Piezoelectric motor drive system and control method

Abstract

The present invention relates to a drive system and a method for controlling 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 adapted to convert a periodic drive signal into a PWM signal and transmit the PWM signal to the transmitting inductance by switching the at least two switching elements. A receiving inductance and a capacitive piezoelectric actuator forming a low-pass filter are located in a chamber. At least one wall of the chamber is configured as a solid dielectric barrier, and the transmitting inductance is adapted to inductively transmit the PWM signal to the receiving inductance through the solid dielectric barrier. The system and method enable wireless transmission of signals in a sealed environment, such as a vacuum environment.

Description

[Technical Field]

[0001] The present invention relates to a drive system and a control method for a piezoelectric motor with wireless transmission of control signals. [Background technology]

[0002] Piezoelectric resonant motors (e.g., ultrasonic motors) or inertial motors, such as those used in positioning stages, require a periodic signal, e.g., with a sine wave, square wave, or sawtooth wave, to activate the piezoelectric actuator in the stator, i.e., to cause vibration or periodic deformation of the actuator. The vibration motion or deformation in the stator is then transmitted to the moving element (slider or rotor) via a friction coupling, thereby moving the moving element in the desired manner.

[0003] In a piezoelectric inertial actuator, the tangential component of the reciprocating motion during vibration or deformation of the piezoelectric actuator induces motion at the contact point between the driven element and the actuator located on the stator. In one direction of the tangential motion, the actuator is slowly activated, i.e., slowly deformed. During the activation period of the "stick phase" or "slow phase," static friction exists between the actuator and the driven element, allowing the driven element to keep up with the slow deformation motion of the actuator. In the opposite direction of the tangential motion, the piezoelectric actuator is deactivated or deformed at a higher speed compared to its initial position. During this time of 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, causing the actuator to slide along the driven element so that the driven element cannot keep up with the fast motion of the actuator. During such cycles of stick and slip phases, the driven element takes microscopically small motion steps. The accumulation of these microscopic motion steps produces a macroscopic motion of the actuated element.

[0004] Fig. 1 shows a stator 10 of a piezoelectric inertia motor, which comprises an elastic frame 14, a friction element 12 provided for frictional contact with the driven element, and a screw 13 for preload adjustment or tolerance compensation. As shown in Fig. 1, the stator of the inertia motor may have two actuators 11a, 11b, for example, a multi-layer actuator having multiple layers of superposed piezoelectric material and electrodes between them, each with a capacitance Ca1, Ca2. One of the two actuators expands during operation, while the other contracts to cause a reciprocating tangential movement of the friction element, as shown by arrows 15.

[0005] Figure 2 shows the stator 20 of a piezoelectric inertia motor with a single actuator 21 as the driving source, with like elements designated as in Figure 1. Only one electrical channel need be connected to the actuator.

[0006] Figure 3 illustrates a piezoelectric multilayer actuator. Multilayer actuators in an electrical circuit can be understood as capacitive elements. For clarity, the actuators are referred to herein as "capacitive piezoelectric actuators." They are typically used in analogy to capacitors in low-pass filters.

[0007] In the inertial motor shown in Figure 1, the two piezoelectric actuators can be driven by two anti-phase (inverted) sawtooth signals. The expansion and contraction of the two actuators occur synchronously in opposite directions. Therefore, while one actuator is expanding, the other actuator is contracting.

[0008] For example, the signal applied to the actuators of a piezoelectric inertia motor may have an idealized sawtooth waveform, such as that shown in Figure 4. During the slow or stick phase, one of the two actuators slowly expands while the other slowly contracts. This slow expansion and contraction of the piezoelectric actuators corresponds to the slow charging and discharging of a capacitor.

[0009] Accordingly, during the fast or sliding phase, one piezoelectric actuator rapidly expands while the other rapidly contracts. This rapid expansion or contraction also corresponds to the rapid charging or discharging of a capacitor. In this disclosure, the piezoelectric actuators are primarily treated like capacitor elements used in filter elements of a drive circuit.

[0010] In Figure 4, the two depicted waveforms correspond to the control signals of two actuators that are expanding and contracting in opposite directions in the stator of a piezoelectric inertia motor. For actuators with only one piezoelectric actuator, it is sufficient to consider one of the two sawtooth waveforms.

