Shock-resistant drive unit

Abstract

A drive unit for driving a passive element (4) with respect to an active element (1), comprising a resonator (2) and excitation means (23), and two arms (21, 22) having contact elements (31, 32) that are movable by a vibrating motion and thereby drive the passive element (4). The resonator (2) is attached to the base element (5) by a fixing element (29). For at least the first arm (21) and for its contact elements (31, 32), there exists a shortest path to the nearest fixing element (29) through the active element 1. The shortest path does not cross the contour of the excitation means (23), or if it does cross, the area of the overhanging portion of the excitation means (23) is less than 10% of the area of the excitation means (23). As a result, the excitation means is less likely to be damaged due to the force on the arm.

Description

Technical Field

[0001] The present invention relates to the field of small drive devices, such as piezoelectric drive devices. More specifically, it relates to a drive unit as recited in the preamble of the independent claims.

[0002] Such drive devices are disclosed, for example, in the applicant's International Publication No. WO 2006 / 000118 (or US Patent No. 7,429,812), International Publication No. WO 2019 / 068708, International Publication No. WO 2020 / 229290 (or European Patent Application Publication No. EP 3736965 or US Patent Application Publication No. 2022 / 216851), International Publication No. WO 2021 / 037779 (or European Patent Application Publication No. EP 3787178), and International Publication No. WO 2021 / 209559. There is a need to further improve such drive devices, especially by making them resistant to failures due to mechanical shock and / or fatigue fracture.

[0003] More specifically, when viewed in the direction in which the arm extends, it is desirable that the overall length of such a drive device be short. This runs counter to the need to minimize the length of the arm so that the arm can vibrate in an optimal frequency range taking into account further constraints. The length of the arm that vibrates effectively can be increased by joining the arm to the respective connection regions of the drive device in the arm mounting region disposed under the excitation means. A part of the arm designed to vibrate can be attached to the excitation means using a relatively elastic binder (with respect to the excitation means and the resonator). Thus, the arm in the region coupled to the excitation means can still vibrate with the amplitude necessary to operate the drive device. However, it has been found that in the region where the arm is coupled to the excitation means, the excitation means is prone to cracking and breakage.

[0004] Therefore, an object of the present invention is to create a drive unit of the type described at the beginning that overcomes the above-mentioned drawbacks.

[0005] These objects are achieved by the drive unit according to claim 1. The drive unit serves to drive a passive element relative to an active element, and the active element · comprises a resonator and at least one excitation means for exciting vibrations in the resonator, · the resonator comprises at least two arms extending from a connection region of the resonator, · the resonator and the at least two arms extend parallel to a reference plane, · the at least one excitation means extends parallel to the reference plane and is attached to the resonator in a contact region, · at least one of the at least two arms comprises a corresponding contact element at an outer end of the arm, · the contact element is movable by the oscillatory movement of the corresponding arm, · the passive element is configured to be driven or moved relative to the active element by these oscillatory movements, · the passive element comprises at least one contact region, and each contact region is arranged to contact a corresponding contact element, Here, the resonator is attached to the base element by at least one fixing element. In an embodiment, the fixing element is arranged in a direction in which the arm extends with respect to the connection region, or in a direction perpendicular to the direction in which the arm extends. In an embodiment, the fixing element is arranged in a direction opposite to the direction in which the arm extends with respect to the connection region.

[0006] For at least a first arm of the at least two arms, with respect to its contact element, there is a shortest path through the active element to the nearest fixing element of the at least one fixing element, and the following conditions are satisfied.

[0007] · At a convex portion towards the reference plane, the shortest path does not intersect the contour of the excitation means, and thus does not pass through a part of the excitation means protruding above the resonator, or · When the shortest path passes through a part of the excitation means that protrudes above the resonator, in the convex part to the reference plane, the area of this protruding part is less than 10% of the area of the excitation means, particularly less than 5%, and particularly less than 2%.

[0008] In an embodiment having a second arm, this can also hold a further shortest path from the second contact element to its nearest fixed element.

[0009] In an embodiment, this condition is satisfied for two of at least two arms, particularly for all arms of at least two arms.

[0010] The fixed element arranged as described above (in the direction in which the arm extends with respect to the connection region, or in a direction perpendicular to the direction in which the arm extends) excludes a drive unit in which one or more fixed elements are exclusively arranged on the side of the connection region away from the direction in which the arm extends, that is, on the side opposite to the side where the arm extends.

