Mounting device for piezoelectric motor elements - Patents.com

Abstract

A piezoelectric actuator is described that includes a piezoelectric motor element having a top surface and a bottom surface, and a connecting element that includes an arm having a flexure hinge for contacting the piezoelectric motor element at different fixed positions located at node positions of a bending mode of the piezoelectric motor element, the flexure hinge allowing the piezoelectric motor element to move in a normal direction and such that the flexure hinge is rigid in a tangential direction, whereby the flexure arm is fixed to the piezoelectric motor element by a fixing means.

Description

[Technical field]

[0001] FIELD OF THEINVENTION The present invention relates to a piezoelectric motor, e.g., an ultrasonic piezoelectric motor, and a method for mounting elements of a piezoelectric motor. More particularly, the present invention relates to a method and system for connecting or mounting piezoelectric motor elements, e.g., ultrasonic piezoelectric motor elements, to a stator component of a positioning device. [Background technology]

[0002] 2. Background of the Invention Piezoelectric actuators are often used in many applications that require a high degree of miniaturization. However, the biggest limitation of a typical piezoelectric positioner is that its displacement is very small. To counter this effect, several principles of piezoelectric motors with unlimited range of motion have been presented.

[0003] Three main types of piezoelectric motors are designed with infinite stroke: (1) stepper motors, (2) stick-slip / inertia drive motors, and (3) resonant motors. Stepper motors have high holding force but are often too slow for many applications. Stick-slip motors achieve speeds on the order of 10 mm / s but often produce excessive vibration. Resonant motors, often called "ultrasonic" due to their high operating frequency, in contrast, achieve maximum speeds on the order of 100 mm / s or more. This is because the piezoelectric elements in a resonant motor are excited with a drive signal whose frequency is close to the motor's two natural frequencies. A typical piezoelectric motor, for example, has longitudinal and lateral translation natural modes that are nearly coincident in frequency.

[0004] Miniature ultrasonic piezoelectric motors feature high power efficiency compared to electric motors of the same size. Due to their compactness and efficiency, they are often used in handheld devices. Ultrasonic piezoelectric motors are quiet motors due to their high frequency operation. Another advantage of these motors is that they do not have a transmission system like gears or belts. Therefore, the actuation mechanism is less complicated and there is no mechanical backlash. This means that these motors can achieve better positioning accuracy. Even when shut down, these motors still exert a holding force, so the position of the sample being moved is fixed. Some applications also require that the actuation is backdrivable. This means that the sample can still be moved manually and the effects of hard collisions can be limited, for example when hitting a hard target. Like other piezoelectric motors, ultrasonic piezoelectric motors are often used in specific environments such as high or ultra-high vacuum, when avoiding magnetic fields, and in cryogenic environments. However, these motors are also used in atmospheric applications, typically when both small size and high speed are required.

[0005] Although several ultrasonic motors that operate via resonant vibration modes have been designed over the past few years, they still suffer from several drawbacks.

[0006] Japanese Patent Laid-Open Publication No. 7-107758 discloses an ultrasonic actuator that applies high-frequency voltages of different phases to two sets of electromechanical energy converters. Standing wave vibration is generated in a resonator, and the node part of this standing wave vibration is fixed by a holding means using an elastic hinge structure.

[0007] European Patent Application Publication No. 0978886 discloses an ultrasonic motor intended to reduce leakage of driving force generated by a piezoelectric element and efficiently transmit the driving force to a moving member. The ultrasonic motor includes a piezoelectric element that vibrates in response to an input driving signal to generate a driving force, and a support member that supports the piezoelectric element on a substrate. The support member has a signal supply function that supplies a driving signal to the piezoelectric element. As a result, there is no need to provide a separate signal transmission means, and vibration caused by the piezoelectric element is less likely to leak than in the conventional configuration. As a result, the ultrasonic motor efficiently transmits the driving force to the moving member. In addition, the support member is made elastic by providing a constriction, so it also has a pressing function that presses the piezoelectric element against the moving member. In this case, vibration leakage is further reduced.

[0008] Nevertheless, there remains a need for compact ultrasonic piezoelectric motors and piezoelectric motors that are easy to install. Summary of the Invention [Problem to be solved by the invention]

[0009] Summary of the Invention SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide a good mounting system and method for mounting the components of an ultrasonic piezoelectric motor. [Means for solving the problem]

[0010] An advantage of an embodiment of the present invention is that the motor element is held in place by removing the appropriate degree of freedom of the piezoelectric motor element. An advantage of an embodiment of the present invention is that all but one degree of freedom of the piezoelectric motor element is removed. An advantage of an embodiment of the present invention is that the motor can be moved in a direction perpendicular to the sliding direction to generate a preload force between the drive contact of the motor and the traction surface of the positioning device.

[0011] An advantage of embodiments of the present invention, but the invention is not limited thereto, is that the preload force can be applied by a mechanical spring component.

[0012] An advantage of embodiments of the present invention is that the mounting does not impede the ultrasonic drive vibrations that occur when exciting the piezoelectric motor at its resonant frequency. An advantage of embodiments of the present invention is that the fixing points are selected such that there is no or minimal interaction with the eigenmodes of the piezoelectric motor at resonance. The latter results in good forces and speed of movement of the positioner.

