite the generator and to process the signals received from the receiver of acoustic ultrasonic waves.

[0025] Using an actuator in the positioning unit not only as a control element but also as a generator or receiver of acoustic ultrasonic waves gives the positioning unit entirely new qualitative properties. This avoids the costly installation of additional discrete transmitters and receivers. The failure probability of the positioning unit or positioning device is increased due to the absence of additional system components.

[0026] The resonance analyzer processes the signal from the current sensor, stores it along with the signal from the measuring generator, and compares and analyzes two recorded resonance signals or spectra. Efficient and appropriate neural network algorithms are used for this comparison and analysis. If defined deviations are detected in the analyzed resonance patterns, a visual or other warning is issued. The data can also be transmitted from the resonance analyzer to a computer screen via an optional interface. An operator can then perform a visual analysis or inspection of the measurement data as needed.

[0027] An advantageous embodiment of the positioning device according to the invention provides that the measurement signal generator is configured to generate an electrical sinusoidal voltage with a periodic frequency sweep. This allows the positioning unit to be periodically excited in a specific range, so that a resonance pattern is generated in a defined frequency range, which can then be analyzed.

[0028] Another advantageous embodiment of the positioning device according to the invention provides that the defect analysis device includes a linear or clocked broadband output voltage or current amplifier, which amplifies the signal generated by the measurement signal generator in the necessary frequency range for excitation of the generator. In addition, it can be advantageous for the defect analysis device to use the same power output stage as the output voltage or current amplifier for the measurement signal generator, which is used to control the actuator from the control controller.

[0029] It can be advantageous for the defect analysis device to include a white noise generator, and it is particularly advantageous if the measurement signal generator is suitable for generating this white noise. The white noise comprises a broad spectrum of frequencies with a constant power spectral density within a defined frequency range. The signal can be advantageously used as a broadband and efficient excitation for the positioning unit to obtain its resonance image.

[0030] Furthermore, it can be advantageous for the position controller or the trajectory and signal generator of the controller to be implemented using an integrated circuit, such as a Digital Signal Processor (DSP) or a Field Programmable Gate Array (FPGA), and for the measurement signal generator and the resonance analyzer to be implemented as a single program module in the same integrated circuit. Particularly in cost-sensitive applications, it is beneficial to integrate the functions of the defect analysis device into the same integrated circuit that is already used for the control tasks of the positioning unit.

[0031] Furthermore, it can be advantageous for the resonance analyzer to have a data interface to a screen for visual monitoring of a resonance image. The data is transmitted from the resonance analyzer to a computer monitor via this interface. An operator can then perform a visual analysis or check of the measurement data as needed.

[0032] Furthermore, it can be advantageous for the defect analysis device to include a current sensor for acquiring a signal generated by an actuator or receiver. The electrical current flowing through the actuator or receiver contains information about the resonance pattern of the positioning unit or device. The current sensor converts the current generated by the receiver into an electrical voltage U'i, amplifies it, and makes it available to the resonance analyzer. The current conversion can be achieved using a resistor followed by amplification, or by a transistor, transformer, or operational amplifier. An optocoupler can also be advantageously used for this purpose. When using an optocoupler or transformer, the actuator is advantageously galvanically isolated from the defect analyzer.

[0033] Furthermore, it can be advantageous to position at least one generator or receiver between solid joints. Positioning the generator and receiver of acoustic ultrasonic waves between solid joints such as flexural joints, torsion joints, or flexural guides allows for better acoustic stabilization. When exciting or receiving acoustic ultrasonic waves, the generator and receiver are subjected to less stress from surrounding mechanical components. Their vibration in the ultrasonic range is thus less affected. The mechanical quality of these resonant circuits is thereby increased, and less power is required to excite the generator. The sensitivity of the receiver is also enhanced.

[0034] It can be advantageous if the movement of the drive element is guided by the solid joints between which the generator or receiver is arranged, or by additional solid joints of the positioning unit.

[0035] Furthermore, it can be advantageous for the coupling of the drive element to the element to be positioned to be achieved via a fixed connection or a frictional contact. A positioning unit in which the movement or deformation of the actuator is transmitted via the drive element to the element to be positioned through a frictional contact enables qualitative monitoring of the frictional contact of the positioning unit. Thus, any deterioration of the frictional contact due to potential contamination of the friction pair can be directly detected through acoustic analysis. Similarly, delamination of a friction rail with which the drive element is in frictional contact can be detected on the element to be positioned.With a fixed connection between the drive element and the element to be positioned, the movement of the drive element is directly transferred to the element to be positioned, which can be extremely precise and with high resolution, although a comparatively small travel distance is possible due to the limited deformation of the actuator.

[0036] Furthermore, it can be advantageous for a generator or receiver to be formed from at least part of an actuator. In the case of a multilayer actuator, at least some of the actuator's layers form a generator or receiver. By partially or selectively utilizing the piezoelectric material for a generator or receiver, improved acoustic matching of ultrasonic waves to the mechanical environment can be achieved. In the case of a multilayer actuator, for example, only one layer or approximately half of all layers can be used for a generator or receiver. The layers are electrically connected accordingly, and the necessary electrical leads are routed from the positioning unit. The control of the actuator and the generator, as well as the acquisition of the signal from the receiver, takes place in the controller.

[0037] It can be advantageous for the generator or receiver formed by at least part of the actuator to have no actuating function, i.e., no function that causes deformation or movement, and to be connected to the remaining part of the actuator via an acoustic connection with low acoustic resistance. The resulting separation of the generator or receiver from the ultrasonic acoustic waves allows for the realization of a structure that can be used independently of its actuating function.

[0038] It can also be advantageous to use a generator from one actuator and a receiver from another actuator to detect defects in the positioning unit. In a positioning unit with multiple actuators, a generator of acoustic ultrasonic waves from one actuator and a receiver from another actuator can thus be used. The resulting spatial separation, i.e., spacing, between the generator and receiver of acoustic ultrasonic waves allows for the time-of-flight measurement of an acoustic signal pulse. This time-of-flight measurement of the acoustic signal represents another method for detecting resonances or defects in the positioning unit.

