Piezoelectric inertia drive

Abstract

The invention relates to a piezoelectric inertia drive (1) comprising: a drive device (2) having a drive element (5) which comprises contact elements (9, 10) having an inner peripheral surface (4) that has a thread (3); an element (6) to be driven having an outer peripheral surface (8) provided with a thread (7); and an electric excitation device (16) for electrically controlling the drive device (2), wherein the element (6) to be driven is in threaded engagement with the drive elements (5). The contact elements (9, 10) are positioned symmetrically with respect to a virtual diametrical separating plane (P) and engage around at least part of the element (6) to be driven, wherein the contact elements (9, 10) are directly or indirectly connected to a base element (14) and to one another, and the drive device (2) has at least two multilayer piezoelectric actuators (11) which have a virtual actuator longitudinal axis (19) and which are positioned with a first side (12) on the base element (14) and with another side (13) that is opposite the first side (12) on the contact element (9, 10), and the electric excitation device (16) contains at least two generators (17, 18) which provide electrical voltages for exciting the piezoelectric actuators (11).

Description

Description Piezoelectric inertial drive

[0001] The invention relates to a piezoelectric inertial drive.

[0002] Piezoelectric inertial drives are known from the prior art, in which the frictional contact is implemented in the form of a threaded engagement. They can be used, for example, as spindle drives in various types of mechanisms, such as linear drives, precision closure and dosing systems, valves, precision cutting drives, control drives, precise positioning devices such as technological coordinate tables, multi-coordinate positioning devices, tripods or hexapods, optical laser systems and similar devices, and precision medical devices such as pumps, syringes, insulin pumps, or bone lengthening devices.

[0003] Lasers are used in many areas of technology, such as metrology, medical technology, and metalworking. Typically, the laser beam is precisely directed using tilting mirrors. The required precision of the laser beam is achieved with micrometer screws, which are often manually adjusted. However, there are several applications where manually adjusting the tilting mirrors is either impossible or undesirable, for example, within a vacuum chamber, in a lithography machine, or on a total station.

[0004] For the automatic positioning of tilting mirrors, inertial piezoelectric drive devices are often used. In an inertial drive, a driven element, i.e., the rotor or runner, is connected or coupled to a piezoelectric actuator via a friction contact. The movement sequence of such inertial drives consists of two phases: in the first phase, the piezoelectric actuator is slowly extended and transmits the corresponding movement to the driven element due to static friction. In the second phase, which follows the first, a rapid Contraction of the actuator occurs. Due to its inertia, the driven element cannot follow the rapid movement of the actuator and remains in its position. This results in relative movement (gliding) between the actuator and the driven element; that is, the actuator slips, and sliding friction prevails in the frictional contact. Naturally, it is possible to reverse the timing of the two previously mentioned phases, so that in the first phase, rapid extension with relative movement or sliding between the actuator and the driven element occurs without any driving motion, and in the second phase, a slow contraction of the actuator takes place, during which static friction causes the driven element to be pulled along, thus generating a corresponding driving motion.

[0005] The applicant's DE 102021 113 751 A1 describes a drive device for driving a spindle, comprising two actuator devices, wherein the actuator devices act on an actuating device and a frame device, and a drive of the spindle is realized via corresponding surface sections provided for contact with the spindle at two different contact points.

[0006] The patent application US 2011 / 0109197A1 discloses a drive device with a drive shaft surrounded by a rotatably mounted drive element, wherein several contact elements evenly distributed around the circumference are pressed against the drive shaft. The drive element is set into a rotary motion by two diametrically opposed actuators, which perform a co-directional drive movement. This rotary motion is transmitted to the drive shaft via the contact elements. Due to the application of a sawtooth stress to the actuators, a stick-slip drive method results, enabling continuous rotary motion of the drive shaft.

[0007] EP 1 396 012 B2 teaches a piezoelectric drive with a piezoelectric element coupled to a resonator with a horn, wherein suitable vibrations for driving are transmitted from the piezoelectric element to The vibrations of the horn are transmitted to the resonator and in particular to the horn, which in turn can be pressed against the surface of a driven element, and the vibrations of the horn lead to a driving of the driven element.

[0008] DE 102010 022 812 B4 describes an ultrasonic motor with a ring-shaped ultrasonic actuator for generating a traveling wave, which is transmitted to a contact element arranged on the inner circumference of the ultrasonic actuator, which is in threaded engagement with a threaded rod to be driven, thus resulting in a rotational movement of the threaded rod.

