DE102022114863B3 - ultrasonic motor - Google Patents

Abstract

The invention relates to an ultrasonic motor which has at least one piezoelectric ultrasonic actuator (1) with at least one generator (12) for generating a planar acoustic traveling wave, an element (2) to be driven with an external thread and a drive element (6) with a thread (8 ) provided inner circumferential surface (7) and an outer circumferential surface, the drive element being inserted into the ultrasonic actuator (1), so that it surrounds the drive element (6) via an inner circumferential surface on its outer circumferential surface, the element to be driven (2) and Drive element (6) is in threaded engagement and the planar acoustic traveling wave can be transferred from the ultrasonic actuator (1) to the drive element (6) and thus a rotation of the element (2) to be driven can be caused. The ultrasonic actuator (1) has the shape of a polygonal plate (4) with two large main surfaces (19) and at least three smaller side surfaces (18) connecting the two main surfaces (19), and it comprises at least one active generator (13) for generation a planar acoustic standing wave, the maximum oscillation speed of which is in the area of the inner peripheral surface of the ultrasonic actuator (1).

Description

The invention relates to an ultrasonic motor.

Piezoelectric friction contact drives are known from the prior art, in which the friction contact is designed in the form of a threaded engagement. They can be used, for example, as spindle drives in various types of mechanisms, such as in linear drives, in precise closure and metering systems, in valves, in precise cutting drives, in control drives, in precise positioning devices, such as in technological coordinate tables, in multi-coordinate positioning devices, in tripods or hexapods , in optical laser systems and similar devices, and in precision medical devices, e.g. pumps, syringes, insulin pumps or devices for bone lengthening.

Lasers are used in many areas of technology, be it in metrology, medical technology, metal processing, etc. The laser beam is usually precisely directed or guided with the help of tilting mirrors. The required precision of laser beam steering is achieved with the help of micrometer screws. These are often operated manually. However, there are a number of applications in which manual adjustment of the tilting mirrors is not possible or undesirable, for example within a vacuum chamber, in a lithography machine or a tachymeter.

Piezoelectric friction contact drives are often used to automatically position the tilting mirrors. Here, an element to be driven, i.e. the rotor or rotor, is connected or coupled to the actuator by a frictional contact, with a targeted deformation or movement of the actuator caused by electrical control being transmitted to the element to be driven by means of the frictional contact.

The DE 10 2009 049 719 A1 The applicant describes a plate-shaped actuator which has two electrodes on its upper side and on its underside, spaced apart by a separating area, the electrodes on the upper side being arranged offset from the electrodes on the underside.

From the DE 10 2016 110 124 A1 The applicant is aware of an ultrasonic motor which has a rectangular piezoelectric ultrasonic actuator on which two friction elements are arranged at a distance from one another, and the ultrasonic actuator is divided in the form of a plate into two pairs of diagonally opposite sections, with a part of an acoustic generator in each of the diagonal sections Standing waves are arranged, and a total of two generators are present, each consisting of two parts that can be operated in antiphase.

The US 2005 / 0 275 318 A1 discloses a stacked piezoelectric transducer in which the electrodes arranged on the respective surfaces of the individual layers have a design that differs from one another, which takes into account the different expansion behavior of the transducer along the stacking direction.

The WO 2022/176560 A1 teaches a rotary ultrasonic motor in which a shaft to be driven is operatively connected to a rotor via a spring element, the rotor being driven via a vibrator in which traveling waves are generated.

From the US 5,410,206 A or the EP 2 676 361 B1 Constructions of an inertial drive are known in which the part to be moved is a screw. This is screwed into a threaded nut and is in frictional contact with it. The threaded nut is in turn connected directly or indirectly to a piezo actuator, which sets the screw in motion based on the principle of inertia. The main disadvantage of this inertia drive is a relatively low speed of the part or screw to be moved. This is due to the inertia-based drive principle of the motor. The piezo actuator cannot drive the screw faster than a few 10 kHz, because when a certain frequency is exceeded, the static friction between the actuator and the screw changes into sliding friction, which results in a relative movement or sliding between the actuator and the screw comes without the screw being driven and simply stops.

From the DE 10 2008 023 478 A1 an ultrasonic drive with a hollow cylindrical oscillator is known, the inner cylinder surface being in effective contact with an element to be driven.

The US 4,734,610 A discloses a vibrating wave motor having a circular vibrating member having a thread and coupled to a unit that generates a traveling wave in the vibrating member, said traveling wave traveling along a circumferential direction of the vibrating member. A movable part is in effective contact with the vibration part and engages with its correspondingly designed thread in the thread of the vibration part.

The DE 44 38 876 B4 describes a piezoelectric motor with a stator on which a piezoelectric oscillator is arranged, and with a rotor, the rotor being in operative contact with the piezoelectric oscillator. The piezoelectric oscillator has three ultrasonic wave generators.

From the publication US 4,734,610 A a piezoelectric ultrasonic motor with a threaded contact or with a threaded engagement between a driving element and an element to be driven is known. In one embodiment, the driving element is designed as a thin-walled nut made of metal and the element to be driven is designed as a threaded rod, the nut and the threaded rod being in frictional engagement. Thin piezoelectric discs are glued to the end faces of the nut. The mother takes on the task of the acoustic resonator, and the piezoelectric disks form the surfaces for the exciters of the acoustic traveling wave in the thin-walled mother. The acoustic traveling wave formed in the nut and the thread or friction contact between the nut and the threaded rod results in a rotation of the threaded rod, which ultimately results in a linear movement of the threaded rod.

A disadvantage of the ultrasonic motor after the US 4,734,610 A is that in the actuator of this motor the volume of the metal nut is significantly larger than the volume of the piezoelectric exciter. A small electromechanical coupling coefficient is therefore characteristic of such an actuator. Therefore, this motor only allows low movement speeds and a small pulling force, and also requires high excitation voltages. Because of the high electrical voltages, the actuator heats up significantly due to the electrical losses in the piezoceramic. This heating leads to a reduction in the operational safety of the engine.

The publication US 6,940,209 B2 discloses a piezoelectric ultrasonic motor with a threaded contact between a driving element and an element to be driven. According to one embodiment, the driving element is a metal tube on which piezoelectric exciter plates are arranged. There is a threaded insert in the metal tube. The element to be driven is designed as a threaded rod and is in frictional engagement with the threaded insert. The metal tube represents an acoustic resonator, and the piezoelectric excitation plates arranged on it generate an elastic traveling wave in the tube, which is aligned longitudinally to the axial axis of the tube. The traveling wave is transmitted to the threaded insert, and the threaded or frictional contact between the threaded insert and the threaded rod results in a rotation of the threaded rod and thus ultimately a linear movement of the threaded rod.

Disadvantageous with the one from the US 6,940,209 B2 well-known motor is that bending vibrations are used in it. This reduces the electromechanical coupling coefficient, which reduces the speed of movement and the pulling force. At the same time, the electrical excitation voltage increases. As in the case of the previously mentioned US 4,734,610 A At high excitation voltages, the actuator heats up significantly due to the electrical losses in the piezo ceramic, which reduces the operational reliability of the motor.

Another disadvantage of the ultrasonic motors according to the publications US 4,734,610 A and US 6,940,209 B2 is the fact that their dimensions cannot be increased in order to achieve greater tensile and holding forces, which severely limits their possible area of application.

From the generic DE 10 2010 022 812 B4 is an ultrasonic motor based on the principle of electrical excitation of running ultrasonic waves in a piezoceramic actuator. The ultrasonic motor comprises at least one one-piece annular piezoelectric ultrasonic actuator with at least one generator for generating a plane acoustic traveling wave, a substantially annular contact element with an outer and inner circumferential surface and an element to be driven. The contact element is completely surrounded by the actuator on its outer peripheral surface. The contact element is provided with a thread on its inner peripheral surface and is in threaded engagement with the element to be driven which is provided with an external thread. The flat acoustic traveling wave created by electrical excitation in the actuator is transmitted to the contact element, so that the element to be driven rotates.

