Piezo motor

0001The invention relates to a piezomotor consisting of at least one piezoelectric component connected to a resonator and a movable element interacting with the resonator.

0002Piezomotors of the type mentioned are known from the prior art created by the applicant. Here, piezoelectric components that perform mechanical vibrations when a suitable electrical voltage is applied are coupled to a resonator, which in turn rests against a movable element. The resonator converts the vibrations of the piezoelectric component into preferably elliptical vibrations of the contact area of ​​the resonator that touches the movable element. The movable element preferably moves in a first direction when a first voltage is applied at a first frequency, in a second, preferably opposite direction when a second voltage is applied at a second frequency.

0003With these piezomotors, with particularly low energy consumption and particularly inexpensive manufacture of the piezomotors, electrically operated actuating elements for the human ear can be moved silently over distances that can be set extremely precisely. These piezomotors are used when a compact design requires a motor with a small footprint, or when no or only small magnetic fields may arise during operation.

0004Piezomotors are mass-produced products that generate movement of individual elements in children's toys, for example, or that electrically extend or adjust a large number of components in vehicles, such as the ashtray or exterior mirrors.

0005The piezoelectric component and the resonator are exemplary in the <patcit id="pcit0001" dnum="DE10062672A1"><text>DE 100 62 672 A1</text></patcit> and the unpublished German patent application with the file number <patcit id="pcit0002" dnum="DE10141820"><text>101 41 820.5</text></patcit> described. The resonator is coupled to the piezoelectric component and transmits its vibrations to the movable element. The resonator preferably vibrates in the area of ​​its natural vibrations. An exemplary design of the piezo motor is already in the<patcit id="pcit0003" dnum="WO0141228A1"><text>WO 01 / 41228A1</text></patcit> or in the parallel application with the file number <patcit id="pcit0004" dnum="EP0103245W"><text>PCT / EP01 / 03245</text></patcit> described.

0006In the piezomotors commonly used, the excitation signal was transmitted to the piezoelectric component at such a frequency that the resonator is excited to self-oscillate. These resonance frequencies generate a high vibration amplitude and are therefore generally regarded as advantageous operating modes with advantageous performance features of the piezomotor. In this case, the forces and speeds occurring in the area of ​​the contact surface between the resonator and the movable element are understood as performance features.

0007In the series production of piezo motors, it is important to achieve high reproducibility of the vibration modes transmitted from the piezoelectric component to the resonator. In particular, the vibration modes in the area of ​​the contact surface between the resonator and the element that can be moved by the transmitted vibrations are of crucial importance.

0008The type of vibration modes on the contact surface is essentially dependent on the geometry of the resonator and the position and clamping of the piezoelectric component within the resonator. It has been shown in practice that in the production of piezomotors, the reproducibility of the desired operating modes and performance features of the piezomotor requires in many cases a reworking of the piezomotors.

0009It is therefore an object of the invention to provide a piezomotor which does not have the disadvantages of the prior art and to provide a method which substantially simplifies the manufacture of piezomotors and their excitation.

0010This object of the invention is achieved by the piezomotor with the features of claim 1. Advantageous embodiments of the invention can be found in the respective dependent claims.

0011The object is accordingly achieved with a piezo motor with at least one piezo element which is connected to a resonator and sets it in vibration and optionally an elastic element for pressing the resonator against an element to be driven, the resonator having a plane of symmetry and the resonator having at least two Operating frequencies (f₁, f₂) can be operated and the piezo element and / or the elastic element are arranged on the resonator in such a way that the plane of symmetry does not represent a plane of symmetry of the piezo motor, so that with the resonator the movable element at the two operating frequencies (f₁, f₂) can be driven in two opposite directions, and the piezo element protrudes from a main surface of the resonator parallel to this plane of symmetry, so that the piezo element is arranged eccentrically to at least one plane of symmetry of the resonate.

0012The upper operating frequency preferably does not exceed the lower operating frequency by more than 1.5 times.

0013The operating frequencies are preferably below half the frequency value which results from the wave propagation speed for longitudinal waves of the resonator material divided by the largest resonator dimension.