[0011] The sawtooth signal waveforms of the control signals for the actuators may each have a flat section between the slow and fast phases or at the transition from the slow to the fast phase, as shown in the idealized form in FIG.

[0012] Although ultrasonic motors or piezoelectric ultrasonic motors are typically controlled by sine or sinusoidal waveforms, respectively, the signal waveforms described above can be used to operate ultrasonic motors or resonant motors in general as well.

[0013] FIG. 6 corresponds to FIG. 22 of DE 102020132640 B3, which describes wireless driving of a piezoelectric motor. A periodic drive signal for the motor is applied to a transmitting coil. A receiving coil receives the drive signal in a contactless manner and provides energy to the motor's actuator. The received signal is filtered by an LC configuration between the receiving coil and the actuator capacitance. The voltage drop across the actuator is the drive signal for the piezoelectric motor.

[0014] The periodic drive signal that operates the stator is generated by a pulse-width modulation (PWM) signal, the frequency of which is 5 to 10 times higher than the operating frequency of the piezoelectric motor.

[0015] When using the aforementioned piezoelectric motors 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 consideration. For example, in a vacuum environment, the cable connections are established using special interface connections. Summary of the Invention [Means for solving the problem]

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

[0017] By wireless transmission of the signals proposed to drive the piezoelectric motors, and possibly other signals such as position feedback signals for transmitting the position of elements driven or positioned by the motors or actuators, such as the platform of a positioning stage, sealing of cables inserted into the chamber or cable connections can be omitted. Furthermore, cable interference or signal or field interference caused by cables can be reduced or minimized. Small positioning stages used in vacuum chambers are mentioned immediately as an example.

[0018] The present disclosure provides drive systems and methods that allow for wireless transmission of coded drive signals for piezoelectric motors or actuators from a transmitting coil or transmitting inductance to a receiving coil or receiving inductance through a glass or dielectric barrier into a chamber, particularly a sealed or hermetically closed chamber such as a vacuum chamber.

[0019] Reference herein to inductance or capacitance refers to a component having inductive or capacitive properties, respectively, unless expressly stated otherwise. Inductance is currently understood to mean, among other things, a coil, while capacitance is currently understood to mean, among other things, a piezoelectric actuator that behaves electrically like a capacitor.

[0020] The steps of the proposed method can be summarized as follows: 1) A DC, sawtooth, or sinusoidal actuation signal waveform in the DC range or in the range between 20 kHz and approximately 200 kHz is first converted into a PWM signal with a frequency of 1 MHz or higher to actuate the transmit coil. In the case of a DC signal, the width of the PWM signal is constant or varies very slowly.

[0021] 2) These PWM signals are transmitted to the transmitting coil or transmitting inductance, respectively. The generated electrical energy is then received by the receiving coil or receiving inductance, respectively, on the other side of a glass or dielectric barrier in a closed environment or chamber. The received signals are filtered on the receiving coil side. On the receiving side, the receiving coil in the stator and the piezoelectric actuator can be connected in parallel or series. Various electrical networks and filtering techniques can be applied there. The LC configuration of the receiving coil (L) and capacitance (C) of the piezoelectric element in the stator acts as a filter. The voltage waveform resulting from the accumulation in the piezoelectric actuator exhibits a sine wave or sawtooth waveform. These signals allow the motor to be operated without any physical (cable or wire) connection between the driving side or actuation side and the motor.

[0022] Several parameters can be used in a piezoelectric motor to control the position and velocity of an element driven or positioned by the motor, such as the platform of a positioning stage. For example, i) the signal strength of an electrical switching element, such as a voltage source in a half- or full-bridge topology, that activates the transmitting inductance; ii) the operating frequency of the piezoelectric motor or the frequency of a PWM signal; or iii) driving the transmitting inductance with a waveform of sudden amplitude accumulation (burst) to obtain small steps of the motor for short-term activation of the transmitting inductance. The parameters listed above can be further adapted to specific applications, such as the distance between the transmitting coil and the receiving coil, the thickness of the glass or dielectric barrier, the material of the glass or dielectric barrier, etc.

