METHOD FOR OPERATING AN ULTRASONIC MOTOR

Description

[0001] The invention relates to a method for operating an ultrasonic motor according to claims 1 to 4.

[0002] From DE 10 2005 010 073 B4 a method for controlling or operating an ultrasonic motor is known, in which the movement control of the element to be driven is carried out by the acoustic standing waves generated in its ultrasonic actuator in the form of a rectangular plate and by the static bending of the ultrasonic actuator.

[0003] In the ultrasonic actuator, both acoustic bending standing waves, which propagate along its length L and along its height H, and acoustic longitudinal standing waves, which propagate along its length L, are generated.

[0004] For technical reasons, the thickness B of the piezoelectric plate of the ultrasonic actuator is limited to the value H / 4. Therefore, it is impossible to achieve a friction contact length greater than H / 4 with the ultrasonic motor known from DE 10 2005 010 073 B4. This limits the maximum force that can be generated by the ultrasonic motor and the corresponding mechanical power.

[0005] If higher driving forces or higher mechanical performance are required, two or more ultrasonic motors connected or coupled in parallel can be used.

[0006] However, a disadvantage of such a coupling is that, in practice, ultrasonic motors exhibit a relatively large variation in their operating (resonance) frequencies. This is due to the technologically induced variation in the density and hardness of the piezoelectric ceramics that occurs during the manufacturing of ultrasonic actuators.

[0007] The difference in the operating frequencies of the individual ultrasonic motors leads to a reduction in the overall power of the ultrasonic motors connected in parallel and to unstable operation due to the transfer or transition of the operating frequency of one motor to another.

[0008] Furthermore, the use of multiple motors is associated with higher costs.

[0009] Other actuator concepts with several active sub-areas can be seen, for example, in US 2004 / 017134 A1, US 5 616 980 A or DE 10 2014 205577 A1.

[0010] It is therefore an object of the invention to provide a method for operating an ultrasonic motor with which an ultrasonic motor with a higher driving force, a higher mechanical power and a higher operational stability can be realized compared to the methods known from the prior art.

[0011] This object is achieved by a method for operating an ultrasonic motor according to claim 1, wherein the subsequent subclaims 2 to 4 represent at least expedient developments.

[0012] The method according to the invention is divided into the following steps: Providing an ultrasonic actuator made of a piezoelectric, electrostrictive, or magnetostrictive material in the form of a plate whose width B is greater than its thickness D and smaller than its length L, and which plate has two main surfaces, two side surfaces extending along the length, and two end surfaces extending along the width, and which has a transverse plane of symmetry S1 that runs perpendicular to the main surfaces and the side surfaces and parallel to the end surfaces, and a longitudinal plane of symmetry S2 that runs perpendicular to the side surfaces and the end surfaces and parallel to the main surfaces, wherein a friction element intended for contact with an element to be driven is arranged on at least one of the end surfaces of the ultrasonic actuator, and the ultrasonic actuator comprises four identical volume regions,which are arranged both symmetrically with respect to the transverse plane of symmetry S1 and symmetrically with respect to the longitudinal plane of symmetry S2, and each of the volume regions, together with excitation electrodes and general electrodes arranged on and / or in the ultrasonic actuator, forms both a generator for generating acoustic standing waves and a generator for generating static bending deformations; providing an electrical excitation device which supplies only one electrical alternating voltage U1 or two electrical alternating voltages U1, U2 and also two static electrical voltages E1, E2; applying the alternating voltage U1 to the electrodes of two of the four generators G1, G2, G3, G4 or applying one of the two alternating voltages U1, U2 to the electrodes of two of the generators G1, G2, G3, G4 and applying the other alternating voltage U1, U2 to the electrodes of the other two generators G1, G2, G3,G4 to form an acoustic standing wave in the ultrasonic actuator in a dynamic operating mode, or applying one of the two static electrical voltages E1, E2 to the electrodes of two of the four generators G1, G2, G3, G4 and applying the other static electrical voltage E1, E2 to the electrodes of the other two generators G1, G2, G3, G4 to form a static bending deformation in a static operating mode.

[0013] The dynamic operating mode and the static operating mode are executed independently of each other, and can preferably be executed one after the other such that the dynamic operating mode is followed by the static operating mode.

[0014] Within the dynamic operating mode, either the single alternating voltage U1 is applied simultaneously to two of the four generators G1, G2, G3, G4 or each of the two alternating voltages U1, U2 is applied to a generator pair consisting of two interacting generators, for example U1 to G1 and G4 and U2 to G2 and G3, to form an acoustic standing wave in the ultrasonic actuator, while in a static operating mode the two static electrical voltages E1, E2 are applied simultaneously to all four generators G1, G2, G3, G4 to form a static bending deformation of the ultrasonic actuator.

[0015] It may be advantageous that in the dynamic operating mode when the two alternating voltages U1, U2 are applied, each of the two generator pairs, to which the same alternating voltage U1, U2 is applied, forms an acoustic standing wave in the ultrasonic actuator, which corresponds to a superposition of the second mode of a bending standing wave and the first mode of a longitudinal standing wave.

