Ultrasonic actuator and motor having such an ultrasonic actuator

Abstract

The present invention relates to an ultrasonic actuator (1) in the form of a plate (2) having a bottom surface (3), a cover surface (4) geometrically similar to the bottom surface, and side surfaces (5) interconnecting the bottom surface and the cover surface, the plate comprising an electromagnetic material, electrodes (6, 6', 7, 7') for inducing periodic deformation of the plate arranged on the bottom surface of the plate and on the cover surface opposite the bottom surface of the plate, the bottom surface (3) having at least two faces (8, 8') arranged parallel to each other and forming contact portions (50, 50') of the lateral surfaces (5), the two parallel faces of the bottom surface together with connecting lines (9, 9') interconnecting the respective end points of the parallel faces (8, 8') form a parallelogram (10) inscribed in the bottom surface, within which angles different from 90° are enclosed between adjacent faces. The present invention also relates to a motor including such an ultrasonic actuator.

Description

[Technical field]

[0001] The invention, according to the general wording of claim 1, relates to an ultrasonic actuator in the form of a plate having a bottom surface, a cover surface geometrically similar to the bottom surface, and side or transverse surfaces interconnecting the bottom surface and the cover surface, the plate having an electromechanical material, electrodes being arranged on the bottom surface of the plate and on the cover surface opposite the bottom surface of the plate in order to excite a periodic deformation of the plate, the bottom surface having at least two parallel sides defining side contact sections, the two parallel sides of the bottom surface forming a parallelogram inscribed in the bottom surface together with connecting lines interconnecting the respective end points of the parallel sides. The invention further relates to a motor with such an ultrasonic actuator forming an ultrasonic motor.

[0002] In this context, the term "electromechanical material" as used above and below should be understood as a material that undergoes a mechanical deformation upon application of a voltage and the generation of a corresponding electric field. In particular, this includes materials with piezoelectric properties, such as piezoelectric ceramic materials, but also materials with electrostatic properties, for example.

[0003] Such ultrasonic actuators and ultrasonic motors incorporating them can be used in small, inexpensive devices that consume little energy, such as small cameras, lenses for mobile phones and smartphones, and small storage devices, which require small size, high positioning accuracy, and low energy consumption by the drive. [Background technology]

[0004] Ultrasonic actuators for ultrasonic motors are known from US 5 672 930 and US 5 665 918 and are designed as complex compound oscillators consisting of a resonator to which a piezoelectric excitation plate is bonded. The disadvantage of these actuators is that they have a relatively complex structure and are expensive to manufacture. They are therefore excluded as inexpensive, mass-produced products for use in small devices.

[0005] Furthermore, from document US6 765 335 B2, an ultrasonic actuator for ultrasonic motors is known, in which the resonator is formed as a rectangular piezoelectric plate. This ultrasonic actuator is characterized by a simple design and an easily controllable manufacturing technology, and for that reason seems suitable as a low-cost mass-produced product. However, the disadvantage of this ultrasonic actuator is found in the fact that a relatively high power is required for its operation, which leads to an increase in energy consumption. Therefore, such ultrasonic actuators are also excluded for use in small devices, in which a correspondingly low energy consumption is required.

[0006] The ultrasonic actuator known from EP 2 153 476 B1 may indeed solve the above problems in that it is of relatively simple design and at the same time has low power consumption with high operational stability or safety. Nevertheless, with the ultrasonic actuator disclosed in EP 2 153 476 B1, the realization of a corresponding ultrasonic motor is associated with higher costs, in particular with regard to the structure of the armature of such a motor. In this case, the realization of a constant contact force of the rotor against the ultrasonic actuator over the entire travel distance of the armature, which is necessary for a permanently reliable operation, proves to be rather costly. Summary of the Invention [Problem to be solved by the invention]

[0007] It is therefore an object of the present invention to provide an ultrasonic actuator which, in addition to a simple design and low electrical energy consumption, also has properties which enable the realization of a simply constructed but durably reliable motor which can be manufactured and assembled in an easy manner, in particular in large quantities, and which may have good scalability or miniaturization capabilities. [Means for solving the problem]

[0008] This object is solved by an ultrasonic actuator of the type mentioned at the outset, in which, with respect to a parallelogram inscribed in the base, angles deviating from 90 degrees are in any case included between abutting or adjacent or adjacent sides, i.e. the inscribed parallelogram is not a right-angled parallelogram.