[0013] The fixed points are the locations where the piezoelectric element is fixed to other elements. Apart from the drive contacts, these are the only locations where the piezoelectric element makes contact with surrounding elements.

[0014] An advantage of embodiments of the present invention is that the method and system have no or minimal play or backlash in the drive direction of the motor.

[0015] An advantage of embodiments of the present invention is that the mounted motor elements are realised in a very compact manner, thus resulting in a compact system.

[0016] An advantage of embodiments of the present invention is that it allows the attachment of the motor elements to be achieved by inexpensive manufacturing processes, such as stamping, laser cutting, etc., and has low manufacturing costs. An advantage of embodiments of the present invention is that the assembly time is short.

[0017] An advantage of embodiments of the present invention is that a method and system is provided that provides symmetry and reduces the effect on motor resonance modes.An advantage of embodiments of the present invention is that good thermal stability of the resulting positioning system is obtained.An advantage of embodiments of the present invention is that great symmetry of the device is obtained, improving stability.

[0018] This object and optionally one or more advantages are met by the mounting method and the resulting system according to the present invention. The dependent claims relate to preferred embodiments.

[0019] The present invention relates to a piezoelectric actuator, for example an ultrasonic piezoelectric actuator, comprising a piezoelectric motor element having a top surface and a bottom surface; A connection element comprising arms with flexure hinges for fixing a piezoelectric motor element at different fixing positions located at nodal positions of one or more bending modes of the piezoelectric motor element, The flexure hinge is such that it allows the piezoelectric motor element to move in the normal direction, the flexure hinge being rigid in the tangential direction, whereby the flexure arm comprises a connecting element fixed to the piezoelectric motor element by a fixing means.

[0020] In some embodiments, the connection element may comprise two foil elements, one top connection foil element disposed on the top side of the piezoelectric motor element and one bottom connection foil element disposed on the bottom side of the piezoelectric motor element, in some embodiments, both the top connection foil element and the bottom connection foil element may have arms with flexure hinges.

[0021] The flexure hinges for contacting the piezoelectric motor element may be configured to contact the piezoelectric motor element at a top surface of the piezoelectric motor element and a bottom surface of the piezoelectric motor element, respectively.

[0022] Alternatively, a single connection element may be provided having arms with flexure hinges that contact the piezoelectric motor element at their circumferential surfaces.

[0023] When referring to a foil in embodiments of the present invention, this can refer to a film-like structure or thin layer, but can also encompass thicker layers, such as, for example, thin plates. In some embodiments, such plates can, for example, be bent.

[0024] In embodiments of the present invention, when it is stated that the piezoelectric motor element is capable of moving in the normal direction and the flexure hinge is stiff in the tangential direction, it refers to the fact that the flexure hinge is perpendicular to the extension mode of movement at the location of the fixed point. The normal direction may also be defined as being radial to the center location.

[0025] The flexure arms may be secured to the piezoelectric motor element using an adhesive. The adhesive may be an epoxy adhesive or an acrylate or polyurethane.

[0026] The piezoelectric motor element may have a hole extending through the piezoelectric motor element from the top surface to the bottom surface, and the connection element may further comprise a connection portion disposed through the hole in the piezoelectric motor element, the connection portion mechanically connecting the top connection foil element and the bottom connection foil element, whereby the different fixing positions are disposed away from the hole, and at the position of the hole, the connection element and the piezoelectric motor element are not in contact with each other.

[0027] The connection may include a spacer ring for spacing the top and bottom connecting foil elements.

[0028] The outer diameter of the spacer ring may be substantially smaller than the inner diameter of the bore of the piezoelectric motor element. In some embodiments, the outer diameter of the spacer ring may be 50 μm smaller than the inner diameter of the bore. In some embodiments, substantially smaller than the inner diameter may be less than 90%, such as less than 80%, such as less than 70% of the inner diameter of the bore.

[0029] The connection may comprise two shim elements, for example shim rings, that provide a mechanical connection between the top and bottom connecting foil elements and help space the foil elements from the piezoelectric motor element.

[0030] The dimensions of the connections may be such that there is a play between the shim element and the top and bottom surfaces of the piezoelectric motor element in the range of 2 μm to 50 μm, such as 2 μm to 20 μm, for example about 10 μm.

[0031] In an embodiment of the invention, no forces are generated in the direction of the vertical axis during operation, therefore any play in this direction does not cause undesirable play or backlash in the drive direction.

[0032] A flexible circuit may be provided between the piezoelectric motor element and the connecting foil for electrically connecting to the electrodes of the piezoelectric motor element.

[0033] Although flexible circuits for connecting piezoelectric motor elements provide a quick and accurate method for electrically connecting electrodes within the piezoelectric motor elements, such electrodes within the piezoelectric motor elements can also be connected by electrical wiring.

[0034] The piezoelectric actuator may further comprise a suspension element for suspending the piezoelectric motor element such that the piezoelectric motor element is free to move in a direction perpendicular to the drive direction while preventing undesired movement in the drive direction.