[0039] The invention further relates to a method for operating the previously described positioning device for predicting or detecting defects arising in the positioning device or in its positioning unit. According to the invention, a method for operating the positioning device is provided with a positioning unit comprising a piezoelectric actuator, a drive element movable by the actuator and provided for coupling with an element to be positioned, and a controller, wherein the positioning device includes a defect analysis device for detecting defects in the positioning unit, wherein, in the case that the positioning unit has a single actuator, this actuator comprises a generator and a receiver of acoustic ultrasonic waves, and in the case that the positioning unit has multiple actuators,at least one of the actuators comprises at least one acoustic ultrasound wave generator and at least one other actuator comprises at least one acoustic ultrasound wave receiver, and the defect analysis device has a measurement signal generator for generating a measurement signal in the form of an alternating electrical voltage for exciting the generator(s), wherein the defect analysis device has a resonance analyzer for analyzing an electrical signal generated by the receiver(s), wherein a generator is periodically supplied with an electrical measurement signal from the measurement signal generator in the form of an alternating electrical voltage, and mechanical resonances of the positioning unit are periodically recorded by a receiver.and the emergence of new resonances, or the disappearance or modification of previously existing resonances, is detected and analyzed by the resonance analyzer by comparing a resonance image of the positioning unit before normal operation with a resonance image of the positioning unit during normal operation in order to predict or detect defects in the positioning unit, wherein the comparison of the resonance image before normal operation with a resonance image during normal operation is carried out according to one of the following alternatives (A), (B), (C), (D), (E): (A) the measurement signal generator produces an electrical sinusoidal voltage, the frequency of which changes periodically from an initial to an final value, to determine the resonances that were previously present and have now disappeared or changed; (B) the measurement signal generator produces a measurement signal whose frequency value is equal to a measurable resonance frequency value of an actuator,wherein the resonant frequency belongs to the various types of acoustic ultrasonic waves and wherein, after a brief excitation of a generator at the resonant frequency, the decay of the positioning unit is recorded via a receiver and, in order to detect a change in resonance, the recorded decay curve is compared with a decay curve recorded at an earlier time; (C) the measurement signal generator produces a measurement signal whose frequency value of the measurement signal is equal to a measurable resonant frequency value of the positioning unit, wherein, after a brief excitation of a generator, the decay behavior of the positioning unit is recorded in order to detect a change in resonance and is compared with a decay behavior recorded at an earlier time; (D) the measurement signal generator produces a measurement signal whose frequency value of the measurement signal is equal to at least one measurable resonant frequency value of the positioning unit,(E) the measurement signal generator produces a measurement signal whose frequency value is substantially equal to a measurable resonance frequency value of the positioning unit, and during or after a brief excitation of a generator, the reflected pulse is received by a receiver, and parameters of the reflected pulse are recorded for the purpose of detecting a resonance change and compared with parameters received at an earlier time.

[0040] Each component of the positioning unit represents a mechanical oscillator, exhibiting a resonance determined by its dimensions, material properties, and installation method. Cracks in components of the positioning unit, delamination in the multilayer structure of a multilayer actuator, material fatigue in solid-state joints, and other defects in the positioning unit lead to changes in its acoustic characteristics. New resonances emerge, existing resonances change, or even disappear.

[0041] The method according to the invention provides that the actuator, in addition to functioning as an actuating element, i.e., generating a movement of the drive element for the purpose of positioning an element to be positioned due to a deformation of the actuator, is also used or operated as a generator or receiver of acoustic ultrasound waves, wherein these acoustic ultrasound waves are used to detect defects in the positioning unit.

[0042] For this purpose, the actuator(s) are periodically subjected to an electrical measurement signal from the measurement signal generator of the defect analysis device. The measurement signal can be an alternating voltage or an alternating current. The actuator or generator excites acoustic ultrasonic waves throughout the entire positioning unit. These waves, as mechanical resonances of the entire positioning unit and the actuator itself, are periodically recorded by the actuator or receiver and made available to the resonance analyzer for processing. The resonance analyzer processes the signal from an optional current sensor and stores this signal as well as the signal from the measurement signal generator.

[0043] In a further step, the resonance analyzer compares and analyzes two recorded signals or resonance spectra from the positioning unit. This comparison identifies previously present resonances that have now disappeared or changed, as well as registering newly generated resonances. Appropriate and efficient neural network algorithms are used for this comparison and analysis. If defined deviations are detected in the analyzed resonance patterns, a visual or other warning is issued.

[0044] The inventive method for predicting and detecting defects in the positioning unit and its components enables automatic monitoring of the positioning unit's condition and timely replacement or maintenance when defects occur. The use of a piezoelectric actuator in the positioning unit, not only as an actuator but also as a generator or receiver of ultrasonic acoustic waves, gives the positioning unit entirely new properties. The inventive positioning device and the corresponding inventive method, in particular, eliminate the need for costly installation of additional discrete transmitters and receivers.

[0045] In this process, the actuator(s) are driven either by a power output stage with a direct current voltage or by a low-frequency alternating current voltage, or by an amplifier with a high-frequency alternating current voltage. Low frequency is defined here as a voltage whose frequency is at least three times lower than the frequency of the lowest resonance of the positioning unit. High frequency is defined as a voltage frequency that is nearly equal to or higher than the lowest resonance frequency of the positioning unit. Switching is accomplished by an optional commutator. When the piezoelectric material of the actuator is driven by an electrical voltage, it expands or contracts depending on the polarity of the voltage, thereby performing a positioning function.It transmits this expansion or contraction to the drive mechanism connected to it, which in turn is intended to be coupled to an element to be positioned, and via this coupling a positioning movement of the element to be positioned can be achieved.