[0023] In addition to the drive signals of the motors, signals or information regarding the position of the element to be driven or positioned can be transmitted wirelessly, for example through optical communication, in particular for closed-loop control of its position or for corresponding closed-loop circuits. Energy for corresponding positioning device components can be transmitted to the signal generating side in a manner similar to wireless charging.

[0024] According to a first aspect of the present invention, a drive system comprises a piezoelectric motor, at least two switching elements, a transmitting inductance electrically conductively connected to the at least two switching elements, a control device adapted to convert a periodic drive signal into a PWM signal and to transmit the PWM signal to the transmitting inductance by switching the at least two switching elements, a chamber, preferably a hermetically sealed chamber having walls at least partially configured as a solid dielectric barrier, and a receiving inductance, wherein the piezoelectric motor comprises a capacitive piezoelectric actuator, the receiving inductance and the capacitive piezoelectric actuator being located within the chamber and forming a low pass filter, and the transmitting inductance is adapted to inductively transmit the PWM signal to the receiving inductance through the solid dielectric barrier.

[0025] For example, the drive system may further comprise a positioning device driven by a piezoelectric motor in the form of a positioning stage having a stationary substrate acting as a stator and a platform movable relative to the substrate, the positioning device being located within the chamber.

[0026] For example, the transmitting inductance and the receiving inductance are a first transmitting inductance and a first receiving inductance, and the drive system further includes a second transmitting inductance, a second receiving inductance, a position signal transmitting device adapted to generate and transmit a signal corresponding to the position of an element of the positioning device to be positioned based on an output signal of a position determination device associated with the positioning device, and a position signal receiving device adapted to detect the signal generated and transmitted by the position signal transmitting device and obtain information about the position of the element to be positioned, the second receiving inductance and the position signal transmitting device being located within the chamber, and the position signal receiving device being located outside the chamber, the control device being adapted to generate a signal for supplying energy to the position signal transmitting device or the position determination device and to transfer the energy to the second transmitting inductance, the second transmitting inductance being adapted to inductively transmit a signal for supplying energy to the second receiving inductance through a solid dielectric barrier, and the position signal transmitting device being adapted to transmit an optical signal to the position signal receiving device through the solid dielectric barrier.

[0027] For example, the location signal transmitting device may be formed by a plurality of light emitting diodes, and the location signal receiving device may be formed by a plurality of photodetectors.

[0028] For example, the position determining device may be formed by an optical encoder. For example, the drive system includes an electrical energy storage device for supplying energy to the position signal transmitting device or the position determining device, the electrical energy storage device being located within the chamber and adapted to receive electrical energy from the second receiving inductance.

[0029] For example, the electrical energy storage device is a rechargeable battery or a supercapacitor.

[0030] For example, a piezoelectric motor is an inertial motor, and a capacitive piezoelectric motor is a multi-layer actuator.

[0031] For example, the solid dielectric barrier may be made of glass or an infrared transparent material. According to a second aspect of the present invention, a method for controlling a piezoelectric motor includes converting a periodic drive signal into a PWM signal having 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 through a solid dielectric barrier to a receiving inductance, the receiving inductance forming a low-pass filter together with a capacitive piezoelectric actuator of the piezoelectric motor.

[0032] For example, the control method includes: generating, based on an output signal of a positioning device associated with the positioning device, a signal for energizing a positioning device for determining the position of an element of the positioning device positioned by the piezoelectric motor or for energizing a position signal transmitting device adapted to generate and transmit a signal corresponding to the position of the element to be positioned; passing a signal to a second transmitting inductance to energize a position determining device or a position signal transmitting device; inductively transmitting a signal through a solid dielectric barrier to a second receiving inductance for energizing a position determining device or a position signal transmitting device; obtaining information regarding the location of the element to be located by transmitting a signal from the location signal transmitting device that has passed through the solid dielectric barrier to a location signal receiving device adapted to detect the signal generated and transmitted by the location signal transmitting device; The method further includes the step of detecting the signal from the location signal transmitting device by the location signal receiving device.

[0033] For example, the control method further comprises the step of storing the electrical energy received by the second receiving inductance for supplying energy to the position determining device and / or the position signal transmitting device.

[0034] 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.

[0035] For example, the position determining device is formed by an optical encoder. For example, a piezoelectric motor is an inertial motor, and a capacitive piezoelectric actuator is a multi-layer actuator.