Disadvantageous with the drive according to the DE 10 2010 022 812 B4 is the fact that in order to counteract the torque developed by the motor during operation, the actuator is clamped on its outer peripheral surface with the help of a holding element or glued into it. This causes the actuator to be strongly damped, which means that the oscillation amplitude of the contact element becomes smaller and the torque and speed decrease. Therefore the one from the DE 10 2010 022 812 B4 Known ultrasonic motor requires a relatively high electrical voltage to operate, which causes the actuator to become warm and the efficiency of the motor decreases.

Another disadvantage of the ultrasonic motor after the DE 10 2010 022 812 B4 B4 is a low reliability of the adhesive connection of the contact element with the piezoelectric actuator with a large diameter of the contact element. The contact element is glued into the piezoelectric actuator. With a relatively large outer diameter of the contact element (from approx. 60 mm), the size of the outer circumferential surface becomes critical for an adhesive connection. When the actuator is heated during operation, mechanical stresses arise in the adhesive boundary layer between the piezoelectric material of the actuator and the metallic or ceramic contact element due to different expansion coefficients, which can cause the adhesive to fail. In such a case, the contact element can no longer transmit the movement to the element to be driven.

The object of the invention is therefore to provide an ultrasonic motor which overcomes the disadvantages of the ultrasonic motors known from the prior art and which in particular has a high level of efficiency and can therefore be operated with a comparatively low electrical voltage, so that it only moves during operation slightly or not heated at all, which ensures high operational reliability. Furthermore, it is an object of the invention to provide an ultrasonic motor that can be operated with a simply constructed and therefore more cost-effective electrical excitation device.

This task is solved by an ultrasonic motor according to claim 1, the subsequent subclaims describing at least useful developments.

The ultrasonic motor according to the invention has at least one piezoelectric ultrasonic actuator, which comprises or contains at least one generator for generating a planar acoustic traveling wave. Furthermore, the ultrasonic motor according to the invention has a drive element and an element to be driven by the drive element, the drive element having a threaded inner peripheral surface and thus an internal thread, as well as an outer peripheral surface, and the drive element being inserted into the ultrasonic actuator in this way and preferably glued into it that an inner peripheral surface of the ultrasonic actuator surrounds or surrounds the drive element on its outer peripheral surface.

The element to be driven has an external thread which is in engagement with the internal thread of the drive element and through the thread engagement the planar acoustic traveling wave generated by the generator of the ultrasonic actuator can be transferred from the ultrasonic actuator to the drive element, whereby a rotation of the element to be driven can be caused.

The actuator of the ultrasonic motor according to the invention is designed as a polygonal plate or polygonal disk, i.e. as a plate or disk whose thickness is significantly smaller than its remaining dimensions, the plate or disk having a polygonal shape. The polygonal plate or disk has two large main surfaces and at least three smaller side surfaces or peripheral surfaces connecting the two main surfaces. Due to the polygonal shape of the actuator and the resulting eigenmodes for standing waves, it is particularly possible to fasten the actuator or the polygonal plate in a holder with low losses and without strong damping.

The ultrasonic actuator or the polygonal plate has at least one active generator for generating a planar acoustic standing wave. The specific standing waves that can be generated in this way have the advantage that the maximum of their vibration amplitudes in the radial and circumferential directions is present essentially on the thread surface or in the area of the thread surface of the drive element inserted into the actuator and coupled to it, so that the drive energy of the drive element is extremely efficient can be transferred to the element to be driven which is in threaded engagement with it.

If the indefinite article is used for a feature in the text - as above and possibly also below - then when the same feature is mentioned subsequently, the use of the definite article explicitly refers to the quantity information implied by the indefinite article, without this becoming a should lead to a corresponding restriction to precisely this quantity.

It can be advantageous for the contour of the polygonal plate to have the shape of a triangle with three side or circumferential surfaces or a square or a rectangle with four side or circumferential surfaces each or a pentagon with five side or circumferential surfaces or a hexagon has six side or peripheral surfaces or an octagon with eight side or peripheral surfaces. The actuator can be held on the corresponding side surfaces with low losses. A contour of the polygonal plate with more than eight side or peripheral surfaces is also conceivable.

The provision of several outer peripheral surfaces of the drive element makes it possible to reduce the adhesive surface and thus the To increase the reliability of the adhesive connection of the drive element when the actuator heats up during operation.

It is particularly advantageous if the ultrasonic actuator or the polygonal plate only has an active generator of acoustic standing waves. This enables the use of a simple single-phase electrical excitation device for electrical excitation of the ultrasonic actuator.

It can also be advantageous for the ultrasonic actuator or the polygonal plate to have two active generators, through whose simultaneous excitation a planar acoustic standing wave can be generated in it. By influencing the phase angle and the amplitude ratio of the corresponding two excitation voltages, the trajectory of a friction contact point of the drive element can be changed and the movement properties of the part to be driven can thus be influenced.

It can also be advantageous that the planar acoustic traveling wave can be caused by superimposing two or more than two planar standing waves of the same frequency. This results in a particularly effective and reliable drive of the element to be driven.

It can also be advantageous that longitudinal standing waves can be generated in the polygonal plate along its circumference or along one of its diagonals or along a direction that runs perpendicular to the side or circumferential surfaces. In addition, it can be advantageous that a bend in the plane about the axial axis can be stimulated in the polygonal plate. Furthermore, it can be advantageous that further planar standing waves can be excited in the polygonal plate. Such standing waves have a particularly high coupling factor.

It can also be advantageous for the drive element to be a disk with a round, triangular, square, square, pentagonal, hexagonal, octagonal or an n-sided polygonal contour. As a result, in the case of an adhesive connection between the drive element and the ultrasonic actuator, the adhesive surface between these two elements is reduced, whereby mechanical stresses can be reduced and the reliability of the adhesive connection can be increased.

Furthermore, it can be advantageous for the drive element to have recesses in the form of openings or slots, whereby the openings can be round or elongated openings. In addition, it can be advantageous for the drive element to be formed from individual segments. This makes it possible to reduce the mechanical stresses on the contact surface between the drive element and the ultrasonic actuator or the polygonal plate when the ultrasonic actuator heats up or when there are large vibration amplitudes on the ultrasonic actuator, which increases the operational reliability of the motor.

It can be of particular advantage here that the recesses are filled with a sound-absorbing material, whereby parasitic vibrations of the ultrasonic actuator or the polygonal plate are effectively dampened, resulting in a more effective drive via the frictional contact between the drive element and the element to be driven.

In addition, it can be advantageous that an elastic contour element, preferably made of a metallic or a ceramic material, is arranged on the side or peripheral surfaces of the polygonal plate. The use of such an elastic element, which compresses the ultrasonic actuator, increases the strength of the ultrasonic actuator. This makes it possible to apply higher power to the actuator, which results in a higher movement speed of the element to be driven.

It can be advantageous for the element to be driven to be designed as a solid or as a hollow threaded rod with at least one longitudinal opening or at least one slot, which preferably runs in the axial direction. This reduces the start and stop times of the ultrasonic motor, as well as its amplitudes of parasitic oscillations.

In the event that the element to be driven is designed as a hollow threaded rod, it can be advantageous if the corresponding cavity in the element to be driven is filled with a sound-absorbing material. This makes it possible to reduce the parasitic vibrations that arise in the element to be driven, thereby improving the engine function.

In addition, it can be advantageous for the ultrasonic motor to have a pressing device with which the element to be driven is pressed against the drive element and which acts on the element to be driven in a direction that runs longitudinally to the vertical axis of the ultrasonic actuator. This ensures reliable operation of the ultrasonic motor.

It can be advantageous if the pressing device is designed as part of the element to be driven or is arranged in it. This leads to a simplified construction or it enables particularly compact dimensions of the ultrasonic motor.

It can also be advantageous if the ultrasonic actuator is held on its outer peripheral surfaces. This makes it possible to achieve a particularly simple and loss-free holder.

Furthermore, it can be advantageous for the ultrasonic motor to have a fastening device for the ultrasonic actuator or the polygonal plate, the fastening device comprising acoustic resonance elements with the aid of which the ultrasonic actuator can be connected to a base plate or to a motor housing. The acoustic resonance elements can reduce the mechanical losses at the fastening points.

It may prove advantageous that each of the generators of planar standing waves has a three-layer structure consisting of an excitation electrode, a common electrode and a piezoelectric material arranged between the two electrodes between them, or a multilayer or multilayer structure in which the electrode layers and the layers of piezoelectric material are arranged alternately. The multilayer or multilayer structure allows the electrical excitation voltage to be reduced.