[0009] Due to the specific shape of the inscribed parallelogram, the respective sides arranged parallel to one another cannot be completely overlapped by moving along the respective side normals, as in the case of a right-angled parallelogram. In other words, the normals passing through the centers of the respective corresponding sides do not intersect, but are arranged parallel and offset with respect to one another. In this case, if a force acts along the normal to the contact part or contact surface, for example due to the running surface of the mover, which is moved relative to the ultrasonic actuator, pressing against the contact part or contact surface formed by the corresponding side of the lateral surface of the ultrasonic actuator, a torque that tends to rotate the ultrasonic actuator is generated. The corresponding counter torque acting on the running surface may be used to generate a defined contact force of the guide part or guide part connected to or integral with the mover, against the guide element of the guide device. In this way, the mechanical preload on the ultrasonic actuator, which is necessary for an optimized operation of the corresponding ultrasonic motor, and the above-mentioned contact pressure of the guide part against the guide element of the guide device, preferably a sliding guide, can be realized simultaneously, for example via the running surface which is an integral part of the mover.

[0010] In this regard, it may be advantageous for the larger interior angle of the inscribed parallelogram to have a value between 93° and 105°, preferably between 95° and 99°. The smaller interior angle of the inscribed parallelogram therefore has a value between 87° and 75°, preferably between 85° and 81°. With such a geometry of the inscribed parallelogram, in the case of a corresponding ultrasonic motor, in which the running surface of the mover is pressed against the contact part of the ultrasonic actuator, a counter torque can be applied to the guide device connected to the mover, which is favorable for a permanent and reliable operation of the ultrasonic motor, whereas with smaller values ​​of the larger interior angle, a torque or counter torque sufficient for this purpose may no longer be achieved. Larger values ​​of the larger interior angle result in less stable and less defined vibrations of the ultrasonic actuator, which in turn results in a lower positioning accuracy and in a more irregular drive with the corresponding ultrasonic motor.

[0011] It may be advantageous that the base, or the cover surface arranged parallel thereto and geometrically similar and preferably of the same shape, is an octagon, and in any case that a trapezoid, preferably an isosceles trapezoid, borders on both sides of the inscribed parallelogram, the base of each trapezoid coinciding with the respective long side of the inscribed parallelogram. The resulting prismatic shape of the ultrasonic actuator allows a particularly effective excitation of deformations available for driving the mover at a relatively low material cost.

[0012] In the case of isosceles trapezoids, it may be advantageous for the length of the diagonal of one trapezoid to be substantially the same as the distance between the base of the trapezoid and the side opposite it or between the base of the other trapezoid. These geometric ratios result in an ultrasonic actuator whose width is less than twice its height and therefore has a relatively small footprint, thereby requiring less material. In addition, such geometric ratios of the ultrasonic actuator result in a third dimension being superimposed on the vibration mode used. One dimension of the vibration mode can be suppressed by external influences without the used vibration mode disappearing. This increases the overall robustness of the motor against external influences and the mechanical environment of the actuator.

[0013] The present invention further relates to a motor having an ultrasonic actuator as described above, comprising a mounting device for fixedly mounting the ultrasonic actuator, and a mover that is movable relative to the ultrasonic actuator and is in direct or indirect frictional contact with the ultrasonic actuator, the mounting device comprising at least four retaining portions that contact the ultrasonic actuator in different areas, of which two retaining portions are mechanically rigid and form rigid retaining portions and two retaining portions have elastic properties and form elastic retaining portions.

[0014] In this case, it may be advantageous for the rigid retaining portion and the elastic retaining portion, respectively, to be arranged diagonally opposite one another.

