Patent Publication Number: US-2022216851-A1

Title: Drive unit and method for operating a drive unit

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to the field of miniaturised drives, for example piezoelectric drives. More particularly, it relates to a drive unit and a method for operating a drive unit. 
     Description of Related Art 
     Such drives are disclosed, for example, in the applicant&#39;s WO 2006/000118 A1 or U.S. Pat. No. 7,429,812 B2. There is a need for further improvement of such drives, in particular by simplifying their construction and making them better suited for miniaturisation and mass production. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to create a drive unit of the type mentioned initially, with a simplified construction and/or increased performance, and a method for operating such a drive unit. 
     According to a first aspect of the invention, a drive unit for driving a passive element relative to an active element is provided, wherein the active element includes:
         a resonator and at least one excitation means for exciting oscillations in the resonator,   the resonator including at least two arms extending from a connection region of the resonator,   the connection region and the arms extending in parallel to a reference plane,   a first arm of the arms including, at an outer end of the arm, a contact element,   the contact element being movable by way of oscillating movements of the first arm,   the passive element being arranged to be driven and moved relative to the active element by way of these oscillating movements;   the passive element includes a first contact area, the first contact area being arranged to be in contact with the first contact element.       

     Therein the at least two arms extend in a substantially symmetric manner from the connection region;
         the resonator and its parts are integrally shaped as a single piece of material;   and the second arm is arranged not to come into contact with the passive element.       

     The invention according to the first aspect can be implemented alone or in combination with the invention according to one or more of the other aspects. 
     Thus, the second arm does not drive the passive element. By having only one arm driving the passive element, one or more of the following becomes possible:
         A rotary drive can be configured to have a further arm that acts as a bearing, opposite of the first arm, for the passive element, and does not impart a torque driving the passive element. The further arm and the driving arm can be in the same (reference) plane as the resonator, simplifying the construction.   A pre-stress force, acting in parallel to the reference plane or resonator plane, can be applied, e.g. by such a further arm, and can also act on a driven part.   A linear drive can be configured to have an arbitrary long range of linear motion within the plane of the resonator, as opposed to a drive in which the passive element moves between two arms of the active element in said plane.       

     Typically, the movement of the contact element is of a generally elliptic shape, and a direction of the movement—clockwise or counter clockwise, seen in a projection onto the reference plane—can be controlled by an excitation frequency of the excitation means, as explained in the applicant&#39;s prior WO 2006/000118 A1 or U.S. Pat. No. 7,429,812 B2. 
     In embodiments, the resonator and its parts are manufactured of a single piece of sheet material, in particular, sheet metal. 
     In embodiments, the second arm is arranged to move with oscillating movements that balance the oscillating movement of the first arm. 
     That is, when the excitation means is excited with a frequency for driving the passive element relative to the active element, the first arm and second arm vibrate with movements that balance one another. 
     A resonator of the kind presented here typically has a resonator axis that corresponds to an axis of symmetry of the geometric shape of the resonator. For a resonator of generally planar shape, the resonator axis lies in its reference plane. The symmetry relative to the resonator axis is understood to correspond to the general shape of the arms, and may not be perfect with regard to details of the shape of the arms. 
     Thus, while the at least two arms extend in a substantially symmetric manner from the connection region, they can differ in details of their shape or contour. For example, one arm can be shorter than the other, measured in the direction in which the arms extend. For example, it can be up to 10% or up to 20% or up to 30% or up to 40% shorter than the other arm. 
     The arms being arranged symmetrically to one another, with regard to the resonator axis or to a point of symmetry, allows movements of the arms, when they oscillate, to balance each other. As a result, the oscillating movement of the resonator can be made essentially symmetric with respect to the resonator axis. 
     In embodiments, one or more attachment regions at which the resonator is attached to another element that carries the resonator, lie on the resonator axis. 
     In embodiments, the centre of the excitation means lies on the resonator axis (both being projected onto the reference plane). 
     In embodiments, the resonator axis corresponds to areas of the resonator where, in operation of the active element, the amplitudes of oscillation are lowest. 
     In embodiments, the first arm and second arm are arranged in 2-fold rotational symmetry to one another, with an axis of symmetry being normal to the reference plane. 
     2-fold rotational symmetry is a special case of axisymmetry, in which a body is matched with itself by a 0° rotation about the axis of symmetry. 
     In embodiments, the first arm and second arm are arranged in mirror symmetry to one another, with a mirror plane being normal to the reference plane, the first arm and second arm being arranged at opposite sides of the mirror plane and
         either the first arm and second arm extend in a direction normal to the mirror plane,   or the first arm and second arm extend in a direction normal to the mirror plane.       