• 1: erfindungsgemäßer Ultraschallmotor mit einem durch eine elektrische Erregervorrichtung einphasig angesteuerten Ultraschallaktor
• 2a)-e): Darstellungen zur Erläuterung des Funktionsprinzips des erfindungsgemäßen Ultraschallmotors, wobei die Darstellungen a) und b) Deformationsphasen der Polygonalplatte bzw. des Ultraschallaktors zeigen, und die Darstellungen c) bis e) Trajektorien eines Oberflächenpunktes einer Innenumfangsfläche des Ultraschallaktors bei entsprechender elektrischer Ansteuerung zeigen
• 3: erfindungsgemäßer Ultraschallmotor mit einem durch eine elektrische Erregervorrichtung zweiphasig angesteuerten Ultraschallaktor
• 4: erfindungsgemäßer Ultraschallmotor mit einem durch eine elektrische Erregervorrichtung dreiphasig angesteuerten Ultraschallaktor
• 5: mögliche Ausführungsformen der Polygonalplatte bzw. -scheibe eines erfindungsgemäßen Ultraschallmotors
• 6: Ultraschallaktor eines erfindungsgemäßen Ultraschallmotors mit einer hexagonalen Form bzw. Kontur und einem darin eingesetzten Antriebselement mit kreisförmiger Kontur
• 7 mit Darstellungen 34 bis 40: unterschiedliche Ausführungsformen des Antriebselements eines erfindungsgemäßen Ultraschallmotors
• 8: Ultraschallaktor eines erfindungsgemäßen Ultraschallmotors mit einer hexagonalen Kontur sowie einem darin eingesetzten Antriebselement mit hexagonaler Kontur und elastischen Konturelementen
• 9 mit Darstellungen 48 bis 55: mögliche Ausführungsformen des anzutreibenden Elements eines erfindungsgemäßen Ultraschallmotors
• 10, 11: Schnittdarstellungen zur Veranschaulichung möglicher Eingriffsgeometrien zwischen dem anzutreibenden Element und dem Antriebselement eines erfindungsgemäßen Ultraschallmotors
• 12: erfindungsgemäßer Ultraschallmotor mit einer von außen auf das anzutreibende Element wirkenden Anpressvorrichtung
• 13: erfindungsgemäßer Ultraschallmotor mit einer innerhalb des anzutreibenden Elements angeordneten Anpressvorrichtung
• 14, 15: erfindungsgemäße Ultraschallmotoren mit unterschiedlichen Ausführungsformen für die Halterung des Ultraschallaktors
• 16 mit Darstellungen 76 bis 78: mögliche Ausführungsformen für das Antriebselement eines erfindungsgemäßen Ultraschallmotors
• 17: Anordnung des Antriebselements gemäß Darstellung 78 von 16 in einem erfindungsgemäßen Ultraschallmotor
• 18: erfindungsgemäßer Ultraschallmotor mit mehreren Ultraschallaktoren
• 19: Darstellung zur Illustration der elektrischen Ansteuerung der Generatoren eines erfindungsgemäßen Ultraschallmotors
• 20: Ausführungsform eines Generators zur Erzeugung von Stehwellen in dem Ultraschallaktor eines erfindungsgemäßen Ultraschallmotors mit einer einzigen piezoelektrischen Schicht
• 21: Ausführungsform eines Generators zur Erzeugung von Stehwellen in dem Ultraschallaktor eines erfindungsgemäßen Ultraschallmotors mit einer mehrschichtigen Struktur
• 22 mit Darstellungen a) bis d): Simulationen der Deformationen eines Ultraschallaktors quadratischer Kontur eines erfindungsgemäßen Ultraschallmotors bei Erregung unterschiedlicher planarer akustischer Stehwellen
• 23 mit Darstellungen a) bis c): Simulationen der Deformationen eines Ultraschallaktors hexagonaler Kontur eines erfindungsgemäßen Ultraschallmotors bei Erregung unterschiedlicher planarer akustischer Stehwellen
• 24: Abbildungen zur Erläuterung des Funktionsprinzips des erfindungsgemäßen Ultraschallmotors gemäß den 3 und 4, wobei Darstellung a) einer Draufsicht, und Darstellung b) einer Seitenansicht entspricht
• 25: Elektrische Beschaltung des erfindungsgemäßen Ultraschallmotors nach 1 für eine einphasige Erregung
• 26: Elektrische Beschaltung des erfindungsgemäßen Ultraschallmotors nach 1 bzw. 3 für eine zweiphasige Erregung
• 27: Elektrische Beschaltung des erfindungsgemäßen Ultraschallmotors nach 4 für eine dreiphasige Erregung

Advantages and expediencies of the invention become clearer from the following description of preferred exemplary embodiments based on the figures. Show it:

• 1 : Ultrasonic motor according to the invention with an ultrasonic actuator controlled in a single phase by an electrical excitation device
• 2a)-e ): Representations to explain the functional principle of the ultrasonic motor according to the invention, where the representations a) and b) show deformation phases of the polygonal plate or the ultrasonic actuator, and the representations c) to e) show trajectories of a surface point of an inner circumferential surface of the ultrasonic actuator with appropriate electrical control
• 3 : Ultrasonic motor according to the invention with an ultrasonic actuator controlled in two phases by an electrical excitation device
• 4 : Ultrasonic motor according to the invention with an ultrasonic actuator controlled in three phases by an electrical excitation device
• 5 : possible embodiments of the polygonal plate or disk of an ultrasonic motor according to the invention
• 6 : Ultrasonic actuator of an ultrasonic motor according to the invention with a hexagonal shape or contour and a drive element with a circular contour inserted therein
• 7 with representations 34 to 40: different embodiments of the drive element of an ultrasonic motor according to the invention
• 8th : Ultrasonic actuator of an ultrasonic motor according to the invention with a hexagonal contour and a drive element inserted therein with a hexagonal contour and elastic contour elements
• 9 with representations 48 to 55: possible embodiments of the element to be driven of an ultrasonic motor according to the invention
• 10 , 11 : Sectional views to illustrate possible engagement geometries between the element to be driven and the drive element of an ultrasonic motor according to the invention
• 12 : Ultrasonic motor according to the invention with a pressing device acting from the outside on the element to be driven
• 13 : Ultrasonic motor according to the invention with a pressing device arranged within the element to be driven
• 14 , 15 : Ultrasonic motors according to the invention with different embodiments for holding the ultrasonic actuator
• 16 with representations 76 to 78: possible embodiments for the drive element of an ultrasonic motor according to the invention
• 17 : Arrangement of the drive element according to illustration 78 of 16 in an ultrasonic motor according to the invention
• 18 : Ultrasonic motor according to the invention with several ultrasonic actuators
• 19 : Illustration to illustrate the electrical control of the generators of an ultrasonic motor according to the invention
• 20 : Embodiment of a generator for generating standing waves in the ultrasonic actuator of an ultrasonic motor according to the invention with a single piezoelectric layer
• 21 : Embodiment of a generator for generating standing waves in the ultrasonic actuator of an ultrasonic motor according to the invention with a multi-layer structure
• 22 with representations a) to d): Simulations of the deformations of an ultrasonic actuator with a square contour of an ult according to the invention rapid sound motors when exciting different planar acoustic standing waves
• 23 with representations a) to c): Simulations of the deformations of an ultrasonic actuator with a hexagonal contour of an ultrasonic motor according to the invention when exciting different planar acoustic standing waves
• 24 : Illustrations to explain the functional principle of the ultrasonic motor according to the invention according to 3 and 4 , where representation a) corresponds to a top view, and representation b) corresponds to a side view
• 25 : Electrical circuit of the ultrasonic motor according to the invention 1 for single-phase excitation
• 26 : Electrical circuit of the ultrasonic motor according to the invention 1 or. 3 for a two-phase excitation
• 27 : Electrical circuit of the ultrasonic motor according to the invention 4 for three-phase excitation

According to 1 the ultrasonic motor according to the invention has an ultrasonic actuator 1 and an element 2 to be driven. The ultrasonic actuator 1 in the form of a rectangular disk or plate is made of a piezoelectric ceramic and corresponds to a polygonal plate or disk 4. The polygonal plate 4 has an eccentrically arranged opening or opening 5, on the inner peripheral surface of the opening or the Breakthrough 5 has a thin-walled drive element 6 compared to the diagonal dimensions of the ultrasonic actuator 1. The drive element 6 and the opening 5 have a round shape, although an n-polygonal shape is also conceivable.