[0009] The publication DE 199 09 913 A1 discloses an electromechanical drive device with a rotor mounted and driven in a bearing device and a piezo element, wherein the bearing device has a rotor receptacle which can be driven by the piezo element.

[0010] From US patent 5,410,206 A, a piezoelectric inertial drive for the rotary driving of a driven element in the form of a spindle is known. In this drive, the spindle is gripped on both sides by a piezoelectrically driven actuator consisting of two threaded clamping jaws, which are in frictional contact with the spindle. One of the two clamping jaws is connected to a piezoelectric actuator, which, based on the inertial principle, sets the threaded rod in motion or rotation. The second clamping jaw presses the threaded rod against the first clamping jaw, thereby supporting the rod's rotation.

[0011] The main disadvantage of the spindle drive of US 5 410 206 A is that the drive motion differs for the two directions of rotation of the spindle, because the piezoelectric actuator behaves differently with respect to extension and compression. The drive thus exhibits different characteristics in the two drive directions, resulting in different step sizes and travel speeds in the different directions of rotation of the spindle. To linearize the drive characteristics, Special control measures are required in the control electronics. A further disadvantage is that the second clamping jaw slows the spindle, resulting in reduced efficiency of the drive device.

[0012] The object of the invention is therefore to provide a piezoelectric inertial drive, in particular for driving a spindle, which has symmetrical drive characteristics and thus, in the case of a spindle as the driven element, drives it in the same way and preferably identically in both directions of rotation, and which also has a high efficiency, so that a reduced drive power is possible.

[0013] This problem is solved by a piezoelectric inertial drive according to claim 1, wherein the subsequent subclaims describe at least advantageous further developments.

[0014] If the indefinite article is used for a characteristic in the text – as above and possibly also below – then a subsequent mention of the same characteristic using the definite article will explicitly refer to the quantity implied by the indefinite article, without this leading to a corresponding restriction to precisely that quantity.

[0015] The piezoelectric inertial drive according to the invention comprises a drive device with a drive element having contact elements, each contact element having an inner circumferential surface with a thread. The piezoelectric inertial drive according to the invention further comprises a driven element with an outer circumferential surface provided with a thread, and an electrical excitation device for electrically controlling the drive device, wherein the driven element is in threaded engagement with the drive element.

[0016] The contact elements are arranged symmetrically with respect to a virtual diametrical separation plane (P) and at least partially encompass the element to be driven, wherein the contact elements are directly or are indirectly connected to a base element and additionally to each other, and the drive device has at least two piezoelectric and preferably multilayer actuators with a virtual actuator longitudinal axis, which are arranged with a respective first side on the base element and with a respective other side opposite the first side on the respective contact element, and the electrical excitation device includes at least two generators that provide electrical voltages for exciting the piezoelectric actuators.

[0017] The symmetrical arrangement of the contact elements or piezoelectric actuators results in a symmetrical and uniform drive of the drive element or contact elements, thereby achieving essentially the same speed and step size of the driven element in both directions of rotation. The contact elements not only support or mount the driven element, but both contribute to its drive or propulsion. Thus, neither contact element slows down the driven element, resulting in a correspondingly high efficiency of the piezoelectric inertial drive according to the invention.

[0018] According to the invention, the contact elements of the drive element are connected to each other via an elastic element and to two or four elastic elements of carriers of the base element by means of connecting elements, wherein the piezoelectric actuators are pre-tensioned in the axial direction by the elastic elements of the carriers of the base element by means of the connecting elements. The elastic element for connecting the contact elements of the drive element enables the generation of a torque acting on the driven element when the piezoelectric actuators are activated and deformed accordingly. The elastic elements of the carriers of the base element enable the piezoelectric actuators to be pre-tensioned in the axial direction by means of the connecting elements. With four elastic elements of the carriers, a symmetrical construction that counteracts or compensates for any bending of the supports.

[0019] It can be advantageous for each virtual actuator longitudinal axis to be arranged parallel to the virtual diametrical separation plane (P). This allows the force acting on the contact elements to be maximized.

[0020] It can also be advantageous for the piezoelectric inertial drive to have elastic elements connected to the base element, which press the contact elements against the driven element. The connection of the elastic elements to the base element creates a leverage effect and generates torque on the driven element. Furthermore, the connection of the elastic elements to the base element absorbs any adverse external forces acting perpendicular to the actuator's longitudinal axis.