     In embodiments, the mirror plane includes the resonator axis. In this case, it is also the case that the first arm and second arm are arranged at opposite sides of the resonator axis and extend—depending on the embodiment—in a direction parallel to or perpendicular to the resonator axis, respectively. 
     In embodiments, the passive element is arranged to move with a linear movement when driven by the first arm. 
     In embodiments, the passive element is arranged to move with a rotary movement when driven by the first arm. 
     In embodiments, the active element comprises, in addition to the first arm and second arm, a bearing arm, the bearing arm including a bearing region by means of which, in particular when the active element is not being excited, the bearing arm applies a pre-stress force on the passive element against the first arm, in particular the first contact element of the first arm. 
     The pre-stress force can be generated by a permanent deformation of the bearing arm, in particular by flexion, torsion and/or shearing of the bearing arm. 
     In embodiments, when the active element is excited, with a frequency for driving the passive element relative to the active element by means of the first arm, the bearing arm oscillates without imparting forces to the passive element that drive the passive element relative to the active element. 
     In embodiments, when the active element is excited, with a frequency for driving the passive element relative to the active element by means of the first arm, a bearing region of the oscillating bearing arm alternatingly moves towards the passive element, thereby coming into contact with the passive element, and away from the passive element, thereby losing contact with the passive element. 
     In embodiments, when the excitation means is excited with a frequency for driving the passive element relative to the active element by means of the first arm, the bearing arm includes at least three nodes of oscillation. 
     The bearing arm is distinct from the second arm and from the first arm. In other words, the bearing arm and second arm and first arm are not the same arm. 
     In embodiments, the bearing region includes bearing fingers between which the passive element is arranged. 
     In embodiments, the connection region is substantially of rectangular shape. The excitation means typically is substantially rectangular as well. Sides of a rectangle corresponding with a rectangular approximation of the connection region can be aligned in parallel with sides of a rectangle corresponding with a rectangular approximation of the excitation means. 
     The resonator and its parts being integrally shaped means, in other words, that the parts of the resonator, such as the connection region, first and second arms, attachment regions, and optionally a bearing arm are manufactured as a single part with the resonator. This can be done, for example, by stamping or cutting the resonator from a piece of sheet metal, or by casting, or by an additive manufacturing process. 
     The method for operating a drive unit includes the steps of exciting the active element with a frequency for driving the passive element relative to the active element by means of the first arm by performing an oscillating movement that, and for intermittently holding and releasing the passive element relative to the active element by means of the bearing arm. 
     Depending on the frequency, the active element can drive the passive element to move in a first direction, or in a second direction opposite to the first direction. In embodiments, the movement by the passive element is a translational movement. In others, it is a rotational movement. 
     According to a second aspect of the invention, a drive unit for driving a passive element relative to an active element is provided, wherein the active element includes:
         a resonator and at least one excitation means for exciting oscillations in the resonator,   the resonator including at least one arm extending from a connection region of the resonator,   the connection region and the at least one arm extending in parallel to a reference plane,   the at least one arm including, at an outer end of the arm, a contact element,   the contact element being movable by way of oscillating movements of the at least one arm,   the passive element being arranged to be driven and moved relative to the active element by way of these oscillating movements;   the passive element includes a first contact area, the first contact area being arranged to be in contact with the first contact element.       

     Therein a resilient pre-stress element is arranged to apply a pre-stress force pushing, in particular when the active element is not being excited, at least the first contact element towards the first contact area, and in that
         the passive element is held in place against the active element by means of the pre-stress force.       