[0035] The suspension element may comprise two suspension foils, one suspension foil arranged on a top side of the piezoelectric motor element and one suspension foil arranged on a bottom side of the piezoelectric motor element.

[0036] The suspension foil may be arranged such that the suspension foil is located on a side of the connecting foil facing away from the piezoelectric motor element, and the suspension foil and connecting foil are spaced apart from each other by a shim element.

[0037] The suspension foils, the shim elements and the connecting foils may be mechanically connected to one another. The suspension foils, the shim element and the connecting foils may be mechanically connected to each other using connections that extend through a central hole in the piezoelectric motor element.

[0038] The piezoelectric motor element may be in the form of a plate. The electrodes may be electrically connected and configured such that driving the electrodes induces an in-plane mode.

[0039] Taking into account the polarity of the piezoelectric motor elements, the electrodes can be electrically connected and configured such that actuation of the electrodes induces in-plane bending and / or in-plane expansion modes.

[0040] Taking into account the polarity of the piezoelectric material, the electrodes can be electrically connected and configured such that actuation of the electrodes induces alternating in-plane bending and in-plane expansion modes.

[0041] In some embodiments, the electrodes can be configured so that an in-plane mode is used.

[0042] An in-plane bending mode may be a vibration mode in which adjacent corners move in opposite directions, and an in-plane expansion mode may be a vibration mode in which different corners of the top surface move in the same direction, either outward or inward, in sync.

[0043] In another aspect, the present invention relates to a piezoelectric actuator, the piezoelectric actuator comprising: a piezoelectric motor element having a top surface and a bottom surface; a connecting element comprising two foil elements, one top connecting foil element arranged on the top side of the piezoelectric motor element and one bottom connecting foil element arranged on the bottom side of the piezoelectric motor element, the top connecting foil element and the bottom connecting foil element contacting the piezoelectric motor element at different fixed positions, such that the connecting element holds the piezoelectric motor element in a fixed position without disturbing the natural modes of the piezoelectric motor element at resonance; the piezoelectric motor element has a hole extending through the piezoelectric motor element from the top surface to the bottom surface; The connection element further comprises a connection portion arranged through a hole in the piezoelectric motor element, the connection portion mechanically connecting the top connection foil element and the bottom connection foil element, whereby the different fixing positions are arranged away from the hole, whereby the connection element and the piezoelectric motor element do not contact each other at the position of the hole.

[0044] The fixed locations may be on the top and / or bottom surfaces of the piezoelectric element, or the fixed locations may be on the sides of the piezoelectric motor element.

[0045] An advantage of embodiments of the present invention is that they provide a compact piezoelectric motor. The connection may include a spacer ring for spacing the top and bottom connecting foil elements.

[0046] The outer diameter of the spacer ring may be substantially smaller than the inner diameter of the bore of the piezoelectric motor element. In some embodiments, the outer diameter of the spacer ring may be 50 μm smaller than the inner diameter of the bore. In some embodiments, substantially smaller than the inner diameter may be less than 90%, such as less than 80%, such as less than 70% of the inner diameter of the bore.

[0047] The connection may comprise two shim elements, for example shim rings, that provide a mechanical connection between the top and bottom connecting foil elements and help space the foil elements from the piezoelectric motor element.

[0048] The dimensions of the connections may be such that there is a play between the shim element and the top and bottom surfaces of the piezoelectric motor element in the range of 2 μm to 50 μm, such as 2 μm to 20 μm, for example about 10 μm.

[0049] An advantage of an embodiment of the invention is that during operation no forces occur in the direction of the vertical axis, and therefore any play in this direction does not cause undesirable play or backlash in the drive direction.

[0050] A flexible circuit may be provided between the piezoelectric motor element and the connecting foil for electrically connecting to the electrodes of the piezoelectric motor element.

[0051] Although flexible circuits for connecting piezoelectric motor elements provide a quick and accurate method for electrically connecting electrodes within the piezoelectric motor elements, such electrodes within the piezoelectric motor elements can also be connected by electrical wiring.

[0052] The piezoelectric actuator may further comprise a suspension element for suspending the piezoelectric motor element such that the piezoelectric motor element is free to move in a direction perpendicular to the drive direction while preventing undesired movement in the drive direction.

[0053] The suspension element may comprise two suspension foils, one suspension foil arranged on a top side of the piezoelectric motor element and one suspension foil arranged on a bottom side of the piezoelectric motor element.

[0054] The suspension foil may be arranged such that the suspension foil is located on a side of the connecting foil facing away from the piezoelectric motor element, and the suspension foil and connecting foil are spaced apart from each other by a shim element.

[0055] The suspension foils, the shim elements and the connecting foils may be mechanically connected to one another. The suspension foils, the shim element and the connecting foils may be mechanically connected to each other using connections that extend through a central hole in the piezoelectric motor element.

[0056] The piezoelectric motor element may be in the form of a plate. Taking into account the polarity of the piezoelectric motor elements, the electrodes can be electrically connected and configured such that actuation of the electrodes induces in-plane bending and / or in-plane expansion modes.

[0057] Taking into account the polarity of the piezoelectric material, the electrodes can be electrically connected and configured such that actuation of the electrodes induces alternating in-plane bending and in-plane expansion modes.