[0021] It can also be advantageous for the drive device to include an elastic element that presses the contact elements against the driven element. Such an elastic element allows a force acting perpendicular to the longitudinal axis of the driven element to be applied, pressing the contact elements against the driven element.

[0022] It can also be advantageous for the base element to have two movable elements and two elastic elements, through which the contact elements are pressed against the element to be driven.

[0023] Furthermore, it can be advantageous for the drive element to have an elastic element that pre-tensions the corresponding piezoelectric actuator in the axial direction. It can be particularly advantageous for the drive element to also have a connecting element that, in conjunction with the elastic element, pre-tensions the corresponding piezoelectric actuator, thus enabling an increased pre-tension. In particular, multi-layer piezoelectric actuators require an axial pre-tension force to prevent delamination of the layers.

[0024] The invention further relates to a drive device with a drive element comprising contact elements with a threaded inner circumferential surface, a driven element with a threaded outer circumferential surface, and an electrical excitation device for electrically controlling the drive device, wherein the driven element is in threaded engagement with the drive elements, and the contact elements are arranged symmetrically with respect to a virtual diametrical dividing plane and at least partially surround the driven element, wherein the contact elements are directly or indirectly connected to a base element, and the drive device comprises at least two multilayer piezoelectric actuators with a virtual actuator longitudinal axis, which are arranged with a respective first side on the base element and with a respective other side opposite the first side on the respective contact element.and the electrical excitation device includes at least two generators that provide electrical voltages for exciting the piezoelectric actuators, wherein the drive element is designed as a two-part element and is connected by means of connecting elements to two or four elastic elements of supports of the base element, and the piezoelectric actuators are pre-tensioned in the axial direction by the elastic elements via the connecting elements. With such a drive device, a larger feed amplitude of the driven element is achievable.

[0025] It can be advantageous for the driven element to be designed as a hollow threaded rod and for the corresponding cavity to be filled with a sound-absorbing material. This makes it possible to reduce any parasitic vibrations that may arise in the driven element, thereby improving the driving function of the piezoelectric inertial drive.

[0026] Furthermore, it can be advantageous for the thread of the driven element or the thread of the contact elements to be made of an abrasion-resistant material or coated with an abrasion-resistant layer. is equipped with a coating that results in reduced wear and a longer service life. It is also conceivable that the driven element or the contact elements are made of an abrasion-resistant material.

[0027] It can be advantageous for the piezoelectric inertial drive to have a contact device that presses the driven element against the drive element and acts directly or indirectly on the driven element in the axial direction. This results in a higher contact force, which in turn generates a greater torque from the piezoelectric inertial drive.

[0028] Furthermore, it can be advantageous for the piezoelectric inertial drive to have two or more drive units acting on a common driven element, with the drive units fixed relative to each other by elastic elements. Using multiple drive units increases the driving force of the piezoelectric inertial drive. The elastic elements prevent movement of the drive units in the direction they point towards each other, but allow movement in other degrees of freedom. This prevents the driven element from jamming, especially if it is in the form of a threaded rod or a spindle.

[0029] Furthermore, it can prove advantageous that the electrical excitation device is designed to generate two complementary sawtooth-shaped electrical voltages U1 and U2 to excite the piezoelectric actuators. This leads to particularly efficient operation of the piezoelectric inertial drive.

[0030] The advantages and expediencies of the invention will become clearer from the following description of preferred embodiments with reference to the figures. These show:

[0031] Fig. 1: Perspective view of a piezoelectric inertial drive not belonging to the invention

[0032] Fig. 2: Perspective view of the drive device of the piezoelectric inertial drive according to Fig. 1

[0033] Fig. 3: Perspective view of a multi-layer actuator for a piezoelectric inertial drive according to the invention.

[0034] Fig. 4: Perspective view of a drive device not belonging to the invention

[0035] Fig. 5: Perspective view of a drive device not belonging to the invention

[0036] Fig. 6a): Two different perspective views of an embodiment of a drive device of a piezoelectric inertial drive according to the invention; Fig. 6b): Exploded view of the drive device according to Fig. 6a)

[0037] Fig. 7a): Two different perspective views of a further embodiment of a drive device of a piezoelectric inertial drive according to the invention; Fig. 7b): Exploded view of the drive device according to Fig. 7a)

[0038] Fig. 8: Two different perspective views of a further embodiment of a drive device of a piezoelectric inertial drive according to the invention.