[0016] However, it can also be advantageous that in the dynamic operating mode when the two alternating voltages U1, U2 are applied, one of the two generator pairs, to which one of the alternating voltages U1, U2 is applied, forms an acoustic standing wave in the ultrasonic actuator, which corresponds to the second mode of a bending standing wave, and the other of the two generator pairs, to which the other alternating voltage U1, U2 is applied, forms an acoustic standing wave in the ultrasonic actuator, which corresponds to the first mode of an acoustic longitudinal standing wave.

[0017] It may be advantageous for the static bending deformation of the ultrasonic actuator to occur in a plane that is substantially parallel to the end faces.

[0018] It may also be advantageous for the ratio of the length L to the thickness D of the ultrasonic actuator to be in the range between 3.5 and 4.5.

[0019] It may also be advantageous that the surfaces formed by the elliptical movement paths of points of the friction element or by the direction of movement of an element to be driven by the ultrasonic motor are arranged perpendicular to the main surfaces of the ultrasonic actuator.

[0020] Furthermore, it may be advantageous that the generators G1, G2, G3, G4 for forming acoustic standing waves and for forming static bending deformations are each formed by strip-shaped excitation electrodes and strip-shaped general electrodes arranged alternately on the two main surfaces, wherein the strip-shaped electrodes run parallel to the transverse symmetry plane S1 and the polarization direction of the piezoelectric or electrostrictive or magnetostrictive material arranged between the strip-shaped electrodes runs perpendicular to the strip-shaped electrodes.

[0021] It may be advantageous that the distance between adjacent strip-shaped electrodes is equal to or less than half the thickness D of the ultrasonic actuator.

[0022] In addition, it may be advantageous that the generators for forming acoustic standing waves and for forming static bending deformations are formed from flat, separate excitation electrodes arranged on the two main surfaces and a single flat general electrode arranged within the ultrasonic actuator coinciding with its longitudinal symmetry plane S2, wherein the polarization direction of the piezoelectric or electrostrictive or magnetostrictive material arranged between the flat electrodes is perpendicular to the flat electrodes.

[0023] Furthermore, it may be advantageous for the ultrasonic motor to have clamping elements for holding the ultrasonic actuator, wherein the clamping elements are arranged in regions of the minima of the vibration velocities of acoustic bending standing waves excited in the ultrasonic actuator.

[0024] Further details of the invention are described in the drawings using schematically illustrated embodiments. They show: Figure 1 : Embodiment of an ultrasonic motor suitable for operation according to the method according to the invention in the form of a linear drive Figure 2 : Embodiment of an ultrasonic motor suitable for operation according to the method according to the invention in the form of a rotary drive Figure 3 : Geometric structure of an ultrasonic actuator of an ultrasonic motor suitable for operation with the method according to the invention Figure 4 : Ultrasonic actuator according to Fig. 3 with a friction element arranged on one of its end faces Figure 5 , Figures 23 to 26: different views of an ultrasonic actuator according to the Figures 3 and 4 with a possible embodiment for the electrodes of the ultrasonic actuator Figure 6, Figures 34 to 37: different views of an ultrasonic actuator according to the Figures 3 and 4 with another possible embodiment for the electrodes of the ultrasonic actuator Figure 7 , Figure 46: perspective view of the ultrasonic actuator according to Figure 5 with friction element arranged on one of its front sides; Figure 47: perspective view of the ultrasonic actuator according to Figure 6 with a friction element arranged on one of its front sides Figure 8 , Figure 48: electrical circuit for operating the ultrasonic actuator according to Figure 5 with the method according to the invention using a single alternating voltage U1; Figure 49: Block diagram with an electrical excitation device for carrying out the method according to the invention using a single alternating voltage U1 Figure 9, Figures 66 and 67: States of maximum deformation due to the second mode of a bending standing wave (dynamic operating mode) formed in an ultrasonic actuator controlled according to the method according to the invention; Figures 68 and 69: States of maximum deformation due to the first mode of a longitudinal standing wave (dynamic operating mode) formed in an ultrasonic actuator controlled according to the method according to the invention Figure 10 : Representation of a possible movement trajectory of a point of the friction element of an ultrasonic actuator controlled by the method according to the invention (dynamic operating mode) Figure 11 , Illustrations 73 and 74: States of maximum deformation due to the static bending deformation formed in an ultrasonic actuator controlled by the method according to the invention (static operating mode) Figure 12: Representation of a possible movement trajectory of a point of the friction element of an ultrasonic actuator controlled by the method according to the invention (static operating mode) Figure 13 , Figure 78: electrical circuit for operating the ultrasonic actuator according to Figure 5 with the method according to the invention using two alternating voltages U1 and U2; Figure 79: Block diagram with an electrical excitation device for carrying out the method according to the invention using two alternating voltages U1 and U2 Figure 14 : Figure 83: electrical circuit for operating the ultrasonic actuator according to Figure 5with the method according to the invention using two alternating voltages U1 and U2, each of the alternating voltages generating an independent standing wave in the ultrasonic actuator; Figure 84: Block diagram with an electrical excitation device for carrying out the method according to the invention using two alternating voltages U1 and U2 Figure 15 , Figure 85: electrical circuit for operating the ultrasonic actuator according to Figure 6 with the method according to the invention using a single alternating voltage U1; Figure 86: Block diagram with an electrical excitation device for carrying out the method according to the invention using a single alternating voltage U1 Figure 16 , Figure 87: electrical circuit for operating the ultrasonic actuator according to Figure 6with the method according to the invention using two alternating voltages U1 and U2; Figure 88: Block diagram with an electrical excitation device for carrying out the method according to the invention using two alternating voltages U1 and U2 Figure 17 , Figure 89: electrical circuit for operating the ultrasonic actuator according to Figure 6 with the method according to the invention using two alternating voltages U1 and U2, each of the alternating voltages generating an independent standing wave in the ultrasonic actuator; Figure 90: Block diagram with an electrical excitation device for carrying out the method according to the invention using two alternating voltages U1 and U2 Figure 18 : Embodiment of an ultrasonic motor suitable for operation according to the method according to the invention in the form of a linear drive