[0015] In addition, the mounting device may advantageously include two further retaining portions each contacting a side area of ​​the ultrasonic actuator located between the side areas of the ultrasonic actuator contacted by the respective rigid retaining portion and the respective elastic retaining portion.

[0016] In one embodiment, the motor may be configured such that the mover comprises two elongated parallel running surfaces which directly or indirectly contact the ultrasonic actuator at the contact portions and clamp it therebetween. As a result of the clamping force introduced through the contact portions, a torque acts on the ultrasonic actuator due to the specific geometry of the ultrasonic actuator, whereby the ultrasonic actuator is pressed against the respective rigid retaining portions of the mounting element at the respective portions of the lateral surfaces.

[0017] In this case, it may be advantageous for the mover to include a guide part with at least two guide parts spaced apart from one another, the guide parts being engaged with guide elements or guide parts enabling the sliding movement. In the case of guide elements, these are present separately, in the case of guide parts, these are preferably an integral part of the mounting device. The guide parts are preferably formed integrally with the guide part, and the guide parts are preferably formed integrally with the mover.

[0018] In the following, embodiments of an ultrasonic actuator and a corresponding motor according to the present invention will be described with reference to the corresponding figures, in which the same reference numbers refer to the same parts in the different figures. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a top view of the bottom surface of an ultrasonic actuator according to the present invention. [Figure 2A] 2 is a different perspective view of the ultrasonic actuator according to FIG. 1; FIG. [Figure 2B] 2 is a different perspective view of the ultrasonic actuator according to FIG. 1; FIG. [Diagram 3] FIG. 3 is a perspective view of an embodiment of a motor having an ultrasonic actuator according to FIGS. 1 and 2; [Figure 4] FIG. 4 is a diagram of a mounting device for an ultrasonic actuator of the motor according to FIG. 3. [Diagram 5] FIG. 4 is a side view of the motor according to FIG. [Figure 6]FIG. 3 is a perspective view of an embodiment of a motor having an ultrasonic actuator according to FIGS. 1 and 2; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] 1 shows in plan view the bottom surface 3 of an ultrasonic actuator 1 according to the invention, which has the shape of an octagonal plate 2 or an octagonal prism, so that the cover surface opposite the bottom surface 3, which is not visible in FIG. 1, has the same shape as the bottom surface 3, and the side surface 5 connecting the bottom surface 3 and the cover surface is arranged perpendicular to the bottom surface 3 and perpendicular to the cover surface. However, it is also conceivable that embodiments of the ultrasonic actuator 1 differ from one another in the shape of the bottom surface 3 and the shape of the cover surface with geometric similarity, so that the side surface 5 is not arranged perpendicular to the bottom surface 3 or the cover surface.

[0021] The octagonal shape of the base 3 and the corresponding prismatic shape of the ultrasonic actuator result in a side surface 5 having eight mutually distinguishable sections, with sides 8 and 8' forming contact portions 50 and 50' of the side surface 5. The contact portions 50 and 50' are provided to come into direct or indirect contact with elements of a corresponding ultrasonic motor driven by the ultrasonic actuator.

[0022] Two of the short sides of the base 3, namely sides 8 and 8', are arranged parallel to each other at a distance, and sides 8 and 8' cannot be completely overlapped by moving the sides along their respective side normals. In other words, sides 8 and 8' are arranged offset from each other when viewed in their direction of extension. Similarly, two connecting lines 9 and 9' interconnecting the corresponding end points of sides 8 and 8' respectively, result in a parallelogram 10 inscribed in the base 3, which is not a rectangle or in which adjacent or abutting sides enclose an angle between them that deviates from 90°. In this case, the two larger angles 11 of the parallelogram are 97°, and as a result, the smaller angle of the parallelogram is 83°.