     The invention according to the second aspect can be implemented alone or in combination with the invention according to one or more of the other aspects. 
     Thus, the pre-stress force acts not only between the active element and passive element, improving the driving effect of the oscillating movement of the one or more arms, but also allows to simplify the construction of the drive, and in particular of a joint between the active element and passive element, typically between a base element and a driven part on which the active element and passive element are mounted. 
     The passive element being held in place means that if it were not for the pre-stress force, the passive element—and optionally further elements connected to the passive element—would be free to move out of its or their place relative to the active element. In other words, without the pre-stress force acting, the active element and passive element would fall apart. 
     In embodiments, the passive element and the active element are arranged to move a driven part relative to a base element, the driven part being partly constrained in its movement relative to the base element by means of a joint, and the driven part is held in the joint by means of the pre-stress force. Again: without the pre-stress force, the base element and driven part would be free to move out of their place relative to one another. 
     In embodiments, the pre-stress force acts within the resonator plane, and thus in parallel to the reference plane. 
     Generally, not only one but two or more drive units can be arranged to move a driven part relative to a base element. 
     In embodiments, the joint is a rolling joint including rollers arranged between the base element and the driven part. 
     The rollers can be, for example, spherical, cylindrical or barrel-shaped rollers. 
     In embodiments, the pre-stress force acts on all the rollers of the rolling joint. 
     In other words, all the rollers are arranged at locations where the pre-stress force pushes the active element and the passive element towards one another. 
     In embodiments, the joint is a rotary joint, a linear joint or a planar joint. 
     In embodiments, the joint allows for relative movement of the driven part relative to the base element along a linear axis or within a plane, and limits the relative movement in a direction that is normal to said linear axis or plane, and does not constrain the relative movement in the opposite direction, and wherein the pre-stress force constrains the relative movement in the opposite direction. 
     In embodiments, the joint allows for relative movement of the driven part relative to the base element around an axis of rotation, and limits the relative movement in a direction that is normal to said axis of rotation, and does not constrain the relative movement in the opposite direction, and wherein the pre-stress force constrains the relative movement in the opposite direction. 
     According to a third aspect of the invention, a drive unit for driving a passive element relative to an active element is provided, wherein the active element includes:
         a resonator and at least one excitation means for exciting oscillations in the resonator,   the resonator including at least two arms extending from a connection region of the resonator,   the connection region and the arms extending in parallel to a reference plane,   each of the arms including, at an outer end of the arm, a respective contact element,   the contact elements being movable by way of oscillating movements of the respective arm   the passive element being arranged to be driven and moved relative to the active element by way of these oscillating movements;   the passive element includes a first and a second contact area, each contact area, being arranged to be in contact with a respective one of the first and second contact elements.       

     Therein the resonator includes
         a pivot section about which the resonator is arranged to rotate relative to the base element,   a counterforce section including a resilient part of the resonator, which when mounted on the base element is elastically deformed by a pre-stress torque around the pivot section, caused by a pre-stress force acting between the resonator and the passive element at the contact areas.       

     The invention according to the third aspect can be implemented alone or in combination with the invention according to one or more of the other aspects. 
     This makes it possible to simplify construction of the drive and associated parts, in particular for miniaturisation of the drive. 
     In embodiments, when no external forces are applied to the resonator and its arms they extend in parallel to the reference plane. When mounted in another element, such as the base element and/or when in contact with the passive element, parts of the resonator, in particular its arms and/or counterforce sections can be elastically deformed and moved out of the reference plane. Correspondingly, the pre-stress force can act at an angle to the resonator or the reference plane. The angle can be more than 75°, more than 85° and in particular a right angle. 
     In embodiments, the resonator can be manufactured as a flat object, with all its elements in parallel to the reference plane, and can then be plastically deformed prior to being mounted with other elements of the drive unit. 
     In embodiments, the counterforce section, in particular when not deformed, extends within the reference plane at the same side of the pivot section as the arms. 
     In embodiments, the counterforce section, in particular when not deformed, extends within the reference plane at the opposite side of the pivot section as the arms. 
     In embodiments, the counterforce section, in particular when not deformed, extends at an angle to the reference plane. 
     According to a fourth aspect of the invention, a drive unit for driving a passive element relative to an active element is provided, wherein the active element includes:
         a resonator and at least one excitation means for exciting oscillations in the resonator,   the resonator including at least two arms extending from a connection region of the resonator,   the connection region and the arms extending in parallel to a reference plane,   at least one of the arms comprising, at an outer end of the arm, a contact element,   the contact element being movable by way of oscillating movements of the at least one of the arms,   the passive element being arranged to be driven and moved relative to the active element by way of these oscillating movements;   the passive element includes at least one contact area, the at least one contact area being arranged to be in contact with a respective contact element.       