[0058] An in-plane bending mode may be a vibration mode in which adjacent corners move in opposite directions, and an in-plane expansion mode may be a vibration mode in which different corners of the top surface move in the same direction, either outward or inward, in sync.

[0059] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

[0060] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. Further features of the invention will be apparent from the examples and the drawings.

[0061] BRIEF DESCRIPTION OF THE DRAWINGS [Brief description of the drawings]

[0062] [Figure 1] 1 illustrates a schematic of a motor element of an ultrasonic piezoelectric motor having a mounting mechanism according to an embodiment of the present invention. [Diagram 2] 2 shows a cross-sectional view of the motor element shown in FIG. 1 taken along line AA. [Diagram 3] 1 shows an overview of motor elements of an ultrasonic piezoelectric motor with mounting features according to an embodiment of the present invention. [Figure 4] 1 shows a cross-sectional view of a motor element of an ultrasonic piezoelectric motor with mounting features according to an embodiment of the present invention. [Diagram 5] 1 shows a detailed view of a portion of a cross section of a motor element of an ultrasonic piezoelectric motor with mounting features according to an embodiment of the present invention. [Figure 6] 1 illustrates the different components (layers) of an ultrasonic piezoelectric motor with a mounting mechanism according to an embodiment of the present invention; [Figure 7] 1 illustrates the different components (layers) of an ultrasonic piezoelectric motor with a mounting mechanism according to an embodiment of the present invention, showing a flexprint. [Figure 8] 1 shows the different components (layers) of an ultrasonic piezoelectric motor with an attachment mechanism according to an embodiment of the present invention, and shows the connecting foils. [Figure 9]1 illustrates the different components (layers) of an ultrasonic piezoelectric motor with an attachment mechanism according to an embodiment of the present invention, and illustrates a suspended foil that can be used in an embodiment of the present invention. [Figure 10] 1 illustrates an example of a piezoelectric motor according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] The drawings are only schematic and non-limiting. In the drawings, the size of some elements may be exaggerated and not drawn to scale for illustrative purposes. Any reference signs in the claims should not be construed as limiting the scope. The same reference signs in different drawings refer to the same or similar elements.

[0064] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with respect to certain embodiments and with reference to certain drawings, but the invention is not limited thereto, but only by the claims. The drawings described are only schematic and non-limiting. In the drawings, the size of some elements may be exaggerated and not drawn to scale for illustrative purposes. When the term "comprising" is used in this specification and claims, it does not exclude other elements or steps. When an indefinite or definite article is used when referring to a singular noun, such as "a" or "an", "the", this includes a plural of that noun, unless otherwise stated. When the term "comprising" is used in the claims, it should not be interpreted as being limited to the means listed thereafter, and it does not exclude other elements or steps. Thus, the scope of the expression "apparatus comprising means A and B" should not be limited to an apparatus consisting of only components A and B. This means that, in the context of the present invention, the relevant components of the apparatus are only A and B. Furthermore, terms such as first, second, third, etc. in the specification and claims are used to distinguish between similar elements and are not necessarily intended to describe a sequential or chronological order. It is to be understood that terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein may operate in other sequences than as described or illustrated herein. Furthermore, terms such as top, bottom, upper, lower, etc. in the specification and claims are used for descriptive purposes and are not necessarily intended to describe relative positions. It is to be understood that terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein may operate in other orientations than as described or illustrated herein.

[0065] In the drawings, like reference numbers indicate like features, and a reference number appearing in more than one figure refers to the same element.The drawings and the detailed description that follows show particular embodiments of actuators, and more particularly, piezoelectric actuators.

[0066] In embodiments of the present invention, reference to a piezoelectric material refers to a material that exhibits the effect of an electric charge accumulating in response to an applied mechanical stress. Conversely, application of an electric field to a piezoelectric material causes the material to undergo deformation resulting in a displacement.

[0067] Reference to an actuator in embodiments of the present invention refers to an active element, preferably in the form of a piezoceramic block or a stack of different piezoceramic layers, comprising for example a piezoelectric material and electrodes. The actuators used in embodiments of the present invention can be of any type: piezoelectric, magnetostrictive or electrostrictive actuators.

[0068] In embodiments of the present invention, reference to a motor, for example a piezoelectric motor, refers to a motor that includes an actuator, for example a piezoelectric ceramic actuator.

[0069] In embodiments of the present invention, reference to suspension or suspension foil refers to a component or mechanism that supports the motor and presses it against the load with a force that creates a preload.

[0070] In embodiments of the present invention, references to contact may refer to, for example, the location where a tip of a motor according to an embodiment of the present invention contacts the surface of a driven object.

[0071] In embodiments of the present invention, when referring to a fixed position, it refers to the position / location where the flexible hinge is fixed to the piezoelectric motor.

[0072] In embodiments of the present invention, references to preload refer to a static force acting on an actuator or motor according to embodiments of the present invention, acting substantially perpendicular to the direction of load movement.

[0073] In the present embodiments, reference to a load or stage refers to a component or structure that is (is) driven by a motor according to the present embodiments.