[0023] On both sides of the inscribed parallelogram 10, with respect to the base 3, the respective isosceles trapezoids 12, 12' are adjacent, and their respective bases 13, 13' coincide with the respective long sides of the inscribed parallelogram 10 corresponding to the respective connecting lines 9, 9'. The length of each diagonal 14 of the trapezoids 12, 12' is substantially the same as the shortest distance 15 between the side 16, 16' facing the base 13, 13' of one trapezoid and the base 13, 13' of the other trapezoid 12, 12'. In this case, the side 16, 16' also represents the short side of the shape of the base 3 and is arranged parallel to the base 13, 13' of the respective trapezoid 12, 12'.

[0024] Due to the fact that the inscribed parallelogram 10 deviates from a right-angled parallelogram, the side normals extending from the midpoints of the sides 16, 16' of each right-angled trapezoid that are opposite and parallel to the bases 13, 13' do not intersect but extend parallel to and spaced apart from each other.

[0025] 2A shows the ultrasonic actuator 1 according to FIG. 1 in a perspective view directed mainly towards the bottom face 3. Two identically formed electrodes 6 and 6' arranged in mirror images of each other are located on the octagonal bottom face 3 and are separated from each other by an intervening gap and are thereby electrically insulated from each other. In addition to the contact portions 50 and 50' formed by the sides 8 and 8' of the bottom face 3, the long sides of the bottom face 3 form portions 52, 52', 54 and 54' of the side faces 5, and the remaining two short sides 16 and 16' of the bottom face 3 form or define portions 56 and 56' of the side faces 5.

[0026] FIG. 2B shows the ultrasonic actuator of FIG. 1 in a different perspective view, so that here mainly the cover surface 4 can be seen. As on the bottom surface 3, two identically shaped mirror image electrodes 7 and 7' are located on the cover surface 4, which are also spaced apart from each other by an intervening separation gap and are therefore electrically insulated from each other. The two electrodes 7 and 7' on the cover surface are arranged in a mirror image with respect to the two electrodes 6 and 6' mounted on the bottom surface 3. It is also conceivable to arrange more than two electrodes on the bottom surface 3 and the cover surface 4, respectively. Furthermore, it is conceivable that the number of electrodes on the bottom surface and the number of electrodes on the cover surface are different, for example, two electrodes may be arranged on the bottom surface, while only one electrode may be arranged on the cover surface.

[0027] The contact parts 50, 50' represent corresponding surfaces of the ultrasonic actuator 1 and may be in direct contact with an element, such as a mover, that is moved or adjusted relative to the ultrasonic actuator 1. However, since direct contact may lead to increased wear of the electromechanical material of the ultrasonic actuator 1, which usually has rather poor frictional properties, it is preferred that the contact parts 50 and 50' are provided with friction elements optimized in terms of friction and wear properties. In the presence of friction elements arranged in the contact parts 50 and 50', an indirect contact is achieved between the contact parts 50 and 50' of the ultrasonic actuator and the element that is moved or adjusted relative to the ultrasonic actuator 1.

[0028] Figure 3 is a perspective view of a potential embodiment of a motor 100 realized as a linear drive with an ultrasonic actuator 1 according to Figures 1 and 2. Here, the ultrasonic actuator is inserted into a mounting device 110, which itself is connected in a manner not visible in Figure 3 to a higher stationary element, for example a base, whereby a stationary mounting of the ultrasonic actuator is achieved.

[0029] The mover 120 is arranged movably opposite or relative to the ultrasonic actuator in the form of a spatially structured sheet, and two elongated running surfaces 122, 122' are integrally formed with the mover 120 and arranged parallel to each other, which indirectly contact the contact portions 50, 50' of the ultrasonic actuator via friction elements not visible in FIG. 3.

[0030] Due to its special design, the mover 120 is endowed, inter alia, with specific elastic properties, so that the running surfaces 122, 122' after the insertion of the mounting device 110 into the mover 120 are pressed with a defined force against the friction elements or contact parts 50, 50'. This force ensures, on the one hand, that the ultrasonic actuator receives a preload necessary for a reliable and defined operation, and, on the other hand, due to the geometry of the ultrasonic actuator according to the invention, that the ultrasonic actuator is subjected to a torque in the counterclockwise direction, thereby pressing the ultrasonic actuator firmly against the mounting device 110, so that the ultrasonic actuator is held firmly in the mounting device 110.