[0011] Therefore, there is at least one fixed element as described above, and for each contact element, there is a nearest fixed element and a corresponding shortest path.

[0012] The shortest path constitutes a direct force path along which most of the force acting on the outer end of the arm is transmitted to the fixed element. Such a force may be parallel to the reference plane or perpendicular to the reference plane.

[0013] The reason for the crack in the excitation means observed in the prior art is that inertial forces may be generated in the arm due to mechanical shocks to the drive device, and depending on how the arm and the excitation means are shaped and attached to each other, it is judged that excessive force may act on the excitation means. Since the excitation means is typically a relatively hard and rigid piezoelectric crystal, cracks may occur.

[0014] In an embodiment, when the shortest path between the contact element and the nearest fixed element passes through the overhanging portion of the piezo, it is perpendicular to the arm extension, and when an acceleration of 100'000 g is applied in a direction included in the plane of the excitation means, the maximum stress in the piezo remains less than 100 MPa. This value is the tensile strength of a typical piezo.

[0015] By providing a path through which the force acting on the arm is transmitted to the fixed element with minimal or no effect on the excitation means, the cause of cracking of the excitation means is reduced or completely eliminated.

[0016] When the shortest path does not intersect the contour of the excitation means at all, the material of the resonator absorbs most of the movement of the arm in the event of an impact. When the shortest path intersects the contour, the likelihood of cracking increases with the size of the overhanging portion.

[0017] The overhanging portion of the excitation means is a part of the excitation means where there is no resonator at the convex portion to the reference plane.

[0018] The width of the excitation means can be defined as the extension of the excitation means in the axial direction of the resonator. The contour of the excitation means is the contour seen at the convex portion on the reference plane. Typically, the contour is rectangular. Typically, the excitation means is a rectangular piezoelectric element.

[0019] In an embodiment, the description made regarding the first arm and its associated first contact element, as well as the first arm mounting area, etc., is also applicable to the second arm of at least two arms and its corresponding second contact element and arm mounting area, etc.

[0020] In an embodiment having a second arm, there may be a further shortest path from the second contact element through the resonator and the fixed element, and this fixed element may be the same as that associated with the shortest path of the first arm, or may be a separate additional fixed element.

[0021] In an embodiment, the nearest fixing element is arranged on the same side of the connection region as the first arm.

[0022] In an embodiment, the nearest fixing element is arranged on the fixing region of the resonator, the fixing region extends in the same direction as the first arm from the connection region, and the resonator comprises a bridge connecting the first arm to the fixing region.

[0023] The bridge defines an opening or hole of the resonator, and the opening is between the first arm, the connection region, the fixing region, and the bridge. The opening or hole is partially covered by the exciting means. The opening may extend relatively far under the contour of the exciting means (as seen in the convex part of the reference plane). Nevertheless, since the force is received by the bridge, the influence of the force on the arm that affects the exciting means is significantly reduced.

[0024] In an embodiment having a second arm, there may be a second bridge connecting the second arm to the fixing region.

[0025] In an embodiment, the nearest fixing element is arranged on the first arm, between the outer end of the first arm where the first contact element is arranged and the inner end of the first arm where the first arm is attached to the connection region.

[0026] In an embodiment having a second arm, the nearest fixing element is arranged on the second arm, between the outer end of the second arm where the second contact element is arranged and the inner end where the second arm is attached to the connection region.

[0027] In an embodiment, on the convex part of the reference plane, the nearest fixing element is arranged on the resonator at a position perpendicular to the direction in which the first arm extends with respect to the exciting means.

[0028] In an embodiment having a second arm, this may also hold a further fixing element. Typically, the fixing element and the further fixing element are arranged on both sides of the resonator with respect to the exciting means.

[0029] In an embodiment, the resonator comprises a lateral extension that spaces the fixed element from the connection region.

[0030] In an embodiment having a second arm, the resonator may comprise a further lateral extension that spaces a further fixed element from the connection region, typically in a direction opposite to the direction of the lateral extension.

[0031] In an embodiment, the lateral extension comprises a bend. In an embodiment, at a convex portion of the reference plane, the connection region comprises a lateral notch that extends into the connection region in a direction perpendicular to the direction in which the first arm extends.