0014The resonator preferably has two main surfaces which are arranged substantially parallel to one another, are uniform and have the same size. A two-dimensionality of the resonator is thus achieved, in which the geometry does not change in a direction which is essentially perpendicular to the plane spanned by the main surfaces.

0015The person skilled in the art understands that the principle of two-dimensionality is also realized if transition areas, for example edges or corners, are chamfered or rounded off by production, post-processing or wear and an insignificant change in the geometry in the thickness direction can thus be determined.

0016The main surfaces of the resonator are those surfaces which are parallel to the planes spanned by the main axes of the resonator, that is to say its length and width axes.

0017Due to the comparatively simple, essentially two-dimensional geometric design of the resonator, it is possible to design the general structural conditions in such a way that the operating properties of the piezo motor can be predetermined with sufficient accuracy. This makes it possible to dispense with post-processing of the piezomotors and to reduce the reject rate to a minimum. It is also possible to generate a motor drive with small vibration amplitudes, which can preferably also be operated outside of its resonance frequencies. This eliminates the need for extensive post-processing of the piezo motors. In addition, a broadband excitation with less demands on the accuracy of the drive electronics can take place. It was therefore extremely surprising for the person skilled in the art that when a two-dimensional resonator geometry is implemented, a piezomotor can be produced in which a particularly complex control electronics system can be dispensed with.

0018This also results in the design of the piezo motor, the possibility of disregarding the known force-dependent shift of the resonance frequencies of the resonator upon contact with the movable element. Finally, the vibrations of the piezo motor are preferably almost independent of the contact of the resonator with the movable element.

0019In a preferred embodiment of the invention, the cross section of the resonator remains constant in a direction that is perpendicular to the main surfaces. This creates a particularly simple form of two-dimensionality in which the vibration behavior of the piezo motor can be changed, for example, particularly simply by changing the thickness of the resonator. As a result, the parameter space is restricted in such a way that a mathematical modeling and prediction about the vibration properties of the piezo motor is significantly facilitated.

0020In a preferred embodiment of the invention, the piezoelectric component is produced in a monolithic construction. In a particularly preferred embodiment of the invention, electrodes made of copper are introduced into this monolithic piezoceramic, which intermesh like a comb. Such piezoelectric components are in the German patent application with the file number<patcit id="pcit0005" dnum="DE10146704"><text>101 46 704.4 </text></patcit>described. This patent application is hereby also introduced as a reference and is therefore considered part of the disclosure. The ceramic is preferably made in one piece

0021The movable element can have any shape and can be moved as desired. For example, a rod-shaped element can be moved back and forth along its longitudinal axis. Likewise, a circular movable element can be rotated clockwise and counterclockwise about an axis of rotation. There is also no restriction on the material of the movable member. However, in the long-term frictional forces occurring at the contact surface between the resonator and the movable element, a material is advantageous that has a particularly long-term resistance to abrasion. In an advantageous embodiment of the invention, the movable element therefore consists of an at least partially fiber-reinforced plastic, preferably glass ball, mineral fiber, carbon fiber and / or glass fiber reinforced plastic. Carbon fiber is particularly advantageous because of the combination of high rigidity and conductivity that can be used to determine the position. In a particularly advantageous manner, this creates a device which, due to its low mass, has an equally low inertia.

0022The vibration behavior of the piezo motor depends both on the geometry of the resonator and the shape and position of the clamped piezoelectric component and on the manner in which it is suspended. The shape of the resonator is advantageously chosen so that the mechanical impedance, which represents a frequency-dependent relationship between the speed of the contact point to the movable element and the force acting there, is sufficiently large. The force acting on the movable element is particularly preferably so great that it has no significant influence on the vibrations of the resonator. In this particularly preferred case, the vibrations of the resonator according to the invention are largely decoupled from the influences of the contact with the movable element, that is to say independently of the movable element used or the load situation of the piezomotor.