[0046] Besides its actuating function, the actuator, or a part thereof, also functions as a generator or receiver of ultrasonic acoustic waves. When a generator is subjected to a measurement signal from an amplifier, ultrasonic acoustic waves are excited in its vicinity or in the positioning unit. These waves are received by a receiver and converted into an electrical current. The current IA flowing through the actuator reaches the optional current sensor, which converts it into an electrical voltage Ui, and then processes it further by the resonance analyzer.

[0047] It can be advantageous to detect newly occurring resonances, or to detect the disappearance or modification of previously existing resonances, by calculating the magnitude of the electrical impedance |Z| of the positioning unit as a function of frequency. For this purpose, the frequency of the measurement signal voltage UMG is varied according to a frequency sweep from an initial value fA to a final value fE, and the current value IA flowing through the receiver, as well as the phase angle value, are measured. φ The current and voltage UA are measured as a function of frequency and recorded together with the voltage. To detect resonances, the impedance curve |Z| = UA / IA as a function of frequency is calculated from these measurements. Then, the impedance curve Z (|Z| = f(f)) and the frequency curve are used to determine the... φ (f) the resonance analyzer determines the presence of new or the absence of previously existing mechanical resonances.

[0048] The impedance curve contains all resonances of the positioning unit. The occurrence of defects in system components of the positioning unit causes the emergence of new resonances within the unit or a change in the previously existing resonance pattern. These changes are easily recognizable in the impedance curve. They can be advantageously identified in the resonance analyzer using neural network pattern recognition algorithms.

[0049] It can also be advantageous to measure and record, along with the voltage, the current flowing through the receiver and the phase angle between the current and voltage as a function of frequency during the frequency sweep. From these measurement series, the impedance magnitude |Z| and the phase angle φ are plotted in a Nyquist diagram to detect resonances. The Nyquist diagram allows for a particularly advantageous representation of the frequency response of the positioning unit due to the simultaneous display of the impedance magnitude and the phase angle.

[0050] Furthermore, it can be advantageous that during the frequency sweep, the initial frequency value of the measurement signal is equal to or slightly lower than the lowest measurable resonant frequency value of an actuator, and the final resonant frequency value of the measurement signal is equal to or slightly higher than the resonant frequency value of the highest measurable resonance of an actuator, where both the lowest and the highest resonant frequency values ​​can belong to the different types of acoustic ultrasonic waves, for example, the longitudinal, bending, radial, shear, or other vibration modes of the actuator.

[0051] The preferably multilayered piezoelectric actuator is an essential component of the positioning unit of the positioning device. The actuator possesses specific eigenmodes and associated eigenresonances. The actuator's eigenresonances can be identified before installation in the positioning unit. After installation, they are present in the resonance pattern of the positioning unit when excited and are thus also detectable. By exciting the positioning unit in the frequency range of the actuator's resonance frequencies, defects in this actuator can be specifically detected.

[0052] Furthermore, in frequency sweeping, it can be advantageous if the initial frequency value of the measurement signal is equal to the lowest resonant frequency value of an actuator, which is determined by its length, and the final frequency value of the measurement signal is equal to twice the resonant frequency value, which is determined by half the actuator length.

[0053] During operation, the actuator is typically subjected to particularly high stresses due to longitudinal expansion. This type of stress often leads to cracks between the individual layers and delamination in the case of multilayer actuators. These types of defects can be specifically detected by exciting and performing resonance analysis of the positioning unit in the frequency range of the actuator's longitudinal and bending vibration modes.

[0054] Furthermore, it can be advantageous during frequency sweeping to vary the frequency of the electrical measurement voltage logarithmically or according to another suitable function from the initial to the final value. This allows for a rapid defect test of the positioning unit or for the detection of the resonances of a positioning unit to be adapted to a specific acoustic profile.

[0055] Furthermore, it can be advantageous for the measurement signal to be white noise, allowing the current flowing through the actuator to be measured and recorded. The measurement series is then subjected to a Fourier transform, a discrete Fourier transform (DFT), or a fast Fourier transform (FFT) to detect resonances. This process identifies newly created, disappeared, or changed resonances. Fourier transforms can be efficiently implemented in a DSP or FPGA, enabling rapid analysis. The result of a Fourier transform readily displays resonances as amplitudes, thus facilitating the efficient detection of changes in the resonance image of the positioning unit.

[0056] Furthermore, it can be advantageous if the frequency value of the measurement signal is equal to a measurable resonance frequency value of the actuator, whereby the resonance can belong to the various types of acoustic ultrasonic waves, for example the longitudinal, bending, radial, shear or other vibration modes of the actuator, and after a short excitation of a generator at this resonance frequency, the decay of the positioning unit is recorded by means of a receiver, and furthermore, in order to detect a change in resonance, the recorded decay curve is compared with the decay curve recorded at an earlier time.

[0057] The electric current of a positioning unit driven by a piezoelectric actuator decays after the actuator is triggered or excited to a resonance approximately according to the function I = I₀ EXP(-λt)sin(ωt), where I is the current, I₀ is the initial current, λ is the decay constant, ω is the angular frequency, and t is the time. If one of the resonances changes due to a defect, this change can be detected by the decay behavior, specifically by changes in the amplitude decay function Ai = I₀ EXP(-λt), the decay time, or the frequency of the decaying oscillation. The decay time and decay function of the oscillation can be recorded quickly and easily using a microprocessor-based measuring device. Defects occurring in the actuator can be identified by comparing decay curves.

[0058] It can be advantageous for the frequency value of the measurement signal to correspond to a measurable resonant frequency of the positioning unit. Following a brief excitation of a generator, the decay behavior of the positioning unit is recorded to detect any changes in resonance and compared with decay behavior recorded at an earlier time. By observing changes in specific resonances of the positioning unit, defects in its components or structural parts can be detected.

[0059] It can also be advantageous for the frequency value of the measurement signal to be equal to a measurable resonant frequency value of the positioning unit, whereby, during the excitation of a generator for the purpose of detecting a change in resonance, the internal resistance R i =UA / I Ar of the positioning unit is determined and compared with an internal resistance recorded at an earlier time.