[0032] The lateral notch increases the length of the vibratable first arm. Thereby, the vibration frequency of the first arm is reduced compared to a resonator without the lateral notch or the first arm. The actual effect is to have a shorter resonator with one or more arms of essentially the same vibration frequency. In an embodiment, the lateral notch extends under the excitation means and is covered by the excitation means.

[0033] In an embodiment having a second arm, the resonator may comprise a further lateral notch that extends into the connection region in a further direction perpendicular to the directions in which the first arm and the second arm extend, the further direction typically being opposite to the direction in which the lateral notch extends.

[0034] In an embodiment, the resonator is formed as a single piece from a flat piece of material, in particular by stamping or laser cutting.

[0035] In an embodiment, the excitation means may comprise a rectangular element, in particular a piezoelectric element, attached to one side of the resonator and optionally a second such element attached to the opposite side of the resonator.

[0036] In an embodiment, the excitation means is attached to the resonator by a bonding material, and the elastic modulus (Young's modulus) of the bonding material is lower than 1 / 10 of the elastic modulus of the resonator material.

[0037] This allows for a slight movement of the resonator with respect to the excitation means, enabling more vibration modes than with a stiffer bonding material.

[0038] In an embodiment, at least one fixing element is attached to a fixing point of the resonator or a fixing line of the resonator.

[0039] In an embodiment, such a fixing point or fixing line is arranged in a punctiform or linearly extending region of the resonator that is a node of the vibration of the resonator in the vibration mode when operating the driving device.

[0040] In an embodiment, one or more of such fixing points or fixing lines each have an area of less than 5%, particularly less than 2%, of the total area of the smallest rectangle circumscribing the resonator (as seen in the convex part of the reference plane). With respect to the width of the resonator (in the direction perpendicular to the direction in which the arm extends and within the reference plane), the diameter of such a fixing point may be less than 1 / 10 of the width. In an absolute sense, this may mean that the area of the fixing point or fixing line is less than 0.5 square millimeters, particularly less than 0.25 square millimeters. The corresponding resonator may have dimensions of 5×10, particularly 4×8, particularly 3×4 millimeters.

[0041] The subject matter of the present invention will be described in more detail in the following text with reference to the exemplary embodiments shown in the accompanying drawings.

Brief Description of the Drawings

[0042]

Figure 1

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Mode for Carrying Out the Invention

[0043] In principle, the same or functionally identical parts are given the same reference numerals in the figures.

[0044] FIG. 1 schematically shows in exploded view the elements of a prior art drive unit having an active element 1 and a passive element 4. The active element 1 comprises a resonator 2 or resonator plate 2 and two excitation means 23. From the connection region 20 of the resonator 2, a first arm 21 and a second arm 22 extend in the same direction corresponding to the resonator axis 24. The resonator 2 and the arms 21, 22 extend parallel to a reference plane 28. At the ends of each arm, there are respectively a first contact element 31 and a second contact element 32 which are designed to contact the passive element 4 by contacting the first contact region 41 and the second contact region 42 of the passive element 4 and to move the passive element 4. These contact regions are not necessarily in a fixed relationship with respect to the moving passive element 4. Rather, these are the positions where the contact regions 31, 32 are currently in contact with the passive element 4 when the passive element 4 rotates about the axis of rotational movement 25 (FIG. 1) or translates with respect to the active element 1 (FIG. 2).

[0045] As described in the above-mentioned U.S. Patent No. 7,429,812, it is possible to change the excitation frequency of a voltage generator that drives the excitation means 23, which may be a piezoelectric element, and different modes of mechanical vibration of the arm are generated according to the frequency. For example, in one mode, both the contact regions 31 and 32 rotate clockwise when viewed at the convex portion of the reference surface, in another, both rotate counterclockwise, and in another mode, one rotates clockwise and the other rotates counterclockwise. As another example, in one mode, the contact regions 31 and 32 move back and forth at a first angle, and in another mode, they move back and forth at a second angle. Depending on the suspension of the passive element, i.e., whether it is rotary or linear or a combination of rotary and linear, the passive element moves accordingly.