0023Likewise, the vibration behavior of the resonator can be changed by the clamping of the piezoelectric component in the resonator and the relative position of the piezoelectric component and / or the clamping to the resonator. In a preferred embodiment of the invention, the piezoelectric component can be clamped in the resonator in such a way that the piezoelectric component is arranged eccentrically to at least one plane of symmetry or the resonator. As a result, the symmetry of the resonator is deliberately disturbed in such a way that operating modes arise which are neither categorized as purely longitudinal modes nor as torsion modes or bending modes. Such non-pure operating modes also occur in small piezomotors at low operating frequencies. There is thus preferably the possibility of using the vibrations that occur as operating modes even with small piezomotors and / or low operating frequencies, as a result of which different, preferably opposite, directions of propulsion of the movable element can be generated at two frequencies. The use of the non-pure vibration modes allows the frequencies to be advantageously placed close to one another, which is not possible for multiple directions with pure vibration modes and has advantages for the control. The symmetry of the piezo motor according to the invention can also or additionally be deliberately disturbed by an elastic element which is arranged asymmetrically with respect to the symmetry plane of the resonator.

0024These non-pure operating modes can also be generated by deliberately disturbing the symmetry of the resonator. The resonator of a piezo motor therefore often has no plane of symmetry or axis of symmetry. In a preferred embodiment of the invention, the resonator has an opening for receiving the piezoelectric component. The symmetry of the resonator is disturbed here by the position of this opening, the side walls delimiting the opening preferably having different cross sections at least over a partial length. In an extremely preferred embodiment of the invention, this is achieved in that the opening is arranged laterally offset from the longitudinal axis in the resonator.

0025In a further particularly preferred embodiment of the invention, the symmetry of the resonator is disturbed by the fact that at least one of the side walls delimiting the opening does not have a cross section which is constant in the longitudinal direction.

0026Likewise, in a further particularly preferred embodiment of the piezomotor according to the invention, at least one of the side walls in the longitudinal direction can be odd, in particular curved or undulating. In addition, in further particularly preferred configurations, the symmetry of the resonator is disturbed by attaching one or more additional masses or else additional stiffeners or weakenings. These particularly simple constructive measures also change the vibration behavior of the resonator in such a way that advantageous operating modes occur which cannot be classified as purely longitudinal, torsional or bending modes.

0027The symmetry of the resonator can also be disturbed by the type and position of the clamping of the piezoelectric component in the resonator. In a preferred embodiment of the invention, this clamping of the piezoelectric component does not take place over the entire width of the opening, but via comparatively small contact areas with the resonator. These contact surfaces are preferably arranged asymmetrically to the plane of symmetry of the resonator, wherein the piezoelectric component can be arranged symmetrically to the plane of symmetry of the resonator. As a result, a mounting of the piezoelectric component that is asymmetrical with respect to the plane of symmetry of the resonator is achieved in a particularly simple manner, in which the variation of the clamping takes place via a displacement of the contact surfaces protruding from the resonator and / or the piezoelectric component.

0028In a preferred embodiment of the invention, the piezomotor has a single piezoelectric component. In a particularly preferred embodiment of the invention, this piezoelectric component has two terminals via which one or more electrical excitation frequencies are transmitted to the piezoelectric component. A terminal in the sense of the invention is understood to be a coherent, electrically conductive area on or within the ceramic, on which the electrical potential is predetermined from the outside.

0029In a very particularly preferred embodiment of the invention, the piezoelectric components or the piezoelectric component are excited with exactly one signal. In an extremely preferred embodiment of the invention, the motor generates a macroscopic movement when activated with a sine or square wave signal. As a result, a particularly simple construction of a piezo motor according to the invention is preferably achieved, in which the drive electronics are also designed to be particularly simple and in which a macroscopic movement of the element to be driven is nevertheless achieved. The elaborate generation of the usual excitation signals which run essentially in the shape of a sawtooth can be dispensed with.

0030According to the invention, the element to be driven can be driven in two different directions at two different operating frequencies. In a particularly preferred embodiment of the invention, the contact surface swings in two different directions. In this way, a device is obtained which preferably allows the movable element to be moved back and forth by changing the operating frequency, without the need to guide the element to be driven.

0031It is an advantageous embodiment of the invention if the resonator at the contact point to the movable element executes vibrations with amplitudes in the same order of magnitude for both operating frequencies. This ensures that the movable element can be moved back and forth with the same large features as force or speed without additional control effort.