[0036] For example, the solid dielectric barrier may be made of glass or an infrared transparent material. Further details, advantages and features of the invention will emerge from the following specification and drawings, to which explicit reference is made for all details not described herein. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 1 shows a stator of a piezoelectric inertia motor with two actuators. [Figure 2] FIG. 2 shows the stator of a piezoelectric inertia motor with one actuator. [Figure 3] FIG. 3 is a diagram showing a piezoelectric multilayer actuator. [Figure 4] FIG. 4 shows idealized signal waveforms for a piezoelectric inertial motor. [Figure 5] FIG. 5 shows idealized signal waveforms for a piezoelectric inertial motor. [Figure 6] FIG. 6 is a diagram showing the circuit topology. [Figure 7] FIG. 7 shows a drive system for a piezoelectric motor. [Figure 8] FIG. 8 is a diagram showing the circuit topology. [Figure 9] FIG. 9 is a diagram showing the positioning stage. [Figure 10] FIG. 10 is a diagram showing the circuit topology. [Figure 11] FIG. 11 is a diagram showing the circuit topology. [Figure 12] FIG. 12 is a diagram showing the positioning signal. [Figure 13] FIG. 13 is a diagram showing the positioning signal. [Figure 14] FIG. 14 is a diagram showing the components for operating an incremental encoder. DETAILED DESCRIPTION OF THE INVENTION

[0038] A drive system according to an exemplary embodiment is shown in FIG. 7. As shown, the drive system includes a controller 710 adapted to generate or import a periodic drive signal for the piezoelectric motor and convert the signal into a PWM signal. The periodic drive signal may be one of the signal waveforms described above, such as a sawtooth or sinusoidal signal or a rectangular waveform. Using this PWM signal, the controller switches at least two switching elements S1 and S2, shown in FIG. 8. By switching the switching elements S1 and S2, the controller 710 transmits the PWM signal to a receiving coil or inductance 730 that is electrically conductively connected to the two switching elements S1 and S2.

[0039] As also shown in Figures 7 and 8, the drive system includes a chamber 750, for example a vacuum chamber, thereby enclosing a vacuum environment.

[0040] On at least one side, the chamber is provided with a solid dielectric barrier at least partially forming one sidewall of the chamber. For example, the solid dielectric barrier may be made of an optically transparent material such as glass or an infrared-transparent dielectric. Of course, the dielectric material of the barrier must be transparent to the signal output by the transmitting inductance.

[0041] Disposed within the chamber is a receiving coil or inductance 735 and at least one capacitive piezoelectric actuator 820. The receiving inductance 735 receives the PWM signal inductively transmitted by the transmitting inductance 730 through the solid dielectric barrier of the chamber 750.

[0042] As shown in Figure 8, the receiving inductance 735 and the two piezoelectric actuators 820, 825 are electrically conductively connected to each other. The receiving inductance 735 and the 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 formed by the receiving inductance 735 and the capacitive piezoelectric actuators 820, 825 filters the received PWM signal by charging and discharging the actuator capacitance, thus generating a drive signal for the piezoelectric motor that mimics the drive signal generated or input by the control device 710 in that the corners of the rectangular signal are rounded during the filtering process. Modulation with multiple sinusoidal waveforms is also possible.

[0043] The piezoelectric motor may be part of a positioning device, for example in the form of a positioning stage 760, adapted to move or position its platform or table as the positioned element. As shown in Figure 7, a positioning stage (piezoelectric stage 760) including a piezoelectric motor with a capacitive piezoelectric actuator is located within chamber 750.

[0044] 8 illustrates a circuit topology according to an exemplary embodiment of the present invention. The illustrated configuration is a full-bridge switching topology (or H-bridge switching topology) in which a transmitting or sending inductance is electrically connected to two switching elements S1 and S2 on one side of the transmitting inductance and to two more switching elements S1′ and S2′ on the other side. The transmitting inductance 730 is connected to a first potential +Vin1 via switching elements S1 and S1′ and to a second potential, currently represented as ground potential, via switching elements S2 and S2′.

[0045] For high-frequency switching operation (at least 1 MHz), the switching element controls the transmitting inductance 730 at the operating frequency. The switching element can be, for example, a GaN (Gallium Nitride) transistor, as it is suitable for high-frequency operation. The PWM signal varies the transmitted energy according to the waveform of the output signal, which is its input. The receiving inductance 735 receives the transmitted signal and transmits it to the piezoelectric actuators 820 and 825.