     Therein the at least one contact area has a concave shape, with two inner surfaces opposing one another, with the respective contact element being arranged to move between the two inner surfaces and make contact at the two inner surfaces. 
     The invention according to the fourth aspect can be implemented alone or in combination with the invention according to one or more of the other aspects. 
     This makes it possible to move parts, to which the active and passive element relative are attached, relative to one other in a direction normal to a linear movement axis of the drive. Thereby, the contact element is held between the concave part and so does not lose contact. 
     In embodiments, the at least one contact area has a U-shape, with two arms, and wherein the respective contact element is arranged to move between the two arms of the U-shape and make contact at inner surfaces of the two arms of the U-shape. 
     In embodiments the at least one contact area is manufactured in one piece as a bent piece of sheet metal. 
     In embodiments, the contact elements include flat contact surfaces. 
     In embodiments, a resonator length is defined as the dimension of the resonator along the resonator axis, from the ends of the arms to the opposing ends of their counterweight sections, and wherein the extension (d) of each flat contact surface, projected onto the reference plane, is between one tenth and one hundredth of the resonator length, in particular between one twentieth and one eightieth of the resonator length. 
     In embodiments, the length of the resonator is between three and five millimetres, in particular four millimetres, and the extension (d) of the flat region is between 0.05 millimetres and 0.15 millimetres, in particular between 0.08 millimetres and 0.12 millimetres, in particular 0.1 millimetres. 
     In embodiments, the surface of the resonator and/or the passive element is treated with high precision vibratory finishing or chemical polishing. 
     In embodiments, a wear suppressing element is arranged on the passive element in the contact areas. 
     In embodiments, the wear suppressing part is made of a material with a higher degree of hardness than a surrounding region of the passive element or is created by a hardening treatment of the material of the passive element. 
     In embodiments, the wear suppressing part is made of a ceramic material. 
     In general, for all aspects, it can be the case that a width of the first and second arms is more that 10% and less than 60% or less than 40% of a width of the connection region, measured in the same direction as the width of the arms and in parallel to the reference plane. 
     In general, for all aspects, it can be the case that a length of the first and second arms is more than 20%, or more than 40% or more than 60% or more than 80% or more than 100% of a length of the connection region, measured in the same direction as the length of the arms and in parallel to the reference plane. 
     In general, for all aspects, it can be the case that the connection region and an excitation means have an area, when projected onto the reference plane, of less than a hundred or less than fifty or less than twenty-five square millimetres. 
     Further embodiments are evident from the dependent patent claims. Features of the method claims may be combined with features of the device claims and vice versa. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings, which schematically show: 
         FIG. 1  a drive with an active element including a resonator with a pair of arms, of which only one is in contact with and drives a passive element; 
         FIG. 2  a resonator with a pair of arms in a different arrangement; 
         FIG. 3  a drive with an additional arm acting as a bearing; 
         FIG. 4-6  different arrangements of arms for this type of drive; 
         FIG. 7-9  different arrangements with pre-stress elements; 
         FIG. 10-12  views of a drive unit in which a pre-stress force holds a base element and a driven part together; 
         FIG. 13  a resonator with an integral counterforce section for generating the pre-stress force; 
         FIG. 14-16  different configurations of the counterforce section; 
         FIG. 17  a drive unit in which the active element contacts and drives a concave region of the passive element; 
         FIG. 18  the same, in an exploded view; 
         FIG. 19  a detail of a contact element; and 
         FIG. 20-23  embodiments with rotating passive elements. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In principle, identical or functionally identical parts are provided with the same reference symbols in the figures. 