[0039] Fig. 9a)-c): Different embodiments for a driven element of an inertial drive according to the invention in the form of a threaded rod

[0040] Fig. 10a), 10b): Different perspective views of a piezoelectric drive with two drive devices not belonging to the invention and a common driven element.

[0041] Fig. 11, Fig. 12: Different embodiments of a piezoelectric drive according to the invention with two drive devices and a common driven element.

[0042] Fig. 13a): Basic structure of an electrical excitation device of a piezoelectric inertial drive according to the invention; Fig. 13b): Representation of the time course of the electrical voltages generated by the excitation device according to Fig. 13a) and the resulting movement of the driven element.

[0043] Fig. 14a)-d): Maximum deformations of the drive device according to Figures 2, 5, 6 and 8 calculated using the finite element method (FEM) when the actuators are controlled to generate a drive movement of a driven element in a clockwise or counterclockwise direction.

[0044] The piezoelectric inertial drive 1 shown in Fig. 1, which is not part of the invention, comprises a threaded driven element 6 in the form of a spindle and an electrical excitation device 16. The inertial drive 1 includes a drive device 2 driven by two multilayer piezoelectric actuators 11. The drive device is divided by a virtual diametrical plane P, which passes through the center point or axis of the driven element 6.

[0045] The drive device 2 has a drive element 5 with two contact elements 9 and 10 arranged symmetrically with respect to the diametrical plane P, which are integrally formed with the drive element 5. Each of the contact elements 9, 10 has a threaded inner circumferential surface 4. The two contact elements 9, 10 engage the driven element 6 from two sides, and the driven element 6 is in a threaded friction engagement with the two contact elements 9, 10. Each of the piezoelectric actuators 11 is supported with one side 12 against a base element 14. The other and opposite side 13 of the respective piezoelectric actuator 11 is connected to the respective contact element 9, 10 of the drive element 5. It is conceivable that the piezoelectric actuators 11 are fixed to the base element 14 with side 12 by adhesive bonding. Each of the contact elements 9, 10 has two elastic sections 20.

[0046] The excitation device 16 includes two electrical generators 17, 18 that generate complementary sawtooth-shaped electrical voltages U1, U2. The excitation device 16 is equipped with the piezoelectric actuators. 11 electrically connected via electrical connections 21 provided on the actuators. By controlling the actuators of the drive device with the electrical excitation device 16, the object to be driven is Element 6 is set directly into a rotational movement and indirectly into a translational movement. The element 6 to be driven can be equipped with adhesive pockets 12 for filling with an adhesive in order to additionally fix the piezoelectric actuators 11.

[0047] Fig. 2 shows a detailed view of the drive device 2 of the piezoelectric inertial drive 1 according to Fig. 1. The drive device 2 comprises the drive element 5 and piezoelectric multilayer actuators 11. The drive device 2 is divided into two equal symmetrical halves by the virtual diametrical plane P. The contact elements 9, 10, which are integrally formed with the drive element 5, each have an inner circumferential surface 4 with a thread. The piezoelectric actuators are supported at one side 12 by the base element 14 of the drive element 5 and are connected to the drive element 5 at the other opposite side. The support points are located between the two actuators. Their virtual longitudinal axes 19 run parallel to the virtual diametrical plane P. The piezoelectric actuators have electrical connections 21.A mounting hole 23 serves to screw the drive device 2 to a base body or a device housing. The mounting holes 24 serve to fix elastic elements not shown in Fig. 2. Furthermore, the drive element 5 has four elastic sections 20. The elastic sections enable the contact elements 9, 10 to be pressed against the element 6 to be driven. An optional elastic element 27 in the form of a coil spring can be placed in the bore 22, which pulls the contact elements 9, 10 together and thus presses them against the element to be driven.

[0048] Fig. 3 shows a multilayer piezoelectric actuator 11 for use in a piezoelectric inertial drive according to the invention. The individual actuator layers 26 each have electrodes on their large surfaces and piezoelectric material arranged between them. All adjacent layers 26 have an opposing electrical orientation, indicated by the arrows P. Polarization occurs. Electrodes with the same polarity are connected to each other and connected to the electrical terminals 21.

