Drive system and control method for a piezoelectric motor

Abstract

The present invention relates to a drive system and a control method for a piezoelectric motor of such a drive system. A transmitting inductance is connected in an electrically conductive manner to at least two switching elements. A control device is suitable for converting a periodic drive signal into a pulse width modulation (PWM) signal and forwarding it to the transmitting inductance by switching the at least two switching elements. A receiving inductance and a capacitive piezoelectric actuator, which form a low-pass filter, are situated inside a chamber. At least one wall of the chamber is in the form of a fixed dielectric barrier, and the transmitting inductance is suitable for inductively transmitting the PWM signal to the receiving inductance through the fixed dielectric barrier. The provided system and method make it possible to wirelessly transmit signals into a sealed environment such as a vacuum environment.

Description

[0001] Drive system and control method for a piezoelectric motor

[0002] The present invention relates to a drive system and a control method for a piezoelectric motor with wireless transmission of the control signal.

[0003] Piezoelectric resonance motors (e.g., ultrasonic motors) or inertial motors, such as those used in a positioning stage, require periodic signals with, for example, sinusoidal, rectangular, or sawtooth waveforms to activate a piezoelectric actuator in the stator, i.e., to induce vibration or periodic deformation of the actuator. The vibrating movement or deformation of the actuator in the stator is then transmitted via friction coupling to the moving element (slider or rotor), thereby setting it in the desired motion.

[0004] In piezoelectric inertial actuators, the tangential component of the back-and-forth motion during vibration or deformation of the piezoelectric actuator generates a movement at a contact between a driven element and the actuator mounted on a stator. In one direction of the tangential movement, the actuator is slowly activated, i.e., slowly deformed. During this activation period, the "stick phase" or "slow phase," static friction exists between the actuator and the driven element, so that the driven element follows the slow deformation movement of the actuator. In the opposite direction of the tangential movement, the piezoelectric actuator is deactivated, or deformed, more quickly relative to its initial position.During this time, the "slip phase" or "fast phase," the inertial force acting on the driven element is greater than the frictional force between the actuator and the driven element, resulting in sliding friction between the two, and the actuator slides along the driven element, unable to follow the actuator's rapid movement. During such a cycle of sticking and sliding phases, the driven element makes a microscopically small movement step. The accumulation of these microscopic movement steps generates a macroscopic movement of the driven element.

[0005] Fig. 1 shows a stator 10 of a piezoelectric inertia motor, which comprises an elastic frame 14, a friction element 12 intended for frictional contact with a driven element, and screws 13 for adjusting preload and compensating for tolerances. As shown in Fig. 1, the stator of an inertia motor can have two actuators 11a and 11b, for example, multilayer actuators with several superimposed layers of piezoelectric material and electrodes in between, each having capacitances Ca1 and Ca2. During operation, while one of the two actuators expands, the other actuator contracts to generate the back-and-forth tangential movement of the friction element, illustrated by an arrow 15.

[0006] Fig. 2 shows a stator 20 of a piezoelectric inertia motor with a single actuator 21 as the drive source, where similar elements have the same designation as in Fig. 1. Here, only one electronic channel needs to be connected to the actuator.

[0007] Fig. 3 shows a diagram of a piezoelectric multilayer actuator. Piezoelectric actuators can be considered capacitive elements in electronic circuits. For clarity, the present description refers to actuators as "capacitive piezoelectric actuators." Generally, they are used herein in the same way as a capacitor in a low-pass filter.

[0008] In an inertial motor as shown in Fig. 1, the two piezoelectric actuators can be driven by two antiphase ("mirrored") sawtooth-like signals. In this case, the extension and contraction of the two actuators occur synchronously in opposite directions. Thus, while one actuator expands, the other contracts.

[0009] For example, a signal applied to the actuator of a piezoelectric inertial motor has the idealized sawtooth waveform shown in Fig. 4. During the slow phase, or stick phase, one of the two actuators slowly expands while the other slowly contracts. This slow expansion and contraction of a piezoelectric actuator is analogous to the slow charging or discharging of a capacitor.

[0010] Accordingly, during the fast phase or sliding phase, one piezoelectric actuator rapidly expands while the other piezoelectric actuator rapidly contracts. This rapid expansion or contraction also bears an analogy to the rapid charging or discharging of a capacitor. In the present disclosure, piezoelectric actuators are largely treated like capacitor elements used in filter components of drive circuits.