[0074] It should be noted that the geometry of the piezoelectric motor elements is not limiting to the embodiments of the invention. By way of example, and not of limitation to the embodiments of the invention, a particular embodiment is described with reference to a piezoelectric motor element having the same geometry as described in EP-A-3535842 in the name of the applicant, and such a piezoelectric motor element may be driven in the same manner as described in EP-A-3535842, for example using the same modes. EP-A-3535842 discloses that the electrodes can be electrically connected and configured such that driving the electrodes induces in-plane bending and / or in-plane expansion modes, taking into account the polarity of the piezoelectric material. In a preferred embodiment of EP-A-3535842, the resonant modes are achieved by exciting or energizing two pairs of electrodes with two AC voltages, while varying the phase difference between the two AC voltages and / or the voltage amplitude. These voltages excite the horizontal eigenmodes of the actuator, e.g. in-plane bending modes, and the vertical eigenmodes, e.g. in-plane expansion modes, resulting in an elliptical movement of the contact area. When the contact area (tip) is pressed against a surface, the surface is driven relative to the actuator at a speed and direction according to the selected trajectory.

[0075] Nevertheless, embodiments of the invention are not limited by the geometry of the piezoelectric motor element or the mode used to drive the piezoelectric motor element, but by the features defined in the independent claims.

[0076] Although example embodiments of the present invention may refer to specific excitation modes, embodiments are not limited thereto and also encompass piezoelectric motors driven using different excitation modes.

[0077] In a first aspect, the present invention relates to a piezoelectric actuator comprising a piezoelectric motor element made of a piezoelectric material. The piezoelectric material may be a piezoelectric plate, but embodiments are not limited thereto. The piezoelectric motor element has a top surface and a bottom surface. The piezoelectric actuator also comprises at least one contact point for contacting a load to be actuated. The at least one contact point is disposed on a third circumferential surface of the ceramic piezoelectric material. In an embodiment of the present invention, the attachment and contacting are performed at two separate locations on the piezoelectric material.

[0078] The piezoelectric actuator also comprises a connection element. In some embodiments, the connection element comprises two foil elements, i.e. one top connection foil element arranged on the top side of the piezoelectric motor element and one bottom connection foil element arranged on the bottom side of the piezoelectric motor element. In some embodiments, a single connection foil or plate is provided. According to an embodiment of the invention, the connection element has arms with flexure hinges for fixing the piezoelectric motor element at different fixing positions arranged at node positions of one or more bending modes of the piezoelectric motor element.

[0079] Alternatively, a single connection element may be provided having arms with flexure hinges that contact the piezoelectric motor element at their circumferential surfaces.

[0080] The flexure hinge allows the piezoelectric motor element to move in the normal direction and is such that the flexure hinge is stiff in the tangential direction, whereby the flexure arm is fixed to the piezoelectric motor element by a fixing means.

[0081] Embodiments of the invention may further typically comprise at least one set of electrodes disposed on the top surface of the piezoelectric material and at least one electrode disposed on the bottom surface of the ceramic piezoelectric material. Taking into account the polarity of the ceramic piezoelectric material, the electrodes may be electrically connected and configured such that actuation of the electrodes induces in-plane bending and / or in-plane expansion modes. As shown, this may be provided using a flexible circuit, although embodiments are not limited thereto. Further standard and optional features are described below with reference to exemplary embodiments.

[0082] In a second aspect, the present invention relates to a motor comprising a piezoelectric actuator according to the first aspect. In embodiments of the present invention, reference to a motor refers to a combination of at least the actuator described above in combination with a suspension and an applied preload.

[0083] By way of example, and not limitation, the piezoelectric actuator will be further described with reference to the drawings, which show standard and optional components of exemplary embodiments of the invention, and it should be noted that although reference is made to a motor, when elements of a piezoelectric actuator are described, reference is made to the actuator itself as well.

[0084] In an embodiment of the invention, the connection comprises two foil elements arranged on the top and bottom sides of the motor element. In a particular embodiment, each foil contacts the motor in four places, although the embodiment is not limited thereto. At the location of these fixing points, the motor moves / vibrates only in the normal direction (nodes of bending mode). The foil elements have four arms with bending hinges that allow this normal vibration. In the tangential direction, however, the hinges are completely rigid. Some examples of materials that can be used are ferrous materials, non-ferrous materials, engineering plastics, etc. In a preferred embodiment, the contact between the motor element and the bending arms is realized by an epoxy adhesive. Alternatively, other types of adhesives, such as acrylates or polyurethanes, can also be used. Nevertheless, alternatively, another type of adhesive or even another type of fixation, such as soldering or brazing, can also be used. In some embodiments, the shape of the arm end is designed such that the capillary forces acting on the uncured adhesive form a meniscus shape that holds the adhesive in place during curing.

[0085] The combination of the top and bottom connecting foils holds the motor elements in position by removing two lateral and all rotational degrees of freedom. This is done with a very stiff, backlash-free connection in the drive direction without interfering with the intended natural modes of the motor.