[0049] Fig. 4 shows a drive device 2 of an inertial drive not belonging to the invention. In this embodiment of the drive device 2, both contact elements 9, 10 of the drive element 5 are connected by an elastic element in the form of a coil spring 27 and thus pressed against the driven element 6. Other shapes for the elastic element are conceivable, for example, in the form of a flat spring. The drive element 5 of the embodiment shown in Fig. 4 also has elastic elements 30 and movable elements 31, which press the contact elements 9, 10 against the element to be driven. In addition, each of the contact elements 9, 10 has an elastic element 28. The elastic elements 28 enable a preload of the piezoelectric actuators in the axial direction. An additional preload force is achieved by means of the connecting elements 29 in the form of screws.

[0050] Fig. 5 shows another drive device 2 of an inertial drive 1, not belonging to the invention. In this embodiment of the drive device 2, both contact elements 9, 10 of the drive element 5 each have an elastic element 32. The elastic elements 32 are connected to the elastic element 33. The elastic elements 32 and 33 enable the contact elements 9, 10 to be pressed against the element to be driven. The contact elements 9, 10 are connected to the base section 14 via the elastic elements 32 and 33.

[0051] Fig. 6a) shows two different perspective views of an embodiment of a drive device 2 of a piezoelectric inertial drive 1 according to the invention. The contact elements 9, 10 of the drive element 5 are connected to each other via an elastic element 34. The base element 14 has two supports 35, via which the drive element 5 is connected to the base element 14 by means of the connecting elements 36. The supports 35 have elastic sections 37 that allow for pre-tensioning of the piezoelectric actuators 11. axial direction or along its virtual longitudinal axis. Fig. 6b) shows the drive device 2 according to Fig. 6a) in a corresponding exploded view.

[0052] Fig. 7a) shows two different perspective views of a further embodiment of a drive device 2 of a piezoelectric inertial drive 1 according to the invention. Here, the contact elements 9, 10 of the drive element 5 are connected to each other via an elastic element 34. The base element 14 has four supports. 35, via which the drive element 5 is connected by means of the connecting elements 36 is connected to the base element 14. The supports 35 have elastic sections 37 that allow the piezoelectric actuators 11 to be pre-tensioned in the axial direction. Fig. 7b) shows the drive device 2 according to Fig. 7a) in a corresponding exploded view.

[0053] Fig. 8 shows two different perspective views of an alternative embodiment of a drive device 2 of a piezoelectric inertial drive 1 according to the invention. Here, the drive device 2 has a two-part drive element 15. The contact elements 9, 10 of the drive element 15 are not connected to each other. The base element 14 has two supports 35, via which the drive element 15 is connected to the base element 14 by means of the connecting elements 36. The supports 35 have elastic sections 37 that allow the piezoelectric actuators 11 to be pre-tensioned in the axial direction.

[0054] Figures 9a) to 9c) show different embodiments of a driven element 6 of an inertial drive 1 according to the invention in the form of a threaded rod. According to Fig. 9a), the driven element 6 is designed as a fully threaded rod 38 made of a hard and abrasion-resistant material, such as heat-treated steel, oxide, or metal ceramic. Furthermore, according to Fig. 9b) and Fig. 9c), it is possible to design the driven element 6 as a hollow threaded rod 40, wherein the corresponding inner opening 41 has a round shape. However, other geometries of the inner opening are also conceivable, such as a Polygonal shape. A rod 42 made of sound-absorbing material can be inserted into the opening 41 of the hollow threaded rod 40, as shown in Fig. 9c). This rod 42 is made of an elastic material such as rubber. The elastic material can be filled with hard particles such as metal particles. Alternatively, the rod 42 could be made of a viscoelastic material, such as a thermoplastic material, which could be filled with particles such as metal and / or rubber particles. Furthermore, the rod 42 could also be made of a hard porous material, such as porous oxide ceramic, the pores of which are filled with a viscous material. Numerous other materials or material mixtures with a high sound absorption coefficient are conceivable for the rod 42.The rod 42 can, for example, also be made of a hard material such as steel, oxide ceramic, metal ceramic, wherein a layer of sound-absorbing material 43 (e.g. rubber, epoxy resin or similar) is arranged between the rod 42 and the drive element 5.