[0011] In Fig. 4, the two sketched waveforms correspond to the control signals for two oppositely expanding and contracting actuators in a stator of a piezoelectric inertial motor. For actuators with only a single piezoelectric actuator, it is sufficient to consider one of the two sawtooth waveforms. Sawtooth-shaped signal waveforms of the control signals for the actuators can have flattened sections between the slow and fast phases, or at the transition from the slow to the fast phase. This is shown in an idealized manner in Fig. 5.

[0012] Although ultrasonic motors or piezoelectric ultrasonic motors are usually driven with sinusoidal or sinusoidal-like signal waveforms, the signal waveforms described above can also be used to drive an ultrasonic motor or a resonance type motor in general.

[0013] Fig. 6 corresponds to Fig. 22 of DE102020132640B3, which describes a wireless drive of a piezoelectric motor. A periodic drive signal for the motor is applied to a transmitting coil. The receiving coil receives the drive signal contactlessly and supplies the motor actuators with power. The received signal is filtered by the LC configuration of the receiving coil and actuator capacitances. Voltage drops in the actuators are the drive signals for the piezoelectric motor.

[0014] The periodic drive signals that cause the movement of the stator are generated by pulse width modulation (PWM) signals, with the frequency of the PWM signals being 5 to 10 times higher than the operating frequency of the piezoelectric motor.

[0015] When using the aforementioned piezoelectric motor in a protected or even sealed environment, such as a vacuum chamber, it is generally desirable for the drive and control electronics to be located outside the protected or sealed environment. In any case, the corresponding cables or cable connections must be taken into account. In a vacuum environment, for example, the cable connection is made using special interface connectors.

[0016] The present invention proposes, in order to overcome difficulties in the use of cables or wires, a wireless drive method or control method and a drive system for a piezoelectric motor or actuator, wherein the drive or control signals for the motor or actuator are transmitted through a glass wall or similar wall into a protected environment such as a chamber, and in particular into a sealed chamber.

[0017] With the proposed wireless transmission of signals for driving the piezoelectric motor, and possibly also other signals such as position feedback signals for transmitting the position of an element to be driven or positioned by the motor or actuator, such as the platform of a positioning table, sealing the cable feedthrough into the chamber or the cable connection can be eliminated. Furthermore, cable interference or interfering signals or fields caused by the cables can be reduced or minimized. One example of this is a small positioning table used in a vacuum chamber.

[0018] The present disclosure provides a drive system and a method which enable coded drive signals for a piezoelectric motor or actuator to be transmitted wirelessly from transmitting coils or inductors to receiving coils or inductors through a glass or dielectric barrier into a chamber, in particular a sealed or hermetically sealed chamber such as a vacuum chamber.

[0019] Whenever inductances or capacitances are mentioned herein, they are understood to mean a component with inductive or capacitive properties, respectively, unless explicitly stated otherwise. An inductance is understood here in particular to mean a coil, while a capacitance is understood here in particular to mean a piezoelectric actuator that behaves electrically like a capacitor.

[0020] The process of the proposed procedure can be summarized as follows:

[0021] 1) DC, sawtooth, or sinusoidal drive signal waveforms in the range of direct current (DC) or in the range of 20 kHz to approximately 200 kHz are first converted into PWM signals with frequencies above 1 MHz to drive the transmitting coil(s). In the case of DC signals, the width of the PWM signals is either constant or changes very slowly.

[0022] 2) These PWM signals are transmitted to the transmitting coil(s) or inductors. The generated electrical energy is then absorbed by the receiving coil(s) or inductors on the other side of the glass or dielectric barrier within the closed environment or chamber. The absorbed signals are filtered on the receiving coil(s). On the receiving side, the receiving coils and the piezoelectric actuator(s) in the stator can be connected in parallel or in series. Various electrical network and filtering techniques can also be applied. The LC configuration of the receiving coil (L) and the capacitance (C) of the piezoelectric elements in the stator acts as a filter. The voltage waveforms resulting from accumulation at the piezoelectric actuators represent sinusoidal or sawtooth waveforms.These signals enable the motor to operate without a physical (cable or wired) connection between the drive or control sides and the motor.

[0023] To control the position and speed of an element to be driven or positioned by the motor, such as the platform of a positioning table, several parameters can be used in piezoelectric motors, for example: i) signal strengths of the electronic switching elements, such as the source voltage of a half- or full-bridge topology, which drives the transmitting inductor, ii) operating frequency of the piezoelectric motor or frequency of the PWM signal, or iii) driving the transmitting inductor(s) with waveforms of sudden amplitude accumulation (English "brush") in order to obtain small steps of the motor, for which the inductors are activated for a short time.The parameters listed above are also adapted to the specific application, such as the distance between the transmitting and receiving coil, the thickness of the glass or dielectric barrier, the material of the glass or dielectric barrier, etc.