0032In a particularly advantageous embodiment of the invention, these vibrations have amplitudes of 50 nm-50 μm, preferably 500 nm-20 μm. In a very preferred embodiment of the invention, the amplitude of the vibrations is 1 µm - 5 µm. This enables a particularly advantageous utilization of the vibrations carried out by the resonator.

0033In an advantageous embodiment of the piezomotor according to the invention, the drive modes of the piezomotor have speed profiles in the contact area with the movable element for different directions of movement of the movable element that do not run parallel to one another. This ensures that the operating modes have different orientations at one or more points on the contact surface. The orientation of the operating modes is the spatial preferred direction of the movement of a material point, for example the semiaxis of an elliptical movement or the tangent to the trajectory when contact occurs between the resonator and the movable element.

0034In a particularly advantageous embodiment of the invention, the orientations of the operating modes span an angle of more than 30 ° and less than 150 °, preferably 70 ° to 110 °.

0035In a further advantageous embodiment of the invention, the movable element is driven in two opposite directions at two different frequencies, preferably two resonance frequencies. In this case it is advantageous if the phase of current and voltage falls within the resonance-antiresonance pairs corresponding to the resonance frequencies.

0036In the described resonance-anti-resonance pairs, it is observed that the amplitude ratio of current and voltage in the piezoelectric component having capacitive properties increases essentially linearly with frequency. In addition, due to the capacitive properties, there is a phase shift of current and voltage of 90 °. In the vicinity of an excitation frequency suitable for operation, the current rises disproportionately as a function of the frequency, then drops to zero and finally returns to the capacitive behavior.

0037In a particularly advantageous embodiment of the invention, the phase within the resonance-anti-resonance pairs drops by at least 30 °, preferably by more than 45 °, in particular by more than 60 °. In addition, in a very preferred embodiment of the invention, the phase drop is of the same order of magnitude for both resonance-antiresonance pairs.

0038The resonator is preferably pressed against the movable element via an elastic element, in particular a spring, wherein it is preferably ensured that the resonances of the elastic element, in which a large part of the kinetic energy of the piezo motor is absorbed by the elastic element, outside the operating frequencies for the piezomotor. This ensures that there is no so-called dynamic eradication, that is to say the counteraction of the resonance frequencies of the elastic element and of the resonator. Unwanted resonances of the suspension are thus excluded from the operating frequency ranges.

0039In a further advantageous embodiment of the invention, the largest proportion of the deformation energy generated during operation of the piezo motor is stored in the resonator at all operating frequencies. In this case, the resonator effectively acts as an energy store for the piezo motor. The energy component stored in the resonator is preferably at least 60%, particularly preferably at least 90%, of the mechanical energy generated during operation of the piezo motor.

0040In a preferred embodiment of the invention, a portion of at least 30%, preferably at least 60%, in particular at least 90% of the total energy is stored in those parts of the piezomotor according to the invention which can be easily manufactured in series. These are mainly the resonator and the spring. In particular, if the spring for suspending the piezo motor is additionally connected to a frame or the like, particularly good energy storage is provided if the transition from the spring to the frame is also designed to be reproducible. By storing the majority of the energy in the resonator, the spring and, if appropriate, the frame, it is possible to dispense with a particularly precise manufacture of the piezoelectric component without adverse effects on the reproducibility of the piezo motor.

0041The spring via which the piezomotor is connected to the suspension is preferably a leg spring. In a particularly preferred embodiment of the invention, the turns of this leg spring do not abut one another, so that the spring dissipates only little energy even in the case of large vibration amplitudes transmitted from the resonator to the spring. This is preferably also supported by the fact that the pitch of the spring windings exceeds the diameter of the spring wire by an amount that is greater than the vibration amplitudes that occur. Likewise, the spring can preferably be statically preloaded such that the spring windings expand under the load.

0042The wire of the spring can preferably also have an out-of-round cross section at least over a partial length. This ensures additional security against rotation with particularly simple means.

0043In a further advantageous embodiment of the invention, the mechanical impedances or admittances of the piezo motor, in particular at the contact point of the resonator with the movable element, are so great that the vibrations carried out by the resonator are independent of the size, shape, orientation and movement of the element to be driven .