[0025] Figure 1shows an embodiment of an ultrasonic motor in the form of a linear drive suitable for operation with the method according to the invention. The ultrasonic motor comprises an ultrasonic actuator 1 in the form of a rectangular piezoelectric plate 2 with two largest main surfaces 13 and 14, two side surfaces 15 extending along the length of the ultrasonic actuator, and two end surfaces 16 extending along the width of the ultrasonic actuator. Attached to the end surface 16 facing an element 5 to be driven is a friction element 3, which is pressed against the friction surface 4 of the element 5 to be driven with a force F by means of a spring element 10.

[0026] The element 5 to be driven is designed as a body 6 mounted longitudinally displaceably in the housing 8 by means of the bearing 7.

[0027] The ultrasonic actuator 1 is held in the housing 8 via clamping elements 9.

[0028] The contact force F generated by the spring element 10 acts on the ultrasonic actuator 1 via the sound-insulating base 11.

[0029] In addition to the Figure 1 In addition to the rod shape shown, the body 5 to be driven can also be designed as a plate, a table or in another similar shape.

[0030] The arrows with the index v indicate the direction of movement of the element 5 to be driven.

[0031] Figure 2 shows a further embodiment of an ultrasonic motor suitable for operation with the method according to the invention in the form of a rotary drive, in which the element 5 to be driven is designed as a rotary or rotating body 12 in the form of a disk.

[0032] The rotating or rotational body 12 can also be only part of a disk, although many other shapes are also conceivable, such as a ring or part of a ring, a cylinder or part of a cylinder and a sphere or part of a sphere.

[0033] Figure 3 illustrates the geometric structure and the geometric relationships of an ultrasonic actuator of an ultrasonic motor suitable for operation with the method according to the invention. The ultrasonic actuator has the shape of a rectangular plate 2, wherein the plate is made entirely of piezoelectric ceramic. The piezoelectric plate 2 has two main surfaces 13, 14, two side surfaces 15, and two end surfaces 16. The plate has a length L, a width B, and a thickness D, with the ratio of length L to thickness D being between 3.5 and 4.5.

[0034] The length-to-thickness ratio L / D determines the position of the resonance frequency Fp2 of the second mode of the acoustic bending standing wave, which propagates along the length L and along the thickness D, relative to the resonance frequency Fp1 of the first mode of the acoustic longitudinal standing wave, which propagates along the length L.

[0035] For a ratio L / D between 3.5 and 4.5, the resonance frequencies Fp2 and Fp1 are close to each other or coincide.

[0036] The width B of the piezoelectric plate 2 is greater than its thickness D and smaller than its length L.

[0037] The plate 2 can be divided by the virtual vertical symmetry plane S1, which runs perpendicular to the side surfaces 15 and parallel to the end surfaces 16. The symmetry plane S1 divides the length L and, accordingly, the main surfaces 13, 14 of the plate 2 into two equal parts.

[0038] Furthermore, the plate 2 can be divided by the virtual longitudinal symmetry plane S2, which is perpendicular to the end faces 16 and parallel to the main planes 13, 14. The plane S2 divides the thickness D and, accordingly, the end faces 16 of the plate 2 into two equal parts.

[0039] The dashed lines 17 and 18 illustrate the intersection of the symmetry planes S1 and S2 with the surfaces 13, 14, 15, 16 of plate 2. The two planes S1 and S2 divide plate 2 into the four equal volume areas 19, 20, 21 and 22.

[0040] Figure 4 shows the ultrasonic actuator according to Fig. 3 with a friction element 3 arranged on one of its end faces 16.