[0060] When defects develop in the positioning unit, some previously existing resonances are altered. The resonance curve of a mechanical oscillator is characterized by its loss resistance Rv, referred to here as the internal resistance Ri. Each resonance of the positioning unit represents an oscillator exhibiting an internal resistance Ri. Ri is changed by developing defects. The internal resistance Ri can be determined by measuring the electrical voltage UAr across the actuator and the current IAr through the actuator at a defined resonance frequency fr. Measuring the voltage UAr and the current IAr can be easily implemented and quickly analyzed using a microcontroller-based measuring device.

[0061] It can also be advantageous if the frequency value of the measurement signal is equal to a measurable resonance frequency value of the positioning unit, wherein, during or after excitation of a generator for the purpose of detecting a change in resonance, the reflected pulse is recorded by a receiver and its parameters are compared with those of a previously recorded reflected pulse.

[0062] To detect defects, the transit time, amplitude, or shape of the reflected pulse can be used. The ultrasonic pulse can be transmitted by a generator of one actuator and received by a receiver of another actuator. Capturing the resonance change of the positioning unit by exciting a short pulse and evaluating parameters of a reflected pulse enables rapid defect identification of the positioning unit. The measurement signal can contain multiple pulses. These pulses can also be amplitude- or phase-modulated.

[0063] It can also be advantageous to perform resonance recording and defect analysis during the normal operating mode of the positioning unit. The resonance pattern of the positioning unit is recorded once during initial commissioning and then periodically or repeatedly during normal operation. The measurements are compared with the initial recording and analyzed. This allows the condition of the positioning unit to be monitored without interrupting its operation.

[0064] Furthermore, it can be advantageous for the recorded resonance image to be analyzed visually by an operator. This makes it possible to intervene in cases of ambiguous resonance images or to initiate the replacement of the defective positioning unit or its components. For this purpose, the device according to the invention can include a computer with a screen or monitor.

[0065] Further details, advantages and features of the invention will become apparent from the following description and the drawings, to which express reference is made with regard to all details not described in the text. They show; Fig.1 Schematic representation of a positioning device according to the invention Fig.2 : Schematic representation of an embodiment of a piezoelectric multilayer actuator of a positioning unit with a generator and a receiver of acoustic ultrasonic waves Fig.3 a) Voltage of the measurement signal generator U MG with a variable frequency; b) FEM model of a multilayer actuator with delamination of the layer structure, excited by the measurement signal according to Fig. 3a)-3c ) Exemplary course of the electrical impedance of an intact actuator as a function of frequency f, excited by the measurement signal according to Fig. 3a ); d) Exemplary course of the electrical impedance of an actuator with delamination as a function of frequency f, excited by the measurement signal according to Fig. 3a ) Fig.4 a) FEM model of the positioning unit according to the invention with an actuator which has a delamination of the layer structure, excited by the measurement signal according to Fig. 3a ); b) exemplary course of the magnitude of the electrical impedance |Z| of the positioning unit as a function of frequency with an intact and a cracked actuator as a function of f, excited by the measurement signal according to Fig. 3a ) Fig.5 a) White noise signal; b) Amplitude spectrum of the positioning unit, excited by a measurement signal generator with the white noise signal according to Fig. 5a ) Fig.6 : Exemplary current decay curves of the positioning unit with an intact and a delaminated actuator Fig. 7 Current resonance curve of the positioning unit to illustrate the measurement of the loss resistance Fig. 8a)-8c ): Different forms of ultrasound pulses; d) Echo of ultrasound pulses Fig. 9 : Principle diagram of a possible circuit-technical realization of simultaneous normal operation of an actuator of a positioning unit of a positioning device according to the invention with the resonance analysis mode, wherein 9a) illustrates the connection of a power output stage and a current or voltage amplifier to the actuator via an inductor or via a capacitor, while 9b) shows the connection of a power output stage to the actuator via a transformer Fig. 10 : Positioning device with common power stage and simultaneous arrangement of the measurement signal generator, the resonance analyzer and the control controller in the same integrated circuit Fig. 11a)-11e ): Basic structure of a current sensor in different designs Fig. 12 : Schematic representation of a positioning unit with several multi-layered actuators, in which the coupling between the drive element and the element to be positioned is realized via a friction contact. Fig. 13 : Actuator with area-specific utilization of the layers to realize a generator and a receiver Fig. 14 : Exemplary realization of a generator or a receiver as a part connected to the actuator, but not acting as an actuator

[0066] Fig. 1 schematically illustrates a positioning device 1 according to the invention for detecting defects in a positioning unit 2 driven by an actuator 4.

[0067] The positioning device 1 comprises, in addition to the positioning unit 2, the controller 3. The positioning unit 2 comprises, besides a single piezoelectric and multilayer actuator 4, which is configured to function not only as a motion or drive unit but also as a generator 12 and a receiver 13 of acoustic ultrasonic waves, a drive element 5 moved or driven by the actuator 4, which is coupled to an element 6 to be positioned by a fixed connection. Furthermore, the positioning unit 2 includes a Fig. 1 Position sensor not shown.

[0068] The actuator 4 is supported at both ends by retaining elements 21, which are connected to a frame surrounding the actuator via solid joints 9, so that the drive element 5 integrated into the frame is coupled to the actuator 4 via the solid joints 9 and movements or deformations of the actuator 4 can be transmitted to the drive element 5.

[0069] The piezoelectric actuator 4 is composed of several layers 11, each layer consisting of two electrodes and a polarized piezoelectric material positioned between them. Possible polarization directions of the individual layers are shown in Fig. 1 marked with the arrows P.