The polygonal plate 4 is separated by two mutually perpendicular cutting planes P1, P2, which pass through the middle of the opposite outer peripheral or side surfaces 18. The opening 5 is arranged asymmetrically with respect to the cutting plane P1 and symmetrically with respect to the cutting plane P2. It is conceivable that the polygonal plate 4 could also be made of another piezoelectric material, e.g. B. a single-crystalline material. The inner peripheral surface 7 of the drive element 6 has a thread, not shown, with a thread height q. The element 2 to be driven is designed as a solid or solid threaded rod or threaded rod 9 with a thread 11 on its outer peripheral surface 10, the thread 11 also having a thread height q. The element 2 to be driven is screwed into the drive element 6. The thread on the inner peripheral surface 7 of the drive element 6 and the thread 11 on the outer peripheral surface 10 of the element 2 to be driven form a friction contact.

Furthermore, the polygonal plate or disk 4 of the in 1 Ultrasonic actuator 1 shown has an active generator 13 for a planar standing wave. An active generator for a planar standing wave is to be understood as meaning a generator which is actually electrically excited during operation of the actuator by means of an electrical excitation device 3 and only this active generator generates a planar acoustic standing wave.

The generator 13 is arranged asymmetrically with respect to the cutting planes P1 and P2. A planar standing wave is to be understood as meaning a wave that propagates in the plane of the polygonal plate, the oscillation amplitude of the material particles of the polygonal plate being at least one order of magnitude smaller in the axial direction than in the directions of the plate plane.

To realize a movement of the element 2 to be driven in 1 For the ultrasonic motor shown, only one active acoustic wave generator 13 is sufficient, although it can also be advantageous for two or more than two active acoustic wave generators 13 to be present.

The point 22 indicates a small area on the inner peripheral surface of the polygonal plate 4, which, when the active generator 13 is excited, has an in 2 elliptical trajectory 23 shown passes through.

To realize a reversible movement 26, 27 of the element 2 to be driven, the in 1 . Ultrasonic motor shown is equipped with two standing wave generators 13, with only one of them being the active generator 13 in operation for the respective direction of movement 26 or 27.

Each of the two generators 13 is connected with its connections 15 and 16 via a changeover switch 25 to the electrical excitation device 3, which consists of an electrical generator 17 for an electrical alternating voltage U1. The alternating electrical voltage generator 17 is intended to electrically excite the active generator 13. Changing the direction of movement 26 or 27 of the element 2 to be driven takes place by switching the electrical excitation device 3 between the two active generators 13 using the switch 25. The single-phase control of the ultrasonic actuator 1 enables a simple electronic switching of the electrical excitation device 3.

2 Figures a) and b) illustrate instantaneous deformations of the polygonal plate at π/2 and 3π/2 of its oscillation period when an active generator 13 is excited, calculated using FEM. The point 22 located on the inner peripheral surface 7 passes through an elliptical trajectory 23.

In the representations c) and d) of 2 is the polygonal plate 4 of the in 1 illustrated ultrasonic motor for realizing a reversible movement of the element 2 to be driven. The first generator 13 (see 2c )) connected to the excitation device 3. The elliptical trajectory of the point 22 runs tangentially to the opening 5 and at an angle α to the cutting plane P2. For a second direction of movement 26 or 27, the second generator 13 is connected to the excitation device 3, so that the elliptical trajectory changes its inclination mirror-symmetrically with respect to the section plane P2 ( 2d )).

2e) illustrates the polygonal plate 4 of in 1 shown ultrasonic motor, wherein the first generator 13 and the second generator 13 are active at the same time. For this purpose, both generators are supplied with two electrical voltages at the same time. The possible trajectories of point 22 are indicated by dashed ellipses. By changing the phase angle between the two control voltages and their voltage amplitudes, it is possible to change the trajectory and thus influence the movement of the element 2 to be driven.

According to the 3 and 4 is the ultrasonic actuator 1 of an ultrasonic motor according to the invention here as a square ( 3 ) or hexagonal ( 4 ) Polygonal plate 4 made of a piezoelectric ceramic, which has an opening or a breakthrough 5, with a thin-walled drive element 6 sitting on the inner peripheral surface of the polygonal plate 4 compared to the diagonal dimensions of the ultrasonic actuator 1. It is conceivable that the polygonal plate 4 could also be made of another piezoelectric material, e.g. B. a single-crystalline material. The drive element here has a round shape, although an n-polygonal shape is also possible.

The polygonal plate 4 of the ultrasonic motor according to 3 and 4 comprises at least one generator 12 for a planar traveling wave, which is formed from two or more than two active generators 13 for planar standing waves. The in 3 The ultrasonic motor shown contains two active generators 13. They are spatially arranged offset from each other by 90 °. The generators 13 are part of the polygonal plate 4 or are designed integrally with it, so that no acoustic boundary is formed between them, ie the acoustic waves pass freely and without reflection at the geometric boundary from one generator 13 into an adjacent generator 13.

Each of the generators 13 is connected with its connections 15 and 16 to the electrical excitation device 3, which consists of two or more than two electrical generators 17 for alternating electrical voltages U1...Un. The generators 17 are intended for electrically exciting the generators 13 of the planar standing waves. In 1 For reasons of clarity, only two generators 17 for the electrical alternating voltages U1 and U2 are shown, with two-phase control of the generators 13 and the generator 12 for a traveling wave. The generators are rotated relative to each other about the vertical axis 14 of the ultrasonic actuator 1 in such a way that the planar standing waves generated by them are shifted by λ/4, ie by 90°, relative to one another. For this purpose, the two generators 17 of the electrical excitation device 3 each provide an electrical alternating voltage, the frequency of which essentially corresponds to the resonance frequency of the plane acoustic standing waves generated, the phase of each voltage being shifted by plus 90° or minus 90° relative to one another, and the amplitudes of the electrical voltages are equal. The two-phase control of the generator 12 or the generators 13 enables a relatively simple electronic circuit of the electrical excitation device 3.

The in 4 Ultrasonic motor shown is different from the one in 3 Ultrasonic motor shown in that here the polygonal plate 4 has a hexagonal contour and a three-phase control of the generators 13 or the generator 12 takes place to generate a traveling wave. For reasons of clarity, 4 only three generators 13 are shown. The generators are rotated relative to each other about the vertical axis 14 of the ultrasonic actuator 1 in such a way that the plane standing waves generated by them are shifted relative to one another by λ/3, ie by 120°. For this purpose, the three generators 17 of the electrical excitation device 3 each provide an electrical alternating voltage, the frequency of which essentially corresponds to the resonance frequency of the plane acoustic standing waves generated, the phase of each voltage being shifted by 120° relative to one another and the amplitude of the electrical voltages being the same. The contour of the polygonal plate 4 in 2 and 3 Ultrasonic motors according to the invention shown can also be a triangle, a pentagon or an n-polygon.

5 shows 28 to 33 different embodiments of the polygonal plate 4 of an ultrasonic motor according to the invention. The polygonal plate has two large main surfaces 19 and at least three outer peripheral or side surface surfaces 18. The polygonal plate can be triangular (see illustration 28), square (see illustration 29), rectangular (see illustration 30), pentagonal (see illustration 31), hexagonal (see illustration 32) or octagonal (see illustration 33). or have a different type of n-sided polygonal contour. In the 5 The pointed corners of the polygonal plate shown can be separated or rounded.

6 shows the ultrasonic actuator 1 in the form of a hexagonal or hexagonal polygonal plate 4 of the ultrasonic motor according to 4 . The drive element 6 is inserted into this with a round contour. P denotes the diameter of the circle C connecting all vertices of the polygonal plate, while S denotes the circumference of the circle C. The thickness of the ultrasonic actuator 1 or the polygonal plate 4 between the main surfaces 19 is h. H denotes the radial distance between the inner circumferential surface 7 of the drive element 6 and the circle C. Furthermore, D denotes the diameter based on the inner circumferential surface 7 of the drive element 6 and L the circumference based on the inner circumferential surface 7 of the drive element 6. The sizes D and L refer each to the corresponding dimension that is at half the thread height q (see 10 and 11 ) is available. The wall thickness of the drive element 6, ie the thickness in the radial direction, is t.