[0046] The following embodiments operate according to the same basic principle. Unless otherwise specified, the elements described so far, if present, have essentially the same functions. The arms 21 and 22 can be adapted to the movement of a linear drive device or a rotary drive device according to the embodiment. The position of the excitation means 23 with respect to the resonator 2 is schematically represented by a rectangle corresponding to the contour of the excitation means 23 attached to one or both sides of the resonator 2.

[0047] FIG. 2 shows a prior art linear drive unit having inwardly extending protrusions 33, 34 and outwardly extending contact elements. The first arm 21 includes a first protrusion 33 or convex portion in the direction of the second arm 22. The second arm 22, which is essentially a mirror image of the first arm 21 with respect to the resonator axis 24, includes a second protrusion 34 in the direction of the first arm 21. Thus, both protrusions 33, 34 extend towards the resonator axis 24, i.e., towards the inside of the drive unit.

[0048] The first arm 21 comprises a first contact element 31 that projects away from the second arm 22, i.e., in a direction opposite to the direction in which the first protrusion 33 extends. Similarly, the second arm 22 comprises a second contact element 32 that projects away from the first arm 21, i.e., in a direction opposite to the direction in which the second protrusion 34 extends. Thus, both contact elements 31, 32 extend away from the resonator axis 24, i.e., towards the outside of the drive device. Here, these come into contact with the first contact region 41 and the second contact region 42 of the passive element 4, respectively.

[0049] The elements of the passive element 4 are schematically represented by two rectangles corresponding to two linear guides movable relative to the active element 1. The two guides on both sides of the passive element 4 are mechanically connected as schematically represented by dashed lines. The mechanical connection may be rigid or elastic, in which case it may be part of a configuration that generates prestress acting on the first contact element 31 and the second contact element 32 via the first contact region 41 and the second contact region 42.

[0050] The first protrusion 33 and the second protrusion 34 are each connected to the remaining portions of the first arm 21 and the second arm 22 by corresponding necks 35. This neck 35 corresponds to a region that is weak in bending along each arm. That is, the rigidity of the arm against bending about an axis perpendicular to the reference plane 28 is lower at the neck 35 than at adjacent locations. During operation, when the arms vibrate, each protrusion acts as a countermass (relative to its respective contact element) and can exhibit an oscillatory motion including a small rotation about its respective neck 35. This enables the respective contact elements arranged at the same end or at each arm to make corresponding movements. This drives the passive element 4 along a linear motion axis parallel to the resonator axis 24.

[0051] The resonator 2 may include at least one or more fixed regions or support regions 27 to which the resonator is attached to a base (not shown). The fixed region 27 is typically located on the resonator axis 24. These typically do not vibrate to a significant extent and are attached to the base. The fixed region 27 can be characterized by additional protrusions such as 27a and 27b to facilitate the electrical connection of the resonator as well as the assembly of the resonator at the base (not shown). One of the fixed regions 27 shown (the one on the right side of the figure) is arranged with respect to the connection region in the direction in which the arm extends, and the other (the one on the left side) is arranged in the opposite direction.

[0052] FIG. 3 schematically shows four different views of the active element according to the first embodiment, namely a perspective view (left), a protrusion onto a reference plane (center), and two protrusions in a direction parallel to the reference plane (top and right).

[0053] In addition to the elements described in the text of FIGS. 1 and 2, the following are shown: · The contact region 26 is typically the region where the excitation means 23 is attached to the resonator 2 by a binder, in particular an adhesive. The adhesive may be an epoxy adhesive. The adhesive may be conductive and can help supply power to the excitation means 23.

[0054] · A fixing element 29 by which the resonator 2 is attached to the base element 5. The fixing element 29 typically restricts the movement of the resonator 2 with respect to the base element 5 in all six degrees of freedom.

[0055] · The base element 5 represents a device or component on which the active element 1 and the passive element 4 are arranged and which are movable relative to each other.

[0056] · An arm mounting region 38 to which each arm is attached to the connection region 20 of the resonator 2. In the arm mounting region 38, the relatively elastic arms 21, 22 transition to the relatively rigid connection region 20. Thus, the movement of the outer ends of the arms (comprising the contact elements 31, 32 and the protrusions 33, 34) is mainly absorbed by the arms.