[0024] In addition to the motor drive signal, signals or information regarding the position of the element to be driven or positioned can also be transmitted wirelessly, for example, via optical communication, for control, particularly the position, or a corresponding closed control loop. The power for the components of a corresponding position-determining device can be transmitted to the signal-generating side in a manner similar to wireless charging.

[0025] According to a first aspect of the present invention, a drive system is provided, comprising a piezoelectric motor, at least two switching elements, a transmitting inductance electrically connected to the at least two switching elements, a control device suitable for converting a periodic drive signal into a pulse width modulation (PWM) signal and passing it on to the transmitting inductance by switching the at least two switching elements, a chamber, preferably a hermetically sealed chamber, having a wall that is at least partially designed as a solid dielectric barrier, and a receiving inductance, wherein the piezoelectric motor comprises a capacitive piezoelectric actuator, wherein the receiving inductance and the capacitive piezoelectric actuator are located within the chamber and form a low-pass filter, and the transmitting inductance is suitableto inductively transmit the PWM signal to the receiving inductance through the solid dielectric barrier.

[0026] For example, the drive system also comprises a positioning device to be driven by the piezoelectric motor, for example in the form of a positioning table with a stationary base acting as a stator and with a platform movable relative to the base, wherein the positioning device is located within the chamber.

[0027] For example, the transmitting inductance and the receiving inductance are a first transmitting inductance and a first receiving inductance, and the drive system also comprises a second transmitting inductance, a second receiving inductance, a position signal transmitting device which is suitable for generating and transmitting signals corresponding to the position of an element of the positioning device to be positioned on the basis of an output signal of a position determining means assigned to the positioning device, and a position signal receiving device which is suitable for detecting the signals generated and transmitted by the position signal transmitting device and for deriving therefrom information about the position of the element to be positioned, wherein the second receiving inductance and the position signal transmitting device are located within the chamber,and the position signal receiving device is located outside the chamber, and the control device is adapted to generate a signal for supplying power to the position signal transmitting device or the position determining means and to transmit it to the second transmitting inductance, and the second transmitting inductance is adapted to inductively transmit the signal for supplying power to the second receiving inductance through the fixed dielectric barrier, and the position signal transmitting device is adapted to transmit the light signals through the fixed dielectric barrier to the position signal receiving device.

[0028] For example, the position signal transmitting device may be formed by a plurality of light-emitting diodes, and the position signal receiving device may be formed by a plurality of photodetectors.

[0029] For example, the position determining means can be formed by an optical encoder.

[0030] For example, the drive system comprises an electrical energy storage device for supplying energy to the position signal transmitting device or the position determining means, wherein the electrical energy storage device is located within the chamber and is suitable for receiving electrical energy from the second receiving inductance.

[0031] For example, the electrical energy storage device is a rechargeable battery or a supercapacitor. For example, the piezoelectric motor is an inertial motor, and the capacitive piezoelectric actuator is a multilayer actuator.

[0032] For example, the solid dielectric barrier is made of glass or of a material that is transparent to infrared radiation.

[0033] According to a second aspect of the present invention, there is provided a control method for a piezoelectric motor, comprising the steps of: converting a periodic drive signal into a pulse width modulation (PWM) signal having a higher frequency than the drive signal, passing the PWM signal to a transmitting inductor, inductively transmitting the PWM signal from the transmitting inductor to a receiving inductor through a fixed dielectric barrier, wherein the receiving inductor forms a low-pass filter with a capacitive piezoelectric actuator of the piezoelectric motor.

[0034] For example, the tax procedure also includes the following steps:

[0035] Generating a signal for supplying energy to a position-determining means for determining the position of an element of a positioning device to be positioned by the piezoelectric motor or for supplying energy to a position-signal transmitting device which is suitable for generating and transmitting signals corresponding to the position of the element to be positioned on the basis of an output signal of the position-determining means associated with the positioning device;

[0036] Passing the signal for supplying power to the position determining means or the position signal transmitting device to a second transmitting inductance;

[0037] Inductively transmitting the signal for powering the position determining means or the position signal transmitting device to a second receiving inductance through the fixed dielectric barrier;

[0038] Transmitting the signals of the position signal transmitting device through the solid dielectric barrier to a position signal receiving device which is suitable for detecting the signals generated and transmitted by the position signal transmitting device and deriving therefrom information about the position of the element to be positioned; and

[0039] Detecting the signals of the position signal transmitting device by the position signal receiving device. For example, the control method further comprises the step of storing the electrical energy received by the second receiving inductance to supply power to the position-determining means and / or the position signal transmitting device.