It can be advantageous to design the ultrasonic actuator 1 or the polygonal plate 4 in such a way that L is equal to or approximately equal to 2 H, where the ratio D to H is equal to µ 0.63 or µ 1.27; µ*1.91; µ*2.54; µ*3.18; µ*3.82; µ 4.45 etc. (generally µ (0.63 + n 0.64) with n = natural number). In this case, μ is a coefficient that lies between 0.8 and 1.5 and which depends on the ratio of the modulus of elasticity of the piezoelectric material of the ultrasonic actuator 1 to the modulus of elasticity of the material of the drive element 6. The thickness h of the ultrasonic actuator 1 is chosen so that it is smaller than H/3. The wall thickness t of the drive element 6 is smaller than H/8. It is particularly advantageous if S is a multiple of H.

The thin-walled drive element 6 is made of a hard, abrasion-resistant material whose hardness and abrasion resistance exceeds the hardness and abrasion resistance of the piezoelectric material of the ultrasonic actuator. Examples of such materials are heat-treated steel, oxide ceramics based on alumina, zirconium oxide, sialon, silicon nitride, metal ceramics based on tungsten carbide and titanium carbide. The thin-walled drive element 6 is directly bonded to the ultrasonic actuator using an organic adhesive (e.g. epoxy resin). The adhesive can contain solid non-organic components such as: B. contain oxide ceramic particles, metal particles or metal ceramic particles. It is also conceivable to realize the drive element 6 with the polygonal plate 4 by a connection that forms during the sintering of the polygonal plate 4. During the sintering process of the piezoelectric material, strong chemical bonds can build up with the material of the drive element 6, which lead to a very strong connection between the ultrasonic actuator 1 or polygonal plate 4 and the drive element 6.

The drive element 6 can be indirectly connected to the ultrasonic actuator via an intermediate element (not in 6 shown). This intermediate element preferably has a thickness k, where k is less than 0.1 H. It is advantageous if the intermediate element consists of a material whose modulus of elasticity and coefficient of thermal expansion correspond approximately to the modulus of elasticity and the coefficient of thermal expansion of the piezoelectric material of the ultrasonic actuator. An example of such a material is a special oxide or metal ceramic. The intermediate element can be connected to the polygonal plate 4 of the ultrasonic actuator 1 by a cohesive connection, realized via a slightly melting glass. It is also conceivable to realize a connection between the intermediate element and the polygonal plate 4 of the ultrasonic actuator 1 by a connection that forms during the sintering of the polygonal plate 4. During the sintering process of the piezoelectric material, strong chemical bonds can build up with the material of the intermediate element, which lead to a very strong connection between the ultrasonic actuator and the intermediate element.

7 shows different embodiments for the drive element 6 in illustrations 34 to 40. The drive element 6 is designed as a ring or hollow cylinder with circular outer and inner circumferential surfaces according to illustration 34, while according to illustration 35 it has an outer contour with eight surfaces 41 that can be distinguished from one another, a hexagonal contour or shape. Through such a multi-surface design of the outer circumference of the drive element, mechanical stresses can be reduced when the drive element is adhesively connected to the polygonal plate, which increases the reliability of this adhesive connection, particularly with large diameters. In representations 36 to 38 of 7 the drive element has a round shape Openings or recesses or openings 42 (illustration 36) or elongated openings or openings 43, 44 (illustrations 37 and 38). In addition, the drive element 6 can also have slots 45, which are shown in FIG. 39 of 7 are not continuous. According to representation 40 of 7 The slots can also be continuous, so that the drive element 6 consists of individual ring or hollow cylinder segments. It is conceivable that the openings or openings 42, 43, 44 or the slots 45 are filled with a sound-absorbing material.

8th shows an ultrasonic actuator of an ultrasonic motor according to the invention in the form of a polygonal plate 4 having six outer peripheral or side surfaces 18 according to illustration 32 of 5 or according to 6 , in which a drive element 6 having eight outer peripheral surfaces, ie a hexagonal shape according to illustration 35 of 7 is used. On its outer circumferential or side surfaces 18, the polygonal plate 4 is provided with an elastic contour element 47, which tensions or biases the polygonal plate 4 in the radial direction. The elastic contour element 47 has a thickness d that is less than 0.1 H (see 6 ) and is made of steel. The elastic contour element 47 can also be made of oxide ceramic, aluminum oxide or another hard ceramic. It is pressed onto the outer peripheral or side surfaces 18 of the polygonal plate 4. In addition, it is also conceivable to shrink the elastic contour element 47 onto the outer circumferential surfaces 18 of the polygonal plate or to stick it onto them using an organic adhesive (e.g. epoxy resin).

9 shows in the representations 48 to 55 different embodiments for a driven element 2 of an ultrasonic motor according to the invention. According to representation 48 of 9 The element to be driven is designed as a fully threaded rod made of a hard and abrasion-resistant material (e.g. heat-treated steel, oxide or metal ceramic). In addition, as shown, it is the 49-52 and 55 of 9 possible to design the element to be driven as a hollow threaded rod, with the corresponding inner opening or cavity 57 having a round shape. However, other geometries of the inner opening are also conceivable (e.g. a polygonal shape). According to illustration 50 of 9 a rod 58 made of a sound-absorbing material can be used. This rod 58 is made of an elastic material such as. B. Rubber. The elastic material can be filled with hard particles such as B. be filled with metal particles. In addition, it is also conceivable that the rod 58 is made of a viscoelastic material, e.g. B. a thermoplastic material, the viscoelastic material containing particles, e.g. B. can be filled with metal and / or rubber particles. Furthermore, the rod 58 can also be made of a hard porous material, such as. B. made of porous oxide ceramic, the pores of which are filled with a viscous material. A variety of other materials or material mixtures with a high sound absorption factor for the rod 58 are conceivable. The rod 58 can, for example, also be made of a hard material such as steel, oxide ceramic, metal ceramic, with a layer of sound-absorbing material (e.g. rubber, epoxy resin or similar) being arranged between the rod 58 and the element 2 to be driven.

According to illustration 51 of 9 the rod 58, like the element 2 to be driven, is designed as a hollow rod, and the rod 58 has an axially arranged opening 60 in which there is a further sound-absorbing rod 61, with a layer 59 between the rod 58 and the sound-absorbing rod 61 sound-absorbing material is arranged. According to representations 52 and 55 of the 9 The element to be driven, which is designed as a hollow threaded rod, can have 2 longitudinal openings 62 or longitudinal slots 63. According to representations 53 and 54 of 9 The element 2 to be driven, which is designed as a fully threaded rod, can have one or more longitudinal slots 63.

10 shows a possible thread engagement between a drive element 6 and an element 2 to be driven of an ultrasonic motor according to the invention. Here, the thread 8 provided on the drive element 6 and the thread 11 provided on the element 2 to be driven have an isosceles triangular shape. The thread pitch can be 0.1mm to a few mm per thread, while the thread height is q.

This shows differently 11 a further possible thread engagement between a drive element 6 and an element 2 to be driven of an ultrasonic motor according to the invention. Both threads 8, 11 have a non-isosceles triangular shape. In principle, by choosing a suitable thread shape, it is possible to increase the force developed by the ultrasonic motor. To increase strength and abrasion resistance, the surface of the threads 8 and 11 can be provided with a solid, abrasion-resistant material layer. For example, layers made of CrN, CrCN, (Cr, W)N, (Cr, Al)N, NbN-CrN, TiN, TiCN, (Ti, Al)N or V2O5 are suitable for this.

After 12 is the element 2 to be driven of an ultrasonic motor according to the invention with the aid of a pressing device 64, comprising a Leaf spring 65, pressed against the drive element 6. In a manner not shown, the element 2 to be driven can also be pressed against the drive element 6 with the aid of a helical spring, which acts on the element 2 to be driven along the vertical axis 14 of the ultrasonic actuator or the polygonal plate 1. At the in 12 In the construction shown, the ultrasonic actuator 1 or the polygonal plate 4 is supported and held by an elastic ring 66 located on a motor housing 67. Here, the elastic ring 66 supports the ultrasonic actuator 1 at the points of minimum vibration speeds of the large main surfaces 19, whereby the mechanical losses in the elastic ring 66 are reduced. The elastic ring 66 is made of rubber, but can also be made of polyurethane or Teflon.