[0057] · The recess 39 of the resonator 2 corresponding to the protruding portion of the excitation means 23. The recess 39 is, in the convex portion with respect to the reference plane 28, a region where the excitation means 23 exists and the resonator 2 does not exist. With respect to the excitation means 23, the recess 39 coincides with the protruding portion of the excitation means 23. If the recess 39 (or the protruding portion) is too large to handle, the movement of the outer end portion of the arm may cause the movement of the arm where the arm and the excitation means 23 overlap, and may cause cracks in the relatively brittle excitation means 23.

[0058] · One or more bridges 51, each bridge 51 being a part of the resonator 2 and constituting a link between the respective arms 21, 22 and the fixing element 29. The bridge 51 forms the shortest path from the contact element to the fixing element 29 and can absorb the force acting on the outer end portion of each arm, thereby reducing the force acting on the excitation means 23.

[0059] One or more fixing elements 29 by which the resonator 2 is attached to the base element 5 can be mounted by various methods such as adhesion, soldering, or welding. Alternatively or additionally thereto, for example, a secure fitting by means of a clamp, a snap-action connection part, riveting, or hot stamping (such as a stub formed on the base element 5 and passing through a hole of the resonator 2) may be used. The region of the fixing point or fixing line is the contact region between the resonator 2 and the base element 5 measured at the convex portion with respect to the reference plane.

[0060] The fixing element 29 is in a mirror-symmetric arrangement, particularly where the resonator axis 24 is the axis of symmetry. The active element 1 includes two excitation means 23 attached to both sides of the resonator 2. In particular, the two excitation means 23 have congruent shapes and are arranged symmetrically with respect to the resonator 2.

[0061] Figures 4 to 11 schematically show two different views of the active element according to different embodiments, namely a perspective view (left) and a convex portion to a reference plane (right). For clarity, some reference numerals are omitted. In each case, the approximation of the shortest path of one arm is represented by a thick line.

[0062] Figure 4 shows a first embodiment having a shortest path from the first contact element 31 to a single fixed element 29 located on the resonator axis 24. The shortest path passes through the bridge 51, thereby bypassing the connection region 20 and the excitation means 23.

[0063] Figure 5 shows a second embodiment having a shortest path from the first contact element 31 to a single fixed element 29 located on the resonator axis 24. The shortest path passes through the resonator 2 and remains within the plane of the resonator 2 without passing through the overhanging region of the excitation means 23.

[0064] Figure 6 shows a third embodiment having a shortest path from the first contact element 31 to a fixed element 29 located on the first arm 21. The shortest path passes along the short portion of the first arm 21, thereby completely avoiding the excitation means 23.

[0065] Figure 7 shows a fourth embodiment in which the shortest path from the first contact element 31 to the fixed element 29 is arranged with respect to the excitation means 23 and the connection region 20 in a direction perpendicular to the direction in which the arm extends. The shortest path bypasses the excitation means 23 after passing through the entire first arm 21.

[0066] FIG. 8 shows a fifth embodiment in which the shortest path from the first contact element 31 to the fixed element 29 is arranged with respect to the excitation means 23 and the connection region 20 in a direction perpendicular to the direction in which the arm extends. The fixed element 29 is separated from the connection region 20 by a lateral extension 53 of the resonator 2. The lateral extension 53 may be linear or may have at least one angle as shown in the figure. The lateral extension 53 can lower the resonance frequency of the suspension of the active element 1 with respect to the base element 5. In this way, the resonance frequency is shifted away from the frequency band in which the arm is driven.

[0067] The shortest path passes through the entire first arm 21, then bypasses the excitation means 23, and then passes along the lateral extension 53.

[0068] FIG. 9 shows a sixth embodiment having the same shortest path as FIG. 5, but in which the arms do not have the respective protrusions 33, 34.

[0069] Also in the first to sixth embodiments and the eighth to tenth embodiments, the shortest path between the contact point and the closest fixed point does not cross the overhang of the piezo.

[0070] Figure 10 shows a seventh embodiment having a shortest path from the first contact element 31 along the first arm 21, through the excitation means 23, through the fixed region 27 to the fixed element 29. Since the resonator 2 has the recess 39, the shortest path passes through the excitation means 23 outside the plane of the resonator 2. Therefore, the shortest path crosses the overhang of the excitation means 23 (corresponding to the recess 39 of the resonator 2). At the convex portion to the reference plane 28, the shortest path passes through a part of the excitation means 23 that projects into the resonator 2. As long as the area of this overhang is less than the reference safety factor FSR of 10% of the area of the excitation means 23, particularly less than 5%, particularly less than 2%, the excitation means 23 has a sufficiently low possibility of cracking during an impact that affects the first arm 21. In Figure 10, for the sake of explanation, the area of the lower overhang of the two overhangs at the convex portion to the reference plane parallel to the paper surface is hatched. The area of the excitation means 23 is equal to the area of the rectangular contour of the excitation means 23.