[0055] Figures 10a) and 10b) show different perspective views of a piezoelectric inertial drive 1 (not part of the invention) with two drive devices 2 according to Figures 2, 4, and 5 and a common driven element 6. The drive devices 2 are held at a distance from each other by means of elastic elements 44. The elastic elements 44 are fixed to the base element 14 by means of fastening elements in the form of set screws screwed into the bores 45. It is also conceivable to fix the drive devices 2 to each other by means of flat elastic elements in the form of leaf springs. The mounting bore 46 serves to attach the piezoelectric inertial drive to a base body or device housing. It is conceivable to use three or more drive devices 2 instead of the two drive devices shown here.

[0056] Fig. 11 shows an embodiment of a piezoelectric inertial drive 1 according to the invention with two drive devices 2 as shown in Fig. 6 and a common driven element 6. The drive devices 2 are held at a distance from each other by means of elastic elements 44. The elastic elements are fixed to the base element 14 by means of fastening elements in the form of set screws screwed into the bores 46. It is conceivable to use three or more drive devices 2 instead of the two shown here.

[0057] Fig. 12 shows a further embodiment of a piezoelectric inertial drive 1 according to the invention with two drive devices 2 as shown in Fig. 7 and a common driven element 6. The drive devices 2 are held at a distance from each other by means of elastic elements 44. The elastic elements are fixed to the base element 14 by means of fastening elements in the form of set screws screwed into the bores 46. It is conceivable to use three or more drive devices instead of the two shown here.

[0058] Fig. 13a) illustrates the basic structure of an electrical excitation device for a piezoelectric inertial drive according to the invention. The excitation device can be implemented in a microcontroller, an FPGA, or from discrete integral circuits. The excitation device includes a phase accumulator (PA) 47, a pulse width modulator or pulse density modulator (PWM or PDM) 48, a switched power output stage (PLC) 49, a low-pass filter (LP) 50, a current sensor 51, and a current control unit 52.

[0059] The phase accumulator 47 represents an incrementing or decrementing n-bit register that generates a linearly increasing or decreasing binary number. The PWM or PDM 48 modulates the pulse width or pulse density of a high-frequency square wave carrier signal according to the binary number (ramp function) generated by PA 47. The frequency fcar of the carrier signal is preferably 10 times the frequency fexc at which the piezoelectric actuators are excited. higher. The ramp-function-modulated square wave carrier voltage is further amplified by the PLC 49 and passed on to the piezoelectric actuators 11 via the LP (50). The generators 17, 18 are two transistor bridge or half-bridge circuits within the switched power output stage 49. The electrical current of the actuators 11 is measured by the current sensor (CS) 51, compared with a reference signal, and forwarded to the current control unit (CCU) 52. The current control unit (CCU) 52 regulates the electrical current according to the specified reference signal and thus influences the extension of the piezoelectric actuators.

[0060] Fig. 13b corresponds to a representation of the time course of the electrical voltages U1 , U2 generated by the excitation device 16 according to Fig. 13a and the movement S of the driven element 6 generated thereby.

[0061] The piezoelectric actuators of the inertial motor according to the invention are driven in four time intervals by two alternating voltages U1 and U2 of the same amplitude but opposite polarity. During the first time interval, within time t1, the voltage U1 of the generator 17 increases linearly to the maximum value U1max with a slope Kup (ramp function), while the voltage U2 of the generator 18 has an identical but negative slope -Kup, i.e., it falls to the negative maximum value -U2max. In the second time interval, i.e., within time t2, the amplitudes of both voltages U1 and U2 remain unchanged. Subsequently, within time t3, the voltage U1 decreases with a slope -Kdw, and the voltage U2 increases with Kdw. Within time t4, the amplitude of the voltages U1 and U2 is zero. The frequency fexc of the alternating voltages LH , U2 is the same and is a few tens of kHz.The rise time t1 is significantly shorter than the fall time t3.

[0062] Figures 14a) to 14d) show maximum deformations of the drive device according to Figures 2, 5, 6 and 8, calculated using FEM, when the actuators are controlled to generate a drive movement of a driven element in a clockwise or counterclockwise direction. Fig. 14a) shows the corresponding deformations in a drive device 2 according to Fig. 2, Fig. 14b) shows the corresponding deformations in a drive device 2 according to Fig. 5, Fig. 14c) shows the corresponding deformations in a drive device 2 according to Fig. 6 and Fig. 14d) shows the corresponding deformations in a drive device according to Fig. 8.