[0046] The switching elements S1 and S2 are repeatedly switched in opposite directions between two switching states, ON and OFF. For example, in order for a sawtooth signal to charge the actuator capacitance during the sticking phase of a piezoelectric motor, the time component of the ON switching state of switching element S1 at the diagonally rising edge is greater than the time component of the OFF switching signal. At the sharp drop of the sawtooth profile, the time component of the OFF switching state of switching element S1 dominates, which causes a discharge during the slipping phase. In order to discharge during the sticking phase and charge during the slipping phase, the time components of the switching states of switching element S1 must be reversed.

[0047] It is also possible to vary the time components of the two switching states during the sticking phase, depending on the waveform of the basic (periodic) drive signal. For example, the time component of the first switching state (ON or OFF) of the switching element S1 can be increased relative to the other, i.e., the time component of the second switching state, during the sticking phase, and then, at the beginning of the slipping phase, the respective time components are swapped or reversed.

[0048] Furthermore, the waveform of the periodic drive signal is not limited to the sine, sawtooth, and square waveforms described above, but may also be a mixture or combination of the aforementioned waveforms. For example, a square or sawtooth waveform may be approximated by a sinusoidal function in a Fourier synthesis or similar synthesis.

[0049] In the H-switching topology of FIG. 8, switching element S1' switches like switching element S1, and switching element S2' switches like switching element S2.

[0050] Depending on the piezoelectric motor's configuration, the piezoelectric motor may include one or more capacitive piezoelectric actuators. Figures 8 and 10 show a configuration in which a receiving inductance 735 is electrically conductively connected to two capacitive piezoelectric actuators 820, 825, with the two actuators connected in series. The polarization directions of the two actuators are aligned in opposite directions, so that one actuator is charged during the sticking phase while the other is discharged. The charging process is then reversed during the sliding phase. In such a configuration, one actuator expands while the other contracts.

[0051] Alternatively, two capacitive piezoelectric actuators can also be connected in parallel and connected with a receiving inductance 735. This is shown in FIG.

[0052] In addition to the H-bridge or full-bridge topology shown in Figure 8, other switching topologies are possible. For example, a half-bridge may be used instead of a full-bridge, as shown in Figure 10. A dual full-bridge with additional switching elements on either side of the receiving inductance 730 is also possible.

[0053] Furthermore, multiple actuators or electrodes in an inertial or ultrasonic motor can be individually activated or driven by individual switching elements and through separate pairs of transmitting and receiving inductances.

[0054] As shown in Figures 8 and 11, capacitive piezoelectric actuators can be connected in parallel or in series. In both connections, their polarization directions are opposite to each other, so that the voltage generated across the receiving inductance causes one actuator to expand while the other contracts.

[0055] 7, a drive system according to an embodiment of the present invention comprises a position signal transmitting device formed by a plurality of light emitting diodes 770, 772 located in the chamber and adapted to generate an optical signal corresponding to the position at which an element of the positioning device is located, said position being determined by a positioning device in the form of a positioning stage, in this case a platform or table, moved by a piezoelectric motor, the optical signal being generated based on the output signal of the positioning device.

[0056] Outside the chamber, the system according to the described embodiment comprises a position signal receiving device formed by a plurality of photodetectors or photosensors 780-782 adapted to detect the optical signals of the light emitting diodes 770-772. Each of the photosensors 780-782 corresponds to a respective one of the plurality of light emitting diodes 770-772 and is adapted to detect the optical signal from the corresponding light emitting diode transmitted from the respective light emitting diode through a solid dielectric barrier to a corresponding photodetector.

[0057] In addition to the aforementioned pair of first transmitting inductance 730 and first receiving inductance 735 for transmitting a 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 within the chamber 750.

[0058] The control device 710 is adapted to generate a signal to energize at least the light emitting diodes 770-772 and to transmit the energy to the second transmitting inductance 740. The second transmitting inductance 740 is adapted to inductively transmit the signal to energize the light emitting diodes 770-772 through the solid dielectric barrier 755.