[0070] The controller 3, which has the function of controlling or regulating the actuator 4 or the positioning unit 2, exciting the generator 12 with a measurement signal, and processing the signal coming from the receiver 13, comprises a control controller 14, a defect analysis device 16, which excites the generator 12 and records and analyzes the signal from the receiver 13, and optionally a commutator 31. The commutator 31 switches between actuator operation of the actuator 4 and sensor operation, in which the actuator or a part thereof functions as generator 12 or receiver 13. Furthermore, the controller 3 can have an interface to a computer 29 with a screen on which the defect analysis can be performed visually by an operator.

[0071] The control controller 14 includes a power output stage 15 for the actuator 4, a trajectory and signal generator 19, a controller 18 for the position and optionally for the speed and acceleration of the positioning unit 2.

[0072] The defect analysis device 16 comprises a current-voltage amplifier 17 for the generator 12, a measurement signal generator 22, a current sensor 23 for the signal generated by the receiver 13, and a resonance analyzer 24.

[0073] Fig. 2 Figure 1 illustrates a schematic representation of a preferred embodiment of the piezoelectric actuator 4 with a generator 12 and a receiver 13. The layers 11 of the actuator 4 are formed by conductive metallized surfaces and a polarized piezoelectric material located between them. In one possible variant of the electrical polarization of the layers 11, the polarization vectors of the adjacent layers are directed oppositely to each other. The electric polarization vector is in Fig. 2 as well as indicated by an arrow P in the corresponding other figures. Layers 11 are electrically connected in parallel and mechanically in series.

[0074] Fig. 3a ) illustrates the voltage U MG of the measurement signal generator with a variable frequency, while Fig. 3b ) the FEM model of a multilayer actuator 4 with a delamination of the layer structure is illustrated. Fig. 3c Figure 1 illustrates an exemplary curve of the electrical impedance of an intact actuator as a function of frequency f. Resonances of three vibration modes of the actuator 4 can be seen here, namely the first, the third and the fifth longitudinal mode. Fig. 3d Figure 4 illustrates an exemplary curve of the electrical impedance of actuator 4 with delamination as a function of frequency f. Additional resonances can be seen here, which have arisen due to the delamination.

[0075] Fig. 4a ) shows the FEM model of a positioning unit 2 with an actuator 4 according to Fig. 1 , which exhibits delamination of the layer structure. Fig. 4b Figure 1 illustrates an exemplary curve of the magnitude of the electrical impedance of a positioning unit 2 as a function of frequency, with an intact and a cracked actuator 4 as a function of f. Due to delamination in the actuator 4, the impedance curves differ significantly. Resonances that were present with an intact actuator have disappeared, and new resonances due to delamination have appeared.

[0076] Fig. 5a ) illustrates the amplitude spectrum of the positioning unit excited by white noise, while Fig. 5b ) corresponds to the current flowing through the actuator 4 or the receiver 13, which is subjected to a Fourier transformation and recorded as a function of frequency.

[0077] Fig. 6 This illustrates, as an example, the current decay curves of a positioning unit 2 with one intact and one delaminated actuator. The actuator was excited at one of its resonant frequencies. The decay curve of the positioning unit with a damaged actuator, with the amplitude decay function Ai2, decays faster than Ai1 with the intact actuator due to the altered resonant frequency and the decay constant λ2. Due to the delamination, the oscillation period T2 has decreased in the amplitude decay function Ai2.

[0078] Fig. 7 illustrates a current resonance curve of a positioning unit 2 according to Fig. 1 This is excited at one of its resonances by a sine wave measurement signal of amplitude UAr. The current IAr flowing through receiver 13 is measured. Ri = UAr / IAr is determined by the defect analysis device and compared with a previously measured value. A warning is issued if a defined deviation occurs.

[0079] Fig. 8 Figure 1 illustrates different forms of the ultrasonic pulses emitted by a generator 12 and the ultrasonic pulses reflected by the positioning unit 2 and detectable by the receiver 13. The ultrasonic pulses can be described as follows: Fig. 8a ) exhibit an exponential increase as well as an exponential decrease, according to Fig. 8b ) only exhibit exponential decay, or according to Fig. 8c ) also exhibit different rise and fall times. The ultrasound pulses are characterized by their amplitude Ap, frequency fp, duration τ, rise and fall times fAn, fAp, and transit time tp.

[0080] Fig. 9 This illustrates the basic structure of a possible circuit implementation for simultaneous normal operation of the positioning device or positioning unit with a resonance analysis mode. According to Fig. 9a The power output stage 15 is connected to the actuator 4 via an inductor L. The current or voltage amplifier 17 excites the actuator 4 or the generator 12 via a capacitor C. The capacitor C isolates the power output stage 15 from the amplifier 17 with respect to DC current. Conversely, the inductor L isolates the amplifier 17 from the power output stage 15 with respect to AC current. Fig. 9b The power output stage 15 is connected to the actuator 4 via the secondary winding of the transformer T. The current or voltage amplifier 17 excites the generator 12 via the primary winding of the transformer T. The transformer T provides DC isolation between the power output stage 15 and the amplifier 17.

[0081] Fig. 10 illustrates a positioning device 1 with a positioning unit 2 according to Fig. 1 , in which the same power output stage 15 is used by the defect analysis device as the output voltage or current amplifier for the measurement signal generator 22 as is used by the control controller to drive the multilayer actuator. In this case, the power output stage 15 has a sufficient bandwidth to meet the requirements for generating acoustic ultrasonic waves by the actuator or generator 12. This saves the cost and space of installing a separate amplifier.

[0082] Fig. 10 further illustrates an embodiment of the positioning device 1 in which the measuring signal generator 22 and the resonance analyzer 24 are housed in the same integrated circuit 30 as the control controller 14.

[0083] Fig. 11 This illustrates the basic structure of possible circuits for the initial processing of the electrical signal coming from receiver 13 in the form of a current or a voltage. Accordingly Fig.11a The current IA coming from receiver 13 can be represented by the voltage U i using a resistor. Through the circuit in which the Fig.11b The current IA coming from receiver 13 is converted into a voltage U' i using a transistor. Fig.11c The current IA coming from receiver 13 is converted into a voltage U' i using an optocoupler. In the Fig.11d In the circuit arrangement shown, the current IA coming from receiver 13, or the voltage UA, is converted into a voltage U' i by means of a transformer. The in Fig.11e The circuit arrangement shown converts the current IA coming from receiver 13, or the voltage UA, into the voltage U' i using an operational amplifier.