       FIG. 1  shows a drive with an active element  1  including a resonator  2  with a pair of arms, a first arm  21  and a second arm  22 , of which only the first arm  21  is in contact with and drives a passive element passive element  4 . The arms  21 ,  22  and attachment regions  14  are attached to a connection region  20  of the resonator  2 . The attachment regions  14  serve to mount the resonator  2  to another part, such as a base element  5  (illustrated in  FIGS. 7 to 12 ) An excitation means  23 , for example, a piezoelectric element, is arranged on the connection region  20 . The excitation means  23  can include two separate elements, arranged on opposing sides of the excitation means  23  (visible in  FIGS. 11, 13, 18 ). The resonator  2  and the excitation means  23  are flat elements, stacked onto one another and extending in parallel to a reference plane  28 . Upon excitation by an alternating voltage with an excitation frequency, the arms  21 ,  22  oscillate and, depending on the frequency, a first contact element  31  of the first arm  21  is made to performs a roughly elliptical movement. Depending on the frequency, the movement can be clockwise (as illustrated by an arrow) or counter clockwise. Thereby, the first contact element  31  repeatedly contacts and drives a first contact area  41  of a passive element  4  relative to the active element  1 . In this embodiment, the passive element  4 , by bearing means not shown in the figure, can move along a linear movement axis  26 . 
     The first arm  21  and second arm  22  extend from the connection region  20  in a substantially symmetric manner, and can differ in details of their shape, in particular their contour, if they are manufactured from a flat piece of material. A resonator axis  24  corresponds to an axis of symmetry at which the resonator  2 , in particular the connection region  20  and the arms  21 ,  22 , can be mirrored, except for the abovementioned details of the arms. Movement of the connection region  20  and the arms  21 ,  22 , when excited by the excitation means  23 , can be generally symmetric, with the same axis of symmetry. Nodes of this movement, that is, regions of minimal movement, can be located on the resonator axis  24 . Attachment regions  14  for mounting the active element  1  on another element, can also be located on the resonator axis  24 . 
       FIG. 2  shows a resonator with a pair of arms in a different arrangement: while in  FIG. 1  the arms  21 ,  22  extend in parallel to the resonator axis  24 , in  FIG. 2  they extend at a right angle to the resonator axis  24 . The resonator  2  can be arranged to drive only one passive element  4  (not shown in  FIG. 2 ) with only the first arm  21 , the second arm  22  serving to balance the movement of the first arm  21 . 
       FIG. 3  shows a drive with, in addition to the elements already presented, a bearing arm  8  acting as a bearing, supporting a passive element  4  which in this case is arranged to rotate relative to the active element  1 . Here too, driving the passive element  4  is effected by the first contact element  31  contacting and driving a first contact area  41  of the passive element  4  by oscillating movements. Simultaneously, a bearing region  81  of the bearing arm  8  oscillates towards and away from the passive element  4 . In  FIG. 3 , this movement is represented by a double arrow. In this manner, the bearing arm  8  reduces contact forces acting on the passive element  4  while the first contact element  31  drives the passive element  4 . Thereby, movement of the passive element  4  is facilitated. 
     The movement of the bearing arm  8  and thereby of the bearing region  81  can be synchronised with the movement of the first arm  21  by adjusting the length of the bearing arm  8 . Given two oscillating frequencies for driving the first arm  21  to move the passive element  4  in the two opposite directions, the length of a bending section  84  of the bearing arm  8  can be chosen such that for both of these two frequencies the bending section  84  oscillates to move the bearing region  81  as described above. The two frequencies can be chosen close to one another, such that the first arm  21  oscillates in different directions according to the frequency, but the mode of oscillation of the bearing arm  8  is essentially the same for both frequencies. 
     Depending on the excitation frequency, the bearing arm  8  will exhibit corresponding modes of oscillation. Such a mode can be characterised by the location of nodes of the oscillation. For example, there can be at least three nodes:
         one near a point where the bearing arm  8  is attached to the connection region  20 , for example at the C-shaped bend in  FIG. 3 ;   one near a point where the bearing arm  8  changes direction, for example at the L-shaped bend in  FIG. 3 ; and   one near the bearing region  81 .       