[0031] A torque applied to the ultrasonic actuator thus induces a counter-clockwise torque, which acts on the mover 120. Designed integrally with the mover 120 are two guide parts 125 and 125' which are spaced apart from one another and have different shapes, as well as two bearing parts 126 and 126' which are arranged opposite one another and are not visible in Fig. 3. It is also conceivable to provide the guide parts 125, 125' and / or the bearing parts 126, 126' as separate components and to connect them to the mover 120, for example by means of a screw or adhesive connection.

[0032] The guide portions 125, 125' are in sliding engagement with two round bar-like guide elements 130, 130' made of steel and arranged parallel to each other. It is also conceivable to use ceramic guide elements 130, 130' as well. The guide part 124 with its guide portions, together with the guide elements 130, 130', forms a sliding guide, which serves to compensate for the friction already generated by the shape of the running surfaces 122, 122' and their contact conditions with the friction elements of the ultrasonic actuator, making the linear motion of the mover 120 more accurate.

[0033] The counter torque acting on the mover 120 ensures that the guide portions 125 and 125' are in a defined contact with the upper guide element 130 of FIG. 3. The guide portions 125 and 125' each have an opening through which the guide element 130 protrudes. The cross section of the guide portions 125, 125' is not circular, but each has a V-shaped area, two sides of which serve to support the guide element 130. In the case of the guide portion 125 on the left side of FIG. 3, the V-shaped portion points downwards, whereas in the case of the guide portion 125' on the right side of FIG. 3, the V-shaped portion points upwards. Now, the counter torque acting on the mover 120 supports the V-shaped portions or their sides of the guide portions 125, 125' with a defined force against the guide element 130, so that at the same time a defined mutual alignment is achieved between the guide element 130 and the guide portions 125, 125'.

[0034] The force with which the sides or legs of the V-shaped areas of the guide parts 125, 125' are pressed against the guide element 130 can be influenced by the forces acting on the ultrasonic actuator 1 through the running surfaces 122, 122' of the mover 120, which mainly depend on the elastic properties of the sheet metal of the mover 120, its geometry and the geometry of the ultrasonic actuator. The higher these forces and, as a result, the torque acting on the ultrasonic actuator, the higher the corresponding counter torque acting on the mover. Now, the further away the guide parts 125, 125' are from each other, the lower the contact force of the sides or legs of the V-shaped areas of the guide parts 125, 125' against the guide element 130 due to the increasing lever length. The adjustment of these contact forces can therefore be achieved by the spacing of the guide parts 125, 125'.

[0035] The thus formed plain bearings or sliding guides are easy to assemble, relatively simple to realize and therefore generally cost-effective. The contact forces may be adjusted in particular so that low frictional resistances arise, within which the ultrasonic actuators must function. At the same time, such sliding guides can withstand high mechanical loads and exhibit high running precision.

[0036] Figure 4 shows only the mounting device 110 with the ultrasonic actuator 1 according to Figures 1 and 2 inserted in an isolated manner and thus as a detail of the motor according to Figure 3. The mounting device 110 made of polyetheretherketone (PEEK) has a total of six holding parts 111, 111', 112, 112', 113, 113', which contact the ultrasonic actuator at different parts 52, 52', 54, 54', 56, 56' of its side surface 5 and thus clamp or hold the ultrasonic actuator firmly. Other materials for the mounting device 110 are likewise conceivable, in particular polymeric materials, such as polyoxymethylene (POM) or polyamide (PA).

[0037] The two retaining parts which contact the ultrasonic actuator at its longer side portions 52', 54 are designed to be mechanically less elastic and therefore more rigid, forming correspondingly rigid retaining parts 111, 111', whereas the two other retaining parts which likewise contact the ultrasonic actuator at different longer side portions 52, 54' are mechanically elastic and therefore have elastic properties, forming correspondingly elastic contact parts 112, 112'. The retaining parts 113, 113' contact the ultrasonic actuator at its shorter side portions 56, 56' and are also less mechanically elastic.