[0040] For example, the position signal transmitting device is formed by a plurality of light-emitting diodes and the position signal receiving device is formed by a plurality of photodetectors.

[0041] For example, the position determining means is formed by an optical encoder.

[0042] For example, the piezoelectric motor is an inertial motor and the capacitive piezoelectric actuator is a multilayer actuator.

[0043] For example, the solid dielectric barrier is made of glass or of a material that is transparent to infrared radiation.

[0044] Further details, advantages, and features of the invention will become apparent from the following description and the drawings, to which reference is expressly made for all details not described in the text. They show:

[0045] Fig. 1 a stator of a piezoelectric inertia motor with two actuators.

[0046] Fig. 2 a stator of a piezoelectric inertia motor with an actuator.

[0047] Fig. 3 a piezoelectric multilayer actuator.

[0048] Fig. 4 an idealized waveform of a signal for a piezoelectric

[0049] Inertial motor.

[0050] Fig. 5 an idealized waveform of a signal for a piezoelectric

[0051] Inertial motor.

[0052] Fig. 6 a circuit topology.

[0053] Fig. 7 a drive system for a piezoelectric motor.

[0054] Fig. 8 a circuit topology.

[0055] Fig. 9 a positioning table.

[0056] Fig. 10 shows a circuit topology. Fig. 11 shows a circuit topology.

[0057] Fig. 12 Positioning signals.

[0058] Fig. 13 Positioning signals.

[0059] Fig. 14 Components for the operation of an incremental encoder.

[0060] A drive system according to an exemplary embodiment is shown in Fig. 7. As can be seen, the drive system comprises a control device 710 suitable for generating or reading in a periodic drive signal for a piezoelectric motor and converting it into a PWM signal. The periodic drive signal is, for example, one of the signal waveforms mentioned above, such as a sawtooth or sinusoidal signal or square wave. Using this PWM signal, the control device switches at least two switching elements S1 and S2, which are shown in Fig. 8. By switching the switching elements S1 and S2, the control device 710 transmits the PWM signal to a transmitting coil or inductor 730, which is electrically connected to the two switching elements S1 and S2.

[0061] As also shown in Figures 7 and 8, the drive system includes a chamber 750, which is, for example, a vacuum chamber and thus encloses a vacuum environment.

[0062] On at least one side, the chamber has a solid dielectric barrier, which at least partially forms a side wall of the chamber. For example, the solid dielectric barrier consists of a light-transmitting material such as glass or a dielectric transparent to infrared radiation. Of course, the dielectric material of the barrier must be transparent to the signal radiated by the transmitting inductor.

[0063] Within the chamber are a receiving coil or inductor 735 and at least one capacitive piezoelectric actuator 820. The receiving inductor 735 receives the PWM signal, which is inductively transmitted by the transmitting inductor 730 through the dielectric barrier of the chamber 750.

[0064] As can be seen in Fig. 8, the receiving inductor 735 and two piezoelectric actuators 820, 825 are electrically connected to one another. The receiving inductor 735 and the capacitive piezoelectric actuators 820, 825 form a low-pass filter for the PWM signal, which, in the case of a sinusoidal output voltage, has a rectangular shape after PWM conversion. The low-pass filter consisting of the receiving inductor 735 and the capacitive piezoelectric actuators 820, 825 filters the received PWM signal due to the charging and discharging of the actuator capacitance, thereby generating a drive signal for the piezoelectric motor. This drive signal emulates the drive signal generated or input by the control device 710 by rounding off the corners of the rectangular signal during filtering. Modulation with a variety of sinusoidal waveforms is also possible.

[0065] The piezoelectric motor is, for example, a component of a positioning device in the form of a positioning table 760 and is suitable for moving or positioning its platform or table as an element to be positioned. As shown in Fig. 7, the positioning table ("piezo table" 760), including the piezoelectric motor, which includes the capacitive piezoelectric actuator, is located within the chamber 750.

[0066] Fig. 8 shows a circuit topology according to an exemplary embodiment of the present invention. The arrangement shown is a full-bridge switching topology (or H-bridge switching topology), in which the transmitting inductance is electrically connected to two switching elements S1 and S2 on one side relative to the transmitting inductance and to two further switching elements ST and S2' on the other, opposite side. The transmitting inductance 730 is connected to a first potential +Vin1 via the switching elements S1 and ST and to a second potential, represented here as ground potential, via the switching elements S2 and S2'.