0044In another advantageous embodiment of the piezomotor according to the invention, the drivable element is operated at two different operating frequencies (f₁, f₂), preferably resonance frequencies, driven in two opposite directions, the operating frequencies within two frequency intervals (Δf₁, Δf₂), which are both at a minimum distance (Δf) from each other and within a maximum interval width (Δf_Max), which in turn lies within the range of influence of the electrical resonance of a resonant circuit that the piezoelectric component forms with a coil in the control electronics.

0045This advantageously ensures that even with manufacturing tolerances and the resulting fluctuations in the operating frequency, it is ensured that an interval (Δf) is defined for each desired operating frequency, in which all piezo motors according to the invention in one series have exactly one of their operating frequencies, for example alone have the operating frequency for the forward drive of the movable element. In addition, when using an adaptive control electronics, which generates a broadband control signal, it is ensured that within a predetermined maximum frequency interval (Δf_Max) there is only one operating frequency that can be used to drive the drivable element. The risk of exciting a wrong resonance or several oppositely acting resonances with the same signal is thus reliably prevented.

0046However, the minimum distance between the operating frequency intervals is preferably also so small that the capacitive reactive component of the piezo motor can be compensated for by the inductance of a single coil of the control electronics. The maximum frequency interval (Δf_Max) for both operating frequencies is preferably so large that the intervals of both operating frequencies (Δf₁, Δf₂) lie within the resonance influence of a single electrical resonant circuit, which is formed by the inductively acting coil of the control electronics and the capacitively acting piezomotor. This makes it possible to manufacture the control electronics with particularly simple means.

0047In a particularly preferred embodiment of the invention, the control electronics together with the piezomotor generate an oscillating circuit with the frequency f_ethat in the frequency interval between f_e, and f_eh acts as a band stop. In a very particularly preferred embodiment of the invention, the control of the motor is particularly favorable if the following dependencies apply to the individual variables:<maths id="math0001"><math display="block"><msub><mi mathvariant="normal">f</mi><mi>el</mi></msub><mo mathvariant="normal">></mo><mn mathvariant="normal">2</mn><mo mathvariant="normal">/</mo><mn mathvariant="normal">3</mn><mo>⁢</mo><msub><mi mathvariant="normal">f</mi><mi mathvariant="normal">e</mi></msub><mspace width="1em" /><mi>and</mi><mspace width="1em" /><msub><mi mathvariant="normal">f</mi><mi>eh</mi></msub><mo mathvariant="normal"><</mo><mn mathvariant="normal">2</mn><mo>⁢</mo><msub><mi mathvariant="normal">f</mi><mi mathvariant="normal">e</mi></msub><mn mathvariant="normal">.</mn></math><img file="EP1520338B1_D0001.tif" /></maths>

0048The dependencies are particularly preferred for: <maths id="math0002"><math display="block"><msub><mi mathvariant="normal">f</mi><mi>el</mi></msub><mo mathvariant="normal">></mo><mn mathvariant="normal">4</mn><mo mathvariant="normal">/</mo><mn mathvariant="normal">5</mn><mo>⁢</mo><msub><mi mathvariant="normal">f</mi><mi mathvariant="normal">e</mi></msub><mspace width="1em" /><mi>and</mi><mspace width="1em" /><msub><mi mathvariant="normal">f</mi><mi>eh</mi></msub><mo mathvariant="normal"><</mo><mn mathvariant="normal">4</mn><mo mathvariant="normal">/</mo><mn mathvariant="normal">3</mn><mo>⁢</mo><msub><mi mathvariant="normal">f</mi><mi mathvariant="normal">e</mi></msub><mn mathvariant="normal">.</mn></math><img file="EP1520338B1_D0002.tif" /></maths>