13 shows a further embodiment for an ultrasonic motor according to the invention. Here, the element 2 to be driven is slotted and has correspondingly elastically deflectable legs 69. A shaped spring 68 is arranged in the cavity 57 of the element 2 to be driven, which acts on the legs 69 of the element 2 to be driven and thus presses it against the drive element 6. At the in 13 In the construction shown, the ultrasonic actuator 1 or the polygonal plate 4 is held by means of the two annular supports 70, which support it in the points of minimum vibration speeds of the large main surfaces 19, which results in a reduction in the mechanical losses in the supports 70. The supports 70 are made of a hard and heat-resistant rubber. They can also be made of Teflon or another heat-resistant polymer material.

14 illustrates another possible embodiment of an ultrasonic motor according to the invention, which here has a hexagonal ultrasonic actuator 1 or polygonal plate 4 and in which a housing 67 consists of two parts 71.

After 15 The ultrasonic motor according to the invention shown there has an ultrasonic actuator 1 or a polygonal plate 4 with a hexagonal contour, which is held on its outer peripheral or side surfaces 18 via a holder 72. For this purpose, the holder 72 has a thin hexagonal holding element 73 into which the ultrasonic actuator 1 is pressed or glued. To reduce mechanical losses, the holder 72 has projections or acoustic resonance elements 74, with the help of which the holding element 73 is connected to a base plate 75. By attaching the ultrasonic actuator 1 or the polygonal plate to its outer peripheral surfaces 18 with the aid of the holding element 73 with the resonance elements 74, the mechanical rigidity of the ultrasonic motor increases.

According to representations 76 and 77 of 16 the drive element 6 has projections or acoustic resonance elements 74. According to representation 78 of 16 the projections or resonance elements 74 of the drive element 6 are connected to the base plate 75. Fastening the ultrasonic actuator 1 via the drive element 6 with the help of the projections 74 also increases the rigidity of the ultrasonic motor significantly. The design of the projections 74 as acoustic resonance elements, in which one of the overtones coincides with the resonance frequency f0, leads to a reduction in mechanical losses.

17 shows an exploded view of an ultrasonic motor according to the invention, in which a square ultrasonic actuator 1 with a drive element 6 according to illustration 78 of 16 is combined, the drive element 6 having projections or resonance elements 74, which in turn are connected to the base plate 75.

According to 18 The ultrasonic motor according to the invention shown there has several ultrasonic actuators 1 or polygonal plates 4. The four ultrasonic actuators 1 or polygonal plates 4 are connected to one another via the resonance elements 74, each of the resonance elements 74 in turn being connected to the drive element 6. It is conceivable, instead of the four ultrasonic actuators 1 shown here, to use only two or three, or even more than four ultrasonic actuators 1 or polygonal plates 4 for the ultrasonic motor according to the invention.

19 shows a schematic top view of an ultrasonic actuator 1 or a polygonal plate 4 of an ultrasonic motor according to the invention with an n-polygonal contour for the arrangement of the generators 12 for the planar traveling wave and the active standing wave generators 13 for a planar standing wave. Here, the generators 12 - relative to the vertical axis 14 - are shifted relative to one another by the wavelength λ, ie by the angle 2π. To generate a traveling wave in each of the generators 12 with the aid of two standing waves, the standing wave generators 13 must be shifted relative to one another - based on the vertical axis 14 of the ultrasonic actuator 1 - by the angle λ/4 or π/2. To generate a traveling wave with a number of standing wave generators n≥3, the standing wave generators 13 in each of the generators 12 must be shifted relative to one another - based on the vertical axis 14 of the ultrasonic actuator 1 - by the angle λ/n or 2π/n. In this case, the traveling and standing waves they generate are also shifted from one another by the angle λ/n or 2π/n.

In each generator for a planar traveling wave or in each traveling wave generator 12, the active generators for a planar standing wave or the standing wave generators 13 of one and the same standing wave can be in phase or out of phase with one another. Those from the in 19 Electrical alternating voltages U1 to Un generated by generators 17, not shown, which are applied to the traveling wave generators 12 or the active standing wave generators 13, represent periodic voltages of one and the same frequency and can have a sine, a triangular, a trapezoidal shape or any other shape own. It is advantageous if the amplitudes of these voltages are the same. The phases of these voltages U1 to Un are preferably around the angle +/-90° (π/2) or around the angle +/-120° (2π/3)) or another angle 2π/n, which results from the number n is determined, which indicates the number of active standing wave generators 13 of which each traveling wave generator 12 consists, shifted from one another.

20 shows a possible embodiment of a generator 13 for a planar standing wave or a standing wave generator 13. This has a three-layer structure which consists of an excitation electrode 79, a general electrode 80 and a polarized piezoelectric ceramic layer 81 between them. In the 20 Arrows shown indicate the polarization direction of the piezoceramic layer 81.

According to 21 The generator 13 has a multilayer structure with alternately arranged layers of the excitation electrode 79, the general electrode 80 and the piezoceramic 81 between them. The arrows in 21 indicate the polarization direction of the piezoceramic layers 81, whereby the polarization directions of adjacent generators 13 can be directed in the same direction or differently. With a multilayer structure of the generator 13 or the generators 13, the voltage supply to the ultrasonic motor according to the invention can take place with a lower voltage.

22 Using illustrations a) to d), illustrates the formation of different waves in a polygonal plate of an ultrasonic motor according to the invention that is excited with the help of an active generator. Illustrations a) to d) show the maximum deformations of the polygonal plate calculated using FEM with the corresponding wave formation. A standing bending wave of the polygonal plate can be in its plane ( 20a) ), a longitudinal standing wave in the direction of the perimeter of the polygonal plate ( 20b) ), a longitudinal wave in the direction of the diagonal of the polygonal plate ( 20c )) or a longitudinal wave in the direction perpendicular to the side surfaces of the polygonal plate ( 20d )) be encouraged. The excitation of other planar modes is possible, as is the excitation of the above-mentioned standing waves of a higher order.

23 illustrates possible standing waves or the resulting maximum deformations in the polygonal plate 4 of the in. using appropriate FEM calculations 4 Ultrasonic motor shown, excited with the help of an active generator 13. A standing bending wave of the polygonal plate can be in its plane ( 21 a) ), a longitudinal standing wave in the direction of the perimeter of the polygonal plate ( 21 b) ), a longitudinal wave in the direction of the diagonal of the polygonal plate ( 21c) ), or a longitudinal wave in the direction perpendicular to side surfaces of the polygonal plate ( 21d) ) or encouraged. The excitation of other planar modes as well as the excitation of the above-mentioned standing waves of a higher order are also possible.

24 serves to explain the drive principle in the 3 and 4 Ultrasonic motors according to the invention shown. Here, in illustration a), the polygonal plate 4, into which the drive element 6 is inserted and connected to it, and the element 2 to be driven, which is in threaded engagement with the drive element 6, is shown in plan view. The points 82 lie on the inner peripheral surface 7 or the thread 8 of the drive element 6. When a traveling wave propagating in the direction of the arrow 83 is excited (rotating) in the ultrasonic actuator 1 or in the polygonal plate 4, the points 82 move on the closed round ones Movement trajectories 84. The movement trajectories 84 can also be elliptical, for example. The arrow 85 illustrates the direction of movement of the material points. The frictional contact between the drive element 6 and the element 2 to be driven, ie the thread contact or thread engagement, causes the element 2 to be driven to rotate in the direction indicated by arrow 26. The representation b) is the corresponding side view to the representation a) of 24 . The arrow 27 indicates the direction of the longitudinal movement of the element 2 to be driven, which results from the rotation of the same.