[0086] In some particular embodiments, the connection foils are separated by spacer rings and shim rings. This layer of stacked elements is pressed together by a bolt connection through a central hole. There is no mechanical contact between the motor and the connection elements around the central mounting hole of the motor. The outer diameter of the spacer ring is significantly smaller than the inner diameter of the central hole of the piezoelectric motor. In some embodiments, the outer diameter of the spacer ring may be 50 μm smaller than the inner diameter of the hole. In some embodiments, substantially smaller than the inner diameter may be less than 90%, such as less than 80%, such as less than 70% of the inner diameter of the hole. In the vertical / axial direction, there is a minimal amount of play between the shim ring and the top / bottom surface of the motor. The amount of such play may be in the range of 2 micrometers to 20 micrometers, such as about 10 micrometers. During operation, no forces are generated in the vertical / axial direction. Any play in this direction does not cause undesirable play or backlash in the drive direction.

[0087] Instead of a central or non-central mounting hole, the connecting foils may be held together by connections located on the outside of the piezoelectric motor elements.

[0088] As mentioned above, between the motor and the connecting foil, in some embodiments, a flex printed circuit is provided which makes the electrical connections to the different electrodes of the motor elements. Another solution for this could be simple wires.

[0089] 1 and 2 show a first view and a cross-sectional view of a piezoelectric motor element and a connecting foil, and in this example the mechanical connection between the connecting foil via a hole through the piezoelectric motor element.

[0090] In an embodiment of the invention, the piezoelectric actuator may also comprise a suspension element. In some embodiments, the suspension element may be two suspension layers. In one embodiment, the suspension element adds another foil on both the top and bottom sides of the motor. In some embodiments, a suspension structure, for example a piezoelectric with two connecting foils attached to a thick suspension element, is provided. The system can provide sufficient tilting stiffness. The function of these foils is to allow the motor element to move freely in a direction perpendicular to the drive direction while preventing undesired movements in the drive direction. These suspension foils are also provided with flexure hinges that allow them to move freely over a certain distance. Such a distance may be between 0.1 mm and 1 mm, for example about 0.5 mm. The hinges are rigid in the drive direction and in the torsion direction. The suspension foils are attached with their connecting foils on both sides of the motor element in this example. A shim ring is installed between both layers. There is some flexibility in the vertical / axial direction and in the two tilt directions. However, this flexibility is not a problem since no forces are generated in these directions. 3 to 5 show the suspension layers and how they are configured relative to the connection layers and the piezoelectric motor elements.

[0091] FIG. 6 shows a piezoelectric motor that may be used in embodiments of the present invention, FIG. 7 shows a flexible print that may be used in embodiments of the present invention, FIG. 8 shows a connecting foil that may be used in embodiments of the present invention, and FIG. 9 shows a suspension foil that may be used in embodiments of the present invention.

[0092] It would be possible to use other methods for this suspension function, such as small guideways, etc. However, the other methods are not as compact and introduce mechanical play in the drive direction.

[0093] In this embodiment, the stack of suspension foils, shim rings and connecting foils is held together by a bolt and an internally threaded pin that passes through the central hole of the motor. The tightening torque needs to be sufficient to withstand the driving forces and torques of the motor. The central pin is also responsible for the alignment of all the components.

[0094] The combination of the motor element with the connecting and suspension layers forms a motor unit that is easily installed on the stator of the positioning device. The final element is a spring that presses the drive contact of the motor against the traction surface of the device. The spring may be a simple U-spring that provides an equal preload at the top and on both sides of the motor unit. Again, other solutions are possible, but this U-spring results in a very compact realization.

[0095] In one particular embodiment, the connecting layer and the suspension layer can be combined into a single layer. In another particular embodiment, the electrical connection and the mechanical connection, for example via a flexible circuit, can be combined into a single layer.

[0096] In the above exemplary embodiments, the different parts of the connection element or the connection element and the suspension element are held together using bolt and screw connections, however alternative means for holding these parts together can be used, such as press fit connections, shrink fit connections, adhesives, etc.

[0097] In one particular embodiment, a square piezoelectric element is used whereby the connecting foils are connected to the piezoelectric element via fixing points, one on each side of the piezoelectric element, and the connecting foils are fixed to the piezoelectric element via bending arms and hinges. An example of such an embodiment is shown in FIG.

[0098] Further by way of example, a piezoelectric motor according to an embodiment of the invention is shown in FIG. 10. Different orientations applicable to the system are shown in the figure. It can be seen that the fixed points for fixing the hinges to the piezoelectric elements are located at the nodes of the bending mode. The fixed points are placed on the nodes of the bending mode. The length direction (longitudinal direction) of the arms is perpendicular to the local movement direction of the other mode. Such a mode may be a bending or an expansion mode. The length direction is defined by the line connecting the hinge and the fixed point.

[0099] It should be noted that while the embodiments of the invention described above use bending and expansion modes, embodiments of the invention may use other bending modes as well, whereby the fixed points are located at the nodes of the bending modes, and the flexible hinges are located perpendicular to the local motion of the other modes.

[0100] In another aspect, the invention relates to a piezoelectric actuator comprising a piezoelectric motor element having a top surface and a bottom surface, and a connecting element comprising two foil elements, one top connecting foil element disposed on the top side of the piezoelectric motor element and one bottom connecting foil element disposed on the bottom side of the piezoelectric motor element, the top connecting foil element and the bottom connecting foil element contacting the piezoelectric motor element at different fixed positions on the top surface of the piezoelectric element and the bottom surface of the piezoelectric motor element respectively, such that the connecting element holds the piezoelectric motor element in a fixed position without disturbing the natural modes of the piezoelectric motor element at resonance.