[0067] In high-frequency switching mode (at least 1 MHz), the switching elements drive the transmitting inductor 730 at its operating frequency. The switching elements can be GaN (gallium nitride) transistors, for example, as these are suitable for high-frequency operation. The PWM signal causes the transmitted energy to vary according to the input waveform of the output signal. The receiving inductor 735 receives the transmitted signal and feeds it to the piezoelectric actuators 820 and 825.

[0068] The switching elements S1 and S2 are repeatedly switched in opposite directions between two switching states, on and off. For example, with a sawtooth signal, the time component of the on switching state for the switching element S1 on the diagonally rising edge is greater than the time component of the off switching signal in order to charge the actuator capacitance during the holding phase of the piezoelectric motor. At the steep decline of the sawtooth profile, the time component of the off switching state at the switching element S1 predominates, causing discharging during the sliding phase. For discharging in the holding phase and charging in the sliding phase, the time components of the switching states at the switching element S1 must be reversed.

[0069] It is also possible for the time components of the two switching states to vary within the sticking phase, depending on the waveform of the underlying (periodic) drive signal. For example, the time component of the first switching state (on or off) at switching element S1 can increase compared to the time component of the other, second switching state within the sticking phase, and at the beginning of the sliding phase, the time components are then swapped or vice versa.

[0070] Furthermore, the waveform of the periodic drive signal is not limited to the aforementioned sinusoidal, sawtooth, and square waveforms; hybrids or combinations of the aforementioned waveforms are also possible. For example, a square wave or a sawtooth wave can be approximated by sinusoidal functions in a Fourier sum or a similar sum.

[0071] In the H-switching topology of Fig. 8, the switching element S1 ' is switched equal to the switching element S1 and the switching element S2' is switched equal to the switching element S2.

[0072] Depending on the design of the piezoelectric motor, it can comprise one or more capacitive piezoelectric actuators. Figures 8 and 10 show an arrangement where the receiving inductance 735 is electrically connected to two capacitive piezoelectric actuators 820 and 825, and the two actuators are connected in series. The polarization directions of the two actuators can be arranged opposite to each other, so that one actuator is charged and the other discharged during a sticking phase, and reversed charging processes occur in the sliding phase. In such a configuration, one actuator contracts while the other actuator expands.

[0073] Alternatively, two capacitive piezoelectric actuators can also be connected in parallel and connected to the receiving inductor 735. This is shown in Fig. 11.

[0074] In addition to the H-bridge or full-bridge topology shown in Fig. 8, other switching topologies are possible. For example, a half-bridge can be used instead of the full bridge, as shown in Fig. 10. Furthermore, a double full bridge with additional switching elements on both sides of the transmitting inductor 730 is also possible.

[0075] Furthermore, it is possible for multiple actuators or electrodes in an inertial or ultrasonic motor to be individually excited or driven by separate switching elements and via separate pairs of transmitting and receiving inductors. As shown in Figures 8 and 11, the capacitive piezoelectric actuators can be connected in parallel or in series. In both connections, their polarization directions are opposite to each other. This means that the voltage generated at the receiving inductor causes one actuator to expand while the other simultaneously contracts.

[0076] As also shown in Fig. 7, the drive system according to one embodiment of the present invention may comprise a position signal transmitting device formed by a plurality of light-emitting diodes 770 to 772 located within the chamber and adapted to generate light signals corresponding to a position, determined by a position-determining means, of the element to be positioned of the positioning device in the form of a positioning table, which in this case is the platform or table of the positioning table and is moved by the piezoelectric motor. The light signals are generated based on an output signal of the position-determining means.

[0077] Outside the chamber, the system according to the described embodiment comprises a position signal receiving device formed by a plurality of photodetectors or photosensors 780 to 782, which are suitable for detecting the light signals of the light-emitting diodes 770 to 772. Each of the photosensors 780 to 782 corresponds to a respective light-emitting diode from the plurality of light-emitting diodes 770 to 772 and is suitable for detecting a light signal of the corresponding light-emitting diode, which is transmitted from the respective light-emitting diode through the fixed dielectric barrier to the corresponding photodetector.

[0078] In addition to the previously described pair of first transmitting inductance and first receiving inductance 730 and 735 for transmitting the drive signal for the piezoelectric motor, the drive system of the described embodiment includes a second transmitting inductance 740 outside the chamber 750 and a second receiving inductance 745 inside the chamber 750.

[0079] The control device 710 is adapted to generate a signal at least for supplying power to the light-emitting diodes 770 to 772 and to transmit it to the second transmitting inductance 740. The second transmitting inductance 740 is adapted to inductively transmit the signal for supplying power to the photodiodes 770 to 772 through the fixed dielectric barrier 755.