[0038] The force F acting on the two friction elements 20 from the running surfaces 122, 122' of the mover 120 is shown in Fig. 4, as is the torque M acting from it on the ultrasonic actuator 1, which tends to rotate the ultrasonic actuator counterclockwise. This torque M causes the side parts 52', 54 to be pressed more strongly against the rigid contact parts 111 and 111', while the contact parts 111 and 111' are supported more firmly. At the same time, the side parts 52, 54' tend to move away from the elastic contact parts 112, 112' due to the acting torque M, but their elastic properties ensure a constant contact with these side parts 52, 54', and the pressing force of the elastic contact parts 112, 112' against the side parts 52 and 54' is independent of the acting torque M.

[0039] FIG. 5 shows the motor of FIG. 3 in a side view, the line of sight coincides with the drive direction. Here, in particular, the cross-sectional shapes of the guide parts 125, 125' and the bearing parts 126 and their engagement with the guide elements 130, 130' are illustrated. The guide part 125 facing forward in FIG. 5 has a V-shaped part facing downwards, the guide element 130 rests on or is supported by both sides or legs of the V-shaped part. The guide part 125' facing backward in FIG. 5, which is only partially visible, has a V-shaped part facing upwards, the guide element 130 again rests on both sides or legs of this V-shaped part. The counter torque acting on the mover, due to the torque acting on the ultrasonic actuator via the mover, therefore serves to press and simultaneously align the guide element 130 in the guide parts 125, 125'. Opposite the guide parts 125 and 125' are the respective bearing parts 126, 126', of which only the forward-facing bearing part 126 is visible. It has a right-angled groove-shaped recess in which the guide element 130' is mounted with a clearance. The bearing part 126' has the same cross-sectional shape as the bearing part 126. The bearing parts 126 and 126' serve to prevent the bearing part 124 of the armature 120, which is fixedly connected thereto, from rotating around the guide element 130.

[0040] Figure 6 is a perspective view of a further possible embodiment of a motor 100 realized as a linear drive with an ultrasonic actuator 1 according to Figures 1 and 2. Here, the mounting device 110 is configured in the same way as in Figures 3 or 4 and comprises an elongated guide portion 116, 116' formed integrally therewith, against which guide portions 125, 125' in the form of curved or angled bars formed integrally with the mover 120 in the form of a spatially structured metal sheet are supported, of which only the guide portion 125 is visible in Figure 6. Taking over the function of the guide element 130 of Figures 3 and 5 by the guide portions 116, 116' formed integrally with the support device 110 allows a much more compact design of the motor with ultrasonic actuator according to the invention, which has fewer components and is also easier and faster to assemble. [Explanation of symbols]

[0041] List of reference symbols: 1: Ultrasonic actuator 2: Plate 3: Bottom surface (of plate 2) 4: Cover surface (of plate 2) 5: Side (of Plate 2) 6,6': Electrode 7,7': Electrode 8,8': Side (of base 3) 9,9': Connection wire 10: Parallelogram (inscribed in base 3) 11: The larger interior angle (of inscribed parallelogram 10) 12,12': Trapezoid (with base 3) 13,13': Base (of trapezoid 12,12') 14: Diagonal (of trapezoid 12, 12') 15: Distance (between sides 16, 16' opposite bases 13, 13' of trapezoids 12, 12' and the base of the other trapezoid) 16,16': (sides opposite to the bases 13,13' of the trapezoids 12,12') 20:Friction element 50: (Side 5) Contact part 52,52': (side 5) part 54,54': (side 5) part 56,56': (Side 5) part 100:Motor 110: Mounting device (for motor 100) 111, 111': rigid holding portion (of holding device 110) 112, 112': Elastic holding portion (of holding device 110) 113, 113': holding portion (of holding device 110) 116, 116': Guide portion (of holding device 110) 120: Mover 122, 122': running surface (of the movable element 120) 125, 125': Guide portion (of the mover 120) 126, 126': Bearing portion (of the mover 120) 130,130': Guide element