25 illustrates a possible electrical connection of the ultrasonic actuator 1 or the polygonal plate 4 of the ultrasonic motor according to the invention 3 with an electrical excitation device 3. Here, an electrical alternating voltage U1 from the generator 17 is passed to either the first or the second active standing wave generator 13 to excite the polygonal plate 4 or to generate a movement of the element 2 to be driven via the changeover switch 25. The frequency of the generator 17 corresponds to Frequency of the longitudinal standing wave to be excited in the polygonal plate 4 in the direction of its diagonal. The change in the direction of movement of the element 2 to be driven takes place by actuating the switch 25.

26 illustrates a further possible electrical connection of the ultrasonic actuator in the form of a polygonal plate 4 of the ultrasonic motor according to the invention 3 with an electrical excitation device 3. Here, two electrical alternating voltages U1, U2 from the generator 17 are simultaneously applied to excite the polygonal plate 4 or to generate a movement of the element 2 to be driven via the changeover switch 25 to the first and the second active generator for a standing wave 13 directed. The frequencies of the generators 17 are equal to the frequency of the longitudinal standing wave to be excited in the polygonal plate 4 in the direction of its diagonal. The phase shift between the voltages U1, U2 and their amplitudes can take on any values. The change in the direction of movement of the element 2 to be driven takes place by actuating the switch 25. It is also possible to reverse the direction of movement by changing the phase shift between the voltages U1, U2 by ±90°.

It is also possible in 3 illustrated ultrasonic motor according to the invention with the electrical excitation device 3 with the help of the in 26 to connect the circuit shown, whereby for the generation of a running wave the phase shift between the voltages U1, U2 is 90 ° (π / 2) and where their amplitudes are the same.

27 illustrates a possible electrical connection of the ultrasonic actuator in the form of a polygonal plate 4 of the ultrasonic motor according to the invention 4 with three generators for standing waves 13 with an electrical excitation device 3. Here, three electrical alternating voltages U1, U2, U3 from the generator 17 are simultaneously applied to the three active ones to excite the polygonal plate 4 or to generate a movement of the element 2 to be driven via the changeover switch 25 Standing wave generators 13 guided. The frequencies of the generators 17 are equal to the frequency of the planar standing waves to be excited in the polygonal plate 4, shown in 23 . The phase shift between the voltages U1, U2 to generate a traveling wave is 120° (2π/3) and their amplitudes are the same. The change in the direction of movement of the element 2 to be driven takes place by actuating the switch 25. It is also possible to reverse the direction of movement by changing the phase shift between the voltages U1, U2 by ±120°.

The creation of standing waves or eigenmodes in various geometric bodies is defined by boundary conditions. Features such as angles, surfaces, openings, etc. represent the most important boundary conditions for the appearance (i.e. the eigenshape) of the standing waves (i.e. the modes) that occur in a geometric body. Therefore, the eigenmodes belonging to a geometric body are specific and characteristic of it. Planar eigenmodes of plates or disks represent a subset of standing waves in which the oscillation of the material points of the body occurs mainly in the plane of the plate. The oscillation amplitudes in a direction perpendicular to the large plate sides are at least an order of magnitude smaller than in the other two directions perpendicular to them and do not arise directly due to the wave process, but are caused by transverse contractions as a side effect of the waves propagating within the plane of the plate. Planar eigenmodes have a high coupling factor. Their piezoelectric excitation is very efficient, i.e. a high proportion of the electrical energy is converted into the mechanical energy of the vibrations.

In the embodiment of the ultrasonic motor according to the invention according to 1 The piezoelectric ultrasonic actuator 1, designed as a polygonal plate 4, has two generators 13 for generating standing waves. The electrical excitation device 3 generates an alternating electrical voltage with a sine, triangular, rectangular or any other shape, the main harmonic of which corresponds to the resonance frequency or close to the resonance frequency of the first or second mode of the acoustic longitudinal standing wave, which is longitudinal to the diagonal 24 of the polygonal plate 4 spreads, lies. When connecting the excitation electrodes 20 and the reference electrode 21 of a generator 13 to the electrical excitation device 3 (see 1 and 26 ) an acoustic longitudinal standing wave is generated in the polygonal plate 4, which propagates along its diagonal 20. The ultrasonic actuator 1 or the polygonal plate 4 begins in the 2a) and 2 B) to swing in the form shown. The point 22 lying below the intersection of the diagonals 24 on the inner peripheral surface of the polygonal plate 4 moves on an elliptical movement path 22 inclined at an angle α to the plane P2 (see the 2c ) and 2d)). Since the drive element 6 is thin-walled and is acoustically rigidly connected to the polygonal plate 4, the nearby points of the thread surface also move along a tangential elliptical Train. Because of the eccentric arrangement of the opening 5, this movement of the drive element 6 creates a friction force which gives the element 2 to be driven a torque.

An active standing wave generator 13 is sufficient to generate the movement of the element 2 to be driven. To realize a reversible movement of the element 2 to be driven, the in 1 Ultrasonic motor shown has two generators 13 of acoustic standing waves, with only one of them being the active generator during operation for the respective direction of movement.

Each generator 13 is connected with its connections 15 and 16 via the changeover switch 25 to the electrical excitation device 3, which includes an electrical generator 17 for the electrical alternating voltage U1. The generator 17 is intended to electrically excite the active generator 13. The change in the direction of movement of the element 2 to be driven takes place by switching the electrical excitation on the part of the generator 17 between the two active generators 13 using the switch 25. By operating the changeover switch 25, it is possible to apply the electrical voltage provided by the electrical excitation device 3 from the generator 17 to the first or second generator 13 and vice versa. By switching, the angle of inclination α of the movement path 23 of the drive element 6 is reversed. This leads to a reversal of direction 26, 27 of the element 2 to be driven. Single-phase control of the ultrasonic actuator 1 enables a particularly simple electronic circuit of the electrical excitation device 3.

However, it can also be advantageous to excite the ultrasonic motor according to the invention by means of a two-phase excitation device with any phase shift and different amplitudes, as is somewhat the case in 27 is shown. Both standing wave generators 13 are active at the same time. The direction of movement of the element 2 to be driven is reversed by exchanging the excitation between the two active generators 13 using the switch 25. Furthermore, it is possible to influence the elliptical trajectory 23 of the contact point 22 in the frictional contact by changing the phase angle and the amplitudes of the electrical voltages U1, U2 and thus change the speed and torque of the ultrasonic motor. This two-phase excitation makes it possible to significantly increase the linearity of the movement speed of the element to be driven at low speeds of less than 1 micrometer/s.

The ones in the 3 and 4 The advantageous embodiments shown for an ultrasonic motor according to the invention work as follows: an electrical voltage U1, U2, ..., Un is applied to each of the generators 13 of the planar standing wave by the generator 17. This voltage excites the corresponding generator 13, which in turn generates a planar standing wave of the corresponding order in the polygonal plate 4, in which the maximum of the oscillation amplitude of the polygonal plate 4 is located in the radial direction on the threaded surface 7 of the drive element 6 or adjacent to the threaded surface 7. The representations a) to d) of the 22 and 23 show the deformation images of the polygonal plate 4 when such a wave is generated in this embodiment variant of the ultrasonic motor. The shape of the deformation of the standing wave used is determined by the boundary conditions of the polygonal plate 4, ie by its outer surfaces, angles and its inner opening 5. The wave generated represents a planar standing wave in which the oscillation amplitude of the polygonal plate 4 in the axial direction is more than an order of magnitude smaller than the oscillation amplitude in the directions perpendicular to it, ie in the directions parallel to the large main sides. The vibrations of the material points mainly take place in the plane of the polygonal plate 4. When all generators 13, of which the generator 12 or the generators 12 consist or consist, are excited at the same time, a plane traveling wave propagates in the polygonal plate 4.

In practice, this means that the deformation patterns of the polygonal plate 1 (see illustrations a) to d) vary depending on the sign of the phase shift between the standing waves 22 and 23 ) begin to rotate clockwise or counterclockwise.

When a planar traveling wave propagates in the direction indicated by arrow 83 24 In the specified direction within the polygonal plate 4, the points 82 of the thread surface 7 of the thread 8 move on circular or elliptical movement paths 84 in the direction indicated by arrow 85. Since the excited wave represents a planar wave, all points 82 lying on top of one another (in the axial direction) along the inner circumferential surface 7 of the drive element 6 have the same diameter of the movement paths 84.