[0080] The position-determining means assigned to the positioning device in the form of a positioning table is, for example, an encoder, such as an optical encoder such as an optical incremental encoder. In an optical incremental encoder, electronic components are used to activate a light source, for example in the form of a light-emitting diode (LED) or a laser, and a photodetector of the incremental encoder. These will also be referred to below as the incremental encoder light source and incremental encoder detector to distinguish them from the plurality of LEDs 770 to 772 and photodetectors 780 to 782 for signal transmission through the barrier 755 for determining the position of the platform of the positioning table by the control unit 710. The incremental encoder light source and incremental encoder detector can be located on opposite sides of a linear scale or graduated disk.However, the present disclosure is not limited to any incremental encoder type. The use of scale facets, from which the light from the incremental encoder light source is reflected and passes through an index grating to the incremental encoder detector, is also conceivable.

[0081] In addition to the incremental encoder light source, e.g., an LED or laser, and the incremental encoder detector, e.g., an optical sensor, an incremental encoder typically includes electronic components for signal conditioning. All of these components must be supplied with electrical energy. A power source with a voltage of 3.5 V or 5 V, for example, is used to supply the incremental encoder with the required energy.

[0082] With the described embodiment, on the one hand, the electrical energy for both the position signal transmitting device or the light-emitting diodes 770 to 772, as well as for the position determining means associated with the positioning device, is transmitted wirelessly through the dielectric barrier into the chamber by means of the second transmitting and receiving inductances 740 and 745.

[0083] On the other hand, the output signal of the incremental encoder detector, which originates, for example, from the linear scale, is also transmitted wirelessly. The output signal can be in the form of three channels A, B, and Z and is transmitted as feedback or control signals to the control device 710, so that the control device can determine the position of the platform of the positioning table and, based on this, control the capacitive piezoelectric actuators 820 and 825 accordingly for controlled positioning of the platform. For this purpose, the control signals (A, B, Z) are converted into an optical signal by the light-emitting diodes 770 to 772, for example in the form of LEDs or lasers, transmitted through the dielectric barrier, and converted back into electrical signals outside the chamber 750 by the photodetectors 780 to 782, which are then forwarded to the control device 710.With this wireless, optical transmission of the control signals for position determination to the control device 710, the control signals A, B, and Z can be transmitted wirelessly from the chamber 750.

[0084] A wired incremental encoder typically requires at least the following 5 wires: Vcc, GRN (ground), channel A, channel B, and channel Z. The Vcc and ground wires provide the electrical source voltage for powering the incremental encoder components, while channels A, B, and Z are used for position determination by the control device.

[0085] In contrast to the wired technology, the present embodiment provides a technology by which the energy required for propulsion and position determination, or the corresponding signal transmission, is wirelessly transported into and out of the chamber through the dielectric barrier. Thus, cables or wires leading through the chamber's boundaries, as well as corresponding sealing of the chamber, are eliminated.

[0086] Example incremental encoder signals are shown schematically in Figures 12 and 13. Channels A and B are each rectangular waveforms that indicate the position data. If the signal from channel A leads the signal from channel B, as shown in Fig. 12, then the platform of the positioning table moves in a certain direction, for example, to the right. If channel B leads, as shown in Fig. 13, the platform of the positioning table moves in the opposite direction, for example, to the left. Channel Z is a single pulse that serves as a reference pulse. To determine the position, the number of pulses of signals A and B is counted and compared with the reference signal. The resulting number provides information about the position of the platform of the positioning table.

[0087] As described, in the present embodiment, the signals for channels A, B, and Z are transmitted wirelessly through the dielectric barrier using LEDs and photosensors, rather than transmitting them via cables from chamber 750 to controller 710. To this end, the square-wave signals of channels A, B, and Z control LEDs 770 to 772 by switching them on and off, thus generating light signals or optical signals. The optical signals are converted back into electrical signals by photodetectors 780 to 782. These electrical signals are then used by controller 710 as control signals or feedback for positioning the platform of the positioning stage.

[0088] Thus, in the present embodiment, light-emitting diodes 770 to 772 and photodetectors 780 and 782 for transmitting the output signal of the incremental encoder are provided in addition to the incremental encoder light source and the incremental encoder detector.

[0089] In addition to the incremental encoder, the LEDs 770 to 772 are also supplied with energy by the power supply signal, which is transmitted into the chamber by means of second inductors 740 and 745 and is stored there, if present, by the electrical energy storage device.