[0084] The Figuren 1 , 7 and 10 Figure 1 illustrates a schematic representation of a positioning unit 2 in which a single multilayer piezoelectric actuator 4, which also forms the generator 12 and the receiver 13, is arranged between solid body joints 9.

[0085] Fig. 12 Figure 1 shows a schematic representation of a positioning unit 2 with several, i.e., a total of four, multilayer piezoelectric actuators 4, each actuator being arranged in or between solid-state joints 9. The ends of each actuator 4 rest against holding elements 21. The motion transmission from the drive element 5 of the actuator 4 to the element 6 to be positioned takes place via a frictional contact, in which the drive element 5 comes into frictional contact with a friction rail 26 of the element 6 to be positioned. The element 6 to be positioned is linearly mounted and guided by a guide device 20. A position sensor 28 serves to detect the position of the element 6 to be positioned.

[0086] Fig. 13 Figure 1 illustrates a multilayer actuator 4 in which only some layers 11 are used for the implementation of the generator 12 and receiver 13. It is conceivable to use a different number of layers for the generator 12 than for the receiver 13. In the upper position of the commutator 31, the actuator layers are connected to the power output stage 15. The actuator is in control or drive mode. By switching to the lower position, the actuator layers designated for the generator or receiver function are connected to the power output stage, thus forming the generator 12 or the receiver 13, respectively. The actuator current IA is converted into the voltage Ui by the current sensor 23 and further processed by the resonance analyzer 24.

[0087] Fig. 14 Figure 1 illustrates an exemplary realization of the generator 12 or receiver 13 as a part connected to the actuator, but not itself acting as an actuator, i.e., not performing a deformation when an electrical voltage is applied. The layers of the generator 12 and receiver 13 of acoustic ultrasonic waves exhibit opposite polarizations. The generator 12 and receiver 13 are connected to the rest of the actuator via an acoustic connection with low acoustic resistance, so that the acoustic ultrasonic waves are not significantly reflected or attenuated by the boundary layer. Such a connection can be achieved, for example, by sintering the actuator to the generator or receiver. It is also possible to join the components in a furnace using low-melting-point glass or a similar hard material.

[0088] The functioning of the positioning device 1 according to the invention, or of the method according to the invention, is explained by means of the Fig. 1 The process is explained below. In a first step, an etalon measurement is performed. For this purpose, the resonance image of the intact positioning unit 2 is recorded by the defect analysis device 16 during its initial commissioning. The piezoelectric actuator 4, in its function as a generator of acoustic ultrasonic waves 12, is supplied with an electrical measurement signal by the measurement signal generator 22. The measurement signal represents an electrical voltage with a frequency f. The measurement signal voltage is amplified by the current-voltage amplifier 17 and passed on to the generator 12 via the commutator 31. This excites the generator 12, which then generates ultrasonic waves that are emitted into the positioning unit. The propagation of the ultrasonic waves excites resonant vibrations in components of the positioning unit as well as in the actuator itself.These resonant vibrations in turn generate acoustic ultrasound waves, which reach the receiver 13 together with the reflected ultrasound waves and are detected by it in the form of a change in current.

[0089] The current IA from receiver 13 reaches the current sensor 23 of the defect analyzer, is converted by the sensor into a voltage U i, and is then passed on to the defect analyzer 16. In the defect analyzer, the current IA, or its representation, the voltage U i, the voltage U MS coming from the measurement signal generator 22, and the phase angle value are measured. φ The current IA and the voltage U MS were recorded, stored, and a resonance image of the positioning unit was created from it.

[0090] The positioning unit then begins operation to perform the intended positioning tasks. The trajectory and signal generator 19 controls the actuator 4 with a control signal, amplified by the power output stage 15 or routed via the commutator 31. The actuator moves the drive element 5 and the element to be positioned, coupled to it, into a positioning motion. The positioning can be controlled by the controller 18 using the position sensor 28.

[0091] After a certain operating time, a condition or defect diagnosis of the positioning unit is performed. For this purpose, a measurement corresponding to the first step of the method according to the invention is carried out. The generator 12 is supplied with an electrical measurement signal by the measuring signal generator 22. This excites the generator 12, which then generates ultrasonic waves that are emitted into the positioning unit. The propagation of the ultrasonic waves excites resonant vibrations in components of the positioning unit as well as in the actuator itself. These resonant vibrations, in turn, generate acoustic ultrasonic waves, which reach the receiver 13 together with the reflected ultrasonic waves and are detected by it in the form of a change in current.

[0092] The current IA from receiver 13 reaches the current sensor 23 of the defect analyzer, is converted by the sensor into a voltage U i, and is then passed on to the defect analyzer 24. In the defect analyzer, the current IA, or its representation, the voltage U i, the voltage U MS coming from the measurement signal generator 22, and the phase angle value are measured. φ The current IA and the voltage U MS were recorded, stored, and a resonance image of the positioning unit was created from it.

[0093] In a subsequent process step, the resonance analyzer 24 compares the currently generated resonance image of the positioning unit with the resonance image of the intact positioning unit. This determines the presence of a new, a change in, or the absence of previously existing mechanical resonances. For this purpose, suitable algorithms, such as those of neural networks, are implemented in the resonance analyzer. If a defined deviation is detected in the current measurement from the standard measurement, indicating an impending failure of the positioning unit, the defect analysis device issues a warning.