[0071] The above upper limit of the reference safety factor FSR is based on typical dimensions and materials used for the resonator 2 and the excitation means 23, namely, stainless steel 1.4310 and a piezoelectric crystal material. In embodiments with different materials, the adapted safety factor FSA can be determined from the reference safety factor FSR based on the following material properties of the piezoelectric element acting as the resonator 2 and the excitation means 23.

[0072] · t_p: The thickness of the piezoelectric element, Reference value t_p_ref = 150 micrometers.

[0073] · s_p: The compliance of the piezoelectric element, Reference value s_p_ref = 15e-12 m2 / N.

[0074] · E_r: The Young's modulus of the material of the resonator, Reference value E_r_ref = 195 GPa.

[0075] · rho_r: The density of the material of the resonator, Reference value rho_r_ref = 7900 kg / m3.

[0076] Considering the characteristics of arrangements different from the reference, the compliance safety factor is as follows. FSA = FSR(t_p s_p E_r / rho_r) / (rho_r_ref / (t_p_ref s_p_ref E_r_ref)) FIG. 11 shows an eighth embodiment having a shortest path as in FIGS. 5 and 9. The resonator 2 includes associated notches 52, 52', i.e., lateral notches 52, 52', for each arm. The notches extend from the side surface of the resonator 2 facing in a direction perpendicular to the direction in which the corresponding arm extends, toward the connection region 20. In other words, the notch 52 extends in a direction orthogonal to the direction in which the arm extends. The notch 52 increases the length of the corresponding arm and decreases its resonance frequency. Thereby, while maintaining the resonance frequency of the arm within a desired range, the overall length of the active element can be shortened.

[0077] FIG. 12 shows a ninth embodiment having a shortest path similar to FIG. 4, but with the first and second contact elements 31, 32 facing outward.

[0078] FIG. 13 shows a tenth embodiment of an asymmetric drive device having a shortest path similar to FIG. 6.

[0079] Embodiments can be described as implementing different combinations of features, which correspond to the type of drive device and the type of attachment.

[0080] The types of drive devices are as follows. A. "Inner simple" - an inner drive device without a counter mass (FIGS. 7, 9, 10, 11) B. "Inner counter mass" - an inner drive device having a counter mass at the end of the arm on the outside (FIGS. 4, 5, 6) C. "Outer simple" - an outer drive device without a counter mass (FIG. 12) D. "Outer counter mass" - an outer drive device having a counter mass inside the arm (FIG. 2) E. "Rotating" - an asymmetric drive device in which particularly one arm is vibrating but not being driven (FIG. 13) Further details and the operating principle of the rotary drive device are described in International Publication No. 2020 / 229290, which is hereby incorporated by reference in its entirety. In particular, refer to FIGS. 3-6 and the related descriptions.

[0081] The types of attachments are as follows. U. Bridge (FIGS. 4, 12) V. Arm (FIGS. 6, 13) W. Central part (FIGS. 5, 9, 10) X. Central part with (lateral) notch 52 (FIG. 11) Y. Side fixing part (FIG. 7) Z. Side fixing extension part (FIG. 8) The combinations of the drive devices and the types of attachments disclosed in this specification are as follows.

[0082] · AU, AV, AW, AX, AY, AZ; · BU, BV, BW, BX, BY, BZ; · CU, CV, CW, CX, CY, CZ; · DU, DV, DW, DX, DY, DZ; · EU, EV, EW, EX, EY, EZ; Although the present invention has been described in this embodiment, it is clearly understood that the present invention is not limited thereto and can be embodied and implemented in various other ways within the scope of the claims.