[0063] The piezoelectric inertial drive 1 according to the invention and its excitation device 16 function as follows: the generators 17, 18 of the excitation device 16 generate two sawtooth-shaped electrical voltages U1, U2 with the same time course, the same voltage magnitude, and opposite polarity (see Fig. 13). The time course of the electrical voltages U1, U2 has two regions t1, t3 with different slopes. In the first region t1, the slope is small. In this region, the magnitude of the voltages U1, U2 increases slowly to their final values ​​U1max, U2max. In the second region t3, with a large slope, the magnitude of the voltages U1, U2 decreases very rapidly. The difference is preferably one order of magnitude. Furthermore, there can be two additional regions t2, t4 in the time course of the voltages U1, U2 in which the magnitudes of the voltages U1, U2 remain unchanged.

[0064] To excite the piezoelectric inertial drive 1, the voltages U1 and U2 are applied to each piezoelectric actuator 11 at time t=0 (see Fig. 12b). The actuator subjected to positive voltage U1 then expands slowly, while the actuator subjected to negative voltage U2 contracts. Due to the expansion and contraction of the actuators, the drive element 5 of the drive device 2 connected to them undergoes a deformation as shown in Fig. 14. The inner circumferential surfaces 4 of the drive element 5, which are in contact with the driven element 6 via thread friction, impart a rotation to it due to the static friction force acting between them. The direction of rotation depends on the polarity of the voltages U1 and U2, or rather the direction of deformation of the actuators, and is indicated by arrows in Fig. 13a).

[0065] After the phase of small slope t1, phase t2 can occur, in which the actuator voltages remain unchanged and the driven element 6 comes to rest. In the subsequent phase of large slope t3, the magnitudes of the voltages U1 and U2 decrease very rapidly. The actuators follow the electrical voltages and simultaneously change their direction of deformation. That is, the previously extended actuator contracts, and the contracted one expands. Since the driven element has mass, it cannot follow the actuator movement or the movement of the drive element due to inertia and remains in its position. Due to the forces occurring in the frictional contact, static friction transitions into sliding friction. The surfaces of the frictional contact between the drive element and the driven element slide against each other. Phase t4 then follows, in which the electrical voltages U1 and U2 are zero and the driven element is at rest.The motion sequence repeats periodically at a frequency of a few kHz at most. The driven element is directly set into rotational motion and indirectly into linear motion. To reverse the direction of motion of the driven element, the voltages U1 and U2 are interchanged.

[0066] Reference symbol list 1 Piezoelectric inertia antenna 2 Drive device 3 threads (of the inner circumferential surface 4) 4 Inner perimeter area 5, 15 Drive element 6 element to be driven 7 threads (of the element to be driven 6) 8 Outer circumferential area (of the element to be driven 6) 9, 10 Contact element (of the drive element 5) 11 multilayer piezoelectric actuator 12, 13 pages (of the multilayer piezoelectric actuator 11) 14 Basic element 16 Excitation device 17, 18 Generators of electrical voltage 19 virtual longitudinal axis 20 elastic element 21 electrical connections of the actuator 22 spring bore 23 Mounting holes 24 Mounting hole of an elastic element 25 adhesive pouches 26 piezoelectric layer (of actuator 11) 27, 28 elastic element 29 Connecting element 30 elastic element 31 movable element 32, 33, 34 elastic element 35 supports (of the base element 14) 36 Connecting element 37 elastic element 38 threaded rod 39 driving element in the form of a monolithic rod Hollow thread rod Axial opening in the element to be driven sound-absorbing rod Layer of sound-absorbing material, elastic element, 46 mounting holes Phase accumulator (PA) Pulse width or pulse density modulator (PWM or PDM) switched power output stage (PLC) Low-pass filter (LP) Current sensor (CS) Power Control Unit (CCU)