Claims

1. An ultrasonic actuator (1) in the form of a plate (2) having a bottom surface (3), a cover surface (4) that is geometrically similar to said bottom surface (3) and side surfaces (5) interconnecting said bottom surface (3) and said cover surface (4), said plate (2) comprising an electromechanical material, said electrodes (6, 6', 7, 7') being arranged on said bottom surface (3) of said plate (2) and on said cover surface (4) opposite said bottom surface (3) for exciting a periodic deformation of said plate (2), said bottom surface (3) having at least two sides (8, 8') arranged parallel to each other and forming contact portions (50, 50') of said side surfaces (5). the two sides of the base (3) arranged parallel to each other form a parallelogram (10) inscribed in the bottom (3) together with connecting lines (9, 9') connecting end points of the sides (8, 8') arranged parallel to each other, an angle other than 90° is defined between the abutting sides in the inscribed parallelogram (10), the base (3) is an octagon, trapezoids (12, 12') are in contact with each side of the inscribed parallelogram (10), and base sides (13, 13') of each trapezoid (12, 12') coincide with the respective long sides of the inscribed parallelogram (10).

2. 2. Ultrasonic actuator according to claim 1, characterized in that the larger interior angle (11) of the inscribed parallelogram has a value between 93° and 105°, preferably between 95° and 99°.

3. 2. An ultrasonic actuator according to claim 1, characterized in that each trapezoid (12, 12') is an isosceles trapezoid.

4. 4. The ultrasonic actuator according to claim 3, wherein the length of each diagonal (14) of the trapezoids (12, 12') is substantially the same as the distance (15) between the side (16, 16') opposite the base (13, 13') of one trapezoid (12, 12') and the base (13, 13') of the other trapezoid (12, 12').

5. A motor (100) comprising the ultrasonic actuator (1) according to any one of the preceding claims, a mounting device (110) for fixing and holding the ultrasonic actuator, and a mover (120) movable relative to the ultrasonic actuator (1) and in frictional contact with the ultrasonic actuator (1).

6. 6. The motor (100) of claim 5, characterized in that the mounting device (110) comprises at least four retaining portions (111, 111', 112, 112', 113, 113') which contact the ultrasonic actuator (1) at different portions (52, 52', 54, 54', 56, 56') of the side surface (5), two of the at least four retaining portions being mechanically rigid and forming rigid retaining portions (111, 111') and two of the at least four retaining portions having elastic properties and forming elastic retaining portions (112, 112').

7. 7. Motor according to claim 6, characterized in that the rigid retaining portion (111, 111') and the elastic retaining portion (112, 112') are respectively arranged diagonally opposite each other.

8. 8. Motor according to claim 6 or 7, characterized in that the mounting device (110) comprises two further retaining portions (113, 113') each in contact with one portion (56, 56') of a different portion (52, 52', 54, 54', 56, 56') of the side surface (5) of the ultrasonic actuator (1) located between the areas of the side surface (5) contacted by the respective rigid retaining portion (111, 111') and the respective elastic retaining portion (112, 112').

9. The motor according to any one of claims 5 to 8, characterized in that the mover (120) comprises two elongated, mutually parallel running surfaces (122, 122') which are in direct or indirect contact with the ultrasonic actuator (1) at their contact portions (50, 50') and clamp the ultrasonic actuator (1) between them so that a torque acts on the ultrasonic actuator (1), whereby in each case portions (52, 52', 54, 54') of the different portions (52, 52', 54, 54', 56, 56') of the side surfaces (5) which are in contact with a rigid retaining portion (111, 111') are pressed against the rigid retaining portion (111, 111').

10. The motor according to any one of claims 5 to 9, characterized in that the mover (120) includes at least two guide portions (125, 125') spaced apart from each other, which contact a separately provided guide element (130, 130') or a guide portion (116, 116') of the mounting device (110) to enable a sliding relative movement between the guide portions (125, 125') and the guide element (130, 130') or the guide portions (116, 116').

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