0049In an extremely preferred embodiment of the invention, the dependencies are: <maths id="math0003"><math display="block"><msub><mi mathvariant="normal">f</mi><mi>el</mi></msub><mo mathvariant="normal">></mo><mn>6</mn><mo mathvariant="normal">/</mo><mn mathvariant="normal">7</mn><mo>⁢</mo><msub><mi mathvariant="normal">f</mi><mi mathvariant="normal">e</mi></msub><mspace width="1em" /><mi>and</mi><mspace width="1em" /><msub><mi mathvariant="normal">f</mi><mi>eh</mi></msub><mo mathvariant="normal"><</mo><mn mathvariant="normal">6</mn><mo mathvariant="normal">/</mo><mn mathvariant="normal">5</mn><mo>⁢</mo><msub><mi mathvariant="normal">f</mi><mi mathvariant="normal">e</mi></msub><mn mathvariant="normal">.</mn></math><img file="EP1520338B1_D0003.tif" /></maths>

0050As a result, control of the piezo motor can be set particularly well, and the power consumption is also particularly low.

0051In an advantageous embodiment of the invention, the operating frequency intervals Δf and an operating frequency f exist for the minimum distance₁ following dependencies: <maths id="math0004"><math display="block"><mn mathvariant="normal">0</mn><mo mathvariant="normal">,</mo><mn mathvariant="normal">025</mn><mo mathvariant="normal">⋅</mo><msub><mi mathvariant="normal">f</mi><mn mathvariant="normal">1</mn></msub><mo mathvariant="normal">≤</mo><mi mathvariant="normal">Δf</mi><mo mathvariant="normal">≤</mo><mn mathvariant="normal">1</mn><mo mathvariant="normal">⋅</mo><msub><mi mathvariant="normal">f</mi><mn mathvariant="normal">1</mn></msub></math><img file="EP1520338B1_D0004.tif" /></maths> and preferred <maths id="math0005"><math display="block"><mn mathvariant="normal">0</mn><mo mathvariant="normal">,</mo><mn mathvariant="normal">1</mn><mo mathvariant="normal">⋅</mo><msub><mi mathvariant="normal">f</mi><mn mathvariant="normal">1</mn></msub><mo mathvariant="normal">≤</mo><mi mathvariant="normal">Δf</mi><mo mathvariant="normal">≤</mo><mn mathvariant="normal">0</mn><mo mathvariant="normal">,</mo><mn mathvariant="normal">3</mn><mo mathvariant="normal">⋅</mo><msub><mi mathvariant="normal">f</mi><mn mathvariant="normal">1</mn></msub><mn>.</mn></math><img file="EP1520338B1_D0005.tif" /></maths>

0052In a preferred embodiment of the invention, the electromechanical coupling of the piezoceramic component to the vibrations of the resonator is for the respective operating modes, ie the distance between a resonance frequency f₁ or f₂ and the subsequent antiresonance frequency f in the frequency band₁'or f₂'At least 500 Hz, preferably more than 2 kHz, particularly preferably more than 5 kHz.

0053In a further preferred embodiment of the invention, the current consumption of the piezomotor is within said frequency intervals (Δf₁, vf₂) only at the maximum operating frequencies. This ensures an optimal efficiency of the piezo motor when excited with signals that are within the specified frequency interval.

0054In a particularly preferred embodiment of the invention, the distance between the different frequency pairs (f₁, f₁') and (f₂, f₂') of the same order of magnitude. In a further preferred embodiment of the piezo motor according to the invention, the resonator has in the range of an integer multiple of the frequencies (f₁, f₂) no resonances or resonances with only a small coupling and / or amplitude. This ensures that there are no or only slight harmful influences from the overtones of a non-harmonic electrical excitation of the piezo motor.

0055The ratio of the distance from f1 to f1 'to the distance f2 to f2' is preferably between 0.25 and 4.

0056In a further preferred embodiment of the piezomotor according to the invention, the electromechanical coupling factor (EMCF) of the individual resonance frequencies, in particular the operating modes of the piezomotor, is at least 0.01, preferably 0.04, in particular more than 0.1. In addition, it is advantageous if the coupling factor for both operating modes is of the same order of magnitude.

0057Another aspect is a method for producing resonators of a piezo motor according to the invention. The preferably essentially two-dimensional resonators are produced here, for example, by cutting a profile rod, which is produced, for example, during extrusion to length.

0058The manufacturing process for the piezomotors is significantly simplified by the use of the resonators, the shape of which is essentially only variable in two dimensions. The process offers a high degree of reproducibility of the desired vibration modes as well as a particularly low reject rate in production.