[0041] The plate 2 of the ultrasonic actuator 1 is divided into four equal or identical volume areas 19, 20, 21 and 22, each volume area together with Figure 4Not shown, corresponding electrodes form a generator G1, G2, G3, G4 for generating acoustic standing waves and for generating static bending deformations. The respective generator G1, G2, G3, G4 can be formed by the entire volume of the corresponding volume region 19, 20, 21, 22, or only by a part of the corresponding volume region.

[0042] Figure 5 shows in figures 23 to 26 different views of an ultrasonic actuator according to the Figures 3 and 4 with a possible embodiment for the electrodes of the ultrasonic actuator.

[0043] While illustrations 23 and 26 show the electrode structure on the side surfaces 15, illustrations 24 and 25 illustrate the electrode structure on the main surfaces 13 and 14.

[0044] The individual generators G1, G2, G3, and G4 comprise strip-shaped excitation electrodes 27 and strip-shaped general electrodes 28 arranged on the main surfaces 13 and 14 of the plate 2, with piezoelectric and piezoceramic material located between adjacent strip-shaped electrodes 27 and 28, respectively. The arrows with the index p indicate the polarization direction of the piezoceramic between the electrodes 27 and 28.

[0045] The generator G1 comprises strip-shaped excitation electrodes 27 and strip-shaped general electrodes 28, which are arranged on the main surface 13 and can be assigned to the volume region 19, as well as the piezoceramic material which is arranged between the strip-shaped electrodes 27 and 28.

[0046] The generator G2 comprises strip-shaped excitation electrodes 27 and strip-shaped general electrodes 28, which are arranged on the main surface 13 and can be assigned to the volume region 20 of the plate 2, as well as the piezoceramic arranged between the electrodes 27 and 28.

[0047] The generator G3 comprises strip-shaped excitation electrodes 27 and strip-shaped general electrodes 28, which are arranged on the main surface 14 and can be assigned to the volume region 21 of the plate 2, as well as the piezoceramic arranged between the electrodes 27 and 28.

[0048] Finally, the generator G4 comprises strip-shaped excitation electrodes 27 and strip-shaped general electrodes 28, which are arranged on the main surface 14 and can be assigned to the volume region 22 of the plate 2, as well as the piezoceramic arranged between the electrodes 27 and 28.

[0049] The strip-shaped excitation electrodes 27 of the generator G1 have the terminal 29 arranged on the side surface 15, while the strip-shaped excitation electrodes 27 of the generator G2 have the terminal 30 arranged on the same side surface 15.

[0050] The strip-shaped excitation electrodes 27 of the generator G3 have the terminal 31, and the strip-shaped excitation electrodes 27 of the generator G4 have the terminal 32, wherein both terminals 31 and 32 are arranged on the same side surface 15, which is opposite the side surface on which the terminals 29 and 30 are arranged.

[0051] The general strip-shaped electrodes 28 have the terminal 33, which is arranged on both side surfaces 15.

[0052] All strip-shaped electrodes 27 and 28 are arranged parallel to the symmetry plane S1, and the polarization direction of the piezoceramic of the piezoelectric plate 2 between the electrodes 27 and 28 is perpendicular to the electrodes 27 and 28.

[0053] The distance k between adjacent strip-shaped excitation electrodes 27 and strip-shaped general electrodes 28 is equal to or smaller than half the thickness D of the piezoelectric plate 2.

[0054] The width m of the strip-shaped electrodes 27 and 28 is in the range between 0.1 and 0.5 mm.

[0055] The strip-shaped electrodes 27 and 28 can be applied to the main surfaces 13 and 14 of the plate 2 by a chemical deposition process of nickel, or by vacuum deposition, or by thermal deposition of chromium, copper, or nickel, or by ion plasma sputtering of chromium, copper, nickel, or gold. The structure of the strip-shaped electrodes 27 and 28 can be created by laser milling, lithographic-chemical etching, spraying, or a mask printing process.

[0056] The number of strip-shaped electrodes 27 and 28 on the surfaces 13 and 14 is limited only by the technological manufacturing possibilities.

[0057] For the generators G1, G2, G3 and G4 with the strip-shaped excitation electrodes and the general electrodes 27 and 28 according to Figure 5 The piezoelectric coefficient d 33 is used to excite the acoustic standing waves in the ultrasonic actuator.

[0058] Figure 6 shows in figures 34 to 37 different views of an ultrasonic actuator according to the Figures 3 and 4 with a further embodiment for electrodes arranged on the ultrasonic actuator.

[0059] Illustration 34 of Figure 6 shows a side view of the ultrasonic actuator, Figure 35 shows the view of the underside of the ultrasonic actuator, Figure 36 shows the view of the top of the ultrasonic actuator and Figure 37 shows the view of the side surface 15 which is opposite to the side surface shown in Figure 34.

[0060] In this exemplary embodiment of an ultrasonic actuator of an ultrasonic motor according to the invention, the individual generators G1, G2, G3 and G4 comprise flat excitation electrodes 38, flat general electrodes 39 and the piezoceramic material arranged between the electrodes.