[0094] Several advantageous methods can be used to create the resonance image of the positioning unit. For example, the positioning unit 2 can be supplied with an electrical measurement signal from the measuring signal generator 22, which represents an electrical voltage with a variable frequency f (see [reference]). Figs. 3 and 4 The frequency f changes from an initial to a final value. In the resonance analyzer 24, the current IA flowing through the receiver 13, or its image, the voltage U i, the voltage U MS coming from the measurement signal generator 22, and the phase angle value are measured. φ The relationship between the current IA and the voltage U MS is recorded as a function of frequency f. From these stored measurement series, the function of the impedance magnitude |Z| = UA / IA as a function of frequency is calculated to detect resonances of the positioning unit. From the frequency-dependent impedance curve, the resonance analyzer creates the resonance image of the positioning unit and generates a defect prediction or diagnosis.

[0095] Furthermore, the positioning unit 2 can be supplied with an electrical measurement signal from the measuring signal generator 22, which represents an electrical voltage with a specific frequency f. The resonance image is then generated based on parameters of individual resonances (see [reference]). Figs. 6 und Fig.7 ).

[0096] In a further advantageous method, the positioning unit 2 is supplied with a short-duration electrical measurement signal of at least a specific frequency f by the measuring signal generator 22. The resonance image of the positioning unit is created based on parameters of the reflected ultrasonic waves (see Fig. 8 The resonance analyzer records and analyzes the duration of the reflected impulse(s), the amplitude, the travel time, or the shape.

[0097] When manually creating the resonance image of the positioning unit and performing its visual analysis, the data from the defect analysis device is output to computer 22 with a screen and analyzed by an operator. Reference symbol list:

[0098] 1 Positioning device 2 Positioning unit 3 Controller 4 Actuator 5 Drive element 6 Element to be positioned 9 Solid-state joint 11 Piezoelectric layers (of actuator 4) 12 Acoustic ultrasound generator 13 Acoustic ultrasound receiver 14 Control controller 15 Power output stage 16 Defect analyzer 17 Current or voltage amplifier 18 Position, velocity, or acceleration controller 19 Trajectory and signal generator 20 Guide device 21 Holding element (of actuator 4) 22 Measurement signal generator 23 Current sensor 24 Resonance analyzer 26 Friction rail 28 Position sensor 29 Computer 30 Integrated circuit (e.g., FPGA, DSP) 31 Electronic commutator 32 Layers of the acoustic ultrasound generator and receiver 33 Interconnect layer of the actuator with the acoustic ultrasound generator and receiver

Claims

1. Positioning device (1), comprising a positioning unit (2) with a piezoelectric actuator (4), a drive element (5) movable by the actuator (4) and provided for coupling to an element (6) to be positioned, and a controller (3), wherein the positioning device (1) comprises a defect analysis device (16) for detecting defects in the positioning unit (2), wherein, in the case that the positioning unit (2) comprises a single actuator (4), the actuator (4) comprises a generator (12) and a receiver (13) of acoustic ultrasonic waves, and, in the case that the positioning unit (2) comprises a plurality of actuators (4), at least one of the actuators (4) comprises at least one generator (12) of ultrasonic acoustic waves and at least another one of the actuators (4) comprises at least one receiver (13) of ultrasonic acoustic waves, and wherein the defect analysis device (16) comprises a measurement signal generator (22) for generating a measurement signal in form of an electric voltage for exciting the or a generator (12), characterized in that the defect analysis device (16) comprises a resonance analyzer (24) for analyzing an electric signal generated by the or a receiver (13), wherein, for predicting or detecting defects arising within the positioning unit, the resonance analyzer (24) is configured such that the same determines and analyzes the emergence of new resonances or the disappearance or change of previously existing resonances by comparing a resonance image before normal operation with a resonance image during normal operation, wherein the resonance analyzer (24) is configured to carry out the comparison of the resonance image before normal operation with a resonance image during normal operation according to one of the following alternatives (A), (B), (C), (D), (E): (A) the measurement signal generator (22) is configured such that, in order to determine the resonances which were previously existing and have now disappeared or have changed, it generates an electrical sinusoidal voltage whose frequency changes periodically from an initial to a final value, (B) the measurement signal generator (22) is configured such that the frequency value of the measurement signal is equal to a measurable resonance frequency value of an actuator (4), wherein said resonance frequency belongs to the various types of ultrasonic acoustic waves and wherein after a short excitation of a generator (12) at the resonance frequency, the decay of the positioning unit (2) is recorded via a receiver (13) and thereafter, for the purpose of detecting a resonance change, the recorded decay curve is compared with a decay curve recorded at an earlier time; (C) the measurement signal generator (22) is configured such that the frequency value of the measurement signal is equal to a measurable resonance frequency value of the positioning unit (2), wherein after a short excitation of a generator (12) the decay behavior of the positioning unit (2) is recorded for the purpose of detecting a resonance change and compared with a decay behavior recorded at an earlier time; (D) the measurement signal generator (22) is configured such that the frequency value of the measurement signal is equal to at least one measurable resonance frequency value of the positioning unit (2), wherein during the excitation of a generator (12) for the purpose of detecting at least one resonance change, the internal resistance Ri=UA / IAr of the positioning unit (2) is determined and compared with a value of the internal resistance of the positioning unit (2) recorded at an earlier time; (E) the measurement signal generator (22) is configured such that the frequency value of the measurement signal is substantially equal to a measurable resonance frequency value of the positioning unit (2), and in this case, during or after a short excitation of a generator (12), the reflected pulse is picked up by a receiver (13), parameters of the reflected pulse being recorded for detecting a resonance change and being compared with parameters recorded at an earlier time.

2. Positioning device (1) according to claim 1, characterized in that the measurement signal generator (22) is configured according to alternative (A) and such that it changes the frequency of the measurement signal from an initial value to a final value and, in the process, measures the current value flowing through a receiver (13) and the phase angle value between the current and the voltage in the form of a function of the frequency and records it together with the voltage, and in that the resonance analyzer (24) is configured such that, from the series of measurements for detecting resonances, the function of the impedance magnitude |Z| is formed as a function of the frequency, and from the impedance the presence of new or the change or absence of previously detected mechanical resonances is determined.