Claims

Claims Claim 1 Piezoelectric inertial drive (1) comprising a drive device (2) with a drive element (5) comprising contact elements (9, 10) with an inner circumferential surface (4) having a thread (3), a driven element (6) with an outer circumferential surface (8) provided with a thread (7), and an electrical excitation device (16) for electrically controlling the drive device (2), wherein the driven element (6) is in threaded engagement with the drive elements (5), and the contact elements (9, 10) are arranged symmetrically with respect to a virtual diametrical dividing plane (P) and at least partially surround the driven element (6), wherein the contact elements (9, 10) are directly or indirectly connected to a base element (14) and to each other, and the drive device (2) comprises at least two multilayer piezoelectric actuators (11) with a virtual actuator longitudinal axis (19),the piezoelectric actuators (11) are arranged with a respective first side (12) on the base element (14) and with a respective other side (13) opposite the first side (12) on the respective contact element (9, 10), and the electrical excitation device (16) includes at least two generators (17, 18) that provide electrical voltages for exciting the piezoelectric actuators (11), characterized in that the contact elements (9, 10) of the drive element (5) are connected to each other via an elastic element (34) and to two or four elastic elements (37) of carriers (35) of the base element (14) by means of connecting elements (36), wherein the piezoelectric actuators (11) are pre-tensioned in the axial direction by the elastic elements (37) by means of the connecting elements (36). Claim 2 Piezoelectric inertial drive (1) according to claim 1 , characterized in that each virtual actuator longitudinal axis (19) is arranged parallel to the virtual diametrical plane (P). Claim 3 Piezoelectric inertial drive (1) according to claim 1 or 2, characterized in that it has elastic elements (20) which are connected to the base element (14) and through which the contact elements (9, 10) are pressed against the element (6) to be driven. Claim 4 Piezoelectric inertial drive (1) according to one of the preceding claims, characterized in that the drive device (2) comprises an elastic element (27) by which the contact elements (9, 10) are pressed against the element (6) to be driven. Claim 5 Piezoelectric inertial drive (1) according to one of the preceding claims, characterized in that the base element (14) has two movable elements (31) and two elastic (30) elements by which the contact elements (9, 10) are pressed against the element (6) to be driven. Claim 6 Piezoelectric inertial drive (1) according to one of the preceding claims, characterized in that the drive element (5) has an elastic element (28) by which the corresponding piezoelectric actuator (11) is pre-tensioned in the axial direction. Claim 7 Piezoelectric inertial drive (1) according to claim 6, characterized in that the drive element (5) has a connecting element (29) by which the corresponding piezoelectric actuator (11) is pre-tensioned in conjunction with the elastic element (28). Claim 8 Piezoelectric inertial drive (1) comprising a drive device (2) with a drive element (5) comprising contact elements (9, 10) with an inner circumferential surface (4) having a thread (3), a driven element (6) with an outer circumferential surface (8) provided with a thread (7), and an electrical excitation device (16) for electrically controlling the drive device (2), wherein the driven element (6) is in threaded engagement with the drive elements (5), and the contact elements (9, 10) are arranged symmetrically with respect to a virtual diametrical dividing plane (P) and at least partially surround the driven element (6), wherein the contact elements (9, 10) are directly or indirectly connected to a base element (14), and the drive device (2) comprises at least two multilayer piezoelectric actuators (11) with a virtual actuator longitudinal axis (19),which are connected to the base element (14) with a respective first side (12) and with a respective, other and opposite side (12) to the first side (12) are arranged on the respective contact element (9, 10), and the electrical excitation device (16) includes at least two generators (17, 18) that provide electrical voltages for exciting the piezoelectric actuators (11), characterized in that the drive element is designed as a two-part element (15) and is connected by means of connecting elements (36) to two or four elastic elements (37) of carriers (35) of the base element (14), and the piezoelectric actuators (11) are pre-tensioned in the axial direction by the elastic elements (37) by means of the connecting elements (36). Claim 9 Piezoelectric inertial drive (1) according to one of the preceding claims, characterized in that the element to be driven (6) is designed as a hollow threaded rod and the corresponding cavity (26) is filled with a sound-absorbing material (28). Claim 10 Piezoelectric inertial drive (1) according to one of the preceding claims, characterized in that the thread of the element to be driven (6) or the thread of the contact elements (9, 10) is made of an abrasion-resistant material or is provided with an abrasion-resistant layer. Claim 11 Piezoelectric inertial drive (1) according to one of the preceding claims, characterized in that it has a pressing device with which the element to be driven (6) is pressed against the drive element (5) and which acts directly or indirectly on the element to be driven (6) in an axial direction. Claim 12 Piezoelectric inertial drive (1) according to one of the preceding claims, characterized in that it has two or more drive devices (2) which act on a common driven element (6), wherein the drive devices (2) are fixed against each other by elastic elements (44). Claim 13 Piezoelectric inertial drive (1) according to one of the preceding claims, characterized in that the electrical excitation device (16) is configured to provide two complementary to generate sawtooth-shaped electrical voltages U1 , U2 to excite the piezoelectric actuators (11).

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