[0059] The position-determining device associated with the positioning device in the form of a positioning stage is, for example, an encoder, such as an optical encoder or an optical incremental encoder. In an optical incremental encoder, electrical components are used to activate a light source, for example in the form of a light-emitting diode (LED) or laser, and an incremental encoder photodetector. These will be referred to below as an incremental encoder light source and an incremental encoder detector to distinguish them from the plurality of light-emitting diodes 770-772 and photodetectors 780-782 that transmit signals through the solid dielectric barrier 755 to determine the position of the positioning stage platform via the control unit 710. The incremental encoder light source and the incremental encoder detector may be located on opposite sides of a linear scale or graduated disk. However, the present disclosure is not limited to any type of incremental encoder. The use of scale facets that reflect light from the incremental encoder light source through an index grating to the incremental encoder detector is also contemplated.

[0060] In addition to the incremental encoder light source, for example in the form of an LED or laser, and the incremental encoder detector, for example in the form of an optical sensor, an incremental encoder typically comprises electronic components for signal conditioning. All of these components must be supplied with electrical energy. For example, a power supply with a voltage of 3.5 V or 5 V is used to provide the necessary energy for the incremental encoder.

[0061] On the other hand, in the described embodiment, electrical energy for both the position signal transmitting device or LEDs 770-772, as well as for the position determining device associated with the positioning device, is wirelessly transmitted into the chamber through the dielectric barrier by the second transmitting inductance 740 and the second receiving inductance 745.

[0062] On the other hand, output signals of incremental encoder detectors, e.g., output signals generated by a linear scale, are also transmitted wirelessly. The output signals may be in the form of three channels A, B, and Z and transmitted as feedback or closed-loop control signals to controller 710. As a result, the latter can determine the position of the platform of the positioning stage and control capacitive piezoelectric actuators 820 and 825 accordingly, thereby activating the platform positioning in a closed-loop manner. For this purpose, the closed-loop control signals (A, B, Z) are converted into optical signals by light-emitting diodes 770-772, e.g., in the form of LEDs or lasers, transmitted through a dielectric barrier, and converted back into electrical signals by photodetectors 780-782 outside chamber 750, which are then transmitted to controller 710. This wireless optical transmission of the closed-loop control signals for position determination to controller 710 allows control signals A, B, and Z to be transmitted wirelessly from chamber 750.

[0063] A hardwired incremental encoder typically requires at least five wires: Vcc, GRN (ground), Channel A, Channel B, and Channel Z. The Vcc and ground wires provide the electrical power supply voltages for energizing the incremental encoder components, while Channels A, B, and Z are used for position determination by the controller.

[0064] In contrast to wired techniques, the present embodiment provides a technique in which the energy required in the chamber for actuation and position determination, or the corresponding signal transmission, respectively, is transferred and provided inside and outside the chamber wirelessly through a dielectric barrier, so that cables or wires routed through the boundaries of the chamber and through the respective ceilings of the chamber can be omitted.

[0065] Exemplary incremental encoder signals are shown schematically in FIGS. 12 and 13. Channels A and B each have a rectangular waveform representing position data. If the signal from Channel A leads the signal from Channel B, as shown in FIG. 12, the positioning stage platform moves in a particular direction, e.g., to the right. If the signal from Channel B leads, as shown in FIG. 13, the positioning stage platform moves in the opposite direction, e.g., to the left. Channel Z is a single pulse that serves as a reference pulse. To determine position, the number of pulses in signals A and B are counted and compared to the reference signal. The resulting numerical value provides information about the position of the positioning stage platform.

[0066] As described, in this embodiment, the signals for channels A, B, and Z are transmitted wirelessly through a dielectric barrier using LEDs and optical sensors, rather than being transmitted from chamber 750 to controller 710 through wires. To this end, each of the square waveform signals for channels A, B, and Z controls LEDs 770-772 by switching them on and off, which in turn generates a light or optical signal. The optical signals are reconverted into electrical signals by photodetectors 780-782. These electrical signals are then used by controller 710 as closed-loop control signals or feedback for positioning the positioning stage platform.

[0067] In this embodiment, light emitting diodes 770-772 and photodetectors 780, 782 are therefore provided to transmit the output signal of the incremental encoder to the incremental encoder detector in addition to the incremental encoder light source.