0059In an advantageous embodiment of the method, a preferably extruded profile rod is cut to length perpendicular to the longitudinal axis of the strand. In a particularly preferred embodiment of the method, however, the cutting takes place at an angle α &lt;90 ° from the longitudinal axis of the strand. In this way, resonators with an asymmetry with respect to the plane of symmetry can be produced in a particularly simple manner, the main surfaces of which are not perpendicular to one another and in which no right-angled transitions from the main to the side surfaces are realized.

0060The resonators can also be produced by cutting them out, preferably punching them out of sheet metal with a constant thickness. The cutting out, in particular punching out, is preferably carried out at an angle not equal to 90 °. As a result, a resonator can also be produced in a particularly simple manner in large numbers, in which the main surfaces are exactly parallel to one another and, however, the transitions from the main surfaces to the side surfaces are preferably not configured at right angles. As a result, the manufacture of resonators in which non-right-angled transitions from the main to the side surfaces are implemented is optimized in a particularly simple manner.

0061Finally, a further aspect is a method for excitation of the piezo motor according to the invention with control electronics, in which the excitation frequency is controlled on the basis of the current increase and / or the respective phase minimum and / or the phase change as a function of the frequency.

0062The control electronics searches for the most favorable excitation frequency for the piezomotor using the effect described above and known as a resonance-anti-resonance pair. In a preferred embodiment of the method according to the invention, the excitation frequencies are generated offset by the control electronics at defined intervals from the determined phase minimum.

0063In the case of piezomotors with a plurality of directions of movement, the excitation frequencies are preferably set such that the phase between the resonance-antiresonance pairs corresponding to the operating frequencies drops in each case by a sufficiently large amount.

0064The invention is described below with reference to <figref idref="f0001 f0002 f0003 f0004 f0005">Figures 1 - 6</figref> explained in more detail. However, the figures alone show exemplary embodiments of the invention and in no way limit the general inventive concept.<dl id="dl0001"><dt><b>Figure 1</b></dt><dd>shows a side view of a piezo motor according to the invention, which drives a wheel,</dd><dt><b>Figure 2</b></dt><dd>shows a section through the piezomotor and a plan view of a piezomotor according to the invention,</dd><dt><b>Figure 3</b></dt><dd>shows the representation of the vibrations of a resonator and a piezoelectric component clamped in the resonator in diagram form,</dd><dt><b>Figure 4</b></dt><dd>1 shows a first representation of the course of the force of the piezo motor according to the invention as a function of the frequency,</dd><dt><b>Figure 5</b></dt><dd>shows a representation of different curves of the force of a piezo motor according to the invention at different operating frequencies.</dd><dt><b>Figure 6</b></dt><dd>shows a representation of different versions of the resonator</dd></dl>

0065In <figref idref="f0001"><b>Figure 1</b></figref> a side view of a piezo motor 1 according to the invention is shown, which cooperates with a wheel 4 at the contact point 13 and can rotate the wheel 4 in two directions about the axis 5, which is perpendicular to the plane of the paper. The piezomotor 1 consists of a resonator 2 with two parallel and uniform main surfaces 6, 7, in which a piezoelectric component (not shown) is arranged. The resonator 2 is also connected via a spring 12 and a screw 10 to an indicated frame 18.

0066In <figref idref="f0002"><b>Figure 2</b></figref> a section through and a plan view of a piezomotor 1 according to the invention is shown. The resonator 2 has a symmetry plane 8. In the resonator 2 there is an opening 14 which is delimited by the side walls 25, 26. A piezoelectric component 3 is thus clamped between the contact surfaces 20, 21 within the opening 14. Furthermore, the resonator is connected to a leg spring 12. The piezoelectric component and the leg spring are arranged on the resonator in such a way that their symmetry has been deliberately disturbed, so that the plane of symmetry of the piezo motor (not shown) does not coincide with the plane of symmetry 8 of the resonator.