[0090] Alternatively, it is also possible to arrange an incremental encoder such that the incremental encoder light source and / or scale are located inside the chamber and the incremental encoder detector is located outside the chamber, so that the incremental encoder light source and incremental encoder detector themselves are used as light-emitting diodes and photosensors for determining the position of the element of the positioning device to be positioned by the piezoelectric motor, which are then forwarded to the control device 710 as channels A, B and Z.

[0091] In general, it is also conceivable that the position data are processed within the chamber and then sent outside the chamber via a single channel, i.e. serially.

[0092] As also described, the power for the source voltage Vcc is transmitted wirelessly through the dedicated second pair of transmitting and receiving inductors 740 and 745. Since feedback for positioning is needed when the positioning stage is in use, the power for the electronic components of the incremental encoder is required shortly before use.

[0093] For this purpose, the drive system, as shown in Fig. 14, may include an electrical energy storage device 1410 within the chamber 750, which is adapted to receive electrical energy from the second receiving inductance 745. For example, the electrical energy storage device 1410 may be a rechargeable battery or a supercapacitor.

[0094] The second pair of inductors 740 and 745 can thus be used, for example, to charge a rechargeable battery or a supercapacitor used to store electrical energy before or at system startup. When the positioning system is switched on, the second inductors 740 and 745, controlled, for example, by the controller 710, can immediately begin charging the battery or supercapacitor on the side of the positioning table. An initialization time can be used for this before the system begins positioning. Fig. 14 schematically shows components for supplying the incremental encoder electronics with electrical energy. A half-bridge switching configuration with switching elements S3 and S4, which are switched by the controller 710, connects the second transmitting inductor 740 and a capacitor 1450.The second transmitting coil transmits a signal to power the incremental encoder electronics to the second receiving inductor 740 through the dielectric barrier 755. The signal is rectified by a rectifier 1420 and can also be filtered. The rectified voltage charges a battery or supercapacitor as an electrical energy storage device 1410. This stored electrical energy supplies the electronic components of the incremental encoder 1430 with electrical energy.

[0095] As previously described, according to one embodiment of the present invention, electrical energy for driving one or more capacitive electric actuators 820 and 825 is transmitted wirelessly by means of transmitting and receiving inductors 730 and 735 through a dielectric solid barrier 755 forming the outer wall of a chamber 730 containing a positioning stage 760. The capacitive piezoelectric actuators may be piezoelectric inertial motor actuators that form a low-pass filter with the receiving inductor 735 and filter the high-frequency PWM signal, thereby obtaining a drive signal for the inertial motor.

[0096] Alternatively, the described wireless energy transport by means of (first) transmitting and receiving inductances through a dielectric barrier can also be used to drive an actuator of an ultrasonic motor.

[0097] In both inertial motors and ultrasonic motors, the capacitive piezoelectric actuator(s) can be multilayer actuators. Multilayer actuators act electrically like a comparatively large capacitance and, together with a coil, can form a low-pass filter more effectively than a single-layer or bulk actuator. Therefore, when using multilayer actuators for the piezoelectric motor, and especially for a piezoelectric ultrasonic motor, an additional energy compensation circuit is unnecessary. For example, a PWM signal with a frequency of 1 MHz can be filtered or converted by the appropriately designed low-pass filter to the operating frequency of a piezoelectric ultrasonic motor with a multilayer actuator, approximately 20 kHz.

[0098] In summary, the present invention relates to a drive system and a control method for a piezoelectric motor of such a drive system. A transmitting inductance is electrically conductively connected to at least two switching elements. A control device is suitable for converting a periodic drive signal into a pulse width modulation (PWM) signal and passing it on to the transmitting inductance by switching the at least two switching elements. Within a chamber are a receiving inductance and a capacitive piezoelectric actuator, which form a low-pass filter. At least one wall of the chamber is designed as a solid dielectric barrier, and the transmitting inductance is suitable for inductively transmitting the PWM signal to the receiving inductance through the solid dielectric barrier. This enables wireless transport ora wireless transmission of signals for the drive, but also for determining the position of an element of a positioning device to be positioned, arranged in a chamber, and in particular a hermetically sealed chamber.

Claims

PATENT CLAIMS:

1. A drive system comprising: a piezoelectric motor; at least two switching elements (S1, S2); a transmitting inductance (730) electrically connected to the at least two switching elements (S1, S2); a control device (710) capable of converting a periodic drive signal into a pulse width modulation (PWM) signal and passing it on to the transmitting inductance by switching the at least two switching elements (S1, S2); a chamber (750) having a wall configured at least partially as a solid dielectric barrier (755); and a receiving inductance (735); wherein the piezoelectric motor comprises a capacitive piezoelectric actuator (820);wherein the receiving inductance (735) and the capacitive piezoelectric actuator (820) are located within the chamber (750) and form a low-pass filter, and the transmitting inductance (730) is adapted to inductively transmit the PWM signal to the receiving inductance (735) through the fixed dielectric barrier (755); 2. Drive system according to claim 1, wherein the chamber is a hermetically sealed chamber.