[0068] In addition to the incremental encoder, the light emitting diodes 770-772 are also energized by an energy supply signal, which is transmitted into the chamber through the second inductances 740, 750, if present, and stored by the electrical energy storage device.

[0069] Alternatively, the incremental encoder can be positioned so 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 optical sensors to determine the position of the elements of the positioning device positioned by the piezoelectric motor, which are communicated to the controller 710 as channels A, B, and Z.

[0070] In general, it is contemplated that the position data may be processed within the chamber and then transmitted outside the chamber, for example serially, via a single channel.

[0071] As further described, energy for the Vcc supply voltage is transmitted wirelessly through a pair of second transmitting inductances 740 and second receiving inductances 745 provided for this purpose. Since feedback for positioning is required when the positioning stage is in use, energy for the electronic components of the incremental encoder is required shortly before use.

[0072] 14, the drive system may comprise an electrical energy storage device 1410 in the chamber 750 adapted to receive electrical energy from the second receiving inductance 745. For example, the electrical energy storage device 1410 is a rechargeable battery or a supercapacitor.

[0073] Therefore, the pair of second inductances 740 and 745 can be used before or during system startup, for example to charge a rechargeable battery or supercapacitor used to store electrical energy. When the positioning system is switched on, the second inductances 740, 745, controlled for example by the control device 710, can immediately start charging said battery or supercapacitor on the positioning stage side. An initialization time can be used for this purpose before the system starts positioning.

[0074] 14 shows a schematic diagram of components for supplying electrical energy to the incremental encoder electronics. A half-bridge switching arrangement including switching elements S3 and S4, switched by a controller 710, connects a second transmitting inductance 740 and a capacitor 1450. The second transmitting coil transmits a signal to the second receiving inductance 740 through a dielectric barrier 755 to energize the incremental encoder electronics. The signal is rectified by a rectifier 1420 and may be additionally filtered. The rectified voltage charges a battery or supercapacitor as an electrical energy storage device 1410. This stored electrical energy supplies electrical energy to the electronics of the incremental encoder 1430.

[0075] As previously mentioned, according to one embodiment of the present invention, electrical energy for driving one or more capacitive electric actuators 820, 825 is transmitted wirelessly by transmitting inductance 730 and receiving inductance 735 through a dielectric solid barrier 755 forming the outer wall of chamber 730 in which positioning stage 760 is located. The capacitive piezoelectric actuators can be actuators of piezoelectric inertial motors, where a drive signal for the inertial motor is obtained by filtering a high frequency PWM signal together with receiving inductance 735 to form a low pass filter.

[0076] Alternatively, the described wireless energy transmission by a (first) transmitting inductance and a receiving inductance through a dielectric barrier can also be used to drive the actuator of an ultrasonic motor.

[0077] In inertial motors as well as ultrasonic motors, capacitive piezoelectric actuators can be multilayer actuators. Multilayer actuators behave electrically like relatively large capacitances and, together with the coil, can form a more effective low-pass filter than single-layer or bulk actuators. Therefore, when using multilayer actuators for piezoelectric motors, especially piezoelectric ultrasonic motors, additional energy compensation circuits are unnecessary. For example, a PWM signal with a frequency of 1 MHz can be filtered or converted to an operating frequency of approximately 20 kHz for a piezoelectric ultrasonic motor with a multilayer actuator by a correspondingly configured low-pass filter.

[0078] In summary, the present invention relates to a drive system and control method for a piezoelectric motor, such as a drive system. A transmitting inductance is electrically conductively connected to at least two switching elements. A control device is adapted to convert a periodic drive signal into a PWM signal and transmit the PWM signal to the transmitting inductance by switching the at least two switching elements. A receiving inductance forming a low-pass filter and a capacitive piezoelectric actuator are located in a chamber. At least one wall of the chamber is configured as a solid dielectric barrier, and the transmitting inductance is adapted to inductively transmit the PWM signal to the receiving inductance through the solid dielectric barrier. This allows wireless transfer or transmission of signals for driving, but also for determining the position of an element of a positioning device within the chamber, in particular a hermetically sealed chamber.