[0061] The flat excitation electrodes 38 are arranged on the main surfaces 13 and 14 at a distance from each other, while the flat general electrode 39 is arranged on the inner surface 40 of the piezoelectric plate 2, which coincides with the longitudinal plane of symmetry S2.

[0062] The polarization directions of the piezoelectric material of the ultrasonic actuator are perpendicular to the flat electrodes 38 and 39.

[0063] The generator G1 comprises the planar excitation electrode 38 arranged on the main surface 13, which can be assigned to the volume region 19 of the plate 2, and the section of the planar general electrode 39 arranged on the inner surface 40, which can be assigned to the volume region 19.

[0064] The generator G2 comprises the planar excitation electrode 38 arranged on the main surface 13, which can be assigned to the volume region 20 of the plate 2, and the section of the planar general electrode 39 arranged on the inner surface 40, which can be assigned to the volume region 20.

[0065] The generator G3 comprises the planar excitation electrode 38 arranged on the main surface 14, which can be assigned to the volume region 21 of the plate 2, and the section of the planar general electrode 39 arranged on the inner surface 40, which can be assigned to the volume region 21.

[0066] The generator G4 comprises the planar excitation electrode 38 arranged on the main surface 14, which can be assigned to the volume region 22 of the plate 2, and the section of the planar general electrode 39 arranged on the inner surface 40, which can be assigned to the volume region 22.

[0067] The flat excitation electrodes 38 of the generators G1, G2, G3 and G4 each have a substantially centrally arranged electrical connection 41, 42, 43 and 44, while the flat general electrode 39 has two electrical connections 45, each of the electrical connections being arranged on a side surface 15.

[0068] In the embodiment of the generators G1, G2, G3 and G4 with flat excitation electrodes 38 and flat general electrodes 39 according to Figure 6 The piezoelectric coefficient d 31 is used to excite the acoustic standing waves.

[0069] The flat excitation electrodes 38 can be manufactured from the materials and according to the technologies as previously described for the strip-shaped excitation electrodes and general electrodes with regard to Figure 5 described.

[0070] The flat general electrodes 39 are located on the inner surface 40 and can be made of copper, silver, palladium, or an alloy in an inert gas atmosphere by a synthesis process together with the piezoceramic of the piezoceramic plate 2. The flat general electrodes 39 can also be made of electrically conductive ceramic.

[0071] Illustration 46 of Figure 7 shows in perspective view the ultrasonic actuator according to Figure 5 with friction element 3 arranged on one of its end faces 16, while illustration 47 of Figure 7 in perspective view the ultrasonic actuator according to Figure 6 with friction element 3 arranged on one of its end faces 16. It can be seen that in both cases the friction element 3 is arranged essentially centrally with respect to the thickness D and extends over the entire width B of the ultrasonic actuator 1.

[0072] Illustration 48 of Figure 8 shows an electrical circuit for operating the ultrasonic actuator 1 according to Figure 5 with the method according to the invention, wherein the ultrasonic actuator 1 has strip-shaped excitation electrodes 27 and strip-shaped general electrodes 28, and the electrical circuit comprises isolating capacitors C1, C2, C3 and C4 and isolating resistors R1, R2, R3 and R4.

[0073] The capacitance of the isolation capacitors C1, C2, C3 and C4 is preferably equal to or greater than the electrical capacitance Co of the actuator 1 between the electrodes 27 and 28 of the generators G1, G2, G3 and G4.

[0074] The isolation resistors R1, R2, R3 and R4 preferably have a value 5 to 10 times greater than the characteristic resistance Xo of the capacitance Co, with Xo=1 / 2pFgCo, where Fg is the operating frequency of the ultrasonic motor.

[0075] Illustration 49 of Figure 8shows a block diagram relating to an electrical excitation device 50 for carrying out the method according to the invention.

[0076] The excitation device 50 comprises a single-phase generator 51 for an alternating electrical voltage U1 at the terminal 52, a changeover switch 53 with the terminals 54, 55 and 56, an electrical generator 57 for a static electrical control voltage Es at the terminal 58, linear amplifiers 59 and 60 for a static electrical voltage with the terminals 61 and 62, to which the static electrical voltages E1 and E2 are applied and a controller 63 with an input 64.

[0077] All blocks of the excitation device 50 have the general output 65.

[0078] By means of the excitation device 50, control can be carried out both in the dynamic regime (dynamic operating mode) and in the static regime (static operating mode).

[0079] With a dynamic single-phase control according to Figure 8 or Figure 15 the generator 51 provides the single-phase alternating electrical voltage U1 with the frequency Fg, which is equal to the frequency Fp2 or equal to the frequency Fp1 or which is between these frequencies or close to these frequencies.

[0080] On the one hand, the voltage U1 is applied via terminal 54 of the switch 53 and the capacitors C1 and C4 to the terminals 29 and 32 of the excitation electrodes 27 of the generators G1 and G4. On the other hand, the voltage U1 is applied via the common output 65 to the input 33 of the common electrodes 28 of the generators G1 and G4.