[0101] According to an embodiment of the invention, the piezoelectric motor element has a hole extending through the piezoelectric motor element from the top surface to the bottom surface. The hole may be centrally located or located at any other suitable position. According to an embodiment of the invention, the connection element further comprises a connection portion arranged through the hole of the piezoelectric motor element, the connection portion mechanically connecting the top connection foil element and the bottom connection foil element, whereby the different fixing positions are arranged away from the hole, and at the position of the hole the connection element and the piezoelectric motor element are not in contact with each other. The piezoelectric motor element may be as described in the first aspect. The connection element may be as described in the first aspect. The piezoelectric actuator may also comprise a suspension element, which in one example may be as described in the first aspect.

[0102] According to embodiments of the invention, the connections may comprise, for example, bolts and screws that hold the elements together, nevertheless alternatives such as press-fit connections, shrink-fit connections, adhesives, etc. may also be used.

[0103] Further features may be as described in the first aspect. The piezoelectric actuator or motor elements may further be as described in EP 3535842, although embodiments are not limited thereto.

[0104] Terms Particular embodiments of the present invention are described by the following numbered clauses:

[0105] 1. A piezoelectric actuator comprising: a piezoelectric motor element having a top surface and a bottom surface; a connecting element having arms with flexure hinges for contacting the piezoelectric motor element at different fixed positions located at nodal positions of one or more bending modes of the piezoelectric motor element; a flexure hinge allowing the piezoelectric motor element to move in the normal direction and being stiff in the tangential direction, whereby the flexure arm is fixed to the piezoelectric motor element by a fixing means; A piezoelectric actuator comprising:

[0106] 2. The piezoelectric actuator of claim 1, wherein the bending arm is secured to the piezoelectric motor element using an adhesive.

[0107] 3. A piezoelectric actuator as described in any of the preceding clauses, wherein the connection element comprises two foil elements, one top connection foil element disposed on a top side of the piezoelectric motor element and one bottom connection foil element disposed on a bottom side of the piezoelectric motor element, the top connection foil element and the bottom connection foil element having arms with flexure hinges for contacting the piezoelectric motor element and configured to contact the piezoelectric motor element at the top surface of the piezoelectric motor element and the bottom surface of the piezoelectric motor element, respectively.

[0108] 4. A piezoelectric actuator as described in clause 3, wherein the piezoelectric motor element has a hole extending through the piezoelectric motor element from the top surface to the bottom surface, and the connecting element further comprises a connecting portion disposed through the hole in the piezoelectric motor element, the connecting portion mechanically connecting the top connecting foil element and the bottom connecting foil element, whereby the different fixing positions are disposed away from the hole and at the position of the hole the connecting element and the piezoelectric motor element are not in contact with each other.

[0109] 5. The piezoelectric actuator of clause 4, wherein the connection portion comprises a spacer ring for spacing the top and bottom connecting foil elements.

[0110] 6. A piezoelectric actuator as described in clause 5, wherein an outer diameter of the spacer ring is substantially smaller than an inner diameter of the bore of the piezoelectric motor element.

[0111] 7. A piezoelectric actuator as described in any of the preceding clauses, wherein the connection portion provides a mechanical connection between the top connecting foil element and the bottom connecting foil element and comprises two shim elements, e.g. shim rings, which help space the foil elements from the piezoelectric motor element.

[0112] 8. A piezoelectric actuator as described in clause 7, wherein the dimensions of the connection are such that there is a play of the order of 2 μm to 20 μm between the shim element and the top and bottom surfaces of the piezoelectric motor element.

[0113] 9. A piezoelectric actuator according to any of the preceding clauses insofar as it is dependent on clause 3, in which a flexible circuit is provided between the piezoelectric motor element and the connecting foil for electrical connection to electrodes in the piezoelectric motor element.

[0114] 10. A piezoelectric actuator according to any of the preceding clauses, further comprising a suspension element for suspending the piezoelectric motor element such that the piezoelectric motor element is free to move in a direction perpendicular to the drive direction while preventing undesired movement in the drive direction.

[0115] 11. A piezoelectric actuator as described in clause 10, wherein the suspension element comprises two suspension foils, one suspension foil arranged on a top side of the piezoelectric motor element and one suspension foil arranged on a bottom side of the piezoelectric motor element.

[0116] 12. A piezoelectric actuator as described in clause 11 insofar as it is dependent on clause 3, wherein the suspension foil is arranged on a side of the connecting foil facing away from the piezoelectric motor element, and the suspension foil and the connecting foil are spaced apart from each other by a shim element.

[0117] 13. The piezoelectric actuator according to clause 12, wherein the suspension foils, the shim element and the connecting foils are mechanically connected to each other.

[0118] 14. A piezoelectric actuator as described in clause 13, wherein the suspension foils, the shim element, and the connecting foils are mechanically connected to each other using connections that extend through a central hole of the piezoelectric motor element.