3. Drive system according to claim 1 or 2, further comprising a positioning device (760) to be driven by the piezoelectric motor, which is located within the chamber (750).

4. The drive system of claim 3, wherein the transmitting inductance (730) and the receiving inductance (735) are a first transmitting inductance and a first receiving inductance, further comprising: a second transmitting inductance (740); a second receiving inductance (745); a position signal transmitting device suitable for generating and transmitting signals corresponding to the position of an element of the positioning device to be positioned on the basis of an output signal of a position-determining means assigned to the positioning device, and a position signal receiving device suitable for detecting the signals generated and transmitted by the position signal transmitting device and deriving therefrom information about the position of the element to be positioned, wherein the second receiving inductance (745) and the position signal transmitting device are located inside the chamber, and the position signal receiving device is located outside the chamber, and the control device (710) is suitableto generate a signal for supplying energy to the position signal transmitting device or the position determining means and to transmit it to the second transmitting inductance, the second transmitting inductance (740) is adapted to inductively transmit the signal for supplying energy to the second receiving inductance (745) through the fixed dielectric barrier (755), and the position signal transmitting device is adapted to transmit the light signals through the fixed dielectric barrier (755) to the position signal receiving device (780-782).

5. Drive system according to claim 4, wherein the position signal transmitting device is formed by a plurality of light-emitting diodes (770-772), and the position signal receiving device is formed by a plurality of photodetectors (780-.

6. Drive system according to claim 4 or 5, wherein the position determining means is formed by an optical encoder.

7. A drive system according to any one of claims 4 to 6, further comprising an electrical energy storage means (1410) for supplying power to the position signal transmitting device or the position determining means, the electrical energy storage means being located within the chamber and being adapted to receive electrical energy from the second receiving inductance (745).

8. Drive system according to claim 7, wherein the electrical energy storage device is a rechargeable battery or a supercapacitor.

9. Drive system according to one of claims 1 to 8, wherein the piezoelectric motor is an inertial motor or an ultrasonic motor, and the capacitive piezoelectric actuator is a multilayer actuator.

10. A drive system according to any one of claims 1 to 9, wherein the solid dielectric barrier is made of glass or of material transparent to infrared radiation.

11. A control method for a piezoelectric motor, comprising the steps of: Converting a periodic drive signal into a pulse width modulation (PWM) signal that has a higher frequency than the drive signal, Transmitting the PWM signal to a transmitting inductance, and inductively transmitting the PWM signal from the transmitting inductance to a receiving inductance through a fixed dielectric barrier, wherein the receiving inductance forms a low-pass filter with a capacitive piezoelectric actuator of the piezoelectric motor.

12. The control method according to claim 11, wherein the PWM signal is transmitted from a first transmitting inductance to a first receiving inductance, further comprising the steps of: Generating a signal for supplying energy to a position-determining means for determining the position of an element of a positioning device to be positioned by the piezoelectric motor or for supplying energy to a position-signal transmitting device which is suitable for generating and transmitting signals corresponding to the position of the element to be positioned on the basis of an output signal of the position-determining means associated with the positioning device; Passing the signal for supplying power to the position determining means or the position signal transmitting device to a second transmitting inductance; Inductively transmitting the signal for powering the position determining means or the position signal transmitting device to a second receiving inductance through the fixed dielectric barrier; Transmitting the signals of the position signal transmitting device through the solid dielectric barrier to a position signal receiving device which is suitable for detecting the signals generated and transmitted by the position signal transmitting device and deriving therefrom information about the position of the element to be positioned; and Detecting the signals of the position signal transmitting device by the position signal receiving device.

13. A control method according to claim 12, further comprising: Storing the electrical energy received by the second receiving inductance to power the position determining means or the position signal transmitting device.

14. A control method according to claim 12 or 13, wherein the position signal transmitting device is formed by a plurality of light-emitting diodes and the position signal receiving device is formed by a plurality of photodetectors.

15. Control method according to one of claims 12 to 14, wherein the position determining means is formed by an optical encoder.

16. The control method according to any one of claims 11 to 15, wherein the piezoelectric motor is an inertial motor or an ultrasonic motor, and the capacitive piezoelectric actuator is a multilayer actuator.

17. A control method according to any one of claims 11 to 16, wherein the solid dielectric barrier is made of glass or of a material transparent to infrared radiation.

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