0067In <figref idref="f0003"><b>Figure 3</b></figref> The vibrations of the individual areas of a resonator 2 and a piezoelectric component 3 clamped in the resonator 2 are shown in vector form. In this illustration, the vectors have an x ​​and a y component. The orientation of the vibrations of the individual surface elements results from the alignment of the vectors; the length of the vectors is proportional to the amplitude of the vibrations. The vibrations carried out by the piezoelectric component 3 clamped within the resonator 2 are transmitted to the resonator 2 via the contact surfaces 20, 21. In this embodiment, the piezoelectric component 3 protrudes from the second main surface 16 of the resonator 2 facing the movable element (not shown). The vibration in the contact area 13 of the resonator 2 finally exerts the force necessary for the movement of the movable element (not shown), the points of the contact area can move on elliptical paths, the vectors then indicate the alignment of the major axes of these ellipses.

0068In <figref idref="f0004"><b>Figure 4</b></figref> the diagrammatic representation of a course of the force F exerted by a piezomotor according to the invention as a function of the excitation frequency f is shown. Components are not shown in this figure. The piezomotor 1 is designed in such a way that it operates in a frequency interval Δf₁ and a maximum at frequency f₁ a movement of the movable element with the maximum force F₁ generated. The piezomotor also generates at a frequency interval Δf₂ a movement of the movable element in the opposite direction and exercises at the frequency f₂ the maximum force F₂ out.

0069In <figref idref="f0004"><b>Figure 5</b></figref> a representation of different profiles of the force F of a piezo motor according to the invention at different operating frequencies f is shown. This representation indicates schematically that during series production of the piezo motors according to the invention, fluctuations in the thrust forces F also occur due to production fluctuations, which fluctuations can occur both at different frequencies f and at different maxima F. In general, however, the piezomotors produced and classified as functional have an operating frequency within the frequency interval Δf_f have. In this frequency range, the piezomotors must generate thrust in a first direction at at least one frequency in this range, the magnitude of this thrust having to be higher than F._f. Furthermore, the motors must within a further frequency interval Δf_b have a further operating frequency at which thrust is generated in a second direction, which is preferably opposite to the first direction. This boost must also be greater than or equal to F_b be. Preferably, none of the piezomotors manufactured in series produces a thrust in the first frequency range that runs in the second direction. Similarly, no motor generates thrust in the first direction in the second frequency range. This makes it possible to design the control electronics so that they have a broadband signal with a frequency interval Δf_f or Δf_b outputs and with which it is nevertheless ensured that none of the motors is excited to thrust in the opposite direction. These frequencies can be implemented as a frequency mix, as a chronologically separate sequence of frequencies, or as a mix of these two techniques. The piezomotors according to the invention are also designed such that the frequency intervals Δf_f and Δf_b lie within the effective range of a resonant circuit acting as a band stop. This resonant circuit is preferably formed with a single coil within the control electronics and the capacitive piezo motor. In the<figref idref="f0004">Figure 5</figref> the dash-dotted line 17 shows the frequency-dependent course of the AC resistance of an oscillating circuit, which at frequency f_e in the interval of f_el to f_eh acts as a band stop.

0070In <figref idref="f0005">Figure 6</figref> examples of alternative forms of the resonator are shown. In particular, notches (9) can be introduced which have a positive influence on the vibration behavior and manufacture of the motor.

List of reference numerals:

0071<dl id="dl0002" compact="compact"><dt>1</dt><dd>Piezomotor</dd><dt>2</dt><dd>Resonator</dd><dt>3</dt><dd>piezoelectric component</dd><dt>4</dt><dd>movable element</dd><dt>5</dt><dd>Axis of rotation</dd><dt>6</dt><dd>first main surface of the resonator</dd><dt>7</dt><dd>second main surface of the resonator</dd><dt>8</dt><dd>Central longitudinal axis</dd><dt>10</dt><dd>screw</dd><dt>12</dt><dd>elastic element</dd><dt>13</dt><dd>Contact point of the resonator with the movable element</dd><dt>14</dt><dd>Opening in the resonator</dd><dt>18</dt><dd>frame</dd><dt>20</dt><dd>first contact area</dd><dt>21</dt><dd>second contact area</dd><dt>23</dt><dd>Spring coils</dd><dt>25</dt><dd>first side wall of the opening</dd><dt>26</dt><dd>second side wall of the opening</dd></dl>