3. Positioning device (1) according to any one of the preceding claims, characterized in that the defect analysis device (16) comprises a white noise generator.

4. Positioning device (1) according to any one of the preceding claims, characterized in that the defect analysis device (16) comprises a current sensor (23) for detecting an electrical signal generated by a receiver (13), wherein a resistor, a transistor, a transformer, an optocoupler or an operational amplifier is used for detecting a current.

5. Positioning device (1) according to any one of the preceding claims, characterized in that an actuator (4) is designed as a multilayer piezoelectric actuator.

6. Positioning device (1) according to any of the preceding claims, characterized in that a generator (12) or a receiver (13) forms part of an actuator (4) and comprises no actuating function.

7. Positioning device (1) according to claim 6, characterized in that the part of an actuator (4) forming a generator (12) or a receiver (13) is connected to the remaining part of the same actuator (4) by an acoustic connection with a low acoustic resistance.

8. Positioning device (1) according to any one of the preceding claims, characterized in that a generator (12) is formed in one actuator (4) and a receiver (13) is formed in another and spaced actuator.

9. Method for operating the positioning device (1) comprising a positioning unit (2) with a piezoelectric actuator (4), a drive element (5) which movable by the actuator (4) and which is provided for coupling to an element (6) to be positioned, and a controller (3), wherein the positioning device (1) comprises a defect analysis device (16) for detecting defects in the positioning unit (2), wherein, in the case that the positioning unit (2) comprises a single actuator (4), the actuator (4) comprises a generator (12) and a receiver (13) of acoustic ultrasonic waves and, in the case that the positioning unit (2) comprises a plurality of actuators (4), at least one of the actuators (4) comprises at least one generator (12) of ultrasonic acoustic waves and at least another one of the actuators (4) comprises at least one receiver (13) of ultrasonic acoustic waves, and wherein the defect analysis device (16) comprises a measurement signal generator (22) for generating a measurement signal in form of an electric voltage for exciting the or a generator (12), characterized in that the defect analysis device (16) comprises a resonance analyzer (24) for analyzing an electric signal generated by the or a receiver (13), wherein a generator (12) is periodically supplied with an electrical measuring signal of the measuring signal generator (22) in the form of an electrical alternating voltage and wherein mechanical resonances of the positioning unit (2) are periodically picked up with a receiver (13), and wherein by means of the resonance analyzer (24) comparing a resonance image of the positioning unit (2) before normal operation with a resonance image of the positioning unit (2) during normal operation the emergence of new or the disappearance or the change of previously existing resonances are detected and analyzed for predicting or detecting defects in the positioning unit (2), wherein the comparison of the two resonance images comparing the resonance image made before normal operation with the resonance image made during operation is carried out according to one of the following alternatives (A), (B), (C), (D), (E): (A) the measurement signal generator (22), for determining the resonance image, generates an electrical sinusoidal voltage, the frequency of which changing periodically from an initial to a final value, (B) the measurement signal generator (22) generates a measurement signal, the frequency value of which is equal to a measurable resonance frequency value of an actuator (4), wherein said resonance frequency belongs to the various types of ultrasonic acoustic waves and wherein after a short excitation of a generator (12) at the resonance frequency, the decay of the positioning unit (2) is recorded via a receiver (13) and thereafter, for the purpose of detecting a resonance change, the recorded decay curve is compared with a decay curve recorded at an earlier time; (C) the measurement signal generator (22) generates a measurement signal, the frequency value of which is equal to a measurable resonance frequency value of the positioning unit (2), wherein after a short excitation of a generator (12) the decay behavior of the positioning unit (2) is recorded for the purpose of detecting a resonance change and compared with a decay behavior recorded at an earlier time; (D) the measurement signal generator (22) generates a measurement signal, the frequency value of which is equal to at least one measurable resonance frequency value of the positioning unit (2), wherein during the excitation of a generator (12) for the purpose of detecting at least one resonance change, the internal resistance Ri=UA / IAr of the positioning unit (2) is determined and compared with a value of the internal resistance of the positioning unit (2) recorded at an earlier time; (E) the measurement signal generator (22) generates a measurement signal, the frequency value of which is substantially equal to a measurable resonance frequency value of the positioning unit (2) and in this case, during or after a short excitation of a generator (12), the reflected pulse is picked up by a receiver (13), parameters of the reflected pulse being recorded for detecting a resonance change and being compared with parameters recorded at an earlier time.

10. A method according to claim 9, characterized in that, in alternative (A), the frequency of the measurement signal is changed from an initial to a final value, and thereby the current value flowing through a receiver (13) and a phase angle value between the current and the voltage are measured in the form of a dependency of the frequency and recorded together with the voltage, and from the series of measurements for detecting resonances the function of an impedance |Z| in dependency of the frequency is formed, and from the impedance amount |Z| the presence of new or the change or absence of previously detected mechanical resonances is determined.

11. A method according to claim 9 or 10, characterized in that, in alternative (A), the function of the impedance amount |Z| in dependency of the frequency with the phase angle is represented in a Nyquist diagram, from which the presence of new or the change or the absence of previously detected mechanical resonances is determined.

12. Method according to any one of claims 9 to 11, characterized in that, in alternative (A), the initial frequency value of the measurement signal is equal to the lowest detectable resonance frequency value of an actuator (4) and the final frequency value of the measurement signal is equal to the resonance frequency value of the highest measurable resonance of an actuator (4), wherein both the lowest resonance frequency value and the highest resonance frequency value belong to the different types of ultrasonic acoustic waves.

13. A method according to any one of claims 9 to 12, characterized in that, in alternative (A), the initial frequency value of the measurement signal corresponds to the lowest resonance frequency value of an actuator (4) determined by its length, and the final frequency value of the measurement signal corresponds to twice the resonance frequency value determined by half the actuator length.

14. A method according to any one of claims 9 to 13, characterized in that, in alternative (A), the frequency of the measurement signal is logarithmically varied from the initial to the final value.