Claims

1. A drive unit that drives a passive element (4) with respect to an active element (1), wherein the active element (1) is The device comprises a resonator (2) and at least one excitation means (23) for exciting vibrations within the resonator (2), The resonator (2) comprises at least two arms (21, 22) extending from the connection region (20) of the resonator (2), The resonator (2) and the at least two arms (21, 22) extend parallel to the reference plane (28), The at least one excitation means (23) extends parallel to the reference plane (28) and is attached to the resonator (2) in a contact region (26), At least one of the two arms (21, 22) is provided with a corresponding contact element (31, 32) at the outer end of the arm. The contact elements (31, 32) are movable by the vibrational motion of the corresponding arms (21, 22), The passive element (4) is arranged to be driven or moved relative to the active element (1) by these vibrational movements. The passive element (4) comprises at least one contact region (41, 42), and each contact region (41, 42) is arranged to be in contact with the corresponding contact elements (31, 32). The resonator (2) is attached to the base element (5) by at least one fixed element (29), For at least one of the two arms (21, 22), the first arm (21) has a contact element (31, 32) and a shortest path exists through the active element (1) to the nearest fixed element (29) among the at least one fixed element (29), provided the following conditions are met: - In the convex portion on the reference surface (28), the shortest path does not intersect with the contour of the excitation means (23), and therefore does not pass through a part of the excitation means (23) that protrudes over the resonator (2), or - When the shortest path passes through a portion of the excitation means (23) that protrudes over the resonator (2), the area of ​​the protrusion on the reference plane is less than 10 percent, particularly less than 5 percent, and particularly less than 2 percent, of the area of ​​the excitation means (23). A drive unit characterized by satisfying the following conditions.

2. The drive unit according to claim 1, wherein the above condition is satisfied for two of the at least two arms (21, 22), in particular for all of the at least two arms (21, 22).

3. The drive unit according to claim 2, wherein the nearest fixed element (29) is located on the same side as the first arm (21) with respect to the connection region (20).

4. The drive unit according to any one of claims 1 to 3, wherein the nearest fixed element (29) is located on a fixed region (27) of the resonator (2), the fixed region (27) extends from the connection region (20) in the same direction as the first arm (21), and the resonator (2) includes a bridge (51) connecting the first arm (21) to the fixed region (27).

5. The drive unit according to any one of claims 1 to 3, wherein the nearest fixed element (29) is positioned on the first arm (21) between the outer end of the first arm (21) on which the first contact element (31) is located and the inner end of the first arm (21) on which the first arm (21) is attached to the connection region (20).

6. The drive unit according to claim 1 or 2, wherein, in the convex portion on the reference surface (28), the nearest fixed element (29) is positioned on the resonator (2) in a direction perpendicular to the direction in which the first arm (21) extends, relative to the excitation means (23).

7. The drive unit according to claim 6, wherein the resonator (2) includes a lateral extension (53) that separates the fixed element (29) from the connection region (20).

8. The drive unit according to any one of claims 1 to 3, wherein the connection region (20) in the protrusion on the reference surface (28) has a lateral notch (52) extending in the connection region (20) in a direction perpendicular to the direction in which the first arm (21) extends.

9. The drive unit according to any one of claims 1 to 3, wherein the fixed element (29) is in a mirror-symmetric arrangement in which the resonator axis (24) is the axis of symmetry.

10. The drive unit according to any one of claims 1 to 3, comprising two excitation means (23) attached to both sides of the resonator (2), wherein the two excitation means (23) have a congruent shape and are arranged symmetrically with respect to the resonator (2).

11. The drive unit according to any one of claims 1 to 3, wherein the resonator (2) is formed from a flat material piece, particularly by stamping or laser cutting, as a single piece.

12. The drive unit according to any one of claims 1 to 3, wherein the excitation means (23) comprises a rectangular element, particularly a piezoelectric element, attached to one side of the resonator (2), and optionally a second such element attached to the opposite side of the resonator (2).

13. The drive unit according to claim 11, wherein the excitation means (23) is attached to the resonator (2) by a coupling material, and the elastic modulus of the coupling material is lower than 1 / 10 of the elastic modulus of the resonator material.

14. The drive unit according to any one of claims 1 to 3, wherein the at least one fixed element (29) is attached to a fixed point of the resonator or a fixed line of the resonator.

15. The drive unit according to any one of claims 1 to 3, wherein the at least one fixing element (29) is arranged in the direction in which the arms (21, 22) extend with respect to the connection region, or in a direction perpendicular to the direction in which the arms extend.

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