[0081] The voltage U1 dynamically controls the generators G1 and G2, whereby these generators simultaneously generate in actuator 1 the second mode of an acoustic bending standing wave, which propagates along the length L and along the thickness D (see also illustrations 66 and 67 in Figure 9), and the first mode of an acoustic longitudinal standing wave propagating along the length L (see figures 68 and 69 of Figure 9 ), generate.

[0082] The dotted lines in Figures 66 and 67 of Figure 9 show the shape of the maximum deformation of plate 2 when the second mode of the acoustic bending standing wave propagates in it.

[0083] The dotted lines in Figures 68 and 69 of Figure 9 show the shape of the maximum deformation of plate 2 when the first mode of the acoustic longitudinal standing wave propagates in it.

[0084] The superposition of the bending standing wave and the longitudinal standing wave results in the point 70 (as well as other points) of the friction surface 71 of the friction element 3 moving continuously on an elliptical trajectory 72 in the direction indicated by the arrows and the index +Vd, as shown in Figure 10The shape of the ellipse and its inclination to the friction surface 4 depend on the selected ratio L / D.

[0085] The elliptical movement paths 72 of the point 70 and the other point-forming surfaces of the friction element 3 are perpendicular to the main surfaces 13 and 14 of the piezoelectric plate 2 of the actuator 1.

[0086] Since the friction surface 71 of the friction element 3 is pressed by a force F against the friction surface 4 of the element 5 to be driven, the elliptical movement path 72 leads to a continuous movement of the element 5 to be driven in the direction indicated by the arrow with the index +Vd.

[0087] When the changeover switch 53 is moved to the contact position with the terminal 56 (dotted line in Figure 49 of Figure 8), the electrical voltage U1 reaches the terminals 30 and 31 of the electrodes 27 and 28 of the generators G2 and G3, whereby these generators are dynamically excited.

[0088] As a result, the generators G2 and G3 simultaneously generate in actuator 1 the second mode of the acoustic bending standing wave, which extends along the length L and along the thickness D (see figures 66 and 67 of Figure 9 ) and the first mode of the acoustic longitudinal standing wave, which propagates along the length L (see figures 68 and 69 of Figure 9 ) spreads.

[0089] When the switch 53 is actuated, the phase shift between the flexural standing wave propagating in actuator 1 and the acoustic longitudinal standing wave changes by 180°. This reverses the direction of movement of the points 70 on their trajectories 72, indicated by the arrow and index -Vd. This also reverses the direction of movement of the driven element 5. The driven element then moves in the opposite direction, indicated by the arrow and index -Vd.

[0090] The directions of movement of the element 5 to be driven (in the Figures 1, 2 , 10 , 12 and 18 shown with arrow and index V or Vd) run perpendicular to the main surfaces 13 and 14 of the piezoelectric plate 2 of the actuator 1.

[0091] In the dynamic operating mode of the method according to the invention, the drive path of the driven element 5 is in principle unlimited, while a minimum drive step of the driven element 5 is determined by the surface roughness of the friction surfaces 71 and 4 of the friction element 3 and the driven element 5. In the optimal case, the length of a drive step is between 0.05 and 0.1 µm.

[0092] The static operating mode of the method according to the invention is as follows: first, the dynamic operating mode is stopped by moving the changeover switch 53 into the contact position with the terminal 55. In this position of the changeover switch 53, the generators G1, G2, G3, and G4 are no longer dynamically controlled, since the electrical voltage U1 is not applied to the electrodes 27 and 28.

[0093] The dynamic electrical voltage generator 57 provides the static electrical control voltage Es at terminal 58, which can vary in the range from +Es through the value 0 to -Es. This voltage is amplified by the linear amplifiers 59 and 60.

[0094] As a result, the static electrical voltage E1 is present at terminal 61 of amplifier 59, which varies in the range from +E through the value 0 to -E. The inverted static electrical voltage E2 is present at terminal 62 of amplifier 60, which varies in the range between -E and +E.

[0095] On the one hand, voltage E1 is applied via resistors R1 and R2 to terminals 29 and 30 of excitation electrodes 27 of generators G1 and G2. On the other hand, voltage E1 is applied via common terminal 65 to terminal 33 of common electrodes 28 of generators G1 and G2.

[0096] Furthermore, the voltage E2 reaches the terminals 29 and 30 of the excitation electrodes 27 of the generators G3 and G4 via the resistors R3 and R4, and on the other hand, the voltage E2 reaches the terminal 33 of the common electrodes 28 of the generators G3 and G4 via the common terminal 65.

[0097] The electrical voltages E1 and E2 applied to the generators G1, G2 and G3, G4 of the actuator cause the piezoelectric plate 2 to be statically bent or deformed, as can be seen from the dotted lines in Figures 73 and 74 of Figure 11 shown.