Since the thread surface 7 of the drive element 6 is in contact with the thread surface 10 of the threaded rod 9 and these surfaces are pressed together, the circular movement of the points 82 leads to a rotation in the direction indicated by arrow 86 of the element 2 to be driven in the form of the threaded rod 9.

The peculiarity of the movement paths 84 of the points 82 significantly increases the efficiency of the frictional contact, since the maximum force with which the polygonal plate acts on the element 2 to be driven is determined by the maximum frictional force at rest between the surfaces 7 and 10. The rotation of the element 2 to be driven in the drive element 6 in the direction indicated by arrow 26 leads to the direction indicated by arrow 27 in 24 specified axial direction, ie to a longitudinal displacement or longitudinal movement.

The change in the direction of propagation of the traveling wave leads to a change in the direction of rotation of the element 2 to be driven and to a change in the axial direction, i.e. the longitudinal displacement.

Since the drive element 6 is thin-walled, i.e. its thickness t is significantly smaller than the width of the polygonal plate 4 in the radial direction, the vibration of the ultrasonic actuator 1 is only slightly disturbed or changed by the drive element connected to it. Therefore, the electromechanical coupling coefficient of the Ultrasonic actuator is determined by the electromechanical coupling coefficient of the polygonal plate 4. This means that the electromechanical coupling coefficient of the ultrasonic actuator 1 is maximized in the ultrasonic motor according to the invention. This significantly increases its oscillation speed and thus the maximum possible load on the ultrasonic actuator 1, which also results in an increased holding force of the ultrasonic motor according to the invention.

Reference symbol list

1

Ultrasonic actuator

2

element to be driven

3

electrical excitation device

4

Polygonal plate

5

Breakthrough or opening (of the polygonal plate 4)

6

Drive element

7

Inner peripheral surface (of the drive member 6)

8th

Thread (the inner peripheral surface 7)

9

Threaded rod

10

Outer peripheral surface (of the threaded rod 9)

11

Thread (the threaded rod 9)

12

Generator (a planar traveling acoustic wave)

13

active generator (a planar acoustic standing wave)

14

Vertical axis (of the polygonal plate 4)

15, 16

Connection (of the generator 13)

17

Generator of an electrical alternating voltage

18

Side surface (of the polygonal plate 4)

19

Main surface (of the polygonal plate 4)

20

Excitation electrode (of the generator 13)

21

general or reference electrode

22

Point (on the inner peripheral surface of the polygonal plate 4)

23

elliptical trajectory (of point 22)

24

Diagonal (of polygonal plate 4)

25

electrical switch (for the direction of movement of the element 2 to be driven)

26

Direction of rotation (of the element 2 to be driven)

27

Feed direction (of the element 2 to be driven)

41

Circumferential surface (of the drive element 6)

42-44

Openings or breakthroughs (of the drive element 6)

45

Slot (of the drive element 6)

46

Segment (of the drive element 6)

47

elastic contour element

57

Cavity (of the element 2 to be driven)

58, 61

sound-absorbing rod

59

Layer of sound-absorbing material

60

Fixing opening (of the sound-absorbing rod 61)

62

Longitudinal opening (of the element 2 to be driven)

63

Slot (of the element to be driven 2)

64

Pressing device

65

leaf spring

66

elastic ring

67

Motor housing

68

Form spring

69

elastically deflectable leg (of the element 2 to be driven)

70

support

71

Part (of the motor housing 67)

72

holder

73

Holding element (of the holder 72)

74

Resonance element

75

base plate

79

Excitation electrode (of the generator 13)

80

common electrode (of generator 13)

81

piezoceramic layer

82

Point (on the inner peripheral surface 7)

83

Arrow (to indicate the direction of propagation of the plane traveling wave)

84

Trajectory (of point 82)

85

Arrow (to indicate the direction of movement of point 82 on trajectory 84)

86

Arrow (to indicate the direction of rotation of the element to be driven 2)

87

Arrow (to mark the longitudinal direction of the element to be driven 2)

Claims (20)

Ultrasonic motor, comprising at least one piezoelectric ultrasonic actuator (1) with at least one generator (12) for generating a planar acoustic traveling wave, an element (2) to be driven with an external thread (11) and a drive element (6) with a thread (8) provided inner circumferential surface (7) and an outer circumferential surface, the drive element being inserted into the ultrasonic actuator (1), so that it surrounds the drive element (6) via an inner circumferential surface on its outer circumferential surface, the element to be driven (2) and the drive element (6 ) are in threaded engagement and the planar acoustic traveling wave can be transferred from the ultrasonic actuator (1) to the drive element (6), so that a rotation of the element (2) to be driven can be caused, and the ultrasonic actuator (1) has at least one active generator (13) for generating a planar acoustic standing wave, the maximum oscillation speed of which is present in the area of the inner peripheral surface of the ultrasonic actuator (1), characterized in that the ultrasonic actuator (1) has the shape of a polygonal plate (4) with two large main surfaces (19) and at least three has smaller side surfaces (18) connecting the two main surfaces (19). ultrasonic motor Claim 1 , characterized in that the contour of the polygonal plate (4) has the shape of a triangle or a square or a rectangle or a pentagon or a hexagon or an octagon. ultrasonic motor Claim 1 or 2 , characterized in that the planar acoustic standing wave can be generated by simultaneously controlling two active generators (13) of the ultrasonic actuator. Ultrasonic motor according to one of the preceding claims, characterized in that the planar acoustic traveling wave can be generated by superimposing at least two planar acoustic standing waves of the same frequency. Ultrasonic motor according to one of the preceding claims, characterized in that longitudinal standing waves can be excited in the polygonal plate (4) along its circumference or along one of its diagonals or along a direction perpendicular to one of its side surfaces. Ultrasonic motor according to one of the preceding claims, characterized in that the polygonal plate (4) can be excited by longitudinal standing waves in such a way that a bend in the plane of the polygonal plate about the axial axis results. Ultrasonic motor according to one of the preceding claims, characterized in that the drive element (6) has the shape of a ring or has a ring-like shape, the contour of which corresponds to an n-sided polygon with n>2, where n corresponds to a natural number. Ultrasonic motor according to one of the preceding claims, characterized in that the drive element (6) has recesses in the form of openings (36, 37, 38) or slots (39). ultrasonic motor Claim 8 , characterized in that the recesses are filled with a sound-absorbing material. Ultrasonic motor according to one of the preceding claims, characterized in that the drive element (6) is formed from individual segments (40). Ultrasonic motor according to one of the preceding claims, characterized in that an elastic contour element is arranged on the side surfaces (18) of the polygonal plate (4). Ultrasonic motor according to one of the preceding claims, characterized in that the element (2) to be driven is designed as a threaded rod which has at least one longitudinal opening (62) or at least one slot (63). ultrasonic motor Claim 12 , characterized in that the at least one longitudinal opening (62) or the at least one slot (63) runs parallel to the longitudinal axis of the threaded rod. ultrasonic motor Claim 12 , characterized in that the threaded rod is hollow and the corresponding cavity (57) is filled with a sound-absorbing material. Ultrasonic motor according to one of the preceding claims, characterized in that it has a pressing device (64) with which the element (2) to be driven is pressed against the drive element (6) and which acts on the element to be driven (2) in a direction which runs along a vertical axis of the polygonal plate (4). ultrasonic motor Claim 15 , characterized in that the pressing device (64) is part of the element (2) to be driven or is arranged on it. Ultrasonic motor according to one of the preceding claims, characterized in that the polygonal plate (4) is designed to be held via its side surfaces (18). Ultrasonic motor according to one of the preceding claims, characterized in that the element (6) to be driven has at least one acoustic resonance element (74) which serves to hold the polygonal plate (4). Ultrasonic motor according to one of the Claims 1 until 17 , characterized in that it has a holder (72) with a holding element (73) for the polygonal plate (4), the holder (72) having at least one acoustic resonance element (74) through which the polygonal plate (4) is connected to a base plate (75) or is connected to a motor housing (67). Ultrasonic motor according to one of the preceding claims, characterized in that the at least one active generator for generating a planar acoustic standing wave (13) is either a three-layer structure with an excitation electrode (79), a common electrode (80) and one arranged between the excitation electrode and the common electrode piezoelectric material, or has a multilayer structure in which layers of excitation electrodes, general electrodes and layers of piezoelectric material arranged between them are arranged alternately.

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