     When the drive is not excited, the bearing arm  8  is at rest and exerts a pre-stress force that pushes the passive element  4  towards and against the first contact element  31 , and thereby inhibits movement of the passive element  4 . 
       FIGS. 4-6  show different arrangements of arms for this type of drive in a very schematic representation.  FIG. 4  corresponds to the arrangement of  FIG. 3 , the arms running in parallel to the resonator axis  24 .  FIG. 5  represents an arrangement in which the arms running at right angles to the resonator axis  24 .  FIG. 5  represents an arrangement in which the arms are arranged in a point wise or 2-fold rotational symmetry. In these arrangements, the oscillations of the two arms can balance one another. 
       FIGS. 7-9  show different arrangements with pre-stress elements, in a highly schematic representation. Each shows a kinematic chain, from the active element  1  to the passive element  4 , with the active element  1  being linked to a base element  5  and the passive element  4  being linked to a driven part  7  (Generally, this association is a matter of convention: depending on the point of view, the active element  1  can be considered to be linked to a driven part and the passive element  4  to a base element). The base element  5  and driven part  7  are linked by a joint such as a linear joint  52 , or planar joint completing the chain. The same kinematic chain, but with a rotary joint  52 ′, is shown in  FIGS. 21-23 . The joint can be implemented with rollers  54  between the base element  5  and driven part  7 . The chain includes a resilient pre-stress element  6  for exerting a force between the active element  1  and the passive element  4  and also on the joint. The pre-stress element  6  can be arranged at one of various locations along the chain.
         According to  FIG. 7 , the pre-stress element  6  is arranged between two parts of the base element  5 , or between the base element  5  and the active element  1 .   According to  FIGS. 8 and 9 , it is arranged between two parts of the driven part  7 , or between the driven part  7  and the passive element  4 . In  FIG. 8 , the direction of movement or linear movement axis  26  of the passive element  4  relative to the active element  1  is normal to the active element&#39;s  1  resonator axis  24 , in  FIG. 9 , it is parallel.       