[0098] The direction of the static bending is determined by the polarity of voltage E1 relative to the polarity of voltage E2. The magnitude of the static bending is determined by the magnitude of the voltages E1 and E2.

[0099] If the stress E1 is equal to the stress +E and the stress E2 is equal to the stress -E, the plate 2 bends as shown in Figure 73 of Figure 11 shown. The point 70 on the friction surface 71 of the friction element 3 moves on the path 75 to the position 76, as in Figure 12 shown.

[0100] Since the friction surface 71 of the friction element 3 is pressed by a force F against the friction surface 4 of the element 5 to be driven, the displacement of the point 70 to the position 76 leads to a translation of the element 5 to be driven by the distance +d in the direction indicated by the arrow and index +Vs.

[0101] When the polarity is changed (E1 equals -E and E2 equals -E), the plate 2 bends as shown in Figure 74 of Figure 11 In this case, the point 70 on the friction surface 71 of the friction element 3 moves along the path 75 to the position 77 (see Figure 12 ).

[0102] The displacement of point 70 to position 77 results in a translation of the element 5 to be driven by the distance -d in the direction shown by arrow and index -Vs.

[0103] In the static operating mode of the method according to the invention, the maximum displacement is + / -d, i.e., the maximum step length of the driven element 5 is determined by the maximum value of the voltages E1 and E2. The maximum step length can reach values ​​between 0.1 and 1 µm.

[0104] The minimum step length is determined by the stiffness of the clamping elements 9. It can be in the range of 0.1 to 1 nm.

[0105] The dynamic operating mode of the method according to the invention can also be realized by means of a two-phase electrical voltage. The illustrations 78 and 79 of Figure 13show a corresponding electrical circuit or a corresponding block diagram.

[0106] In a two-phase control, the generator 80 provides two alternating electrical voltages U1 and U2 with the same frequency Fg for the terminals 81 and 82.

[0107] The voltages U1 and U2 are shifted from each other by the phase angle fg + / -90° or by a different angle.

[0108] On the one hand, the voltage U1 is applied via the terminal 81 and the capacitors C1 and C4 to the terminals 29 and 32 of the excitation electrodes 27 of the generators G1 and G4, and on the other hand, the voltage U1 is applied via the general terminal 65 to the terminal 33 of the general electrodes 28 of the generators G1 and G4.

[0109] Furthermore, the voltage U2 is applied via the terminal 82 and the capacitors C2 and C3 to the terminals 30 and 31 of the excitation electrodes 27 of the generators G2 and G3, and the voltage U2 is applied via the general terminal 65 to the terminal 33 of the general electrodes 28 of the generators G2 and G3.

[0110] Each of the two pairs of generators G1, G4 and G2, G3 simultaneously generates in actuator 1 the second mode of an acoustic bending standing wave, which is oriented along the length L and along the thickness D (see illustrations 66 and 67 in Figure 9 ) and the first mode of a longitudinal acoustic standing wave, which propagates along the length L (see figures 68 and 69 in Figure 9 ).

[0111] The superposition of acoustic bending standing wave and acoustic longitudinal standing wave results in the point 70 of the friction surface 71 of the friction element 3 moving continuously on the elliptical movement path 72, as in Figure 10This leads to a displacement or drive of the element 5 to be driven.

[0112] By reversing the phase shift angle fg, the direction of movement of the element to be driven is changed.

[0113] Furthermore, the method according to the invention can be used to implement the dynamic operating mode with a two-phase electrical voltage with independent simultaneous generation of acoustic standing waves by two pairs of generators, such as G1 and G3 and G2 and G4. The illustrations 83 and 84 of Figure 14 show a corresponding electrical circuit for this form of excitation.

[0114] In this case, generators G1 and G3 form antiphase generators, and generators G2 and G4 represent in-phase generators.

[0115] The generator pair G1, G3 generates in actuator 1 the second mode of an acoustic bending standing wave, which is propagated along the length L and along the thickness D (see figures 66 and 67 of Figure 9 ). The pair of generators G2, G4 generates in actuator 1 the first mode of an acoustic longitudinal standing wave, which propagates along the length L (see figures 68 and 69 of Figure 9 ) spreads.

[0116] The superposition of acoustic bending and longitudinal standing waves leads to the fact that the points 70 of the friction surface 71 of the friction element 3 are arranged according to Figure 10 move continuously on the elliptical movement path 72. This results in a drive movement of the element 5 to be driven.

[0117] The illustrations 85 and 86 of Figure 15show an electrical circuit for implementing the method according to the invention with an ultrasonic actuator 1, in which the generators G1, G2, G3 and G4 have flat excitation electrodes 38 and flat general electrodes 39 according to illustration 47 of Figure 7 The dynamic operating mode is achieved using the single-phase electrical voltage U1.

[0118] The functional principle of the circuit according to Figure 17 is analogous to that in Figure 8 functional principle shown.