[0119] 15. A piezoelectric actuator according to any preceding clause, wherein the piezoelectric motor element is plate-shaped.

Claims

1. A piezoelectric actuator, comprising: A piezoelectric motor element having a top surface and a bottom surface; A connecting element comprising an arm having a flexure hinge for contacting the piezoelectric motor element at different fixed positions located at one or more bending mode node positions of the piezoelectric motor element, wherein the longitudinal direction of the arm having the flexure hinge is arranged perpendicular to the movement of the expansion mode at each fixed point such that at the fixed point, the piezoelectric motor element can move only radially with respect to the central position, whereby the flexure arm is fixed to the piezoelectric motor element by fixing means, and a connecting element; A piezoelectric actuator comprising the same.

2. The piezoelectric actuator according to claim 1, wherein the flexure hinge is rigid in the tangential direction.

3. The piezoelectric actuator according to claim 1 or 2, wherein the connecting element comprises four arms having flexure hinges.

4. The piezoelectric actuator according to claim 1 or 2, wherein the flexure arm is fixed to the piezoelectric motor element using an adhesive.

5. The connecting element comprises two foil elements, one top connecting foil element is disposed on the top side of the piezoelectric motor element, one bottom connecting foil element is disposed on the bottom side of the piezoelectric motor element, and the top connecting foil element and the bottom connecting foil element have the arms having flexure hinges for contacting the piezoelectric motor element, and are configured to contact the piezoelectric motor element at the top surface of the piezoelectric motor element and the bottom surface of the piezoelectric motor element, respectively. The piezoelectric actuator according to claim 1 or 2.

6. The piezoelectric motor element has a hole extending from the top surface to the bottom surface through the piezoelectric motor element, and the connecting element further comprises a connecting portion disposed through the hole of the piezoelectric motor element, and the connecting portion mechanically connects the top connecting foil element and the bottom connecting foil element. The piezoelectric actuator according to claim 5.

7. The piezoelectric actuator according to claim 6, wherein the different fixed positions are arranged away from the hole so that the connecting element and the piezoelectric motor element do not contact each other at the position of the hole.

8. The piezoelectric actuator according to claim 7, wherein the connecting portion comprises a spacer ring for separating the top connecting foil element and the bottom connecting foil element.

9. The piezoelectric actuator according to claim 8, wherein an outer diameter of the spacer ring is substantially smaller than an inner diameter of the hole of the piezoelectric motor element.

10. The piezoelectric actuator according to claim 1 or 2, wherein the connection part includes two shim elements, such as shim rings, which provide a mechanical connection between the top connection foil element and the bottom connection foil element and help to space the foil elements apart from the piezoelectric motor element.

11. The piezoelectric actuator according to claim 10, wherein the dimensions of the connection part are such that there is a clearance of about 2 μm to 20 μm between the shim elements and the top surface and the bottom surface of the piezoelectric motor element.

12. The connection element includes two foil elements. One top connection foil element is disposed on the top side of the piezoelectric motor element, and one bottom connection foil element is disposed on the bottom side of the piezoelectric motor element. The top connection foil element and the bottom connection foil element have the arm having a bending hinge for contacting the piezoelectric motor element, and are configured to contact the piezoelectric motor element at the top surface of the piezoelectric motor element and the bottom surface of the piezoelectric motor element, respectively. The piezoelectric actuator according to claim 1 or 2, wherein a flexible circuit for electrical connection to an electrode in the piezoelectric motor element is provided between the piezoelectric motor element and the connection foil.

13. The piezoelectric actuator according to claim 1 or 2, further comprising a suspension element for suspending the piezoelectric motor element such that the piezoelectric motor element can move freely in a direction perpendicular to the driving direction while preventing unwanted movement in the driving direction.

14. The piezoelectric actuator according to claim 13, wherein the suspension element includes two suspension foils. One suspension foil is disposed on the top side of the piezoelectric motor element, and one suspension foil is disposed on the bottom side of the piezoelectric motor element. **Claim 15**: The connection element comprises two foil elements. One top connection foil element is disposed on the top side of the piezoelectric motor element, and one bottom connection foil element is disposed on the bottom side of the piezoelectric motor element. The top connection foil element and the bottom connection foil element have the arm with a bending hinge for contacting the piezoelectric motor element, and are configured to contact the piezoelectric motor element at the top surface of the piezoelectric motor element and the bottom surface of the piezoelectric motor element, respectively. The piezoelectric actuator according to claim 14, wherein the suspension foil is disposed on a side surface of the connection foil where the suspension foil faces outward from the piezoelectric motor element, and the suspension foil and the connection foil are arranged to be spaced apart from each other by a shim element. **Claim 16** The piezoelectric actuator according to claim 15, wherein the suspension foil, the shim element, and the connection foil are mechanically connected to each other. **Claim 17** The piezoelectric actuator according to claim 16, wherein the suspension foil, the shim element, and the connection foil are mechanically connected to each other using a connection portion extending through the central hole of the piezoelectric motor element. **Claim 18** The piezoelectric actuator according to claim 1 or 2, wherein the piezoelectric motor element is plate-shaped.

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