     The pre-stress elements  6  not only exert a pre-stress force between the active element  1  and the passive element  4 , but also on the joint between the driven part  7  and the base element  5 . If rollers  54  are present in the joint, the pre-stress force also acts on them. The pre-stress force pushes the driven part  7  and base element  5  towards each other. This allows to simplify the construction of the joint, since elements that would otherwise be necessary to hold the driven part  7  and base element  5  in place against one another can be omitted. 
     In other embodiments there can be two or more pre-stress elements  6 . 
     In other embodiments, a rotary or a spherical joint is present between the base element  5  and driven part  7 , with a limited range of angular movement and with rollers on one side of the joint only. This corresponds to an arrangement as that of  FIG. 7  but with facing sides of the driven part  7  and base element  5  forming concentric cylinders or spheres, separated by the rollers  54 . 
       FIGS. 10-12  show views of a drive unit in which a pre-stress force holds a base element  5  and a driven part  7  together, as explained above with reference to  FIGS. 7-9 . A difference from these figures is that both arms of the resonator  2  contact the passive element  4 , by means of a first contact element  31  on the first arm  21  and a second contact element  32  on the second arm  22 . Two rollers  54  are shown in the exploded view of FIG.  11 . Instead of a third roller, a sliding contact is present between the base element  5  and driven part  7 . 
       FIG. 13  shows a resonator  2  with an integral counterforce section  62  for generating the pre-stress force, as used in the arrangement of  FIGS. 10-12 . In addition to the connection region  20  with arms  21 ,  23 , the resonator  2  also includes counterforce sections  62 , which can be integrally shaped with the other parts of the resonator  2 . When mounted in the driven part  7 , the resonator  2  is free to rotate—to a certain extent—around a pivot section  61  of the resonator  2 . The resonator  2  and in particular the counterforce sections  62  and a pivot section  61  are elastically deformed, as shown in  FIGS. 10 to 12 , by forces acting on the contact elements  31  and  32  an on force application regions  63  at which the counterforce sections  62  are clamped under corresponding parts of the base element  5 . This elastic deformation corresponds to the pre-stress force that is exerted, on the one hand, between the first contact element  31 , second contact element  32  and the passive element  4 . On the other hand the pre-stress force is exerted, by pressing the passive element  4  and the entire driven part  7  downward towards the base element  5 , onto the rollers  54  of the joint between the driven part  7  and base element  5 . 
       FIGS. 14-16  show different configurations of the counterforce section  62  in a schematic representation.  FIG. 14  shows the configuration of  FIG. 13 , with the arms  21 ,  22  being parallel to the counterforce section  62  and the reference plane  28  when not loaded, and bent apart from one another at the pivot section  61  when loaded by the forces acting on the contact elements  31 ,  32  and the force application regions  63 .  FIG. 15  shows a configuration in which the counterforce section  62  extends upwards at an angle to the arms  21 ,  22 . In another embodiment, it extends downwards at an angle.  FIG. 15  shows a configuration in which the counterforce section  62  extends in parallel to the arms  21 ,  22  but in the opposite direction when not loaded. 
       FIG. 17  shows a drive unit in which the active element contacts and drives a concave region of the passive element, and  FIG. 18  shows the same, in an exploded view. The active element  1  includes elements as already presented above. The passive element  4  includes a attachment sections and an attachment hole  47  for attaching it to, for example a driven part  7  or base element  5 . A first attachment section  45  supports a first contact area  41  and a second attachment section  46  supports a second contact area  42 . Each contact area  41 ,  42 , and optionally the entire passive element  4  is manufactured from a flat part of a sheet material, for example, sheet metal. The contact areas  41 ,  42  are bent to form a concave shape, in particular a U-shape. Each contact element  31 ,  32  is arranged to contact a respective contact area  41 ,  42  by reaching into this concave shape. The passive element  4  can be driven to move along the linear movement axis  26 . The attachment sections  45 ,  46  are relatively stiff in the movement direction and relatively elastic in directions normal to the linear movement axis  26 . This allows the drive to absorb misalignment and movement in these directions. At the same time, the concave shape of the respective contact area  41 ,  42  keeps the contact elements  31 ,  32  within the contact area  41 ,  42 . 
       FIG. 17  also shows a contact element  13  clamping two piezo plates constituting the excitation means  23  against the connection region  20 . Electrical contacts for driving the piezo plates are constituted on the one hand by the contact element  13  and on the other hand by the resonator  2  and its attachment regions  14 . 
     In other embodiments, not shown in the figures, the second arm  22  does not come into contact with a corresponding second contact area  42 . The passive element  4  is thus driven only by the first arm  21 . 
       FIG. 19  shows an extension d of a contact surface of a contact element  31  in the reference plane  28 . The extension can be related to a resonator length, the resonator length being defined as the dimension of the resonator along the resonator axis  24 , from the ends of the arms  21 ,  22  to the opposing ends of their counterweight sections (if present). In other words, the resonator length is the size of the resonator  2  in the direction along resonator axis  24 , without fixation or support area(s)  27 . The extension d of the flat contact surface is measured on a projection of the flat region projected onto the reference plane  28 . 
     The contact surface includes the surface that intermittently comes into contact with the passive element  4 . With its shape corresponding to the shape of the surface of the corresponding contact area on the passive element  4 , contact forces are distributed over the contact surface and thereby wear of the contact element is reduced. 
     In the embodiment of  FIG. 19 , the contact surface is flat, and the location of the flat contact surface corresponds to the passive element  4  being arranged as in one of  FIGS. 9 to 18 . In the embodiments according to  FIGS. 1, 7 and 8 , the flat contact surface can be arranged on the respective contact element  31  facing the passive element  4 . 
     In the embodiments according to  FIGS. 3 and 20 to 23 , the contact surface can be curved, according to an outer radius of the passive element  4 , and arranged on the respective contact element  31  facing the passive element  4 . The extension d of the contact surface is measured along the arc following the curve of the surface. 
       FIG. 20-23  show embodiments with rotating passive elements  4  and/or driven parts. The kinematic structure corresponds to that of  FIGS. 1, 7, 8 and 9 , respectively, but with a rotary joint  52 ′ instead of the linear joint  52 . The remainder of the function and interaction of the active element  1  and passive element  4  are the same.
         According to  FIG. 20 , the passive element  4  of  FIG. 1 , instead of being linearly movable along the linear movement axis  26 , is rotatable around a rotary movement axis  26 ′.   According to  FIG. 21 , a pre-stress element  6  is arranged between two parts of the base element  5 , or between the base element  5  and the active element  1 .   According to  FIGS. 22 and 23 , the pre-stress element  6  is arranged between two parts of the driven part  7 , or between the driven part  7  and the passive element  4 . In  FIG. 22 , the tangential direction of movement of the passive element  4  at the first contact area  41  is approximately normal to the active element&#39;s  1  resonator axis  24 , in  FIG. 23 , it is parallel, or approximately parallel.       

     While the invention has been described in present embodiments, it is distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practised within the scope of the claims.