[0119] The illustrations 87 and 88 of Figure 16 show an electrical circuit for realizing the dynamic operating mode of the method according to the invention by means of an electrical two-phase voltage U1, U2, wherein the generators G1, G2, G3, G4 of the controlled ultrasonic actuator 1 have flat excitation electrodes 38 and flat general electrodes 39.

[0120] The functional principle of the circuit in Figure 16is analogous to that in Figure 13 functional principle shown.

[0121] The illustrations 89 and 90 of Figure 17 show an electrical circuit for realizing the dynamic operating mode of the method according to the invention by means of an electrical two-phase voltage U1, U2, wherein the generators G1, G3 and G2, G4 are excited or stimulated independently of one another.

[0122] The functional principle of the circuit in Figure 17 is analogous to the one in Figure 14 functional principle shown.

[0123] Figure 18 shows an ultrasonic motor suitable for operation according to the method according to the invention, which has an additional ultrasonic actuator 91 in addition to the main ultrasonic actuator 1.

[0124] In this motor design, clamping elements 92, which are firmly connected to the motor housing 8, are used to secure actuators 1 and 91. Actuators 1 and 91 are pressed against the clamping elements 92 from two opposite sides by means of stops 93 and flat springs 94. Stops 93 contact actuators 1 and 91 at the minimum vibration velocities of the bending standing waves.

[0125] The friction elements 3 of the actuators 1 and 91 are pressed against the friction surface 4 of the element 5 to be driven by means of the spring 95, which acts on the actuators 1 and 91 via the levers 96 mounted in the axes 97.

[0126] This makes it possible to precisely balance the forces F which press the friction elements 3 of the actuators 1 and 91 against the friction surface 4 of the element 5 to be driven.

Claims

1. Method for operating an ultrasonic motor, comprising the steps of: - providing an ultrasonic actuator (1) made of piezoelectric or electrostrictive or magnetostrictive material in the form of a plate (2) whose width B is greater than its thickness D and smaller than its length L, and said plate (2) comprises two main faces (13,14), two side faces (15) extending along the length, and two end faces (16) extending along the width, and comprises a transverse plane of symmetry S1 which runs perpendicular to said main faces (13, 14) and said side faces (15) and parallel to said end faces (16), and a longitudinal plane of symmetry S2 which runs perpendicular to said side faces (15) and said end faces (16) and parallel to said main faces (13, 14), where a friction element (3) intended for contacting an element (5) to be driven is arranged on at least one of said end faces (16) of said ultrasonic actuator (1), and said ultrasonic actuator comprises four identical volume regions (19, 20, 21, 22) which are arranged symmetrically in relation to said transverse plane of symmetry S1 as well as symmetrically in relation to said longitudinal plane of symmetry S2, and each of said volume regions (19, 20, 21, 22) together with excitation electrodes (27, 38) and general electrodes (28, 39) arranged on and / or in said ultrasonic actuator (1) forms a generator (G1, G2, G3, G4) for forming acoustic standing waves as well as a generator (G1, G2, G3, G4) for forming static bending deformations; - providing an electrical excitation device (50) which delivers one electric alternating voltage U1 or two electric alternating voltages U1, U2 and two static electric voltages E1, E2; - applying said alternating voltage U1 to said electrodes (27, 28, 38, 39) of two of said four generators G1, G2, G3, G4 or applying one of said two alternating voltages U1, U2 to said electrodes (27, 28, 38, 39) of two of said generators G1, G2, G3, G4 and applying the other alternating voltage U1, U2 to said electrodes (27, 28, 38, 39) of said two other generators G1, G2, G3, G4 for forming an acoustic standing wave in said ultrasonic actuator in a dynamic operating mode, or applying one of said two static electric voltages E1, E2 to said electrodes (27, 28, 38, 39) of two of said four generators G1, G2, G3, G4 and applying said other static electric voltage E1, E2 to said electrodes (27, 28, 38, 39) of said other two generators G1, G2, G3, G4 for forming a static bending deformation in a static operating mode.

2. Method according to claim 1, characterized in that in the dynamic operating mode, when applying said two alternating voltages U1, U2, each of said two pairs of generators, to which the same alternating voltage U1, U2 is applied, forms an acoustic standing wave in said ultrasonic actuator (1) which corresponds to a superposition of the second mode of a bending standing wave and the first mode of a longitudinal standing wave.

3. Method according to claim 1, characterized in that in the dynamic operating mode, when applying said two alternating voltages U1, U2, one of said two pairs of generators, to which one of said alternating voltages U1, U2 is applied, forms an acoustic standing wave in said ultrasonic actuator (1) which corresponds to the second mode of a bending standing wave, and the other of said two pairs of generators, to which said other alternating voltage U1, U2 is applied, forms an acoustic standing wave in said ultrasonic actuator (1) which corresponds to the first mode of an acoustic longitudinal standing wave.

4. Method according to one of the preceding claims, characterized in that the static bending deformation of said ultrasonic actuator (1) takes place in a plane that runs substantially parallel to said end faces (16).