Claims

1. A drive system comprising: a piezoelectric motor; At least two switching elements (S1, S2); a transmitting inductance (730) electrically conductively connected to the at least two switching elements (S1, S2); a control device (710) adapted to convert a periodic drive signal into a pulse-width modulation (PWM) signal and to transmit the PWM signal to the transmitting inductance by switching the at least two switching elements (S1, S2); a chamber (750) having walls configured at least in part as a solid dielectric barrier (755); a receiving inductance (735); the piezoelectric motor comprises a capacitive piezoelectric actuator (820); 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 solid dielectric barrier (755).

2. The drive system of claim 1 , wherein the chamber is a hermetically sealed chamber.

3. 3. The drive system of claim 1 or 2, further comprising a positioning device (760) driven by the piezoelectric motor and located within the chamber (750).

4. the transmitting inductance (730) and the receiving inductance (735) are a first transmitting inductance and a first receiving inductance, a second transmitting inductance (740); a second receiving inductance (745); a position signal transmitting device adapted to generate and transmit a signal corresponding to the position of an element of the positioning device being positioned based on an output signal of a position determining device associated with the positioning device; a location signal receiving device adapted to detect the signal generated and transmitted by the location signal transmitting device and for obtaining information about the location of the element to be positioned by detecting the signal; the second receiving inductance (745) and the location signal transmitting device are located within the chamber, and the location signal receiving device is located outside the chamber; the control device (710) is adapted to generate a signal for supplying energy to the position signal transmitting device or the position determining device and to transmit the energy to the second transmitting inductance; the second transmitting inductance (740) is adapted to inductively transmit the signal to energize the second receiving inductance (745) through the solid dielectric barrier (755); The drive system of claim 3, wherein the position signal transmitting device is adapted to transmit an optical signal through the solid dielectric barrier (755) to the position signal receiving device (780-782).

5. The location signal transmitting device is formed by a plurality of light emitting diodes (770-772), 5. The drive system of claim 4, wherein the position signal receiving device is formed by a plurality of photodetectors (780-782).

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

7. further comprising an electrical energy storage device (1410) for supplying energy to the location signal transmitting device or the location determining device; The drive system of any one of claims 4 to 6, wherein the electrical energy storage device is located within the chamber and adapted to receive electrical energy from the second receiving inductance (745).

8. The drive system of claim 7 , wherein the electrical energy storage device is a rechargeable battery or a supercapacitor.

9. the piezoelectric motor is an inertial motor or an ultrasonic motor; A drive system according to any one of claims 1 to 8, wherein the capacitive piezoelectric actuator is a multi-layer actuator.

10. 10. The drive system according to claim 1, wherein the solid dielectric barrier is made of glass or a material that transmits infrared rays.

11. A method for controlling a piezoelectric inertia motor, comprising: converting the periodic drive signal into a PWM signal having a higher frequency than the drive signal; transmitting the PWM signal to a transmitting inductance; inductively transmitting the PWM signal from the transmitting inductance to the receiving inductance through a solid dielectric barrier; The receiving inductance forms a low pass filter together with a capacitive piezoelectric actuator of the piezoelectric motor.

12. The PWM signal is transmitted from a first transmitting inductance to a first receiving inductance; generating, based on an output signal of a positioning device associated with the positioning device, a signal for energizing a positioning device for determining a position of an element of the positioning device positioned by the piezoelectric motor, or for energizing a position signal transmitting device adapted to generate and transmit a signal corresponding to the position of the element to be positioned; transmitting the signal to a second transmitting inductance for supplying energy to the position determining device or the position signal transmitting device; inductively transmitting the signal for energizing the position determining device or the position signal transmitting device through the solid dielectric barrier to a second receiving inductance; transmitting the signal from the location signal transmitting device through the solid dielectric barrier to a location signal receiving device adapted to detect the signal generated and transmitted by the location signal transmitting device, and obtaining information regarding the location of the element to be positioned by detecting the signal; The control method according to claim 11 , further comprising the step of detecting the signal from the location signal transmitting device by the location signal receiving device.

13. The control method of claim 12 , further comprising storing the electrical energy received by the second receiving inductance for providing energy to the position-determining device or the position signal transmitting device.

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

15. The control method according to any one of claims 12 to 14, wherein the position determining device is formed by an optical encoder.

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

17. The control method according to any one of claims 11 to 16, wherein the solid dielectric barrier is made of glass or a material that transmits infrared rays.

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